PLANT NUTRITION

PHOTOSYNTHESIS EQUATION

+ water = glucose + oxygencarbon dioxide

6CO2 + 6H2O C6H12O6 + 6O2

Photosynthesis

• Green plants (producers) can use light energy to make their own food

• This process is called photosynthesis

• Green plants are green because they contain a chemical called chlorophyll. This chemical is used to trap light energy.

• Chlorophyll is contained in the chloroplasts of plant cells

• Light energy is used to change carbon dioxide and water into starch and oxygen

• The word equation for photosynthesis is

carbon + water starch + oxygendioxide

Light energy

Function of leaves

• Trap light energy for photosynthesis

Producing sugar from photosynthesis

• Exchange of gases – oxygen and carbon dioxide

Leaves

Leaf structure

Greener on top

CO2 gets in here

THE LEAF!

• A leaf is an example of a plant organ

• It is composed of many tissues that work together.

• The tissues are designed to maximise the levels of photosynthesis.

The upper surfaceCuticle

Upper Epidermis

Palisade Mesophyll

Chloroplasts

Upper Surface• The leaf needs some protection from things

such as : storms, pollution, plant eaters,

• It has developed a tough, upper epidermal layer with a protective waxy cuticle on the out side

• This is the layer that is in direct contact with the sunlight which is needed for photosynthesis

• Therefore cells which contain lots of chloroplasts are found in the upper surface

The Middle Tissues

Spongy Mesophyll

Cuticle

Upper Epidermis

Palisade Mesophyll

Middle of a Leaf• There are more cells with large amounts of chloroplasts

in them

• The cells are shaped so that there can be as many of them as possible, like square blocks

• Then there is also some more odd shaped cells which are surrounded by large air spaces.

• The spongy mesophyll are basically like sponges - they soak up the water and the gases during photosynthesis and pass on the products to the cells next to them

• These are important as they have a large surface area to transport things.

Leaf diagram – palisade layer

CO2

Most chlorophyll

Leaf cell - palisade

Position?

Upper surface of leaf

Features?

Box shape

Chloroplasts

Function?Photosynthesis

STRUCTURE OF THE CHLOROPLAST1. The stripes are the

membranes called thylakoids , on which the chlorophyll molecules are kept.

2. In the fluid called stroma there are starch grains where the chloroplast stores the sugar.

3. Chloroplast can move around inside cells. On dull day they move to the end of the cell, to the top edge of leaf and on bright day they spread out.

Gas exchange

• Leaves are designed to allow carbon dioxide to get to the main chlorophyll layer at the top of the leaf

• They have small holes called stomata on the under surface

• Each hole is open & closed by 2 guard cells

Stoma is a small holeIts size is controlled by 2 guard cells

closed open

Stoma function is for gas exchange in the leaf

Carbon dioxide

oxygenGuard cell

Provided plant is photosynthesising

Starch Test a Leaf

Effect of Temperature

• Photosynthesis is a metabolic pathway that requires enzymes to catalyse each step in the process.

• Thus temperature affects the rate of the action of the enzymes and the rate of photosynthesis.

• Photosynthesis has an optimum temperature.

Effect of Carbon Dioxide

• At low concentrations of CO2, the rate of photosynthesis is reduced.

• As CO2 concentration increases so does the rate of photosynthesis up to a point.

• At high concentrations of C02 there is no further increase in the rate of photosynthesis.

Effect of Light Intensity

• At low light levels, the rate of photosynthesis is reduced.

• As the level of light increases so does the rate of photosynthesis up to a point.

• At high light levels there is no further increase in the rate of photosynthesis.

Limiting Factors

• For photosynthesis to occur the following criteria need to be fulfilled:– presence of chlorophyll

– presence of light

– presence of carbon dioxide

– presence of water

– suitable temperature

• The factor furthest away from its optimum value will limit the amount of photosynthesis.

• This is then the Limiting Factor.