TRANSPORT IN PLANTS

Question 1

XYLEM

Answer 1

xylem are the tissues that transports water in stem and leaves of plants.

Question 2

cohesion-tension theory

Answer 2

• water vapour evaporates out of the stomata by transpiration. this loss in water volume creates a lower pressure.
• more water is pulled up to the xylem to replace the lost water.
• due to the presence of hydrogen bonds in the water molecule, they are cohesive ( they stick together) and forms a column of water within the xylem.
• the molecules are also adhere ( stuck to the walls of xylem) which helps to pull the water column upwards.
• as this column of water is pulled up the xylem, it creates tension.

Question 3

transpiration

Answer 3

transpiration is the loss of water through the stomata of the leaves.

Question 4

factors affecting transpiration rate

Answer 4

light, temperature,humidity,wind.

Question 5

light

Answer 5

positive correlation between light and transpiration - more light causes more stomata to open for co2 to enter for photosynthesis - larger surface area for evaporation

Question 6

temperature

Answer 6

positive correlation - more heat means more ke - faster molecules so more evaporation.

Question 7

humidity

Answer 7

negative correlation - more water vapor in air makes the water potential positive outside the leaf - reducing the water potential gradient.

Question 8

wind

Answer 8

positive correlation - wind blows away humid air containing water vapour - so transpiration occurs.

Question 9

phloem

Answer 9

phloem are the tissues adapted for transfer of solutes specially sugars like sucrose.

Question 10

cell types in phloem tisssues

Answer 10

sieve tubes and companion cells

Question 11

sieve tubes

Answer 11

sieve tubes are living cells that forms a tube for transport of solutes. they dont have a nucleus and only few organelles so they need a companion cells.

Question 12

companion cells

Answer 12

there is a companion cell for each sieve tube which carry out living functions for sieve cells like providing energy for active transport of solutes.

Question 13

translocation

Answer 13

translocation is the movement of solutes. its an energy requiring process that happens in the phloem.

Question 14

source and sinks

Answer 14

source is where the solutes are made and sinks are where the solutes are used up.

Question 15

mass flow hypothesis

Answer 15

• active transport is used to actively load the solutes from the companion cells into the sieve of phloem tubes at the source.
• this lowers the water potential so water enters the tube by osmosis through xylem and companion cells which creates a high pressure inside the sieve tubes at the source end of phloem.
• at the sink end, solutes are removed from thr phloem to be used up which increases the water potential so water leaves the tube by osmosis. this lowers the pressure inside the sieve tube.
• the result is a pressure gradient from source end to sink end and the gradient pushes solutes along the sieve tubes towards the sink.