Overview
How can we tell whether something is alive? This chapter begins with a snail in a still shell and a fast-moving car, and shows that one feature such as movement is not enough. Living beings share a set of characteristics: they move, need food, grow, respire, excrete, respond to stimuli, reproduce and eventually die. You will see each of these in both animals and plants, from the stomata through which leaves exchange air to the folding leaves of the touch-me-not. A fair experiment with four pots of bean seeds shows that seeds need air and the right amount of water to germinate, while most do not need light. Another experiment shows that roots grow downwards and shoots grow upwards and towards light, and you meet J. C. Bose and his crescograph. You then follow the life cycle of a bean plant from seed to flower to fruit and back to seed. Finally you study two animals whose bodies change greatly as they grow: the mosquito, with its egg, larva, pupa and adult, and how to break its cycle; and the frog, from spawn to tadpole, froglet and adult. The chapter ends by comparing the life cycles of plants and animals.
हिंदी में पढ़ें
किसी चीज़ को सजीव क्या बनाता है, बीज का अंकुरण, जड़ और प्ररोह कैसे बढ़ते हैं, और सेम के पौधे, मच्छर तथा मेंढक के जीवन चक्र।
Learning Objectives
- Distinguish living beings from non-living things using a set of characteristics
- Explain movement, nutrition, growth and respiration in plants and animals
- Explain excretion, response to stimuli, reproduction and death with examples
- Identify the conditions needed for seed germination from a fair experiment
- Describe how roots and shoots respond to light and direction
- Describe the stages in the life cycle of a flowering plant
- Describe the life cycle of a mosquito and ways to prevent mosquito breeding
- Describe the life cycle of a frog and compare the life cycles of plants and animals
Topics in this chapter
8 topics · tap a topic title to jump straight to it.
Living or non-living: how do we decide?
1Think first
2The idea, in plain words
On a morning walk, a girl bends to pick up a shell lying still on the path. Her mother stops her: the shell may be the home, and a part of the body, of a living snail. How can something that is not moving be alive? And how can a car, which moves very fast, be not alive?
Start by listing. Look around your classroom: a pencil, a book, a pigeon at the window, a plant in a pot, a car outside. Sort them into living and non-living and write a reason for each. Most of us say the pigeon is living because it moves. But the car moves too, and we know it is not alive. So movement alone cannot be the test.
Compare with yourself. You are a living being. A good way to decide is to ask: what can I do that a car cannot? You grow taller every year; a car stays the same size. You eat food; a car does not eat (fuel is not food that builds its body). You breathe all the time. You sweat and go to the toilet. You pull your foot away from a thorn. You were once a baby, born of your parents; no car was ever born of another car.
These are the characteristics of living beings. Scientists have listed them carefully:
- They move (in some way).
- They need food (nutrition).
- They grow.
- They respire (breathing is part of this).
- They excrete (remove wastes).
- They respond to stimuli.
- They reproduce.
- They eventually die.
A living being shows all of these. A non-living thing may show one or two (a car moves; a crystal can “grow” bigger), but never all of them together. That is why we must look at the whole list, not at one feature.
What about the snail? Inside its shell the snail breathes, eats leaves, grows, and lays eggs. The shell lying still does not mean the snail is dead or non-living. Carefully observing all the characteristics, not just one, gives the right answer.
3Worked example
- A pigeon is living: it eats, grows, breathes and lays eggs.
- A car is non-living even though it moves.
- A snail inside a still shell is living.
4Your turn
Why is movement alone NOT a good test for life?
5Remember this
Movement, food, growth and breathing
1Think first
2The idea, in plain words
Let us look at the characteristics one by one, starting with four of them.
1. Movement. Animals move from place to place. Plants do not, but they do show movement. Flowers open in the morning. Climbers such as money plant wind their tendrils or stems around any support near them. The insect-eating plant Drosera has saucer-shaped leaves covered with hair-like parts with sticky tips; when an insect lands, these hairs bend inwards and trap it. So movement is a feature of all living things, even if plants move slowly and in one place.
