Biology

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Diffusion

Diffusion

DIFFUSION is the spreading out of particles in a gas, or of the particles of a substance in a solution. 

(http://www.desadoc.com/wordpress/wp-content/uploads/2014/10/diffusion-pic.gif)

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Different kinds of cells

Different kinds of cells

Bacterial cells have a simpler structure than plant and animal cells

(http://www.bbc.co.uk/staticarchive/0b398673bbf5ca2a2788756bc9d8c76da87b8678.jpg)

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Organisation of the body

Organisation of the body

Large multicellular organisms, such as humans, have bodies that are organised into different ORGAN SYSTEMS.

(http://www.teachpe.com/images/digestive_system.jpg)

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Organs and organ systems

Organs and organ systems

Organs

ORGANS are made of tissues. An organ, such as the stomach, may contain several different kinds of tissue. The tissues in an organ work together to carry out the particular function of the organ.

(http://adapaonline.org/images/biobook_images/stomach_tissues.gif)

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Plant organs

Plant organs

In the same way that humans have organs, plants have organs too.

Some plant organs are shown in the diagram.

(http://www.clipartbest.com/cliparts/KTn/ekK/KTnekK5Ac.gif)

Each plant organ is made up of several different plant tissues. The tissues work together so that the organ can carry out its function well.

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Photosynthesis

Photosynthesis

PHOTOSYNTHESIS is the process that plants use to make their own food.

This equation summarises what happens in photosynthesis. Each stage of the process is controlled by enzymes.

(http://www3.syngenta.com/country/uk/SiteCollectionImages/LearningZone/KS345_new/Chemistry/ISE/photo1.png)

EXAM ALERT

Remember that during photosynthesis there is an energy transfer from light energy to chemical energy stored in the sugars produced.

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Limiting factors

Limiting factors

Light intensity, carbon dioxide availability and temperature affect the RATE OF PHOTOSYNTHESIS. Any one of these may be the LIMITING FACTOR at any time:

  • a shortage of light (low light intensity)
  • low temperature
  • a shortage of carbon dioxide

Practical note: You can measure the effect of different factors on the rate of photosynthesis by measuring the rate at which oxygen is produced by plant or algal cells. Remember that oxygen is a by-product of photosynthesis.

Limiting factors in greenhouses

Some crops, such as tomatoes, can be grown in greenhouses. This can help the grower earn more money than growing the crops outside.

Enironment in greenhouse changed by:

  • keeping lights on when outside it is dull or dark
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