Photosynthesis and Organisms in their environment

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* Green plants and algae use light energy to make their own food. They obtain the raw materials they need to make food from air and the soil

* The conditions the plant is grown in can be changed to promote growth.

 Carbon dioxide +  Water --> Oxygen + Glucose 

During photosynthesis: 

  • The chlorophyll which is found in the chloroplasts absorb light energy, this energy is used by converting carbon dioxide and water into glucose. Oxygen is produced as a by-product.
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How plants use glucose

  • Some of the glucose produced during photosynthesis is used immediately, and may also be converted into insoluble starch for storage. Starch is insoluble in water- so it can be stored in large amounts without affecting the water balance of the plant.
  • Plants use it for respiration to provide energy for cell functions such as growth and reproduction.
  • Some of the glucose in plants may be used to produce fat or oil for storage, in the production of cellulose which strengthens the cell wall or to produce proteins.
  • To produce amino acids, by combining sugars with mineral ions and nitrate ions that are absorbed from the soil. These amino acids are then built up to become proteins to be used in the cells.
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The rate of photosynthesis

The rate of photosynthesis may be limited by:

-Shortage of light

-Low temperature

-Shortage of carbon dioxide

All these factors can be manipulated artificially to increase the rate of photosynthesis in food crops.

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Limiting factors

LIGHT, TEMPERATURE AND AVAILABILITY OF CARBON DIOXIDE- may all be a factor that limits photosynthesis.


-The more a plant photosynthesises, the more biomass it makes, and the faster it grows. Fast and big products = profit.

*Farmers may use 'Polytunnels'- used for growing crops ranging from tomatoes to strawberries. Within the glass structure, the environment is more controllable than the outside. Light intensity, temperature and carbon dioxide levels are all varied to get the fastest possible rate of photosynthesis.   

*Plants can even be grown in water with a perfect balance of mineral ions instead of soil- This technique is called HYDROPONICS.

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Organisms in their environment

Living organisms form communities, with the different animals and plants depending on each other. E.g. in the Arctic, plants are very small, this affects the numbers of herbivores that can survive in that area.

Factors affecting living organisms are:

  • Temperature
  • Nutrients
  • Amount of light
  • Availability of water
  • Availability of oxygen and carbon dioxide
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Measuring the Distribution of organisms

Measuring the Distribution of organisms:

-QuadratsSquare frame made of wood/metal that you lay on the ground, outlining your sample area. Quadrats are used to investigate the size of a population of plants/ very slow moving animales like snails, sea anemones. Sample size must be kept the same every time covering as many areas as possible, to make sure the results are as valid as possible. SAMPLE AREAS MUST BE CHOSEN AT RANDOM. (to ensure the results reflect the true distribution of organisms)

Quantitative sampling: take a number of random readings and find mean.- used to compare distribution of same organisms in different habitats or variety of organisms in a number of different habitats. Also used to measure changes in the distribution of organisms over time. To do this repeat measures at regular time intervals. 

MEAN: Add all the readings and divide by no. of readings. - RANGE: minimum - maximum

MEDIAN: middle value of the range. - MODE: most occuring value

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Measuring the Distribution of organisms

-Sampling along a transect:

A line transect: NOT randomA tape is stretched between two points. You sample the organisms along that line at regular time interbals using a quadrat. THIS SHOWS US HOW THE DISTRIBUTION OF ORGANISMS CHANGES ALONG THAT LINE/ light levels and soil pH that might affect the growth of plants along that transect.

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