movement of water in plants

Question 1

describe the function of xylem tissue.

Answer 1

(non living tissue) transports water and mineral ions from roots through the stem, up the plant to the leaves of the plant.

Question 2

suggest how xylem tissue is adapted to its function.

Answer 2

cells are joined with no end walls forming a long continuous tube - water flows as a continuous column.
cells contain no cytoplasm/organelles so its easier for water to flow.
contains thick cell walls with lignin - provides support to withstand tension and prevent water loss.
pits are in the side walls around xylem vessels to control water exit.

Question 3

state one which in which xylem is adapted to be protected from animals.

Answer 3

parenchyma packs around the xylem which stores food and tannin (unpleasant smelling chemical to prevent attacks from animals)

Question 4

explain the cohesion-tension theory of water transport in the leaf.

Answer 4

• water evaporates from mesophyll cells into air spaces and water vapour diffuses through open stomata (water lost from leaf by transpiration)
• reducing water potential (and creates tension in xylem vessels)
• so water id drawn out of xylem down a water potential gradient.

Question 5

describe cohesion of water molecules.

Answer 5

water molecules are cohesive - they stick together so as one water molecule moves up the xylem, it pulls another water molecule up with it.

Question 6

describe adhesion of water molecules.

Answer 6

water molecules are adhesive - they stick to certain surfaces like the walls of the xylem vessels.

Question 7

explain the cohesion-tension theory of water transport in the xylem and roots.

Answer 7

• tension created in xylem.
• hydrogen bonds result in cohesion between water molecules so water is pulled up as a continuous column.
• water also adheres to walls of the xylem.
• water enters roots via osmosis.

Question 8

state the different environmental variables that affect transpiration rate.

Answer 8

light intensity
temperature
wind intensity
humidity

Question 9

how does light intensity affect transpiration rate?

Answer 9

• increases rate of transpiration
• stomata open for photosynthesis, allowing more water to evaporate faster (stomata close dark so there is a low transpiration rate)

Question 10

how does temperature affect transpiration rate?

Answer 10

• increases rate of transpiration
• as temp increases, water molecules gain kinetic energy so water evaporates faster from stomata.
• high rate of photosynthesis so more stomata open so theres more area for evaporation.

Question 11

how does wind intensity affect transpiration rate?

Answer 11

• increases rate of transpiration
• wind blows away water molecules from around stomata
• decreasing water potential of air around stomata.
• increasing water potential gradient so more evaporation of water (faster)

Question 12

how does humidity affect transpiration rate?

Answer 12

• decreases rate of transpiration
• more water in the air than in the plant as water moves out the plant by osmosis.
• decreasing water potential gradient.
• so less evaporation of water.