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GCSE Biology · GCSEChapter 8 · Plant tissues and transport
GCSE · Chapter 8

Plant tissues and transport

By the end of this chapter you will be able to

  • Label a leaf and describe how each layer is adapted
  • Compare xylem and phloem, and say which way each carries substances
  • Explain how light, temperature, humidity and air movement change the rate of transpiration
  • Use a potometer to investigate a factor, and calculate a rate
  • Explain the roles of water, nitrate and magnesium in a plant

You should already know

  • Osmosis and diffusion (Chapter 3)
  • Photosynthesis is covered in Chapter 9; leaves are its main site

Where this leads

  • Photosynthesis (Chapter 9)
  • Growth and plant hormones (Chapter 12)
  • Ecology and water cycles (Chapter 17)

GCSE Biology. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Describe the structure of roots, stems and leaves, and the tissues in them, Describe the xylem and phloem, and what each transports, Explain transpiration, the factors that affect it, and the role of stomata and guard cells, Investigate the effect of a factor on transpiration, using a potometer, Describe the uses of water in plants, and the roles of nitrate and magnesium.

Exercise P  Do you remember?

1
FWhat is 2 x 2 x 5? Write the number.
2
FWhich process moves water across a partially permeable membrane? Write the word.
3
FWhich gas enters a leaf and is used in photosynthesis? Write the words.
4
FWhich part of a cell contains chlorophyll? Write the word.
5
FWhat is 3 divided by 4, written as a decimal? Write the number.
8.1

Roots, stems and leaves

GCSE
Describe the structure of roots, stems and leaves, Label a leaf and explain how it is adapted
Video lesson: Roots, stems and leavesComing soon
Context. Ali grows a bean plant on a windowsill. He notices the roots spread out, the stem stands upright, and the leaves are flat and wide. “Why is each part shaped like this?” he asks. Each part has a job, and its tissues are arranged to do it.

Roots anchor the plant and absorb water and mineral ions from the soil. Their root hair cells have a large surface area. Stems support the leaves and carry substances between roots and leaves. Leaves are the main site of photosynthesis, and they are adapted to let in light and carbon dioxide while losing little water.

Plant tissues are grouped into vascular bundles (xylem and phloem), which run through the roots, stems and leaves.

veinupper epidermis (waxy cuticle)palisade mesophyllspongy mesophyll (air spaces)lower epidermisstomata (pores) on the lower surface, controlled by guard cells
Cross-section of a leaf with its layers, and a stoma on the lower surface
root hair cells on the surfacexylem (red) and phloem (yellow) in the middle
Cross-section of a root, with xylem and phloem in the centre

Key ideas

  • Roots anchor the plant and absorb water and mineral ions.
  • Root hair cells increase the surface area for absorption.
  • Stems support the leaves and carry substances.
  • The waxy cuticle reduces water loss from the upper surface of the leaf.
Worked example 8.1.1
Name the layer of the leaf where most photosynthesis happens. Write the words.

Method. Recall the cells that contain many chloroplasts.

  1. Recall. The palisade mesophyll has many chloroplasts and is packed with cells.
    many chloroplasts
  2. Name it. So the layer is the palisade mesophyll.
    palisade mesophyll
  3. Write the answer.
    palisade mesophyll

Check. The spongy mesophyll has air spaces, for gas exchange. ✓

Worked example 8.1.2
Name the layer on the upper surface of the leaf that reduces water loss. Write the words.

Method. Recall the waxy layer.

  1. Recall. A waxy layer covers the upper epidermis.
    waxy layer
  2. Name it. This layer is the waxy cuticle.
    waxy cuticle
  3. Write the answer.
    waxy cuticle

Check. The cuticle is waterproof. ✓

Worked example 8.1.3
Name the structure of the root that increases the surface area for absorbing water. Write the words.

Method. Recall the root structure.

