From Cells to Multicellular Organisms - Transport Systems and Blood Composition

[[Major Transport Mechanisms[[

  • Both plants and animals require transport mechanisms to move digested material and respiratory gases from the external environment into cells.
  • In humans (and most mammals), material is typically transported in a liquid medium. These are:
  1. Tissue fluid (or intercellular fluid)
  2. Blood
  3. Lymph

[[How do these Mechanisms Work?[[

  • Tissue fluid surrounds all individual cells and is the conduit for gases and nutrients in the blood. These must travel across the phospholipid bilayer.
  • Blood moves through our arteries, veins and capillaries via our circulatory system. This system is vital for gas exchange.
  • Lymph fluid is fundamental in our immune system as this is where white blood cells are stored.

[[The Structure of our Blood[[

Human blood contains FOUR different components:

  1. Red blood cells (also called erythrocytes)
  2. White blood cells (also called leucocytes)
  3. Plasma proteins
  4. Platelets

*These are suspended in a straw coloured fluid called plasma.

[[Erythrocyte Advantages[[

  • Erythrocytes have a biconcave shape which maximises their SA:V ratio.
  • This aids with oxygen capacity and allows them to fit through narrow capillaries is your extremities.

[[Red Blood Cells[[

  • Within red blood cells is the red pigment known as haemoglobin.
  • It attracts oxygen - each haemoglobin molecule contains a polypeptide chain and an iron- containing ‘haem’ group. Each haem group can carry one oxygen molecule. However, a single RBC can carry 1000 million oxygen molecules!
  • A low amount of haemoglobin due to lack of RBC’s is called Anaemia

[[Blood Clotting[[

Blood clotting is essential when external (or internal) tissue is damaged.

However, this process requires a complex series of reactions to take place.

  1. You cut yourself on a shard of glass.
  2. Platelets then adhere to your damaged tissue and release a lipoprotein called thromboplastin.
  3. This attracts more platelets to the site of the tissue damage to ‘plug’ the area.
  4. Thrombin (a clotting factor) then converts fibrinogen in blood plasma into strands of fibrin which form a ‘net’ and start the healing process.

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[[Recap Questions[[

  1. Explain why it is important for large organisms to have transport systems.    * Multicellular organisms need efficient transportation systems because simple diffusion would be too slow to transport nutrients and remove waste.
  2. Identify the constituents of blood.    * Red blood cells (also called erythrocytes)    * White blood cells (also called leucocytes)    * Plasma proteins    * Platelets
  3. Explain how the structure of erythrocytes aids its function.    * Erythrocytes have a biconcave shape which maximises their SA:V ratio. This aids with oxygen capacity and allows them to fit through narrow capillaries is your extremities.

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