Biology Experiment Flashcards
(19 cards)
investigate the effects of light intensity, light wavelength, temperature and
availability of carbon dioxide on the rate of photosynthesis using a suitable
aquatic plant,
Preliminary work:
- Method to measure vol of oxygen produced
- Range of distances between lamp and plant ‘
- Suitable temp & time frame & co2 & pH to collect gas
Method:
- DV - volume of oxygen produced -> divide by the time taken -> rate of
photosynthesis
- IV - light intensity -> change distance of lamp from apparatus
- CV - pH (buffer sol) + CO2 conc. (conc. / vol of sodium hydrogencarbonate sol.) +
wavelength of light (controlled by light filters) + temp (thermostatically controlled
water bath)
- Cut the stem of pondweed (same mass, age) under water + wipe any oxygen
bubbles on its leaves
- Place it upside down in the boiling tube of the photosynthometer (cut end of the stem
above) -> allow oxygen to bubble out
- Submerge in the sodium hydrogencarboate sol (3g of NaHCO3 + water)
- Adjust the temp -> 25
- Wrap half the beaker w aluminium foil -> light can reach plant on one side
- Place the desk lamp a certain distance away from the photosynthometer -> leave for
5 mins to acclimatise
- Fill the capillary tube w coloured liquid / water
- Measure distance moved by the coloured drop in 2 mins / 5
- Volume of oxygen produced = pi x r ^2 x l
- Rate = vol of oxygen / time
- Repeat & calculate mean
Limitations:
- Difficult to measure volume of oxygen accurately
- Difficult to control light intensity
- Difficult to control surface area of leaves
- Difficult to control all factors affecting photosynthesis / growth
Carry out a study of the ecology of a habitat, such as using quadrats and
transects to determine the distribution and abundance of organisms, and
measuring abiotic factors appropriate to the habitat
Preliminary practical work:
- Sampling method to determine dependent variable
- Area / time for sampling
- Range / numbers of independent variable e.g. suitable length of transect to show
changes / determine distance between quadrats / find a suitable range of distances
- Time scale to find effect of independent variable
- Method to count the number of organisms
- Method to measure the independent variable e.g. light intensity, humidity, etc.
Method:
Random sampling: (often investigating abundance - quadrat)
e.g. testing the hypothesis: difference in number of grasshoppers living on unused gravel
road and a natural gravel area
- The DV is the number of grasshopper per unit area
- Place 10 1x1m quadrats randomly (use a random coordinate generator) over the field
- Count the no. of grasshoppers in each quadrat (a half filled box → counted as one
box → calculate % of full boxes counted OR if the species is small & hard to
distinguish then measure abundance by % coverage OR if the species is easy to
count → record species frequency + abundance)
- Repeat for the other quadrats & calculate the mean
- Control light intensity (measure using light meter) + soil pH (pH meter) + temp
(atmospheric thermometer) + wind speed (using a anemometer) + same day & time
(CV)
- Repeat with other fields
Systemic sampling: (often influence of abiotic factor - transect)
- Chose an area w an environmental gradient (IV) (temp changes / amount of sunlight
changes: shade → light, etc.).
- Lay belt transect across the gradient.
