Cbse guide

Friday, September 25, 2020

Class 7 back exercise NCERT

Back exercise

Chap 1

Q.6. Fill in the blanks:

(a) Green plants are called ________________ since they synthesise their own food.

(b) The food synthesised by the plants is stored as ________________ .

(d) During photosynthesis plants take in ________________ and release ________________ .

Ans. (a) autotrophs (b) starch (c) chlorophyll (d) carbon dioxide, oxygen

Q.7. Name the following:

(i) A parasitic plant with yellow, slender and tubular stem.

(ii) A plant that has both autotrophic and heterotrophic mode of nutrition.

(iii) The pores through which leaves exchange gases.

Ans. (i) cuscuta (ii) Insectivorous plant (iii) Stomata

Q.8. Tick the correct answer:

(a) Amarbel is an example of:

(i) Autotroph (ii) Parasite (iii) Saprotroph (iv) Host

(b) The plant which traps and feeds on insects is:

(a) Cuscuta (ii) China rose {iii) Pitcher plant (iu) Rose

Ans. (a) (ii) Parasite (b) (iii) Pitcher plant

Q.9. Match the items given in Column I with those in Column II:

Chlorophyll --- > Leaf

Nitrogen ----- > Rhizobium

Cuscuta ------ > Parasite

Animals ------ > Heterotrophs

Insects -------- > Pitcher plant

Q.10. Mark T’ if the statement is true and ‘F’ if it is false:

(i) Carbon dioxide is released during photosynthesis. (T/F)

(ii) Plants which synthesise their food themselves are called saprotrophs. (T/F)

(iii) The product of photosynthesis is not a protein. (T/F)

(iv) Solar energy is converted into chemical energy during photosynthesis. (T/F)

Ans. (a) F (ii) F (iii) T (iu) T

Q.11.Choose the correct option from the following.

Which part of the plant takes in carbon dioxide from the air for photosynthesis?

(i) Root hair (ii) Stomata (iii) Leaf veins (iv) Sepals

Ans. (ii) Stomata

Q.12. Choose the correct option from the following:

Plants take carbon dioxide from the atmosphere mainly through their:

(i) Roots (ii) Stem (iii) Flowers (iv) Leaves

Ans. (iv) Leaves

Chapter :- 2

Q.1.Fill in the blanks:

(a) The main steps of nutrition in humans are ___________, ___________, ___________ , ___________ and ___________

(b) The largest gland in the human body is ___________.

(d) The inner wall of the small intestine has many finger-like outgrowths called ___________

(e) Amoeba digests its food in the ___________ .

Ans.(a) ingestion, digestion, absorption, assimilation, egestion

(b) liver (c) digestive (d) villi (e) food vacuole.

Q.2. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) Digestion of starch starts in the stomach. (T/F)

(b) The tongue helps in mixing food with saliva. (T/F)

(d) The ruminants bring back swallowed grass into their mouth and chew it for sometime. (T/F)

Ans. a) F (b) T (c) T (d) T

Q.3.Tick (S) mark the correct answer in each of the following:

(a) Fat is completely digested in the

(i) stomach (ii) mouth (in) small intestine (iv) large intestine

(b) Water from the undigested food is absorbed mainly in the:

(i) Stomach (ii) Food pipe (iii) Small intestine (iv) Large intestine

Ans.(a) (iii) Small intestine (b) (iv) Large intestine

Q.4.Match the items of column I with those given in column II:

Food components ---- > Products of digestion

Carbohydrates ------ > Sugar

Proteins --------> Amino acids

Fats ---------- > Fatty acids and glycerol

Q.9. Which part of the digestive canal is involved in:

(i) Absorption of food ________ .

(ii) Chewing of food ________ .

(iii) Killing of bacteria ________ .

(iv) Complete digestion of food ________ .

(v) Formation of faeces ________ .

Ans. (i) Small intestine (ii) Mouth (iii) Stomach (iv) Small intestine (v) Large intestine

Q.11. Match the items of Column I with suitable items in Column II.

Salivary gland----- > Saliva secretion

Stomach------ > Acid release

Liver ------- > Bile juice secretion

Rectum ----- > Storage of undigested food

Small intestine ---- > Digestion is completed

Large intestine ------ > Absorption of faeces.

Chap 3:-

Q.2. The silkworm is (a) a caterpillar (b) a larva. Choose the correct option.

(i) (a) (ii) (b) (iii) both (a) and (b) (iv) neither (a) nor (b)

Ans. (iii) both (a) and (b).

Q.3. Which of the following does not yield wool?

(i) Yak (ii) Camel (iii) Goat (iv) Woolly dog

Ans. (iv) Woolly dog

Q.5. Given below is a sequence of steps in the processing of wool. Which are the missing steps? Add them.

Shearing, ________ , sorting,________, __________

Ans. Shearing, scouring, sorting, picking out of burrs, colouring, rolling.

Q.7. Out of the following, which are the two terms related to silk production? Sericulture, floriculture, moriculture, apiculture and silviculture.

Hints: (i) Silk production involves cultivation of mulberry leaves and rearing silkworms. (ii) Scientific name of mulberry is Morus alba.

Ans. (i) Sericulture (ii) Moriculture

Q.8 Match the words of Column 1 with those given in Column 2:-

Scouring --------> cleaning sheared skin

Mulberry leaves ------> Food of silk worm

Yak -------- > Wool yielding animal.

Cocoon--------- >Yields silk fibres

Chap :- 4

Q.3.Fill in the blanks

The hotness of an object is detetmined by its ____________ .

(b) Temperature of boiling water cannot be measured by a ____________ thermometer.

(d) No medium is required for transfer of heat by the process of ____________.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ____________

(f) Clothes of ___________ colours absorb heat better than clothes of light colours.

Ans. (a) temperature (b) clinical (c) Celsius (d) radiation (e) conduction (f) dark

4. Match the following :-

(i) Land breeze blows during - > night

(ii) Sea breeze blows during - > day

(iii) Dark coloured clothes are preferred during ------- > winter

(iv) Light coloured clothes are preferred during ----- > summer

Q.8. One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be:

(a) 80°C (b) More than 50°C but less than 80°C

(c) 20°C (d) Between 30°C and 50°C

Ans.(d) Between 30°C and 50°C.

Q.9. An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(d) increase the temperature of both.

Ans. (b) not flow from iron ball to water or from water to iron ball

Q.10. A wooden spoon is dipped in a cup of ice-cream. Its other end:

(a) becomes cold by the process of conduction

(b) becomes cold by the process of convection

(d) does not become cold

Ans.(d) does not become cold.

Q.11.Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:

(a) copper bottom makes the pan more durable

(b) such pans appear colourful

(d) copper is easier to clean than the stainless steel

Ans.(c) copper is better conductor of heat than the stainless steel

Chap :-5

Q.2.Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Ans.Ammonia has basic nature

Q.6.Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turns red litmus blue. (T/F)

(ii) Sodium hydroxide turns blue litmus red. {T/F)

(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)

(id) Indicator is a substance which shows different colours in acidic and basic solutions. . (T/F)

(v) Tooth decay is caused by the presence of a base. (T/F)

Ans.(1) F (ii) F (iii) T (iv) T (V) F

Q. 11. Consider the following statements:

(a) Both acids and bases change colour of all indicators.

(b) If an indicator gives a colour change with an acid, it does not give a change with a base.

(d) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?

(i) All four (ii) (a) and (d) (iii) (b) and (c) (iv) only (d)

Ans. (ii) (a) and (d)

Chap 6

Q.1.Classify the changes involved in the following processes as physical or chemical changes:

(a) Photosynthesis

(b) Dissolving sugar in water

(c) Burning of coal

(d) Melting of wax

(e) Beating aluminium to make aluminium foil

(f) Digestion of food

Ans.(a) Chemical change (b) Physical change

(e) Physical change (/) Chemical change

Q.2.(a) Cutting a log of wood into pieces is a chemical change. (True/ False)

(b) Formation of manure from leaves is a physical change. (True/ False)

(c)Iron pipes coated with zinc do not get rusted easily. (True/ False)

(d)Iron and rust are the same substances. (True/ False)

(e)Condensation of steam is not a chemical change. (True/ False)

Ans. (a)False

Correct statement: Cutting a log of wood into pieces is an irreversible physical change.

(b)False

Correct statement: Formation of manure from leaves is a chemical change.

(d)False

Correct statement: Iron and rust are two different chemical substances.

(e)True

Q.3.Fill in the blanks in the following statements:

(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

(b) The chemical name of baking soda is .

(d) Changes in which only ____________ properties of a substance change are called physical changes.

(e) Changes in which new substances are formed are called _____________ changes..

Ans. (a)calcium carbonate

(b) sodium hydrogen carbonate

(d) physical

(e) chemical

Q.11. The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change- A) then it bums (Change-B). The following statements pertain to these changes. Choose the correct one.

(i) Process-A is a chemical change.

(ii) Process-B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Ans. (ii) Process-B is a chemical change.

Q.12.Anaerobic bacteria digest animal waste and produce biogas (Change-A). The biogas is then burnt as fuel (Change-B). The following statements pertain to these changes. Choose the correct one.

(i) Process-A is a chemical change.

(ii) Process-B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Ans.(iii) Both processes A and B are chemical change

Chap :- 7

Q.3.Fill in the blanks

(i) The average weather taken over a long time is called __________

(ii) A place receives very little rainfall and the temperature is high throughout the year, the climate of that place will be ________ and _________

(iii) The two regions of the earth with extreme climatic conditions are __________ and ____________

Ans. climate of the place (ii) hot, dry (iii) polar, tropical regions

Q.4.Indicate the type of climate of the following areas:

(a) Jammu and Kashmir:

(b) Kerala:,

(c) Rajasthan:

(d) North-east India:

Ans.(a) Jammu and Kashmir—moderately hot and moderately wet climate.

(b) Kerala—very hot and wet climate.

(d) North-east India—The north eastern India receives rain for a major part of the year, hence wet climate.

Q.5.Which of the two changes frequently, weather or climate?

