2. Genes and health
2.a Gas exchange, cell membranes and transport
Gas exchange
Diffusion
● Net movement of non-polar particles from an area of high concentration to low
concentration down a concentration gradient
● Passive process (does not require energy)
● SA:V ratio, diffusion distance and concentration gradient all affect rate of diffusion
Fick’s law
● Fick’s law is used to determine the rate of diffusion, it states that the larger the
surface area, difference in concentration and the shorter the diffusion distance the
quicker the rate
Adaptations of the lungs
In mammals, lungs are adapted for rapid gas exchange in the following ways:
● They have a large surface area due to the presence of many alveoli which increase
the surface area:volume ratio
● Good supply of circulating blood to the lungs which carries carbon dioxide to the
lungs and oxygen away from them ensures that the concentration gradient is
steep – high concentration of oxygen and low concentration of carbon dioxide is
maintained by mechanical ventilation
● They have a short diffusion distance as the alveoli are just one cell thick
Cell membranes and the transport of substances
Structure and features of cell membranes
● Partially permeable
● Composed of a phospholipid bilayer
● Fluid mosaic model
● Contains glycoprotein receptors, cholesterol, channel
and carrier proteins, glycolipids
Phospholipids
● Have a hydrophilic phosphate head that attracts water and a hydrophobic fatty acid
chain tail that repels water
The movement of substances
1. Diffusion
- Passive movement of small, non-polar, soluble molecules
- Area of high concentration to low down concentration gradient
, 2. Genes and health
- Molecules move directly through bilayer
- Affected by surface area, diffusion distance and diffusion gradient
2. Facilitated diffusion
● Requires channel protein
● Transports polar, charged and insoluble molecules
3. Osmosis
● Passive movement of water molecules from high concentration to low down
concentration gradient
● Through partially permeable membrane
4. Active transport
● Transports all types of molecules through carrier proteins
● Against concentration gradient
● Requires ATP
5. Endocytosis
● Transports large particles
● Particles enclosed in vesicles made from cell membrane and enter cell
● Active process
6. Exocytosis
● Transports large particles
● Particles enclosed in vesicles fused with cell membrane and exit cell
● Active process
2.b Proteins and genetics
Mononucleotides
Structure of DNA
● Bases
- Adenine-Thymine, Guanine-Cytosine
- Adenine and guanine are purine so contain two nitrogen rings, cytosine and
thymine are pyrimidines contain one nitrogen ring
● Nucleotide
- Deoxyribose pentose sugar
- Phosphate group
- Base
● Bonding
- Phosphodiester bond between phosphate and sugar
- Hydrogen bonds between bases
- Hydrogen bonds holding structure
● Structure
- Double stranded
- Alpha double helix
- Sugar-phosphate backbone
2.a Gas exchange, cell membranes and transport
Gas exchange
Diffusion
● Net movement of non-polar particles from an area of high concentration to low
concentration down a concentration gradient
● Passive process (does not require energy)
● SA:V ratio, diffusion distance and concentration gradient all affect rate of diffusion
Fick’s law
● Fick’s law is used to determine the rate of diffusion, it states that the larger the
surface area, difference in concentration and the shorter the diffusion distance the
quicker the rate
Adaptations of the lungs
In mammals, lungs are adapted for rapid gas exchange in the following ways:
● They have a large surface area due to the presence of many alveoli which increase
the surface area:volume ratio
● Good supply of circulating blood to the lungs which carries carbon dioxide to the
lungs and oxygen away from them ensures that the concentration gradient is
steep – high concentration of oxygen and low concentration of carbon dioxide is
maintained by mechanical ventilation
● They have a short diffusion distance as the alveoli are just one cell thick
Cell membranes and the transport of substances
Structure and features of cell membranes
● Partially permeable
● Composed of a phospholipid bilayer
● Fluid mosaic model
● Contains glycoprotein receptors, cholesterol, channel
and carrier proteins, glycolipids
Phospholipids
● Have a hydrophilic phosphate head that attracts water and a hydrophobic fatty acid
chain tail that repels water
The movement of substances
1. Diffusion
- Passive movement of small, non-polar, soluble molecules
- Area of high concentration to low down concentration gradient
, 2. Genes and health
- Molecules move directly through bilayer
- Affected by surface area, diffusion distance and diffusion gradient
2. Facilitated diffusion
● Requires channel protein
● Transports polar, charged and insoluble molecules
3. Osmosis
● Passive movement of water molecules from high concentration to low down
concentration gradient
● Through partially permeable membrane
4. Active transport
● Transports all types of molecules through carrier proteins
● Against concentration gradient
● Requires ATP
5. Endocytosis
● Transports large particles
● Particles enclosed in vesicles made from cell membrane and enter cell
● Active process
6. Exocytosis
● Transports large particles
● Particles enclosed in vesicles fused with cell membrane and exit cell
● Active process
2.b Proteins and genetics
Mononucleotides
Structure of DNA
● Bases
- Adenine-Thymine, Guanine-Cytosine
- Adenine and guanine are purine so contain two nitrogen rings, cytosine and
thymine are pyrimidines contain one nitrogen ring
● Nucleotide
- Deoxyribose pentose sugar
- Phosphate group
- Base
● Bonding
- Phosphodiester bond between phosphate and sugar
- Hydrogen bonds between bases
- Hydrogen bonds holding structure
● Structure
- Double stranded
- Alpha double helix
- Sugar-phosphate backbone
