TRANSPIRATION

Question 1

how does the structure of the xylem relate to its function? (3)

Answer 1

-long continuous columns made of dead tissue allowing transpiration of water.
-contains pits allowing water to move sideways between vessels.
-thickened with lignin, providing structural support.

Question 2

what is meant by the apoplastic pathway? (1)

Answer 2

a method of osmosis through the root hair cells, where water moves through the cell walls and intracellular spaces. This pathway can only be used until water reaches the Casparian strip.

Question 3

What is meant by the symapthic pathway? (1)

Answer 3

a method of osmosis through the root hair cells, where water moves through the cytoplasm. To begin this pathway, water must be actively transported into cells.

Question 4

What is the cohesion-tension theory? (3)

Answer 4

water molecules form hydrogen bonds with each other, causing them to ‘stick’ together (cohesion). The surface tension of the water also creates this ‘sticking’ effect. Therefore as water is lost through transpiration, more can be drawn up the stem from the roots.

Question 5

How does root pressure effect water movement? (2)

Answer 5

high mineral content gives the root low water potential, meaning that there is a strong osmotic flow into the roots. This creates a weak push effect, moving water from the roots into the stem.

Question 6

How does temperature effect rate of transpiration? (2)

Answer 6

A higher temperature increases random motion and rate of evaporation, therefore increasing the rate of transpiration.

Question 7

How does light intensity effect rate of transpiration? (2)

Answer 7

A higher light intensity increases the rate of photosynthesis, causing more stomata to open for gas exchange, therefore increasing rate of transpiration.

Question 8

How does humidity effect the rate of transpiration? (2)

Answer 8

High humidity means that the water content of the air next to the leaf is high. This reduces the concentration gradient, therefore decreasing rate of transpiration.

Question 9

How does air movement effect the rate of transpiration? (2)

Answer 9

Large amounts of air movement blow moist air away from leaves, creating a steep concentration gradient. Therefore increasing the rate of transpiration.