Chapter 1 "Crop production and management"
Question 4.
Write a paragraph in your own words on each of the following.
(a) Preparation of soil
(b) Sowing
(c) Weeding
(d) Threshing
Answer:
(a) Preparation of soil: Soil preparation is necessary before growing a crop. It involves tilling and loosening the soil. This allows the roots to penetrate deep in the soil and to breath easily even when they are deep.
b) Sowing: The process of putting seeds into the soil is called sowing. The tool used traditionally for sowing seeds is funnel-shaped. Nowadays a seed drill is used for sowing with the help of tractors. This tool sows the seed uniformly at a proper distance and depth.
c) Weeding: Some undesirable plants grow along with crop and these unwanted plants are called weeds. The process of removing these unwanted plants is called weeding.
d) Threshing: The process of separating the grain seeds from the chaff is called threshing.
Question 5.
Explain how fertilisers are different from manure.
Ans:-
Fertilisers:-
(i) A fertiliser is an inorganic salt
(ii) A fertiliser is prepared in factories.
(iii) A fertiliser does not provide any humus to the soil.
(iv) Fertilisers are very rich in plant nutrients like nitrogen, phosphorus and potassium.
Manures:-
(i) Manure is a natural substance obtained by the decomposition of cattle dung, human waste and plant residues.
(ii) Manure can be prepared in the fields.
(iii) Manure provides a lot of humus to the soil.
(iv) Manure is relatively less rich in plant nutrients.
Question 6.
What is irrigation? Describe two methods of irrigation which conserve water.
Answer:
The artificial method of watering the plants for assisting in their growth is called irrigation. Main sources of irrigation are wells, tube-wells, ponds, lakes, rivers.
Two methods which help us to conserve water are::-
i) Sprinkler irrigation system: This irrigation system has an arrangement of vertical pipes with rotating nozzles on the top. It is more useful in the uneven and sandy land where sufficient water is not available.
ii) Drip irrigation system: This irrigation system has an arrangement of pipes or tubes with very small holes in them to water plants drop by drop just at the base of the root. It is very efficient as water is not wasted at all.
Question 7.
If wheat is sown in the kharif season, what would happen? Discuss.
Answer:
Wheat crop is sown from November/December to March/April. It is grown in winter and requires less water. If wheat is sown in Kharif season, its production will be decreased considerably.
Question 8.
Explain how soil gets affected by the continuous plantation of crops in a field.
Answer:
Continuous plantation of crops makes the soil poorer in certain nutrients as the crops take up nutrients from the soil. The soil becomes infertile. It does not get enough time to replenish the nutrients.
Question 9.
What are the weeds? How can we control them?
The undesirable and unwanted plants which grow naturally along with the crop are called weeds.
The growth of weeds can be controlled by adopting many ways.
Tilling before sowing of crops helps in the uprooting and killing of weeds, which may then dry up and get mixed with the soil.
Weeds are also controlled by using certain chemicals, called weedicides. Weedicides are sprayed in the fields to kill the weeds.
Chapter 2 Microorganisms : Friend and foe
Question 4.
Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
The microorganisms cannot be seen with our naked eyes because they are very small in size.
Some of these, such as fungus growing on bread, can be seen with a magnifying glass.
Other cannot be seen without the help of a microscope
Question 5.
What are the major groups of microorganisms?
Answer:
Microorganisms are classified on the basis of their size into four major groups. These groups are:
(a) Bacteria
(b) Fungi
(c) Protozoa
(d) Some algae
Question 6.
Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Rhizobium, Clostridium and Azotobacter
Question 7.
Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
Microorganisms are useful to us in many ways. For example,
- Bacteria like Lactobacillus convert milk into curd.
- Bacteria are also involved in the making of cheese.
- Acetobacter aceti is used for producing acetic acid from alcohol.
- Yeast is used in the commercial production of alcohol, wine and bakery products.
- Some specific microorganisms are helpful in manufacturing of antibiotics.
- Microorganisms act as cleansing agents and decompose the waste products into manure.
- Dead or weakened microbes are used in the preparation of vaccines.
- Some bacteria fix atmospheric nitrogen and increase soil fertility.
- Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption.
- Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed
Question 8.
Write a short paragraph on the harms caused by microorganisms.
Answer:
Microorganisms are harmful to us in many ways. For example,
Common ailments like cold, influenza (flu), cough, polio, chicken pox are caused by viruses.
Anthrax is a dangerous human and cattle diseases is also caused by bacteria.
Diseases like dysentery and malaria are caused by protozoa.
Ringworm is caused by fungi.
Several microbes causes diseases in plants and thus reduces the yield. Citrus canker, a bacterial disease, affects trees of citrus fruit and is spread by air.
