Mass Transport in Plants

Question 1

What is transpiration?

Answer 1

The evaporation of water from the leaves through the stomata

Question 2

What is cohesion?

Answer 2

Water molecules sticking together because they are polar

Question 3

What is the role of the xylem?

Answer 3

To transport water and minerals upwards

Question 4

What is the xylem?

Answer 4

Hollow tubes made up of dead cells with no cell walls

Question 5

What is the cohesion-tension theory?

Answer 5

Transpiration of water through the stomata creates low pressure at the top of the xylem so water is pulled up the xylem creating tension, water can be sucked up the tube because they stick together due to cohesion

Question 6

What are the four factors affecting the rate of transpiration?

Answer 6

1) Temperature2) Light3) Humidity4) Wind

Question 7

How does temperature affect the rate of transpiration?

Answer 7

Higher temperatures mean more kinetic energy which will lead to faster evaporation and a faster rate of transpiration

Question 8

How does light affect the rate of transpiration?

Answer 8

More stomata are open at a greater light intensity therefore the rate of evaporation will increase

Question 9

How does humidity and wind affect the rate of transpiration?

Answer 9

They affect the water vapour gradient, a steeper gradient (dry/windy) will lead to a greater rate of transpiration

Question 10

What is the role of the phloem?

Answer 10

It transports glucose and amino acids both up and down and it is made up of living cells

Question 11

What cells make up phloem?

Answer 11

Sieve tube cells and companion cells

Question 12

What are sieve tube cells?

Answer 12

Living cells with little cytoplasm and organelles that are hollow

Question 13

What are companion cells?

Answer 13

Cells with many organelles that support sieve tube cells with ATP as sieve tube cells have no mitochondria

Question 14

What are sieve plates?

Answer 14

thin pores between sieve tube cells

Question 15

In what ways can we provide evidence for mass flow/translocation?

Answer 15

By radioactive labeling and ringing experiments

Question 16

How can we carry out radioactive labeling?

Answer 16

By growing plants in radioactive carbon-14 and measuring the carbon-14 as it moves down the trunk/stem

Question 17

How can we carry out ringing experiments?

Answer 17

Remove bark in a ring from a tree trunk (will contain phloem not xylem) to prevent movement of solutes. A bulge will form above the ring and that fluid will contain more solutes than fluid below the ring providing evidence that solutes move down. However, theory isn’t perfect or fully understood

Question 18

What happens at the source?

Answer 18

There is a high concentration of solute and the solute is actively transported into the source from companion cells. This decreases water potential and water moves into the phloem by osmosis from xylem and companion cells. A high hydrostatic pressure is created.

Question 19

What happens at the sink?

Answer 19

Sink has a low concentration of solute because it uses it/breaks it down or coverts it into something else which increases water potential and water moves back out of phloem by osmosis decreasing the pressure in the phloem

Question 20

What do guard cells help in?

Answer 20

Transpiration because they open and close the stomata

Question 21

What happens to the rate of translocation at a high atmospheric pressure?

Answer 21

Increase because wind moves from high atmospheric pressure to low atmospheric pressure (gas moves from high to low)

Question 22

Why can steroid hormones easily pass through the plasma membrane by simple diffusion?

Answer 22

They are lipid soluble

Question 23

What does transport of food material in higher plants take place through?

Answer 23

Sieve elements

Question 24

The water column in the xylem does not usually break / fracture during transpiration because of…

Answer 24

Cohesion and adhesion

Question 25

Transpiration is regulated by the movements of…

Answer 25

Guard cells of the stomata

Question 26

Passive absorption of water by the root system is the result of…

Answer 26

Tension in the cell sap due to transpiration

Question 27

In which plants, there will be no transpiration?

Answer 27

Aquatic, submerged plants