L1 - animal transport

• Substances needed to be transported around the body:

  -$O_2(g)$

  -$C_6H_{12}O_6(aq)$

  -$H_2O(l)$

  -$CO_2(g)$

  -urea

  -waste products

  -hormones

  -ATP

  -antibodies

  -antitoxins

  -$HCO_3^-(aq)$ (carbonic acid)(acts as a buffer)
• Why do multicellular organisms need a transport system:

  -low surface area to volume ratio

  -diffusion distance is too great

  -they are very metabolically active, they need to supply reactants for respiration and remove waste products

  -need a good supply of nutrients
• Fish:

  -have a single circulation system

  -blood flows from the heart to the gills and then on to the body before returning to the heart
• Disadvantages of single circulation systems:

  -heart cannot pump at high pressure

  -reduced blood pressure in capillaries of gills to reduce chance of damage

  -slow rate of flow in rest of body

  -limited rate of delivery of oxygen and glucose to tissues
• Pulmonary circuit delivers blood to the lungs
• Systemic circuit delivers blood to the body muscles
• Human heart as a double pump:

  -mammalian heart is divided down the middle

  -right side pumps deoxygenated blood to the lungs to receive oxygen (pulmonary system)

  -left side pumps oxygenated blood to the rest of the body (systemic system)
• Blood pressure must not be too high for the blood entering the lungs, otherwise it can damage capillaries. However, blood needs to be pumped at high enough pressure to get to all parts of the body, especially for a highly metabolically active organism such as a mammal. A double circulatory system means pulmonary pressure can be low, whilst separate systemic pressure can be high, in order to pump blood at higher pressure around the body to the respiring cells
• Advantages of a double circulatory system:

  -heart can increase blood pressure after blood passes through lungs

  -increased speed of delivery

  -increased blood pressure in systemic system, oxygen and glucose get to tissues quickly

  -lower blood pressure in pulmonary system decreases the chance of damaging capillaries in the lungs
• Single circulation: blood passes through heart once per complete circuit
• Double circulation: blood passes through heart twice per complete circuit
• Single circulation:

  -blood pressure reduced as blood passes through the gill capillaries, slowing down flow to the rest of the body

  -limits the rate of delivery of oxygen and nutrients to cells and removal of waste

  -sufficient for animals with a lower metabolic rate that do not need to maintain body temperature
• Double circulation:

  -the oxygenated blood can be pumped rapidly and at high pressure to the body, necessary for higher metabolic rates and need to maintain body temperature through respiration

  -need to deliver and remove materials to and from cells rapidly, achieved by delivering blood at high pressure to tissues

  -the blood pressure must not be too high in the pulmonary circulation, otherwise it may cause damage to the delicate capillaries in the lungs
• Closed circulation of a fish:

  -blood is enclosed inside blood vessels

  -$O_2(g)$diffuses into blood from gills

  -heart pumps blood into arteries, veins and them to the capillaries

  -$O_2(g)$and glucose can diffuse from blood into cells via the tissue fluid. but blood remains in the vessels
• Features of a closed system:

  -blood always remains in blood vessels

  -tissue fluid bathes the organs
• Advantages of a closed system:

  -blood is pumped at a higher pressure

  -oxygen and nutrients can be unloaded faster at the cells

  -carbon dioxide can be removed faster

  -amount of blood flowing to a particular tissue can be adjusted
• Open circulatory system

  
• Haemolymph: “insect blood” only transports food, nitrogenous waste and immune cells
• In open circulatory systems, blood flows freely through the body cavity. Body movement can help to move the blood around
• Open circulatory systems:

  -the heart is segmented, contracting in a wave, starting at the back

  -blood pumped into a single main artery, which opens up into body cavity

  -blood flows around insect’s organs and back to heart via valves

  -the open system supplies cells with nutrients and transports substances, but not oxygen as this is done by the tracheal system
• Problems with open circulation:

  -blood is under low pressure so flows slowly

  -these animals cannot rely on blood to transport oxygen and carbon dioxide

  -in larger organisms this low pressure would mean that organs would get very little food and it wouldn’t be supplied fast enough

  -steep diffusion gradient cannot be maintained

  -amount of blood flowing to each tissue cannot be varied

  -circulation is affected by (lack of) body movements