Transpiration

What are xylem vessels?

Long tubes made of dead tissue that transport water and minerals

Why are xylem vessels made of dead tissue?

To form a continuous column for water movement

What structures allow sideways movement of water in xylem?

Pits

What substance strengthens xylem vessels?

Lignin

Why is lignin deposited in spiral patterns?

To provide strength while allowing flexibility

What is transpiration?

The loss of water vapour from leaves through stomata

Where does water enter a plant?

Through the roots

Where does water leave a plant?

Through stomata in the leaves as water vapour

What gases move through stomata?

Carbon dioxide enters, oxygen and water vapour exit

What is the transpiration stream?

The movement of water up the stem through xylem

Why is the transpiration stream important?

It supplies water for photosynthesis, growth and elongation

How does transpiration help with temperature control?

Evaporation of water cools the plant

How does transpiration supply minerals?

Minerals are dissolved in water moving up the xylem

What type of transport moves water from xylem to mesophyll cells?

Osmosis

What happens to water at the mesophyll cell surfaces?

It evaporates into intercellular air spaces

How does water vapour leave the leaf?

By diffusion down a water vapour potential gradient through stomata

What is a potometer used to measure?

The rate of transpiration

How does a potometer work?

Water lost by transpiration is replaced by water in a capillary tube

What is measured in a potometer experiment?

Movement of a meniscus or air bubble

Why does a potometer measure transpiration indirectly?

Because it measures water uptake not water loss

How does number of leaves affect transpiration?

More leaves increase the rate of transpiration

How do stomata number and size affect transpiration?

More or larger stomata increase transpiration

How does a waxy cuticle affect transpiration?

It reduces water loss

How does light intensity affect transpiration?

Increased light increases transpiration

How does temperature affect transpiration?

Higher temperature increases transpiration

How does humidity affect transpiration?

Higher humidity decreases transpiration

How does air movement affect transpiration?

Increased air movement increases transpiration

How does water availability affect transpiration?

Low water availability reduces transpiration

What are xerophytes?

Plants adapted to live in dry conditions

Why do xerophytes have small leaves?

To reduce surface area for water loss

How does a thick waxy cuticle help xerophytes?

It reduces evaporation

How does densely packed mesophyll reduce water loss?

It reduces air spaces for evaporation

How do xerophytes respond to low water availability?

They close their stomata

What is the function of hairs and pits in xerophytes?

They trap moist air and reduce the water vapour potential gradient

Why do some xerophytes roll their leaves?

To trap moist air and reduce exposure of stomata