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

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

1. Uses of circulatory systems

   • Removal of toxic waste products
   • Providing nutrients and oxygen to cells

2. Factors affecting need for a circulatory system

   • Size
     • Bigger organisms have more layers of cells, so diffusion is too inefficient. Transport needed instead.
   • Surface area to volume ratio
     • Lower surface area to volume ratio, more necessary a circulatory system is.
   • Level of metabolic activity
     • More active the organism, more necessary a supply of nutrients and oxygen to supply energy

3. Features of a good transport system

   • Efficient
     • Tubes to carry fluid by mass flow
     • Two circuits - one picks up oxygen, other delivers oxygen
   • Effective
     • Fluid to carry:
       • Nutrients
       • Oxygen
       • Waste
     • A pump to create pressure to push fluid
     • Exchange surfaces to allow substances to enter/exit e.g. capillaries

4. Circulatory system

   • Single
     • Fish
       • Heart => gills => body => heart
     • Blood pressure drops as blood passes through the tiny capillaries of the gills
       • Blood has a low pressure towards body, so slow flowing
         • Delivery and removal rate is limited
   • Double
     • Mammals
       • One carries blood to lungs, other carries oxygen and nutrients to tissues
       • Heart => body => heart => lungs => heart
     • Blood pressure low in pulmonary circulation
       • Systemic circulation carries blood at a higher pressure.
         • Mammals are active so more energy is needed. Rate of delivery/removal is increased.