Bhendi yellow vein mosaic disease is caused by a virus and is spread by insects in lady fingers. These make the food poisonous causing serious illness and even death. This food-borne illness is called food poisoning.
Question 9.
What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:
Antibiotics are the medicines which kill or stop the growth of the disease-causing microbes. They are manufactured by growing specific microorganisms. They are used to cure a variety of diseases.
It is important to take antibiotic only on the advice of a qualified doctor.
One must finish the course prescribed by the doctor to make the drug more effective.
Antibiotics must not be taken unnecessarily because it may kill beneficial bacteria also.
Antibiotics are however, not effective against cold and flu as they are caused by viruses.
Chapter 3 :- Synthetic fibres and plastic
Explain why some fibres are called synthetic.
Answer:
Some fibres are called synthetic fibres because they are made by man using chemicals.
Question 4.
Give examples which indicate that nylon fibres are very strong.
Answer:
The following examples indicate that nylon fibres are very strong.
- They are used for making parachutes and ropes for rock climbing.
- They are used in making seat-belts, fishing nets, tyre cord, a string for sports rackets and musical instruments.
Question 5.
Explain why plastic containers are favoured for storing food.
Answer:
Plastic containers are favoured for storing food because of the following reasons:
- the plastics do not react with the food stored in them.
- the plastics are lightweight and are strong.
- they are easy to handle and safe.
Question 6.
Explain the difference between thermoplastic and thermosetting plastics.
Answer:
Thermoplastics:-
(i) These plastics softened on heating and can be bent easily.
(ii) They do not lose their plasticity.
(iii) Examples are polyethene, PVC, etc.
Thermosetting plastics:-
(i) These plastics when moulded once, can’t be softened again.
(ii) They lose their plasticity.
(iii) Examples are bakelite and melamine.
Question 7.
Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plugboards
Answer:
(a) Since, thermosetting plastics are a bad conductor of heat and do not get heated up while cooking, they are used for making saucepan handles.
(b) Since thermosetting plastics are a bad conductor of electricity and the electric current does not pass through such plastics, they are used for making electric plugs/switches/plugboards.
Question 8.
Categorise the materials of the following products into ‘can be recycled’ and ‘can not be recycled’.
Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer:
Can be recycled:-Plastic toys carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs.
Cannot be recycled:-
Telephone instruments, cooker handles, ballpoint pens, electrical switches.
Question 9.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
He should buy cotton shirts. This is because cotton has more capacity to hold moisture than synthetic clothes. In summers we have extensive sweating which is easily soaked by cotton shirts and hence, cotton clothes are much better than the clothes made from synthetic material.
Question 10.
Give examples to show that plastics are non-corrosive in nature.
Answer:
Non reactive is resistant to get destroyed by chemical action.
Following are the examples that show that plastics are non-corrosive in nature.
- Plastic containers do not react with items stored in it.
- They do not get rusted when exposed to moisture and air.
- They do not decompose when left in open for a long period.
Question 11.
Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Answer:
No, the handle and bristles of a toothbrush should not be made of the same material.
This is because our gums are soft and the bristles should be made of soft material so that it does not harm the gums.
On the other hand, the handles should be made up of hard material so that it can give a firm grip.
Chapter 4
Question 5.
Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.
Ans:-
Question 6.
Give reasons for the following.
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Answer:
(a) Aluminium is highly malleable and it can be easily beaten in sheets to make its foil for wrapping purposes. It is also soft and does not react with food items. That is why aluminium foils are used . to wrap food items.
(b) Immersion rods made up of metallic substances because metals are good conductors of heat and electricity. They get hot very soon on the passage of electric current and warm the water.
(c) Copper is less reactive than zinc. So it cannot displace zinc from its solution.
(d) Sodium and potassium are highly reactive, so they are stored in kerosene.
Question 7.
Can you store the lemon pickle in an aluminium utensil? Explain.
Answer:
No, we cannot store lemon pickle in an aluminium utensil because aluminium is a metal and metals readily react with acids to produce hydrogen. When aluminium comes in contact with lemon, which is acidic, would react to give hydrogen and the pickles will be spoiled.
Question 9.
What happens when
(a) Dilute sulphuric acid is poured on a copper plate?
(b) Iron nails are placed in a copper sulphate solution?
Write word equations of the reactions involved.
Answer:
(a) No reaction will take place because copper is very less reactive.
(b) Iron being more reactive than copper will replace copper from its solution and brown coating of copper is deposited on the iron nails. Also, the blue colour turns green.
Iron + Copper sulphate (solution) → Iron sulphate (solution) + Copper
Question 10.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
(b) Write down the word equations of all the reactions taking place in this process.
