T6 - 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 e.g. nitrates are required to
produce proteins

Question 3

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

Answer 3

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 4

Name the two plant transport tissues

Answer 4

Xylem
Phloem

Question 5

What is the function of the xylem?

Answer 5

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

Question 6

Describe how the xylem is adapted to its function

Answer 6

• 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 7

What is the function of the phloem?

Answer 7

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 8

What is transpiration?

Answer 8

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

Question 9

Where does the majority of transpiration take place?

Answer 9

Leaves

Question 10

Describe the process of transpiration

Answer 10

• 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 11

How does the transpiration stream transport mineral ions?

Answer 11

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

Question 12

What are stomata?

Answer 12

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

Question 13

What are guard cells?

Answer 13

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

Question 14

What factors affect the rate of transpiration? (3)

Answer 14

Light intensity
Temperature
Air movement

Question 15

Describe how high light intensity affects the rate of transpiration

Answer 15

• 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 16

Describe how low light intensity affects the rate of
transpiration

Answer 16

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

Question 17

Describe how temperature affects the rate of transpiration

Answer 17

• 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 the rate of transpiration increases

Question 18

Describe how air movement affects the rate of transpiration

Answer 18

• 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 19

What is translocation?

Answer 19

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 20

What is ATP

Answer 20

An energy-carrying molecule found in the cells of all living things

Question 21

Describe how leaves are adapted for photosynthesis and gas exchange

Answer 21

• 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 22

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

Answer 22

• 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 23

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

Answer 23

• 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