BIOLOGY FORM 4 CHAPTER 3 NOTES
1. Cells of living organisms need to exchange materials with the environment and these
materials include:
a) Substances that are required by the cells
Respiratory gases such as O2 are taken in from the environment for the
respiration
Nutrients and water, where heterotrophic organisms digest their food into
soluble molecules before they absorbed and used
Autotrophic organisms absorb CO2, water and mineral ions for photosynthesis
b) Substances to be eliminated from the cells
Excretory products such as CO2 and nitrogenous waste such as ures which are
waste products of metabolism
2. Exchange of materials occurs across the plasma membrane which is composed of
phospholipids, proteins and carbohydrates arranged in a fluid mosaic structure
3. The phospholipids are arranged in a bilayer form, with their polar, hydrophilic heads
facing outwards so they can interact in water
4. The hydrophobic fatty acid tails face away from water and point towards each other in
the middle of the bilayer
5. This hydrophobic phospholipid bilayer acts as a barrier that effectively isolates the two
aqueous environments on either side of the membrane
6. Proteins that span the membrane are usually involved in transporting substances
across the membrane and they include carrier proteins and pore proteins
7. Proteins with carbohydrates attached are called glycoproteins, while phospholipids
with carbohydrates attached are called glycolipids
8. The cholesterol helps regulate fluidity of the membrane and decreases the
permeability of the membrane to ions
9. The plasma membrane has a selectively permeable membrane nature due to the
a) Phospholipid bilayer being a selectively barrier to molecules and ions
b) Specificity of transport proteins on the membrane
10.The movement of soluble substances across the plasma membrane can be through
diffusion, osmosis and active transport
11.Diffusion is the net movement of molecules and ions from an area of high concentration
to an area of low concentration
12.Diffusion is a passive process where no energy is involved and substances can only
move down their concentration gradient
13.Factors which influence the rate of diffusion across a plasma membrane include:
a) Concentration gradient
b) Temperature
c) Diffusion distance (thickness of membrane)
d) Surface area of membrane
1. Cells of living organisms need to exchange materials with the environment and these
materials include:
a) Substances that are required by the cells
Respiratory gases such as O2 are taken in from the environment for the
respiration
Nutrients and water, where heterotrophic organisms digest their food into
soluble molecules before they absorbed and used
Autotrophic organisms absorb CO2, water and mineral ions for photosynthesis
b) Substances to be eliminated from the cells
Excretory products such as CO2 and nitrogenous waste such as ures which are
waste products of metabolism
2. Exchange of materials occurs across the plasma membrane which is composed of
phospholipids, proteins and carbohydrates arranged in a fluid mosaic structure
3. The phospholipids are arranged in a bilayer form, with their polar, hydrophilic heads
facing outwards so they can interact in water
4. The hydrophobic fatty acid tails face away from water and point towards each other in
the middle of the bilayer
5. This hydrophobic phospholipid bilayer acts as a barrier that effectively isolates the two
aqueous environments on either side of the membrane
6. Proteins that span the membrane are usually involved in transporting substances
across the membrane and they include carrier proteins and pore proteins
7. Proteins with carbohydrates attached are called glycoproteins, while phospholipids
with carbohydrates attached are called glycolipids
8. The cholesterol helps regulate fluidity of the membrane and decreases the
permeability of the membrane to ions
9. The plasma membrane has a selectively permeable membrane nature due to the
a) Phospholipid bilayer being a selectively barrier to molecules and ions
b) Specificity of transport proteins on the membrane
10.The movement of soluble substances across the plasma membrane can be through
diffusion, osmosis and active transport
11.Diffusion is the net movement of molecules and ions from an area of high concentration
to an area of low concentration
12.Diffusion is a passive process where no energy is involved and substances can only
move down their concentration gradient
13.Factors which influence the rate of diffusion across a plasma membrane include:
a) Concentration gradient
b) Temperature
c) Diffusion distance (thickness of membrane)
d) Surface area of membrane
