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Biology Unit 6 Summary Seite 1
Investigate the effect of caffeine on the heart rate of Daphnia
Dependent variable
Heart rate
Independent variable
Concentration of caffeine solution
Control variable
Temperature, species/age/sex/size of Daphnia, oxygen supply, pH, Volume of solution, time
Safety
If a stroboscope is used and you suffer from photosensitive epilepsy take appropriate precaution.
Ethical
Stress, pain, death, has right to live
Procedure
(1) Place a few strands of cotton wool on a cavity slide
(2) With a pipette transfer one large Dapphnia to the cavity slide and add one or two drops of
distilled water
(3) View the Daphnia under a microscope and focus on it’s heart
(4) Use a stopwatch to record the number of heart beats per minute by working in pairs (one
counting, one stopping). Do a blind study to avoid bias. Record the heart rate at intervals of 2
mins over a 10 mins period.
(5) Repeat 1-4 with other water fleas and fresh cavity slides but instead of using water use a 0.5
% caffeine solution. Repeat with 1%, 1.5% and 2% caffeine solution
Limitations
Hard to control environmental factors, hard to count heartbeat, genetic variety
Biology Unit 6 Summary Seite 2
Investigate the Vitamin C content of fruit juice
Dependent variable
Vitamin C content
Independent variable
% vitamin C solution, different fruit juices
Control variable
DCPIP concentration, DCPIP volume, concentration of vitamin C solution, use fresh juices, dilute Vit.C
solution of DCPIP decolourises too fast. Temperature, pH
Safety
DCPIP stains clothes so don’t spill it
Procedure
(1) With a pipette add 1 cm^3 of 1 % DCPIP solution into a test tube
(2) With a burette add 1 % Vitamin C solution drop by drop to the DCPIP shaking the tube gently
until the DCPIP decolourises. Record the volume of Vit.C solution that was added
(3) Repeat 1-2 3times and calculate a mean
(4) The 1 % Vit.C solution contains 10 mg of Vit.C in 1 cm^3. Calculate the mass of Vit.C required
to decolourise DCPI
(5) Repeat 1-3 using fruit juice you are testing for.
(6) Use the Value calculated in (4) to work out how much Vit.C the fruit juice contains in
mg/cm^3
(7) 0.6 cm^3 of 1% Vitamin C decolourises 1 cm^3 of 1% DCPIP. 1 cm^3 of 1 % Vitamin C
solution contains 10 mg of Vitamin C 6 mg of Vitamin C needed to decolourise 1 cm^3 of
DCPIP
6 mg / cm^3 juice required = content
Limitations
Pre-handling (storage), fruit juice is coloured so it’s hard to tell when it exactly decolourised, may
need less than a drop to decolourise
Biology Unit 6 Summary Seite 3
Effect of temperature on beetroot membrane
Dependent variable
Colour leaking out (% absorbance)
Independent variable
Temperature
Control variable
Size of cork borer, lengths of slices, lengths of time left in water bath, volume of water in boiling
tube, species/age of beetroot, part of beetroot
Safety
Take care using a cork borer and knife and water bath at high temperature
Procedure
(1) Cut 8 1cm slices from a single beetroot using a size 4 cork borer
(2) Place the slices in a beaker of distilled water. Leave overnight to wash away excess dye.
(3) Place 8 labelled boiling tube each containing 5 cm^3 distilled water into water bath at 0, 10,
20, 30, 40, 50, 60, 70 °C. Leave for 5 mins until water reaches required temperature.
(4) Place one of the sections into a of the boiling tubes and leave for 30 mins in water bath
(5) Remove beetroot by spearing with a pointed seeker to not squeeze it. Shake the solution to
disperse the dye.
(6) Switch on the colorimeter and set it to read 0% absorbance
(7) Set the filter dial to the blue/green filter
(8) With a pipette measure 2 cm^3 of distilled water into the cuvette without touching the
clouded side. Place the cuvette into colorimeter
(9) Adjust the colorimeter to read 0 absorbance for clear water
(10) Place 2 cm^3 of dye solution into a colorimeter cuvette and take reading for absorbency.
