8. Transport in plants

Question 1

State the functions of xylem and phloem:

Answer 1

(a) xylem – transport of water and mineral ions, and support

(b) phloem – transport of sucrose and amino acids

Question 2

Relate the structure of xylem vessels to their function

Answer 2

(a) thick walls with lignin

(b) no cell contents

(c) cells joined end to end with no cross walls to form a long continuous tube

Question 3

root hair cells and state their functions

Answer 3

absorb water and mineral ions from soil.

large surface area of root hairs increases the uptake of water and mineral ions

Question 4

pathway taken by water through the root, stem and leaf—

Answer 4

root hair cells, root cortex cells, xylem, mesophyll cells

Question 5

Describe transpiration

Answer 5

the loss of water vapour from leaves

transpiration pull draws up a column of water molecules, held together by forces of attraction between water molecules

water evaporates from the surfaces of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour

the large internal surface area provided by the interconnecting air spaces between mesophyll cells and the size and number of stomata increases water vapour loss.

Question 5

effects on the rate of transpiration of varying the following factors

Answer 5

temperature

wind speed

humidity

Question 6

Explain how and why wilting occurs

Question 6

describe translocation, source and sink

Answer 6

the movement of sucrose and amino acids in phloem from sources to sinks

(a) sources as the parts of plants that release sucrose or amino acids
(b) sinks as the parts of plants that use or store sucrose or amino acids

Question 6

Explain why some parts of a plant may act as a source and a sink at different times