The Living Organisms and their Surroundings class 6th

 Assignment 

Lesson :The Living Organisms and their Surroundings 

Why is reproduction important for organisms? 

Fill in the blanks: 

(a) Saline water, hot air and sand are ................ components of a habitat. 

(b) The habitat of plants and animals that live in ................ is called the aquatic habitat.

(c) ................ enable a plant or an animal to live in its surroundings. 

(d) Plants and animals that live on land are said to live in ................ habitats

Paheli has a rose plant in her garden. How can she increase the number of rose plants in the garden? 

Why do desert snakes burrow deep into the sand during the day? 

Write the adaptation in aquatic plants due to which 

(a) submerged leaves can bend in the flowing water. 

(b) leaves can float on the surface of water. . 

Mention one adaptation present in the following animals: 

(a) In camels to keep their bodies away from the heat of sand. 

(b) In frogs to enable them to swim. 

(c) In dolphins and whales to breathe in air when they swim near the surface of water.

Some desert plants have very small leaves whereas some others have only spines. How does this benefit the plants? 

What are the specific features present in a deer that helps it to detect the presence of predators like lion? 

Read the features of plants given below: (a) Thick waxy stem (b) Short roots

(c) Cone shaped plants (d) Sloping branches (e) Small or spine-like leaves (f) Hollow stem 

Choose the type of plant for every feature given in a, b, c, d, e and f from the list given below: Aquatic plant, Desert plant, Mountainous plant

What are the adaptive features of a lion that helps it in hunting?

Answers 

1.Reproduction is very important for living organisms as it helps them to produce young ones of their own kind and maintains the continuity of life.

2.(a) abiotic ( non-living)

(b) water

(c) Adaptations

(d) terrestrial

3.Paheli can increase the number of rose plants in the garden by planting stem cuttings of rose plant. It is a common method of plant propagation in which 20-30 cm long pieces of one year old stems are cut and their lower ends are planted in the soil.

4. As the deeper layers of sand are cooler, so desert snakes burrow deep into the sand to stay away from heat of the desert during day time.

5.(a) Submerged leaves are long narrow and ribbon – like which can easily bend in flowing water and withstand water currents without getting damaged, e.g., tape grass.

(b) Stems/stalks of floating leaves are long, hollow and light which help the leaves to float over water surface.

6.(a) Long legs of camel help to keep the upper part of the body away from the heat of the sand on the ground.

(b) Webbed feet enable frog to swim in water.

(c) Blow holes present in dolphins and whales help them to breathe in air when they swim near the surface of water

7.Small leaves and spines are modifications of leaves, which are adaptations of plants to live in desert habitat. In these modifications the surface of leaf lamina is reduced thereby reducing water loss by transpiration.

8.Specific features present in deer that help them to detect the presence of predators like lion are:

(i) Long ears to hear and recognise movement of predators.

(ii) Eyes on the sides of its head which allow it to look in all directions.

9.(a) Desert plant

(b) Aquatic plant

(c) Mountainous plant

(d) Mountainous plant

(e) Desert plant

(f) Aquatic plant

10. Adaptive features of a lion that help it in hunting are as follows :

Brown body colour helps it to hide in dry grassland for avoiding detection by its prey.

 Eyes placed in front allow it to know the exact location and movements of its prey.

Strong paws, sharp teeth and long claws help it to catch and kill the prey.

Structure of atom Lesson 4 class 9th Chemistry

 Chapter 4 class 9th notes 

Introduction : 

• Till now we have learnt that matter is made up of atom and molecules

• Atom of same element are identical 

• Atom of different elements are different .

• But the ques arises in what sense these are different?

• THis was a major challenge to scientists to give answer .

• This mystery was solved towards the end of 19th century by scientists like J.J Thomson , Goldstein, Rutherford, Chadwick , Bohr and many more. 

• With their researches , it was established that atom is not as simple as was predicted by Dalton . 

• It is made up of a large number of particles out of which the most important are Electrons , protons and Neutrons 

Charged particles  in matter 

The electric nature of matter was indicated quite early in the form of fictional electricity. It was produced by rubbing two articles together such as glass rod with silk or fur . As a result of rubbing , they got electrically charged . As matter is constituted by atoms , this suggested the presence of charge in an atom. 

