Required practicals 1-6

Question 1

What is required practical 1?

Answer 1

Investigation into the effect of a named variable (temperature) on the rate of an enzyme-controlled reaction.
Milk contains a protein called casein which, when broken down, causes the milk
to turn colourless. Trypsin is a protease enzyme which hydrolyses the
casein protein.
IV- Temperature
DV- Time it takes for milk to hydrolyse
CV- Amount of trypsin solution, milk suspension, HCL, etc.

Question 2

What is required practical 2?

Answer 2

Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index
DV- Mitotic index
CV-same root tip, stain, magnification

Question 3

What is required practical 3?

Answer 3

Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue
-Potato chips in lower concentrations of glucose solution will increase in mass,
whilst those in the higher concentrations of glucose solution will decrease in
mass
-In the dilute glucose solutions, the solution has a higher water potential than
the potato, so water passively moves via osmosis to the area of lower water
potential (the potato). This causes the potato to increase in mass.
-In concentrated glucose solutions, water will move out of the potato, thus the
potato will decrease in mass.
IV- Sucrose concentration
DV- Change in potato mass, water potential
CV- Size of potato chips, amount of time in test tube, amount of water

Question 4

What is required practical 4?

Answer 4

Investigation into the effect of a named variable on the permeability of cell-surface membranes
-The permeability of a membrane can be measured by using beetroot cells, which
contain a purple pigment called betalain. When the cell-surface membrane has a
higher permeability, more pigment leaks out of cells. The permeability can therefore be
measured by the amount of pigment leaked from beetroot cells into an aqueous
solution using a colorimeter.
-As the temperature increases, the permeability of the cell-surface membrane
also increases. This is because the proteins in the membrane denature as the
heat damages the bonds in their tertiary structure. This creates gaps in the
membrane, so it is easier for molecules to pass through it.
-At low temperatures, phospholipids have little energy and are packed closely
together to make the membrane rigid. This causes a decrease in permeability
and restricts molecules from crossing the membrane.
IV- Temperature
DV- Absorbence (pigment amount), permeability of membrane
CV-Beetroot cube size, time left in test tube

Question 5

What is required practical 5?

Answer 5

Dissection of animal or plant gas exchange system or mass transport system or of organ within such a system
Hazards- biohazard (contamination), disinfectant (flammable), sharp tools (cuts)

Question 6

What is required practical 6?

Answer 6

Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth
Aseptic techniques are used to avoid contamination of the sample from outside
substances such as microorganisms. This is important to get reliable and repeatable
data.
If there is a larger inhibition zone around the antibiotic, it has killed more
bacteria. Therefore, the larger the inhibition zone, the better the antibiotic works.
Some antibiotics will have no/very little inhibition zone. This shows that the
bacteria are resistant to this antibiotic and are not killed by it.
Aseptic techniques are used to avoid contamination of the sample from outside
substances such as microorganisms. This is important to get reliable and repeatable
data.
IV- Antibiotic, aseptic technique
DV- Zone of inhibition
CV- Disinfection, methods