The document summarizes the circulatory system and transport of substances in humans and other organisms. It explains that diffusion is how unicellular organisms exchange substances, while multicellular organisms and larger animals have developed circulatory systems using blood and blood vessels to transport nutrients, gases, wastes, and other materials throughout their bodies. The human circulatory system consists of the heart, blood composed of plasma and cellular components like red blood cells, and a network of arteries, veins, and capillaries to deliver oxygen and pick up carbon dioxide from tissues via blood flow.

2.  The exchange of substances between the organism
and the environment usually takes place through
diffusion.
 The exchange of substances occurs rapidly if:
a) surface area in contact with environment
is large.
b) volume of organism is small.
c) total surface area/volume ratio (TSA/V) of the
organism is large.
d) distance between source of substances and
body cells is near.
e) high concentration gradient is maintained between
source and body cells.

3.  Unicellular organisms may obtain their
nutrients and oxygen by diffusion alone but
multicellular organisms are more complex
and bigger in size.
 Organisms that are small in size have a large
total surface area to volume (TSA/V) ratio.
 Large organisms have a small TSA/V ratio.
Hence, the rate of diffusion is higher in small
size organisms than the large ones.
 The transport system in humans and animals
are called the circulatory system.

4.  The circulatory system:
a) delivers nutrients and oxygen to cells.
b) carries waste products away from cells.
c) protects the body from infections.
 The circulatory system in humans and
animals consists of blood, blood vessels and
heart.
 Blood is the type of connective tissue made
up of plasma, blood cells and platelets.
 Heart function as a muscular pump that
circulates blood throughout body.
 Blood vessels are vessels consisting arteries,
capillaries and veins.

5.  Blood is the medium of transport in humans and
animals.
 Haemolymph is a blood-like nutritive fluid which
fills entire body cavity (haemocoel) and
surrounds all cells.
 Blood has three general functions which is
transport, regulate and protect.
 Blood transports:
a) oxygen from lungs to cells of whole body
and carbon dioxide from cells to lungs.
b) nutrients, hormones and antibodies
throughout the body.
c) waste products away from cells to organs of
excretory system.

6.  Blood regulates pH of body fluids, body
temperature and water content of cells.
 Blood protects us:
a) from excessive blood loss in an injury
through the mechanism of blood clotting.
b) from diseases and helps to fight against
infections.
 Haemolymph transports water, inorganic salts
and organic compounds throughout the
haemocoel.
 In insects, respiratory gases are transported
via tracheal system.

7.  Human blood is made up of 55% plasma and
45% cellular components such as
erythrocytes, leucocytes and platelets.
 Blood plasma is the main transport medium.

8.  Cellular components of blood consist of red
blood cells (erythrocytes), white blood cells
(leucocytes) and platelets.

9.  Erythrocytes (red blood cells):
a) shaped like a biconcave disc (thinner in
the centre than at the edge).
b) does not have nucleus.
c) is small
d) has elastic membrane which enables it to
squeeze easily into tiny blood capillaries.
e) lifespan is about 120 days.
 A single erythrocyte contains about 250 million
molecules of haemoglobin.
 Haemoglobin:
a) is an oxygen-carrying protein pigment that
gives erythrocyte its red colour.
b) contains a haem group which contains iron
atom and is the site of oxygen binding.

10.  As erythrocytes mature, they lose their
nuclei and mitochondria, giving them the
distinctive biconcave-disc shape.
 Leucocytes (white blood cells) are:
a) colourless, have nuclei and mitochondria,
irregular in shape and make up less than
1% of volume of blood.
b) larger than red blood cells.
c) made by stem cells in the bone marrow.
 Their collective function is to fight infections
in various ways.
 Most activities of leucocytes takes place in
the interstitial fluid outside the blood
vessels.

11.  Platelets are fragments of large cells from
the bone marrow.
 Platelets have no nucleus.

12.  Three types of human blood vessels which is
arteries, veins and capillaries.
 Walls of arteries and veins consist of
epithelial tissues surrounded by smooth
muscles and connective tissues.
 The thick, muscular and elastic walls enable
arteries to withstand the high pressure of
blood flowing.
 Pulmonary artery is the only artery that
carries deoxygenated blood from heart to
lungs.
 Pulmonary vein is the only vein that carries
oxygenated blood from lungs to heart.

13.  Arterioles are small arteries that branch into
a network of capillaries.
 Capillaries are tiny, thin-walled blood vessels
where respiratory gases, nutrients, waste
products and hormones are exchanged by
diffusion between blood and interstitial
fluid.
 Walls of the capillaries are only one cell
thick.