Flashcards in SB8 Deck (43)
What does the rate of diffusion depend on?
Concentration difference (gradient)
How does distance affect rate of diffusion?
Substances diffuse more quickly when they haven’t as far to move.
How does concentration difference (gradient) affect rate of diffusion?
Substances diffuse faster if there’s a big difference in concentration between the area they are diffusing from and the area they are diffusing to.
If there are lots more particles on one side, there are more there to move across.
How does surface area affect rate of diffusion?
The more surface there is available for molecules to move across, the faster they can get from one side to the other.
Where does gaseous exchange take place?
What is the job of the lungs?
Its to transfer oxygen to the blood and to remove waste carbon dioxide from it.
What are the steps in gaseous exchange?
1. Blooding arriving at the alveoli has just returned to the lungs from the rest of the body, so it contains lots of CO2 and not much O2. This maximises concentration gradient for the diffusion of both gases.
2. O2 diffuses out of the air in the alveoli (where concentration of O2 is high) and into the blood (where O2 is low). CO2 diffuses in the opposite direction to be breathed out.
How are the alveoli specially adapted?
1. Moist lining for dissolving gases.
2. A good blood supply to maintain the concentration gradients.
3. Very thin walls - minimises distance.
4. Large surface area - happen faster + more.
What is Fick’s law?
Rate of diffusion - (proportional to) -
Surface area x concentration difference / thickness of membrane.
What happens if the rate of diffusion doubles?
The SA or concentration difference doubles.
The thickness of the membrane halves.
What is the job of red blood cells (erythrocytes)?
To carry oxygen from the lungs to all the cells in the body.
How are red blood cells adapted?
They have a biconcave disc shape to give a large surface area for absorbing oxygen.
They don’t have a nucleus allowing them to carry more oxygen.
It also contains haemoglobin.
What do white blood cells do?
Defend against infection.
What are the two types of white blood cell?
What do phagocytes do?
They can change shape to engulf unwelcome microorganisms
What do lymphocytes do?
They produce antibodies against microorganisms.
Some also produce antitoxins to neutrilise any toxins produced by the microorganisms.
What do platelets do?
Help blood clot.
What are platelets?
Small fragments of cells. They have no nucleus.
What can lack of platelets cause?
Excessive bleeding an bruising.
What is plasma?
Its the pale straw coloured liquid which carries everything in the blood.
What does plasma carry?
Red and white blood cells and platelets.
Nutrients like glucose and amino acids.
Carbon dioxide - from organs to lungs.
Urea - from liver to kidneys.
Antibodies and antitoxins produced by white blood cells.
What are the three types of blood vessels?
What do arteries do?
They carry blood away from the heart.
What do capillaries do?
They are involved in the exchange of materials at the tissues.
What do veins do?
They carry blood to the heart.
What are the features of arteries?
1. The walls are strong and elastic as blood is under high pressure.
2. Thick walls.
3. The contain a thick layer of muscle to make them strong and elastic fibres to allow them to stretch and spring back.
Usually carry oxygenated blood.
What are the features of capillaries?
1. Really small
2. Narrow so they can fit into the gaps between cells.
3. They have permeable walls, so substances can diffuse in and out.
4. Their walls are one cells thick increasing the rate of diffusion.
What are the features of veins?
1. Thinner walls because the blood is under lower pressure.
2. They have valves to stop the back flow of blood.
They usually carry deoxygenated blood.
What’s the equation for cardiac output?
Heart rate x stroke volume.