Topic 3 Transport in plants

Question 1

Why can unicellular organisms rely on diffusion?

Answer 1

• large sa vol ratio

- oxygen + nutrients can diffuse directly and quickly in and out of cell

Question 2

Why do larger organisms need a transport system?

Answer 2

• small sa vol ratio
• diffusion doesn’t occur quickly enough to sustain them
• larger organisms require organ systems w/ specialised adaptations to supply all their cells w nutrients + oxygen and collect waste (thru diffusion) to be excreted from the body

Question 3

What is the function of the waxy cuticle?

Answer 3

• prevent water loss

Question 4

What is the function of the upper epidermis?

Answer 4

Thin + transparent to allow more light through to chloroplasts

Question 5

What is the function of the palisade cells?

Answer 5

• contain lots of chloroplasts to absorb more light

Question 6

What is the function of the spongy layer?

Answer 6

Contains lots of air spaces to allow carbon dioxide to diffuse through leaf and increase the surface area

Question 7

What is the function of the stomata?

Answer 7

• holes in the leaf to allow carbon dioxide to diffuse in and oxygen to diffuse out

Question 8

What is the function of the guard cells

Answer 8

To open and close the holes in the leaf

To close to prevent water loss

Question 9

What does the xylem do?

Answer 9

• transports water and dissolved minerals from the roots to the other parts of plant

Question 10

What does the phloem do?

Answer 10

• transports sucrose + amino acids between leaves + other parts of plant

Question 11

Describe the structure of xylem cells

Answer 11

• only transports from roots to shoots
• no cell wall so form continuous tubes
• hollow + strengthened through lignin
• xylem cells are dead

Question 12

Describe the structure of phloem cells

Answer 12

• living
• sieve plates between cells where cell walls have partially broken down
• form continuous tubes

Question 13

How are xylem and phloem arranged inside the root?

Answer 13

In vascular bundles

• xylem always on inside and phloem on outside

Question 14

Explain how water is absorbed by root hair cells

Answer 14

• hair like extension increases the surface area to volume ratio
• thin walls (short distance)
• this increases rate of active transport (absorption of mineral ions)
• the cytoplasm of root hair cell lower water potential than soil
• water moves into root hair cell via osmosis
• higher of nitrates inside root hair cell than in soil
• nitrates move into root hair cell via active transport (+energy)

Question 15

After the water is absorbed by the root hair cells, it moves into the root cortex cells. Explain how this happens.

Answer 15

There is a high water potential in root hair cell whereas there is a low water potential in root cortex cell, since water enters via osmosis (high -> low water potential)

Question 16

What happens after the water moves into the root cortex cells?

Answer 16

Moves into xylem cells (centre of root) via osmosis

Water moves up the xylem in the stem towards leaves via transpiration stream

Water moves from xylem cells into mesophyll cells (palisade + spongy) by osmosis (will be used in photosynthesis or transpiration)

Question 17

What is transpiration?

Answer 17

• loss of water -> evaporation of water at surfaces of spongy mesophyll cells -> diffusion of water vapour through stomata

Question 18

What is the transpiration stream?

Answer 18

• loss of water causes pull - due to COHESION water is drawn up through the xylem to replace the after lost (water potential gradient is created)

Question 19

Why do plants need water?

Answer 19

1. Solvent for mineral ions to be transported around the plant
2. Reactant in photosynthesis
3. Keeps cell turgid providing support to plant
4. Keeps plant cool via evaporation
5. Significant part of cytoplasm where lots of chemical reactions occur

Question 20

How is marram grass adapted to reduce water loss via transpiration?

Answer 20

1. Rolled up leaf - stomata on inside so evaporated water gets trapped
2. Sunken stomata
3. Hairs to trap water
4. Lowers concentration grad between inside + outside of leaf -> less transpiration -> less water loss

Question 21

How does humidity affect transpiration?

Answer 21

Decrease

• leaves surrounded by moist air in high humidity and so conc gradient less steep -> reduces diffusion

Question 22

How does wind speed affect transpiration?

Answer 22

Increase

• high wind speed removes water vapour quickly keeping conc grad steep + speeding up diffusion

Question 23

How does temperature affect transpiration?

Answer 23

Increase

• evaporation + diffusion faster at higher temps due to more kinetic energy of particles

Question 24

How does light intensity affect transpiration?

Answer 24

Increase

• rate of photosynthesis increases -> stomata open wider to allow more co2 into leaf for photosynthesis -> more diffusion to occur (more water lost)