Topic 6 - Plant Structures and Their Functions

Question 1

Define osmosis.

Answer 1

Movement of water molecules from a high concentration to a low concentration through a partially permeable membrane. Requires no energy.

Question 2

Define diffusion.

Answer 2

Particles moving from a high concentration to a low concentration down a concentration gradient. Requires no energy.

Question 3

Define active transport.

Answer 3

Movement of particles from low to high concentration up a concentration gradient, requiring energy.

Question 4

What is the word equation for photosynthesis?

Answer 4

LIGHT
carbon dioxide + water → glucose + oxygen
CHLOROPHYLL

Question 5

What is the symbol equation for photosynthesis?

Answer 5

LIGHT
6CO2 + 6H2O → C6H1206 + 602
CHLOROPHYLL

Question 6

What are the limiting factors of photosynthesis?

Answer 6

• light intensity
• concentration of CO2
• temperature

Question 7

How are mineral ions absorbed by root hair cells?

And why?

Answer 7

Active transport - the concentration of mineral ions is usually higher in the root hair cells rather than the soil.

Question 8

How is water absorbed by root hair cells?

Answer 8

Osmosis.

Question 9

How are root hair cells adapted to their function?

Answer 9

• They are covered in millions of microscopic hairs
• Large surface area
• Thin membrane

Question 10

What does the phloem transport?

Answer 10

Food substances, mainly sucrose.

Question 11

What is translocation?

Answer 11

It is where the phloem transports food substances made in the leaves to the rest of the plant, requiring energy from respiration.

Question 12

What is the structure of the phloem?

Answer 12

It is made of columns of elongated living cells with small pores in the end walls to allow things to flow through.

Question 13

What does the xylem transport?

Answer 13

Water and mineral ions.

Question 14

What is the structure of the xylem?

Answer 14

It is 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.

Question 15

What is lignin?

Answer 15

A complex organic polymer deposited in the cell walls of plants to strengthen them.

Question 16

What is transpiration?

Answer 16

The process where water and mineral ions are transported up the xylem against the force of gravity from the roots and out of the pores of leaves.

Question 17

What factors affect transpiration rate?

Answer 17

• Light
• Wind
• Temperature
• Humidity

Question 18

How does light affect the rate of transpiration?

Answer 18

The stomata open wider, allowing more CO2 into the leaf for photosynthesis and increasing transpiration rate.

Question 19

How does temperature affect the rate of transpiration?

Answer 19

Evaporation and diffusion are faster at higher temperatures.

Question 20

How does humidity affect the rate of transpiration?

Answer 20

Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air.

Question 21

How does wind affect the rate of transpiration?

Answer 21

Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf.

Question 22

What are stomata?

Answer 22

Tiny pores on the surface of a plant.

Question 23

How are stomata adapted to their function?

Answer 23

• They are surrounded by guard cells, which change shape to control the size of the pore. When turgid, the stomata are open. When flaccid, they are closed.

Question 24

What is the function of stomata?

Answer 24

Allow carbon dioxide and oxygen to diffuse directly in and out of a leaf. They also allow water vapour to escape during transpiration.

Question 25

How do you use a potometer to estimate transpiration rate?

Answer 25

1 - Set up the apparatus and record the starting position of the air bubble.
2 - Start a stopwatch and record the distance moved by the bubble per unit time.
3 - Calculating the speed of air bubble movement gives an estimate of the transpiration rate.

Question 26

What does a potometer actually measure?

Answer 26

The water uptake of a plant.

Question 27

What equation do you use to estimate the rate of transpiration?

Answer 27

distance moved ÷ time taken

Question 28

How are leaves adapted for photosynthesis? (3)

Answer 28

Any 3:

• Leaves are broad so there’s a large surface area exposed to light.
• The palisade layer has lots of chloroplasts near the top of the leaf so can get the most light.
• The upper epidermis is transparent.
• Xylem and phloem form a network of vascular bundles, providing the leaf with water for photosynthesis and taking away the glucose produced.
• The epidermal tissues are covered with a waxy cuticle, to reduce water loss by evaporation.

Question 29

How are leaves adapted for gas exchange?

Answer 29

• Lots of stomata to let CO2 diffuse directly into the leaf.
• The spongy mesophyll tissue contains air spaces, which increase the rate of diffusion of gases into and out of the leaf’s cells.

Question 30

How are plants living in hot and dry places adapted to live in extreme environments? (3)

Answer 30

Any 3:

• Small leaves/spines to reduce surface area for water loss.
• Curled leaves/hairs to reduce air flow close to the leaf.
• Thick waxy cuticles to reduce water loss.
• Thick. fleshy stem to store water.
• Fewer stomata/stomata that only open at night/stomata in sunken pits to reduce water loss.

Question 31

What is an auxin?

Answer 31

A plant hormone that controls growth at the tips of shoots and roots.

Question 32

What do auxins do?

Answer 32

Stimulate cell elongation and promotes growth in the shoot but inhibits growth in the root.

Question 33

What is positive phototropism?

Answer 33

Grow towards light. (shoots)

Question 34

What is positive gravitropism?

Answer 34

Grows towards gravity. (roots)