Transport in Humans.

Need for transport system in animals

(i) To transport nutrients required by the organism from the point of absorption to all different
parts of the body.
(ii) To facilitate the removal of metabolic wastes from the body to the excretory organs.
(iii) To transport gases in the body.

Note.

 Single celled (unicellular) organisms can get their supplies of oxygen and food nutrients
by diffusion through the membrane of their cell which is in direct contact with the
outside.
 Because they are so small, it doesn’t take too long to pass the substances through the cell
membrane and into the cell.
 We say they have a large surface area to volume ratio and therefore they do not require
a specialised transport system to supply the cell and remove waste products.
 Multicellular organisms have a small surface area to volume ratio so they need a well-
developed transport system as diffusion alone is not enough for materials to reach all the
cells.
 This means that they need to develop specialized areas of their body to get certain things
that they need (eg, in humans, lungs: get oxygen for the body cells, digestive system: gets
food for the body cells) and then develop a system that can deliver it quickly to all the
cells in different areas of the body.
 Plants also have transport systems consisting of tubes through which fluids flow,
transporting different substances to different areas of the plant, but the movement is not
driven by a pump as in animals.
 The path in the body through which material circulates is called the circulatory system.
 The human circulatory system consists of:

(i) The blood.

(ii) The heart.

(iii) The blood vessels.

Composition of blood.

 Blood consists of red blood cells, white blood cells, platelets and plasma

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Blood Plasma
 It is the liquid part of blood. It is pale yellow liquid that carries blood cells, nutrients,
hormones, enzymes, carbon dioxide, oxygen, urea and heat.
 It is made up of 90% water and 10% dissolved substances.

Functions of plasma.
(i) It transport digested food (glucose, amino acids, fatty acids and glycerols from the digestive
system to the body cells.
(ii) It transports carbon dioxide from the body cells to the lungs to be breathed out.
(iii) It transports nitrogenous wastes such as urea from the liver to the kidneys.
(iv) It transport hormones from the glands that produce them to where they are required.
(v) It transports antibodies to all over the body to protect the body from infection.
(vi) It distributes heat hence regulating the body temperature in the body.

Cellular components.

(i) Red blood cells.

 These cells are formed in the bone marrow. They have a life span of 21 days.
 They transport oxygen to body cells.
 They contain a red pigment called haemoglobin which combines with oxygen to form
unstable compound called oxyhaemoglobin. This happens in the lungs.
 When the blood reaches the body cells, the oxyhaemoglobin split into oxygen and
haemoglobin. The oxygen then diffuses into the body cells.

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 Adaptation of Red Blood Cells.

(i) They do not have a nucleus - This gives them more space to absorb more oxygen.

(ii) Biconcave shape – To increase the surface area for more oxygen to enter and leave the cell.

(iii) Thin cell surface membrane- This reduces the diffusion distance to allow oxygen to diffuse
in and out faster.

(iv) They are small and flexible – This allows them to fit and squeeze into the narrow capillaries
without getting stuck.

(v) They are numerous in number to carry more oxygen.

(iv) They contain haemoglobin. This helps in transporting oxygen . Haemoglobin is an iron
containing protein.

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White Blood Cells.

 They are also formed in the bone marrow.

 They have a nucleus
 They have colourless cytoplasm. They lack haemoglobin.
 They are part of the immune system, they defend the body against disease causing
microoraginisms.
 There are two types; Phagocytes and Lymphocytes.

(i) Phagocytes.

 They are irregularin shape.

 They have a lobed nucleus.
 They have granules in their cytoplasm to produce enzyme which help in degesting the
pathogen.They change their shape by producing extentions of their cytoplasm to engulf
or surround the pathogen in a vacoule. The phagocyte then secretes enzymes in the
vacoule to digest the micro-organism. This process is called phagocytosis.
 An increase in number of white blood cells indicates the presence of pathogens in the
body.

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(b) Lymphocytes.

 They are formed in lymphatic nodes.

 They have a round nucleus.
 They produce antibodies to fight against diseases. An antibody is a protein produced by
lymphocytes to destroy a pathogen. Pathogens have a chemical on their surface which is
called antigen.
 Antigens therefore is a protein that stimulates production of antibodies from
lymphocytes.
 Antibodies perform their function in four ways;
(i) They cause the bacteria to stick to each other so that phagocytes can identify them and
digest them by phagocytosis.
(ii) They act as labels on pathogens for phagocytes to identify them and digest them.
(iii) They cause bacterial cells to burst.
(iv) They neutralise poisons (toxins) Produced by the bacteria.

Immunity, Vaccines and Vaccination.

 A vaccine. Is a preparation of a weakened or dead pathogen that is given to stimulate the

lymphocytes to produce antibodies without causing severe infection. This improves
immunity, ability to fight a disease.
 Vaccination is the administration of antigens to stimulate the immune system of an
individual to develop immunity to a disease.
 Each pathogen has a unique antigen so the lymphocytes produce different antibodies
specific to a given pathogen.

How Lymhocytes help us to become immune to a disease.

When a pathogen enters your body, lymphocytes produce antibodies to destroy the pathogens.
Some antibodies become memory cells which enable the formation of future antibodies against
that pathogens. Memory cells remain in the blood for many years, if the same pathogen re-infects
, the memory cells start to produce antibodies faster and in great quantities whch quickly rise to
kill the pathogen before it reaches a point where it can cause the disease. This is called natural
immunity.

The production of antibodies following the first exposure to a foreign antigen is called the
primary immune response while the memory cells produce secondary immune response.

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Artificial immunity.

 A person can be given artificial immunity through vaccination.

 When a vaccine against a certain pathogen is introduced into the body it will not cause
the disease but will stimulate the lymphocytes to produce antibodies.
 Some lymphocytes reamin in the blood as memory cells which enable the formation of
future antibodies against the pathogen with that specific antigen.
 The vaccine can contain the following.

(i) Weakened strain of the pathogen eg TB, Polio and measles.

(ii) Dead pathogens eg Typhoid and whooping cough.

(iii) Just the antigen themselves eg Influenza

(iv) Harmless bacteria are genetically modified to produce antigens used as vaccines.

(v) Toxins are extracted from the bacteria and neutralised to make them harmless and used as
vaccines.