B8 Photosynthesis

• Endothermic reaction - energy is transferred from environment to the chloroplast by light
• Energy used to convert C02 and water to glucose and oxygen as a by-product 

                                      light

Carbon Dioxide + Water ---> Glucose + Oxygen

Extra energy required for photosynthesis to take place is transferred from the environment by light

Glucose produced is used immediately as well as converted into starch and stored

Leaf adaptations

• Broad leaves = big SA for light to fall on
• Thin leaves = short diffusion distances
• Chlorophyll in chloroplasts = to absorb light
• Air spaces = allow C02 to get to cells and oxygen to leave by diffusion

Light intensity

The brighter the light, the faster the rate of photosynthesis

Temperature

As the temperature rises, the rate of photosynthesis increases because the reaction speeds up. 

Photosynthesis controlled by enzymes. At temps too high, enzymes will denature and photosynthesis rate will fall

Carbon Dioxide concentration

Plants require C02 to make glucose. Increasing the C02 concentration, increases,photosynthesis rate. 

C02 concentration rises at night because plants respire then but do not photosynthesise

In a science lab, the concentration of C02 can be increased artificially so it's no longer the limiting factor. 

Chlorophyll levels in leaf

Less chlorophyll = less photosynthesis

If a plant does not have enough minerals e.g. magnesium it cannot make chlorophyll. The rate of photosynthesis would fall and the plant would die.

Light intensity and the inverse square law 

As the distance of light from the plant increases, the light intensity decreases

The light intensity increases or decreases in inverse proportion to the square of the distance. 

Light intensity ∝ 1/distance²

For respiration

• Glucose is broken down using oxygen to provide energy for the cells to carry out respiration. 
• Glucose + Oxygen ---> Carbon Dioxide + Water 
• Respiration is the opposite of photosynthesis

Cellulose and starch

• Plants build glucose into complex carbohydrates such as cellulose - to strengthen cell walls.
• Plants convert some glucose produced in photosynthesis as insoluble starch to be stored in the cells
• Starch = stored in leaves and kept as an energy store for low light levels
• Starch stored in tubers and bulbs for winter.

Nitrates, proteins and carnivorous plants 

Plants use glucose from photosynthesis to make amino acids. 

Sugars + nitrate ions + other mineral ions. 

Amino acids built into proteins such as enzymes. This uses energy from respiration.

Making lipids

Plants use some of the glusocse from photosynthesis and energy transferred from respiration to build up oils and fats 

As energy store or to strengthen cell walls

Summary of plant's glucose usage 

Plant and algal cells use the glucose produced in photosynthesis for:

- respiration

- to convert soluble glucose into insoluble starch for storage

- to convert glucose into cellulose for strengthening cell walls

- to produce amino acids for proteins using nirate ions and glucose 

- to produce fats or oils for storage 

Greenhouses

A greenhouse environment is much more controllable.

Atmosphere warmer inside than out = speeds up rate of photosynthesis so plants grow faster and give crops earlier. 

Hydroponics 

• Commercial greenhouses can control temperature, light levels, C02 concentration and minerals in the soil to get fastest possible rates of photosynthesis. 
• Enormous
• Controlled using computer sofware (very expensive)
• Fast turnover and high profits
• Crops can be grown where land is poor

Economics

The cost of providing the conditions that give the highest yields may be too expensive and may wipe out the profits.