  1. Recall. Long, thin extensions of the root increase the surface area.
    long, thin extensions
  2. Name it. These are root hair cells.
    root hair cells
  3. Write the answer.
    root hair cells

Check. They absorb water by osmosis. ✓

Watch out

Watch out: the palisade layer is near the top of the leaf, not the bottom. The stomata are on the lower surface.

Exam tip

Exam tip. When you label a leaf, name the layer and its function. “Palisade mesophyll: photosynthesis” scores more than the layer alone.

Try it (with your teacher). With your teacher, look at a prepared slide or labelled diagram of a leaf cross-section. Label the upper epidermis, palisade mesophyll, spongy mesophyll, vein and lower epidermis.

Exercise 8A  Roots, stems and leaves

1
FName the tissue that carries water up the stem. Write the word.
2
FName the layer of the leaf that contains many chloroplasts and is near the top. Write the words.
3
FName the pores on the lower surface of a leaf. Write the word.
4
FName the cells that open and close the stomata. Write the words.
5
FName the layer of the leaf with air spaces that aid gas exchange. Write the words.
6
FName the layer that covers the upper surface of the leaf and reduces water loss. Write the words.
7
FName the part of a root that increases the surface area for absorption. Write the words.
8
FWhat do the roots of a plant anchor? Write the words. Accept the plant to the soil.
9
FName the tissue that carries sugars through a plant. Write the word.
10
PSWhy does the leaf have many chloroplasts in the palisade layer? Write one sentence. Accept any sentence that says photosynthesis happens there, so the chloroplasts are near the light.
11
PSA plant has long, thin root hairs. Explain why this helps the plant, in one sentence. Accept any sentence that says the large surface area helps the roots absorb more water and mineral ions.
12
PSName the tissues in the centre of the root. Write the words.
13
RChallenge: explain why the stomata are on the lower surface of the leaf, not the upper one. Write two sentences. Accept any answer that says the lower surface is cooler and shaded, so less water is lost, and the stomata are protected from the sun.
8.2

Xylem and phloem

GCSE
Describe the structure of xylem and phloem, Explain the direction in which each carries substances
Video lesson: Xylem and phloemComing soon
Context. Priya cuts a stem and looks at the cut end. It is wet and has rings of small tubes. “Which tubes carry water, and which carry the sugars?” she asks. The two tissues are arranged close together, but they do different jobs.

Xylem is made of hollow, dead cells joined end to end to form tubes, strengthened by lignin. It carries water and mineral ions upwards from the roots to the leaves and stems.

Phloem is made of living sieve tubes, with companion cells beside them. It carries sugars (mainly sucrose) from the leaves to where they are needed, and it can carry them up or down. This movement is called translocation.

TissueTransportsMade ofDirection
xylemwater and mineral ionsdead, hollow, strengthened (lignin) cellsupwards, from roots to leaves
phloemsugars such as sucrose (translocation)living sieve tubes with companion cellsup and down
Xylem and phloem compared
rootsstemleafxylem: water upwater upphloem: sugars (both ways)water and minerals travel up the xylem; sugars travel up and down the phloem
Xylem carries water up from the roots; phloem carries sugars up and down

Key ideas

  • Xylem: dead, hollow, lignified tubes; carries water and mineral ions upwards.
  • Phloem: living sieve tubes with companion cells; carries sugars up and down.
  • Translocation is the movement of sugars in the phloem.
  • Xylem and phloem are grouped together in vascular bundles.
Worked example 8.2.1
Name the tissue that carries water and mineral ions up the plant. Write the word.

Method. Recall the water-carrying tissue.

  1. Recall. Xylem carries water and mineral ions upwards.
    upwards
  2. Name it. So the tissue is xylem.
    xylem
  3. Write the answer.
    xylem

Check. Phloem carries sugars. ✓

Worked example 8.2.2
Name the process by which sugars move through the phloem. Write the word.

Method. Recall the movement of sugars.