Ans.Weather

Q.6.Followings are some of the characteristics of animals:

(i) Diets heavy on fruits

(ii) White fur

(iii) Need to migrate

(iv) Loud voice

(v) Sticky pads on feet

(vi) Layer of fat under skin

(vii) Wide and large paws

(viii) Bright colours

(ix) Strong tails

(x) Long and large beak

For each characteristic indicate whether it is adaptation for tropical rainforests or polar regions. Do you think that some of these characteristics can be adapted for both regions?

Ans:-

(i) Diets heavy on fruits --------------- > Tropical rainforest

(ii) White fur --- > Polar region

(iii) Need to migrate --->Polar region

(iv) Loud voice----------- >Tropical rainforest

(v) Sticky pads on feet------------- >Tropical rainforest

(vi) Layer of fat under skin------------------ >Polar region

(vii) Wide and large paws----------------- >Polar region

(viii) Bright colours ------ >Tropical rainforest

(ix) Strong tails --------- >Tropical rainforest

(x) Long and large beak ----------------------- >Tropical rainforest

Q.10.Choose the correct option which answers the following question:

A carnivore with stripes on its body moves very fast while catching its prey. It is likely to be found in:

(i) polar regions (ii) deserts

(iii) oceans (iv) tropical rainforests

Ans. (iv) tropical rainforests

Q.11.Which features adapt polar bears to live in extremely cold climate?

(i) A white fur, fat below skin, keen sense of smell.

(ii) Thin skin, large eyes, a white fur.

(iii) A long tail, strong claws, white large paws.

(iv) White body, paws for swimming, gills for respiration.

Ans.(iv) A white fur, fat below skin, keen sense of smell.

Q.12.Which option best describes a tropical region?

(i) hot and humid

(ii) moderate temperature, heavy rainfall (iii) cold and humid (iv) hot and dry

Ans.(i) Hot and humid

Chap :-8

1.Fill the missing word in the blank spaces in the following statements:

(a) Wind is ___________air.

(b) Winds are generated due to _________ heating on the earth.

(d) Air moves from a region _________of pressure to a region _________of pressure.

Ans.(a) moving (b) uneven

Q.8. Which one of the following places is unlikely to be affected by cyclone?

(i) Chennai (ii) Mangalore

(iii) Amritsar (iv) Puri

Ans.(iv) Amritsar

Q.9.Which of the statements given below is correct?

(i) In winter the winds flow from the land to the ocean.

(ii) In summer the winds flow from the land towards the ocean.

(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.

(iv) The coastline of India is not vulnerable to cyclones.

Ans.(i) In winter the winds flow from the land to the ocean.

Chapter 9

Tick the most suitable answer in question 1 and 2.

In addition to the rock particles, the soil contains

(i) Air and water

(ii) Water and plants

(iii) Minerals, organic matter, air and water

(iv) Water, air and plants

Answer:

In addition to the rock particles, the soil contains

(iii) Minerals, organic matter, air and water.

Q2. The water holding capacity is the highest in

(i) Sandy soil

(ii) Clayey soil

(iii) Loamy soil

(iv) Mixture of sand and loam

Answer:

The water holding capacity is the highest in

(ii) Clayey soil

Q3. Match the items in Column I with those in Column II:

1. A home for living organisms----------> All kinds of soil

2. Upper layer of soi----- > Dark in colour

3. Sandy soil----------> Large particles

4. Middle layer of soil--------> lesser amount of humus

5. Clayey soil -----> small particles and packed light.

Chapter 10

Tick the correct answer:

(a) In cockroaches, air enters the body through

(i) lungs

(ii) gills

(iii) spiracles

(iv) skin

Answer: (iii) spiracles

(b) During heavy exercise, we get cramps in the legs due to the accumulation of

(i) carbon dioxide

(ii) lactic acid

(iii) alcohol

(iv) water

Answer: (ii) lactic acid

(c) Normal range of breathing rate per minute in an average adult person at rest is:

(i) 9 – 12

(ii) 15 – 18

(iii) 21 – 24

(iv) 30 – 33

Answer: (ii) 15 – 18

(d) During exhalation, the ribs

(i) move outwards

(ii) move downwards

(iii) move upwards

(iv) do not move at all

Answer: (ii) move downwards

Mark T if the statement is true and F if it is false:

(i) During heavy exercise the breathing rate of a person slows down. (T/ F)

(ii) Plants carry out photosynthesis only during the day and respiration only at night. (T/ F)

(iii) Frogs breathe through their skins as well as their lungs. (T/ F)

(iv) The fishes have lungs for respiration. (T/ F)

(v) The size of the chest cavity increases during inhalation. (T/ F)

Answer:

(i) F

(ii) F

(iii) T

(iv) F

(v) T

Chapter 11

Q.1.Match structures given in Column I with functions given in Column II

1. Stomata. -------> Transpiration

2. Xylem-----> Transport of water

3. Root hairs----- > Absorption of water

4. Phloem-----> Transport of food

Q.2.-Fill in the blanks :

(i) The blood from the heart is transported to all parts of the body by the _____________

(ii) Haemoglobin is present in ___________ cells.

(iii) Arteries and veins are joined by a network of ___________ .

(iv) The rhythmic expansion and contraction of the heart is called ___________

(v) The main excretory product in human beings is ___________

(vi) Sweat contains water and .

(vii) Kidneys eliminate the waste materials in the liquid form called .

(viii) Water reaches great heights in the trees because of suction pull caused by .

Ans.(i) arteries (ii) red blood cells • (in) capillaries (iv) heartbeat (v) urea (vi) salts (vii) urine (viii) transpiration.

Q.3.Choose the correct options:

(a) In plants, water is transported through

(i) Xylem (ii) Phloem (iii) Stomata (iv) Root hair

(b) Water absorption through roots can be increased by keeping the plants

(i) In the shade (ii) in dim light (iii) under the fan (iv) covered with a polythene bag

Ans.(a) (i) Xylem {b) (iii) under the fan

Chap 12

Q.1.Fill in the blanks:

(a) Production of new individuals from the vegetative part of parent is called ___________.

(b) A flower may have either male or female reproductive parts. Such a flower is called _______.

another flower of the same kind is known as __________.

(d) The fusion of male and female gametes is termed as ____________ .

(e) Seed dispersal takes place by means of ________ and __________.

Ans. (a) vegetative reproduction (b) unisexual flower (c) pollination (d) fertilization (e) wind, water

Q.9.Match items in Column I with those in Column II

1. Bud ---> yeast

2. Eyes----> potato

3. Fragmentation-----> Spirogyra

4. Wings------ > Maple

5. Spores ------ > Bread mould

Tick the correct answer:

(a) The reproductive part of a plant is the

(i) leaf (ii) stem (iii) root (iv) flower

(b) The process of fusion of the male and the female gametes is called

(i) fertilisation (ii) pollination (iii) reproduction (iv) seed formation

c) Mature ovary forms the

(i) seed (ii) stamen (iii) pistil (iv) fruit

(d) A spore producing plant is

(i) rose (ii) bread mould (iii) potato (iv) ginger

(e) Bryophyllum can be reproduced by its

(i) stem (ii) leaves (iii) roots (iv) flower

Ans.(a) (iv) flower (b) (i) fertilisation (c) (iv) fruit (d) (ii) bread mould (e) (ii) leaves

Chap 13

Q.1.Classify the following as motion along a straight line, circular or oscillatory motion :

(i) Motion of your hands while running.

(ii) Motion of a horse pulling a cart on a straight road.

(iii) Motion of a child in a merry-go-round. •

(iv) Motion of a child on a see-saw.

(v) Motion of the hammer of an electric bell.

(vi) Motion of a train on a straight bridge.

Ans.(i) Oscillatory motion

(ii) Linear motion

(iii) Circular motion

(iv) Oscillatory motion

(v) Oscillatory motion

(vi) Linear motion

Q.2.Which of the following are not correct?

(i) The basic unit of time is second.

(ii) Every object moves with a constant speed.

(iii) Distances between two cities are measured in kilometers.

(iv) The time period of a given pendulum is not constant.

(v) The speed of a train is expressed in m/h

Ans. (ii), (iv), (v)

.8. Which of the following relations is correct?

(i) Speed = Distance Time

(ii) Speed = Distance/Time

(iii)Speed – Time/Distance

(iv)Speed = 1/Distance Time

Ans. (ii) Speed = Distance/Time is correct

Q.9.The basic unit of speed is:

(i) km/min (ii) m/min (iii) km/h (iv) m/s

Ans. (iv) m/s

10.A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km

Ans.(ii) 25 km

Q.11.Suppose the two photographs, shown in fig. 13.1 and fig. 13.2 of NCERT had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the blue car.

Ans.0.1 cm/s or 10 m/s

Q.12.Fig 13.10 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Ans. ‘A’ is moving faster.

Q.13.Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Ans. (iii)

Chap 14

Q.8.Fill in the blanks:

(a) Longer line in the symbol for a cell represents its ___________terminal

(b) The combination of two or more cells is called a ____________.

(d) The safety device based on the heating effect of electric current is called a _____________.

Ans.(a) positive (b) battery (c) becomes red hot and emits heat (d) fuse.

Q.9.Mark ‘T’ if the statement is true and ‘F’ it is a false:

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. [T/F]

(b) When the electric current through the fuse exceeds a certain limit , the fuse wire melts and breaks. [T/F]

(d) An electric bell has an electromagnet. [T/F]

Ans. (a) F (b) T (c) F (d) T

Chap 15

Q.1.Fill in the blanks:

(a) An image that cannot be obtained on a screen is called ___________ .

(b) Image formed by a convex is __________ always virtual and smaller in size.

(d) An image which can be obtained on a screen is called a __________ image.

(e) An image formed by a concave __________ cannot be obtained on a screen.

Ans.(a) virtual image (b) mirror (c) plane (d) real (e) lens

Q.2.Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)

(b) A concave lens always form a virtual image. (T/F)

(d) A real image cannot be obtained on a screen. (T/F)

(e) A concave mirror always form a real image. (T/F)

Ans. a) F (b) T (c) T (d) F (e) F

Q.3. Match the items given in Column I with one or more items of Column II

1. A plane mirror ---- >The image is erect and of the same size as the object

2. A convex mirror ---- > Can form image of objects spread over a large area

3. A convex lens --- > Used as magnifying glass

4. A concave mirror---- >used by dentist to see enlarged image of teeth

5. A concave lens----- > The image is erect and smaller in size than the object.

Q.9. Which type of mirror can form a real image?