2. Nutrition. All living beings need food. Food gives them the energy and materials they need to live, grow and repair their bodies. Animals eat plants or other animals; green plants make their own food. Insect-eating plants like Drosera get some of their nutrients from the insects they trap.
3. Growth. Can you still wear the clothes you wore four years ago? No, because you have grown. Puppies become dogs, seedlings become trees. Living beings grow by adding new material to their bodies from inside, using the food they take in.
4. Respiration. Count your breaths per minute while sitting, after a short walk, after running and after dancing. The number goes up as you do more work. When we breathe in, air enters our body; when we breathe out, air leaves. Watch a resting dog or cow: its belly rises and falls. Breathing is part of a process called respiration, which releases energy from food. Plants respire too. Their leaves have tiny pores called stomata through which air goes in and out. Stomata are too small to see without a microscope. All living beings respire.
| Activity | Breaths per minute (example) |
| Sitting quietly | about 15 |
| After a short walk | about 20 |
| After running | about 30 or more |
The numbers in the table are only an example; your own counts will be different. The pattern is what matters: the more active you are, the faster you breathe, because your body needs more energy.
3Worked example
- Drosera traps insects with sticky hairs.
- A climber winds around a stick.
- Breathing gets faster after running.
4Your turn
Through which tiny pores do leaves take in and give out air?
5Remember this
Excretion, response to stimuli, reproduction and death
1Think first
2The idea, in plain words
5. Excretion. On hot days white patches often form on shirts near the armpits. They are left by sweat, which carries water and salts out of the body. Urine is another waste that the body removes. Removing waste products from the body is called excretion. Plants excrete too: on grass and rose leaves in the early morning you may see tiny droplets at the leaf edges, which is extra water and minerals given out by the plant. All living beings excrete.
6. Response to stimuli. If you step on a thorn with bare feet, you pull your foot away at once. If you touch a hot cup, you snatch your hand back. The thorn and the hot cup are stimuli (one is a stimulus). A stimulus is anything that makes a living being react. Plants respond to stimuli too:
- The leaves of touch-me-not (chhui-mui, lajjalu, Mimosa) fold up when touched.
- The leaflets of the amla (Indian gooseberry) fold together after sunset; these are sometimes called sleeping leaves. Here the stimulus is the fading light.
7. Reproduction. Cats have kittens, hens hatch chicks, a mango seed grows into a new mango tree. Have you ever seen a baby pencil or a young chair? Never. Reproduction is producing new ones of one’s own kind. It is needed for the continuity of life: without it, every kind of living being would disappear when its members died.
8. Death. When a living being stops showing these characteristics, even though food, air and water are available, it is dead. Every living being eventually dies; non-living things never “die” because they were never alive.
What about a seed? A dry seed in a packet does not seem to grow, eat or move. Yet when it gets water and air, it germinates and grows into a plant. So a seed is a living thing that is resting; it shows its life processes when conditions are right. The next topic tests what those conditions are.
3Worked example
- Sweating removes water and salts.
- Touch-me-not leaves fold when touched.
- A cow gives birth to a calf.
4Your turn
Why is reproduction necessary for living beings?
5Remember this
What does a seed need to germinate?
1Think first
2The idea, in plain words
When a seed sprouts and a tiny root and shoot come out, we say it has germinated. What does a seed need for this? Let us test it fairly with bean seeds.
The four-pot experiment. Take four identical pots of garden soil and sow four bean seeds in each. Keep them for about two weeks as follows:
| Pot | Condition | Air | Water | Light | Germinates? |
| A | Dry soil, in sunlight | Yes | No | Yes | No |
| B | Soil under standing water, in sunlight | No (water fills the spaces) | Too much | Yes | No |
| C | Moist soil, in the dark | Yes | Yes | No | Yes |
| D | Moist soil, in sunlight | Yes | Yes | Yes | Yes |
What the results tell us. Seeds germinate in pots C and D, where they get both air and the right amount of water. In pot A there is no water. In pot B the soil is flooded, the air spaces between the soil particles are filled with water, and the seeds get no air. Pot C shows that light is not needed for bean seeds to germinate.
