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KS3 Science · Year 7Chapter 3 · Specialised cells, tissues and organs
Year 7 · Chapter 3

Specialised cells, tissues and organs

By the end of this chapter you will be able to

  • Link the shape and structure of a specialised cell to its job
  • Describe the structure and job of an animal specialised cell
  • Describe the structure and job of a plant specialised cell
  • Describe how xylem and phloem carry substances around a plant
  • Put the levels of organisation in order: cell, tissue, organ, organ system

You should already know

  • Cell structures and their functions (Chapter 2 of this book)
  • Plant parts and their jobs, from Year 3 and Year 5 Science

Where this leads

  • Enzymes, diffusion and transport in later KS3 and GCSE biology

National Curriculum for England, Key Stage 3 science, Year 7. Content: B2 cells are specialised for particular functions (for example sperm, nerve, muscle, root hair, palisade, xylem and phloem cells), B2 cells group together to form tissues, tissues form organs, and organs form organ systems.

Exercise P  Do you remember?

1
FName the structure in a plant cell that carries out photosynthesis. Write the word.
2
FWhich structure in an animal cell controls the activities of the cell? Write the word.
3
FWhat is the name of the cell structure that releases energy by aerobic respiration? Write the word.
4
FWhich part of a plant takes in water from the soil? Write the word.
5
FWhat is 6 multiplied by 10? Write the number.
3.1

Cells are specialised for a job

Year 7
B2: cells are specialised for particular functions; the shape and structure of a cell match its job
Video lesson: Cells are specialised for a jobComing soon
Story. A nurse, Sam, and a botanist, Ali, meet at a science club. “Your muscle cells must be very different from my leaf cells,” Ali says. “They are,” says Sam. “Each cell is shaped and built for its own job.”

Many cells in a living thing have a particular job. A cell that is adapted to do one job well is called a specialised cell. Its shape and its structures match what it does. For example, a cell that needs a lot of energy has many mitochondria, and a cell that needs to absorb water has a large surface area.

Some cells are not specialised. An amoeba is one cell that does all of its jobs itself.

Key ideas

  • A specialised cell has a shape and structures that match its job.
  • A cell that needs lots of energy has many mitochondria.
  • A large surface area helps a cell absorb substances faster.
  • Structure and function are linked: ask what job the cell does first.
Worked example 3.1.1
A cell needs a lot of energy to move. Which structure would you expect it to have many of? Write the word.

Method. Link the energy need to the structure.

  1. Think about the need. Moving needs energy, and energy is released by aerobic respiration.
    energy
  2. Choose the structure. Mitochondria are where aerobic respiration happens, so a cell that moves needs many of them.
    mitochondria
  3. Write the answer.
    mitochondria

Check. More energy needs more mitochondria. ✓

Worked example 3.1.2
A root cell absorbs water from the soil. Which feature would help it do this best: a smooth surface or a large surface area? Write the words.

Method. Link absorption to the surface.

  1. Think about absorption. Absorbing water works best when a lot of the cell touches the soil.
    touches the soil
  2. Choose. A large surface area lets more water in at once.
    large surface area
  3. Write the answer.
    a large surface area

Check. Root hairs are one way to get a large surface area. ✓

Worked example 3.1.3
Is an amoeba a specialised cell? Write yes or no.

Method. Think about what an amoeba does.

  1. Think about its jobs. An amoeba does all its jobs in one cell, without a special shape for one job.
    all its jobs
  2. Decide. So an amoeba is not a specialised cell.
    no
  3. Write the answer.
    no

Check. Specialised cells are adapted to one job. ✓

Watch out

Watch out: a specialised cell is adapted for one job. Saying that a cell is “good” at something is not enough; name the structure that does the job.

Exam tip

Exam tip. When you describe a specialised cell, name a feature and link it to the job: “it has many mitochondria, so it releases more energy”.

Try it (with your teacher, or a grown-up at home). Look at a labelled diagram of a sperm cell and a nerve cell, in a textbook or on a slide. For each one, write one feature and one job. Do not use any stain or chemicals; this is a drawing task.

