Biology Required Practicals

What factors influence the rate of an enzyme-controlled reaction?

temperature

pH

concentration of substrate

concentration of enzyme

RP 1: effect of variable on rate of enzyme-controlled reaction.

How is a control set up in a practical measuring enzyme activity?

Replace enzyme solution with distilled water or boiled enzyme solution

RP 1: effect of variable on rate of enzyme-controlled reaction.

Outline the procedure to measure effect of temperature on enzyme activity. Use trypsin (enzyme) and milk.

• immerse equal volumes of trypsin and milk (different test tubes) in a water-bath for 5 minutes to equilibrate to temperature.

• mix together and immediately start timing. Record time for milk to be completely hydrolysed- turn colourless.

  • 3 repeats per temperature

RP 1: effect of variable on rate of enzyme-controlled reaction.

How is rate of reaction calculated from time?

1/time

RP 2: calculating mitotic index of plant cells

Where can plant cells undergoing mitosis be found?

meristem tissue at shoot and tips

RP 2: calculating mitotic index of plant cells

Outline the procedure to prepare a root tip slide.

Warm 1M HCl to 60°

Cut a root tip using a scalpel and add the HCl. Leave for 5 minutes.

Remove from HCl and wash with distilled water

Cut tip of root and place on a slide

Add a few drops of stain to make chromosomes visible

RP 3: using a dilution series to produce a calibration curve and identify the water potential of plant tissue

How is a calibration curve used to find the concentration of plant tissue?

Plot a calibration curve of percentage change in mass against concentration. Find the x-intercept where the plant tissue is isotonic to sucrose solution.

RP 3: using a dilution series to produce a calibration curve and identify the water potential of plant tissue

Why are potato disks left in solution for 20 minutes?

To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution

RP 3: using a dilution series to produce a calibration curve and identify the water potential of plant tissue

Outline the procedure used to invest osmosis in potato tissue

Make a serial dilution of 1M sucrose to produce 5 concentrations

Add 5ml to 5 different test tubes

Cut a potato in equal sized chips and weigh

Place a chip in each test tube and wait 20 minutes

Take out, dab excess water and weigh again

Calculate percentage change in mass

RP 3: using a dilution series to produce a calibration curve and identify the water potential of plant tissue

Why is percentage change used rather than actual change in mass?

Potato chips may not have the same starting mass

Percentage change allows comparison

RP 3: using a dilution series to produce a calibration curve and identify the water potential of plant tissue

What are the control variables of this practical?

concentration of sucrose solution

size of potato chip- volume and surface area

length of time left in solution

RP 4: effect of named variable on permeability of cell-surface membranes.

What are two factors that affect cell surface permeability?

temperature

concentration of solvents eg. ethanol

RP 4: effect of named variable on permeability of cell-surface membranes.

How is beetroot used to measure the permeability of cell membranes?

the higher the permeability, the more red pigment that leaks out into surrounding solution in time.

RP 4: effect of named variable on permeability of cell-surface membranes.

Outline the procedure used to investigate the effect of temperature on permeability of membrane.

Cut beetroot into 6 identical cubes with scalpel

Place each cube in a different test tube with equal volumes distilled water

Place each test tube in water baths ranging from 30-80°C. Leave for 20 mins.

Filter each solution into a cuvette and measure absorbance using a colorimeter

RP 5: dissection

What are tips for drawing a labelled diagram?

no shading

single and continuous lines

label lines drawn with ruler

do not cross label lines

no colour

magnification scale

no arrows

RP 6: aseptic techniques to investigate effect of antimicrobial substances on microbial growth

What are the 6 aseptic techniques?

wipe down surfaces with antibacterial cleaner before and after experiment

use a bunsen burner so convection currents draw microbes away from culture

flame the wire loop before use

flame the neck of the bottle before use

keep all vessels containing bacteria open for a limited period of time

close windows and doors to limit air current

RP 6: aseptic techniques to investigate effect of antimicrobial substances on microbial growth

Why is bacteria incubated at 25°C?

to prevent growth of harmful pathogens

RP 6: aseptic techniques to investigate effect of antimicrobial substances on microbial growth

How can you compare the effectiveness of different antibiotics applied to the same bacteria?

measure diameter and calculate area of zone of inhibition

RP 6: aseptic techniques to investigate effect of antimicrobial substances on microbial growth

What does zone of inhibition indicate?

bacteria killed by antibiotic

if there is little/no zone of inhibition, the bacteria is resistant to the antibiotic

RP 6: aseptic techniques to investigate effect of antimicrobial substances on microbial growth

Why should lids no be completely taped to petri dish?

to allow oxygen to enter the petri dish, preventing the growth of harmful anaerobic bacteria

RP 7: use of chromatography to investigate pigments in leaves

What factors affect the rate of migration in different pigments?

solubility

mass

affinity to paper

RP 7: use of chromatography to investigate pigments in leaves

formula of Rf value

distance moved by pigment/distance moved by solvent

RP 7: use of chromatography to investigate pigments in leaves

Outline the procedure of using chromatography to separate photosynthetic pigments

draw a horizontal pencil line 1cm from the bottom of the paper

use a pestle and mortar to grind up the lead sample with acetone to release the pigments

use a capillary tube to transfer pigment to pencil line

suspend the paper in solvent so that level of liquid lies below the pencil line and leave the paper until the solvent has run up the paper near the top

remove the paper from the solvent and draw a pencil line marking where the solvent moved to

calculate Rf value for each spot

RP 8: effect of named factor on rate of dehydrogenase activity in extracts of chloroplasts.

