slide-deck.pptx

• newEditor

Transport systems in plants: xylem and transpiration

Transport and exchange surfaces in plants

I can explain how water and mineral ions are transported through the xylem by transpiration.

pores in the leaf through which water, oxygen and carbon dioxide can diffuse

specialised vessels in plants that transport water and mineral ions

the continuous movement of water from the roots to the leaves through the xylem

substances that are essential for healthy
plant growth, including nitrates and magnesium

mineral ions

stomata

transpiration

xylem

transpiration stream

the loss of water from a plant’s leaves

Transpiration

Transport systems in plants: xylem and transpiration

Water flow through a plant

Structure and adaptations of xylem

Water and mineral ions, including nitrates, are essential for plants to grow and survive.

Water is used in cell cytoplasm and vacuoles to provide turgid strength to cells.

Water is a required reactant for photosynthesis, and mineral ions form part of proteins, chlorophyll and DNA.

water and mineral ions are essential for plants

Water flow through a plant

Water flow through a plant

Water and mineral ions are transported up through the plant through xylem vessels in the stem and leaves.

Water is continually lost from the plant via pores in the leaves called stomata.

Water and mineral ions enter the plant through root hair cells.

Water and dissolved mineral ions are transported up the plant.

Water flow through a plant

… which pulls water with minerals in it up through xylem in the stem …

We can see xylem vessels in celery stems if we break the stem and partly peel it away.

The tough fibres are xylem.

Water flow through a plant

xylem

celery

What do you think would happen to the tubes if we put celery stems in coloured water for an hour or so?

The xylem tubes would be stained.

Water flow through plants

A

xylem

B

stomata

C

root hair cell

D

phloem

1. Describe the roles of the following parts of the plant in moving water and mineral ions around the plant:

   1. root hair cells

   2. xylem

   3. stomata

2. Suggest what might happen if the rate of water lost from the leaves is greater than the rate of water being absorbed by the roots.

Water flow through a plant

1. Describe the roles of the following parts of the plant in moving water and mineral ions around the plant:

   1. root hair cells

b. xylem

c. stomata

Water flow through a plant

Root hair cells absorb water into the plant by osmosis.

Water moves up through the plant through xylem vessels.

Water is lost continuously through open stomata in the leaves. This pulls water up through the plant.

Enter your question here

1. Suggest what might happen if the rate of water lost from the leaves is greater than the rate of water being absorbed by the roots.

Water flow through a plant

You might have suggested:

• If water is lost from the leaves faster than it can be absorbed by the roots, then water may move by osmosis out of cells instead.

• This will cause cells to become flaccid, and the plant to wilt.

Water flow through a plant

Structure and adaptations of xylem

Transpiration

Transport systems in plants: xylem and transpiration

Xylem is found in the roots, stems and leaves of a plant.

xylem

root

stem

leaf

Structure and adaptations of xylem

Xylem vessels form specialised tubes through the plant.

They provide a constant connection from roots, through the stem to the leaves.

Structure and adaptations of xylem

xylem

xylem in a plant stem

This enables water to be transported to all parts of the plant quickly, like a garden hose.

Xylem is made of empty, dead cells, joined end-to-end.

Structure and adaptations of xylem

There are no end walls between each dead cell. This provides an unobstructed tube.

The walls are lined with a polymer called lignin. This makes them tough and keeps them round and open.

The walls are impermeable to water.

There is no cytoplasm.

BlueRingMedia/Shutterstock.com

Xylem can carry water to all parts of the plant because of:

Structure and adaptations of xylem

cross-section view of xylem

• the impermeable, lignified wall

• the lack of end plates between dead cells

Water is not lost or blocked on the way.

Which two features of xylem vessels allow water to move uninterrupted from roots to leaves?

Structure and adaptations of xylem

They have an impermeable, lignified cell wall.

They are only present in the stem and leaves.

They have no end walls.

They transport water and dissolved mineral ions.

