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Problem Solving

p78 How many stomata?

p79 Water content and dry weight.

p85 Use of cobalt choride paper

Bioviewers Box 79

The leaf of a flowering plant

Slide 26

Outer layer- bottom surface

Outer layer- bottom surface

Leaf epidermis with stomata- scanning electron microscope

On the lower surface of the leaf there are tiny pores called stomata (singular- stoma) which open and close.

Stomata let CO2 diffuse in.

Water vapour and oxygen (O2) move out.

Slide 27

Stomata- open

Stomata- open

Stomata have guard cells surrounding them to control their opening & closing.

When there is plenty of water (daytime) the guard cells are turgid and curved.

This opens the stomata and water can escape.

Slide 28

Stomata- closed

Stomata- closed

When there is little water the guard cells are flaccid and less curved.

This closes the stomata and keeps water in the leaf. This happens at night.

Slide 29

General structure

General structure

Vast network of veins

supplies all parts of the plant with essential substances

Structural support

Flat leaf blade

Has large surface area

Absorbs as much sunlight & CO2 as possible


CO2, reaches inner cells easily


Most in lower surface of leaf

Gas & water exchange

Slide 30

Leaf veins

Leaf veins

Leaf veins (and roots and stems) contain the xylem and phloem tubes in vascular bundles.

They run throughout the plant, transporting various substances up and down them.

Slide 31

Transport systems used for?

Transport systems used for?

Plants need to allow:

Gases to get in and out of the leaves.

Water and nutrients to move into the plant from the soil.

Glucose made in photosynthesis to be carried to the rest of the plant.

Giant redwood trees carry water & nutrients over 100m from the soil

Slide 32



Roots have specialised cells called root hair cells, which are long and thin providing a large surface area for the uptake of water and minerals.

Slide 33

Into the root hair cell

Into the root hair cell


The water in the soil has a weak solution of salts

The cell sap has a more concentrated solution

Water moves from the soil into the root hair along a water concentration gradient

Water passes from the soil into root hairs by osmosis

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