Why water? The outer covering of a seed is the seed coat. Water softens it and lets the tiny plant inside, the embryo, become active and start growing.
Why air and soil? The seed uses air from the spaces between soil particles. These spaces also let the young root push through the soil easily.
Light or dark? Most seeds do not need light to germinate, but once a seedling grows leaves it does need sunlight to keep growing. A few kinds are different: seeds of Coleus and Petunia need light, so they should not be buried, while seeds of Calendula and Zinnia need darkness, so they should be covered with soil.
Using this knowledge. Grains and pulses are stored dry, in closed containers, so that they do not get the water they need to sprout or spoil.
3Worked example
- Bean seeds sprout on moist cotton.
- Seeds in waterlogged soil fail to sprout.
- Pulses stored dry do not sprout.
4Your turn
Which conditions are essential for bean seeds to germinate?
5Remember this
Which way do roots and shoots grow?
1Think first
2The idea, in plain words
A seedling has two parts that grow in opposite directions: the root and the shoot. Does the plant decide its direction by itself? What happens if we turn it upside down, or if light comes from only one side?
The experiment. Germinate some bean or gram seeds on moist cloth until each has a small root and shoot. Tie each seedling gently with soft thread onto a wet blotting paper fixed to a glass plate, and stand each plate in a beaker with a little water so the blotting paper stays wet.
| Beaker | Set-up | Light | What happens |
| A | Seedling upright | From all sides | Root grows down, shoot grows up |
| B | Seedling upside down | From all sides | Root bends and turns downward; shoot bends and turns upward |
| C | Seedling upright, inside a box with one hole | From one side only | Shoot bends towards the hole (the light); root still grows downward |
What we conclude. Roots always grow downwards, even if the plant is turned over. Shoots grow upwards, and they bend towards light. This is a clear example of plants responding to stimuli (here, light and the downward pull towards the Earth) by growing in a particular direction. It is also an example of movement in plants: slow, but real.
Why is this useful? Roots going down reach water and minerals in the soil and hold the plant firmly. Shoots growing up and towards light help the leaves get sunlight, which they need to make food.
A pioneer: Jagadish Chandra Bose. The Indian scientist J. C. Bose (1858–1937) built an instrument called the crescograph to record very small movements and growth in plants. With it he could measure how fast plants grow and showed that plants sense and respond to stimuli such as light, heat, electricity and gravity.
Try this. Lay a potted plant on its side for a week. Predict what the shoot will do, then check.
3Worked example
- House plants near a window bend towards it.
- Roots of an upside-down seedling turn downward.
- A potted plant laid on its side turns its shoot upward.
4Your turn
In a box with a hole on one side, the shoot of a seedling grows:
5Remember this
The life cycle of a plant
1Think first
2The idea, in plain words
Plant a bean seed, look after it and observe it for about three months. Note the date and draw a sketch whenever you see a change. You will see a whole life unfold.
| Stage | What you see |
| I. Seed | A seed is sown in moist soil. |
| II. Germination | The seed coat splits; a root grows down and a shoot comes up. |
| III. Leaves | The seedling grows leaves and gets taller. |
| IV. Flowers | After some weeks, flowers appear. |
| V. Fruits | Some parts of the flowers dry and fall; the rest develops into pods (fruits) with seeds inside. |
| Death | After the pods form, the plant slowly turns yellow and dries, even if you keep watering it. |
Sow the seeds from the pods and they give rise to a new generation of bean plants. The whole journey from a seed, to a plant, to the next generation of seeds is called the life cycle of a plant. It is called a cycle because the end (seeds) is the start of the next round.
Questions to ask while you observe.
- How many days pass before the first flower appears?
- Which part of the flower becomes the pod?
- What happens to the plant after the pods form?
Not all plants live the same way. A bean plant completes its life in a few months. A mango or neem tree lives for many years and flowers and fruits again and again. But every plant life cycle has the same idea at its heart: growth, flowering, seeds, and new plants.
