3.2.1-3.2.7

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Why do all living organisms have the need to exchange substances? 3.2.1 
To take oxygen and nutrients in and release generated waste product
What is an exchange site?3.2.1 
Location within an organism where waste products generated or release an oxygen and nutrients are taken in e.b lungs in humans and roots in plants
Why can small organisms exchange substances directly with the environment?3.2.1
-due to their large surface area to volume ratio
- the diffusion / transport distance in these organisms are very small so essential nutrients or molecules are able to reach the necessary parts of the cell effectively
-Smaller organisms also tend to have lower levels of activity and smaller metabolic demands
Why do larger organisms require specialised mass systems? 3.2.1 
- increasing transport distance
-Surface area to volume ratio
-Increasing levels of activity
Why is increasing transport distances a problem? 3.2.1 
In larger organisms, the important exchange site tends to be far away from other cells within the organism. This large transport distance makes simple diffusion slow so it wouldn't be fast enough to meet the metabolic requirements of a cell.
What is mass flow? 3.2.1 
Bulk movement of materials. It is directed movement so involve some sort of force.
What is diffusion like in mass transport systems? 3.2.1 
Some diffusion involved, but only at specific exchange sites at the start and end of the route travelled by the substance (e.g the lungs of the exchange site of the gas exchange system)
What are the benefits of mass transport systems? 3.2.1 
-Bring substances quickly from one exchange site to the other
-Maintain the diffusion gradient at exchange sites and between cells and their fluids surroundings
-Ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
Example of mass transport system 3.2.1
circulatory system, xylem in plants
What is a single circulatory system? 3.2.2 
System where the blood passes through the heart ones during one complete circuit of the body (e.g fish)
What is a double circulatory system? 3.2.2 
System where the blood passes through the heart twice during one complete circuit of the body ;e.g mammals)
Explained single circulatory system in fish - 3.2.2 
- Deoxygenated blood is pumped to the gills from the heart
- The gills are the exchange site where oxygen and CO2 are exchanged with the atmosphere and the blood
-Oxygenated blood flows from the gills to the rest of the body (travels through the capillaries and organs delivering oxygen and nutrients)
-Blood returns to the heart
-The heart only has one atrium and one ventricle
Explained double circulatory system in mammals - 3.2.2 
-blood passes through the heart twice during a single circuit of the body
-So the lean heart has a left and right side with a wall (septum) dividing the two
-blood in the right side of the heart leaves and travels to the lungs
-Blood returns to the left side before being pumped around the rest of the body
-Once blood has passed through all the other organs, it returns to the right side of the heart
Function of the heart - 3.2.2 
A hollow muscular organ located in the chest cavity which acts as a pump to send blood throughout the body
Advantages of double circulatory systems - 3.2.2 
- higher blood pressure maintained an average speed of flow
-This increased pressure and speed helps to maintain a steep concentration gradient which allows for the efficient exchange of nutrients and waste with the surrounding tissue
What side of the heart carries deoxygenated and oxygenated blood? 3.2.2 
Left = oxygenated
Right = deoxygenated
What is a closed circulatory system? 3.2.2 
Blood is pumped around the body and is always contained within a network of blood vessels (all vertebrae and many invertebrates have closed circulatory system)
What is an open circulatory system? 3.2.2 
Blood is not contained within the blood vessels but is pumped directly into body cavities (e.g arthropods and molluscs)
What type of circulatory system do humans have? 3.2.2 
Closed double circulatory system
Circulatory system in insects -3.2.2 
- insects have one main blood vessel (dorsal vessel)
-The tubular heart in the abdomen pumps haemolymph into the dorsal vessel
-The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
-Haemolymph surrounds the organs and eventually re-enters the heart via one-way valves called Ostia
Why are insects able to survive with a less efficient circulatory system? 3.2.2 
Oxygen is delivered directly to their tissues via tracheae that connect directly to the outside