(11) Repeat 4-10 with the other temperatures
Biology Unit 6 Summary Seite 4
Effect of alcohol on beetroot membrane
Dependent variable
Colour leaking out (% absorbance)
Independent variable
Alcohol concentration
Control variable
Size of cork borer, lengths of slices, lengths of time left in water bath, volume of water in boiling
tube, species/age of beetroot, part of beetroot
Safety
Take care using a cork borer and knife and water bath at high temperature
Can stain clothes and skin
Procedure
(1) Cut 8 1cm slices from a single beetroot using a size 4 cork borer
(2) Place the slices in a beaker of distilled water. Leave overnight to wash away excess dye.
(3) Place one of the beetroot sections into a boiling tube containing 5 cm^3 distilled water.
(4) Leave for 30 mins
(5) Remove beetroot by spearing with a pointed seeker to not squeeze it. Shake the solution to
disperse the dye.
(6) Switch on the colorimeter and set it to read 0% absorbance
(7) Set the filter dial to the blue/green filter
(8) With a pipette measure 2 cm^3 of distilled water into the cuvette without touching the
clouded side. Place the cuvette into colorimeter
(9) Adjust the colorimeter to read 0 absorbance for clear water
(10) Place 2 cm^3 of dye solution into a colorimeter cuvette and take reading for absorbency.
(11) Repeat 3-10 with 10, 20, 30, 40, 50, 60, 70 % alcohol solution instead of water
Biology Unit 6 Summary Seite 5
How protease concentration affects initial rate of casein breakdown
Dependent variable
Initial rate of reaction (absorbance/min)
Independent variable
Enzyme concentration
Control variable
Temperature, pH, substrate concentration, substrate volume, volume of protein solution
Procedure
(1) With a pipette add 2 cm^3 milk powder and 2 cm^3 of 0.5 % protease solution into a
cuvette. Mix and put it into a colorimeter and start stop watch.
(2) Measure absorbance at 1 min intervals for 5 mins
(3) Discard the content of the cuvette and rinse with distilled water
(4) Plot a graph of absorbance against time and determine initial rate
(5) Repeat 1-4 with 1, 1.5, 2, 2.5 % enzyme concentration
Safety
All enzymes are potential allergens no skin contact
Biology Unit 6 Summary Seite 6
How catalase concentration affects initial rate of hydrogen peroxide breakdown
Dependent variable
Initial rate of oxygen volume produced per time
Independent variable
Catalase concentration
Control variable
Length/thickness of potato disc, species/age of potato, pH 7, temperature of water bath,
volume/concentration of hydrogen peroxide
Safety
Hydrogen peroxide is corrosive so wear goggles and gloves
Control
0% catalase (no discs)
Procedure
1. Set up apparatus to collect oxygen over water with the collecting tube filled with water and
the screw clip closed
2. Cut 10 discs of potatoes each 0.2 mm thick. Place them in a boiling tube with 5 cm^3 of pH7
buffer solution
3. Add 5 cm^3 of 1 % hydrogen peroxide solution and immediately place bung and delivery
tube firmly into boiling tube. Place the other end of the delivery tube under the collecting
tube.
4. Start stop watch as soon as the first oxygen bubble enter the collecting tube. Collect any gas
produced in a 3 mins period
5. Wash boiling tube and repeat 1-4 with 12, 14, 16, 18 and 20 potato discs.
Limitations
Some O2 might be stuck in test tube, different parts of potato have different catalase concentration,
not same width of discs
Biology Unit 6 Summary Seite 7
Observing mitosis using toluidine blue stain and garlic root tips
Control variable
Species/age of garlic roots, 1M HCl concentration
Safety
1M HCl is an irritant so wear goggles and gloves, toluidine blue is harmful if ingested and will stain