Ans. Concave mirror can form a real image.

Q.10. Which type of lens forms always a virtual image?

Ans. Concave lens always forms a virtual image.

Choose the correct option in Questions 11-13:

Q.11. A virtual image larger than the object can be produced by a

(i) concave lens (ii) concave mirror (iii) convex mirror (iv) plane mirror

Ans. (ii) concave mirror

Q.12. David is observing his image in a plane mirror. Die distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

(i) 3 m (ii) 5 m (iii) 6 m (iv) 8 m

Ans. (iii) 6 m

Q.13. The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear mew mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be

(i) 1 m/s (ii) 2 m/s (iii) 4 m/s {iv) 8 m/s

Ans. (ii) 4 m/s

Chap 16

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)

(b) Water shortage is a problem faced only by people living in rural areas. (T/F)

(d) Rain is the ultimate source of water. (T/F)

Ans. (a) T (b) F (c) F (d) T

Q.6.Fill in the blanks with the appropriate answers: .

(a) People obtain groundwater through and .

(b) Three forms of water are solid, and .

(d) The process of water seepage into the ground is called .

Ans.(a) wells, hand pumps

(b) liquid, gas

(d) infiltration

Q.7.Which one of the following is not responsible for water shortage?

(i) Rapid growth of industries

(ii) Increasing population

(iii) Heavy rainfall

(iv) Mismanagement of water resources

Ans.(iii) heavy rainfall

Q.8.Choose the correct option. The total water

(i) in the lakes and rivers of the world remains constant.

(ii) under the ground remains constant.

(iii) in the seas’and oceans of the world remains constant.

(iv) of the world remains constant.

Ans.(iv) of the world remains constant.

Chap 17

Q.7.Fill in the blank:

(a) The insects, butterflies, honeybees and birds help flowering plants in .

(b) A forest is a purifier of and .

(d) The decaying leaves and animal droppings in a forest enrich the .

Ans. (a) pollination (b) water, air (c) lowest (d) soil as humus.

Q.11.Which of the following is not a forest product?

(i) Gum (ii) Plywood (iii) Sealing wax (iv) Kerosene

Ans.(iv) Kerosene

Q.12.Which of the following statements is not correct?

(i) Forests protect the soil from erosion.

(ii) Plants and animals in a forest are not dependent on one another.

(iii) Forests influence the climate and water cycle.

(iu) Soil helps forests to grow and regenerate.

Ans.(ii) Plants and animals in a forest are not dependent on one another.

Q.13.Micro-organisms act upon the dead plants to produce

(i) sand (ii) mushrooms (iii) humus (iu) wood

Ans. (i) Humus

Chap 18

.1. Fill in the blanks:

(a) Cleaning of water is process of removing __________

(b) Wastewater released by houses is called __________.

(d) Drains get blocked by __________ and __________.

Ans.(a) pollutants (b) sewage (c) sludge (d) (d) chemicals, kitchen waste

.7. Name two chemicals used to disinfect water.

Ans. Chlorine and ozone

Study the following statements about ozone:

(a) It is essential for breathing of living organisms.

(b) It is used to disinfect water.

(d) Its proportion in air is about 3%.

Which of these statements are correct?

(i) (a), (b) and (c) (ii) (b) and (c) (iii) (a) and (d) (iv) All four

Ans. (ii) (b) and (c)

Class 7 chap 15 light

Chap 15 Light notes

Introduction:-

Light is a form of energy which enable us to see world.

Speed of light = 30000Km/sec

Travels along a straight path.

Luminous objects:- Produce their own light .

Eg -- > Sun

Illuminous objects:- Donot Produce their own light . Eg:- Chair

Capable of reflecting light to our eyes coming from luminous objects.

Uses of Light:- Images formed by Mirror and lens

Rainbow formation

Ray of light:- Straight line path of light is called ray of light.

Beam of light:- Bunch of rays of light is called beam of light.

Reflection of light:-

Bouncing back of ray of light into the same medium after striking a polished surface such as mirror is called reflection of light.

Incident ray :- Ray of light that strike the surface.

Reflected ray :- Ray of light sent back by the surface after reflection.

Normal:- Perpendicular to the surface at the point of incident . It is an imaginary line.

Angle of incidence= angle between the Incident ray and normal.

Angle of reflection= Angle between the reflected ray and normal.

Law of reflection:-

1. Angle of incidence= angle of reflection

2. Incident ray, reflected ray and the normal all lie on the same plane.

Types of mirror:- two types

1. Plane mirror

2. Spherical mirror

Plane mirror:- mirror with a flat reflective surface.

Characteristics of image formed by plane mirror:-

1. Virtual and erect image.

2. Same size as that of object.

3. Image formed behind mirror.

4. Distance of the image behind mirror is same as distance of object from mirror.

Virtual image:- Image formed when reflected rays appear to meet. It can't obtained on screen.

Real image:-Image formed when reflected rays actually meet. It can obtained on screen.

Lateral inversion:- In mirror left appears right and right appears left . This is called lateral inversion.

Spherical mirror:- Mirror having spherical reflecting surface.

Two types :-

1. Convex mirror

2. Concave mirror

CONCAVE MIRROR:- mirror whose reflecting surface is curved inward. It is a converging mirror.

CONVEX MIRROR:- Mirror whose reflecting surface is curved outward. It is a diverging mirror.

Use of Convex mirror:-

1. Can use as rear view mirror to get wider field view to help driver to see traffic behind them.

Used of concave mirror:-

1. Doctor use concave mirror for examining eyes, nose, ears and throat.

2. Dentists use concave mirror to see enlarge image of teeth.

3. Reflectors of torches, headlights of cars and scooters are concave in shape.

Lens:- Transparent optical medium bounded by two surfaces at least one being spherical is called lens.

Types of lens:-

1. Convex lens( converging lens)

Thicker at middle and thinner at edges

2. Concave lens( diverging lens)

Thicker at edges and thinner at middle.

Uses:-

1. Magnifying glass.(Convex lens)

2. Used in Spectacles, telescopes and microscopes.

Sunlight:- It is a white light that is made up of seven colours.

Prism:- Transparent element with three rectangular and two triangular surface.

Dispersion of light:-

Splitting of white light into its constituent colours is called dispersion of light. For example :- rainbow is formed when sunlight split into its 7 coloured band (VIBGYOR)

This pattern of colour obtained is called spectrum.

Thursday, August 27, 2020

Obelia

Subject: Coelenterata : Obelia (sea fur)

Systematic position:-

Phylum :- Coelenterata or cnidaria ( Diploblastic, tissue organisation, coelenteron and cnidoblasts)
Class:- Hydroids (fixed polyps; medusa with ectodermal sense organs)
Order:- Hydroida( Fixed polyps; medusa with ectodermal sense organs)
Family:- Campanularidae( cup shaped hydrotheca)
Genus:- Obelia ( Free swimming and discoidal medusae)
Species:- geniculata (Colourless)

Habitat:-

Obelia is a marine, cosmopolitan, polymorphic, colonial and sedentary hydrozoan Coelenterate found attached on the stones, rocks, molluscan shells, ships, weeds, etc. In shallow coastal waters upto the depth of 80 metres.
It is branched like a tree, so called zoophyte (zoo= animal ; phyte = plant) or sea fur.
There are many species of Obelia but the most common species is O. geniculata.

Habits :-

(1) Feeding :-

Obelia is carnivores and feeds upon the living insect larvae, small crustaceans and worms.
Food is captured and paralysed with the help of stinging cells.
Digestion is partly intercellular and partly intracellular.

(2) Reproduction:-

Obelia shows asexual as well as sexual reproduction.
Asexual reproduction occurs by external budding.
In Obelia reproductive zooids are meduse which are inside or dioecious but don't show sexual dimorphism.
Fertilization is external.
Development is indirect and includes a free swimming planula larva which brings about dispersal.
Life history of Obelia shows alternation of generation.

(3) Respiration and Excretion :-

These occur through general body surface.

Morphology :-

(A) Shape, size , colour and symmetry:-

Obelia appears as a network of branched threads giving fur-like appearance, so called sea fur.
It is about 25-30 mm in height, creamish- white or greyish in colour and radially symmetrical.

(B) Two types of filaments:-

Obelia colony is formed of 2 types of filaments:-
(a) Hydrorhizae:- These are horizontal branched which creep over the substratum and fix the colony to the substratum.
(b) Hydrocauli:- These are upright branches.
Each hydrocaulus grows in a scorpioid cymose manner.
Each branch stops growing ends into a zooid and gives rise a new branch.
Adjoining branches are on alternate sides.
So it is formed of lower parts of all the true branches and grows in a zig zag manner.
Each side branch and main hydrocaulus end into a terminal bud which later forms a polyp.

Coelenteron also called gastro-vascular cavity, Is the central cavity running through both types of filaments.
It is bounded by 2 coats:-
(a) Coenosarc:- It is inner and living coat.
It is formed of two layers:-
Inner gastrodermis lining the Coelenteron, and outer epidermal.
Between the two cellular layers is a non- cellular and gelatinous mesoglea.
(b) Perisarc :- It is outer and non-living coat.
It is chitinous in nature and is secreted by myoepithelial cells is epidermis.
In early stages, it is in contact with Coenosarc but later two are separated by a fluid-filled space except at certain points.
It is supportive and protective in function,so acts as exoskeleton.
At the base of zooids and near the bends of the hydrocaulus, Perisarc forms ring like grooves, called perisarcal annuli, which give flexibility to it , so it sways in water to withstand the wave action.

Polymorphism in Obelia :-

Polymorphism us the phenomenon in which a colonial organism is formed of many types of organisms (called zooids in coelenterates) which Differ in structure and function for the benefit of whole Colony.
Obelia is a polymorphic (trimorphic) Coelenterate as the colony has three types of zooids which through are homologous zooids but are specialized in their morphology and physiology.

So polymorphism is associated with division of labour.

