Topic 6 - Plant Structures And Their Functions

Question 1

What happens during photosynthesis?

Answer 1

Photosynthetic organisms, such as green plants and algae use energy from the sun to make glucose.

Question 2

What is the glucose made from photosynthesis used for?

Answer 2

It’s used to make larger, complex molecules that the plants or algae need to grow.

Question 3

What is an organisms biomass?

Answer 3

The mass of living material.

Question 4

Where does photosynthesis happen?

Answer 4

In the chloroplasts.

Question 5

What do the chloroplasts contain which absorbs light?

Answer 5

Chlorophyll.

Question 6

What is the word equation for photosynthesis?

Answer 6

Carbon dioxide + water → glucose + oxygen.

Question 7

What type of reaction is photosynthesis?

Answer 7

Endothermic.

Question 8

What is the rate of photosynthesis affected by?

Answer 8

Light intensity, CO2 concentration and temperature.

Question 9

Which factors can become limiting factors?

Answer 9

All three - light intensity, CO2 and temperature.

Question 10

What role does light play in photosynthesis?

Answer 10

Light transfers the energy needed for photosynthesis to the chloroplasts.

Question 11

What is the effect of light on the rate of photosynthesis?

Answer 11

At first, as the light level is raised, the rate of photosynthesis increases steadily. But this is only true up to a certain point. Beyond that point, it won’t make any difference - it will be either CO2 or temperature which is a limiting factor.

Question 12

What is the effect of carbon dioxide concentration on photosynthesis?

Answer 12

As with light intensity, increasing the CO2 concentration increases with the rate of photosynthesis up to point. After this, CO2 is no longer a limiting factor.

Question 13

Why is temperature usually the limiting factor?

Answer 13

The temperature has to be specific. If it’s too cold, the enzymes needed for photosynthesis work more slowly because they don’t have enough energy. However if the plant gets too hot, the enzymes denature.

Question 14

At what temperature is it too hot for plants?

Answer 14

About 45℃

Question 15

What do the root hair cells do on a plant?

Answer 15

Take in minerals and water.

Question 16

How is the root hair cell adapted to its function?

Answer 16

It has millions of microscopic hairs on each branch of root which gives the plant a large surface area for absorbing water and mineral ions from the soil.

Question 17

How do the roots take in mineral ions?

Answer 17

Mineral ions are absorbed by active transport because the concentration of mineral ions is usually higher in the root hair cells than in the soil around them.

Question 18

How do the roots take in water?

Answer 18

Osmosis.

Question 19

What do the phloem tubes do?

Answer 19

Transport food substances (mainly sucrose) made in the leaves to the rest of the plant for immediate use or for storage.

Question 20

What are phloem tubes made of?

Answer 20

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

Question 21

What is the process of transporting food called?

Answer 21

Translocation. It requires energy from respiration and the transport goes in both directions.

Question 22

What do the xylem tubes do?

Answer 22

They carry water and mineral ions from the roots to the stem and leaves.

Question 23

What are xylem tubes made of?

Answer 23

Dead cells joined end to end with no end walls between them and a hole down the middle. They’re strengthened with a material called lignin.

Question 24

What is the transpiration stream?

Answer 24

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

Question 25

What is transpiration caused by?

Answer 25

The evaporation and diffusion of water from the plant’s surface. Most transpiration happens in the leaves.

Question 26

How is there a constant transpiration stream of water through the plant?

Answer 26

The loss of water through transpiration creates a slight shortage of water in the leaf, so more water is drawn up from the rest of the plant through the xylem vessels to replace it. This in turn means more water is drawn up through the roots.

Question 27

What else does the transpiration stream carry?

Answer 27

Mineral ions that are dissolved in water.

Question 28

What are stomata?

Answer 28

Tiny pores on the surface of the plant that are mostly found on the lower surface of leaves.

Question 29

What is the purpose of stomata?

