Class 9 BiologyChapter 3NCERT 3.1
Tissues, and why plants and animals build them differently
A banyan tree spends its whole life in one spot; a cheetah chases its dinner across the grass. Their tissues explain both.
Think it over
- An amoeba is one cell and does everything itself. What does a body gain by handing different jobs to different cells?
- A mango tree cannot walk to food or shade. What does it need from its tissues that a goat does not?
- Your skin, your blood and your bones are all made of cells. Why do they look and feel so different?
In one minute
- Life is organised in levels: cell, then tissue, then organ, then organ system, then the whole organism.
- A tissue is a group of cells, similar in structure, that work together to do one particular job.
- Sharing out jobs among tissues is division of labour; it makes a many-celled body more efficient.
- Plants stay in one place and need firm support: their cells have rigid cell walls. Animals move, and their cells, with no wall, can change shape.
- Plants and animals also differ in how they get food, move materials and grow, so their tissues differ too.
From one cell to a whole organism
Every plant and animal starts life as a single cell. That cell divides again and again, and the copies do not all stay alike: some become skin that shields you, some become muscle that moves you, some become bone that holds you up, some become nerve that carries messages. Scientists still find this one of the most impressive feats in nature, and they study it closely because understanding it helps in medicine and farming.
In a single-celled organism such as Amoeba, one cell has to feed, move, breathe and get rid of waste all by itself. A many-celled body works more like a large company with departments. Step up the ladder below, for a plant and for an animal.
Tap a rung to read it
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One long muscle cell, able to shorten and pull.
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Many muscle cells side by side, pulling together.
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Muscle, nervous, connective and lining tissues built into one pump.
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The heart and blood vessels, carrying blood all round.
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All the organ systems working together.
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One long cell, joined end to end with others to form a tube.
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Sieve tubes, companion cells and others, carrying food.
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Epidermis, food making tissue, xylem and phloem in one organ.
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Stem, leaves and flowers working together above the ground.
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Root and shoot systems: the whole plant.
Our drawings, not to scale. On the plant ladder you may also meet "shoot system" for the stem, leaves and flowers together.
Look at the second rung. Cells that are alike in structure and team up to do one particular job form a tissue. Several kinds of tissue together build an organ, organs that cooperate make an organ system, and the organ systems together make the organism.
Handing out the jobs this way is called division of labour. Each tissue gets very good at its own task, so the body as a whole runs better and can manage complicated life processes. Two examples from you: muscle tissue moves your body and nervous tissue carries messages around it. Two from a plant: xylem carries water and minerals, and phloem carries food.
- Tissue
- Similar cells working as a team on one specific function.
- Division of labour
- Different tissues doing different jobs, which makes the body more efficient.
- Organ
- A body part built from more than one type of tissue, such as a leaf or the heart.
Quick check
Which list is in the correct order, from smallest to largest?
Show the answer
B. Cell, tissue, organ, organ system Cells group into tissues, tissues build organs, organs work together as organ systems.
A plant that stands, an animal that moves
Start with the biggest difference you can see. A plant is rooted to one spot for its whole life, so it has to stay firm and upright in wind and rain. An animal usually moves about to find food and escape danger (a few, such as sponges, stay fixed). Tap through the four contrasts below.
A plant stays in one place and must stand firm, so each of its cells has a rigid cell wall. Animal cells have no wall and can change shape, which suits a body that moves.
- 1Support
A plant stays in one place and must stand firm, so each of its cells has a rigid cell wall. Animal cells have no wall and can change shape, which suits a body that moves.
- 2Food
A plant makes its own food from sunlight by photosynthesis in its green tissues. An animal eats food made by others, and needs tissues that digest it.
- 3Transport
Plants carry water up and food around in xylem and phloem. Animals use very different tissues, such as blood pumped round the body, to move materials.
- 4Growth
A plant grows from a few growing zones, such as the tips of its shoots and roots. Animals grow in a different pattern, because different tissues are in charge of their growth.
Support. Each plant cell sits inside a rigid cell wall, and millions of walls together make stems stiff and strong. Animal cells have no wall, so they can bend and change shape, and that flexibility is what lets animal bodies run, swim and fly.
Food. Plants make their own food: their green tissues trap sunlight and build food by photosynthesis. Animals take in food made by others, so they need tissues that digest it.
Transport and growth. Plants and animals use quite different tissues to carry food and water around the body, and the tissues in charge of growth are different too, so the two grow in different patterns. The rest of this chapter shows how the build of each tissue suits its job.
Quick check
What lets animal cells change shape easily, which helps animals move?
Show the answer
B. They have no rigid cell wall Without a rigid wall the cell can bend and change shape; plant cells are held in shape by their walls.