Can plants grow without seeds? Some can. New plants of potato grow from its “eyes”, sugarcane from pieces of stem, and rose from cuttings. You will learn about these later.
Linking to the characteristics. In this one activity you can see growth (the plant gets bigger), movement (shoots turning to light), nutrition (it needs water, minerals and sunlight), reproduction (seeds) and death (the plant dries after seeding).
- Seed → germination → seedling with leaves → flowers → fruits with seeds → new seeds sown
3Worked example
- A bean plant flowers and forms pods in a few months.
- Seeds from pods grow into new bean plants.
- A mango tree flowers year after year.
4Your turn
What does a flower develop into?
5Remember this
The life cycle of a mosquito
1Think first
2The idea, in plain words
Mosquitoes are not just a nuisance. Female mosquitoes suck blood and can spread diseases such as malaria, dengue and chikungunya. That is why we are told never to let water stand in coolers, pots, tyres or open containers. What does stagnant water have to do with mosquitoes?
A safety check. Look at standing water around your school or home (with an adult). You may see tiny wriggling creatures of two kinds. These are mosquito larvae and pupae, two stages in a mosquito’s life. They keep coming up to the surface because, though they live in water, they need air to breathe.
The four stages.
| Stage | Where | What happens |
| I. Egg | Laid by the female on or near water | Eggs hatch into larvae |
| II. Larva | In water | Wriggling, worm-like; feeds and grows |
| III. Pupa | In water | Comma-shaped; changes inside into the adult |
| IV. Adult | Rests on the water briefly, then flies off | Lives about 10 to 15 days; the female lays eggs and the cycle continues |
Each stage looks completely different from the next. It is hard to believe a flying mosquito comes out of a pupa! Such big changes in body shape and structure during life are a striking feature of some animals.
Finding the order by experiment. To find which comes first, put a few larvae in one container and a few pupae in another, with the same water. Observe daily. If the larvae become pupae, and adult mosquitoes come out of the pupae, the order must be larva then pupa then adult.
Breaking the cycle. Emptying standing water every week removes the place where eggs, larvae and pupae live. Spraying a thin layer of kerosene oil on water that cannot be emptied cuts off the air, so the larvae and pupae cannot breathe and die.
The silk moth also has four stages: egg, larva, pupa and adult. Before becoming a pupa, the larva wraps itself in a thread it makes; these threads are used to make silk. In India, the Khadi and Village Industries Commission (KVIC) has set up centres for silk production.
- Egg → larva → pupa → adult
3Worked example
- Larvae in a desert cooler with old water
- Kerosene on a drain to kill larvae
- Silk thread from the silk moth larva’s covering
4Your turn
What is the correct order of stages in a mosquito’s life?
5Remember this
The life cycle of a frog
1Think first
2The idea, in plain words
During the rainy season, at the edge of a shallow pond, you may find a mass of white jelly with black dots floating near water plants. This jelly is a cluster of frog eggs called spawn. (If you go to see it, go with an adult, wear full-sleeved clothes and watch quietly from a distance.)
From this spawn, a frog develops through four main stages:
| Stage | Approximate age | Description |
| I A. Spawn (eggs) | Day 1 | Eggs in jelly, in water |
| I B. Embryo | Day 3–4 | The tiny frog develops inside each egg |
| II A. Tadpole with tail | Day 7–10 | Hatches; fish-like, with a tail and no legs; lives in water |
| II B. Tadpole with legs | 8–10 weeks | Grows hind legs but still has a tail |
| III. Froglet | 12 weeks | Looks like a little frog with a short tail; lives in water but spends some time on land |
| IV. Adult frog | 14 weeks | Tail gone, strong legs for jumping; lives both in water and on land |
Each stage is suited to where it lives. The tadpole’s tail helps it swim in water. As the froglet starts going onto land, it loses its tail completely and its legs become strong for jumping and landing. So, besides body shape, the habitat also changes during the frog’s life, from water only to both water and land.