Exercise 3A  Cells are specialised for a job

1
FWhat is a cell that has a shape and structures matching one job called? Write the two words.
2
FWhich structure is found in large numbers in a cell that needs a lot of energy? Write the word.
3
FDoes an amoeba have one specialised job? Write yes or no.
4
FWhich feature of a root cell helps it absorb water: a large surface area or a thick cell wall? Write the words.
5
FIs it true that a cell with a large surface area can absorb substances faster? Write yes or no.
6
FWhat word means the shape and structure of a cell are matched to its job? Write the one word.
7
PSA cell has many mitochondria. Which job does it probably do? Write the words: energy or storage.
8
PSA cell absorbs substances from its surroundings. Which feature would you expect it to have: a large surface area or a small surface area? Write the words.
9
PSRuby says a cell with many chloroplasts is most likely to carry out photosynthesis. Is Ruby right? Write yes or no.
10
PSWorking scientifically: a student says a cell is specialised because it looks different. Give one better reason, using the structure and the job. Write one sentence.
11
RExplain why an amoeba does not need to be specialised. Write one sentence.
12
RChallenge: a muscle cell and a sperm cell both have many mitochondria. Explain why both need energy, but for different jobs. Write one sentence.
3.2

Animal specialised cells

Year 7
B2: sperm cells, nerve cells and muscle cells are specialised for particular functions
Video lesson: Animal specialised cellsComing soon
Story. A football coach says, “Your legs move because the muscles contract, and your brain knows because signals travel along nerves.” Her student asks, “What do the cells look like that do these jobs?”

A sperm cell is built to reach and fertilise an egg. It has a tail to swim, a middle piece packed with mitochondria to release energy, and a head that carries genetic material.

A nerve cell carries electrical signals. It has a long fibre, so signals can travel a long way, and branched ends that connect to other cells.

A muscle cell contracts to make movement. Contracting needs energy, so muscle cells have many mitochondria.

head: genetic materialtail: swimsmitochondria
A sperm cell: a head with genetic material, a middle piece with mitochondria, and a long tail.
cell bodylong fibre carries signals
A nerve cell: a cell body, a long fibre, and branched connections at the end.

The table summarises the three animal specialised cells.

Animal cellFeatureJob
sperm cella long tail and many mitochondriaswims to the egg, with genetic material
nerve cella long fibre and branched endscarries electrical signals
muscle cellmany mitochondriacontracts to make movement

Key ideas

  • A sperm cell has a tail to swim and a head with genetic material.
  • A nerve cell has a long fibre to carry signals over a long way.
  • A muscle cell has many mitochondria to release the energy it needs to contract.
  • Each feature is linked to the job of the cell.
Worked example 3.2.1
Which feature of a nerve cell helps it carry signals over a long distance? Write the words.

Method. Find the feature that is long.

  1. Look at the diagram. The nerve cell has a long fibre.
    long fibre
  2. Link it to the job. The long fibre lets the signal travel a long way without leaving the cell.
    signal travels
  3. Write the answer.
    a long fibre

Check. Branched ends connect to other cells. ✓

Worked example 3.2.2
What does the tail of a sperm cell help it do? Write the word.

Method. Link the tail to a job.

  1. Look at the diagram. The tail is long and thin.
    long and thin
  2. Link it to the job. A long, thin tail helps the sperm cell swim to the egg.
    swim
  3. Write the answer.
    swim

Check. The sperm cell is a single cell with one tail. ✓

Worked example 3.2.3
Why does a muscle cell have many mitochondria? Write the reason in a few words.

Method. Link contraction to energy.

  1. Think about the job. A muscle cell contracts to make movement.
    contracts
  2. Think about the energy. Contracting needs energy, which is released in the mitochondria.
    energy from mitochondria
  3. Write the answer.
    to release energy for contracting

Check. More contraction, more mitochondria. ✓

Watch out

Watch out: a nerve cell is a cell, not a nerve. Nerves are bundles of many nerve cells. A single nerve cell is the specialised unit.

Exam tip

Exam tip. For each animal specialised cell, give the feature and the job: sperm (tail, swims), nerve (long fibre, signals), muscle (mitochondria, contracts).

Try it (with your teacher, or a grown-up at home). With a teacher, look at a labelled diagram of a muscle cell. Count how many times the word “mitochondria” appears in the label, then say why a cell that contracts needs so many. Write one sentence about it.

