Transpiration

Transpiration

Plants are sometimes put into coloured water. The water moves up the xylem to the leaves and petals, giving them a brighter colour!

Do try this at home!

• You can easily try this at home with some cut flowers and food colouring- if you do, send a pic!

Multiple Choice

Which type of plant vessel transports water and minerals?

• Xylem

• Phloem

The Big Question!

How do tall trees get enough water?

How do tall trees get enough water?

• Redwoods are the tallest species of tree in the world. 

• The tallest redwood ever measured was 120 metres tall. That is six times the height of the Angel of the North! 

• How does a plant this size get water from its roots to the branches at the top?

What can you see in this image?

Transpiration

• Water is evaporating from the leaf and collecting in the bag.

• The evaporation of water from leaves is called TRANSPIRATION.

Multiple Choice

The evaporation of water from the leaves of plants is called...

• transpiration

• translocation

• transduction

Transpiration

• Leaves are coated with a waxy, waterproof cuticle, so how does water evaporate out?

Transpiration

• Water evaporates out of tiny holes in the leaf called STOMATA.

• The stomata also allow carbon dioxide in and oxygen out. 

Stomata

• Stomata are formed by guard cells. When the guard cells form the 'C' shape that you can see on the left, the stomata are open.

• When the guard cells lose that shape (as on the right), the stomata are closed.

How do stomata open and close?

• When the guard cells are full of water (turgid), they form the 'C' shape. This is because the inner wall is thickened and cannot stretch as much as the outer wall.

• When they lose water, they become flaccid and the stomata close.

Modelling stomata

• The opening and closing of stomata can be modelled using balloons.

• If a strip of sellotape is placed on one side of the balloon and then the balloon is inflated, the side with the tape cannot stretch.

• This causes the balloon to bend - if you have a long balloon and some tape, you can try this yourself!

Multiple Choice

What are the tiny holes in a leaf called?

• Guard cells

• Stomata

Multiple Choice

What are the cells that surround the stomata called?

• Palisade cells

• Root hair cells

• Guard cells

Multiple Choice

When the guard cells are in a 'C' shape, the stomata are...

• open

• closed

Multiple Choice

When the guard cells are flaccid, the stomata are...

• open

• closed

Multiple Choice

When the guard cells are turgid, the stomata are...

• open

• closed

Multiple Choice

Which way does water move through the stomata?

• Out

• In

• Out and in

What do stomata and transpiration have to do with moving water (and minerals) up a tree?

The transpiration stream!

Transpiration and water movement

• The loss of water from the leaves, pulls more water and minerals up from the roots.

• This is because water molecules are held together by hydrogen bonds so a long chain is formed.

• This is called the TRANSPIRATION STREAM.

Multiple Choice

What is the name of the bond that holds water molecules together?

• Hydrogen

• Ionic

• Covalent

Multiple Choice

As water evaporates from the leaves, it pulls water ____ the stem.

• up

• down

So as water evaporates from the leaves, it pulls up more water from the roots.

...but that's not the only thing that helps water to move.

How does a straw work?

How does a straw work?

• When you suck on a straw, you remove air particles, reducing the pressure.

• The pressure at the base of the straw is now higher, causing the liquid to move up the straw. 

• Water moves from an area of HIGH PRESSURE to an area of LOW PRESSURE - what does this remind you of?

Xylem vessels

• Think of the xylem vessels as being like a bundle of straws.

• As water evaporates from the top, the water pressure falls.

• As water enters at the bottom from the roots, the pressure increases.

• Water moves from a HIGH to LOW pressure so in this case, UP THE STEM!

To summarise

• Water can move 120 metres up a tree using a combination of:

• –the transpiration stream (as water particles evaporate from the leaves, more water particles are pulled up in a long continuous chain).

• –…and a pressure gradient (the evaporation of water from the top of the tree creates a low pressure; the movement of water in from the root creates a high pressure, so water moves up).

Multiple Choice

As water evaporates from the leaves, it creates a ____ pressure at the top of the xylem.

• high

• low

Multiple Choice

As water moves in from the roots, it creates a ____ pressure at the base of the xylem.

• high

• low

Multiple Choice

Water moves from an area of...

• high pressure to an area of low pressure

• low pressure to an area of high pressure

Multiple Choice

Which way does water move?

• Up the xylem vessels

• Down the xylem vessels

• Up and down the xylem vessels