Transpiration

Question 1

What is the function of the xylem?

Answer 1

Transports water and dissolved minerals from the roots
Up through the plant and eventually out through the leaf stomata
(One-way transport)

Question 2

What is the function of the phloem?

Answer 2

Transports dissolved products of photosynthesis in various directions around the plant

Question 3

What is the xylem made up of?

Answer 3

Dead, hollow xylem cells that are stacked on top of each other
End cell walls broken to form continuous tube

Question 4

Why does the xylem have a lack of organelles?

Answer 4

So no restriction to flow

Question 5

What are the walls of the xylem impregnated with?

Answer 5

Lignin

Question 6

What is the function of lignin in xylem cells?

Answer 6

Waterproofs the xylem to stop sideways movement of water

Gives strength to stop the xylem tubes collapsing due to adhesion

Question 7

Other than lignin, what else do xylem walls have?

Answer 7

Pores

Which allow lateral (sideways movement where needed i.e. when a leaf is reached)

Question 8

What does cohesion mean in terms of water?

Answer 8

Water is sticky
Molecules stick to one another with hydrogen bonds
Form continuous column

Question 9

What does adhesion mean in terms of water?

Answer 9

Can also stick to walls of the xylem

Question 10

Describe the cohesion tension theory

Answer 10

• water evaporates from the leaf - transpiration
• pulls columns of water upwards puts xylem under tension - transportation pull
• water adheres to walls of xylem as it is pulled upwards - walls drawn inwards - diameter decreases
• negative pressure in the xylem (tension)
• water is pulled up in a continuous column as it is cohesive

Question 11

What is transpiration?

Answer 11

A passive process

The only energy involved is heat from the sun

Question 12

Describe the process of transpiration

Answer 12

1) energy from the sun
2) so water diffuses into root hair cells from soil by osmosis
3) which decreases the water potential in leaf cells
4) so water is sucked up xylem by mass flow (cohesion tension)
5) so water diffuses through the root cells to the xylem
6) so water diffuses out of the xylem to the leaves
7) cause water to evaporate from spongy cells and diffuse out of the leaves
8) which decreases the water potential in the root xylem
9) which decreases the water potential in the root epidermis cells
10) which decreases the pressure in the xylem

Question 13

What are the factors which affect transpiration?

Answer 13

Light
Temperature
Air movement
Humidity

Question 14

How does light affect the transpiration rate?

Answer 14

The lighter it is the faster the transpiration rate

Stomata open when it gets light to let in CO2 for photosynthesis

Question 15

How does temperature affect the transpiration rate?

Answer 15

The higher the temperature the faster the transpiration rate

Warmer water molecules have more energy so they evaporate from the cells inside the leaf faster
Increases concentration gradient
Faster transpiration rate

Question 16

How does humidity affect the transpiration rate?

Answer 16

The lower the humidity the faster the transpiration rate

If the air around the plant is dry, the concentration gradient between the leaf and the air is increased
Which increases transpiration

Question 17

How does wind affect the transpiration rate?

Answer 17

The windier it is, the faster the transpiration rate

Lots of air movement blows away water molecules from around the stomata
This increases the concentration gradient
Which increases the rate of transpiration