BIOLOGY FORM 5
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SUBTOPICS
• The Importance of Having a Transport System in
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Some Multicellular Organisms
The Circulatory System
The Mechanism of Blood Clotting
The Lymphatic System
The Role of the Circulatory System in the Body’s
Defence Mechanism
Appreciating a Healthy Cardiovascular System
The Transport of Substances in Plants
The Transport of Organic Substances & Water in
Plants
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1.1 - The Importance of Having
a Transport System in Some
Multicellular Organisms
• LEARNING OUTCOMES :
• To identify the problem that could be
faced by multicellular organisms in
obtaining their cellular requirements
& getting rid of their waste products
• To suggest how the problem is
overcome in multicellular organisms
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1.1 - The Importance of Having a
Transport System in Some Multicellular
Organisms
• All living organisms need
to constantly exchange
substances between cells
& their external
environment (food, waste
& gases).
• All this process is
performed by a transport
system.
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• Small organisms have a large total surface area
to volume (TSA/V) ratio. So, diffusion of
substances occurs rapidly (short distance only).
• Some simple organisms such as flatworms have thin
flatten bodies  provide a large surface area
• In Hydra, water enters through the mouth into the
body cavity. As the body wall is only two cell layers
thick, substances can move rapidly into or out of
the body cells.
• Do not require a specialised internal transport
system
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• Larger organisms, increased need for
more nutrients & oxygen to be supplied to
the larger number of cells. Need to
excrete more waste products.
• The size increases, TSA/V ratio
decreases.
• Many of the body cells are too far away
from the external surface or between
different parts of the body.
• Simple diffusion occurs at too slow a rate
to sustain cellular activities.
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• Larger multicellular organisms have
adapted by developing specialised
structures to increase the surface area for
exchange of substances.
• Have developed an internal transport
system of vessels or tubes.
• In human & more complex animals, there
is development of a blood circulation
system to carry the substances.
• In plants, transport of substances is
carried out by the vascular system (xylem
& phloem).
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END
OF
SUBTOPIC 1.1
OPPS…DON’T FORGET TO COPY
EXERCISE ON THE NEXT PAGE!!
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EXERCISE 1.1
1. State two problems faced by multicellular
organisms in obtaining their cellular
requirements & removing waste product.
2. State how these problems are overcome
in multicellular organisms.
3. Explain why unicellular organisms do not
face the problems listed in (Q1).
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Iyah..iyah.
.Iyah….
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