B6 - Plant Structures and Their Functions

Question 1

What is the equation for

photosynthesis?

Answer 1

carbon dioxide + water -> glucose + oxygen

6CO2 + 6H2O -> C6H12O6 + 602

this process requires light and chlorphyll

Question 2

What factors affect

photosynthesis?

(3)

Answer 2

• light intensity
• concentration of CO2
• temperature

Question 3

What are phloem tubes made of?

Answer 3

columns of elongated living cells with small pores in the end walls to allow stuff to flow through

Question 4

What are some key points about

translocation?

(4)

what?
from where to where?
any requirements?
what direction?

Answer 4

• it is the transportation of food substances (mainly sucrose)
• this is from the leaves to the rest of the plant
• it requires energy from respiration
• the transport goes in both directions

Question 5

What are xylem tubes made of?

Answer 5

dead cells joined end to end with no end walls between them and a hole in the middle

they are strengthened with a material called lignin

Question 6

What are some key points about

transpiration?

(3)

what?
from where to where?
any requirements?
what direction?

Answer 6

• it is the transportation of water and mineral ions
• this is from the roots to the stem and leaves
• the transport only goes upwards

Question 7

Define

transpiration stream.

Answer 7

the movement of water from the roots, through the xylem and out of the leaves

Question 8

How does transpiration work?

(4 steps)

Answer 8

1. Transpiration occurs at the leaves.
2. This creates a slight shortage of water in the leaf.
3. More water is drawn up from the rest of the plant through the xylem vessels to replace it.
4. This in turn means more water is drawn up from the roots, and so there’s a constant transpiration stream of water through the plant.

Question 9

Define

stomata.

Answer 9

the tiny pores on the surface of a plant

Question 10

What is the purpose of

stomata?

Answer 10

they allow carbon dioxide and oxygen to diffuse directly in and out of a leaf

they also allow water vapour to escape during transpiration

Question 11

How do guard cells affect the stomata?

Answer 11

when the guard cells are turgid, the stomata are open

when the guard cells are flaccid, the stomata are closed

turgid - swollen with water
flaccid - low on water and limp

Question 12

What 3 key things affect

transpiration rate?

Answer 12

• light intensity
• temperature
• air flow

Question 13

How does

light intensity affect the rate of transpiration?

And why?

Answer 13

the brighter the light, the greater the transpiration rate

this is because the stomata begin to close as it gets darker
photosynthesis can’t happen in the dark, so they don’t need to be open to let carbon dioxide in
when the stomata are closed, very little water can escape

Question 14

How does

temperature affect the rate of transpiration?

And why?

Answer 14

the warmer it is, the faster transpiration happens

this is because when it’s warmer the particles have more energy to evaporate and diffuse out of the stomata

Question 15

How does

air flow affect the rate of transpiration?

And why?

Answer 15

the better the air flow around a leef, the greater the transpiration rate

this is because if air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away, this means there’s a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn’t happen as quickly, if there’s good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf, diffusion then happens quickly from an area of higher concentration to an area of lower concentration

Question 16

State the order of cells in a

typical leaf.

(from top to bottom)

Answer 16

1. Waxy cuticle
2. Upper epidermis
3. Palisade mesophyll tissue
4. Spongy mesophyll tissue (+ air space)
5. Lower epidermis (+ guard cells and stomata)

Question 17

How is the

palisade layer adapted for efficient photosynthesis?

(2 things)

Answer 17

• it has lots of chloroplasts
• it is near the top of the leaf, where it can get the most light

Question 18

How is the

upper epidermis adapted for efficient photosynthesis?

Answer 18

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

Question 19

How is the

waxy cuticle adapted for efficient photosynthesis?

Answer 19

it helps to reduce water loss by evaporation

Question 20

How is the

spongy mesophyll layer adapted for efficient photosynthesis?

Answer 20

it contains air spaces which increase the rate of diffusion of gases into and out of the leaf’s cells

Question 21

What adaptations do plants living in deserts tend to have?

(to help them conserve water)(6)

Answer 21

• small leaves, or spines instead of leaves
• curled leaves, or hairs on the surface of leaves
• thick waxy cuticles
• a thick, fleshy stem which stores water
• fewer stomata or stomata that only open at night
• stomata sunken in pits

Question 22

How do small leaves help a plant to conserve water?

Answer 22

this reduces the surface area for water loss by evaporation

Question 23

How do curled leaves help a plant to conserve water?

Answer 23

this reduces air flow close to the leaf, trapping water vapour near the surface and reducing diffusion from the leaf to the air

Question 24

How do thick waxy cuticles help a plant to conserve water?

Answer 24

they reduce water loss by evaporation

Question 25

How do stomata sunken in pits help a plant to conserve water?

Answer 25

this makes the stomata lower than the surface of the leaf, which reduces air flow close to the stomata

Question 26

Define

auxins.

Answer 26

plant hormones which control growth at the tips of shoots and roots

they move through the plant in solution

Question 27

How do shoots respond to light?

(name and 2 steps)

Answer 27

they are positively phototrophic (grow towards the light)
1. When a shoot tip is exposed to light, it accumulates more auxin on the side that’s in the shaded than the side that’s in the light.
2. This makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light.

Question 28

How do shoots respond to gravity?

(name and 2 steps)

Answer 28

They are negatively gravitropic (grow away from gravity)

1. When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
2. This causes the lower side to grow faster, bending the shoot upwards.

Question 29

How do roots respond to gravity?

(name and 2 steps)

Answer 29

They are positively gravitropic (grow towards gravity)

1. A root growing sideways will also have more auxin on its lower side.
2. But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards.

Question 30

How do roots respond to light?

(name and 2 steps)

Answer 30

They are negatively phototropic (grow away from light)

1. If a root starts being exposed to some light, more auxin accumulates on the more shaded side.
2. The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground.

Question 31

What are some commercial uses of

plant hormones?

(6 uses)

Answer 31

• selective weedkillers
• growing from cuttings with rooting powder
• controlling flower and fruit formation
• producing seedless fruit
• controlling the ripening of fruits
• controlling seed germination

Question 32

What are specifically auxins used for commercially?

(2 things)

Answer 32

• selective weedkillers that only affect broad-leafed plants
• rooting powder which allow cutting to produce roots rapidly and start growing as new plants

Question 33

What are gibberellins used for commercially?

(6 uses)

Answer 33

• making plants flower earlier than they would usually do so
• making plants flower under conditions in which they wouldn’t usually flower
• reducing flower formation which can improve fruit quality
• to allow the fruit in unpollinated flowers to grow (but not the seeds)
• to make sure that seeds will germinate at times of the year that they wouldn’t normally
• to make sure that all the seeds in a batch germinate at the same time

Question 34

What is ethene used for commercially?

Answer 34

to allow unripe fruits to ripen on the way to the supermarket