8: Transport in plants

Question 1

Vascular Bundle

Xylem & Phloem
what it transports, process, direction of flow, cells

Answer 1

xylem + phloem
transport system - has thick cell walls to support the stem and leaf

XYLEM
1. transports WATER, MINERALS by TRANSPIRATION
2. ONE way direction of flow (roots ➝ leaves)
3. Cells - dead
Adaptation: - hollow, dead cells (lose their organelle, cytoplasm) - join in continuous flow of water
- lignin strengthens

PHLOEM

1. transports SUCROSE (glucose + fructose), AMINO ACIDS by TRANSLOCATION
2. BOTH directions
3. Cells - living
4. no nucleus

Question 2

Position of xylem and phloem in a leaf, stem and root

Answer 2

Leaf: Xylem always on top of phloem

Stem: xylem inside of stem; phloem outside

Root: xylem in the middle in an X shape; phloem outside

Question 3

Pathway of water

Answer 3

Root hair cell (osmosis) ➝ root cortex cells ➝ xylem ➝ diffuses into mesophyll cells ➝ used in metabolic reactions

Question 4

Root Hair Cell adaptation

Answer 4

Long root hair extensions = large surface area of root hairs

• increases the rate of the absorption of
• water by osmosis and
• ions by active transport

Question 5

Define Transpiration

Answer 5

• LOSS OF WATER VAPOUR
• from plant leaves by evaporation of water
• at the surfaces of the MESOPHYLL cells
• followed by DIFFUSION of WATER VAPOUR through the STOMATA

Question 6

Explain the effects of variation of temperature and humidity on transpiration rate

Answer 6

higher temp = faster

higher humidity = slower - concentration gradient of water vapour inside is low - diffusion out of plant is slower

Question 7

Explain how and why wilting occurs

Answer 7

Lack of water

water moves out of cells, turgor pressure decreases, strength of cell wall decreases = cannot support plant.

Question 8

Why is water lost from plants?

Answer 8

Plants have

• large SA = for evaporation
• interconnecting air spaces
• stomata (pores) in leaves = to allow water to diffuse out of plants (to limit water loss - plant closes stomata)

Question 9

Explain the mechanism by which water moves upwards in the xylem

Answer 9

• Water evaporates from leaves creating negative pressure in xylem = TRANSPIRATION PULL
• drawn up the xylem in a column (in continuous transpiration steam)
• held together by cohesion

Question 10

Define translocation

Answer 10

• Movement of SUCROSE and AMINO ACIDS in phloem:
• from SOURCE (regions of production) – to SINK (regions of storage OR to regions where they are used in respiration or growth)