Page 71 - Biology Form Two

Biology for Secondary Schools

(ii) movement of oxygen gas from concentration between two areas, a
the blood capillaries to the tissue high rate of diffusion occurs.
fluid;
(iii) movement of oxygen gas from the Surface area to volume ratio: The
tissue fluid to the cell; larger the surface area to volume ratio,
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(iv) movement of carbon dioxide gas the larger the number of particles that
will be able to move in a given time,
from the cell to the tissue fluid; hence, the higher the diffusion rate.

(v) movement of carbon dioxide gas
from the tissue fluid to the blood Distance over which diffusion takes
capillaries; place: When the distance over which

(vi) movement of carbon dioxide gas the material is transported is long,
from the blood capillaries to the the rate of diffusion decreases. If the
alveoli; distance is short, diffusion occurs faster
(vii) movement of air from the because the materials do not have to
atmosphere to the leaves; travel far. For example, in a thin layer

(viii) movement of carbon dioxide gas of cells, the rate of diffusion increases.
from the intercellular space to the
palisade cells; Activity 3.1: Demonstrate diffusion in
liquids
(ix) movement of oxygen gas from the
palisade cells to the intercellular Materials

spaces of spongy mesophyll; Potassium permanganate or copper
(x) movement of oxygen gas from sulphate or laundry blue, beaker or test
the intercellular spaces to the tube, test tube rack, water, a pencil and
atmosphere; a notebook
(xi) movement of water vapour from Procedure
the leaves to the atmosphere; and 1. Half fill one beaker or test tube

(xii) movement of digested food with water. Leave it for some time,
substances from the ileum to the until the water settles completely.
blood circulatory system. 2. Put a crystal of potassium

Factors affecting the rate of diffusion permanganate into the water and
The rate of diffusion can be affected by observe what happens.
the following factors: 3. Describe the colour distribution

Concentration gradient: When in the beaker or test tube.
there is a great difference in molecule

Student’s Book - Form Two 65

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