OCR - A-Level - Biology - Circulatory Transport in Animals

Uses of circulatory systems
1. Removal of toxic waste products
2. Providing nutrients and oxygen to cells
Factors affecting need for a circulatory system
1. Size
  1. Bigger organisms have more layers of cells, so diffusion is too inefficient. Transport needed instead.
2. Surface area to volume ratio
  1. Lower surface area to volume ratio, more necessary a circulatory system is.
3. Level of metabolic activity
  1. More active the organism, more necessary a supply of nutrients and oxygen to supply energy
Features of a good transport system
1. Efficient
  1. Tubes to carry fluid by mass flow
  2. Two circuits - one picks up oxygen, other delivers oxygen
2. Effective
  1. Fluid to carry:
    1. Nutrients
    2. Oxygen
    3. Waste
  2. A pump to create pressure to push fluid
  3. Exchange surfaces to allow substances to enter/exit e.g. capillaries
Circulatory system
1. Single
  1. Fish
    1. Heart => gills => body => heart
  2. Blood pressure drops as blood passes through the tiny capillaries of the gills
    1. Blood has a low pressure towards body, so slow flowing
      1. Delivery and removal rate is limited
2. Double
  1. Mammals
    1. One carries blood to lungs, other carries oxygen and nutrients to tissues
    2. Heart => body => heart => lungs => heart
  2. Blood pressure low in pulmonary circulation
    1. Systemic circulation carries blood at a higher pressure.
      1. Mammals are active so more energy is needed. Rate of delivery/removal is increased.

Zusammenfassung der Ressource

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