3.1.3 - Transport in plants part 2

Question 1

What is a xerophyte ?

Answer 1

Plants with adaptions that enable them to survive in dry habitats or habitats where water is in short supply in the environment

Question 2

Give two examples of xerophytes

Answer 2

Conifers and marram grass

Question 3

In what kind of environment may water loss become a really problem for plants?

Answer 3

Hot, dry, breezy conditions

Question 4

How do sunken stomata help to adapt a plant to hot dry conditions?

Answer 4

• Reduce air movement
• Creating a microclimate of still, humid air
• That reduces the water vapour potential gradient so reduces transpiration

Question 5

How does a reduction in the number of stomata adapt xerophytes?

Answer 5

Reduces water loss by transpiration

Question 6

What is a downside of reduced numbers of stomata?

Answer 6

Reduces the gas exchange that can take place

Question 7

How does a reduction in the number of leaves adapt xerophytes?

Answer 7

Water loss is greatly reduced by minimising the amount of water loss by transpiration

Question 8

How do hairy leaves adapt xerophytes?

Answer 8

• Create a microclimate of still, humid air
• This reduces the water vapour potential gradient
• This minimises the loss of water by transpiration from the surface of the leaf

Question 9

How do curled leaves adapt xerophytes?

Answer 9

• Confine all the stomata within a microenvironment of still, humid air
• To reduce diffusion of water vapour from the stomata

Question 10

How are succulents adapted to their environment?

Answer 10

• Contain specialist parenchyma tissue in stems and roots

- Water in stored in these and then used in times of drought

Question 11

How can losing leaves adapt a xerophyte?

Answer 11

• Leaves are normally lost when water is not available

- This reduces water loss by transpiration

Question 12

How do xerophytes have roots adapted for their environment?

Answer 12

• Long tap roots grow deep into the ground below the surface

- Shallow roots with large surface area are able to absorb surface water before a rain shower evaporates

Question 13

How can some xerophytes ‘avoid the problem’ of their environments?

Answer 13

• Plants die but leave seeds to germinate and grow rapidly when it rains again
• Some survive as storage organs (tubers and bulbs)
• Some plants can be completely dehydrated and recover when it rains again

Question 14

What is a hydrophyte ?

Answer 14

Plants with adaptations that enable them to survive in veery wet habitats or submerged at the surface of the water

Question 15

Give two examples of hydrophytes

Answer 15

Water lilies and water cress

Question 16

What are the problems faced by hydrophytes ?

Answer 16

• Water logging, air spaces in plants need to be full of air not water
• It is important that leaves float on water to enable photosynthesis

Question 17

How does having a thin/no waxy cuticle adapt hydrophytes?

Answer 17

Allows water to be lost through transpiration

Question 18

How does the waxy cuticle of hydrophytes and xerophytes differ ?

Answer 18

Hydrophytes may have a very thin or no waxy cuticle whereas xerophytes have very thick waxy cuticles

Question 19

How does having many stomata that are permanently open adapt hydrophytes?

Answer 19

It maximises gas exchange

Question 20

Why do hydrophytes have reduced structural support?

Answer 20

• Water supports the leaves and flowers

- So no need for strong supporting structures

Question 21

How do wide, flat leaves adapt hydrophytes?

Answer 21

• Spread across the surface of the water

- Capture as much light as possible

Question 22

Why do hydrophytes have small roots?

Answer 22

• Water can diffuse directly into stem and leaf tissue

- So less need for uptake by roots

Question 23

How does having a large surface area of stems and roots under water adapt hydrophytes?

Answer 23

Maximises area for photosynthesis and for oxygen to diffuse into submerged plants

Question 24

How do air sacs adapt hydrophytes?

Answer 24

Enable leaves and/or flowers to float on the surface of the water

Question 25

What are aerenchyma ?

Answer 25

Specialised parenchyma tissue which have many large air spaces

Question 26

How do aerenchyma adapt hydrophytes ?

Answer 26

• Makes leaves and stems more buoyant
• Forms a low resistance pathway for the movement of substances such as oxygen to tissues below water
• This helps the plant to cope with extreme low oxygen conditions, such as mud

Question 27

What is translocation ?

Answer 27

It is the process by which plants transport organic compounds in the phloem from sources to sinks

Question 28

What are assimilates ?

Answer 28

The products of photosynthesis

Question 29

What are the main sources of assimilates in a plant ?

Answer 29

• Green leaves and stems
• Storage organs e.g. tubers and tap roots
• Food stores in seeds when they germinate

Question 30

What are the main sinks in a plant ?

Answer 30

• Roots that are actively absorbing mineral ions
• Meristems that are actively dividing
• Any parts of the plant that are laying down food stores, such as developing seeds, fruits or storage organs

Question 31

Describe how sucrose is transported from the mesophyll cells to the phloem

Answer 31

• Companion cells actively pump H+ ions out of the cell and into surrounding mesophyll cells
• H+ diffuse back into the companion cell, down a diffusion gradient and co-transport sucrose into the companion cell
• Sucrose is co transported against the sucrose concentration gradient into sieve tube elements
• The H+ ions being pumped out make an electrochemical gradient, proton gradient, the energy of the hydrogen proton gradient gives sucrose its energy that it needs to be able to be co transported against its concentration gradient

Question 32

Describe how sucrose is moved along the phloem

Answer 32

• Sucrose enters the phloem which lowers the water potential of the phloem
• Water enters by osmosis
• Water also enters from the xylem
• Water entering the phloem forces the contents to flowthis is known as mass flow

Question 33

Describe how sucrose moves from the phloem to plant cells

Answer 33

• Sucrose and other assimilates leave the phloem by diffusion
• The cells then use the sucrose
• Keeping the sucrose concentration of the cell lower than the xylem and maintaining a concentration gradient

Question 34

What do plant cells use sucrose for ?

Answer 34

• Convert it to starch for storage

- Use it for respiration