  1. Recall. The movement of sugars through the phloem is called translocation.
    translocation
  2. Name it. So the process is translocation.
    translocation
  3. Write the answer.
    translocation

Check. Translocation can go up or down. ✓

Worked example 8.2.3
Explain why the xylem needs to be strong. Write one sentence.

Method. Think about the water moving up.

  1. Think. Water is pulled up the xylem, which needs support.
    pulled up
  2. Conclude. Lignin strengthens the walls so the tubes do not collapse.
    strengthens
  3. Write the answer.
    Lignin strengthens the walls of the xylem, so the tubes do not collapse as water is pulled up.

Check. Dead, hollow cells give an open channel. ✓

Watch out

Watch out: the phloem carries sugars up and down, but the xylem carries water only upwards. Do not say that both carry the same substances in the same direction.

Exam tip

Exam tip. When you compare xylem and phloem, give the substance, the direction and the cell type for each.

Try it (with your teacher). With your teacher, look at a labelled diagram of a stem cross-section, with xylem and phloem marked. Colour the xylem red and the phloem yellow. Label the direction of flow in each.

Exercise 8B  Xylem and phloem

1
FWhich tissue carries water up the plant? Write the word.
2
FWhich tissue carries sugars through the plant? Write the word.
3
FIs the xylem made of living cells? Write yes or no.
4
FName the substance that strengthens the walls of the xylem. Write the word.
5
FIn which direction does xylem carry water? Write the word.
6
FIn which direction does phloem carry sugars? Write the words.
7
FName the living cells that sit beside the sieve tubes in the phloem. Write the words.
8
FName the process by which sugars are moved in the phloem. Write the word.
9
PSWhy does the xylem need to be hollow? Write one sentence. Accept any sentence that says the hollow tubes allow water to move through them with little resistance.
10
PSExplain why sugars in a root must come from the leaves. Write one sentence. Accept any sentence that says the leaves make the sugars by photosynthesis, and the phloem carries them to the root.
11
PSA stem is cut and a ring of bark is removed, which contains the phloem. Predict what happens to the roots, and say why. Accept any answer that says the roots would stop getting sugars and would eventually die.
12
RChallenge: explain why the xylem and phloem are found together in vascular bundles. Write two sentences. Accept any answer that says they are close together so the plant transports water and sugars efficiently to the parts that need them.
8.3

Transpiration and the potometer (required practical)

GCSE
Describe transpiration and the factors that affect it, Investigate a factor using a potometer, Calculate a rate from distance and time
Video lesson: Transpiration and the potometer (required practical)Coming soon
Context. Hana places a leafy shoot in a tube of water with a bubble of air at one end. Over five minutes the bubble moves along the scale. “The shoot is taking up water,” her teacher says, “and most of it is lost from the leaves.”

Transpiration is the loss of water vapour from the leaves, mainly through the stomata. Water evaporates from the spongy mesophyll cells into the air spaces, and then diffuses out through the stomata. This loss creates a pull that draws more water up the xylem from the roots, so transpiration is a driving force for the movement of water.

The rate of transpiration is faster in higher light (stomata open), higher temperature (faster evaporation), lower humidity (a steeper gradient) and more air movement (water vapour is carried away).

In a potometer, a leafy shoot is cut under water and placed in the apparatus. An air bubble moves along the capillary tube as water is taken up. The distance moved in a set time gives a measure of the rate: rate = distance / time.

shoot in waterbubble movesthe distance moved by the bubble is a measure of water uptake
A potometer with a leafy shoot and an air bubble moving along a capillary tube
ConditionDistance moved in 5 min (mm)Rate (mm per min)
still air102
fan on306
lamp close255
dark cupboard51
Distance moved by a bubble in a potometer under four conditions (invented data)

Key ideas

  • Transpiration is water loss from the leaves, mainly through stomata.
  • It is driven by evaporation and diffusion through the stomata.
  • Light, temperature and air movement increase the rate; high humidity reduces it.
  • Rate = distance / time for the bubble in a potometer.
Worked example 8.3.1
Find the rate of the bubble in still air, using the table. Write the number, in mm per minute.