Exercise 3B  Animal specialised cells

1
FWhich specialised cell has a tail to swim with? Write the words.
2
FWhich specialised cell carries electrical signals? Write the words.
3
FWhich specialised cell contracts to make movement? Write the words.
4
FWhich part of a sperm cell carries the genetic material? Write the word.
5
FWhich feature of a muscle cell is linked to its energy needs? Write the word.
6
FIs the long fibre of a nerve cell used to carry signals? Write yes or no.
7
PSWhich of the three animal cells has a middle piece packed with mitochondria? Write the words.
8
PSA nerve cell is much longer than a muscle cell. Which feature of the nerve cell makes this possible? Write the words.
9
PSAli says a sperm cell with no tail could still swim. Is Ali right? Write yes or no.
10
PSWorking scientifically: a student predicts that muscle cells contain fewer mitochondria than nerve cells. Explain why this prediction is not likely. Write one sentence.
11
RExplain how the structure of a sperm cell helps it reach an egg. Write one sentence.
12
RChallenge: explain why a nerve cell has branched ends. Write one sentence.
3.3

Plant specialised cells

Year 7
B2: root hair cells and palisade cells are specialised for absorbing water and minerals, and for photosynthesis
Video lesson: Plant specialised cellsComing soon
Story. Ali is a gardener. He pulls up a young plant and sees fine white hairs on the roots. “What are they for?” he asks. His teacher says, “Each one is a root hair cell, and its shape helps the plant take in water.”

A root hair cell has a long, thin extension that reaches between soil particles. This gives it a large surface area, so it can absorb water and mineral ions from the soil more quickly.

Palisade cells are packed in rows near the top of a leaf, where the light is strongest. They contain many chloroplasts, which carry out photosynthesis.

root hairssoil particlesmore surface area
A root hair cell with many long, thin hairs reaching into the soil.
palisade cells in a row, with chloroplasts (green)light comes from the top
Palisade cells in a row, with green chloroplasts.

The model below compares a root cell with a smooth surface, and one with root hairs. The surface area of the root hair cell is six times the smooth cell.

Root cell modelSurface area (mm²)
smooth cell10
cell with root hairs60

Key ideas

  • A root hair cell has a long, thin hair that gives a large surface area.
  • A large surface area helps the cell absorb water and mineral ions.
  • Palisade cells are near the top of the leaf, and have many chloroplasts.
  • Palisade cells carry out photosynthesis.
Worked example 3.3.1
How many times greater is the surface area of the cell with root hairs than the smooth cell? Write the number.

Method. Divide the bigger area by the smaller area.

  1. Read the areas. The cell with root hairs has an area of 60 mm squared, and the smooth cell has 10 mm squared.
    60 and 10
  2. Divide. Divide 60 by 10 to find how many times greater it is.
    60 / 10 = 6
  3. Write the answer.
    6

Check. 10 x 6 = 60. ✓

Worked example 3.3.2
Where are palisade cells found in a leaf? Write the words.

Method. Find the position in the diagram.

  1. Read the text. Palisade cells are packed in rows near the top of the leaf, where the light is strongest.
    near the top
  2. Name the place. So they are near the top of the leaf.
    near the top of the leaf
  3. Write the answer.
    near the top of the leaf

Check. Light reaches them first. ✓

Worked example 3.3.3
Name the structure in palisade cells that carries out photosynthesis. Write the word.

Method. Recall the structure.

  1. Recall. Chloroplasts carry out photosynthesis.
    chloroplasts
  2. Check. Palisade cells contain many of them.
    many
  3. Write the answer.
    chloroplasts

Check. Chloroplasts are green because of chlorophyll. ✓

Watch out

Watch out: a root hair cell is not a hair on the head. It is a single cell, with one long extension that increases its surface area.

Exam tip

Exam tip. When you describe a root hair cell, link the long extension to a larger surface area, and the larger surface area to faster absorption.

Try it (with your teacher, or a grown-up at home). With a teacher, look at a labelled diagram of a palisade cell and a root hair cell side by side. Write one feature of each, and the job it does. Then explain which of the two has a larger surface area for its job.