Mosquito and frog compared.
| Mosquito | Frog | |
| Stages | Egg, larva, pupa, adult | Egg, tadpole, froglet, adult |
| Early stages live in | Water | Water |
| Adult lives | In air and on land | In water and on land |
| Big changes in shape? | Yes | Yes |
Plants and animals compared. Both begin small, grow, reproduce and die, and their young start the next generation. But a plant usually stays in one place all its life, while many animals move and some, like the frog and mosquito, even change their homes as they grow.
These changes help each kind of living being survive and continue. Looking after ponds, trees and other homes of living things helps keep this living world going.
- Egg (spawn) → embryo → tadpole → tadpole with legs → froglet → adult frog
3Worked example
- Frog spawn near the edge of a pond
- Tadpoles swimming with their tails
- A froglet climbing out onto a leaf
4Your turn
Which stage of the frog has a tail but no legs?
5Remember this
Key Concepts
- Living being
- Anything that shows all the characteristics of life, such as growth, respiration and reproduction.
- Non-living thing
- Something that does not show all the characteristics of life, such as a stone or a car.
- Nutrition
- Taking in food to get energy and materials for life and growth.
- Growth
- An increase in the size of a living being from within, using food.
- Respiration
- The process that releases energy from food; breathing is part of it.
- Stomata
- Tiny pores on the surface of leaves through which air goes in and out.
- Excretion
- Removal of waste products from the body, such as sweat and urine.
- Stimulus
- Anything or any event that makes a living being respond, such as touch, heat or light.
- Reproduction
- Producing new ones of one’s own kind, which keeps life continuing.
- Germination
- The sprouting of a seed into a young plant with a root and a shoot.
- Seed coat
- The outer covering of a seed, softened by water during germination.
- Embryo
- The tiny plant inside a seed that develops into a new plant.
- Crescograph
- An instrument built by J. C. Bose to record the growth and responses of plants.
- Life cycle
- The series of stages a living being passes through, from birth to producing young of its own.
- Larva
- The worm-like stage that hatches from an egg in insects such as the mosquito and silk moth.
- Pupa
- The stage after the larva, in which the body changes into the adult.
- Spawn
- A jelly-covered mass of frog eggs found in water.
- Tadpole
- The young stage of a frog that lives in water and swims with a tail.
- Froglet
- A young frog that has legs and a shrinking tail and begins to spend time on land.
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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Why can we not use movement alone to decide whether something is living? / केवल गति के आधार पर हम यह क्यों तय नहीं कर सकते कि कोई चीज़ सजीव है?
Show answer
Some non-living things such as cars move, and some living things such as plants do not move from place to place, so we must check all the characteristics of life together. / कुछ निर्जीव चीज़ें जैसे कार गति करती हैं और कुछ सजीव जैसे पौधे एक स्थान से दूसरे स्थान नहीं जाते, इसलिए हमें जीवन के सभी लक्षणों को एक साथ जाँचना चाहिए।
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List the characteristics shared by all living beings. / सभी सजीवों में पाए जाने वाले लक्षणों की सूची बनाइए।
Show answer
All living beings move in some way, need food, grow, respire, excrete, respond to stimuli, reproduce and eventually die. / सभी सजीव किसी न किसी प्रकार गति करते हैं, भोजन की आवश्यकता रखते हैं, वृद्धि करते हैं, श्वसन करते हैं, उत्सर्जन करते हैं, उद्दीपनों के प्रति अनुक्रिया करते हैं, जनन करते हैं और अंत में मर जाते हैं।
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Give two examples of plants responding to stimuli. / उद्दीपनों के प्रति पौधों की अनुक्रिया के दो उदाहरण दीजिए।
Show answer
The leaves of the touch-me-not plant fold when touched, and the leaflets of the amla tree fold together after sunset when the light fades. / छुईमुई के पौधे की पत्तियाँ छूने पर मुड़ जाती हैं, और सूर्यास्त के बाद रोशनी कम होने पर आँवले की पत्तियाँ आपस में सिमट जाती हैं।
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What conditions are needed for a bean seed to germinate? / सेम के बीज के अंकुरण के लिए किन परिस्थितियों की आवश्यकता होती है?
