Practicals

Question 1

What is the purpose of switching to a higher power lens during microscopy?

Answer 1

to increase the magnification

Question 2

What is the purpose of using the fine
adjustment knob when observing cells at low power?

Answer 2

to change the focus of the microscope

Question 3

What is the purpose of the microscope slide coverslip?

Answer 3

to hold the biological specimens in place

Question 4

Why is iodine solution commonly used as a stain in onion cell microscopy?

Answer 4

it binds to and stains starch

Question 5

What is the aim of the microbiology practical?

Answer 5

To investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition.

Question 6

What are the independent and dependent variables in microbiology practical?

Answer 6

independent - type of antiseptic or antibiotic applied
dependent - diameter of zone of inhibition

Question 7

What are 3 control variables in the microbiology practical?

Answer 7

temperature of incubation
concentration of antiseptic/antibiotic
duration of incubation

Question 8

What is the method for the microbiology practical?

Answer 8

1) disinfect the area you are working on
2) using a marker, mark onto the bottom of the agar plate: 3 segments with a dot in each and the name of bacteria
3) wash hands with antibacterial handwash
4) Spread bacteria on the agar jelly using a bunsen burner with roaring blue flame to keep everything disinfected. Make sure to be quick and only tilt the lid open.
5) place different antiseptics or antibiotics on the spots in the agar plate by tilting the lid open slightly. If using antiseptics, soak a disc of filter paper in each antiseptic and then place that in the plate
6) place agar plate in incubator at 25 degrees for 48 hours
7) after 48 hrs use a ruler to measure the diameter of the clear zone and then measure the diameter perpendicular to the previous measurement. Use the mean to calculate the area of the clear zone

Question 9

what could be a source of error in the microbiology practical?

Answer 9

contamination from other bacteria
shape of clear zone may be irregular and width difficult to determine

Question 10

What is the aim of the osmosis practical?

Answer 10

to investigate the movement of water by osmosis into or out of plant tissue

Question 11

What is the independent variable in the osmosis practical?

Answer 11

concentration of the salt or sugar solutions

Question 12

What is the dependent variable in the osmosis practical?

Answer 12

change in mass of the potato pieces

Question 13

What are 3 control variables for the osmosis practical?

Answer 13

volume of solution
temperature of solutions
time in solution

Question 14

What is the method for the osmosis practical?

Answer 14

1)use a cork borer to cut 5 potato cylinders
2) trim the cylinders with a sharp knife and ruler to the same length (about 3 cm)
3) measure and record the length and mass of each cylinder using a ruler and mass balance
4) measure 10 cm3 of 1.0M sugar/salt solution and transfer to first boiling tube and label
5) repeat step 4 for all concentrations
6) add a potato cylinder to each tube
7) leave cylinders overnight in a test tube rack
8) remove cylinders and carefully blot dry with paper towels
9) measure length and mass of each cylinder and calculate percentage change

Question 15

What is a source of error in the osmosis practical?

Answer 15

different parts of potato may have different water potentials
different surface areas affecting the rate of osmosis

Question 16

What is the aim of the enzymes and pH practical?

Answer 16

calculate the rate of enzyme activity at different pH values

Question 17

What is the independent variable in the enzymes and pH practical?

Answer 17

pH of buffer solution

Question 18

What is the dependent variable in the enzymes and pH practical?

Answer 18

rate of starch breakdown

Question 19

What are the control variables in the enzymes and pH practical?

Answer 19

temperature of the reaction, concentration of amylase, concentration of starch, volume of solutions

Question 20

What is the method for the enzymes and pH practical?

Answer 20

1) add a drop of iodine to each dimple on a dimple tray
2) add 2cm3 of buffer solution using a syringe (ranging from pH 3.0 - 7.0) into each labelled test tube.
3) immerse a test tube of starch solution, amylase solution, and buffer solution each into a water bath at 25 degrees
4) allow a few minutes for the temperature to equilibrate
5) put the amylase into the buffer solution test tube and then add the starch solution while starting the stopwatch
6) use a pipette to transfer one drop of the combined solution into a dimple every 20s starting with 0s
7) keep repeating step 6 till iodine solution remains brown and doesn’t turn blue-black
8) repeat with different pH of buffer solution

Question 21

What is a source of error in the enzymes and pH practical?

Answer 21

intervals between testing may be too long to accurately find time taken for starch to be completely broken down

Question 22

What is the aim of the photosynthesis practical?

Answer 22

investigate the effect of light intensity on the rate of photosynthesis

Question 23

What is the independent variable in the photosynthesis practical?

Answer 23

light intensity

Question 24

What is the dependent variable in the photosynthesis practical?

Answer 24

number of oxygen bubbles given off

Question 25

What are the control variables in the photosynthesis practical?

Answer 25

size of pondweed, volume of water, temperature of water

Question 26

What is the method for the photosynthesis practical?

Answer 26

1) place a test tube rack containing a boiling tube 10cm away from the light source 2) fill the boiling tube with a fixed volume of sodium bi-carbonate solution 3) place the cut pondweed into the boiling tube with the cut end at the top. Gently push the pondweed down with a glass rod 4) leave the boiling tube to rest for 5 minutes 5) start the stopwatch and count the number of bubbles produced in one minute 6) for each light intensity, repeat the count twice more and take a mean 7) repeat steps 1-6 for 3 more distances/intensities.

Question 27

What is a source of error in the photosynthesis practical?

Answer 27

temperature may also be a factor affecting rate of photosynthesis and may not have been taken into account bubbles may for too quickly to count