GAH Revision Notes
[Topic 2] Genes and Health
,A Level Notes GAH: Diffusion (Fick’s Law) Biology
Fick’s Law
𝑎𝑟𝑒𝑎 𝑜𝑓 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 × 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑖𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
𝑅𝑎𝑡𝑒 𝑜𝑓 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 ∝
𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
→ SA:V ratio determines whether a substance can reach cells be diffusion alone
→ The larger the organism, the smaller the SA:V ratio (diffusion takes longer)
→ Larger SA:V = optimum diffusion rate
Alveoli adapted for gas exchange and diffusion by:
- Large surface area
- Constant blood supply via many capillaries (maintains high conc. difference)
- Thin walls (short diffusion distance between blood and air)
Emphysema (caused by smoking) decreases SA:V of alveoli in lungs (larger diffusion distance). Explain why a person with
emphysema has problems with gas exchange. (4 marks)
✓ Tar from smoking cigarettes sits in alveoli walls which thickens the wall – this increases diffusion distance and
lowers the rate of diffusion
✓ This also increases the SA:V ratio which means it would take longer for the gas exchange of oxygen and carbon
dioxide between the blood capillary and alveoli air
✓ Less blood flow due to destruction of capillaries; less oxygen carried by blood which means there is less surface
area of capillaries
Why can’t large organisms rely on diffusion for the transport of oxygen and glucose? (3 marks)
✓ Large organisms have a lower SA:V ratio which means there is also a larger diffusion distance (diffusion longer)
✓ Large organisms also have a higher metabolic rate which means they require more energy – this cannot be
supplied via diffusion
✓ Therefore, diffusion is ineffective
Explain how rapid gaseous exchange takes place in a mammal. (5 marks)
1) Large surface area provided by alveoli
2) Large surface area provided by capillary network
3) Concentration gradient maintained by {ventilation of / air flow in} the lungs
4) Concentration gradient maintained by {circulation / mass flow} of blood
5) Diffusion pathway is small because alveoli have a thin wall
6) Diffusion pathway is small because capillaries {have a thin wall / are in contact with alveoli / are only one cell thick}
7) Air is warmed because lungs are in core of body
8) Warmer air enables faster {movement / diffusion of gases
9) Reference to {respiratory pigment / haemoglobin / red blood cells} to carry oxygen
, A Level Notes GAH: Cystic Fibrosis Biology
Ciliated cells
✓ Move mucus up trachea
✓ Removes pathogens from airways
Mucus
✓ Protects epithelial cells in respiratory, digestive and
urogenital systems against fungi, bacteria and viruses
✓ Most of the mucus produced us found in the stomach
• Epithelium; the outer layer/surface of an organ
→ Squamous epithelium found in alveoli
→ Columnar epithelium found in intestine + trachea
• Goblet cells in trachea produce mucus
• Mucus is thick and sticky
→ Cilia can’t eject the mucus from the bronchioles
1) A healthy CFTR channel protein transports chloride ions out of cell and into mucus
2) Thus more water moves from cell into mucus by osmosis (Cl- affect osmotic balance)
3) The mucus becomes diluted and is easily removed
CF is caused by a defective CFTR protein
Less chloride ions will enter mucus
Therefore less water moves into mucus
The mucus remains thick and sticky
CFTR; cystic fibrosis transmembrane conductance regulator
Lungs
- Surface area of alveoli reduced
- Pathogens remain in body
Digestive system
- Food in intestine not dissolved/digested
- Poor digestion leads to weight loss + lack of nutrients
Pancreas (exocrine gland which produces enzymes (then released into
pancreatic duct) and produces insulin + glucagon for glucose regulation
- Mucus blocks pancreatic duct
- Digestive enzymes are trapped in pancreas (cysts form)
- Pancreas may be damaged
Intestine
- Reduced digestion in intestine
- Thick mucus lining intestinal wall reduces absorption of nutrients as it is harder for nutrients to diffuse out
Respiratory system
- Cilia can’t move mucus towards throat
- Bronchioles and alveoli blocked (reduced gas exchange)
- Pathogens trapped in mucus may cause infection
Reproductive system
- Sperm duct blocked or absent
- Thick cervical mucus blocks sperm entry