Answer 29

They allow CO2 and oxygen to diffuse directly in and out of the leaf. They also allow water vapour to escape during transpiration because there’s more water inside the plant then outside.

Question 30

What are stomata surrounded by and what is the purpose of them?

Answer 30

They’re surrounded by guard cells which change shape to control the size of the pore. When the guard cells are turgid the stomata are open and when the guard cels are flaccid, the stomata are close.

Question 31

What is the word for swollen with water?

Answer 31

Turgid.

Question 32

What is the word for low on water and limp?

Answer 32

Flaccid.

Question 33

What is transpiration rate effected by?

Answer 33

Light intensity, temperature and air flow.

Question 34

How does light intensity effect the rate of transpiration?

Answer 34

The brighter the light, the greater the transpiration rate. Stomata begin to close as it gets darker because photosynthesis can’t happen in the dark do they don’t need to be open to let CO2 out. When stomata are shut, very little water can escape.

Question 35

How does temperature effect the rate of transpiration?

Answer 35

The warmer it is, the faster transpiration happens. When it’s warm, the water particles have more energy to evaporate and diffuse out of the stomata.

Question 36

How does air flow effect the rate of transpiration?

Answer 36

The better the air flow around the leaf (stronger winds), the greater the rate of transpiration rate. If there’s good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside of the leaf. Diffusion then happens quickly, from an area of higher concentration to an area of lower concentration.

Question 37

How is a leaf adapted for photosynthesis and gas exchange?

Answer 37

1) Leaves are broad so there’s a large surface area exposed to light.
2) The palisade layer has lots of chloroplasts. This means they’re near the top of leaf where they can get most light.
3) The upper epidermis is transparent so light can pass through to palisade layer.
4) Xylem and phloem form a network of vascular bundles which provide leaf with water for photosynthesis and take away glucose produced. Also help support structure.
5) Epidermal tissues covered with waxy cuticle which helps reduce water loss.
6) Lower epidermis has lots of stomata which let C02 diffuse directly into leaf.
7) Spongy mesophyll tissue contain air spaces which increase rate of diffusion of gases in and out of leaves cells.

Question 38

How are cacti adapted to living in extreme environments?

Answer 38

1) It has spines instead of leaves which reduces surface area for water loss by evaporation. Spines also help stop animals eating plant.
2) Thick waxy cuticles reduce water loss by evaporation.
3) Thick fleshy stems which store more water.

Question 39

What other ways can plants be adapted to living in extreme conditions?

Answer 39

1) Curled leaves or hairs on surface of leaves reduces air flow close to leaf, trapping water vapour near surface and reducing diffusion from leaf to air.
2) Fewer stomata or stomata that only open at night.
3) Stomata sunken in pits reduces air flow close to stomata.

Question 40

What are auxins?

Answer 40

Plant hormones which control growth at the tips of roots and shoots. It promotes growth in the shoot but inhibits growth in the roots.

Question 41

Where is auxin produced?

Answer 41

In the tips and it diffuses backwards to stimulate the cell elongation process which occurs in the cells just behind the tips.

Question 42

What are shoots (in terms of phototropism and gravitropism)?

Answer 42

Shoots are positively photographic and negatively gravitropic.

Question 43

What does phototropism mean?

Answer 43

Responses of plants to light.

Question 44

What does gravitropism mean?

Answer 44

Responses of plants to gravity.

Question 45

Why are shoots positively phototropic?

Answer 45

When a shoot is exposed to light, it accumulates more auxin on the side that’s in the shade than the side that’s in the light. This makes the cells elongate more on the shaded side so the shoot bends toward light.

Question 46

Why are shoots negatively gravitropic?

Answer 46

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

Question 47

What are roots (in terms of phototropism and gravitropism)?

Answer 47

Roots are negatively phototropic and positively gravitropic.

Question 48

Why are roots positively gravitropic?

Answer 48

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

Question 49

Why are roots negatively phototropic?

Answer 49

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