Discovery of electrons (e-) and cathode rays : 

First identified by JJ Thomson.

He performed this experiment in discharge tube . It is a long cylindrical tube sealed at both the ends and is fitted with two electrodes. Two electrodes are connected to a source of high voltage called a battery.

The electrodes connected to the negative terminal of the battery is called cathode .

The electrodes connected to the positive terminal of the battery is called anode .

The tube is connected to a vacuum pump so as to reduce the pressure inside the tube to an extent.

Fluorescent material is used on opposite side of cathode .

Observations :

(i) A current of very high voltage was passed through discharge tube under normal pressure of one atmosphere. 

No current passed as air is a bad conductor of electricity.

(ii) The pressure inside the discharge tube was slowly reduced to about 1 mm by working the vacuum pump and then current is passed .

Electricity start flowing and and light was emitted inside the tube. 

(iii) The emossion of light stopped when the pressure inside the tube was further reduced to about 0.01 mm of mercury. 

The wall of tube opposite to cathode glow with greenish light called fluorescence. 

Conclusion : 

Florescence is due to bombardment of the walls of tube by the rays emitted from the cathode . these were known as cathode rays .

Thomson repeat the same experiment by replacing  gases . He got same results.

Since these rays of particles moves towardspositivecharges electrode , so it itself carry negative charge. These negatrive charged particles are called electrons . 

Discovery of protons(p+) and anode rays : 

First identified by E. Goldstein.

He performed this experiment in modified discharge tube.It is a long cylindrical tube sealed at both the ends and is fitted with two electrodes. Two electrodes are connected to a source of high voltage called a battery.

The electrodes connected to the negative terminal of the battery is called cathode .

He used perforated electrode as cathode and placed it in centre and not at end. 

The electrodes connected to the positive terminal of the battery is called anode .

The tube is connected to a vacuum pump so as to reduce the pressure inside the tube to an extent.

Fluorescent material is used on opposite side of anode 

He used hydrogen gas first for his experiment.

Observation : 

Red colour glow on the side opposite to anode .

Conclusion : 

Florescence is due to bombardment of the walls of tube by the rays emitted from the anode. these were known as anode rays .

These rays are also called canal rays as these passed through canal of cathode. 

Thomson repeat the same experiment by replacing  gases . He got different results.

Since these rays of particles moves towards negative charges electrode , so it itself carry positive charge. These positive charged particles are called protons . 

Discovery of Neutrons (n) : 

Rutherford found that except for hydrogen atom , the atomic mass of no other element could be explained by electrons and protons only. . So Rutherford predicted the presence of some neutral particles present in the nucleus of an atom.

These neutral particles were discovered by Chadwick in 1931 , when bombarded a thin foil of beryllium metal with the fast moving alpha particles .

These particles have mass similar to proton but carry no charge.  

How does the atom look like?

Thomson` Model of an atom : 

According to him 

(i)An atom consists of a positively charged sphere and the electrons are embedded in it. 

(ii) The negative and positive charges are equal in magnitude. 

So, the atom as a whole is electrically neutral

Limitations: 

• He could not offer any experimental support to his atomic model.

• He could not explain the results of the experiments carried by Rutherfod and other scientists at a later stage.

Rutherford model of atom: 

 In this experiment, fast moving alpha (α)-particles were made to fall on a thin gold foil. 

• He selected a gold foil of about 1000 atoms thick. 

• the fast-moving α-particles was bombarded on this gold foil. 

Observations 

(i) Most of the fast moving α-particles passed straight through the gold foil. 

(ii) Some of the α-particles were deflected by the foil by small angles. 

(iii) Surprisingly one out of every 12000 particles appeared to rebound

Conclusion: 

 (i) Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected. 

(ii) Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space. 

(iii) A very small fraction of α-particles were deflected by 1800,indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom

Rutherford nuclear model of an atom(features):

(i) There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus. 

(ii) The electrons revolve around the nucleus in circular paths. 