clothes
Procedure
1. Cut 1 cm from several root tips of garlic roots
2. Put root tips into small sample tube with 2 cm^3 1M HCl for 5 mins
3. Put root tips in a watch glass with 5 cm^3 cold water, leave 4-5 mins and let it dry on filter
paper
4. Transfer one of the tips to a clean microscope slide. Cut 2-3mm from rounded growing tips.
5. Gently break up the root tip with a mounted needle. Add 1 small drop of toluidine blue and
leave to stain for 2 mins
6. Cover with a cover slip and blot firmly with filter paper. Press gently to spread the root tip
7. View under microscope (*400 magnification) and observe
Limitations
Cells may be overlapping so hard to see, cells may be damaged
Biology Unit 6 Summary Seite 8
Demonstrating totipotency of plant cells
Independent variable
Seedlings removed parts
Dependent variable
Number of leaves/stem length
Control variables
Temp, time left, V of agar
Extracts: same size, age, species, pH, light intensity,
Safety
Careful when using knife, use aseptic techniques when preparing apparatus. When sugar/nutrients
added to agar pathogenic bacteria may grow don’t open test tube, autoclave
Procedure
1. Sprinkle 50 seeds of white mustard onto a damp sponge placed in a plastic tray, cover w/
transparent cling film and place into propagator to germinate. When seedlings start
unfolding cotyledons (seed leaves) – ready to culture
2. Add 2.5 g of agar powder to 250 cm^3 distilled water. Heat and stir until agar dissolves
3. Pour 2 cm depth into 30 short-necked test tubes and allow to cool and solidify
4. With scissors cut explants
5. Carefully push the cut end of the explants into the agar (one explant into each test tube)
6. Cover tubes with cling film and put into propagator
7. Observe daily, measure stem length before and after experiment, count numbers of leaves
Limitations
Diff to cut explants at same position,
Biology Unit 6 Summary Seite 9
Investigating plant mineral deficiency
Independent variable
Lacks of mineral ions
Dependent variable
Nr and colour of leaves, root length, stem length, mass
Control variable
Age, size, species, set up control w/ all minerals present
Procedure
1. Fill a tube w/ ‘all nutrient’ solution using a measuring cylinder
2. Ccover top of tubes in foil ynd push down on covering so that there is a ‘well’ in the centre
3. Make a small hole in the foil
4. Measure the length of the roots
5. Gently push plantlet roots through hole so it touches solution below
6. Repeat 1-5 using other solutions (measuring cylinder rinsed out between solutions)
7. Wrap tubes in aluminium foil and place them in holder
8. Place into propagator
9. Observe
Biology Unit 6 Summary Seite 10
Extracting fibres from plants
Independent variable
Type of fibre
Dependent variable
Tensile strength
Control variables
Length of fibre, diameter of fibre, age/species of plant, part you take fibres from, how long since
extraction, how weight is attached
Safety
Careful using scalpel, wash hands after handling soaked fibres
Procedure
1. Extract fibres from plants soaked in distilled water over night using scalpel put them into
water until experiment or extract fresh fibres before each repeat
2. Place two clamp stand on table w/ 30 cm between each. Clamp one end of fibre on each
stand by wrapping them around one. Put hook into the middle of the fibre and add 10 g of
weight every 10 sec until fibre breaks. Record weight needed to break fibre.
3. Repeat 5 times for each type
Limitations
Hard to control diameter of fibres, tensile strength may be between 10 g
Biology Unit 6 Summary Seite 11
Antibacterial properties of plants
Independent variable
Type of plant
Dependent variable
Zone of inhibition
Control variable
Only soaked in ethanol
Safety
Methylated spirit toxic/highly flammable so not used when naked flames are in use, use aseptic
techniques (don’t open Petri dish w/ growing microorganism, only bin used Petri dishes after they
have been autoclaved)