(a) She can find the nature of the gas by using a wet litmus paper. After bringing the litmus paper in contact with the gas, if it turns the blue litmus paper into red, it is acidic. Similarly, if it turn the red litmus into blue, it is basic.
(b) (i) Carbon + Oxygen → Carbon dioxide
(ii) Carbon dioxide + Lime water → Milky
Question 11.
One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?
Answer:
The gold jewellery is dipped into an acidic solution called aqua regia (a mixture of hydrochloric acid and nitric acid) for polishing. On dipping the gold jewellery in the acid solution, the outer layer of gold dissolves and the inner shiny layer appears. This causes a slight loss in its weight.
Question 12.
‘Avoid plastics as far as possible’. Comment on this advice.
Answer:
Plastics must be avoided as far as possible.
The materials made of plastics are non-biodegradable.
The use of plastics has a bad effect on the environment
. When the plastics are burnt, it releases a lot of poisonous fumes into the atmosphere causing air pollution.
These plastic materials when eat up by the animals (like cows), choke their respiratory system.
This can cause death of these animals.
The waste plastic articles thrown here and there carelessly get into dirty water drains and sewers, and block them
. In a nutshell, plastics can be considered a threat to our environment.
Question 14.
‘Manufacturing synthetic fibres is actually helping the conservation of forests’. Comment.
Answer:
In the manufacturing of synthetic fibres, we use only chemical substances and no natural materials, thus, in turn, we conserve forests
Chapter 5
Question 1.
What are the advantages of using CNG and LPG as fuels?
Answer:
The advantages of using CNG and LPG as fuels are:
- They burn with a smokeless flame and so does not cause any pollution.
- They leave no ash on burning.
- They are easy to handle and convenient to store.
Question 2.
Name the petroleum product used for surfacing of roads.
Answer:
Bitumen
Question 3.
Describe how coal is formed from dead vegetation. What is this process called?
Answer:
Millions of years ago, trees, plants, ferns and forests got buried below the rocks, soil and sand due to natural processes like flooding, earthquake, etc. Slowly, as more soil deposited over them, they were compressed. This led to the conditions of high pressure and heat. These conditions along with the anaerobic conditions turned the carbon-enriched organic matter of wood into coal.
This slow process of conversion of wood into coal is called carbonisation.
Question 6.
Explain why fossil fuels are exhaustible natural resources.
Answer:
Fossil fuels take millions of years to be formed. They are limited in nature and cannot be replenished easily, once consumed. Hence, they are considered as exhaustible natural resources.
Question 7.
Describe the characteristics and uses of coke.
Answer:
Characteristics of coke: Coke is 98% pure carbon. It is a tough, porous and black substance. It pro-duces a very little smoke.
Uses of coke: Coke is very useful as fuel. It is a good reducing agent. It is widely used in metallurgical processes to reduce metals from their oxides. It is used for producing water gas
Question 8.
Explain the process of the formation of petroleum.
Answer:
Petroleum is formed by the burial of aquatic plants and animals below the sea bed. The marine animals and plants died thousands of years ago and settled down in the bottom of sea. In anaerobic conditions, microorganisms decompose this organic matter. Due to high pressure and heat, the dead remains of tiny plants and animals were slowly converted into petroleum.
Chapter 6
Question 1.
List conditions under which combustion can take place.
Answer:
Combustion can take place in the presence of:
(a) a combustible substance.
(b) oxygen, that is, the supporter of combustion.
(c) attainment of ignition temperature of the substance.
Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer:
The use of CNG in automobiles has reduced pollution in our cities as it is a quality fuel and has some benefits:
(a) It gives out less carbon dioxide gas, carbon monoxide gas, sulphur dioxide and nitrogen dioxide, which is beneficial as they play crucial role in global warming and acid rain.
(b) It leaves behind no residue after its combustion.
Question 4.
Compare LPG and wood as fuels.
Answer:
Question 5.
Give reasons.
(a) Water is not used to control fires involving electrical equipment.
(b) LPG is a better domestic fuel than wood.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Answer:
(a) Since water is a good conductor of electricity, it may result in electric shocks to the person trying to extinguish fire.
(b) LPG is better domestic fuel than wood because it does not produce gases, nor does it leave any residue behind. Moreover, it has more calorific value than wood.
(c) As its ignition temperature is low, the paper by itself catches fire easily. But a piece of paper wrapped around an aluminium pipe does not catch fire easily, as the heat being given gets absorbed by the aluminium pipe and the piece of paper does not get its ignition temperature.
Question 6.
Make a labelled diagram of a candle flame.
Answer:
Question 7.