(1) Hydrants or polyps ( nutritive and protective zooids)

(2) Blastostyles or Gonozooids(budding zooids)

(3) Medusae or Gonophores( sexual zooids)

(1) Hydranth or Polyp:-

(i) Position :-

These are more numerous in number than other zooids.
These are distributed throughout the colony and are terminal in position.

(ii) Structure :-

(a) External structure:-

Polyp or Hydranth is a hollow and cylindrical zooid which is proximally continuous with the hydrocaulus.
It's free distal end is produced into a conical process called oral cone or manubrium or hypostome having a termination and circular mouth.
Oak cone is about one third of total length of zooid.
Arising from the base of Hydranth, there is a ring of 24-30 solid, tapering and fillifo tentacles, each having batteries of stinging cells.
The tentacles are radially arranged to capture the food from all directions.
Hydranth is protected by a cup-shaped and transparent cover called hydrotheca.
So Obelia belongs to sub order Thecata while the hydranths of Bougainvillea and Tubularia have no theca, so placed in sub-order Athecata.
It is formed by the expansion of Perisarc.
Hydrotheca is open at the tip so Hydranth can be protruded.
At its lower end, hydrotheca is produced inward to form a centrally- perforated circular shelplf which keeps a limit on the retraction of polyp.

(b) Coelenteron:-

Mouth of Polyp leads into a small cavity of manubrium, sometimes called gullet, which opens in the Coelenteron of body of Hydranth which in turn is continuous with that of hydrocaulus.

Histologically , living Coenosarc of Hydranth is formed of 2 layers with a non-living and gelatinous mesoglea in between.
So Obelia is a Diploblastic animal.

(A) Epidermis:-

It is outer and thinner layer.
It is formed of 5 types of cells:-

(1) Myoepithelial or epitheliomuscular cells:-

Position and structure:-
These forms the bulk of epidermis.
These are colonial-shaped with their broader side outward.
Their broader sides meet and form a continuous layer except when interrupted by sensory cells and cnidoblasts.

Each Myoepithelial cell is differentiated into 2 parts:-

Epithelial part and muscular part:-

Epithelial part is outer and nucleated part having vacuolated cytoplasm, a layer of secretary granules in its outer part and two supporting fibrils called tonofibrils.
Muscular part is inner and is produced into two or more tail or muscle processes having a contractile myoneme formed of myofilaments.
Myonemes of these cells are arranged along the longitudinal axis so forming a kind of longitudinal muscles which when contract, make the Hydranth small and thick.
Functions:- These are protective, secretory and contractile in function.

(2) Interstitial cells:-

Position and structure:-

These are groups of cells present in the spaces between the inner narrow ends of Myoepithelial cells.
These are mainly present in the basal part tthe polyp.
Each is spherical-shaped, about 5micrometer, with clear cytoplasm and nucleus having 1 to 2 nucleoli.
Position:-
These act as reserve or undifferentiated cells which can differentiate into any type of cell depending upon their requirements, these are called totipotent cells.
So these help in regeneration, budding and reproduction.
Breton showed that these can renew cells within 45 days

(3) Cnidoblasts:-

Position and structure:-

Cnidoblasts ,also called nematoblasts or stinging cells, are present among the Myoepithelial cells on the hypoblast and tentacles.
These are peculiar cell-type of Coelenterates which are also called cnidarians while their study is called Cnidology.
These form ring-like groups called annular batteries on the tentacles.
Each cnidoblast is pear shaped and about 16 micrometer in size.
It has contractile cytoplasm, eccentric nucleus, a sensory trigger hair called cnidocil at it's free distal end and a sac like nematocyst inside.

A namatocyst is differentiated into two parts :-
Capsule and thread tube.
Capsule is oval-shaped, double walled , chitinous sac externally covered by a lid or operculum.
It is filled with a poisonous fluid called hypnotoxic (a mixture of proteins and phenol).
Thread tube is differentiated into basal butt and distal thread tube proper.
Butt is again formed of proximal wider and funnal shaped part with no spines, called shaft, and distal and tapering part with three large-sized stylets or barbs and three spiral rows of spines or barbules, called spinneret.
Thread tube proper is long tube of uniform diameter which ends into a hypodermic needle.
Such nematocyst of Obelia are called penetrants or stenoteles.
On the outer surface of capsule, there are a number of refractile rods, each giving rise to a contractile fibril extending upto the base of cnidoblast.
Another coiled thread, called lasso, also extends the outer surface of the capsule to its base.
These both prevent the protrusion of capsule.

Function:-

when the stinging. Cells are undischarged,spines and stylets of the butt are inward directed and thread tube proper is coiled around the butt as a watch spring.
When stimulated, stimulus is first received by cnidocil and is conducted to contractile cytoplasm, the contraction of which causes the eversion of thread tube, so the spines and styles are now outward directed while the hypodermic needle is injected in the prey to release the hypnotoxin, which paralyses or kills the prey.So the stinging cells of Obelia are called penetrants or stenosis.
It is now proposed that discharge of nematoblasts is probably due to rapid increase in Calcium level and intracapsular pressure inside the capsule of these cells.
Their coordinated discharge is controlled by neural connections .
So the nematoblasts are cells for offence and defence and are involved in food capturing and protection.
Nematoblasts are independent effectors.
These are stimulated by partly mechanical and partly Chemical stimuli.
Once discharged, these are never withdrawn so these move in the Coelenteron and are digested.
New nematoblasts are regenerated from interstitial cells in about 48 hours in the basal parts of the polyps .

4) Sensory cells:-

Position and structure:-

These are present among the Myoepithelial cells of epidermis, especially in hypostome and tentacles.
Each is a columnar and neuro-sensonry cell.
It has a sensory hair on other side and a few modulated nerve fibres on inner side which join the nerve fibres of nerve cells.

Functions:-

These are sensitive to externally stimuli like touch, temperature, light , Chemicals tc so also called receptors.

(5) Nerve cells:-.

Position and structure:-

Nerve cells, also called protoneurons, from an epidermal nerve net on outer border of mesoglea .
These are more developed in the tentacles.
Each is an irregular cell and is differentiated into a central nucleated part called cell body and a number of nerve processes called neuritis .
Depending upon the number of neurites, nerve cells may be bipolar or multipolar.
But neurites are not differentiated into axon and dendron so nerve impulse can travel in any direction so form diffuse type nervous system.
Neurites of adjacent nerve cells coil around one another to form a net , so called plexiform nervous system.
But there is no continuity of their cytoplasm and nerve impulses are conducted only through synapses, so called synaptic nervous system.
Function:- These form a part of sensory-neuro-motor system and conduct the nerve impulses.

(B) Gastrodermis:-

It is inner and thicker .
It forms the bulk of body wall and is digestive, circulatory and muscular in function.

It is formed of following five types of cells:-

(1) Myoendothelial or Endothelio-muscular cells:-

Position and structure:-

These form the bulk of Gastrodermis .
Each is long and columnar cell which is differentiated into 2 parts:-
Endothelial part and muscular part.
Endothelial part is inner and nucleated part having vacuolated cytoplasm and either pseudopodia or 2 flagella .
Their inner free ends also have microvilli to absorb the digested food from the coelenteron.
It's muscular part is outer and is produced into a muscle process having contractile fibrils called myonemes.
Their myonemes are arranged perpendicular to longitudinal axis of hydranthand act as circular muscle fibres.
When contract, these make the polyp long and thin .
Around the mouth these muscle processes act as sphincter.
Function:- These are nutritive, absorptive, muscular and circulatory in function.

(2) Gland cells:-

Position and structure:-

These are modified Myoendothelial cells present only on manubrium and body of hydranth while these are absent on the tentacles.
Each is columnar-shaped like the Myoendothelial cell but is smaller in size and lacks the muscle process.

Function:-

These secrete either mucus (those in manubrium and called mucous gland cells) or digestive enzymes ( those in the body and. Called enzymatic gland cells) so help in ingestion and intercellular digestion of food in coelenteron.

(3) Interstitial cells:-

These are present in groups in the spaces between the outer ends of Myoendothelial cells.
These resemble those of epidermis in their structure and function.

(4) Sensory cells:-

These are present between the Myoendothelial cells of Gastrodermis.
These resemble those e epidermis in their structure and function except that are less in number.

(5) Nerve cells:-

These form a gastrodermal nerve net on the inner border of mesoglea.
These also resemble those of epidermis in their structure and function but are less in number
Epidermal and gastrodermal nerve nets are interconnected by nerve fibres.

(C) Mesoglea:-

Mesoglea , also called mesenchyme, is the middle homogeneous, non-cellular and gelatinous layer of uniform thickness.
It is joint secretary product of both epidermis and Gastrodermis.

It helps in following functions:-

It acts as middle lamella and provides binding surface for the attachment of muscle processes of both epidermis and Gastrodermis.
It is elastic in nature and helps in extension of hydranth .
It acts as the skeleton so provides mechanical support to hydranth

Tuesday, August 25, 2020

Plasmodium Vivax ( the malarial parasite)

Subject: Protozoa:- Plasmodium Vivax ( the malarial parasite)

Systematic position:-

Kingdom:- Protists (Acellular eukaryote)
Phylum:- Protozoa (Heterotrophic and undergoes fission)
Super-Class:- Sporozoa (No organelles of locomotion)
Class- Coccidia (Mature trophozoite is intracellular)
Genus- Plasmodium (True malarial parasite)
Species- vivax ( causes benign tertian malaria as erythrocytic schizogony is completed in 48 hours)

Introduction:-

Malaria is a widely known human disease. It is caused by infection with a pathogenic Protozoan parasite of blood, the plasmodium, whose 60 known species cause malaria in man and other animals.
Four species of Plasmodium are known to cause different types of malaria fever in man.
They are P. vivax , P. malariae and P. falciparum. Female Anopheles mosquitoes transmit Plasmodium from person to person , thus serving as carrier or vector host.
It derives certain proteins from human blood and are important in its egg formation.
Male feeds upon plant juices.
P. vivax is mostly widely studied of Plasmodium.
Hence, the following description is mainly based upon it.