- Place a quadrat at the beginning of the transect -> mark and count the number of
species being investigated in the quadrat (DV)→ find % cover
- Measure the abiotic factor you are investigating in the area e.g. light intensity using a
light sensor / probe
- Repeat by: placing a quadrat every 2m (systemic) down the transect to take samples
(e.g. 10 samples across 20m line) in diff areas across the env. Gradient
- Line transect - tape that is placed → organisms that touch the tape are counted
- Belt transect - two transects with quadrats placed between them to count the number
of species
- Investigation of two areas that are environmentally distinct = random sampling ->
quadrat
- Changes in population along env. Gradient = systematic sampling = transect (chose
belt or line)
- Soil pH
- Light intensity
- Mineral ions / water content in soil
- Wind speed
Limitations: - Difficult to control all the factors affecting the DV e.g. abundance / distribution / yield
- Light intensity / humidity / abiotic variable being investigated can change while
sampling - Age of plant / insect can affect % cover
- Difficult to ensure that each organism is only counted once
- Levels of abiotic factors measured during the day may not be representative of
normal conditions - Determining % cover is subjective
- Only one field was investigated
- Errors in measuring abiotic factor accurately e.g. soil moisture content
- Seasonal variations - affect no. of species present & their abundance
- Weather conditions can prevent certain organisms from being seen
Risks: - Wear protective clothing
- risk of sunburn → wear sun hat / sun cream
- risk of insect bites and allergies
- wear rubber shoes to avoid tripping / slipping
- Thorns → injury
- Dirt & bacteria → infection → wash hands before drinking / eating
Measuring abiotic factors:
Abiotic variable Measuring it
Temp Thermistor
pH Chemical testing kit / pH meter
Light intensity Light metre
Wind speed Anemometer
Slope of incline Clinometer
O2 levels Digital oxygen probe
Water availability Moisture probe or weighing -> drying ->
reweighing
Air spaces Remove a sample and measure volume
without air
Mineral ion content Chemical testing kit
Soil type / structure Measure size of soil particles
CP 12:
Investigate the effects of temperature on the development of organisms (such
as seedling growth rate or brine shrimp hatch rates), taking into account the
ethical use of organisms
Brine shrimp:
Preliminary practical work:
- Suitable number / mass / viability of eggs to use
- Range of independent variables
- Time for eggs to hatch
- Method to count larvae
- Environmental condition to control e.g. temp, salinity, pH, oxygen conc., light intensity
Method:
- DV: number of eggs that hatched
- IV: temperatures - thermostatically controlled water bath (not higher 45 - ethical) /
incubator
- CV: pH (buffer) + salinity of water + light intensity (lamp) + number of eggs + volume
of water used + oxygen conc.
- Put 2g of sea salt + 100cm^3 dechlorinated water -> stir with stirring rod -> dissolve
the salt in a beaker
- Dampen some paper w the salt solution -> use forceps with blunt ends to place 40
brine shrimp eggs on to the paper -> place in the beaker -> let the egg fall off the
paper (leave for 2 mins to do so) -> remove the paper using forceps
- Incubate each beaker at the corresponding temp -> leave for 24 hours
- Place a desk lamp to shine light onto the beaker -> allow brine shrimps that have
hatched to come to the surface
- Use a pipette to remove the brine shrimps that have hatched -> place them into the
beaker containing salt and water and count them
- Repeat & find mean
Limitations:
- Difficult to control all factors affecting brine shrimp hatching as factors may fluctuate
- Difficult to count hatched eggs as they are small
- Limits of measuring effect of independent variable -> viability of eggs + species of
brine shrimps + genetic differences + damage to eggs
Seeds:
Preliminary work:
- Same / suitable variety / source of seeds
- Conditions for germination
- Timescale for measuring germination
- Method to measure % of seeds that have germinated
- Range of IV
Method:
- DV: number of germinating seeds
- IV: temp -> incubator
- CV: storage conditions of seed + age of seeds + light intensity + stage of germination
+ food source
- Use five petri dishes incubated at diff temps
- Layer of cotton wool at the bottom of each petri dish -> place 10 seedlings on each
petri dish using forceps
- Spread the seedlings out -> even distribution across the dish
- Add 30 cm^3 of water (measuring cylinder)
- Incubate for 5 days