(iii) The size of the nucleus is very small as compared to the size of the atom

Drawbacks of Rutherford’s model of the atom:

Maxwell Questioned that:  Any particle in a circular orbit would undergo acceleration. During acceleration, charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. If this were so, the atom should be highly unstable and hence matter would not exist in the form that we know.

So he could not explain the stability of atom .

BOHR’S MODEL OF ATOM:

(i)Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom. 

(ii) While revolving in discrete orbits the electrons do not radiate energy

These orbits or shells are called energy levels. Energy levels in an atom are shown.

These orbits or shells are represented by the letters K,L,M,N,… or the numbers, n=1,2,3,4,….

How are Electrons Distributed in Different Orbits (Shells)? in Different Orbits (Shells)?

The distribution of electrons into different orbits of an atom was suggested by Bohr and Bury. The following rules are followed for writing the number of electrons in different energy levels or shells: 

(i) The maximum number of electrons present in a shell is given by the formula 2n2, where ‘n’ is the orbit number or energy level Hence the maximum number of electrons in different shells are as follows: 

first orbit or K-shell will be = 2 × 12 = 2, 

second orbit or L-shell will be = 2 × 22 = 8,

third orbit or M-shell will be = 2 × 32 = 18, 

fourth orbit or N-shell will be = 2 × 42 = 32, and so on. 

(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8. (iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step-wise manner.

Atomic structure of the first eighteen elements is shown schematically: 

Valency : The combining capacity of an element. It can be 1,2,3 and 4 .

If outermost shell (valence shell) contain 1,2,3 or 4 electrons then the valency is same .

If outermost shell (valence shell) contain 5,6,7 or 8 electrons then the valency will be 8 minus the no. of valence electrons.

ATOMIC NUMBER(Z):

The atomic number is defined as the total number of protons present in the nucleus of an atom

Or 

The number of electrons present in neutral atom. 

Atomic Number = no of protons=no of electrons in neutral atom.

 Mass number(A)::

The sum of the total number of protons and neutrons present in the nucleus of an atom.

Notation for an atom

Isotopes :the atoms of the same element, having the same atomic number but different mass numbers.

Eg.hydrogen protium deuterium, and tritium

Eg. (i) carbon, (ii) chlorine, and , etc

Applications 

(i) An isotope of uranium is used as a fuel in nuclear reactors. 

(ii) An isotope of cobalt is used in the treatment of cancer. 

(iii) An isotope of iodine is used in the treatment of goitre.

The average atomic mass of chlorine atom,

ISOBARS: Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars.

Eg :calcium atomic no 20 and mass no 40 

Argon atomic no 18 and mass no 40 

8th assignment session 2024-25

 Annual syllabus 

1. Reproduction in Animals

2. Reaching the age of adolescence

3. Force and pressure 

4. Friction

5. Chemical effects of Electric current

6. Light

7. Combustion and flame 

Assignment 

Lesson 1 ` Crop production and management`

1.What is a crop?

2. What is ploughing and tilling ? State its advantages.

3. State the important steps taken during crop production.

4. Write short note on the terms : 1. storage and 2. harvesting

5. Propagation of ginger is generally done using

(a) Seed     (b) Stem         (c) root     (d) leaf

6.Which activity of the farmer can promote growth of earthworms and microbes in the field ?

