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  • Created by: Hope
  • Created on: 17-04-14 14:37


Green plants absorb light energy using chlorophyll in their leaves. They use it to react carbon dioxide with water to make a sugar called glucose. They do it to make their own food and obtain the materials they need from the air and soil. The glucose is used in respiration, or converted into starch and stored. Oxygen is produced as a by-product.

Temperature, carbon dioxide, concentration and light intensity are factors that can limit the rate of photosynthsis.


During Photosynthsis.....

  • Light energy is absorbed by a green substance called cholorophyll which is found in choloroplasts in some plant cells and algae
  • This energy is used by converting carbon dioxide (from the air) and water (from the soil) into sugar 
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Factors limiting Photosynthesis

LIGHT - Without light a plant cant photosynthesis very quickly. Increasing the light intensity with speed up photosynthesis 

CARBON DIOXIDE CONCENTRATION - Even if there is a sufficent amount of light a plant cannot photosynthesise with an unsufficient amount of carbon dioxide 

TEMPERATURE - If it gets cold the rate of photosynthesis will decrease. Plants can't respire if it gets too hot 

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Storage and Use of Glucose

Storage- Glucose is needed by cells for respiration but it cant be made at night because there is no light so plants and algae store glucose as insoluable products e.g. Starch, fats and oils 

Uses - 

  • Produce fat or oil for storage 
  • To produce cellulose which stenghtens the cell wall
  • To produce protiens such as enzymes and chlorophyll 
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Organisms and their Environment

Living organisms form communities and we need to understand the relationships within and bewteen these communities. There relationships are affected by external influence.

Physical factors that may affect organisms are:

  • Temperature 
  • Amount of light
  • Avaliability of water
  • Avaliability of nutrients
  • Avaliability of carbon dioxide and oxygen


  • Environment - All the conditions that surround a living organism 
  • Habitat - A place where an organism lives 
  • Population - All the members of a single species that live in a habitat
  • Community - All the populations of different organisms that live together in a habitat 
  • Ecosystem - A community and the habitat in which it lives 
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Collecting Quantitative Data

Transects -

A transect is a line across a habitat or part of a habitat. It can be as simple as a string or rope placed in a line on the ground. The number of organisms of each species can be observed and recorded at regular intervals along the transect.


  • A quadrat is usually a square made of wire. It may contain further wires to mark off smaller areas inside, such as 5 x 5 or 10 x 10 squares. The organisms underneath, usually plants, can be identified and counted
  • It should be placed randomly so that a representative sample is taken
  • The validity and reproducibility of the results increases as the results from more quadrats are analysed

Always use mean median and mode to analyse the results from the transects or quadrets 


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