Learning outcomes:
2.17
describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy
2.18
write the word equation and the balanced chemical symbol equation for photosynthesis
2.19
understand how varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis
2.20
describe the structure of the leaf and explain how it is adapted for photosynthesis
2.21
understand that plants require mineral ions for growth and that magnesium ions are needed for chlorophyll and nitrate ions are needed for amino acids
2.22
describe experiments to investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll
Nutrition in Flowering Plants:

Plants are photoautrophic (i.e. they generate their own “food” using energy from the Sun.) They do this through photosynthesis.

Carbon Dioxide + Water ---> Oxygen + Glucose

6CO2 + 6H2O ---> 6O2 + C6H12O6

Through photosynthesis light energy is converted into chemical energy in the bonds in glucose. Plants use glucose for the following;

- Respiration
- Stored as Starch
- Turned into Cellulose (cellulose is a polymer of glucose)
- Used to make fats and oils

At any point the rate of photosynthesis can be increased by adding more CO2, more water, more light or heating towards optimum temperature (photosynthesis is catalyzed by enzymes). However, at a certain point the addition of more e.g. light will not increase the rate of photosynthesis any further. This is because a second factor is limiting the rate of photosynthesis. Adding more of the rate limiting factor will increase the rate further until another factor becomes limiting.

photo LFs.GIF

You need to know the parts of the leaf and their adaptations.

leaf structure.GIF

In addition to water and CO2 plants also need specific minerals;

Nitrate – used to make amino acids for use in plant proteins
Magnesium – forms part of the chlorophyll molecule
Potassium - essential for cell membranes
Phosphate - essential part of DNA and cell membranes

You need to know an experiment that shows how the rate of p/s is affected by rate-limiting factors. The best example is using pond weed (Elodea) which produces bubbles of O2 as it photosynthesizes.
The rate of bubble production is approximately proportional to the rate of photosynthesis. Therefore, when you add light or give it more CO2, the rate of bubble production increases.

You also need to know an experiment that proves that light and CO2 are essential for the production of starch. A good example is the Geranium plant. It’s leaves normally turn blue-black in the presence of iodine solution showing starch is present (you have to boil it in ethanol first to remove the chlorophyll to show the colour).
However, if one leaf is put in aluminum foil and another is kept with lime water both do not turn blue-black, implying both CO2 and light are essential for starch production and, therefore, essential for p/s.

Leaf Structure and adaptation for photosynthesis

Cuticle - Stops the leaf from losing water (remember, water is used in photosynthesis)
Epidermis - Transparent protective layer. Protects the leaf without inhibiting photosynthesis.
Palisade cells - Are packed full of chloroplasts. Are long and thin so light has to pass through as many chloroplasts as possible.
Air Spaces - Increase the surface area inside the leaf to maximise gas exchange across the surface of the Spongy Mesophyll cells Stoma Allow exchange of CO2 and O2
Guard Cells - Allow the stoma to open and close to stop the leaf losing too much water
Vein (containing Xylem) - Brings a steady supply of water to the leaf.

scool.gif

CO2,