Topic 6 Plant Strucutres and Their Functions

Question 1

Word equation for photosynthesis

Answer 1

carbon dioxide + water -> glucose + oxygen

Question 2

Is photosynthesis exothermic or endothermic?

Answer 2

Endothermic

Question 3

What the glucose from photosynthesis is used for?

Answer 3

To make larger and more complex molecules that the plant needs to grow. Biomass.

Question 4

3 factors that affect photosynthesis

Answer 4

Light intensity, concentration of CO2 and temperature

Question 5

Limiting factor

Answer 5

Stopping photosynthesis from happening any faster.

Question 6

Temperature and rate of photosynthesis

Answer 6

Temperature affects the rate of photosynthesis due to the enzymes involved.
If temp is limiting factor its because it’s too low since enzymes work slower at lower temperatures and reactions are generally slower.
If the plant gets too hot, the enzymes needed for photosynthesis and other reactions will be denatured at 45C.

Question 7

Light and the rate of photosynthesis

Answer 7

As light level is raised, the rate of photosynthesis increases until a point where temperature or CO2 concentration becomes a limiting factor.

Question 8

Inverse square law

Answer 8

Light intensity = 1/(distance)^2

if you half distance, then the light intensity becomes 4 times greater

Question 9

CO2 concentration and the rate of photosynthesis

Answer 9

As CO2 is one of the raw materials needed for photosynthesis, increasing CO2 concentration increases the rate of photosynthesis until either light intensity or temp becomes a limiting factor.

Question 10

Investigating rate of photosynthesis and light

Answer 10

Set up pondweed in water and sodium hydrogencarbonate (releases CO2) with a gas syringe.
Set up white light source at a specific distance and leave pondweed to photosynthesise.
The oxygen will collect in the gas syringe.
Repeat with different distances.

Question 11

Control variables with investigating rate of photosynthesis and light

Answer 11

Temperature by putting conical flask in water bath.

CO2 concentration by adding set volume of sodium hydrogencarbonate in set volume of water.

Question 12

Function of root hair cell and how it helps plants

Answer 12

To take in minerals and water and gives plant large surface area for absorbing water and minerals.
Mineral ions are absorbed by active transport and water is absorbed by osmosis.

Question 13

Phloem tube structure and function (translocation)

Answer 13

Columns of elongated living cells with small pores in the end walls to allow things such as sucrose made in the leaves to move through.
Sucrose is then used for storage or immediate use (growing).
Requires energy from respiration and transport goes in both directions.

Question 14

Xylem tube structure and function

Answer 14

Made of dead cells joined end to end with no end walls between them and a hole down the middle.
They are strengthened with lignin.
They carry water and mineral ions from roots to stem and leaves.
Movement of water is called transpiration.

Question 15

What is transpiration caused by?

Answer 15

By evaporation and diffusion of water from a plant’s surface.

Question 16

Transpiration process

Answer 16

Loss of water in leaf due to evaporation or diffusion in leaf causes shortage of water in the leaf so water is drawn up from the from the rest of the plant through the xylem due to cohesion and adhesion of the water molecules.
Water drawn up from roots creates transpiration stream of water through plant.
Carries mineral ions dissolved in water with it.

Question 17

Stomata

Answer 17

Small pores on the underside of leaves that allow oxygen and CO2 to diffuse in and out of the leaf and water to escape during transpiration.

Question 18

How do guard cells control the stomata?

Answer 18

When the guard cells are turgid, the stoma is open.

When the guard cells are flaccid, the stoma is closed.

Question 19

How does light intensity affect transpiration rate?

Answer 19

Brighter = higher transpiration rate.
Stomata close when it gets darker as photosynthesis can’t happen in the dark so no CO2 needs to be let in.
When the stomata close, little water can escape so low transpiration.

Question 20

How does temperature affect transpiration rate?

Answer 20

Warmer = higher transpiration rate.

When it is warm, the water particles have more energy to evaporate and diffuse out of the stomata.

Question 21

How does air flow affect transpiration rate?

Answer 21

Better air flow means a greater transpiration rate.
If air flow is poor, water vapour just surrounds the leaf and doesn’t move away so a high concentration of water is maintained outside the leaf as well as in the leaf, meaning diffusion happens slowly.
If there is good airflow, the water vapour is swept awat and a low concentration is maintained outside the leaf so diffusion happens quickly.

Question 22

How to estimate transpiration rate

Answer 22

Use a potometer with a bubble of water along a capillary tube with a scale.
Measure distance moved by water per unit of time.
This gives speed of air bubble movement and an estimate of the transpiration rate.

Question 23

How is the leaf adapted for photosynthesis?

Answer 23

Leaves are broad and so a large surface area is exposed to light.

Question 24

How is the palisade layer adapted for photosynthesis?