Distribution:-

Plasmodium vivax is cosmopolitan parasite.
It is wide spread in tropical and temperate countries.
Some species infect migratory birds.

Habitat:-

Plasmodium is endoparasite, found in the blood of man:-
Intracellular in R.B.Cs and parenchymal cells of liver.
Also found in the alimentary canal and salivary glands of female Anopheles Mosquitoes.

Habits:-

Being intracellular parasite, it depends for all vital activities on host.

Life cycle:-

Life cycle of Plasmodium is complicated.
It comprises several stages and requires two hosts for completion- a primary, definitive or principal host and a secondary, intermediate or vector host
Such a two host life cycle is called digenetic.
In human species of Plasmodium, intermediate host is always female Anopheles.
In human body, the parasite multiplies asexually, while is female Anopheles, it undergoes a sexual cycle followed by an Asexual multiplication called sporogony.

Asexual cycle and schizogony in man:-

The adult phase of Plasmodium is called trophozoite.
It occurs in R.B.Cs of man but before invading the R.B.Cs the paradises invade liver cells and undergoes extensive asexual multiplication by Schizogony. The life cycle of Plasmodium in man consists of two phases:-

(1) Exoerythrocytic or hepatic Schizogony

(2) Erythrocytic schizogony

Exoerythrocytic Schizogony:-

(a) Inoculation or Infection:-

A healthy person acquires infection when a female Anopheles Mosquito, containing infective stage of parasite in their salivary glands.
They feed upon human blood which they such, usually during night, by means of their piercing and sucking mouth parts.
The mosquito punctures the host's skin by its proboscis and first introduces some saliva into the wound.
Saliva contains an anticoagulant which prevents clotting of blood during sucking.
This saliva carries thousands of sporozoites into the human blood.

(b) Structure of Sporozoites:-

A sporozoite has a spindle shaped, slightly curved or sickle shaped body tapering at either end .
It is uninucleate organism, measuring 6 micro to 15 micro in length and 0.5-1 micro in width
Each has a covering of firm, but elastic pellicle, containing longitudinal contractile microtubules for its wriggling movements.
It's Anterior end is marked by a minute aperture, the micropyle, followed an apical cap of connective rings.
A pair of long and slender secretory organelles open into the cap
These is a single vesicular nucleus with a centrally located nucleolus and a mitochondrion with tubular cristae, scattered endoplasmic reticulum is also present.

Within half an hour or so after inoculation into human blood, all Sporozoites disappear from the blood.
As they reach into the liver with blood circulation, they make their way out from Blood capillaries and enter into the liver cells.
Here they multiply asexually by Schizogony.
Liver Schizogony has two phases:- pre- erythrocytic and exo- erythrocytic.

(1) Pre- erythrocytic phase:-

In the liver cells, the parasite become spherical and are known as the cryptoschizoites.
In the liver cell, the cryptozoite feeds on cytoplasm and grows into a rounded structure, the pre-erythrocytic schizont also known as cryptoschizont.
The later divides into about 1000 minutes cryptomerozoites by a special type of fission called schizogony ( multiple fission).
This Schizogony is called exo- erythrocytic, because it occurs away from blood R.B.Cs.
The schizont and the liver cell break up and liberate cryptomerozoites into the liver sinusoids.
From the sinusoids, some of these cryptomerozoites invade fresh liver cells to continue Exoerythrocytic Schizogony, while other remain in blood stream and invade R.B.Cs to initiate the erythrocytic cycle.

(iii) Exo-erythrocytic phase:-

Cryptomerozoites enter fresh liver cells to become metacryptozoites or phanerozoites.
The later are of two types- micrometscyptozoites and macrometacryptozoites.
Each micro-metacryptozoite undergoes Schizogony, producing 100 to 10000 minute micro-metacryptozoite which pass into blood stream and invade R.B.Cs for fresh erythrocytic phase.
Schizogony in each macrometacryptozoites, on the other hand, produces only about 64, relatively large macrometacryptomerozoites which invade fresh liver cells to continue Exo-erythrocytic cycle.
Pre and exo-erythrocytic phases of parasite remain immune to the resistance of host and parasitea are not susceptible to the action of any anti-malarial drug.
Also little damage to the host is done during these stages

(iii) Pre-patent and incubation periods:-

The pre- erythrocytic phase is completed in about 8 to 10 days .
This inverval between inoculation and initiation of erythrocytic phase is called Pre-patent period.
The period between infection and appearance of first malarial symptom is the incubation period which is about 10-17 days.

2.Erythrocytic Schizogony:-

This cycle occurs in R.B.Cs and begins when a cryptomerozoites or micro-metacryptomerozoite enters into an R.B.Cs .

It includes the following stages:-

(i) Trophozoite stage:-

Inside the corpuscle, the parasite become rounded and grow.
During the growth period it is called trophozoite.

(ii) Signet ring stage:-

As the trophozoite grows in size, a large non-contractile vacuole appeara in the centre, pushing the cytoplasm and nucleus to a thin peripheral layer.
This stage is clinically referred to as signet ring stage as it resembles the signet ring.

(iii) Amoeboid stage:-

The signet ring trophozoite developes into an active amoeboid trophozoite.
Now, the trophocytes starts feeding more actively upon cytoplasm of host R.B.Cs with the help of pseudopodia.
It secretes out digestive enzymes which liquify, the cytoplasm of R.B.Cs by its partial digestion.
The haemoglobin is not digested
It gets decomposed into a brownish black pigmentz the haematin, which lies in the cytoplasm of trophozoite.
In about 36 hours, the young trophozoite grows into an adult, occupying almost the entire R.B.Cs.
Besides plasmolemma, endoplasmic reticulum, mitochondria, food vacuole, Golgi complex, nucleus etc, a concentric structure of unknown significance has been recently observed in this trophozoite by electron microscopy by Garnham, 1966 and Zinska , 1969.
The host R.B.Cs gets somewhat enlarged and irregular in shape.
At this time, small red eosinophilic granules appear in the cytoplasm of the host corpuscle which are known as Schuffner's granules.

(iv) Schizont :-

The amoeboid trophozoite, after active feeding becomes rounded, grows in size and becomes Schizont.
It now undergoes Schizogony.
It's nucleus undergoes repeated mitotic divisions, forming. 12-24 daughter nuclei, which get arranged at the periphery and cytoplasm masses surrounding them.
Each cytoplasmic mass with one nucleus becomes an oval shaped merozoite.
They are shorter and thicker than the Sporozoite.
A part of the cytoplasm of the Schizont is not used in the formation of merozoite.
This residual cytoplasm contains the haematin and metabolic wastes or toxins produced by the parasites.
The merozoite arranged themselves around the residual cytoplasm like the petals of rose flower.
This stage is called rosette stage.
One complete erythrocytic cycle takes 48 hours in P. vivax.
The residual cytoplasm and haematin are eaten up by special cells, the phagocytes in the spleen, kidney and liver.
The interval between inoculation of Sporozoites into human blood and first attack of the fever is called incubation period.
Repeated erythrocytic cycles results, not only in intermittent attack of fever, but also in a large scale destruction of R.B.Cs, weakening the patient to a considerable extent.
In P.vivax, the erythrocytic Schizogony takes 48 hours and therefore the fever recurs rhythmically every third day.
Destruction of R.B.Cs in erythrocytic Schizogony releases toxins and makes the patient feel chilly.

(v) Formation of gametocytes:-

After a number of erythrocytic cycles, some merozoite, invading fresh R.B.Cs, grow not into normal schizont, but into a different kind of rounded form called gametocytes or gamonts.
These show sexual dimorphism, being of two types.
The male or microgametocyte is smaller and contains a large diffused nucleus.
The gametocytes donot divide, but remain as intracellular parasitrs within their host's blood corpuscles, until they either die or are ingested by the vector, in which they continue their Development.

(2) Sexual cycle of Plasmodium in mosquito :-

(i) Infection of mosquito:-

When a female Anopheles Mosquito sucks blood of the infected person, it receives R.B.Cs containing different stages of erythrocytic cycle, including gametocytes.
In its gut, all stages except the gametocytes are digested
Gametocytes however survive.
They break the corpuscle and become free in the stomach of mosquito.
Their becoming active depends upon temperature.
While the trophozoite and merozoites are active at high temperature (98.6°F) of the human body, the gametocytes need low temperature for further change and therefore, become active only in cold blooded mosquito host.
The Development of the gametocytes in the mosquito's stomach involves two imo events.

(1) Sexual cycle and

(2) Sporogony

Sexual cycle:-

(a) Gametogony or Gametogenesis:-

Gametogony or Gametogenesis means the Development of gametes.
Male and female gametes are dissimilar.
Such gametes are called heterogametes.

Formation of male gametes:-

The male or microgametocyte undergoes Spermatogenesis.
The nucleus of each rapidly divides by meiosis, into 6 to 8 haploid nuclei.
The later migrate to the periphery.
The cytoplasm gathers around these nuclei.
Suddenly each cytoplasmic mass, together with nucleus shoots out from the surface of the microgametocyte in the form of a 20 micro to 25 micro long, whip-like microgametes or sperms.
This process is called as exflagellation.
Soon they become free from the residual cytoplasm and start creeping by lashing movements.

Formation of female gametes:-

A macrogametocyte forms a single female gamete or macrogamete or ovum.
It's nucleus casts off one or two small pieces, which leave the Gametocyte with a bit or cytoplasm.
This converts the macrogametocyte into a microgamete.

(b) Fertilization:-

The megagamete developes a small cytoplasmic projection, the come of reception, on one side.
The nucleus moves into this cone.
One male gamete penetrates the female gametes through this cone.
The nuclei and cytoplasm of the gametes fuse to produce a diploid zygotic nucleus or synkaryon.
Syngamy is heterogamy or anisogamy as the uniting male and female gametes are dissimilar.
Zygotes are formed in the stomach of mosquito about 9 or 10 days after the blood meal.