7. Name the tool used with a tractor for sowing seeds in a field . what are the advantages of using this tool?

8. During which months do farmers grow mustard in India?

9. What is sowing ?

10. Name the two modern methods of irrigation that help us to use water economically.

11. Why can paddy not be grown in the winter season?

Lesson 2 ` Micro- organisms : friend and foe

1.Give one word answers

(a) The process of conversion of sugar into alcohol   

(b)Disease causing microbes     

(c) A virus that feeds on bacteria     

(d)The first scientist to have discovered microorganism     

(e) The scientist who discovered vaccine for smallpopx     

(f) The scientist who discovered fermentation     

(g) An insect which is a carrier of parasites of malaria     

(h) An insect which carries the dengue virus     

(i) A biological nitrogen fixer   

2. What are microorganism ? Where do they live ?

3. How microbes is used in making of curd and bread ?

4. Explain medicinal use of microorganisms.

5. Write some diseases caused by (a) Bacteria     (b) virus     (c) protozoa

6. What are preservatives ? Name some commonly used preservatives .

7. Explain in detail the process of pasteurisation .

8. What do you mean by carrier of disease ? Name two such carriers and the disease they caused .

9. What do you mean by food preservation ? Write some ways to preserve food.

10. Explain nitrogen cycle in detail.

Lesson 3 Coal and petroleum

Lesson 4 Combustion and flame

Q1 Fill in the blanks :

1. A blue flame on a burner shows _____ combustion .

2. Hottest part of the candle is its ____ zone .

3.Mined coal and petroleum are _____ fuels

4. ______ has the highest calorific value among the fuels.

Q2. MCQs

1. Which of the following is not used as fuels?

(a) LPG    (b) CNG     (c) hydrogen     (d) oxygen

2. Combustion is the process of

(a) Production of explosive sound     (b) Formation of carbon dioxide     

(c) vaporisation of a fuel                 (d) burning of fuel emitting heat

3. The colour of the flame with the highest amount of fuels?

(a) white     (b) yellow     (c) red     (d) blue

4. Which of the following is caused by burning of fuels?

(a) Acid rain         (b) global warming     (c) emissin of carbon monoxide     (d) all of these

Q 3. Answer the following questions

1. What are the requisites of combustion ?

2. Explain different types of fuels and their uses .

3. Write a short note on the calorific value of hydrogen . How Will you differentiate an ideal fuel.(characteristics of good fuel)

4. Define the terms :- ignition temperature , calorific value of the fuel , inflammable substances

lesson 5 Conservation of plants and animals

1. Why do some birds migrate from one place to another ?

2. Name any three (a) bird santuaries     (b) wildlife sanctuaries     (c) national parks in India

3. list some of the natural disasters which are a danger to biodiversity

4. Why do we consider tiger an endangered species ?

5. Why each one of us must plant at least one tree in our lifetime?

6. What are the main causes of extinction of species ?

7. What purpose is served by biosphere reserves?

8. How ecosystem is the self supporting system of an organism?

9. Write a report on project tiger.

10. Define endemic species.

11. Write some ways to save paper.

Lesson 6 Reproduction in Animals

1. Short Answer questions

(a) Creation of new life of its own kind

(b)Animals which lay eggs

(c) Animals which give birth to young ones.

(d) A sperm producing organ

(e) Ova producing organs

(f) Product of fertilization

(g) The organ where fertilization takes place in humans

(h) Fusion of gametes

(i) The organ which holds foetus in females .

2. How does hydra reproduce?

3. Explain in detail the male reproductive organs.

4. Explain in detail the female reproductive organs.

5. Explain the `invitro` technique of fertilization ? Why is it necessary to adopt this method of fertilization ?

6. What is a clone? Write advantages and disadvantages of cloning.

7. Describe post fertilisation stages till the formation of foetus in women.

8. Label the parts of female and male reproductive systems:

Lesson 7 Reaching the age of adolescence

Q1 Very short answer questons

(a) Period ofgrowth from childhood to adult

(b) The first menstrual flow

(c) Stoppage of menstruation

(d) The master endocrine gland

(e) The mineral essential component of thyroxine

(f) The hormone which regulates the maturation of testes.

(g) The hormone produced by ovaries on puberty

(h) The oil secreting gland present in the skin

(i) The protruding growth of larynx in male.

