Topic 6.7 To 6.14B Transport 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 eg 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 2 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 (eg mature green leaves) to non-photosynthetic tissues (eg developing seeds) via translocation

Question 11

What are the 2 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:
These 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:
Adajacent 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 Vapor 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 allows 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, therefore 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, therefore 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

Identify the structures of the leaf labelled in the diagram below

Answer 29

A waxy cuticle
B Vascular Bundle
C Upper Epidermis
D Palisade Mesophyll Tissue
E Spongy Mesophyll Tissue
F Lowe Epidermis
G Air filled Space
H Stoma
I Guard Cell

Question 30

Describe how leaves are adapted for photosynthesis

Answer 30

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 (eg chlorophyll) absorb light

Question 31

Describe how tissues of the leaves are adapted for photosynthesis and gas exchange

Answer 31

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 32

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

Answer 32

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