Leaf structure and photosynthesis yr10
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Transcript of Leaf structure and photosynthesis yr10
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.