Topic 6 – Plant Structures and their Functions-Transports in Plants

Question 1

Why do plants require water? (3)

Answer 1

● Photosynthesis
● Maintenance of structure (turgidity)
● Cooling effect

Question 2

Why do plants require mineral ions?

Answer 2

For growth e.g. nitrates are required to produce proteins

Question 3

Which structure in plants is adapted for the uptake of water and minerals?

Answer 3

Root hairs

Question 4

How is water transported into root hairs?

Answer 4

● Lower concentration of water in root hair cells than in the soil
● Water diffuses down its concentration gradient into root hair cells by osmosis

Question 5

How are minerals transported into root hairs?

Answer 5

● Lower concentration of mineral ions in the soil than in the root
● Root hair cells take up mineral ions by active transport

Question 6

Outline how plant roots are adapted for the absorption of water and minerals

Answer 6

Plant roots are composed of millions of root hair cells which have:
● Long hairs that extend from the cell body, increasing the surface area for absorption
● Many mitochondria which produce ATP for active transport of mineral ions

Question 7

Name the two plant transport tissues

Answer 7

Xylem

Phloem

Question 8

What is the function of the xylem?

Answer 8

Transports water and minerals up the plant, from the roots to the leaves via the transpiration stream

Question 9

Describe how the xylem is adapted to its function

Answer 9

● Composed of dead cells laid end-to-end to form a long, hollow, continuous column
● No end walls which provides little resistance to the passage of water
● Thick cell wall strengthened with lignin to provide support

Question 10

What is the function of the phloem?

Answer 10

Transports sugars up and down the stem from photosynthetic tissues (e.g. mature green leaves) to non-photosynthetic tissues (e.g. developing seeds) via translocation

Question 11

What are the two cell types that make up the phloem?

Answer 11

Sieve tube elements

Companion cells

Question 12

Describe how the phloem is adapted to its function

Answer 12

● Sieve tube elements are long, thin cells, laid end-to-end with perforated end plates to enable the flow of sugars. They contain no nucleus and little cytoplasm to allow sugars to flow easily.
● Companion cells (adjacent to sieve tube elements) contain a dense cytoplasm, nucleus and mitochondria. They provide energy for processes in both cell types.

Question 13

What is transpiration?

Answer 13

The loss of water vapour from the parts of a plant exposed to the air due to evaporation and diffusion

Question 14

Where does the majority of transpiration take place?

Answer 14

Leaves

Question 15

Describe the process of transpiration

Answer 15

● Water evaporates from the mesophyll cell surfaces and diffuses out of the stomata
● Water molecules (which have cohesive properties) are drawn up the xylem vessels to replace the water that has been lost
● This causes more water molecules to be absorbed from the soil into root hair cells

Question 16

How does the transpiration stream transport mineral ions?

Answer 16

Mineral ions are dissolved in the water that is carried by the transpiration stream

Question 17

What are stomata?

Answer 17

They are pores found in the lower epidermis of a leaf which allow gas exchange

Question 18

What are guard cells?

Answer 18

Specialised cells surrounding the stoma that change shape to control the size of the pore

Question 19

How do guard cells control the size of stomata?

Answer 19

To open the stomata:
Water enters guard cells. They swell and become turgid. They bend and draw away from each other, opening the stomata.

To close the stomata:
Water leaves guard cells. They become flaccid, closing the stomata.

Question 20

What factors affect the rate of transpiration? (3)

Answer 20

● Light intensity
● Temperature
● Air movement

Question 21

Describe how high light intensity affects the rate of transpiration

Answer 21

● High light intensity, greater number of stomata open to allow gas exchange for photosynthesis
● Rate of photosynthesis increases so more water is taken up from the soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
∴ rate of transpiration increases

Question 22

Describe how low light intensity affects the rate of transpiration

Answer 22

At a low light intensity, fewer stomata are open so the rate of transpiration decreases.

Question 23

Describe how temperature affects the rate of transpiration

Answer 23

● Temperature increases, water molecules have more KE so rate of diffusion increases
● Photosynthesis also increases so more water is taken up from the soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
∴ rate of transpiration increases

Question 24

Describe how air movement affects the rate of transpiration

Answer 24

● Air movement increases, high water concentration gradient maintained between the air spaces in the leaf and atmosphere
● Increased rate of diffusion of water molecules out of the stomata
● Rate of transpiration increases

Question 25

What apparatus is used to measure the rate of transpiration?

Answer 25

Potometer

Question 26

What is assumed when measuring the rate of transpiration using a potometer?

Answer 26

rate of water uptake ≈ rate of transpiration

Question 27

How can the rate of transpiration be calculated using a potometer?

Answer 27

rate of transpiration=

distance moved by bubble / time taken

Question 28

What is translocation?

Answer 28

The movement of sugars (sucrose, amino acids etc.) up and down a plant, from the source to the sink, via the phloem. Requires ATP

Question 29

Describe how leaves are adapted for photosynthesis and gas exchange (biology only)

Answer 29

● Broad - large SA for light absorption
● Thin - short diffusion distance for gases, allows light to reach all cells
● Vascular bundles (xylem and phloem) form a network to deliver water and remove glucose. Also provide support.
● Photosynthetic pigments (e.g. chlorophyll) absorb light

Question 30

Describe how tissues of the leaves are adapted for photosynthesis and gas exchange (biology only)

Answer 30

● Palisade mesophyll layer - receives most light so contains greatest concentration of chloroplasts
● Upper epidermis - transparent, allows light to reach palisade layer
● Spongy mesophyll layer - air spaces increase the rate of diffusion
● Lower epidermis - contains many stomata for gas exchange

Question 31

Describe how plants are adapted to live in hot, dry conditions (biology only)

Answer 31

● Small leaves/spines - reduce SA for water loss
● Thick waxy cuticle - reduces evaporation, conserving water
● Thick stem - provides a storage of water
● Shallow but widespread roots - large SA to absorb water
● Stomata sunken in pits and leaves curled - reduces air flow, lowering diffusion gradient and reducing water loss by evaporation
● Stomata close to reduce water loss