OCR B4 the processes of life notes part 2

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  • Created by: Edd
  • Created on: 10-06-12 13:49

Photosynthesis captures energy for life on Earth. Many chemicals are made to allow life processes to occur in plants. These chemicals can move in and out of cells by the process of diffusion. Osmosis is a specific type of diffusion.


Photosynthesis is a process used by plants in which energy from sunlight is used to convert carbon dioxide and water into molecules needed for growth. These molecules include sugars, enzymes and chlorophyll.

Light energy is absorbed by the green chemical chlorophyll. This energy allows the production of glucose by the reaction between carbon dioxide and water. Oxygen is also produced as a waste product.

This reaction can be summarised in the word equation:

Carbon dioxide + water Reaction (light energy) (http://www.bbc.co.uk/schools/gcsebitesize/science/images/equation_light_energy.gif) glucose + oxygen

Photosynthesis - Higher tier.

The chemical equation for photosynthesis is:

6C O2 + 6H2O Reaction (light energy) (http://www.bbc.co.uk/schools/gcsebitesize/science/images/equation_light_energy.gif) C6H12O6 + 6O2

Glucose from photosynthesis.

Glucose is made up of carbon, hydrogen and oxygen atoms. Glucose made by the process of photosynthesis may be used in three ways:

  1. It can be converted into chemicals required for growth of plant cells such as cellulose.
  2. It can be converted into starch, a storage molecule, that can be converted back to glucose when the plant requires it.
  3. It can be broken down during the process of respiration, releasing energy stored in the glucose molecules.

Plants cells contain a number of structures that are involved in the process of photosynthesis:

Diagram of a plant cell (http://www.bbc.co.uk/schools/gcsebitesize/science/images/add_21c_bio_photosynth.jpg)

Diagram of a plant cell involved in production of glucose from photosynthesis

  • Chloroplasts - containing chlorophyll and enzymes needed for reactions in photosynthesis.

  • Nucleus - containing DNA carrying the genetic code for enzymes and other proteins used in photosynthesis.

  • Cell membrane - allowing gas and water to pass in and out of the cell while controlling the passage of other molecules.

  • Vacuole - containing cell sap to keep the cell turgid.

  • Cell wall - strengthens the cell.

  • Cytoplasm - enzymes and other proteins used in photosynthesis made here.


Dissolved substances have to pass through the cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen.

Diffusion occurs when particles spread. They move from a region where they are in high concentration to a region where they are in low concentration. Diffusion happens when the particles are free to move. This is true in gases and for particles dissolved in solutions. Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. This is how the smell of cooking travels around the house from the kitchen, for example.

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The movement of oxygen and carbon dioxide in and out of leaves during photosynthesis…


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