- Every 24 hours add the same volume of water -> prevents the cotton wool from
drying out
- Count number of germinated seeds after 24 hours
Limitations:
- Difficult to control all factors affecting germination
- Time of germination may be unpredictable
- Germination under controlled conditions -> doesn’t represent the natural growing
conditions
- Some limiting factors not taken into consideration
- Impossible to control natural variation of seeds
- Some seeds may not be viable
- Seeds may need more than one type of mineral for effective growth of plants
CP 13:
Investigate the rate of growth of microorganisms in a liquid culture, taking into
account the safe and ethical use of organisms
Preliminary work:
- Suitable range of IV
- Suitable timescale for growth
- Suitable temp / pH for growth
- Suitable way to count the microorganism
Method:
- DV: number of the microorganism per unit time / absorbance / turbidity
- IV: e.g. temp, pineapple juice
- CV: temp, pH, nutrients in growth medium, volume & conc. of bacterial culture,
composition of growth medium
- Aseptic technique -> sterilising, bunder burner… -> prevent contamination
- Fill 500cm^3 conical flask with 250cm^3 glucose solution (0.5%)
- Add 1.25g of microorganism e.g. yeast -> add it to the flask
- Put on magnetic stirring flea for even stirring the culture / stir with a glass rod
- Add cotton wool to the mouth of the flask -> cover with aluminium foil
- Incubate at room temp
- Zero the colourimeter -> using a cuvette filled with 0.5% glucose solution
- Measure 4cm^3 of the yeast culture (sterile pipette) -> place in clean cuvette ->
measure its absorbance
- Repeat at: 30 min, 1h, 90min, 2h, 5h, 8h, 11h
You can also use a data logger:
- Place a light source on one side of the yeast culture + a light sensor on the opposite
side
- Place a cardboard box with a cut-out over the flask & stirrer & light sensor to prevent
ambient light from reaching light sensor
- Connect light sensor to data logger -> leave to record continuously for 10 - 24 h
Limitation:
- Uneven distribution of microorganisms
- Colourimeter -> some surfaces reflect light away from the light detector -> difficult to
take measurements
- Nutrient conc. In growth medium may vary
- Contamination of culture -> reduce growth rate bc of comp. on nutrients / space
- Colorimeter factors*
Investigate the effect of different antibiotics on bacteria
Preliminary practical work:
- Suitable conditions for bacterial growth
- Suitable time for measurable growth
- Suitable method for measuring effect on antibiotics
- Suitable age / strain of bacteria
- Suitable conc. of antibiotics
- Suitable method to apply antibiotic
Method:
- DV: diameter of zone of inhibition
- IV: antibiotic used
- CV: temp + nutrients in agar + duration of incubation + type of bacteria used + conc.
Of antibiotic used + oxygen conc. + pH of agar - Aseptic technique
- Transfer 2cm^3 of liquid broth -> agar plate (use a sterile pipette)
- Evenly distribute the bacteria across the agar jelly
- Transfer antibiotic filter paper disks to the agar plate + leave distances between them
- Seal the lid of the agar plate -> not all the way -> allow oxygen to enter
- Incubate at 30 degrees for 24 hours
- Measure diameter of zone of inhibition
Limitations: - Difficult to measure the DV
- Difficult to control all factors affecting bacterial growth
- Contamination / difficult to maintain aseptic tech
- Difficult to control conc. of extract
Risks: - Harmful bacteria / infection / pathogens
- Controlling the risk: aseptic technique, incubate below body temperature
Use an artificial hydrogen carrier (redox indicator) to investigate respiration in
yeast
Preliminary practical work:
- Find a suitable mass / conc. / no. of yeast cells that will produce CO2
- Find a suitable method to measure vol. of CO2
- Find a suitable range of temps
Method:
- DV: time taken for colour change to occur
- IV: e.g. temp
- CV: pH (buffer) + conc. / volume of redox indicator + mass / conc. of glucose +
species / strain of yeast
- Add 10g of dried yeast + 50g of glucose to 1dm^3 of distilled water -> mix with
stirring rod
- Allow yeast culture to stabilise for 24 h
- Prepare multiple water baths -> 15, 20, 25, 30, 35 (range of 5 -55)
- Add 10cm^3 of yeast suspension using a pipette to a test tube
- Place 1cm^3 of TTC (redox indicator) into a separate test tube
- Place both test tubes for the same temp and leave them for 5 min to reach the temp
of the water bath
- Quickly pour the TTC onto the yeast -> stir w glass rod -> start stopwatch
- Stop the stopwatch when solution turns red
- Repeat several times for other temps
