Transport in Plants

Question 1

Define transpiration.

Answer 1

The loss of water due to evaporation from a plant through the stomata.

Question 2

Is transpiration an active or passive process?

Answer 2

Passive.

Question 3

How does humidity affect the rate of transpiration?

Answer 3

Higher humidity increases the water potential outside the plant, flattening the water potential gradient, so less transpiration takes place.

Question 4

How does temperature impact the rate of transpiration?

Answer 4

Higher temperatures give more energy to water vapour on the outside of the plant, so it will move away, steepening the water potential gradient and increasing rate of transpiration.

Question 5

How does light intensity impact the rate of transpiration?

Answer 5

The higher the light intensity, the more photosynthesis will occur in the plant, meaning more CO2 is needed, so the stomata open to let in, simultaneously allowing water to be lost by transpiration.

Question 6

How does air movement impact the rate of transpiration?

Answer 6

The more the air moves, the more water vapour will be moved away from the plant, decreasing the water potential outside the plant and steepening the gradient, so rate of transpiration will increase.

Question 7

Describe the structure of xylem vessels.

Answer 7

.Made of dead tissue,
.Walls are lignified, to strengthen them,
.Cells are hollow with no cytoplasm,
.Have pits- areas without lignin where water can move out into cells.

Question 8

What is the function of the xylem?

Answer 8

To transport water and dissolved ions upwards.

Question 9

Define vascular bundle.

Answer 9

Section in the middle of a plant root which contains the phloem and xylem.

Question 10

How do water and ions move into a plant root?

Answer 10

Inside root hair cells are many ions, which means the water potential is lower than on the outside, so water moves into the roots through osmosis, carrying dissolved ions with it.

Question 11

Define cohesion tension theory.

Answer 11

Water molecules are bonded by hydrogen bonds, so water moves as one continuous, unbroken column through the xylem. This is know as the transpiration pull/stream.

Question 12

What part of the plant is the main site of gas exchange?

Answer 12

Spongy mesophyll.

Question 13

What part of the plant is the main site of photosynthesis?

Answer 13

Palisade mesophyll.

Question 14

Describe how water moves from the xylem to the palisade mesophyll.

Answer 14

.Higher WP in xylem than palisade cells,
.Water diffuses down WP gradient into cytoplasm or cell walls of other cells through plasmodesmata,
.Eventually reaches palisade cells.

Question 15

Define translocation.

Answer 15

The process by which organic molecules and some mineral ions are transported between sources and sinks of a plant.

Question 16

Define source of a plant.

Answer 16

The location in a plant where a resource us taken up, eg. leaves for glucose and roots for water.

Question 17

Define sink of a plant.

Answer 17

The location where a resource is used up, eg. roots/flowers/seeds for glucose.

Question 18

Describe a feature of companion cells.

Answer 18

They are high in mitochondria, which produce the necessary ATP to pump hydrogen ions out to create the hydrogen ion gradient.

Question 19

Define mass flow.

Answer 19

Movement of a bulk of substances through a channel in a given time.

Question 20

Why does mass flow happen in translocation?

Answer 20

There is high hydrostatic pressure at the source, and low hydrostatic pressure at the sink, so mass flow occurs down the pressure gradient.

Question 21

How do aphids demonstrate evidence for translocation?

Answer 21

They feed off plants by putting their stylet into the stem. Higher volume of sucrose comes out lower on the stem, closer to the source, which is what is expected with translocation.