Method. Divide the distance by the time.

  1. Read. In still air the bubble moves 10 mm in 5 minutes.
    10 mm
  2. Divide. Rate = 10 / 5 = 2 mm per minute.
    10 / 5 = 2
  3. Write the answer.
    2

Check. 2 x 5 = 10 mm. ✓

Worked example 8.3.2
Name the condition that gives the fastest rate in the table. Write the words.

Method. Find the largest rate in the table.

  1. Compare. The rates are 2, 6, 5 and 1 mm per minute.
    2, 6, 5, 1
  2. Choose. The largest is 6 mm per minute, with the fan on.
    fan on
  3. Write the answer.
    fan on

Check. Moving air carries water vapour away, steepening the gradient. ✓

Worked example 8.3.3
Explain why a fan on the leaves makes transpiration faster. Write one sentence.

Method. Think about the water vapour around the leaf.

  1. Think. The air near the leaf becomes saturated with water vapour when it is still.
    saturated
  2. Conclude. A fan carries this vapour away, so the gradient stays steep and transpiration is faster.
    steep
  3. Write the answer.
    A fan carries water vapour away, keeping the gradient steep, so transpiration is faster.

Check. A steeper gradient speeds up diffusion. ✓

Watch out

Watch out: the potometer measures water uptake, which is close to, but not exactly, the rate of transpiration. Say so in an evaluation.

Exam tip

Safety. Cut the shoot under water with the teacher. Keep the apparatus steady, and wipe up spilt water at once.

Try it (with your teacher). With your teacher, set up a potometer with a leafy shoot. Measure the distance moved by the bubble in 5 minutes in still air, then with a fan on. Calculate the rate for each, and compare.

Exercise 8C  Transpiration and the potometer

1
FWhat is transpiration? Write the words.
2
FThrough which structures does most transpiration happen? Write the word.
3
FIn still air, how far does the bubble move in 5 minutes? Write the number, in mm.
4
FCalculate the rate of the bubble when the lamp is close. Write the number, in mm per minute.
5
FWhich condition gives the slowest rate in the table? Write the words.
6
FName the factor that makes transpiration faster when it is higher. Accept any one: temperature, light, or air movement.
7
FDoes higher humidity increase or decrease the rate of transpiration? Write the word.
8
PSWhy does transpiration increase when it is windy? Write one sentence. Accept any sentence that says the wind carries away water vapour, so the gradient stays steep.
9
PSThe fan-on rate is 6 mm per minute and the still-air rate is 2 mm per minute. How many times faster is the fan-on rate? Write the number.
10
PSExplain why a bubble moving along the tube is a measure of transpiration. Write one sentence. Accept any sentence that says the water taken up by the shoot is replaced by the bubble, so its movement shows the uptake.
11
PSName one control variable in the potometer investigation. Accept any one: the number of leaves, the time, or the size of the shoot.
12
REvaluate the potometer method in one sentence. Accept any sentence that says the method measures water uptake, not transpiration directly, so this is a limitation.
13
RChallenge: a pupil says the bubble moved fastest because the shoot had the most water. Explain why this is not a valid conclusion. Write two sentences. Accept any answer that says the test did not control the variables, and water supply alone is not the reason for the fastest rate.
8.4

Stomata and guard cells

GCSE
Describe the structure and function of stomata and guard cells, Explain how stomata control water loss and gas exchange
Video lesson: Stomata and guard cellsComing soon
Context. Ruth notices that a plant in a sunny window wilts less in the afternoon than one in a dark corner. “The sunny plant must be losing water in a different way,” she says. The answer lies in the stomata, which open and close.

Each stoma (plural stomata) is a pore on the lower surface of the leaf. It is surrounded by two guard cells. When the guard cells take in water and swell, they bend apart and the pore opens. When they lose water and become flaccid, the pore closes.