- rate = 1 / T
Risks: - Allergies to TTC
- High temp of water bath
Limitations: - Difficult to recognize end point
- Difficult to prevent contamination of yeast culture / maintain aseptic tech
- Yeast may change from aerobic to anaerobic respiration during investigation
- Build up of waste products may affect enzymes / slow rate of respiration
CP 16
Use a simple respirometer to determine the rate of respiration and RQ of a
suitable material (such as germinating seeds or small invertebrates)
Preliminary practical work:
- Suitable age of maggots / IV
- Temp for respiration
- Time for measuring vol of gas
- Number of maggots to give suitable results
- Suitable pH for respiration
- Method to measure vol. of oxygen
Method:
- DV: measure volume of oxygen used
- IV: age of maggots
- CV: same mass of soda lime + temp (thermostatically controlled room) + mass of
each maggot / number
- Test tube -> add 5g or soda lime to the test tube (absorb CO2 produced)
- Place a known mass / number of maggots onto a gauze -> place above the soda lime
- Use the syringe to move coloured fluid to the end of the manometer furthest from the
test tube -> mark its position
- Close the 3 way tap to allow now more gas exchange to occur between the
apparatus -> start the stopwatch
- Mark the position of the coloured drop every 5 mins
- Volume of oxygen: use the radius of the tube -> pi x r^2 x h
- Rate = volume / time
- Open the 3 way tap -> use syringe to reset the coloured drop
- Repeat with other ages / age group
Risks:
- Soda lime is corrosive
- Handle live animals w care = ethical
- Allergies
Limitations: - Difficult to measure vol of gas
- Difficult to decide if seeds are germinating at the same rate
- If seeds are viable
- Difficult to prevent contamination of seed
- Difficult to control all factors affecting respiration / RQ
- At higher temps, gases expand -> affect volume recorded
- Carbon dioxide is water soluble so volume of gas recorded may be inaccurate
CP 17:
Investigate the effects of exercise on tidal volume, breathing rate, respiratory
minute ventilation, and oxygen consumption using data from spirometer
traces
Preliminary practical work:
- Suitable way to measure DV
- Suitable intensities of exercise
- Suitable time frame for exercise / measuring DV
- Suitable age groups
- Suitable time scale for measurable effect
Method:
- DV: tidal volume, breathing rate, respiratory minute ventilation, and oxygen
consumption
- IV: Intensity of exercise, duration of same intensity of exercise / same exercise
- CV: same gender, age group, lifestyle, amount of people, health conditions + same
temp, humidity - Calibrate the spirometer:
- Empty it -> no air remains
- Align the pen to paper -> record the results
- Add a set volume of air e.g. 1 dm^3
- Use the vertical scale to calculate how many squares on the graph (kymograph) are
equivalent to the volume of air added to the spirometer - Put a nose clip on the person -> only breathe through their mouth
- Insert sterilised mouthpiece in front of the spirometer into the subjects mouth -> allow
them to breathe normally (acclimatise to apparatus) - Set the kymograph to a rate of 1mm -> turn it on -> rotate
- After exhalation -> adjust the 2 way tap -> subject is now breathing through
spirometer equipment instead of the atmosphere - Record -> normal / resting breathing rate + ask for breathing deeply for one breath ->
breath out as deeply as they can - Observe effect of exercise: switch off the spirometer -> ask to exercise for 2 mins ->
immediately reinsert mouthpiece -> record results for one minute
Risks: - Risk of infection
- Breathing difficulty
- Exposure to soda lime
- Risk of injury
Limitations: - Difficult to control all of the variables affecting vital capacity e.g. genetic variation
- Difficulty in measuring the vital capacity as person may not breathe out as forcefully
as possible - Small sample size -> isn’t representative of all population -> conclusion cannot be
made - Participants will differ in effort in exercise
CP 18:
Investigate the production of amylase in germinating cereal grains
Preliminary work:
- Method to measure clear area / starch digestion
- Range of conc. of IV
- Temp & pH
- Time frame for amylase to be produced / starch digestion
Method:
- The dependent variable is diameter of the clear zone
- IV - conc. of gibberellins (0.0001, 0.001, 0.01, 0.1, 1)
- CV - temp (30) using thermostatically controlled room / incubator + pH using buffer
solution + humidity + light intensity (same distance of lamp) - Collect a number of seeds (15) -> cut them in half (scalpel) -> endosperm & embryo