What is dehydrogenase?

enzyme found in plant chloroplasts that is important in the light-dependent stage of photosynthesis to catalyse the reduction of NADP.

RP 8: effect of named factor on rate of dehydrogenase activity in extracts of chloroplasts.

What is the purpose of DCPIP?

It is a redox indicator dye and acts as an alternate electron acceptor instead of NADP. It turns from blue to colourless when reduced,

RP 8: effect of named factor on rate of dehydrogenase activity in extracts of chloroplasts.

Why is the plant extract chilled in an ice-water bath?

to lower the activity of the enzymes to prevent them from breaking down the chloroplasts.

RP 8: effect of named factor on rate of dehydrogenase activity in extracts of chloroplasts.

How is the control set up?

Fill a cuvette with chloroplast extract and distilled water

RP 8: effect of named factor on rate of dehydrogenase activity in extracts of chloroplasts.

Why are stalks of leaves removed before grinding?

stalks do not contain many chloroplasts

RP 8: effect of named factor on rate of dehydrogenase activity in extracts of chloroplasts.

Outline the procedure of investigating the effect of light intensity on dehydrogenase activity after the chloroplast extract is obtained.

set the colorimeter to the red filter

zero using a cuvette filled with set concentration of chloroplast extract and distilled water

place test tube in the rack 30cm from light source and add DCPIP. Immediately take a sample and add to cuvette and measure absorbance of sample. Take a sample and measure absorbance every 2 minutes for ten minutes.

repeat for different distances of lamp

RP 9: effect of named variable on the rate of respiration of cultures of single-celled organisms

What is the function of methylene blue in this practical?

it is a redox indicator and acts as an alternate acceptor of electrons transferred in ATP synthesis.

turns blue to colourless to indicate end point

RP 9: effect of named variable on the rate of respiration of cultures of single-celled organisms

Outline the procedure to investigate the effect of temperature on the rate of respiration of yeast,

set up water bath to 35°C

add equal volumes of yeast and glucose solution to 3 test tubes. Place test tubes in the water bath and allow to equilibrate for 10 minutes.

Add 2ml of methylene blue to the test tubes and start the timer. Shake for 10 seconds and place back in water bath. Record how long it takes for methylene blue to turn colourless for each test tube

repeat using other temperatures

RP 9: effect of named variable on the rate of respiration of cultures of single-celled organisms

Why does yeast solution need to be buffered?

to maintain a constant pH so that the enzymes are functioning at optimum pH

RP 10: investigation into effect of environmental variable on the movement of an animal

What factors must be controlled when repeating the experiment?

number of animals

environmental conditions

time allowed

RP 10: investigation into effect of environmental variable on the movement of an animal

What statistical test is used to analyse results for this experiment and why?

chi squared

compares expected and observed values to test for a significant difference

RP 11: production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve to identify the concentration of glucose in a urine sample

How can benedict’s solution be used to measure the concentration of glucose in a solution?

use a colorimeter to measure the absorbance of a series of solutions of known concentrations to create a calibration curve. Compare absorbance of an unknown sample with the curve

RP 11: production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve to identify the concentration of glucose in a urine sample

What is the axes in a calibration curve for this experiment?

absorbance against glucose concentration

RP 11: production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve to identify the concentration of glucose in a urine sample

How can you increase the accuracy of the estimate of the unknown glucose solution?

increase the number of concentrations for the calibration curve within the range of concentrations that the unknown solution belongs to.

RP 12: effect of named environmental factor on distribution of a given species

list some abiotic factors

light intensity

humidity

temperature

wind speed

water supply

day length

nutrient supply

rainfall

RP 12: effect of named environmental factor on distribution of a given species

list some biotic factors

competition for resources

predation

disease

RP 12: effect of named environmental factor on distribution of a given species

how is percentage covered calculated?

use a quadrat with squares. Count how many squares the species is present in. Only count a square if more than half of the square is covered. Calculate percentage of squares the species is present in.

RP 12: effect of named environmental factor on distribution of a given species

Outline the procedure for this practical.

choose an area to take samples. Use a random number generator to select 10 random sets of coordinates

place quadrat at coordinates. record percentage cover of chosen species

a measure of the independent variable should also be taken at each coordinate eg. record of light intensity using photometer

RP 12: effect of named environmental factor on distribution of a given species

what is the formula for mark-release-recapture?

population size = (1st sample) x (no in second sample) / no. marked in second sample

RP 12: effect of named environmental factor on distribution of a given species

What are assumptions when using the mark-release-recapture?

no births, deaths or immigrations

random mixing of marked individuals with population

marking does not effect behaviour or chance of survival