Name the unit in which the calorific value of a fuel is expressed.
Answer:
The unit in which the calorific value of a fuel is expressed is kilojoules per kilogram (kJ/kg).
Question 8.
Explain how CO2 is able to control fires.
Answer:
As CO2 is heavier than oxygen, it forms a blanket around fire, because of which the supply of air is stopped. Men over, it brings down the temperature of the burning substance. In these ways, it plays a significant role in controlling fire.
Question 9.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer:
The green leaves hold some amount of water, so its ignition temperature gets increased and it does not burn easily. On the other hand, dry leaves are waterless, so they catch fire easily (having low ignition temperature).
Question 10.
Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer:
A goldsmith uses the outermost zone of a flame, which is non-luminous, to melt gold and silver as it is the hottest zone of the flame, having more temperature.
Question 11.
In an experiment, 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer:
Calorific value of a fuel = Heat Produced Amount of fuel
= 1800004.5 kJ/kg
= 40,000 kJ/kg.
Question 12.
Can the process of rusting be called combustion? Discuss.
Answer:
The process of rusting emits heat during the formation of its oxide. So we can call the process of rusting as slow combustion.
Question 13.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer:
The water which was put by Ramesh will get heated in a shorter time; because he had put it nearer to the hottest zone of the flame.
Chapter 7
Q.1.Name the elements that determine the weather of a place.
Ans. The temperature, humidity, rainfall, wind-speed, etc. are called the elements that determine the weather of a place.
Q.2. When are the maximum and minimum temperature likely to occur during the day?
Ans.The maximum temperature of the day occurs generally in the afternoon and the minimum temperature occurs in the early morning.
.7. The tropical rainforests has a large population of animals. Explain why it is so.
Ans. Because of continuous warmth and rain, the tropical region supports an enormous number and a wide variety of animals
Q.8.Explain with examples, why we find animals of certain kind living in particular climatic conditions.
Ans. Animals are adapted to survive in the conditions in which they live. Features and habits which help them to adapt to their surroundings are the result of evolution. So, to survive in a particular type of climate the animals must have certain adapted features. This is the reason we find animals of certain kind living in particular climatic conditions. For example, animals in the polar region are adapted to the extremely cold climate. They have special characteristics, such as white fur, strong sense of smell, a layer of fat under the skin, wide and large paws for swimming and walking in snow etc
.9. How do elephants living in the tropical rainforests adapt themselves?
Ans. The elephant has adapted to the conditions of rainforest in many remarkable ways. It has a trunk that it uses as a nose because of this it has a strong sense of smell. The trunk is also used by it for picking up food. Its tusks are modified teeth. These can tear the bark of trees that an elephant loves to eat. So, the elephant is able to handle the competition for food very well. Large ears of the elephant help it to hear even very soft sounds. They also help the elephant to keep cool in the hot* humid climate of the rainforest.
Chapter 8
Question 2.
Make a sketch of the human nerve cell. What function do nerve cells perform?
Answer:
Function of nerve cells: The function of the nerve cell is to receive and transfer messages, it helps to control and coordinate the working of different parts of the body.
Question 3.
Write short notes on the following.
(a) Cytoplasm
(b) Nucleus of a cell
Answer:
(a) Cytoplasm: The jelly-like substance found between the nucleus and the cell membrane is called cytoplasm. . Various organelles, like mitochondria, Golgi bodies, ribosomes, etc., of cells are present in the cytoplasm
(b) Nucleus of a cell: Nucleus of a cell is an important component of the living cell. It is located at the centre of the cell. It is separated from the cytoplasm by a membrane called nuclear membrane. It contains genetic material.
Question 4.
Which part of the cell contains organelles?
Answer:
Cytoplasm
Question 5.
Make sketches of animal and plant cells. State three differences between them.
Answer:
Question 6.
State the difference between eukaryotes and prokaryotes.
Solution:
Prokaryotic cells:-
- Membrane bound cell organelles are absent.
- Seen in Bacteria.
- No distinct nucleus.
- No definite nuclear membrane.
- Compartmentalization is not seen
- Chromosome single.
- Membrane bound organelles are present .
- Seen in plants , animals and fungi .
- Distinct nucleus present
- Well defined nucleus ( true nucleus)
- Compartmentalization is seen in eukaryotic cells.
- More than one chromosome
Question 7.
Where are chromosomes found in a cell? State their function.
Answer:
Chromosomes are present in the nucleus. The functions of chromosomes is to carry genes on them and to transfer the character from parents to the next generation.
Question 8.
‘Cells are the basic structural units of living organisms.’ Explain.
Answer:
Different cells combine to form tissues and tissues combine to form organs. Similarly, organs combine to form body. Thus they are termed as the basic structural unit of every living organism.