What do arteries do?-3.2.3 
Transport blood away from the heart at high-pressure to tissues
What do veins do? -3.2.3 
Carry blood towards the heart under low pressure
What are arterioles? -3.2.3 
Arteries branch into narrower blood vessels called arterioles which help transport blood to capillaries
What are venules? -3.2.3 
Narrower blood vessels transport blood from the capillary to the veins
How does the structure of an artery suited to its role? -3.2.3
- narrow lumen to maintain high blood pressure
-Thick layer of elastic tissue to allow artery to expand and recoil to maintain blood pressure
-Thick layer of smooth muscle to allow vessel to constrict and dilate to maintain blood pressure
-Thick collagen and elastic fibres to withstand pressure
How was the structure of a vein suited to its role? -3.2.3 
-wide lumen to reduce resistance of blood flows easier
-Thinner elastic tissue as they don't need to expand or recoil
-Thin layer of smooth muscle as they don't need to constrict or dilate
-Thin collagen has blood flows at low pressure
-valves to prevent backflow of blood
How is the structure of a capillary suited to its role? -3.2.3 
- Very narrow lumen (7um)so red blood cells are squeezed through the lumen, reducing the rate of flow and providing a short diffusion distance for materials to move between the blood and tissue fluid
- Capillary wall consists of single layer of flattened endothelial cells providing a short diffusion pathway
- Gaps between the endothelial cells allow materials to enter and leave the blood (leaky)
What is tissue fluid? - 3.2.4 
A watery substance containing glucose, amino acids, oxygen, and other nutrients. It supplies these to the cells, while also removing any waste materials.
What results in the formation of tissue fluid? - 3.2.4 
As blood passes through capillaries, some plasma leaks out through gaps in the walls of capillaries to surround the cells of the body
What substances are in tissue fluid? - 3.2.4 
Mainly the composition of plasma, but without proteins as they are too large to fit through gaps in the capillary wall so remain in the blood
How does exchange of substances occur? - 3.2.4
Exchange of substances between cells and blood occur via tissue fluid e.g carbon dioxide produced in aerobic respiration will leave a cell and then dissolve into the tissue fluid surrounding it and then move into the capillary
What is hydrostatic pressure?- 3.2.4 
The pressure that the fluid exerts on the walls of its container/ vessel
What is oncotic pressure? - 3.2.4 
pressure created by osmotic effect of dissolved substances in a liquid which lowers the water potential causing water to move into the blood vessel by osmosis
What happens to tissue fluid at the arterial end? - 3.2.4 
- hydrostatic pressure is great enough to force fluid out of capillary
-Proteins remain in blood as they're too large to pass through pools and capillary wall
-This increased protein content creates a water potential gradient between the capillary and the tissue fluid
-At the arterial and the hydrostatic pressure is greater than the osmotic pressure so net movement of water is out of capillaries into tissue fluid
How does water potential gradient change in the capillary? 
The same at both ends of the capillary while the hydrostatic pressure is smaller at the Venus end
What is the relationship between hydrostatic pressure and osmotic pressure in the arterial end? - 3.2.4 
At the arterial and the hydrostatic pressure is greater than the osmotic pressure so net movement of water is out of capillaries into tissue fluid
What happens to tissue fluid at the Venous end? - 3.2.4
-hydrostatic pressure within the capabilities is reduced due to increased distance from the heart and slowing of blood flow as it passes through the capillaries
-Water potential gradient (osmotic pressure) between the capillary and tissue fluid remains the same at the arterial end
-At the Venus and the osmotic pressure is greater than the hydrostatic pressure as water begins to flow back into the capillary from the tissue fluid
What is the relationship between hydrostatic pressure and osmotic pressure in the venous end? - 3.2.4 
At the Venus and the osmotic pressure is greater than the hydrostatic pressure as water begins to flow back into the capillary from the tissue fluid
What happens to fluid loss at arterial end of capillary? - 3.2.4 
-around 90% of fluid lost at the arterial end of capillary is reabsorbed to the Venus end
-The other 10% remains as tissue fluid and is eventually collected by lymph vessels and return to circulatory system