Exercise 3C  Plant specialised cells

1
FWhich cell has a long, thin extension that increases its surface area? Write the words.
2
FWhich mineral is taken in by root hair cells: water, or mineral ions? Write one of them.
3
FWhere are palisade cells found in a leaf? Write the words.
4
FWhich structure in palisade cells is green and carries out photosynthesis? Write the word.
5
FIs the surface area of a root hair cell larger than that of a smooth cell? Write yes or no.
6
FHow many times greater is the root hair surface area than the smooth cell surface area? Write the number.
7
FWhich cell is packed in rows near the top of the leaf, where the light is strongest? Write the words.
8
FDoes a palisade cell carry out photosynthesis? Write yes or no.
9
PSA root hair cell has a surface area of 30 mm squared. The smooth cell has 10 mm squared. How many times greater is the root hair cell? Write the number.
10
PSA plant grows in dry soil. Which cell would absorb more water: a root hair cell or a palisade cell? Write the words.
11
PSWorking scientifically: a pupil says palisade cells have fewer chloroplasts than root hair cells. Is the claim likely to be correct? Write yes or no.
12
RExplain why palisade cells are arranged in rows near the top of the leaf. Write one sentence.
13
RChallenge: explain why a root hair cell is a good example of a cell with a large surface area compared with its volume. Write one sentence.
3.4

Xylem and phloem

Year 7
B2: xylem and phloem cells form tubes that transport water and mineral ions, and sugars, through a plant
Video lesson: Xylem and phloemComing soon
Story. Ruby puts a white flower stem into coloured water and leaves it overnight. In the morning the flower petals have changed colour. “How did the colour get up there?” she asks. Her teacher says, “The water travelled up through tubes in the stem called xylem.”

Xylem is a tissue made of long, hollow tubes. The cells have no end walls, and their walls are strengthened with lignin. Xylem carries water and mineral ions up the plant, from the roots to the leaves.

Phloem is a tissue made of tubes with end plates, called sieve tubes, with companion cells beside them. Phloem carries sugars made in the leaves to the rest of the plant. It can move the sugars up or down.

xylemphloemwater and minerals upsugars up and down
Cross-sections of a xylem vessel (hollow) and a phloem vessel, with the substances each carries.

The table compares the two transport tissues.

TissueWhat it carriesDirection
xylemwater and mineral ionsupwards, from the roots
phloemsugarsup and down the plant

Key ideas

  • Xylem tubes are hollow and carry water and mineral ions upwards.
  • Phloem tubes carry sugars made in the leaves to the rest of the plant.
  • Xylem is made of dead cells with no end walls.
  • Phloem can move substances up or down.
Worked example 3.4.1
Which tissue carries water and mineral ions up the plant? Write the word.

Method. Find the tissue that carries water.

  1. Read the description. The tissue that carries water and mineral ions is xylem.
    xylem
  2. Check the direction. It carries them upwards from the roots.
    upwards
  3. Write the answer.
    xylem

Check. Ruby saw the coloured water rise in the xylem. ✓

Worked example 3.4.2
Which tissue carries sugars from the leaves to the rest of the plant? Write the word.

Method. Find the tissue that carries sugars.

  1. Read the description. Sugars made in the leaves are carried by phloem.
    phloem
  2. Check the direction. Phloem can carry sugars up or down the plant.
    up or down
  3. Write the answer.
    phloem

Check. Phloem carries sugars, not water. ✓

Worked example 3.4.3
In the coloured water test, which tissue carried the coloured water up the stem? Write the word.

Method. Use the story.

  1. Read the story. The coloured water travelled up through tubes in the stem.
    tubes
  2. Name the tissue. The tubes that carry water up the stem are xylem.
    xylem
  3. Write the answer.
    xylem

Check. Xylem carries water up. ✓

Watch out

Watch out: xylem carries water and mineral ions; phloem carries sugars. Do not mix up the two substances, or the two tissues.

Exam tip

Exam tip. For a transport question, name the tissue, the substance it carries, and the direction.

Try it (with your teacher, or a grown-up at home). With a grown-up, stand a white flower stem, such as a white carnation, in a jar of water with a little food colouring, and leave it for a few hours or overnight. Cut across the stem and look for the coloured tubes. Say which tissue carried the colour up the stem.