Answer 24

It has many chloroplasts as it is near the top of the leaf to get the most light.

Question 25

How is the upper epidermis adapted for photosynthesis?

Answer 25

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

Question 26

How are the xylem and phloem adapted for photosynthesis?

Answer 26

The xylem and phloem form a network of vascular bundles which provide leaf with water and take away the glucose produced and help support the structure.

Question 27

How are the epidermal tissues adapted for keeping water?

Answer 27

They are covered in a waxy cuticle which helps reduce water loss by evaporation.

Question 28

How is the leaf adapted for gas exchange?

Answer 28

The lower epidermis has lots of stomata so CO2 can diffuse directly into the leaf.
The spongy mesophyll ltissue has air specas which increases the rate of diffusion of gases in and out of the leaf’s cells.

Question 29

How do small leaves or spines instead of leaves help plants survive in extreme environments?

Answer 29

Reduces surface area for water loss by evaporation. Spines also help stop animals eating the plant for water.

Question 30

How do curled leaves or hairs help plants survive in extreme environments?

Answer 30

They reduce air flow close to the leaf, trapping water vapour near the surface and reducing diffusion of water from leaf to air.

Question 31

How does a thick, waxy cuticle help plants survive in extreme environments?

Answer 31

It reduces water loss by evaporation.

Question 32

How does a thick, fleshy stem help plants survive in extreme environments?

Answer 32

It stores water.

Question 33

How do fewer stomata help plants survive in extreme environments?

Answer 33

The stomata are fewer in number and only open at night to reduce water loss by evaporation.

Question 34

How do stomata sunken in pits help plants survive in extreme environments?

Answer 34

It makes stomata lower than surface of the leaf so airflow close to stomata is reduced.

Question 35

Auxins

Answer 35

Plant hormone that controls growth at the tip of shoots and roots and move around the plant in solution.
Produced in tips and diffuses backwards to stimulate cell elongation.
Promote growth in shoot and inhibit growth in root.

Question 36

How does positive phototropism in shoots work?

Answer 36

When a shoot tip is exposed to light, the auxin accumulates on the shaded side which causes the shoot to grow faster on the shaded side so it bends towards the light.

Question 37

Why are shoots phototropic?

Answer 37

By bending towards light, the shoots will be able to absorb more light for photosynthesis so they will be able to grow.

Question 38

What happens to shoots growing in the dark?

Answer 38

They become tall and spindly because the auxin makes the elongate quickly on all sides as a taller shoot has more chance of finding light.

Question 39

How does negative gravitropism in shoots work?

Answer 39

When a sideway shoot, gravity causes an unequal distribution of auxins with more on the lower side.
This causes the shoot to grow faster underneath and bends it upwards.

Question 40

How does positive gravitropism in roots work?

Answer 40

Sideways root will have more auxin on its lower side.

The auxin inhibits growth so the top elongates faster and the root bends downwards.

Question 41

How does negative phototropism in roots work?

Answer 41

If a root is exposed to light, more auxin accumulates on the shaded side, inhibiting cell elongation. This means the root bends downwards back into the ground.

Question 42

Plant hormones as selective weed killers

Answer 42

Weeds are normally broad-leaved in contrast to grasses and cereals which are narrow-leaved.
Selective weed killers made using auxins only affect broad-leaved plants and the weedkillers disrupt their growth patterns which kills them only.

Question 43

Plant hormones growing cuttings with rooting powder

Answer 43

Adding auxins to cuttings in soil will cause them to produce roots otherwise they wouldn’t.
This enables clones of good plants to be produced quickly.

Question 44

Plant hormones in controlling flower and fruit formation

Answer 44

Gibberellins stimulate seed germination, stem growth and flowering. They can make plants flower earlier than normal or under conditions where they wouldn’t normally flower.
They also can reduce flower formation which in turn improves fruit quality. (In apricot trees many flowers grow which causes the fruit to be small).

Question 45

Plant hormones in producing seedless fruit

Answer 45

Fruit only grows on flowering plants that have been pollinated. Without pollination the fruit and seeds don’t grow.
If gibberellins are applied to unpollinated flowers on some plants, the fruit will grow and the seeds won’t.

Question 46

Plant hormones in ripening of fruits

Answer 46

Can be controlled when they are still on plant or during transport to shops. Allows fruit to be more easily picked when unripe on the plant as they’re damage less easily.
Ethene is added to make the fruit ripen so the fruit will ripen on the way to the supermarket and will be ripe by the time it gets to the shelf.

Question 47

Controlling seed germination with plant hormones

Answer 47

Lots of seeds won’t germinate unless they’ve gone through certain conditions such as a period of cold or dryness.
Seeds can be treated with gibberellins so they can germinate at times when they normally would not.
Also makes sure seeds in a batch will all germinate at the same time.