half -> discard the embryo half (bc this is where gibberellin is produced) - Endosperm half -> sterilise by placing it in sodium hypochlorite for five mins
(disinfectant) - Rinse several times w sterilised water -> blot dry carefully
- Use forceps -> place 3 seeds in each gibberellin solution -> soak for 24 - 48 h ->
place a lid on the solution bottles -> leave slightly unscrewed to allow oxygen to enter - Soak 5 petri dishes (one for each conc.) -> use sterile forceps to place the 3 seeds in
the petri dish - Incubate at 30 degrees for 24 hours (aseptic technique)
- Open the lid slightly -> add potassium iodide / iodine using a syringe
- Presence of starch = no amylase = blue black
- No starch = hydrolysed by amylase = clear area
- Repeat for each conc. + find mean
Risks / hazards: - Seeds = allergies
- Gibberellic acid / solution / disinfectant = irritant
- Risk of contamination = use aseptic tech
Limitations: - Difficult to measure the area
- Difficult to maintain aseptic technique
- Growth regulators in seed may affect amylase production
Habituation:
Investigate habituation to a stimulus.
Preliminary practical work:
- Suitable time intervals between touches
- Method for applying touch / suitable force
- Determining extent of withdrawal
- Conditions for animal to feed
Detailed method:
- DV: extent of withdrawal
- IV: the number of touches
- CV: time intervals between touches + temp (thermostatic tank / water bath) + amount
of food in tank - Method of applying touches: use a glass rod / cotton bud
- Apply touches with the same force
- Allow animal to acclimatise before stimulation begins / between touches
- Measure the extent / length of withdrawal after each touch
- Repeat with another animal + calculate mean
Limitations: - Difficult to determine the extent of withdrawal
- Difficult to control the force that the touch is applied with
- Difficult to ensure that the organism is not already habituated
- Difficult to control age of the organism
Investigate the change in vitamin C content when fruits are stored for 14 days compared
with 28 days.
Collect fruits of the same mass and age and incubate some for 14 days and others for
28 days at the same temperature (25oC)
After storage, create fruit juice using a pestle and mortar and place 20 cm3 of the
fruit juice into a burette
Add 5 cm3 of DCPIP solution into a test-tube and titrate the DCPIP solution with
fruit juice drop by drop and shake gently after each drop
Record the volume of fruit juice required to decolorize DCPIP solution (Blue to colorless)
Repeat the same procedure with other fruits and calculate the mean volume required
to decolorize DCPIP solution
Repeat the same procedure with a standard solution of known vitamin C content then
calculate the mean vitamin C content by using formula (C1 = C2 x V2 / V1)
Investigate the effect of caffeine solution on mitotic index of cells in onion roots
Prepare 5 concentrations of caffeine (20%, 40%, 60%, 80%, 100%)
Collect onion plants of the same age, mass and species and soak each onion plant in
different concentrations of caffeine for 1 hour
Cut the root tips of each onion plant using a sharp knife then add the root tips in
hydrochloric acid for 15 min at 55oC then in acetic orcein stain for 15 min at 55oC, and
control the pH using a buffer and temperature using a thermostatically controlled
water-bath
Rinse the root tips several times with water then place the root tips on the microscopic
slide, and place the coverslip above the root tips then squash gently using the thumb
Observe the root tips on low magnification to locate the sample then on high
magnification to observe mitosis
Count the total number of cells in the sample and the number of cells undergoing
mitosis then calculate mitotic index by dividing number of cells undergoing mitosis over
total number of cells in sample
Repeat with other root tips and calculate mean mitotic index for each caffeine solution
Investigate the effect of antimicrobial compounds in Piper Betle leaves on the growth of the
bacteria (With Agar Plates)
The dependent variable of this investigation is the diameter of the zone of inhibition
Create an extract from the leaves by crushing using a pestle and mortar
Culture the bacteria on several agar plate and perform this under full aseptic
technique (e.g. disinfecting workbench, sterilizing the equipment, keeping a Bunsen
burner close to the working area and minimizing exposure of culture to air)
Collect filter paper discs of the same size and soak some of them in the extract and
some of them in water (as a control for comparison)