(iii) Ookinete:-

The zygote, when formed is rounded and motionless.
After remaining inactive for sometime, each zygote starts elongating and undergoes certain changes so that, in about 9to 10 hours, it becomes 15 micro to 20 micro long and 3 micro thick, worm-like motile organism called vermicular or Ookinete.
The later has dense cytoplasm, a single pseudopodium -like blunt extension, one irregular nucleus, mitochondria, ribosomes, microtubules and 2 or more, non-contractile vacuoles.
The Ookinete pierces through the wall of stomach and comes to rest just beneath it's outermost layer.
Here , it reassumed sphere shape and soon becomes enclosed inside a cyst, about 8 micro to 10 micro in diameter.
The cyst-wall is derived partly from zygote and partly by tissues of stomach wall.
Encysted zygote is called oocyst or sporont.
Just one or two days after fertilization, 50 or more oocysts appear upon the surface of the stomach of the infected mosquito.

(3) Sporogony:-

Each oocyte undergoes asexual multiplication known as Sporogony.
It's nucleus divides repeatedly by mitosis, forming about 10000 minute daughter nuclei within 2-3 days.
At the same time ,the cytoplasm developes large vacuoles and takes up a sponge- like structure, in which numerous irregular cytoplasmic developes large vacuoles and takes up a sponge -like structure, in which numerous irregular cytoplasmic mass are formed connected by protoplamic strands.
Each cytoplasmic mass becomes elongated and spindle shaped.
Together with its nucleus, it now projects into the adjacent vacuole.
These spindle shaped bodies are called sporozoites.
Each sporozoite has tapering ends and a broad middle part containing a single nucleus.
By their pressure, the oocyst ruptures.
Floating freely in haemocoel or body cavity, these reach the salivary glands of the host and become lodged in its common salivary duct in large numbers.
In mosquito, whole sexual cycle is completed with 10-20 days depending upon temperature.

Some characters of P.vivax:-

Geographical distribution:- Tropical and sub-tropical regions
Prepatent period:- 8 days
Duration of erythrocytic cycle :- 48 days
No. Of metacryptozoites formed per Schizont:- 10000
Incubation period :-14 days
Signet ring form in R.B.Cs:- large ring with vacuole and usually one chromatin dot.
Haematin:- Dark brown granules and rodless
Schizont:- Larger than normal erythrocyte.
Gametocyte in R.B.Cs:- Rounded to oval
Microgametes formed:- 4 to 8
Duration of mosquito cycle:- 10 days
Type of malaria:- Benign tertian, death rate low.

Some characters of P.malariae:-

Geographical distribution:- Tropical and sub-tropical regions
Prepatent period:- 7-12 days
Duration of erythrocytic cycle:- 72 hours
No. Of metacryptozoites formed per Schizont :- 2000
Incubation period:- 18-24 days
Signet ring form in R.B.Cs:- Usually one ring and one chromatin dot.
Haematin:- Dark brown to black as coarse granules
Schizont:- Slightly smaller than normal erythrocyte.
Gametocyte in R.B.Cs:- Oval or circular
Microgametes formed:- 2 to 5
Duration of mosquito cycle:- 25-28 days
Type of malaria:- Quartan, severe.

Some characters of P.ovale:-

Geographical distribution:- West Africa and South America
Prepatent period:- 9 days
Duration of erythrocytic cycle:- 48 hours
No. Of metacryptozoites formed per Schizont:- 15000
Incubation period:- 14 days
Signet ring form in R.B.Cs:- Usually one ring and one dot
Haematin:- Dark brown less aboundant coarse granules
Schizont:- Much smaller than a normal erythrocyte.
Gametocyte in R.B.Cs:- Rounded or oval
Duration of mosquito cycle:- 16 days
Type of malaria:- Ovale or mild tertian severe

Some characters of P. falciparum:-

Geographical distribution:- Tropical, sub-tropical and warmer temperate regions.
Prepatent period:- 5-6 days
Duration of erythrocytic cycle:- 36-48 hours
No. Of metacryptozoites formed per Schizont:- 40000
Incubation period:- 12 days
Signet ring form in R.B.Cs:- Small ring situated at edge of R.B.Cs. sometimes 2 chromatin dots.
Haematin:- Dark brown coarse granules in a compact mass.
Schizont:- Smaller than a normal erythrocyte.
Gametocyte in R.B.Cs:-Sausage or crescent shaped
Microgametes formed:- 4 to 8
Duration of mosquito cycle:- 10-20 days
Type of malaria:-Malignant tertian, death rate high

Tuesday, August 18, 2020

PORIFERA : Scypha (sycon)

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Porifera : Scypha (Sycon)

Systematic position:-

Phylum:- PORIFERA

Class :- CALCISPONGIAE

Order :-HETEROCOELA

Family:-SYCETTIDAE

Genus:- Scypha

Habitat:-

Marine, colonial, branched and sedentary sponge of cosmopolitan distribution.
Attached to rocks etc. Just below low tides upto depth of 100 metres in area with strong wave action.
Commonly called Urn-shaped (due to base like shape) or crown sponge ( due to presence of a crawn like oscular fringe).
Commonly found species of Scypha are : S. ciliatum, S. elegans and S. raphanus.

Habits:-

1.) Locomotion:-

Absent due to sedentary mode of life.

2.) Feeding:-

Omnivores and holozoic .
Feeds upon planktons like protozoans, diatoms, bacteria and dead organic particles.
Food is drawn inside the sponge body along with a respiratory cum nutritive water current maintained by constant buy uncoordinated beating of flagella of collar cells.
Digestion is intracellular.

3.) Reproduction:-

shows both asexual and sexual reproduction.
Asexual reproduction occurs by external budding.
Scypha is monoecious or bisexual or hermaphrodite but always shows cross fertilization due to protogynous condition.
Fertilization is internal.
Development is indirect and include a free swimming and ciliated amphiblastula larva for dispersal.

4.) Regeneration:-

H.V. Witson reported very hight power of restorative regeneration is Scypha.

Morphology:-

A.) Shape, size, colour and symmetry:-

vase like shape,
20-25mm in height,
5-6 mm in diameter.
Greyish or light brown coloured and
radially symmetrical

B.) External appearance:-

Body surface is with a regular arrangements of polygonal elevations having groups of needle and spear shaped calcareous spicules so giving bristly appearance.
These elevations are seperated by narrow grooves having groups of small apertures called dermal ostia or inhalent or incurrent pores which lead into a central cavity, called spongocoel, through a system of interconnected canals
The spongocoel opens out by a single, wide and circular aperture called osculum or exhalent or excitement pore present at the distal free end of Scypha.
Osculum is guarded by a funnel shaped collar of long monoaxon spicules called oscular of, which prevents the entry of other animals inside the sponge body through osculum.

Canal system of Sycon:-

Definition:-

Canal system also called aquiferous system, is a system of interconnected canals of different types present inside the sponge body.

Components of Syconoid canal system:- Scypha has Syconoid canal system and is formed of following parts:-

Dermal Ostia:-

Also called inhalent or incurrent pores.
These are groups of small circular apertures present in the grooves lying between the polygonal elevations of the body surface.
These are present in a thin pore membrane which closes the incurrent canal externally.
Dermal Ostia are surrounded by contractile cells, called myocytes, which regulate their opening and closing.
These act as mouths for ingoing water current.

b) Incurrent canals:-

also called inhalent or afferent canals.
These are narrow be squarish canals.
Formed by invaginations of surface ectopinacoderm and end blindly on the inner side just outer to spongocoel.

c) Prosopyles(pros.= Near; Pyle= gate)

These are short, narrow canals(each about 5mm) which connect the incurrent canals with the radial canals.
These are intercellular and not intracellular as in Leucosolenia.

d) Radial canals:-

Also called flagellated canals.
These are wider and octagonal canals.
Each is externally closed just inner to the polygonal surface elevation while internally opens in the excurrent canal by apopyle.
It is lined by a layer of flagellated cells called collar cells or choanocyte these are formed by evagination of wall of spongocoel of Asconoid canal system.
The incurrent and radial canals lie parallel and alternate to each other both vertically and radially.
The arrangement of these canals is such that each radial canal is surrounded by four Incurrent canals and vice versa

e) Apopyle (app=away; Pyle= gate)

Also called internal Ostia.
These are openings of radial canals into excurrent canals.
Each apopyle is a large circular aperture in the centre of a thin partition called diaphragm lying between the radial canal and excurrent canal.
It's size can be regulated by contractile cells, called myocytes, which is surrounded by apopyle and regulate it's opening and closing.

f) Excurrent canals:-

Also called exhalent or efferent canals.
These are small , wide chambers in which radial canals open.
These are lined by pinacocytes and internally open in the spongocoel by wide aperture called gastral ostium.

g) Spongocoel:-

Also called paragastric cavity or atrium or cloaca.
It is narrow and tubular cavity present in the centre of each branch of Sycon.
It is also lined by flat and polygonal pinacocytes.
Spongocoels of different branches are continuous at the base.

h) Osculum:-

Also called exhalent or Excurrent aperture.
It is large circular aperture at the tip of each branch.
It is guarded by a group of monoaxon, needle or spear shaped spicules which collectively form an oscular fringe.
It is also surrounded by contractile cells, myocytes, which form a kind of sphincter which regulates it's opening and closing

Physiology of canal system:-

The flagella of collar cells of radial canals undergo constant but uncoordinated beating and maintain a water current which follows following path:-
Outside water( Dermal Ostia) -- > incurrent canal ( Prosopyles) -- > Radial canals (Apopyles) -- > Excurrent canals ( Gastral Ostia ) --> Spongocoel (Osculum) --> outside.

This ingoing water current helps in following metabolic functione of a sedentary sycon:-

Brings food for nutrition.
Brings oxygen for respiration
Brings sperms of another sponge for reproduction

The outgoing water current also helps in:-

Carries out undigested food for egestion
Carries out nitrogenous wastes for excretion.

Histology of Sycon:-

Histologically the sponge is diploblastic (develops from two primary germ layers).
Even body wall of adult Sycon is formed of 2layers :
A) Dermal layer or Pinacoderm
B) Gastral later or Choanoderm

A) Dermal layer or Pinacoderm:-

It is formed of single layer of large, highly contractile, thin, flat, ectodermal in origin and polygonal cells called pinacocytes.
These pinacocytes are cemented together like the tiles in a floor.
Each cell has a nucleus in its central swollen part.
Dermal layer is differentiated into 2 types:-
Exopinacoderm:- which covers the outer surface of the body
Endopinacoderm:-which lines incurrent canals, Excurrent canals and spongocoel.

