Transport in animals

03.23.2020
09:35:40
Biology/grade 9- today’s topic-Blood- Red blood cells, white blood cells and platelets.(course book- 117 to 120.
Main points:-
Blood consists of red blood cells, white blood cells, platelets and plasma.

Plasma is a straw-coloured liquid that makes up just over half the volume of blood.

Red blood cells

Red blood cells transport oxygen for aerobic respiration. They must be able to absorb oxygen in the lungs, pass through narrow blood vessels, and release oxygen to respiring cells.

Red blood cells have adaptations that make them suitable for this:
They contain haemoglobin - a red protein that combines with oxygen.
They have no nucleus so they can contain more haemoglobin
they are small and flexible so that they can fit through narrow blood vessels.
They have a biconcave shape (flattened disc shape) to maximise their surface area for oxygen absorption.

Types of White Blood Cell
White blood cells are part of the body’s immune system, defending against infection by pathogenic microorganisms
There are two main types, phagocytes and lymphocytes
Phagocytes.
Carry out phagocytosis by engulfing and digesting pathogens.
Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells
Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it.
They can be easily recognised under the microscope by their multi-lobed nucleus and their granular cytoplasm.

Blood Clotting
Platelets are fragments of cells which are involved in blood clotting and forming scabs where skin has been cut or punctured.

Blood clotting prevents continued / significant blood loss from wounds.
Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that could cause infection.
It remains in place until new skin has grown underneath it, sealing the skin again.

How the blood clots:-

When the skin is broken (i.e. there is a wound) platelets arrive to stop the bleeding.
A series of reactions occur within the blood plasma.
Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin and form an insoluble mesh across the wound, trapping red blood cells and therefore forming a clot.
The clot eventually dries and develops into a scab to protect the wound from bacteria entering.