Procedure
1. Put 15 cm^3 sterile nutrient agar into a test tube
2. Place tube into water bath at 97 °C so agar melts.
3. Remove tube using a cloth and allow agar to cool to 50°C
4. w/ pipette pour 1 cm^3 of bacterial broth into a sterile Petri dish using aseptic techniques
5. pour 15 cm^3 of molten agar into dish and replace the lid. Gently push plate back and forth
to mix
6. leave for an hour
7. obtain a plant extract by crushing 3g of plant material w/ 10 cm^3 of industrial Methylated
spirit and shake for 10 minutes (Methylated spirit kills any bacteria that might contaminate
the extract)
8. w/ pipette put 0.1 cm^3 of extract into 13mm Whatman antibiotic assay paper disc
9. let discs dry for 10 mins on open sterile Petri dish
10. repeat 1-9 using other plants
11. use sterile forceps to place test discs into bacterial plate together with suitable control per
plate
12. close Petri dish and tape around but not all around (could lead to growth of anaerobic
bacteria
13. incubate plates for 24 h at 25 °C
14. observe w/out opening plates (bacterial growth looks cloudy)
15. measure 3 diameters of inhibition (clear) zone and calculate a mean
16. don’t throw plates in bin(first autoclaved before thrown in dust bin)
17. wash hands thoroughly w/ soap and water
Biology Unit 6 Summary Seite 12
Study on ecology of a habitat
Procedure
1. plan how reliable/valid data will be collected to test hypothesis. Make following decisions:
most appropriate sampling method used
position/length of transect used
size/nr/position of quadrats used
species of plants/animals
method used to measure abundance
abiotic factor to record – which ones and what method used to measure them
how data will be analysed
how to avoid/minimise risks when completing fieldwork
2. collect data
3. present in appropriate way – for transect (line along which systematic records can be made)
data kite diagram
4. analyse data to reveal patterns and relationships, significant differences, correlation
coefficients,
5. interpret results using biological principles and concepts, discuss limitations and
modifications
Biology Unit 6 Summary Seite 13
Effect of temperature on hatching success of brine shrimps
Independent variable
Temperature
Dependent variable
Nr of hatched eggs
Control variable
Age, species
Brine shrimps
Easy to obtain, simple nervous system, produce many eggs
Ethical issues
Shrimps may die after hatching, stress
Procedure
1. decide on range of temp.from 5 to 35 °C to be tested
2. place 2 g of sea salt into a 100 cm^3 beaker
3. add 100 cm^3 de-chlorinated water and stir until salt dissolves
4. label beaker w/ temp.at which it will be incubated
5. place tiny pinch of egg cysts onto large sheet of white paper
6. pour few drops of salt water on graph paper and dap paper onto white sheet to pick up
around 40 eggs using a magnifying glass to count them. Cut paper so exactly 40
7. put paper into beaker. After 3 mins use pair of forceps to gently remove paper, making sure
all egg cysts have washed off into water
8. repeat 2-7 for other temps
9. repeat 2-8 several times
10. incubate beaker at all temp
11. next day count nr of hatched larvae placing a bright light next to beaker (any larvae will swim
towards light). Using fine glass pipette catch brine shrimp and place into small beaker of salt
water
12. repeat 11 daily for several days
13. release young shrimps into salt water aquarium
14. record results
Limitations
Some may not swim towards light, some eggs not visible, hard to control environmental conditions,
