Topic 6

Question 1

How do the microscopic hairs on a root help it absorb water?

Answer 1

It gives the plant a large surface area so it can absorb more minerals (by active transport- the concentration of mineral ions is higher in the hair cell than it the soil) and water by osmosis.

Question 2

What substances do the phloem tubes transport?

Answer 2

They transport sugar substances (mostly sucrose)

Question 3

Identify 1 feature of the structure of the phloem tubes

Answer 3

They have end walls with small pores to allow substances to flow through

Question 4

What process do the phloem tubes use to transport substances?

Answer 4

Translocation. This requires energy and goes in both directions.

Question 5

What substances do the xylem tubes transport and in which direction?

Answer 5

Water and mineral ions up

Question 6

Identify the stages of how water moves through the plant

Answer 6

Root hair cells - cells in the root - xylem - leaf

Question 7

What is transpiration?

Answer 7

The loss of water from the plant

Question 8

What is transpiration caused by?

Answer 8

Evaporation and diffusion

Question 9

Explain how water moves through a plant in the transpiration stream

Answer 9

Water is lost from the plants leaves by evaporation and diffusion. This creates a slight shortage in the leaves so more water is absorbed to replace it.
The water is cohesive, so as water evaporates from the leaf, it creates a pull motion and pulls water up the xylem. This along with the tension between the water and the walls of the xylem, helps the water travel up the tube. This is cycle is continuous.

Question 10

What are stomata and where are they found?

Answer 10

Tiny pores on the surface of a plant that are mostly found on the lower surface of the leaf

Question 11

What do stomata do?

Answer 11

They allow carbon dioxide and oxygen to diffuse in and out of the leaf as well as water vapour (transpiration).

Question 12

What role do stomata play in transpiration?

Answer 12

Transpiration is a side affect. Leaves must have stomata for gas exchange but because there’s more water inside the plant than outside, water escapes by diffusion

Question 13

How do guard cells control the size of the stomata?

Answer 13

The change shape. When guard cells are turgid (swollen with water) the stomata are open and when they are flaccid (low on water, limp) the stomata are closed.

Question 14

How is the transpiration rate affected by light intensity?

Answer 14

The brighter the light, the greater the transpiration rate. Stomata begin to close as it gets darker. Photosynthesis cant happen in the dark so they don’t need to open for carbon dioxide, therefore little water can escape.

Question 15

How is the transpiration rate affected by temperature?

Answer 15

The warmer it is, the faster transpiration is because the water particles have more energy to evaporate and diffuse out of the stomata.

Question 16

How is the transpiration rate affected by air flow?

Answer 16

The better air flow, the greater the transpiration rate because if air flow is poor, the water vapour surround the leaf. If there is a higher concentration of water inside and outside the leaf, diffusion wont happen as quickly.

Question 17

How are plant hormones used in producing seedless fruit?

Answer 17

Fruit with seeds normally only grow on pollinated flowers. Plant hormones like gibberellins are applied to unpollinated flowers, the fruits will grow but not the seeds.

Question 18

How are plant hormones used in controlling fruit and flower formation?

Answer 18

Gibberellins are plant hormones that stimulate seed germination, stem growth and flowering. They can be used to make plants flower earlier or in conditions they wouldn’t usually.

They can also be used to reduce flower formation because fruits grow from flowers. If there are too much flowers then lots of fruit grow but they’ll be small so the trees can support it. The less flowers, the less fruit and the more nice and big they are.

Question 19

How are plant hormones used in growing from cutting and root powders?

Answer 19

A cutting is a part of a plant that has been cut off. Normally, if you stick cuttings in soil, they wont grow unless you add root powder that contains auxins. They will produce roots rapidly and start growing as new plants. This enables growers to produce clones easily.

Question 20

How are plant hormones used in selective weedkillers?

Answer 20

most weeds growing in fields are broad-leaved, selective weedkillers have been developed from auxins which only effect broad-leaved plants. They disrupt their growth pattern, killing them and leaving grass/crops untouched

Question 21

Name and explain the part of the plant that’s negatively phototropic

Answer 21

Roots grow away from light- if a root is exposed to light, more auxin accumulates on the shaded side which inhibits elongation on that side so the root bends backwards into the ground.

Question 22

Name and explain the part of the plant that is positively gravitrophic

Answer 22

Roots grow towards gravity- a root growing sideways will have more auxins on its lower side but in the roots auxins inhibit growth so the cells on the top will grow faster and bend the root downwards

Question 23

Name and explain the part of the plant that is negatively gravitropic

Answer 23

Shoots grow away from gravity- when a shoot is growing sideways, gravity produces more auxin in the lower side making it grow faster and bend upwards.

Question 24

What do shoots growing in the complete dark look like?

Answer 24

tall and spindly

Question 25

Name and explain the part of the plant that is positively phototrophic

Answer 25

Shoots grow towards light- when a shoot tip is exposed to light, it accumulates more auxins in the side that’s in the shade. This makes the cells elongate faster on the shaded side so the shoot bends towards the light. This means it will be more able to absorb light for photosynthesis.

Question 26

What are auxins?

Answer 26

They are plant hormones that control growth at the tips of the shoots and roots. They move through a plant in solution. They stimulate cell elongation. They promote growth in the shoots but inhibit it in the roots.

Question 27

Explain how 3 features of cacti that are adapted to help it live in extreme environments

Answer 27

1) Small leaves or spines reduce the surface area for water loss by evaporation. Spines also prevent animals eating the plant for water
2) A thicc, fleshy stem to store water
3) Fewer stomata or stomata that only open at night reduce water loss by evaporation

Question 28

How are the tissues of leaves adapted for photosynthesis and gas exchange?

Answer 28

the lower epidermis has lots of stomata which allows carbon dioxide to diffuse directly into the leaf and the spongy mesophyll tissue has air spaces which increases the rate of diffusion.

Question 29

How is the waxy cuticle adapted for photosynthesis and gas exchange?

Answer 29

It is waterproof which reduced water loss by evaporation

Question 30

How is upper epidermis adapted for photosynthesis and gas exchange?

Answer 30

It is transparent so that light can pass through it to the palisade layer.

Question 31

How is palisade layer adapted for photosynthesis and gas exchange?

Answer 31

The palisade layer is near the top of the leaf as it has lots of chloroplasts to get the most light for photosynthesis.

Question 32

How are leaves adapted for photosynthesis and gas exchange?

Answer 32

Leaves are broad, so theres a large surface area exposed to light which is needed for photosynthesis

Question 33

How are plant hormones used in controlling the ripening of fruits?

Answer 33

These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops. Ethene is a plant hormone which causes fruit to ripen.

Question 34

How are plant hormones used in controlling seed germination?

Answer 34

Gibberellins, which are a group of plant hormones responsible for growth and development, are important for initiating seed germination. Low concentrations can be used to increase the speed of germination, and they stimulate cell elongation and cause plants to grow taller.

Question 35

Describe how the xylem is adapted for its function.

Answer 35

Composed of dead cells that are hollow

No end wall so no resistance to passage of water

Strong cell wall with lignin to provide support

Question 36

Two cell types that make up the phloem

Answer 36

Companion cells

Sieve tube elements

Question 37

How are the different cells adapted to its function

Answer 37

Sieve cells have pores and no nucleus little cytoplasm so substances flow easily.

Companion cells have a dense mitochondria, cytoplasm and nucleus and provide energy for processes in both cell types.