Question 9.
Explain why chloroplast are found only in plant cells?
Answer:
Chloroplasts are plastids required for the food making process, called photosynthesis, and thus they are only present in plant cells.
Chapter 9 " Reproduction in animals"
Question 1.
Explain the importance of reproduction in organisms.
Answer:
Reproduction is a vital phenomenon on this planet earth which is essential for existence and continuity of life and species on it, generation after generation.
Question 2.
Describe the process of fertilisation in human beings.
Answer:
In the process of fertilisation, sperms come in contact with an ova (egg). One of the sperms may fuse with the egg. The nuclei of the sperm and the egg fuse to form a single nucleus resulting in the formation of a fertilised egg called zygote. In human being, the fertilisation takes place inside the female body, known as internal fertilisation
Question 5.
Give two differences between a zygote and a foetus.
Answer:
Zygote
(i) It is a single celled, i.e., it contains only one cell.
(ii) It is formed by the fusion of male gamete or sperm and female gamete or ova (egg).
Foetus
(i) It is multicelled, i.e., it contains many cells.
(ii) It is formed by the repeated division of the zygote.
Question 6.
Define asexual reproduction. Describe two methods of asexual reproduction in animals.
Answer:
The mode of reproduction in which only a single parent is involved is called asexual reproduction. In this type of reproduction, sex cells (gametes) are not produced and no fusion of gametes takes place for the reproduction of zygote or offsprings. Asexual reproduction takes place in Amoeba, Hydra, yeast, starfish, sponges, etc.
There are mainly two methods of asexual reproduction:
(i) Binary fission: In binary fission, a single parent cell is divided into two equal individual cells as in Amoeba. It divides into two by division of their bodies, each of them gets one nucleus and develops into separate individual. The figure given below shows how binary fission occurs in Amoeba.
Budding: In budding, the organism develops a bulge called bud which further develops into an adult organism and separates itself from the parent body to lead an independent life. This type of reproduction is shown in Hydra. The following figure shows budding in Hydra.
Question 7.
In which female reproductive organ does the embryo get embedded?
Answer:
Uterus
Question 8.
What is metamorphosis? Give examples.
Answer:
The transformation of larva into an adult involving sudden and abrupt changes in the body of an ani¬mal during the life cycle of an invertebrate or amphibian is called metamorphosis. Example, frog and butterfly.
Question 9.
Differentiate between internal fertilisation and external fertilisation.
Answer:
Internal Fertilisation
(i) The fusion of male gamete or sperm and female gamete or ova occurs inside the body of a female partner, such as human beings, birds, and mammal.
(ii) The female partner lays either fertilised eggs or a fully grown young one.
(iii) Offsprings have a high chance of survival.
External Fertilisation
(i) The fusion of male gamete and female gamete takes place outside the body of a female partner, such as in frog, fish and starfish
(ii) The female partner discharges unfertilised eggs
(iii) Offsprings have a low chance of survival.
Chapter 10 " Reaching the age of adolescence"
Question 1.
What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer:
Hormones
Question 2.
Define adolescence.
Answer:
The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. The period of adolescence is normally 11 years to 19 years.
Question 3.
What is menstruation? Explain.
Answer:
In females, the ova or eggs begin to mature with the onset of puberty (10 to 12 years of age) one egg get matured and is released by one of the ovaries once in about 28 to 30 days. During this period, the wall of the uterus becomes thick so as to receive the fertilized egg. In case it is fertilized, it begins to develop. This results in pregnancy. If the fertilization fails to take place, the ovum or the released egg and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women. This is called menstruation. It occurs once in 28 to 30 days
Question 4.
List changes in the body that take place at puberty.
Answer:
The changes take place differently in the body of boys and girls at puberty. These change may be listed as below:
- There is sudden increase in the height of both boys and girls. However, both reach their maximum height at the age of 17 to 18 years.
- The voice of boys become hoarse and that of girls become shrill.
- Shoulders become broader and muscles grow more prominently in boys. In girls, the regions below the waist becomes wider.
- Hair start growing in different parts of boys and girls.
- In most of the teenagers, due to increased secretion of sweat and sebaceous gland, get acne and pimples on their face.
- Onset of puberty brings changes in secondary sexual characters in both male and female.
- Boys and girls become capable of reproduction.
- In girls, menstruation starts.
- Different types of hormones start to release in initiating a reproductive function.
Question 5.
Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer:
Question 6.
What are sex hormones? Why are they named so? State their function.
Answer:
The hormones which help and control the formation of secondary sexual characters are called sex hormones. They are named so because they control the sexual activities and are secreted by males and females separately.
