B3.2 - transport in plants (6h)

Question 1

What is the success criteria for drawing plan diagrams from micrographs?

Answer 1

1. Use a sharp pencil.
2. Ensure the drawing has correct shape and proportions.
3. Do not draw individual cells.
4. Use continuous lines.
5. Do not use shading.
6. Use a ruler for labeling, touching the region with no arrows.
7. Only label structures/tissues that you can see.
8. Include descriptions of shape and colour in your labeling.
9. Take up more than half of the available space.
10. Give the drawing a title including the specimen, the type of section and the magnification.

Question 2

What are the components of a root?

Answer 2

• Phloem
• Xylem
• Cortex
• Epidermis
• Endodermis

Question 3

What are the components of a stem?

Answer 3

• Phloem
• Xylem
• Cambium
• Cortex
• Epidermis

Question 4

What is a vascular bundle?

Answer 4

Phloem and xylem tubes

Question 5

What is the role of the phloem?

Answer 5

Transports sucrose and other nutrients.

Question 6

What is the role of xylem?

Answer 6

Transports water and dissolved minerals.

Question 7

What is the role of the cortex?

Answer 7

Unspecialised cells that stores nutrients.

Question 8

What is the role of the epidermis in the root?

Answer 8

Protective layer and grows root hairs to increase surface area for water uptake.

Question 9

What is the role of the epidermis in the stem?

Answer 9

Prevents water loss and is a protective layer against infection.

Question 10

What is the role of the cambium?

Answer 10

Contains meristem, providing new cells for growth.

Question 11

How is water transported from roots to leaves through generation of transpiration pull?

Answer 11

1. Water evaporates from the cell walls of spongy mesophyll cells and diffuses into the air spaces.
2. Water vapour passes out of the stomata by diffusion, with guard cells controlling the rate of transpiration.
3. Lost water is replaces from the xylem by capillary action through the cell walls and into the air spaces.
4. Water drawn out of the xylem creates low pressure (negative pressure potentials) and therefore generates tension.

Question 12

How does water flow in the transpiration stream?

Answer 12

Flow of water from roots to leaves in the transpiration stream.
- The tension (transpiration pull) draws water up in the xylem.

Question 13

What causes the continuous column of water?

Answer 13

Cohesion ensures a continuous column of water, allowing water to be pulled against gravity.
- Cohesion in water is due to the polar hydrogen bonding between water molecules.
- Cohesion means the column of water molecules doesn’t break.

Question 14

What is the purpose of adhesion between water molecules and the cell wall?

Answer 14

Adhesion occurs due to hydrogen bonding.
- This creates tension to aid the movement of water against gravity?

Question 15

What is the purpose of cohesion between water molecules?

Answer 15

Cohesion occurs due to hydrogen bonding.
- This means water molecules form a continuous column, aiding the upwards movement of water.

Question 16

How is the xylem adapted for water transport?

Answer 16

• Xylem cells are dead, having no cell contents or plasma membrane.
• Xylem vessels are made of xylem cells joined end-on-end, with incomplete or absent end walls between the cells.
  –> This allows unimpeded flow.
• Xylem cells have thickened cellulose walls and helical rings of lignin.
  –> To withstand the tension of the transpiration pull, resisting the low pressure and preventing vessel collapse.
• Xylem cells have pits that connect neighboring vessels laterally.
  –> Allows the entry and exit of water.