Functions:- It provides protection from mechanical injuries and entry of germs.
It keeps a limit to semi-fluid mesoglea and prevente it's dispersion in water.
Due to its contractile nature, it shortens it's sponge body to great extent.

Modifications of Pinacocytes:-

To perform special functions, pinacocytes are modified into following cell types:-
Porocytes:- also called pore cells.
These are thin walled, tubular cells present in the inner lining of incurrent canals.
These are open at both the ends and have tubular intracellular canals called Prosopyles, which connect incurrent canal to radial canal.
These are present only in young sponge but are absent in the adult sponge.

Myocytes:-

These are elongated, fusiform shaped highly contractile cells which are present around the aperture like dermal Ostia, apopyle and oscula.
These act as sphincter to regulate the opening and closing of these aperture.
Scleroblasts:- These are modified pinacocytes which means migrate into mesoglea and form calcareous spicules, so are also called calcoblasts

B) Gastral layer or Choanoderm:- it is the inner lines only radial canals.
It is formed of large, loosely arranged and flagellated cells called collar cells or choanocytes.

Structure:-

Each choanocytes is an oval or rounded cell having vacuolated cytoplasm, single nucleus and a long , whit like vibratile flagellum on its inner side.
Flagellum arises from a cytoplasmic granules, called centroblepharoplast, a combination of centrioles and blepharoplast.
It is connected to a darkly stained chromatin body called parabasal body, present on the nucleus, by a fine fibril called rhizoplast.
These are endodermal in origin.
The basal part of the flagellum is surrounded by a thin, transparent and contractile collar formed or 20-30 cytoplasmic processes, called microvilli which are about 0.03 to 0.10 micrometer and interconnected by a fibre like material.

Function:-

By constant but uncoordinated beating of their flagella, choanocytes maintain a water current for nutrition, respiration, excretion etc. It also secretes mesoglea.

Mesoglea:-

Also called mesenchyme or mesohyl.
It is middle, transparent, non living and gelatinous layer between the Pinacoderm and Choanoderm of body wall of sponge.
It's matrix is of proteinaceous nature and is mainly secreted by Choanoderm.
It is of uniform thickness except inner to incurrent canals and outer to Excurrent canals where it thickens greatly to form Gastral cortex and dermal cortex respectively.
It also has many free wandering cells on the basis of which mesoglea is called collenchyma or parenchyma.
These cells of mesoglea are derived either from Pinacoderm or from Choanoderm and are of 2 types:-
Scleroblasts:-These are modified pinacocytes which means migrate into mesoglea and form calcareous spicules, so are also called calcoblasts
Amoebocytes:- These are amoeboid shaped cells and are mainly derived from Choanoderm.
These move freely in mesoglea.

On the basis of their function, these are of following types:-

Collencytes or connective tissue cells :- These give rise fine and branched pseudopodia which collectively form a network. These secrete the collagen fibres
Chromocytes or Pigment cells:- These have loose pseudopodia while their cytoplasm has pigment granules so these give colour to sponge
Trophocytes or Nourishing cells:- These also have loose pseudopodia and are adapted to ingest, digest and distribute food.
Thesocytes or Storage cells:- These also have loose pseudopodia and store the reserve food as glycogen, far, glycoproteins or lipoprotein.
Phagocytes:- These also have loose pseudopodia and engulf and remove the damaged tissue
Archaeocytes or Embryonic cell gland cells:- These are large sized amoebocytes having blunt pseudopodia. These are undifferentiated or reserve cells and can differentiate into any other cell type depending upon requirement,so these are also called totipotent cells. These also help in regeneration while the gametes forming archaeocytes are called gonocytes.
Desmocytes or fibre cells:- these are long and slender cells which is present around the longitudinal channels and help in extension of sponge body.

Skeleton of Sycon:-

Scypha has an endoskeleton of large number of microscopic , crystalline, calcareous and needle-like structures called sclerites or spicules present in the mesenchyme of the body wall . These are always calcareous in nature

1) Types and orientation of Spicules:-

On the basis of their number of axes and rays, spicules of Scypha are of two types which are oriented in a characteristic way:-

(a) Monoaxons:-

These have only one axis and are of three types:-
Long, short and spear-like or cube like.
On the basis of their growth, monoaxon may be monoactinal (or uniradiate) called styles, or diactinal (or biradiate) called rhabds.
Long monoaxon spicules surrounded and guard the Osculum by forming an oscular fringe.
Short monoaxons mostly lie parallel to the radial canals.
Spear-shaped spicules, called oxeotea, are partly embedded in the dermal cortex while partly project out over the polygonal elevations to partly cover and protect the dermal Ostia.

(b) Tetraxons:-

These have four aces of growth and are of 2types: tetraradiate and triradiate spicules.
Tetraradiate Spicules have 4 rays.
These generally occur in the Gastral cortex along with the triradiate spicules.
Their one ray projects into the spongocoel.
Triradiate Spicules are formed by the loss of one ray from the tetraradiate Spicules
These generally lie along the radial canals with one ray directed inward.

(ii) Development of spicules:- Spicules are secreted by special amoebocyte called sclerocytes of mesenchyme which are derived from the modified pinacocytes called scleroblasts of Pinacoderm.
One scleroblasts secrets only one ray of a spicule so a Monoaxon spicule is secreted by one scleroblast while a triradiate and tetraradiate Spicules is secreted by three and four scleroblasts respectively.
Scleroblasts secreting calcareous spicules of Scypha are called calcoblasts.

(iii) Development of a Monoaxon spicule:-

A scleroblast becomes binucleate.
A minute and slender axial filament of organic matter is laid between two nuclei which is further deposited with calcium carbonate matter and finally a sheath of organic matter.
Two nuclei are pushed apart by the growth of spicule and finally the scleroblast is divided into two sclerocytes.
Inner sclerocytes is called founder as it is responsible for laying and lengthening of the spicule, while outer sclerocytes is called thickener as it deposits additional layers of calcium carbonate so increasing the thickness of spicules.
CaCO3 used is extracted from the surrounding sea water.
When the spicule is fully formed, both the sclerocytes leave the spicule, the founder first and the thickener later.

Development of a triradiate spicule:- A triradiate spicule is secreted by three scleroblast while come together in the form of a figure of a trifoil.
Each scleroblast becomes binucleate.
A minute Spicule is laid between two nuclei of each scleroblast.
Later these spicules act as three rays which finally meet at their inner ends to form a small triradiate spicule.
Each scleroblast is also finally divided into two sclerocytes so forming a sextet.
Three thickeners lie at the tip of triradiate spicule and increase the length of rays, while three founders remain joined for some time at the junction of three rays and increase their thickness by adding more layers of CaCO3.

Development of Tetraradiate Spicules:-

In the formation of Tetraradiate Spicules, the fourth ray is added to developing triradiate spicule by an additional scleroblast.

(iii) Chemical composition:-

Each calcareous spicule is formed of:-
CaCO3 - 87%
MgCO3 - 7%
Water -. 3%
Small amounts of other minerals.
An axial thread of organic matter, called spiculin.

(IV) Functions of skeleton:-

It provides mechanical support to soft body of sponge.
It gives definite shape to the sponge.
It protects the sponge from the wave actions of sea water
It helps in resisting external pressure.
It protects the sponge from other animals due to bristly nature.
It increases the stiffness of sponge tissue.

Physiology of Sycon:-

Movement:- Being sedentary in its habitat, Scypha has no active organs for locomotion.
It has only local contractile powers which are restricted to within 3 to 4 mm of the point of strong stimulus.
These reactions are slow responses and become noticeable only after one to several minutes of exposure to stimuli.
As sensory and nerve cells are absent in the sponge body, so these contractile cells acr as independent effectors.
The movements of amoebocyte are amoeboid or pseudopodial and not muscular.
The pinacocytes are highly contractile cells.

Nutrition:-

Food:- Scypha is omnivorous Nd holozoic .
It feeds upon planktons like protozoans, bacteria, diatoms and dead organic Matter.
So Scypha is microphagous in its feeding.

Ingestion:-

Scypha is a filter-feeder.
The collar cells or choanocytes maintain a water current by constant but uncoordinated beating of their flagella.
As the flageller beating is directed towards apopyle, which develops a negative pressure in the radial canals
So draw a water current which enters the sponge body through dermal Ostia and reaches the radial canal after passing through the incurrent canals and Prosopyles.
This incoming water current brings fine food particles along with it as dermal Ostia are very minute apertures, the size of which is further regulated by myocytes.
The flagella of choanocytes beat from their base to tip, so the water also flows in the same direction.
The microvilli of collar of choanocytes act as a filter and the food particles are trapped by these microvilli.
The cyclotic flow of protoplasm moves these food partly are trapped by these microvilli.
The cyclotic flow of protoplasts moves these food particles towards the base of microvilli from where these are ingested in the food vacuolate by the choanocytes or directly by underlying amoebocyte with the help of pseudopodia.
Larger food particles may be ingested by the Pinacocytes lining the incurrent canals.

(iii) Digestion:-

Digestion of Scypha is intracellular and occurs in the food vacuole which fuses with the primary lysosome with hydrolytic enzyme to form heterophagosome.
Medium in the food vacuole is first acidic but finally alkaline.
Food vacuole has all the three types of enzymes, Viz. Proteases, carbohydrase and lipase for the Digestion of protein, carbohydrates and fats respectively.
But it is not confirmed whether these enzyme's are secreted by Scypha or by bacteria.

Digestion:-

It may occur by cell to cell diffusion but is generated brought about by special amoebocyte called trophocytes which move about in the mesoglea and distribute nutrients to various cells.

(V) Storage:-

Reserve food is stored as glycogen, fats , glycoprotein or lipoprotein in the special amoebocytes called thesocytes.

(vi) Egestion :-

Choanocytes or amoebocyte, involved in intracellular digestion, throw the indigestible food particles in the radial canals from where these are expelled out along with the outgoing water current.

