B2 - Plant Tissues, Organs And Systems

Question 1

Describe how the structure and function of the leaf is adapted for photosynthesis

Answer 1

The upper epidermis is made up of a very thin layer of epidermal cells and is transparent to maximise the amount of light that can pass through to the palisade layer

Palisade mesophyll is near the upper surface of the leaf to absorb more light for photosynthesis, and it contains many chloroplasts to absorb light energy

Spongy mesophyll is full of air spaces to increase surface area which increases the rate of diffusion of carbon dioxide through stomata to palisade cells

Lower epidermis contains many stomata to allow carbon dioxide in and control the amount of water vapour that can pass out the leaf so more is available for photosynthesis

The xylem tissue have a hollow tube for transporting water and dissolved mineral ions in the transpiration stream, which is used in photosynthesis

Question 2

Describe how water and mineral ions travel in the plant from the roots to the leaves

Answer 2

Water and mineral ions are absorbed by osmosis and active transport by the root hair cells

Transpiration is the loss of water from the plant by evaporation from the surface of the leaves through the stomata, which causes a pull

The absorbed water and dissolved mineral ions move up through the plant as a transpiration stream in the xylem

Question 3

Explain why leaves have more stomata on their lower surface than their upper surface

Answer 3

There is reduced transpiration rate from the upper surface as it is warmer above the leaf because the lower leaf is in shade due to less light

So it does not wilt

Question 4

Explain how plants are adapted to live in hot, dry conditions

Answer 4

Plants have a thick waxy cuticle to prevent water loss by evaporation

They have a smaller surface area, so less transpiration occurs

They have fewer stomata, so less transpiration occurs and stomata close during the day, so that there is reduced transpiration

Widespread roots absorb more water due to larger surface area, meaning there is more water storage tissue so they can survive droughts

Question 5

Describe how guard cells control the opening and closing of stomata

Question 6

Compare the structure and function of phloem and xylem tissue

Answer 6

Structurally, both are tubular and made of cells

Xylem is made of dead cells, whereas phloem is made of living cells

Phloem cells have pores in their end walls, whereas xylem cells do not

Xylem is hollow and does not contain cytoplasm, whereas phloem contains cytoplasm

Xylem contains lignin, whereas phloem does not

Functionally, both transport substances throughout the stream / leaves / roots / plant

Xylem transports water and mineral ions, whereas phloem transports dissolved sugars

Xylem is involved in transpiration, whereas phloem is involved in translocation

Xylem transports Unidirectionally, whereas phloem transport bidirectionally

Question 7

Describe the process of transpiration

Answer 7

When stoma are open, plants lose water vapour

It evaporates from the cells lining the air spaces and then passes out of the leaf through the stomata by diffusion

As water evaporates, more water is pulled through the xylem to take its place. This is known as the transpiration stream.

ANYTHING THAT AFFECTS THE RATE OF EVAPORATION WILL AFFECT TRANSPIRATION

Question 8

Describe the process of translocation

Question 9

What causes transpiration?

Answer 9

Caused by evaporation and diffusion, which causes a shortage of water

This means more water is drawn up from the xylem vessels, causing a constant transpiration stream

Because there is more water inside the plant than outside, the water escapes via diffusion

Question 10

How does light intensity affect the rate of transpiration?

Answer 10

Greater light intensity = greater rate of transpiration.

Photosynthesis cannot happen in the dark, so stomata is closed, meaning very little water is lost

Question 11

How does changing temperature affect the rate of transpiration?

Answer 11

Warmer = greater transpiration

Particles have more energy to evaporate and diffuse out of the stomata

Question 12

How does air movement affect the rate of transpiration?

Answer 12

The better the air movement, the greater the transpiration rate

If air flow around the plant is poor, the water vapour surrounds the leaf. This means there’s a higher concentration of water around the leaf, so the rate of diffusion decreases

Question 13

How does humidity affect the rate of transpiration?

Answer 13

The drier the air around the leaf, the greater the rate of transpiration

If the air is humid, there’s a lot of water around the leaf. This means there’s a greater concentration of water around the leaf than in, so the rate of diffusion decreases

Question 14

What forms a plant organ system?

Answer 14

Roots, stem and leaves

Question 15

What is the role of stomata and guard cells?

Answer 15

Stomata control gas exchange

Guard cells control the opening and closing of the stomata

Question 16

Learn how to draw and observe a transverse section of a leaf

Question 17

Describe the transport of water through a plant from the roots to the atmosphere.

Question 18

Explain how plants transport substances

Answer 18

The phloem tissue transport dissolved sugars from the leaves to the rest of the plant by translocation

Question 19

Describe how a plant controls water loss

Answer 19

The waxy cuticle is a waterproof layer that prevents uncontrolled water loss

Most stomata are found on the underside of leaves, protecting them from the direct light and energy of the sun

Plants can wilt; the leaves collapse and hang down. This reduces the surface area for water loss by evaporation

Stomata can close which prevents most water loss