Biology Topic 2: Movement of Substances

  • Created by: Livy
  • Created on: 25-05-14 13:23


Diffusion is the movement of particles from an area of lower concentration to an area of higher concentration.

This is described as down a concentration gradient.

It is a passive process (does not require energy)

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Factors Affecting Diffusion

1. Concentration gradient (the difference in concentrations)

2. Surface Area:Volume Ratio

3. Adjust temperature 

Factors which Speed Up Diffusion:

Steep concentration gradient

Large surface area:volume ratio

High temperature 

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Osmosis: The Movement of Water

Osmosis is the diffusion of water molecules across a partially-permable membrane from a higher concentration to one with a lower water potential.

When we talk about the number of water molecules free to move we say 'water potential'

The higher the water potential=the more molecules that can move

Water particules are not free to move if they are interracting with a solute dissolbed in the soloution 

The more solute molecules you have dissolved, the fewer free water molecules and the lower the water potential 

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Effects of Osmosis on Plant Cells

Turgid = Cell has absorbed water and swelled. The cytoplasm is under pressure and is pushing against the cell wall

Flaccid = Cell has lost water and isn't swollen. The plant may droop

Plasmolysed = Cell has lost water and the cytoplasm has shrunk. The membrane is pulled away from the cell.

Normal = water uptake = water loss

It's important for plant cells to be turgid as it gives support to the non-woody plants and holds the stem upright. They are also important for opening and closing the stomata. 

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Biological Molecules

Lipids - Fats and Oils

Made of hydrogen, carbon and oxygen

Made of 1 fatty glycerol molecule and 3 fatty acids


Made of carbon, oxygen and hydrogen

Clucose molecules join together to form chains

They can form starch (plants), glycogen (fungi) and cellulose

Proteins - Amino Acid

Made of hydrogen, carbon, oxygen, nitrogen and sometimes sulpher

Made of subunits called amino acids, which join together to form chains (proteins)

There are 20 different types of Amino Acid

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Food Tests

Starch - iodine soloution (orange-black)

Glucose - Benedict soloution (blue-red)

Protein - Buiret soloution (blue-purple)

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Enzymes are proteins. They are biological catalysts, meaning they speed up the rate of reaction without being used themselves. They cause reactions to take place in cells (metabolic reactions)

Enzymes break down things and put them back together

They have an active site (where the reactions take place)

They also have an optimum pH 

They can be denatured by extremes of temperatures of pH

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