Show answer
A bean seed needs air and the right amount of water to germinate; light is not needed for germination, though the seedling needs sunlight later to grow. / सेम के बीज को अंकुरण के लिए वायु और उचित मात्रा में जल चाहिए; अंकुरण के लिए प्रकाश आवश्यक नहीं है, यद्यपि बाद में पौधे को बढ़ने के लिए धूप चाहिए।
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Why do seeds kept in flooded soil fail to germinate? / जलमग्न मिट्टी में रखे बीज अंकुरित क्यों नहीं होते?
Show answer
In flooded soil the spaces between soil particles are filled with water, so the seeds do not get the air they need, and they fail to germinate. / जलमग्न मिट्टी में मिट्टी के कणों के बीच की जगह पानी से भर जाती है, इसलिए बीजों को आवश्यक वायु नहीं मिलती और वे अंकुरित नहीं होते।
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In which directions do the root and shoot of a plant grow? / पौधे की जड़ और प्ररोह किन दिशाओं में बढ़ते हैं?
Show answer
The root always grows downwards, even if the plant is turned over, while the shoot grows upwards and bends towards light. / जड़ हमेशा नीचे की ओर बढ़ती है, चाहे पौधे को उलट दिया जाए, जबकि प्ररोह ऊपर की ओर बढ़ता है और प्रकाश की ओर मुड़ता है।
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Describe the life cycle of a bean plant. / सेम के पौधे के जीवन चक्र का वर्णन कीजिए।
Show answer
A sown seed germinates, the seedling grows leaves, flowers appear, and the flowers develop into pods with seeds; the plant then dries and dies, and its seeds start a new generation. / बोया गया बीज अंकुरित होता है, पौधे में पत्तियाँ आती हैं, फूल खिलते हैं और फूल बीज वाली फलियों में बदल जाते हैं; फिर पौधा सूखकर मर जाता है और उसके बीज नई पीढ़ी शुरू करते हैं।
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Name the stages in the life cycle of a mosquito. How can we prevent mosquitoes from breeding? / मच्छर के जीवन चक्र की अवस्थाओं के नाम लिखिए। हम मच्छरों को पनपने से कैसे रोक सकते हैं?
Show answer
A mosquito passes through egg, larva, pupa and adult; we can prevent breeding by not letting water stand in coolers, pots and containers, and by spreading oil on water that cannot be removed. / मच्छर अंडा, लार्वा, प्यूपा और वयस्क अवस्थाओं से गुज़रता है; कूलर, गमलों और बर्तनों में पानी जमा न होने देकर और न हटाए जा सकने वाले पानी पर तेल डालकर हम इसे पनपने से रोक सकते हैं।
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What is the advantage of a tail to a tadpole? / टैडपोल के लिए पूँछ का क्या लाभ है?
Show answer
A tadpole lives only in water, and its tail helps it to swim; the tail is lost when the froglet begins living on land and uses strong legs to jump. / टैडपोल केवल पानी में रहता है और उसकी पूँछ उसे तैरने में मदद करती है; जब मेंढक का बच्चा ज़मीन पर रहने लगता है और कूदने के लिए मज़बूत टाँगों का उपयोग करता है तो पूँछ समाप्त हो जाती है।
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Give one similarity and one difference between the life cycles of a mosquito and a frog. / मच्छर और मेंढक के जीवन चक्र में एक समानता और एक अंतर बताइए।
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In both, the early stages live in water and the body changes greatly; but a mosquito has larva and pupa stages and its adult flies, while a frog has tadpole and froglet stages and its adult lives in water and on land. / दोनों में प्रारंभिक अवस्थाएँ पानी में रहती हैं और शरीर में बड़े परिवर्तन होते हैं; पर मच्छर में लार्वा और प्यूपा अवस्थाएँ होती हैं और वयस्क उड़ता है, जबकि मेंढक में टैडपोल और छोटे मेंढक की अवस्थाएँ होती हैं और वयस्क पानी व ज़मीन दोनों पर रहता है।
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