[Topic 2] Genes and Health
,A Level Notes GAH: Diffusion (Fick’s Law) Biology
Fick’s Law
𝑎𝑟𝑒𝑎 𝑜𝑓 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 × 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑖𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
𝑅𝑎𝑡𝑒 𝑜𝑓 𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 ∝
𝑑𝑖𝑓𝑓𝑢𝑠𝑖𝑜𝑛 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
→ SA:V ratio determines whether a substance can reach cells be diffusion alone
→ The larger the organism, the smaller the SA:V ratio (diffusion takes longer)
→ Larger SA:V = optimum diffusion rate
Alveoli adapted for gas exchange and diffusion by:
- Large surface area
- Constant blood supply via many capillaries (maintains high conc. difference)
- Thin walls (short diffusion distance between blood and air)
Emphysema (caused by smoking) decreases SA:V of alveoli in lungs (larger diffusion distance). Explain why a person with
emphysema has problems with gas exchange. (4 marks)
✓ Tar from smoking cigarettes sits in alveoli walls which thickens the wall – this increases diffusion distance and
lowers the rate of diffusion
✓ This also increases the SA:V ratio which means it would take longer for the gas exchange of oxygen and carbon
dioxide between the blood capillary and alveoli air
✓ Less blood flow due to destruction of capillaries; less oxygen carried by blood which means there is less surface
area of capillaries
Why can’t large organisms rely on diffusion for the transport of oxygen and glucose? (3 marks)
✓ Large organisms have a lower SA:V ratio which means there is also a larger diffusion distance (diffusion longer)
✓ Large organisms also have a higher metabolic rate which means they require more energy – this cannot be
supplied via diffusion
✓ Therefore, diffusion is ineffective
Explain how rapid gaseous exchange takes place in a mammal. (5 marks)
1) Large surface area provided by alveoli
2) Large surface area provided by capillary network
3) Concentration gradient maintained by {ventilation of / air flow in} the lungs
4) Concentration gradient maintained by {circulation / mass flow} of blood
5) Diffusion pathway is small because alveoli have a thin wall
6) Diffusion pathway is small because capillaries {have a thin wall / are in contact with alveoli / are only one cell thick}
7) Air is warmed because lungs are in core of body
8) Warmer air enables faster {movement / diffusion of gases
9) Reference to {respiratory pigment / haemoglobin / red blood cells} to carry oxygen
, A Level Notes GAH: Cystic Fibrosis Biology
Ciliated cells
✓ Move mucus up trachea
✓ Removes pathogens from airways
Mucus
✓ Protects epithelial cells in respiratory, digestive and
urogenital systems against fungi, bacteria and viruses
✓ Most of the mucus produced us found in the stomach
• Epithelium; the outer layer/surface of an organ
→ Squamous epithelium found in alveoli
→ Columnar epithelium found in intestine + trachea
• Goblet cells in trachea produce mucus
• Mucus is thick and sticky
→ Cilia can’t eject the mucus from the bronchioles
1) A healthy CFTR channel protein transports chloride ions out of cell and into mucus
2) Thus more water moves from cell into mucus by osmosis (Cl- affect osmotic balance)
3) The mucus becomes diluted and is easily removed
CF is caused by a defective CFTR protein
Less chloride ions will enter mucus
Therefore less water moves into mucus
The mucus remains thick and sticky
CFTR; cystic fibrosis transmembrane conductance regulator
Lungs
- Surface area of alveoli reduced
- Pathogens remain in body
Digestive system
- Food in intestine not dissolved/digested
- Poor digestion leads to weight loss + lack of nutrients
Pancreas (exocrine gland which produces enzymes (then released into
pancreatic duct) and produces insulin + glucagon for glucose regulation
- Mucus blocks pancreatic duct
- Digestive enzymes are trapped in pancreas (cysts form)
- Pancreas may be damaged
Intestine
- Reduced digestion in intestine
- Thick mucus lining intestinal wall reduces absorption of nutrients as it is harder for nutrients to diffuse out
Respiratory system
- Cilia can’t move mucus towards throat
- Bronchioles and alveoli blocked (reduced gas exchange)
- Pathogens trapped in mucus may cause infection
Reproductive system
- Sperm duct blocked or absent
- Thick cervical mucus blocks sperm entry
