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2. Diffusion and osmosis

2.1 Diffusion

1 . Diffusion:

The movement of particles form an area of higher concentration to another area of lower concentration down a concentration gradient.

Fig. 2.1 Representation of diffusion

 

2.2 Osmosis

2 . Osmosis:

The movement of water molecules from an area of high concentration to an area of lower concentration through a semi-permeable membrane.

Fig. 2.2 (a)The sugar solution in the bag is more concentrated than the water outside the bag. (b)The water in the bag is more dilute than the sugar solution outside the bag. (c)The sugar solution in the bag is of the same concentration as that of the solution outside the bag.

 

2.3  Cells and Osmosis:

Fig. 2.3 The behaviour of cells in solutions of different concentrations.

 

2.4 Active Transport:

3 . Active Transport:

  • The movement of particle from an area of lower concentration to an area of higher concentration by using energy.

4 . Active transport is involved in a number of processes occurring within an organism. This includes the absorption of:

  • Dissolved mineral salts by the root hairs,
  • Glucose and amino acids by cells in the small intestine of humans

Fig. 2.4 Active transport-molecules diffuse against the concentration gradient from B to A.

 

Concentration gradient:

  • The difference in concentration between a region of a solution or gas that has a high density of particles and a region that has a relatively lower density of particles.

 

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