9.2&9.3 Water Transport In Multicellular Plants&transpiration

Question 1

What takes up water into plants from the soil

Answer 1

Root hair cells

Question 2

How are root hair cells well adapted for exchange surfaces

Answer 2

Microscopic size
Large SA:V ratio
Think surface layer

Question 3

How do root hair cells maintain a water potential gradient

Answer 3

Soil had a high water potential whereas root hair cells contain many solvents so has a low water potential therefor osmosis continually takes place

Question 4

What are the two movements of water across roots

Answer 4

The symplast pathway

The apoplast pathway

Question 5

What is the symplast pathway

Answer 5

Water moves through the symplast which is the continuous cytoplasm of the living plant cells connected through the plasmodesmata

Question 6

How does water move through the symplast pathway

Answer 6

The root hair cell has a high water potential compared to the next cell along so water moves through each cell by osmosis until it reaches the xylem

Question 7

What is the apoplast pathway

Answer 7

Water moves through the apoplast - which are the cell walls and intercellular spaces

Question 8

How does water move through the apoplast

Answer 8

Water fills the intercellular spaces and as water moves into the xylem more water molecules are pulled through the apoplast due to waters cohesive properties
This pull abs cohesion creates a continuous flow of water through the open structure of the cellulose walls

Question 9

Where does water end up reaching after travelling through the apoplast and symplast pathways

Answer 9

The endodermis which is a layer of cells surrounding the xylem

Question 10

What is the casparain strip

Answer 10

A band of waxy material that runs around each endodermal cell forming a waterproof layer

Question 11

What happens when water reaches the casparian strip

Answer 11

It is forced into the cytoplasm of the cell and joins the water in the symplast pathway
It then passes through a selectively permeable membrane leaving any toxic solutes from soil behind

Question 12

Why is the rate of water moving from endodermal cells to xylem high

Answer 12

Xylem has a much lower water potential than endodermal cells

Question 13

What gives water a push up the xylem

Answer 13

Root pressure

The active pumping of minerals into the xylem to produce movement of water

Question 14

What is transpiration in plants

Answer 14

The movement of water out of plants via opened stomata - letting water vapour move out of plants with o2

Question 15

What is the transpiration stream

Answer 15

The movement of water up from the roots to the highest leaves

Question 16

What happens at the start of the transpiration stream

Answer 16

There is a transpiration pull which results in tension in the xylem and this helps water to move across roots from the soil

Question 17

What happens to water molecules at the start of the transpiration stream

Answer 17

Adhesion occurs
They form hydrogen bonds with the carbs in the walls of the narrow xylem vessels
They also form hydrogen bonds with eachother through cohesion
This results in water exhibiting capillary action

Question 18

What is capillary action in transpiration stream

Answer 18

When water rises up narrow tubes against the force of gravity

Question 19

What happens to water after it travels up the xylem in the transpiration stream

Answer 19

Move out of xylem into leaves by osmosis
The water molecules then evaporate from the surface of the mesophyll cells into the air spaces of the leaf and then move out the stomata

Question 20

What is the cohesion tension theory that

Answer 20

Water moves from soil in a continuous stream up xylem and across the leaf

Question 21

What do scientists use To measure transpiration

Answer 21

A potometer

Question 22

How do you measure the rate of water uptake in a transpiration stream

Answer 22

Distance moved by air bubble divided by time taken for air bubble to move that distance

Question 23

What factors affect transpiration

Answer 23

Light intensity 
Humidity 
Temperature 
Air movement 
Soil - water availability