Functions of sex hormones are given below separately:
Male sex hormone: It is also called testosterone. It is secreted by testes and causes changes in secondary sexual character of boys like growth of facial hair like moustache, beard, etc. It also stimulates spermatogenesis.
Female sex hormone: It is also called estrogen. It is secreted by ovaries and controls the secondary sexual characters in females, appearance of mammary glands, etc. It also maintains pregnancy.
Question 8.
Write notes on:
(a) Adam’s apple
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
Answer:
(a) Adam’s apple: During puberty, a change in the voice of boys and girls takes place due to increase in the size of the voice box or larynx. In boys, the voice box tends to protrude out on the upper part of the neck, below the chin and is often referred to as Adam’s apple.
(b) Secondary sexual characters: Those characters which are visible more apparently and help in distinguishing a male from a female are called secondary sexual characters. For example, in girls, breasts and in boys, facial hair, i.e., moustache and beard.
(c) Sex determination in the unborn baby: The sex of a child, i.e., whether it is a male or a female is determined at the time of fertilisation when a male gametes fuse with a female gamete. All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are sex chromosomes. A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) have only one set of chromosomes. The unfertilised egg always has one X chromosome.
But sperms are of two kinds—One having X chromosome, and the other having Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg or ovum at fertilisation, the zygote would develop into a male child. It is thus also clear that the sex chromosomes of the father determine the sex of an unborn baby.
Chapter 11 " Force and pressure"
Question 1.Give two examples each of the situations in which you push or pull to change the state of motion of objects.
Answer:(i) Push: We close drawer by pushing.
We move a wooden box by pushing.
(ii) Pull: We draw water from a well by pulling the rope.
A horse pulls a cart.
Question 2.Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:When we apply force on a rubber band to stretch it and on clay to change its shape.
Question 5:-In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer:
(a) Agents are fingers, object is lemon, effect of force changes the shape of lemon.
(b) Agents are fingers of the person squeezing the tube, object is toothpaste tube and effect of the force can be observed as the paste coming out of the tube (change in shape).
(c) Agent is the load suspended, object is the spring and effort can be seen in the form of elongation of spring on suspension of load (change in shape).
(d) Agent is muscles of athlete, object is athlete himself and effect of the force changes the state of motion of the athlete
Question 6.A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
The force due to hammering causes the change in the shape of the iron and iron can be moulded in the shape of the required tool.
Question 8.Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer:
Forces acting on bucket are as follows:
(i) Muscular force of arms acting upward.
(ii) Force of gravity acting downward.
Both the forces do not bring any change in the state of motion because both of them are acting in equal and opposite directions and thus they cancel each other’s effect.
Question 9.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer:
The forces that act when a rocket leaves launching pad are as follows:
(i) Gravitational force of the earth (downward)
(ii) Frictional force of air (in opposite direction)
Chapter 12 "Friction"
Question 4.
Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Answer:
Frictional force will act upward, i.e., the direction opposite to that of sliding book.
Question 5.
You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Answer:
The layer of soap makes the floor smooth due to which the friction is reduced. This makes the floor slippery and the foot cannot make a proper grip on the floor. Therefore it is difficult to walk on a soapy floor. We may slip on the floor.
Question 6.
Explain why sportsmen use shoes with spikes.
Answer:
Sportsmen use shoes with spikes to increase the friction between shoes and the surface. So the shoes with spikes do not slip while the sportsmen run and play.
Question 7.
Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Answer:
A heavy object produces more friction as it is pressed hard against the opposite surface. So Seema will have to apply a larger force.
Question 8.
Explain why sliding friction is less than static friction.
Answer:
The sliding friction is less than static friction because the sliding object get less time to interlock into the contact points on the floor. So it is somewhat easier to move an object already in motion than to get it started.
Question 9.
Give examples to show that friction is both a friend and a foe.
Answer:
Some points are given below which show that friction is both a friend and a foe:
Friction as a friend:
- It allows us to grip and catch any object.
- It helps us to walk comfortably on the floor.
- It helps to minimise the speed or to stop any moving object.
- It helps us to write.
Friction as a foe:
- It causes wear and tears in objects.
- It causes damage to the parts of machines and tools which further require money to get them repaired.
- It reduces the speed of moving objects, so more force is required.
- It produces hurdles in moving any object freely.
Question 10.
Explain why objects moving in fluids must have special shapes.
Answer:
The objects moving in fluids must have a special shape to overcome the fluid friction acting on them. Efforts are therefore made to minimise the friction, so objects are given special shape having pointed fronts with little broader middle portion which gets tapered at the back called streamlined.
Chapter 13 "Sound"
Question 5.