Exercise 3D  Xylem and phloem

1
FWhich tissue is made of long, hollow tubes that carry water up the plant? Write the word.
2
FWhich tissue carries sugars made in the leaves? Write the word.
3
FName the substance that xylem carries up the plant, other than mineral ions. Write one word.
4
FWhat is the name of the substance that is strengthening the walls of xylem cells? Write the word.
5
FCan phloem move sugars downwards as well as upwards? Write yes or no.
6
FDo xylem tubes have end walls? Write yes or no.
7
PSWhich tissue would carry the dye from the stem to the leaves in the water test, if the dye were a sugar? Write the word.
8
PSRuby says the coloured water is carried up by the phloem. Is she right? Write yes or no.
9
PSWhich two substances does xylem carry? Write the two words or phrases.
10
PSWorking scientifically: a pupil predicts that the coloured water will rise up the xylem more quickly on a hot, dry day. Name one thing the pupil must keep the same to make the test fair. Write one thing.
11
RExplain why xylem cells are strengthened with lignin. Write one sentence.
12
RChallenge: explain why a plant needs both xylem and phloem. Write one sentence.
3.5

From cells to tissues, organs and organ systems

Year 7
B2: cells group together to form tissues; tissues form organs; organs form organ systems
Video lesson: From cells to tissues, organs and organ systemsComing soon
Story. Mo is studying for a test. “I keep mixing up the words,” he says. Ruby explains, “Start small. Cells group into tissues, tissues into organs, and organs into organ systems. Each step adds a bigger job.”

Specialised cells that work together form a tissue, such as muscle tissue or xylem tissue. Several different tissues that work together form an organ, such as the stomach or a leaf. Several organs that work together form an organ system, such as the digestive system.

In plants, the organs include the roots, stem and leaves. The root system and the shoot system are two plant organ systems.

celltissueorganorgan systemcell -> tissue -> organ -> organ system
The levels of organisation: cell, tissue, organ, organ system.

The table shows each level of organisation, and what it is.

LevelWhat it is
cellthe basic unit of life
tissuea group of similar cells that work together
organseveral different tissues that work together
organ systemseveral organs that work together

Key ideas

  • Cells work together to form tissues.
  • Tissues work together to form organs.
  • Organs work together to form organ systems.
  • The order is always cell, tissue, organ, organ system.
Worked example 3.5.1
What is a group of similar cells that work together called? Write the word.

Method. Find the level after the cell.

  1. Read the table. A group of similar cells that work together is a tissue.
    tissue
  2. Check the order. Cell, then tissue, then organ.
    after the cell
  3. Write the answer.
    tissue

Check. Muscle tissue is one example. ✓

Worked example 3.5.2
The stomach is an organ. Which organ system is it part of? Write the words.

Method. Find the system the stomach belongs to.

  1. Read the table. The stomach is part of the digestive system.
    digestive system
  2. Check. The digestive system is made of several organs working together.
    several organs
  3. Write the answer.
    the digestive system

Check. The heart is part of the circulatory system. ✓

Worked example 3.5.3
Put these in order from the smallest to the largest: organ, cell, organ system, tissue. Write the four words.

Method. Use the order of the levels.

  1. Use the order. The order is cell, tissue, organ, organ system.
    cell, tissue, organ, organ system
  2. Check the order. Each level is built from the one before it.
    cell builds tissue, tissue builds organ
  3. Write the answer.
    cell, tissue, organ, organ system

Check. Each level is built from the one before. ✓

Watch out

Watch out: an organ is made of several tissues, not several cells. A tissue is made of one kind of cell that works together.

Exam tip

Exam tip. When you put the levels in order, go from the cell upwards, one level at a time.

Try it (with your teacher, or a grown-up at home). With a grown-up, look at a labelled diagram of the human digestive system. Name one organ, and the tissue it is made of. Say which organ system it belongs to.

