B2 Organisms in the environment

carbon dioxide + water ---> glucose and oxygen

Chlorophyll in the chloroplasts absorb the Sun's energy.

The process:

• Carbon dioxide is taken in by the leaves and water is taken up by the roots
• The chlorophyll traps the light energy needed for photosynthesis
• This energy is used to convert the carbon dioxide and water into glucose
• Oxygen is released as a by-product
• Some of the glucose is converted into insoluble starch for storage

Leaves are well adapted to allow the maximum amount of photosynthesis to take place:

• they have a large surface area for light to fall on
• they contain chlorophyll to absorb light energy
• they have air spaces that allow carbon dioxide to get to the cells and oxygen to leave by diffusion
• they have veins to bring water to the cells of the leaves

The Iodine Test:

• By testing leaves with iodine solution we can identify the starch in the leaf and show that photosynthesis has occurred
• Variegated leaves have patches of green (with chlorophyll) and white (without) 
• Only green patches will turn the iodine solution blue-black to show that starch has been made

Anything which slows down the rate of photosynthesis is a Limiting Factor:

• Light produces the energy for photosynthesis
• If the temperature is too hot or cold, the enzymes will denature and the rate of photosynthesis will fall
• Carbon dioxide shortages can also slow down the rate of photosynthesis

Plants respire 24 hours a day to release energy.

Glucose is soluble in water, but starch is insoluble.

The glucose produced by photosynthesis may be:

• converted into insoluble starch for storage
• used for respiration
• converted into fats or oils for storage
• used to produce cellulose which strengthens cell walls
• used to produce proteins

Plants and algal cells need other materials including nitrate ions to produce the amino acids which make up proteins

Physical factors that may affect the distribution of living organisms include:

• temperature - arctic plants are small which limits the number of plant eaters which can survive in the vicinity
• availability of nutrients
• amount of light - essential for photosynthesis
• availability of water - needed for plants AND animals
• availability of oxygen - water animals can be affected by lack of oxygen dissolved in the water
• availability of carbon dioxide - affects plant growth

Plants supply food for animals, so fewer plants results in few animals.

The distribution of living organisms in their natural environment can be measured by:

• random quantitavive sampling using a quadrat
• sampling along a transect

A quadrat is a square frame made of metal or wood which may be subdivided into a grid.