(vii) Respiration:-

Scypha is aerobic in respiration.
In this, respiration occurs through general body surface as there are no special respiratory organs and cells of both dermal and Gastral layers are in direct contact with water.
This permits direct exchange of gases between oxygen and carbon dioxide of body cells on the principal of diffusion.
Wave action ensures the constant supply of well oxygenated water whose importance is evident from that if the dermal Ostia are blocked with debris particles, then the sponges dies.
The rate of consumption of oxygen by Scypha has been found to range from 0.04 mL to 0.16 mL per gram of fresh weight per hour.
The upper half of the sponge consumes about 10 to 50% more oxygen per gram per hour than the basal half.

(iv) Excretion:-

Scypha is ammonotelic but it has no special excretory structures so ammonia of dermal cells lost by diffusion through the body surface in the surrounding sea water while ammonia of Gastral cells is released in the outgoing water current.
These wastes are carried away from the sponge by wave action.
Some science say that the metabolic wastes are taken up by amoebocyte which generally release them into the Spongocoel to be carried out along with the outgoing water current.

(V) Nervous system and behaviour:-

Scypha has no special sensory or nerve cells so there is no coordinated actions of the whole body but the cells are sensitive and react individually.
This sensitivity is maximally developed at the oscular rim but in other parts the stimuli can be conducted only upto 3 to 4 mm from the point of stimulation so the reactions to stimuli are very slow.
These slow and local reactions of sponges are sufficiently to fulfill the needs of sedentary scycon having only cellular organisation.
The sensitive cells have been found to behave as independent effectors.
Some kind of coordination has been reported among the myocytes surrounding the aperture like dermal Ostia, Apopyles and Osculum. These myocytes , surrounding a common aperture, contra simultaneously.
Tuzet and M Pavan's Dr Ceccatty suggested that the collencytes may act as neurons and form a kind of diffused nervous system connecting the pinacocytes, choanocytes and myocardial.
These neurons may receive and conducting the stimuli.

Reproduction:-

(1) Definition:-

Reproduction is the ability of all living organism to produce young ones similar to themselves in many characters.
It not only halos in survive but also helps in continuity of that race and group immortality.

(2) Types:-

On the basis of presence or absence of gametes, reproduction is of two types:-

(A) Asexual reproduction and

(B) Sexual reproduction

(A) Asexuality reproduction:-

It does not involve formation and fusion of gametes.
Scypha reproduces asexually by external budding.
In this, multicellular outgrowth, called bud, arise from the base of sponge and develops an Osculum at it's distal end.
It may separate from the parent and fix at a new substratum to form a new sponge but may remain attached to the parental body and may develop secondary buds to form a kind of colony.

(B) Sexual reproduction:-

It involves formation and fusion of gametes.

(a) Sexes:-

Scypha is a bisexual or monoecious and hermaphrodite but it always shows cross fertilization due to protogynous condition.

(b) Gonads:-

Gonads in Scypha are temporary as special sex organs are absent.
Archaeocytes or sometimes any amoebocyte or sometimes even choanocytes act as gonocytes or gonads to form the gametes.
For this the choanocytes lose flagellum, withdraw collar and move into the mesoglea to form the gametes.

(c) Gametogenesis:-

It involves formation of gametes.

(1) Spermatogenesis :-

It involves formation of spermatozoa.

In this archaeocytes or amoebocyte or even choanocytes acts as sperm mother cell or spermatogonium.
It gets covered by one or more flattened cover cells which are either derived from amoebocytes or formed by the division of spermatogonium .
The complex structure so formed is called sperm-nest or spermatocyst.
The spermatogonium divides mitotically to form 4-8 spermatocyst, each of which undergoes meiosis to form sperms.
Each sperm is formed of a rounded or oval head and a long vibratile tail.
The tail shows lashing movements which move the sperm in water in search of ovum.

(2) Oogenesis:-

It involves formation of ova.
In this, archaeocytes or amoebocyte or even choanocytes acts as egg mother cell or oogonium or ovocyte. It migrates in the radical canal, undergoes two mitotic divisions to form 4 oocytes.
Each oocyte passes through choanocytes to reach the mesoglea, enlarges in size by engulfing other cells or by receiving nutrition from nutritive trophocytes.
When mature oocyte undergoes meiosis and forms one ovum and two polar bodies.
During oogenesis, oogonium shows the amoeboid movements.
A ripe ovum is a large rounded cell having a large nucleus with a well developed nucleolus.
It lies in the wall of radial canal where waits for the sperm of another sponge.

(d) Fertilization :-

It involves fusion of gametes and is internal as the egg is fertilised in situ.
On maturity, spermatocyst ruptures and sperms are released in the radial canal and are discharged out in the sea water along with outgoing water current through Osculum.
The free sperms along with ingoing water current enter into another sponge and reach radial canals.
A sperm is taken either by wandering amoebocyte or a choanocytes for which the choanocytes loses its flagellum, withdraws the collar and sinks in the mesoglea to carry the sperm to waiting ovum.
Such a choanocytes is called sperm transient or carrier cell.
During fertilization, when sperm transient cell comes in contact with ovum, then the later develops a conical depression to receive sperm. Head of sperm swells up and is surrounded by a capsule while it's tail is lost.
The capsule with sperm head enters the ovum and forms the zygote.
So fertilization in Scypha is internal.
Later the zygote us surrounded by a brood capsule formed by aggregation of amoebocytes.

Development of Embryogeny:-

Development of Scypha started within the brood capsule and occurs in situ.
It involves following steps:-

(a) Cleavage :-

It involves the transformation of a single celled zygote into a single layered hollow spherical blastula large by rapid mitotic divisions of Zygote.
Cleavage in Scypha is holoblastic and unequal.
It starts when the Zygote lies in the mesoglea of the sponge.
First three cleavages are vertical or meridional and produce a pyramidal disc of eight cells called blastomeres.
Fourth cleavage is horizontal or equatorial and slightly above the equator so producing a sixteen celled stage.
At this stage, the blastomeres are arranged in two tiers, each formed of 8 blastomeres.

Depending upon size, blastomeres are of two types:-

(1) Micrometres:-

It forms the upper tier of 8 cells . These will form the Choanoderm.

(2) Macromeres:-

It forms the lower tier of 8 cells.
These lie towards the parent Choanoderm.
These will form the Dermal layer.
The Macromeres donot divide for some time while Micrometres divide by rapid mitosis to increase their number, become columnar and develop inward directed flagella.
Later , a blastocoel or segmented cavity is developed between the tiers of blastomeres.
The Embryo is now called blastula.
(b) Formation of stomoblastula:- Macromeres become rounded, granular and develop a blastopore between them which communicates with the blastocoel.
Blastopore acts as mouth and is used to ingest the surrounding amoebocyte for nutrition.
This feeding blastula like larva is called stomoblastula and is the parasite on its parent.
It's wall is formed of many small, elongated and flagellated Micrometres and 8 spherical and granular Macromeres
(c) Formation of amphiblastula:- Stomoblastula undergoes inversion so the flagella of micromere are now directed outward.
Now the Macromeres multiply grow on all sides and close the mouth.
Now Embryo elongates, ruptures the brood capsule and is released outside through radial canals, Excurrent canal, spongocoel and Osculum.
This free larva is more or less oval shaped.
It's wall is half flagellated of small and narrow flagellated Micromeres and half non-flagellated of large Macromeres and is called amphiblastula.
It is formed in the development of most of the members of O. Calcarea .
It swims freely in sea water keeping its flagellated pole forward, so helps in dispersal of a sedentary adult sponge.

(d) Formation of Gastrula :-

After a brief free-swimming period, flagellated half gets surrounded by non-flagellated micromeres.
This produces a two layered Gastrula larva having a newly formed cavity which opens out by blastopore at the invagination end.
In Gastrula, outer layer is formed of non-flagellated and granular Macromeres while inner layer is formed of small and flagellated Micromeres.
So gastrulation is opposite to inversion.

Metamorphosis:-

Metamorphosis involves the transformation of Gastrula larva into a young sponge.
During this, gastrula fixes itself to some substratum by its blastoporal endz elongates and becomes cylindrical.
Blastopore is closed by growth of both cell- layers while free end develops a perforation called Osculum.
During metamorphosis outer non-flagellated Macromeres flattern to form dermal layer of Pinacocytes and their derivatives like myocytes porocytes and calcoblasts while inner flagellated Micromeres form Gastral layer of choanocytes and line whole of central cavity representing future spongocoel.
Certain dermal cells act as porocyte and develop intracellular Prosopyles which act as dermal Ostia.
Young sponge now resembles the adult Asconoid Leucosolenia and is called Olynthus stage .
Mesoglea is developed between the dermal and Gastral layers and is mainly secreted by Choanoderm, so the sponge wall thickens .

Now this Olynthus stage is transformed into young Syconoid Scypha by following changes:-

(1) Incurrent canals are formed by invagination of dermal layer.
(2) Radial canals are formed by evagination of Gastral layer. The formation of radial canals start from the middle of the body.
(3) incurrent canals GT external bounded by pore membrane having intercellular dermal Ostia.
(4) Choanocytes are restricted in only radial canals.
(5) Scleroblasts and various amoebocyte are developed in mesoglea. Scleroblasts and myocytes are derived from the dermal layer while archaeocytes and other amoebocyte are Developed from the Gastral layer. So the mesenchymal cells are derived both the Embryonic layers.

Peculiarity in development:-

Development of Scypha is characterized by certain peculiar features like:-
(1) Blastula of Scypha is called Stomoblastula as it has mouth to ingest amoebocytes.
(2)Blastula undergoes inversion.
(3) Development includes a partly flagellated and partly non-flagellated amphiblastula larva.
(4) Gastrulation occurs by invagination.
(5) Most peculiar feature of development of Scypha is that the flagellated Micromeres and non-flagellated Macromeres form the Gastral and dermal layer respectively.
It is exactly reverse to the mode of Development in higher animals in which the flagellated and non- flagellated cells of gastrula give rise to outer ectoderm and inner endoderm respectively.
So two layers of a sponge gastrula cannot be called ectoderm and endoderm, and two layers of adult sponge cannot be named epidermis and gastrodermis as in coelenterates.