hard to control genetic diversity
Biology Unit 6 Summary Seite 14
How PCR amplifies DNA
Procedure
1. DNA primers (short sequence of polynucleotides which are complementary to unknown DNA strand.
Required for polymerase to bind and catalyse) are marked w/ fluorescent tags and the sample is
placed in a reaction tube containing DNA polymerase, primers and nucleotides. Tube
undergoes a cycle of temperatures
Biology Unit 6 Summary Seite 15
Gel electrophoresis
Procedure
1. double stranded DNA is cut into fragments by restriction endonucleases
2. DNA fragments pipette into well of an agaros gel in a tank
3. Gel is submerged in a buffer solution and connected to electrodes producing a potential
difference across the gel neg charged DNA fragments move to pos electrode relative to
their size (fragment lengths measure in base pairs, smaller travel further). Fragments
separate into visible bands
4. Gel is fragile
Southern blotting: DNA is transferred onti a nylon membrane by placing it directly onto
gel and a wad of dry absorbent paper on top drawing up buffer solution carrying DNA
fragments up onto membrane – separate into single strannds
5. Incubate membrane w/ excess of labelled DNA probe (complementary to target DNA) – any
unbound probes are then washed away (radioactive, fluorescent)
6. Compare bands to other DNA profile on X-ray/under UV-loght
Biology Unit 6 Summary Seite 16
Effect of different antibiotics on bacteria
Independent variable
Type of antibiotic
Dependent variable
Diameter of inhibition zone
Control variable
Temperature, time incubated, concentration of antibiotic used, nutrients in agar
Safety
Eye protection, use aseptic techniques when transferring bacteria to Petri dish, clean bench w/
antibacterial disinfectant, don’t open Petri dish when incubated, wash hands after handling
equipment w/ bacterial soap
Procedure
1. wash hands w/ bactericidal soap. Spray working area w/ disinfectant spray and wipe w/
paper towel after waiting for disinfectant to act
2. prepare agar plate seeded w/ bacteria
3. Sterilise forceps by flaming them and allow to cool. Pick up disc and soak into antibiotic for 2
minutes. Dry (ethanol before and control) use forceps to put discs onto agar plates only
lift lid so far to put in the disc. Place firmly onto agar and evenly spaced between discs (3
types and control)
Suitable control would be paper disc soaked in water
4. Tape dish w/ two pieces of adhesive tape and incubate upside down for 48 h at 30 °C
5. Wash hand w/ bactericidal soap and clean bench again
6. After incubation measure 3 diameters of inhibition zone and calculate mean (bacterial
growth is opaque, if antibiotic had effect inhibition zone is clear
7. Measure diameter of inhibition zone in mm
Limitations
Bacteria may not be evenly spread on agar, some antibiotics smaller molecule so diffuse faster and
further.
Control variable
Size of disc, use control disc, temperature, humidity, use same concentration of antibiotic
Biology Unit 6 Summary Seite 17
Rate of uptake of oxygen in respiration and rate of respiration
Dependent variable
O2 volume
Control variable
Age, mass, length, sex, species of maggots
V of coloured liquids, temperature
Safety
Eye protection and use spatula when handling soda lime (corrosive)
Procedure
1. Assemble apparatus – use manometer (Druckemessgerät) and syringe draw small volume of
paraffin (cloured liquid) so that’s free from bubbles (should come half way up each side)
2. Place 5 g of maggots into wire basket and insert into boiling tube + replace bung. Place 5 g of
dead organism into other wire basket and insert into tube B
3. Mark starting position of fluid on manometer w/ pen
4. Immerse boiling tubes into water bath and leave for 10 mins
5. Set syringe at 0.5 cm^3 mark
6. Close connection to syringe and atmosphere and immediately start stop watch. Mark
position of fluid on manometer at 1 min intervals for 5 mins
7. Then push syringe plunger so that coloured fluid moves back to starting point. Record
volume on syringe minus star 0.5 cm^3 mark and calculate V of oxygen used
8. Open connection to air
9. Measure distance travelled by liquid during each minute
10. Calculate mean rate of oxygen uptake during 5 mins
11. Repeat 10 times
12. Volume used = distance moved * r^2 * pi
Limitations
Air pressure may move liquid set up control and substract movement of liquid
Biology Unit 6 Summary Seite 18
Lung volumes and rate of breathing
Using spirometer
Independent variable
Exercise, no exercise
Dependent variable
Breaths/min
Procedure
1. Put on noseclip, wait 10 min (acclimatisation)
2. Water tank w7 soda lime lid and fixed V of O2. Lid moves up breath in, lid moves down