The stomata open in light, so that carbon dioxide can enter for photosynthesis. Opening them also allows water vapour to leave, so there is a trade-off. In the dark, or when water is short, the stomata close to conserve water.

open stoma: guard cells swell (turgid)water vapour leaves through the pore
An open stoma with two guard cells
Stomata counts (invented)Stomata per mm2
lower surface240
upper surface20
Counts of stomata on the two surfaces of one leaf (invented data)

Key ideas

  • Guard cells control the opening of the stoma.
  • Stomata open in light, to let carbon dioxide in for photosynthesis.
  • Opening the stomata also lets water vapour out: a trade-off.
  • Stomata close in the dark or in drought, to save water.
Worked example 8.4.1
Name the cells that control the opening of a stoma. Write the words.

Method. Recall the cells beside the pore.

  1. Recall. Two guard cells surround each stoma.
    two guard cells
  2. Name them. So the cells are guard cells.
    guard cells
  3. Write the answer.
    guard cells

Check. Guard cells swell when they take in water. ✓

Worked example 8.4.2
Find how many times more stomata there are on the lower surface than the upper surface, from the table. Write the number.

Method. Divide the lower count by the upper count.

  1. Read. The lower surface has 240 per mm2 and the upper has 20.
    240 and 20
  2. Divide. 240 / 20 = 12.
    240 / 20 = 12
  3. Write the answer.
    12

Check. 20 x 12 = 240. ✓

Worked example 8.4.3
Explain why the stomata close at night. Write one sentence.

Method. Think about the trade-off.

  1. Think. In the dark there is no photosynthesis, so no carbon dioxide is needed.
    no photosynthesis
  2. Conclude. The plant closes the stomata to reduce water loss.
    reduce water loss
  3. Write the answer.
    There is no photosynthesis in the dark, so the stomata close to reduce water loss.

Check. Closing saves water when it is not needed for gas exchange. ✓

Watch out

Watch out: stomata are for both gas exchange and water loss. Do not say that they only let water out.

Exam tip

Exam tip. When you explain stomata, say what the guard cells do and why the pore opening is a trade-off.

Try it (with your teacher). With your teacher, make a leaf impression using clear nail varnish on a leaf surface. Peel it off, and count the stomata under a microscope in one field of view. Repeat for the other surface.

Exercise 8D  Stomata and guard cells

1
FWhere are most stomata found in a leaf: the upper or the lower surface? Write the word.
2
FWhat do the guard cells do when they take in water? Write the words.
3
FWhat happens to the stoma when the guard cells lose water? Write the word.
4
FIn which conditions do stomata open? Write the word.
5
FWhat is the name of the pores on the leaf? Write the word.
6
FHow many guard cells surround each stoma? Write the number.
7
FWhich gas enters the leaf through the stomata for photosynthesis? Write the words.
8
PSOn the upper surface there are 20 stomata per mm2 and on the lower surface there are 240 per mm2. Find the total number of stomata in 2 mm2 of the lower surface. Write the number.
9
PSExplain why a plant closes its stomata in a drought. Write one sentence. Accept any sentence that says closing the stomata reduces water loss when water is in short supply.
10
PSExplain why the stomata are needed for photosynthesis but also cause water loss. Write one sentence. Accept any sentence that says the same opening lets in carbon dioxide and lets out water vapour.
11
RChallenge: a plant wilts on a hot dry day. Explain how closing the stomata helps, and what the cost is. Write two sentences. Accept any answer that says closing reduces water loss, but also reduces carbon dioxide intake for photosynthesis.
8.5

Uses of water and the roles of minerals

GCSE
Describe the uses of water in a plant, Describe the roles of nitrate and magnesium in plant growth
Video lesson: Uses of water and the roles of mineralsComing soon
Context. Ali’s bean plant is growing well but its leaves are turning yellow between the veins. “It needs fertiliser,” his neighbour says. Ali looks up the minerals a plant needs, and finds that two of them are nitrate and magnesium.

Water is used by plants for photosynthesis (a reactant), to keep cells turgid (firm) for support, as a medium for transporting substances, and for cooling through evaporation.