(j) The spoken term used for adolescence

2. How many chances are there in nature that a woman may be a male or a female baby?

3. What is a teenage period in life? Why do we call it teenage?

4. Why doe we call the pituatary gland as master gland ?

Q2. Short Answer Questions

1. What do you mean by the terms menarche and menupause?

2. Why is a diabetic patient advised to take insulin injections?

3. What are the nutritional necessities of adolescence and why?

4. Female foeticide is a crime against humanity .

match the following:

column 1         column II

1. Growth hormones                                             voice box

2.Pituatary gland                                                 thyroxine

3. XX chromosomes                                                male child

4. Adrenal gland                                                     male hormone

5. THYROID gland                                            Adrenaline

6. XY chromosomes                                         female child

7. Pancreas                                                        stoppage of menstruation

8. testosterone                                                 insulin

9. menopause                                                 master gland

10. Adam`s apple                                         pituitary gland

Lesson 8     Force and pressure (Grade8th)

1. It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.

Ans 1 It is difficult to cut cloth using a pair of scissors with blunt blades because blunt blades have more area and due to which applied force produces very less pressure. As we know that pressure is inversely proportional to area of cross-section, so it is difficult to cut cloth from blunt blades.

2.Two women are of the same weight. One wears sandals with pointed heels while the other wears sandals with flat soles. Which one would feel more comfortable while walking on a sandy beach? Give reasons for your answer.

Answer 2. While walking on a sandy surface, one needs the footwears of larger area so that the pressure exerted on the ground is minimum. So, in this case, the woman having the sandals with pointed heels will be less comfortable in walking while the other woman wears sandals with flat soles feels more comfortable while walking on sandy beach.

3. It is much easier to burst an inflated balloon with a needle than by a finger. Explain.

Answer 3. Because needle tip has very less area of cross-section in comparison to that of our finger and we know that pressure exerted by a force is inversely proportional to the area where it has been applied, so pressure exerted will be more by the needle tip than the finger.

4.What do you mean by contact force ? Explain with the help of example. 

Contact forces : Force that arises with the contact of 2 or more objects involved. Examples : Muscular force and Frictional Force

Muscular force is the type of force wherein we use our physical strength to change the state of motion of an object. Eg: Man pushing a car, Bullocks pulling a cart of load, Cycling, Weight Lifting

Frictional Force is a force that acts on all moving objects by the surface which it is in contact with.

The Frictional force is always in the direction opposite to the applied force

5..What do you mean by non contact force ? Explain with the help of example. 

Non-contact forces: Forces that arise without the contact of 2 or more objects involved. Examples: Magnetic Force, Electrostatic Force, Gravitational force

Magnetic Force is a force that attracts certain metal objects (like iron and iron filings) towards a magnet.

Gravitational : it is an attractive force between two massive bodies .

G= (gmM)/r2

Electrostatic force is the force exerted by a charged body on another charged or uncharged body

6. What is meant by atmospheric pressure ? What is the cause of atmospheric pressure?

Atmospheric pressure:- The air all around us also exerts pressure. This is known as Atmospheric Pressure. The value of atmospheric pressure is very high.

Atmospheric pressure is caused by the weight of the air molecules above the Earth's surface, which are pulled downward by the planet's gravitational force.

7.Two objects repel each other. This repulsion could be due to the

(a) frictional force only (b) electrostatic force only

(c) magnetic force only (d) either a magnetic or an electrostatic force

Answer. (d) The reason for repulsions may be either an electrostatic (in case of similar charges) or a magnetic (in case of similar pole_s) force.

8.A brick is kept in three different ways on a table as shown in figure. The pressure exerted by the brick on the table will be

(a) maximum in position A (b) maximum in position C

(c) maximum in position B (d) equal in all cases

Answer. (a) Pressure will be maximum in position A because area of contact is minimum in this case and area is inversely proportional to pressure.

lesson 9 Friction

Q1. Very short answer questions :-

1.In which direction does the force of friction act on a moving object ?

2. Write the factors on which friction between the solid surfaces depends.

3.Write the factors on which the frictional force of an object while moving through a fluid depends .

4. What is the advantage of providing rollers on your travelling suitcase ?

5. What type of shoes are worn by the mountaineers and why?

6. Why do wrestlers generally apply oil on their body while going for wresting ?

Q.2. Short answer questions :-

7. List any three harmful effects of friction .

8. List some ways to reduce friction.

9. What is special about streamlined shape?

10. Give reasons for the following :-

(a) Streamline shape of the fish helps it in swimming in water

(b) Car engine gets heated on running

(c) It is always easier to roll an object than to slide it on the surface.