breathed out. Pen record changes in V as lid moved up and down
Biology Unit 6 Summary Seite 19
Habituation of snails to a stimulus
Independent variable
Time/repeats of stimulus, nr of stimulations
Dependent variable
Time of habituation/eye-stalk re-emerged
Control variable
Temp, light intensity, o2 availability, size, age, variety
Safety
Wash hand after touching snail, take care stimulus doesn’t harm snail
Procedure
1. Collect one giant African land snail and place on a clean, firm surface. Wait few mins until
snail immerged from its shell
2. Dampen a cotton wool bud w/ water
3. Firmly touch snail w/ bud between eye stalks w/ cotton wool bud and immediately star stop
watch. Measure length of time between touch and snail being full emerged from its shell w/
eye stalks fully extended
4. Repeat 3 for 10 touches, timing how long snail re-emerge each time
5. Record results
6. Write null hypothesis
7. Complete a Spearman’s rank correlation test to determine significant correlation
8. Use table of critical value to accept/reject null hypothesis. If calculated value < critical value
null hypothesis accepted
9. Write statistical conclusion
Limitations
Hard to tell when full re-emerged, hard to tell how much pressure to put on and controlling it
Biology Unit 6 Summary Seite 20
Effect of temperature on seed germination
Independent variable
Range of diff temp
Dependent variable
Nr of germinating seeds
Control variable
Time left, pH, Co2 level, water, age, size, variety
Procedure
1. Collect seeds from same parent, plant
2. Put 10 seeds on cotton wool dampened w/ a fixed volume of water and buffer solution
3. Distribute seeds evenly and put into a propagator at 10 °C. Leave for two weeks and water
again carefully
4. Count number of successfully germinated seeds (cotyledons unfolded)
5. Repeat using temps: 15, 20, 25, 30, 35, 40 °C
Limitations
When re-watering it might change temp, hard to control all env. Factors, previous plant treatment
not controlled
Biology Unit 6 Summary Seite 21
Presenting Data – Graphs
Pie charts
Used to display data that are proportions or %
Need a title and a key
Bar charts
Used when independent variable is non-numerical or discontinuous
E.g diff stages of mitosis
Bars shouldn’t touch
Histogram
Used when independent variable is numerical and data are continuous but classified into
groups
E.g nr of leaves of diff lengths
Line graphs
Used to show relationships in data which are not immediately obvious from tables
Biology Unit 6 Summary Seite 23
STATISTICS
Descriptive statistics
Mean or median
Tell sth about set of data
Hypothesis testing statistics
E.g t-test or chi-squared test
Compare sets of data
Null hypothesis
Statement that sais there is no significant difference between two sets of data
1. Find calculated value (number calculated from data using diff tests)
2. Obtain a table of critical values. Extract the critical value that applies to your
combination of circumstances. The smaller the % significance level you pick, the
more certain you will be that you are correct in rejecting null hypothesis. Generally
5% significance level fine
3. Compare calculated and critical value and reject/ accept null hypothesis
Data
Interval data
You have two sets of data and can say by how much bigger/smaller one is
E.g length
Ordinal data
The numerical value gives relative position in a series but does not tell you about the size of
interval between measurements
E.g you can say X is shorter than Y but not by how much
Devise a scale
e.g 1=very small, 2=small, 3= medium etc..
Categorical data
Comprise counts of things in categories
E.g some animals have X and other Y – now you can count frequency of occurrence in each
type ( frequency of X=20 of Y= 21
Biology Unit 6 Summary Seite 24
The Tests
T-test
Tells you if means of two sets of normally distributes (=symmetrical about mean), unmatched
(not associated), continuous data w/ interval level measurements are significantly different
to one another
Null hypothesis – no significant differences between means of the two sets of data
E.g comparing mean masses of plants frown w/ and w/out fertilisers
Spearman’s rank correlation test
Whether two variables are correlated
Use on interval or ordinal data, data in matched pairs (X associated w/ Y)
Null hypothesis – no correlation between two variables
E.g is there a correlation between temp and height of mountain
X^2 (Chi-squared test)
Shows if observed set of data (categorical) differs significantly from what we might expect,
given our null hypothesis
Null hypothesis – no significant diff between observed and expected frequencies
E.g are fruit flies in lab heterozygous?, do snails actively select specific microhabitats?