Plants need mineral ions from the soil. Nitrate is needed to make amino acids and proteins. Magnesium is needed to make chlorophyll. A plant short of magnesium has yellow leaves, because it cannot make enough chlorophyll.

MineralNeeded forDeficiency symptom
nitratemaking amino acids and proteinsstunted growth; older leaves yellow
magnesiummaking chlorophyllyellow leaves, with green veins
The roles and deficiency symptoms of nitrate and magnesium

Key ideas

  • Water is needed for photosynthesis, support (turgor), transport and cooling.
  • Nitrate is needed for amino acids and proteins.
  • Magnesium is needed to make chlorophyll.
  • A plant short of magnesium has yellow leaves.
Worked example 8.5.1
Name a mineral ion needed to make chlorophyll. Write the word.

Method. Recall the mineral in chlorophyll.

  1. Recall. Chlorophyll contains magnesium.
    contains magnesium
  2. Name it. So the mineral is magnesium.
    magnesium
  3. Write the answer.
    magnesium

Check. Nitrate is needed for proteins. ✓

Worked example 8.5.2
Name one use of water in a plant, other than as a reactant. Write the words.

Method. Recall the uses of water.

  1. Recall. Water keeps the cells turgid and gives support.
    turgid
  2. Name one. This is a use of water in the plant.
    support
  3. Write the answer.
    Accept any one: support by turgor, transport of substances, or cooling by evaporation.

Check. Water is used in many ways in a plant. ✓

Worked example 8.5.3
Name the symptom that shows a plant is short of magnesium. Write the words.

Method. Recall where the yellowing appears.

  1. Recall. Magnesium deficiency gives yellowing between the veins of the leaves.
    between the veins
  2. Name it. So the symptom is yellow leaves between the veins.
    yellow leaves between the veins
  3. Write the answer.
    yellow leaves between the veins

Check. Veins stay green. ✓

Watch out

Watch out: the yellow leaves of a magnesium-short plant are yellow between the veins, which is not the same as a plant short of nitrate, whose leaves are often yellow overall.

Exam tip

Exam tip. When you explain a deficiency, name the mineral, what it is needed for, and the symptom it causes.

Try it (with your teacher). With your teacher, look at a leaf that has yellowing between the veins, or a labelled picture of one. Describe the pattern, and suggest which mineral might be lacking.

Exercise 8E  Uses of water and the roles of minerals

1
FName the mineral needed to make chlorophyll. Write the word.
2
FName the mineral needed to make amino acids and proteins. Write the word.
3
FWhat is the effect of a plant having too little magnesium? Write the words.
4
FName one use of water in a plant. Accept any one: photosynthesis, support, transport, or cooling.
5
FWhich mineral is needed for protein production? Write the word.
6
FWhat does turgid mean? Write the word.
7
FWhich leaves turn yellow in a plant short of nitrate: the older or the younger? Write the word.
8
FName the process in which water is lost from a leaf and cools it. Write the word.
9
PSAli’s plant has yellow leaves between the veins. Write which mineral might be lacking. Write the word.
10
PSExplain why a plant with too little nitrate grows poorly. Write one sentence. Accept any sentence that says it cannot make enough amino acids and proteins to grow.
11
PSExplain how the water in the xylem is used in photosynthesis. Write one sentence. Accept any sentence that says water is split during photosynthesis, supplying the hydrogen for glucose.
12
RChallenge: explain why a plant with yellow leaves cannot photosynthesise as well as a healthy plant. Write two sentences. Accept any answer that says less chlorophyll means less light is absorbed, so less glucose is made.

Chapter summary

SkillMethod
XylemDead, hollow, lignified tubes; carries water and mineral ions upwards.
PhloemLiving sieve tubes with companion cells; carries sugars up and down (translocation).
TranspirationWater loss from leaves through stomata; faster in light, heat, dry and windy air.
Stomata and guard cellsGuard cells open the stomata in light and close them to save water.
PotometerMeasures the uptake of water; rate = distance moved / time.
Uses of waterPhotosynthesis, turgor for support, transport, cooling.
MineralsNitrate: amino acids and proteins; magnesium: chlorophyll.

