Transport in animals

• how do single celled organisms obtain nutrients and excrete waste?

  simple diffusion
• how to multicellular organisms receive nutrients and excrete waste?

  through specialised transport systems
• why do multicellular organisms need transport systems?

  They have high metabolic rates which diffusion alone cannot uptake, they have a smaller surface area to volume ratio meaning diffusion is too slow to enable them to survive, and so that different materials can be transported like proteins, food and waste.
• how to calculate surface area to volume ratio

  Side x side x no. of sides / height x length x width
• a circulatory system is comprised of a heart, a fluid for transport and vessels where the fluid can flow.
• what are the two types of circulatory system?

  Open and closed circulatory system.
• in an open circulatory system, the haemolymph is pumped by the heart through short vessels into a cavity, the haemocel. diffusion occurs in the haemocel. when the heart contracts, the haemolymph is reabsorbed via ostia.
• while vertebrates have a closed circulatory system, Insects and Molluscs have open circulatory systems
• in a closed system, blood travels within blood vessels. from the heart, blood is pumped through vessels of decreasing sizes - the capillaries where substances diffuse in and out of the blood. then the blood returns to the heart.
• closed systems an either be single or double circulatory systems. more complex organisms tend to have a double circulatory system.
• a single circulatory system is a transport system where blood only passes through the heart once per circuit.
• a double circulatory system is a transport system where blood passes through the heart twice per circuit.
• Advantages of a single circulation system: the blood circulating the body has already been oxygenated by the gills.
• disadvantages of single circulation system: due to lower pressures, the rate of oxygen delivery is slower, meaning the metabolic rate is not as high as nutrients are not distributed properly.
• advantages of double circulation system: improves body efficiency and ensures the body always has a constant supply of oxygen.