Place the filter paper discs in the agar plates then incubate the agar plates for 24h at
30oC
Remove the petri dishes from incubator and measure the diameter of the zone of
inhibition
Repeat the same procedure with other agar plates and calculate the mean diameter of
zone of inhibition and standard deviation
Investigate the effect of pineapple juice on the growth rate of
the E. coli (With liquid broth)
The dependent variable of this investigation is the change in the number of bacteria per
unit time
Create an extract from the pineapple fruit using a blender
Prepare two liquid cultures, one containing pineapple juice and the other doesn’t
Take samples from both cultures and count the number of the bacterial in each culture
Place them in thermostatically controlled water-bath at 30oC for 24 hours and control
the pH using a buffer solution
Take samples from each culture after 24 hours and count the number of bacteria in each
culture using a hemocytometer
Calculate growth rate by dividing the change in number of bacteria by 24 hours
Limitations:
Difficult to maintain aseptic technique and to prevent contamination
Difficult to measure the diameter of zone of inhibition with precision
Difficult to count the number of bacteria using hemocytometer (as they are not evenly
distributed)
Difficult to control the temperature and pH of the cultures
Investigate the tensile strength of fibers extracted from Kenaf plants
The dependent variable of this investigation is the mass needed to break the fibers
Extract fibers of the same cross-sectional area from the Kenaf plants of the same age
Support the fibers using 2 clamp stands and add 20g of mass till the fibers break
Control the humidity using a dehumidifier and temperature using an air conditioner
Calculate the tensile strength by converting mass to force (x10) then dividing it by cross-
sectional area
Repeat the experiment with other fibers of the same cross-sectional area and
calculate the mean tensile strength of the fibers and standard deviation
Investigate the effect of the sigma extract on the rate of growth of pollen tube
The dependent variable of this investigation is the change in length of the pollen tube
Prepare 2 petri dishes, one containing the sigma extract and the other containing
sucrose solution as a control
Collect pollen grains from plants of the same age and species, and place some pollen
grains in sigma extract and some in sucrose extract
Incubate the petri dishes at 25oC for 30 min and control the pH using a buffer solution
Examine the pollen tubes with a microscope and measure the change in length of pollen
tube using a stage micrometer and eyepiece graticule
Repeat with the other pollen grains and calculate the mean change in length of pollen
tube and standard deviation, then calculate the rate of growth of pollen tube by
dividing the mean change in length over time
Investigate the effect of different concentrations of abscisic acid (ABA) on the production
of amylase from endosperm
The dependent variable of this investigation in the diameter of the clear area
Collect wheat grains of the same mass and species and sterilize the endosperms in
sodium hypochlorite solution for 5 min then rinse the endosperms with water several
times
Soak the endosperms in abscisic acids for 24h then place the endosperms in starch agar
Incubate the petri dish for 24h to maintain the temperature at 25oC, and control the
pH of the petri dish using a buffer solution
Examine the petri dishes after incubation and measure the diameter of the clear area
Repeat this procedure 4 more time with the same concentration and calculate the mean
diameter of the clear area
Repeat the whole experiment other 4 different concentrations of
abscisic acid
Limitations:
Difficult to maintain aseptic technique and prevent contamination of the seeds
Difficult to measure the diameter of the clear area with precision
There may be growth regulators that may affect amylase production
Compare the water potential in tissues of two different species of potato
The dependent variable of this investigation is the change in mass of the potato cubes
Collect tubers from both species from plants of the same age, and cut the tubers to
cubes of the same mass and volume
Place the cubes in a beaker containing pure water and leave them for 30 min, and
control the temperature using a thermostatically controlled water-bath and pH using a
buffer solution
Dry the outer surface of the cubes then measure the final mass of the cubes using
an electronic balance
Repeat the same procedure with other cubes of the same mass and volume and
calculate the mean change in the mass of those potatoes