11. Write advantages of friction .

12. Write methods to increase friction .

Lesson 10 Sound

Lesson 11th Chemical effects of Electric current

1.Name one metal which is a good conductor of electricity.

Ans:- Graphite 

2. Name some liquids which are weak conductors of electricity.

Ans:- Pure water, oil, glycerine

3. What makes tap water a conductor of electricity?

Ans:- Salts dissolved in water make the tap water good conductor of electricity.

4. Which of the two , magnetic compass or LED , is better to use in a tester and why?

Ans:-LED is better to use in a tester because it can detect even small amount of current passes . Also it is not affected by magnet nearby. 

Ans 2

1. What is LED ? Why does the LED have one leg short and the other long?

Ans:- LED is a device which glows a very weak current and it's glow is visible even from a distance. It contains one short leg which is connected to negative terminal of battery and one leg long which is connected to positive terminal of batter in the electric circuit.

2. What do you understand about conductors and non Conductors of electricity?

Ans:- Conductors: the substances through which electric current passes are Called conductors. Example: silver and copper etc.

Non Conductors(Insulators) The substances through which electric current donot passes are called non Conductors (Insulators)

Ex- Wood , plastic etc 

3. What happens when electric current is passed through a cut potato?

Ans:- When electric current is passes through cut potato, a greenish blue spot on the cut potato is formed around the positive terminal showing the change in colour on passing electric current through it. 

4. What are the various applications of Electrolysis?

Ans:- done in class

5. In what way is electroplating useful?

Ans:- done in class

6. With the help of an activity explain electroplating of a piece of iron with copper.

Ans:- Activity to explain the electroplating of a piece of iron with copper.

Material required: iron piece , copper plate , battery , switch , wires copper sulphate solution.

Procedure. To the beaker add 50 ml water and dissolve few crystals of Copper sulphate salt . 

Take a battery of suitable strength and set up the circuit through switch.

Tie the iron key to negative terminal of batter and copper plate to positive terminal of battery.

Suspend both the plates (iron and copper) in the copper sulphate solution.

Put the switch on to pass the current for 15-20 mins . 

Switch off the current after some time.

Observation: the iron key is found with a shiny uniform layer of copper. It has been electroplated with copper.

7. What are the various uses of the chemical effects of electric current?

Ans:- Uses of chemical effects of electric current are listed below: 

1. Electrolysis 

2. Change in colour of metal plate 

3. Electroplating

4. Purification of impure metal.

5. Preparing various compounds.

8. Define the following terms:- 

(a)Electrolyte: a substance that produces an electrically conducting solution when dissolved in water is called electrolyte.

(b) Cathode: It is an electrode with negative charge on it. It is connected to negative terminal of battery.

© Electrolysis: It is the decomposition of a compound from its solution on passing electric current through the electrolytes of solution.

(d) anode: It is an electrode with positive charge on it . It is connected to positive terminal of battery.

(e) electroplating: process of depositing a thin film of desired metal over the object by passing current through an electrolyte in its Electrolytic solution.

(f) Galvanising: The process the depositing a layer of zinc over the other metal is called galvanising. 

lesson 12 Some natural phenomena

Lesson 13 Light

1. Name the following:- 

(a) A highly polished glass with a reflecting surface

(b) Irregular reflection of light

(c) Central coloured part of an eye(d) Muscles which hold the lens in the eye in position.

(e) Instrument with three mirrors which shows multiple images.

(f) Angle between incident ray and the normal.

(g) Deficiency of this nutrient causes night blindness

2. Write uses of periscope and plane mirror.

3. Write some common diseases of the human eye.

4. What makes some people colour blind?

5. How many pictures should appear per second on screen in succession to have a moving picture?

6. Write characteristics of an image formed in a plane mirror.

7. Draw diagrams showing regular and diffused reflection.

8. How will you find out how many images wil be formed when two mirrors are placed at different angles?

9. Explain the function of the following parts of human eye:-

(a) Iris (b) rods (c) Retina (d) optic nerve (e) eye lens (f) cones10. What do you mean by short sightedness and long sightedness?

11. What is cataract and what is it's treatment?