Mann-Whitney U test
Test for differences between population medians
Used in interval or ordinal level data that are unmatched
Null hypothesis – no significant diff between medians of 2 populations
E.g median body masses of X and Y
Biology Unit 6 Summary Seite 25
Satistics overview
Differences (two sites, populations, treatment)
Plot data as histogram
Plot median/mean as bar chart
Null hypothesis:
a. Mann – Whitney U test (sample size – 6-15, comparison of median)
If smallest U calculated </= to U critical H0 rejected at 5 % significance level
b. T-test (sample size > 15 and normally distributed, comparison of mean)
If t calc > that t crit H0 rejected at 5%
Correlation (pos + neg, relationships)
Plot scatter graph – line of best fit
a. Spearman’s rank correlation test
The closer r is to +1 and -1 the stonger correlation
Perfect pos - +1
Perfect neg - -1
Null hypothesis: if Rs calc > than Rs crit H0 rejected at 5%significance level ( =95%
confidence level)
Association (significant diff between observed and expected value)
a. Chi-squared test
Degrees of freedom = nr of phenotypes (samples) -1
Null hypothesis: if x^2 calc > than x^2 crit H0 rejected at 5 %
Biology Unit 6 Summary Seite 26
Ecological sampling
Random sampling
measure % cover and frequency
allows unbiased sample to be taken
pull the numbers from hat or generate by calculator
random numbers used as coordinates
Using a grid:
1. Tape measures put on ground at right angle of each other
2. Use pair of numbers as coordinates to locate sampling positions – 1st random nr gives
position on first tape, 2nd on 2nd tape
3. Fixed objects measured e.g nr of trees random nr to select which trees sampled
Systematic sampling
Measure effect of a factor on distribution of organism
If cond change across habitat transect line is used
Tape measure laid across habitat along which samples are taken
Sample points at regular intervals
Or sample points positioned in relation to some morphological feature
Quadrats
Used for sampling plant communities, slow moving or stationary animals
To find out optimum nr of quadrats required, record nr of species in each quadrat and plot
cumulative results against nr of quadrats until sampling until sampling additional quadrats
doesn’t substantially increase the nr of species recorded
Frame quadrat
Square (usually 0.25m^2 / 50cm*50cm) subdivided into 25 squares (10cm*10cm)
Abundance w/in quadrat estimated (random or systematic sampling)
Point quadrat frame
Enables pins to be lowered onto ground
Each species touched is recorded as a hit
% cover = (hits*100) / (hits+misses)
Biology Unit 6 Summary Seite 27
Methods of measuring abundance
Density
Counts number of individuals in several quadrats and takes mean to give nr/unit area(e.g
m^2). Only if individuals can be distinguished
Frequency
Number or % of sampling units in which a particular species occurs
e.g X recorded in 10 out of 25 squares percentage frequency = 40%
Percentage cover
% of ground covered by species w/in quadrats
Count nr of squares w/in quadrat that plant completely covers
Count those that are only partly covered
Estimate total nr of full squares that would be completely covered
Pitfall trap
Animals that occur on soil surface
Pooter
Animals in vegetation, sampled directly or indirectly after being knocked from the vegetation
onto white sheet)
Tullgren funnel
Insects found in leaf litter
Biology Unit 6 Summary Seite 29
Measuring abiotic factors when sampling the environment
Angle of slope – using clinometer
Aspect – use compass
Temp – use thermometer / temp probe
Light – use light meter
O2 concentration – oxygen probes in aquatic systems
Humidity – use whirling hygrometer. Needs to be spun for 60 sec above vegetation just
before readings taken from wet and dry thermometer and used to determine humidity from
calibration scale
Conductivity – ability of water sample to carry an electric current gives a measure of
dissolved mineral salts. Pure water—0 conductivity, as ion increase conductivity increases
Soil water – sample of soil is dried at 110 °C until no further loss in mass
% soil moisture = ((mass of fresh soil – mass of dry soil)*100) / mass of fresh soil
Soil organic matter – dry soil sample of known mass is heated in a crucible for 15 mins to
burn off all organic matter. Mass is re-measured after soil sample has cooled
% organic matter = ((mass of dry soil – mass of burnt soil)*100) / mass of dry soil
pH universal indicator/pH meter used after mixing a soil sample w/ water