B2 Organisms in the environment

  • Created by: Phoebe
  • Created on: 29-12-12 09:20

2.1 Photosynthesis

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
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2.1 Leaves and the Iodine Test

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
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2.2 Limiting Factors

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
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2.3 How Plants use Glucose

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

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2.5 Organisms in their environment

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.

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2.6 Measuring the distribution of organisms

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.

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