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
No. of oscillation = 40
Total time is taken = 4 seconds
Time period = 4/40= 1/10 sec
Frequency= 40/4 = 10Hz
Question 6.
The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Answer:
Number of vibrations per second = 500
Time period= 1/500= 0.002sec
Question 7.
Identify the part which vibrates to produce sound in the following instruments.
Dholak
Sitar
Flute
Answer:
Stretched membrane
String of sitar
Air column
Question 8.
What is the difference between noise and music? Can music become noise sometimes?
Answer:
The type of sound which are unpleasant to listen is known as noise whereas music is a pleasant sound, which produces a sensation.
Yes, music can become noise when it’s too loud.
Question 9.
List the sources of noise pollution in your surroundings.
Answer:
Following are the major sources of noise pollution:
Sound of vehicles
Sound of kitchen appliances
Sound of bursting crackers
Sound of loudspeakers, TV, transistors
Question 10.
Explain in what way noise pollution is harmful to humans.
Answer:
Noise pollution causes:
(a) Lack of sleep
(b) Anxiety
(c) Hypertension
and these are harmful to health.
Question 11.
Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer:
I would suggest my parents buy a house three lanes away from the roadside because house on the roadside would be much noisy in both days and night due to running vehicles. Whereas, a house three lanes away would be comparatively quieter as the intensity of noise decreases with the distance between the source and the listener
Question 12.
Sketch larynx and explain its function in your own words.
Answer:
Larynx is also known as voice box. It is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for passage of air (Fig. 13.12). When lung force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose.
When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.
Question 13.
Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
Answer:
The speed of light is more than that of the speed of sound. Thus, due to more speed of light it reaches us before sound. So, lightning is seen earlier and thunder is heard later
Chapter 14 " chemical effects of electric current"
Question 2.
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Answer:
The deflection in magnetic needle shows that the circuit is complete and the solution conducts electricity, i.e., it is a good conductor
Question 3.
Name three liquids, which when tested in the manner shown in Fig. 14.5. may cause the magnetic needle to deflect.
Answer:
Vinegar, lemon juice and tap water.
Question 4.
The bulb does not glow in the setup shown in Fig. 14.6. List the possible reasons. Explain your answer.
Answer:
The bulb may not glow because of the following reasons:
(i) The wires in the circuit may be loosely connected.
(ii) The bulb may be fused.
(iii) The cells may be used up.
(iv) The liquid may be an insulator, i.e., a poor conductor of electricity.
Question 6.
Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer:
No, pure water doesn’t conduct electricity. But when salt is dissolved in pure water, it conducts electricity.
Question 7.
In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.
Answer:
The water used in the water hoses is not pure water and is a good conductor of electricity. So, the fire¬men shut off the electric supply before spraying water to save themselves and other people from electrocution.
Question 8.
A child staying in a coastal region test the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you ex¬plain the reason?
Answer:
The seawater contains a huge amount of salts in comparison to drinking water, hence the seawater is a better conductor of electricity and it produces a stronger magnetic field in the wire and hence deflects the compass needle more.
Question 9.
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Answer:
No, it is highly dangerous to carry out the electrical repairs outdoors during the heavy downpour. It can cause electrocution, as water is a good conductor of electricity.
Question 10.
Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reasons?
Answer:
Rainwater is pure water which is an insulator but it gets mixed with air pollutants like sulphur dioxide and nitrogen oxides and form acidic solution, which is a good conductor of electricity. So, the compass needle showed deflection.
Question 11.
Prepare a list of objects around you that are electroplated.
Answer:
Objects that are electroplated are door handles, taps, rims of cycles, showers, the handlebar of cycles and bikes, gas burner, tin cans, metallic almirahs, buckles of belts, etc.
Question 12.
The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Answer:
The thick rod of impure copper plate is to be attached to the positive terminal of the battery because when electric current is passed through the copper sulphate solution, it gets dissociated into copper and sulphate. The free copper, being positively charged, gets drawn to the negative terminal of the battery and gets deposited on it. On the other hand the loss of copper from the solution is regained from the impure copper rod which is attached to the positive terminal of the battery.
Chapter 15 "Some natural phenomena"
Question 4.
Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Answer:
The electric discharge takes place between the body and the sweater due to friction. At the time of electric discharge some energy is released. In this case energy is released in the form of crackling sound.
Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Human body is a conductor of electricity. When a charged body is touched with hand, our body conducts its charges to the earth. Hence, by this way charged body loses its charge
Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Solution:
The destructive energy of an earthquake is measured on a scale called the Richter Scale.
Yes, it would be recorded by seismograph because this scale has the readings from 1 to 10. No it is not likely to cause much damage as earthquakes of magnitude higher than 5 is considered destructive in nature.
