chapter 8

Question 1

Functions of xylem and phloem

Answer 1

Xylem:
- transports water and mineral ions
- gives support

Phloem :
- transports sucrose and amino acids from source to sink
source: leaves
Sink : roots and stems

Question 2

Adaptations of xylem and its functions

Answer 2

1. Has lignified wall : made lignin , waterproof , gives support
2. Hollow and joined end to end forming continuous tube : no cell content , hollow tube to allow water to flow through easily
3. No end walls : form a continuous tube to reduce resistance of waterflow
4. Has pits / holes in cell wall : for lateral movement of water

Question 3

Adaptations of root hair cells and its functions

Answer 3

1. Large surface area : increases rate of absorption of water by osmosis and mineral ions by active transport
2. thin walls : short diffusion distance and faster absorption
3. has mitochondria and carrier protein : provide energy for active transport of mineral ions

Question 4

Describe the pathway of water from roots to leaf

Answer 4

Root hair cell > root cortex cell > xylem > spongy mesophyll cell > air spaces > stomata > air

Question 5

define transpiration

Answer 5

• the loss of water vapour from plant leaves by evaporation of water at the surface of the spongy mesophyll cells , followed by diffusion of water capour through the stomata

Question 6

Function of transpiration in plants

Answer 6

• transporting of water and ions
• providing water to keep cells turgid for support of plant
• providing water to leaf cells for photosynthesis
• keeping leaves cool ( water leaving cells require heat energy. using heat to convert water into water vapour helps cool plant down )

Question 7

describe how transpiration occurs

Answer 7

evaporation takes place from surface of spongy mesophyll cells
many interconnecting air spaces between cells and stomata create a large surface area for gas exchange and diffusion of water vapour

Question 8

explain how and why wilting occurs

Answer 8

water loss by transpiration is greater than water uptake through root
wall of cell not full of water > cell wall cannot support plant and so starts to collapse
plant becomes flaccid and lose turgor pressure

Question 9

define translocation

Answer 9

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

Question 10

describe phloem tube

Answer 10

joined end to end
contain holes in end of cell walls called sieve plates
allows easy transport of substances from one cell to the next

Question 11

explain the different uses of sucrose in a plant

Answer 11

root hair cells convert sucrose to starch and stores it
growing cells make cellulose for cell walls
flowers use sucrose to make attractive nectar and tasty fruits to attract insects
glucose used or respiration

Question 12

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

Answer 12

In summer :
- plants are active photosynthesising
- leaves are major SOURCE , producing glucose constantly
- sink (stem root flowers fruits )

In spring :
- plant not actively photosynthesising
- roots are major SOURCE
- used stored starch and convert back to sucrose
- sinks ( leaves stems flowers fruits )