Practicals

Question 1

What are the variables of Required Practical 1: Inevestigation into the effect of a named variable on the rate of an enzyme.

Answer 1

IV: Temperature/pH/substrate concentration
DV: Rate of reaction (what we measure)
CV: pH, enzyme concentration, substrate concentration

Question 2

What is trypsin?

Answer 2

• Small intestine, hydrolyses peptide bonds in a protein called casein.

Question 3

Procedure of Required Practical 1

Answer 3

1) Take 2 test tubes and draw an X on each tube (control too)
2) Add 10cm^3 of milk powder solution to both solutions
3) Grab two extra tubes and add a pH buffer to one and add 2cm cubed of trypsin to the other with pH buffer
4) Icubate all tubes at 20 degrees celcius
5) Add trypsin and buffer solution to tube T with milk powder and control buffer and immediately start timer
6) investigate how long it takes for X to become visible again because of hydrolysis.

Question 4

Theory of the RP1?

Answer 4

• Rate of reaction is initially slow due to lower kinetic energy so fewer enzyme-substrate complexes are formed.
• Temperature increases so more enzyme-substrate complexes are formed
• Above optimum temperature, enzymes denatures as hydrogen bonds in the active site are broken, so E-S complexes can no longer be formed.

Question 5

Procedure of the root tip practical

Answer 5

1) Take a root of garlic and cut a piece of the root tip - 1cm.
2) Place in heated 1M hydrochloric acid for 5 minutes (55 degrees celcius)
3) Rinse the root in tap water
4) Stain with toulidine blue to make the chromosomes visible.
5) Macerate with a needle.
6) Place tip onto a microscopic slide.
7) Squash by pressing down, not sideways because we don’t want to squash the tissue and break the chromosomes
8) Place under microscope and set objective lens to the lowest magnification
9) Observe the different stages of mitosis.

Question 6

Mitotic index calculation

Answer 6

Number of cells undergoing mitosis/Number of total cells x100

Question 7

What is a dilution series?

Answer 7

• To make a collection of samples with known concentrations, to make progressive dilution.

Question 8

What is a calibration curve

Answer 8

• Graph used to find an unknown concentration and is used to compare to a set of samples of known concentrations.

Question 9

Dilution practical steps?

Answer 9

• Make dilution series of 1M sucrose solution
  1) Make concentrations of 0, 0.2, 0.4, 0.6, 0.8, 1.0 - make up with distilled water.
  2) Make 20centimeters cubed of each solution.
  3) 1 divided by 0.2
  4)

Question 10

Why do we use betalain to measure the permeability of a membrane?

Answer 10

• Using betalain in beetroot cells means more pigment leeks out of the cells and therefore the permeability can be measured by the amount of pigment leaked.

Question 11

Method of permeability practical (RP4)

Answer 11

• Cut beetroots into identical cubes
• Wipe/rinse to clean off any pigment released as a result
• If investigating temperature, place cubes in equal volume of distilled water
• Place each test tube in a water bath that has a variety of temperatures
• Leave for 20 minutes
• Set colourimeter to blue filter and zero using a cuvette with distilled water
• Filter each sample into the cuvette.
• Measure the absorbance for each solution
• High absorption means higher pgiment concentration and hence a more permeable membrane.

Question 12

Results of permeability practical

Answer 12

• As temperature increases, permeability of the cell-surface membrane also increases.
• Temperature destroys proteins in the membrane leaving more spaces for molecules to pass through it.

Question 13

Why do we use dissections?

Answer 13

• Complete understanding of internal biological functions
  (E.G. heart, fish gills, insects or lungs)

Question 14

Ethical issues with dissection

Answer 14

• Not deliberately mistreating deceased animals
• Cutting viscously
• How they are killed to begin with

Question 15

Aseptic techniques?

Answer 15

1) Wipe down surfaces with antibacterial cleaner, both before and afterwards
2) use a bunsen burner in the work space so that convection currents draw microbes away from the culture
3) Flame the wire hoop before transfering bacteria
- Flame the neck of any bottles before using them to prevent bacterial spread
- Keep all vessels containing bacteria open for the minimum amount of time
- Close windows and doors to limit air currents.

Question 16

How to carry out aseptic techniques to investigate antimicrobial substances

Answer 16

1) Carry out aseptic techniques above
- use wire hoop to transfer bacteria from broth to agar plate
2) Spread bacteria evenly over plate using a sterile plastic spreader
3) Use sterile forceps to place the multi disc antibiotic ring on the plate
4) Lightly tape a lid on, invert and incubate at 25 degrees celcius for 48 hours.
5) Sterilise equipments used to handle bacteria and disinfect work surfaces.

6) Measure the diameter of the inhibition zone for each antibiotic
7) Area of inhibition zone: A=Nd squared/4

Question 17

Conclusion of the antimicrobial experiment?

Answer 17

• Large inhibition zone means more bacteria have been killed.

Question 18

Method for chromotography?

Answer 18

1) Draw a straight line in pencil which is approximately 1cm above the bottom of the filter paper being used. Do not use a pen
2) Cut a section of leaf and add acetone and use the pestle to grind up the leaf sample and release the pigments.
3) Use a capillary tube to extract some of the pigment and blot it onto the centre of the pencil line you have drawn.
4) Suspend the paper in the solvent so that the level of the liquid does not lie above the pencil line and leave the paper until the solvent has run up the paper to near the top.
5) Draw a pencil line marking where the solvent moved up to. The pigment should have separated out and there should be different spots on the paper at different heights above the pencil line.
6) Calculate the rF value for each spot (Distance travelled by the solut/solvent)

Question 19

Respiration practical method

Answer 19

1) Set up a water bath at 35 degrees celcius
2) Add 5cm cubed of yeast and glucose into 3 test tubes amd leave for 10 minutes
3) Add 2cm cubed of methylene blue to the test tubes and start the timer. Shake for 10 seconds and place test tube back in the water bath. Record how long it takes for the methylene blue to turn colourless for each test tube
4) Repeat the experiment using temperatures of 40,50,60,70 degrees celcius
5) Find the mean of the results for each temperature and use to calculate the average rate of respiration.

Question 20

Results of the respiration practical

Answer 20

• If the rate of reaction decreases this means rate of respiration also decreases meaning that the methylene blue will take longer to turn colourless when the temperature is further from the optimum.

Question 21

How to investigate simple animal responses?

Answer 21

• Set up choice chamber to have four quadrants as follows: dark and dry, dark and damp, light and dry, light and damp
• Use dark paper to block out the light on one half and use wet paper towels to make damp areas.
• Use a drying agent such as anhydrous calcium chloride to make dry areas.
• Place 10 woodlice in the centre of the choice chamber, using a spoon.
• do not use forceps
• Leave for 10 minutes
• Record how many woodlice are in each quadrants
• Repeat by moving woodlice back to the centre of the choice chamber and repeating steps 3-4.