Question 7.
Suggest three measures to protect ourselves from lightning.
(i) Do not use TV or cable phone during lightning.
(ii) Stay indoor or under covered area.
(iii) Don’t take bath during lightning.
Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer:
A charged balloon is repelled by another charged balloon because both carry same type of charges. On the other hand, an uncharged balloon is attracted by another0 charged balloon as they have opposite charges. We know that same charges repel and opposite charges attract each other.
Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
Electroscope is a device which is used to detect the charge on a body. It works on the principle that like charges repel each other while unlike charges attract each other. It consists of a metal rod with thin metal strip or leaf attached to it at the bottom.
At the top, the metal rod enters in a metallic cup or disc. The bottom of the rod and the metal leaf are enclosed in a glass box for protection. When the disc of the electroscope is touched with a charged ebonite or glass rod, the metal leaves open out or diverge.
The extent of divergence depends upon the amount of charge on the electroscope. When the metal strips repel each other proves that the body is charged because repulsion is the sure test to detect that body is charged or not through an electroscope.
Question 10.
List three states in India where earthquakes are more likely to strike.
Answer:
Kashmir, Rajasthan and Gujarat.
Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Answer:
We will take the following precautions to protect ourselves:
(i) Move to open space. Find a clean spot away from buildings, trees and overhead power lines. Drop to the ground.
(ii) If we are in a car or a bus, will not come out. Drive slowly to a clear spot and remain in it till the earthquake stops.
Question 12.
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer:
No, it is not advisable to carry an umbrella at all. Its metallic objects are more prone to lightning stroke. So an umbrella increases the risk.
Chapter 16 "Light"
Chapter 17 " Stars and the plat system"
Chapter 18 "Pollution of Air and water"
Question 1.
What are the different ways in which water gets contaminated?
Answer:
Following are the ways by which water gets contaminated:
People dispose of garbage in the water.
Many industries discharge their harmful chemicals directly into rivers and streams.
Chemical fertilisers, pesticides and weedicides used in agricultural practices get dissolve in water and are washed away into water bodies from the fields.
Untreated sewage is directly discharged into water from household activities
Question 2.
At an individual level, how can you help to reduce air pollution?
Answer:
I can do the following things to reduce air pollution:
I will use public transport as far as possible.
I will generate awareness among people to reduce air pollution.
I will plant more and more trees because trees help to keep the environment clean and reduce air 1 pollution.
I will not use vehicles for short distances.
Question 3.
Clear, transparent water is always fit for drinking. Comment.
Answer:
No, this is not true that clean, transparent water is always fit for drinking. It is possible that they may carry disease-causing microorganisms. Thus, it is good to purify water before drinking.
Question 4.
You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.
Answer:
These are the measures that would help our town to ensure the supply of clean water to all its residents:
Chlorine tablets should be made available.
Proper cleaning of the water tank from time to time.
The water supply pipes should not come in contact with the sewage pipes.
Question 5.
Explain the differences between pure air and polluted air.
Answer:
Pure air contains 78% nitrogen, 21% oxygen and 0.03% C02. Other gases such as argon, methane, neon, water vapour, etc. are also found in small quantities. When this air is contaminated by unwanted substances which have harmful effect on both living and non-living things like nitrogen oxide, sulphur oxide, carbon monoxide, etc., is said to be polluted.
Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer:
Nitrogen dioxide, sulphur dioxides are the pollutants which react with the water vapour present in atmosphere to form sulphuric acid and nitric acid. These acids come down with the rain, making the rain acidic. This is called acid rain.
Following are the affects of acid rain:
It increases corrosion of metals.
It damages buildings and sculptural materials.
It removes the basic nutrients such as calcium from the soil.
It causes direct damage to plants and crops.
It causes skin eruptions in human being.
Question 8.
Describe the ‘Greenhouse Effect’ in your own words.
Answer:
Basically, the greenhouse effect means warming of the earth’s environment. When the sun’s ray falls on earth, a part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus helps in survival. CO2, methane and CO are the gases responsible for this effect.
Question 10.
Describe the threat to the beauty of the Taj Mahal.
Answer:
Taj Mahal has become a matter of concern due to pollutants in air that are discolouring its white marble. Acid rains due to increasing air pollution has started corroding the marble. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble. Thus making Taj Mahal losing its beauty.
Question 11.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer:
Increased level of nutrients in the water affect the survival of aquatic organisms as these act as nutrients for algae to flourish and once these algae die, they serve as food for decomposers like bacteria and a huge amount of oxygen in water body gets used up. This results in decrease in the oxygen level, which may kill aquatic organisms.