Can you…?

  • I can describe the structure of roots, stems and leaves, and the tissues in them
  • I can compare xylem and phloem by substance, direction and cell type
  • I can explain transpiration and how light, temperature, humidity and wind affect it
  • I can use a potometer and calculate a rate from distance and time
  • I can explain the role of stomata and guard cells, and name the minerals nitrate and magnesium

Key terms

xylem
the tissue that carries water and mineral ions upwards
phloem
the tissue that carries sugars up and down the plant
translocation
the movement of sugars through the phloem
transpiration
the loss of water vapour from a plant, mainly through the stomata
stoma
a pore on the surface of a leaf, surrounded by two guard cells
guard cell
a cell that opens and closes a stoma
lignin
a substance that strengthens the walls of xylem
turgid
firm, because the cell is full of water
potometer
apparatus that measures the uptake of water by a shoot
mesophyll
the tissue inside a leaf where photosynthesis happens

Exercise 8Z  Check-up

1
Name the tissue that carries water and mineral ions up the plant. Write the word.
2
Name the tissue that carries sugars through the plant. Write the word.
3
Name the pores on a leaf through which water vapour leaves. Write the word.
4
Name the mineral needed to make chlorophyll. Write the word.
5
In still air, a bubble moves 10 mm in 5 minutes. Find the rate, in mm per minute. Write the number.
6
Name the condition that gives the largest rate in the potometer table. Write the words.
7
Name the cells that open and close the stomata. Write the words.
8
Name the process in which sugars move through the phloem. Write the word.
9
Explain in one sentence why high humidity decreases transpiration. Accept any sentence that says the gradient for water vapour is smaller, so less water vapour leaves.
10
Give one reason why a plant needs nitrate. Accept any sentence that says nitrate is needed to make amino acids and proteins.

Total 23 marks. Allow about 23 minutes.

Exercise 8X  Exam-style questions

1
FName the tissue that carries water up a plant. Write the word.[1 mark]
2
FName the process of water loss from leaves. Write the word.[1 mark]
3
FName the mineral needed to make amino acids and proteins. Write the word.[1 mark]
4
FDescribe how light affects the stomata, and so the rate of transpiration. Write two sentences. Accept any answer that says light makes the stomata open, which increases the rate of transpiration.[2 marks]
5
FCompare xylem and phloem. Write three points, covering what each carries, the direction, and the cell type. Accept any three correct points, for example xylem carries water upwards and phloem carries sugars up and down.[3 marks]
6
PSIn the potometer data, the bubble moves 30 mm in 5 minutes with the fan on. Find the rate, and say how it compares with 10 mm in 5 minutes in still air. Accept 6 mm per minute, and three times faster.[2 marks]
7
FExplain why a plant needs magnesium, and what the plant looks like if it is short of magnesium. Write two sentences. Accept any answer that says magnesium is needed to make chlorophyll, and the leaves turn yellow between the veins.[2 marks]
8
RExplain how the stomata help the plant to balance gas exchange and water loss. Write three sentences. Accept any answer that says the guard cells open the stomata in light, letting carbon dioxide in, but water vapour is lost, so the plant closes them when water is short.[4 marks]
9
FDescribe the path of water from the soil to the air, naming the tissues and structures on the way. Write four points. Accept any four of: root hair cells; xylem; stem; leaf; stomata; air.[4 marks]
10
RA pupil measures transpiration on two days. On day 1 the air is dry and windy; on day 2 it is humid and still. Predict which day gives the faster rate, and explain why, in two sentences. Accept any answer that says day 1 is faster, because dry, windy air keeps the gradient steep and carries water vapour away.[3 marks]
← Chapter 7: Lungs and gas exchangeChapter 9: Photosynthesis →

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