CB6c/d Absorbing water and mineral ions and transpiration and translocation

Question 1

Why do plants require water

Answer 1

• Photosynthesis
• Maintenance of structure
• 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 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 tissue

Answer 7

Xylem
Phloem

Question 8

What is the function of xylem

Answer 8

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

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 provide 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 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 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 steam transport mineral ions

Answer 16

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

Question 17

What are the 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 change shape to control the size of the pore

Question 19

How do guard cells control the size of the stoma

Answer 19

To open the stomata:

Water enters the 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

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 to 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 so 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 so 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 in 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 the 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