Exercise 3E  From cells to tissues, organs and organ systems

1
FWhat is a group of similar cells that work together called? Write the word.
2
FWhat is a group of different tissues that work together called? Write the word.
3
FWhat is a group of organs that work together called? Write the words.
4
FWhich organ system is the stomach part of? Write the words.
5
FWhich organ system is the heart part of? Write the words.
6
FPut these in order from the smallest to the largest: organ system, cell, organ, tissue. Write the four words in order.
7
FIs a leaf an organ? Write yes or no.
8
PSHow many levels of organisation are listed in the figure? Write the number.
9
PSA stomach is made of several tissues. Is the stomach a tissue or an organ? Write the word.
10
PSMuscle cells work together to contract. What level of organisation have they formed? Write the word.
11
PSWorking scientifically: a pupil says a leaf is a cell. Is the pupil right? Write yes or no.
12
RExplain why cells in a tissue are usually similar. Write one sentence.
13
RChallenge: explain why an organ system can do jobs that a single organ cannot. Write one sentence.

Chapter summary

SkillMethod
Specialised cellsThe shape and structures of a cell match its job.
Animal cellsSperm: tail, middle piece with mitochondria, genetic material. Nerve: long fibre and branched ends. Muscle: many mitochondria.
Plant cellsRoot hair: a large surface area for absorption. Palisade: many chloroplasts near the top of the leaf.
Transport tissuesXylem carries water and mineral ions up. Phloem carries sugars up and down.
OrganisationCell, tissue, organ, organ system.

Can you…?

  • I can link the shape and structure of a specialised cell to its job
  • I can describe a sperm cell, a nerve cell and a muscle cell
  • I can describe a root hair cell and a palisade cell
  • I can say what xylem and phloem carry, and in which direction
  • I can put the levels of organisation in order, and name an example of each

Key terms

specialised cell
a cell whose shape and structures match its job
tissue
a group of similar cells that work together
organ
several different tissues that work together to do a job
organ system
several organs that work together to do a bigger job
xylem
a tissue of hollow tubes that carry water and mineral ions up the plant
phloem
a tissue of tubes that carry sugars up and down the plant
lignin
a substance that strengthens the walls of xylem cells
surface area
the amount of outside surface of an object
mineral ions
substances taken up from the soil by root hair cells

Exercise 3Z  Check-up

1
Which specialised cell has a tail to swim with? Write the words.
2
Which specialised cell has a long fibre to carry electrical signals? Write the words.
3
Which specialised cell has many mitochondria to release energy for contraction? Write the words.
4
Which root cell has a long, thin extension that increases its surface area? Write the words.
5
Which leaf cells are packed in rows near the top, and carry out photosynthesis? Write the words.
6
Which tissue carries water and mineral ions up the plant? Write the word.
7
Which tissue carries sugars up and down the plant? Write the word.
8
A root hair cell has a surface area of 60 mm squared, and a smooth cell has 10 mm squared. How many times greater is the root hair area? Write the number.
9
Put these in order from the smallest to the largest: organ, cell, organ system, tissue. Write the four words in order.
10
Explain how the structure of a root hair cell helps it do its job. Write one sentence.

Total 15 marks. Allow about 15 minutes.

Exercise 3X  Practice test questions

1
FWhich specialised cell has a middle piece with many mitochondria and a long tail? Write the words.[1 mark]
2
RExplain why a muscle cell has many mitochondria. Write one sentence.[2 marks]
3
FWhich tissue carries sugars made in the leaves to the rest of the plant? Write the word.[1 mark]
4
PSA root hair cell has a surface area of 30 mm squared, and a smooth cell has 10 mm squared. How many times greater is the root hair area? Write the number.[2 marks]
5
FName the level of organisation that is a group of organs working together. Write the words.[1 mark]
6
FWhich xylem feature helps the tubes stay strong when water moves up? Write the word.[1 mark]
7
RExplain why palisade cells are near the top of the leaf. Write one sentence.[2 marks]
8
PSRuby says the coloured water in her stem test was carried up by the phloem. Is Ruby right? Write yes or no, and the tissue that is right, in words.[2 marks]
9
PSA pupil says a stomach is a tissue. Is the pupil right? Write yes or no.[1 mark]
10
RExplain why cells in a tissue are usually similar. Write one sentence.[2 marks]
← Chapter 2: Cells and microscopesChapter 4: States of matter and the particle model →

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