1. On the diagram of xylem, label the key features that enable it to transport water up through the plant.

2. Xylem is not found in the growing tips of shoots, where new leaves, buds and stems are growing.
   Suggest why animals often prefer to eat shoots, rather than older leaves and parts of the stem.

Structure and adaptations of xylem

1. On the diagram of xylem, label the key features that enable it to transport water up through the plant.

Structure and adaptations of xylem

1. Xylem is not found in the growing tips of shoots, where new leaves, buds and stems are growing.
   Suggest why animals often prefer to eat shoots, rather than older leaves and parts of the stem.

Structure and adaptations of xylem

You may have suggested that:

• Xylem is fibrous because of the lignin in the walls, and lack of cytoplasm and other cell parts. This makes the tissue hard to chew through and digest.

• New shoots lack xylem, so are less fibrous, easier to eat and digest, more nutritionally beneficial, and often tastier, which is why animals often prefer to eat the younger parts of a plant.

Water flow through a plant

Structure and adaptations of xylem

Transpiration

Transport systems in plants: xylem and transpiration

Leaves have pores (holes) in their surface called stomata.

stomata in the underside of a leaf, observed using a microscope

stomata

Transpiration

guard cells

guard cells change shape to open and close the pore

Transpiration

Most leaves have a waxy cuticle that reduces evaporation, to reduce water loss.

Some water evaporates from cells at the surface of the leaf.

• Water evaporates from cells to become water vapour in the air spaces behind stomata.

• This water vapour diffuses out of open stomata.

Water is lost from leaves. This loss of water is called transpiration.

Most water is lost through open stomata.

waxy cuticle

one of the stomata

Transpiration

Transpiration ensures that
water and mineral ions reach all parts of the plant as required.

Transpiration

It allows water to climb vertically to the top of the tallest trees!

a tall palm tree:
but not the tallest tree in the world!

Transpiration

Whose description of transpiration is correct?

Sam

Alex

Jacob

Transpiration is the movement of water through the plant, caused by osmosis in the roots.

Transpiration is when water is lost from the leaves.

Transpiration is when the plant breathes out water and oxygen.

1. 
   
   
   
   Laura has described a part of transpiration, but left some of the detail out. Expand her description to provide a more complete definition of transpiration.

2. A plant disease called Verticillium wilt is caused by a fungal infection. The fungus infects the plant through the roots, then grows up through the xylem.
   Suggest what effect this might have on the plant.

Transpiration is about water loss.

Transpiration

1. 
   
   
   Laura has described a part of transpiration, but left some of the detail out. Expand her description to provide a more complete definition of transpiration.

Transpiration

Transpiration is about water loss.

• Transpiration is the loss of water from the leaves by evaporation and diffusion through open stomata.

• This creates a constant stream of water flowing up through the plant, called the transpiration stream.

• Water is then replaced by osmosis from the soil into the root hair cells.

1. A plant disease called Verticillium wilt is caused by a fungal infection. The fungus infects the plant through the roots, then grows up through the xylem.
   Suggest what effect this might have on the plant.

Transpiration

You might have suggested that:

• Verticillium wilt blocks the entry of water into the roots and the passage of water up through the xylem.

• This will prevent water from being pulled up the plant by the transpiration stream, causing the plant to wilt and eventually die.

Transport systems in plants: xylem and transpiration

• Water and mineral ions are transported from the roots, up the stem, to the leaves, through xylem vessels.

• Xylem is made of dead, empty cells with no cytoplasm or end plates, with tough cell walls made of lignin which are impervious to water.

• These adaptations keep the xylem vessels open and unblocked, and allow water to move without hindrance up the plant.

• Water is continually lost from the leaves of a plant by evaporation and diffusion through open stomata, in a process called transpiration.

• This pulls water up through the plant from the roots via the xylem, to create the transpiration stream.

© Oak National Academy 2024.

Produced in partnership with University of York Science Education Group.

Licensed on the Open Government Licence v3.0, except where otherwise stated. See Oak terms and conditions.