Summary OCR A Level Biology A* Biodiversity Detailed Notes
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Course
Module 4 - Biodiversity, evolution and disease
Institution
OCR
These A-Level Biology notes are designed for students aiming for top grades and a future in medicine. They are both aesthetic and detailed, offering comprehensive coverage of the syllabus while being visually engaging.
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Biodiversity
1. Biodiversity
Biodiversity
- Biodiversity = a measure of the varia3on found in the living world, the genes that each kingdom contains
and the ecosystems of which they form a part
- Habitat biodiversity = the range of habitats in which different species live e.g. sand dunes, woodland,
meadows, streams, ponds etc
- Species = individual organisms very similar in appearance, anatomy, physiological, biochemistry and
gene3cs, so can interbreed freely to produce fer3le offspring
- Species biodiversity = range of organisms found in a habitat, dependent on species richness – the number
of species of organisms, versus the species evenness = the representa3on of each species
- Gene3c varia3on = between individuals in the same species, can create breeds within a species
Using samples to measure biodiversity of a habitat
- Biodiversity of a habitat is measured through the species present and how many of each
- It is imprac3cal to count every fungi/bacteria/single-celled organism and es3mates vary
- A sample is used to count the organisms in a small por3on and mul3ply to create an es3mate
representa3ve of the habitat
Type of sampling How sampling is carried out Advantages Disadvantages
Random - Randomly select sample sites by Data not biased due May not cover all areas of the habitat
deciding where beforehand to random sampling equally -> species with low presence
- Use randomly generates numbers as may be missed -> underes3mate of
coordinates or use a portable global- biodiversity
posi3oning satellite system to find
the exact posi3on
Non- Opportunis3c - Researcher makes sampling decisions Easier and quicker Data may be biased as the presence of a
random based on prior knowledge or the data than random large/colourful species may en3ce the
they collected sampling researcher to include that one ->
- May deliberately sample an area they overes3mate of its importance ->
can see a par3cular species overes3mate of biodiversity
Stra3fied - Divide habitat into areas that appear All areas of a habitat May lead to over-representa3on of some
different and sample each separately are sampled and areas e.g. dispropor3onate samples
species are not taken in small areas that each look
under-represented different
Systema3c - Samples taken at fixed intervals Useful when there is Only species on the line/within the belt
across the habitat a clear gradient in can be recorded, others will be missed ->
- Line transects and belt transects some environmental underes3mate of diversity
used factor
2. Sampling plants
Sampling a habitat
Prepara<on
- Suitable clothing and footwear for expected weather condi3ons; sampling apparatus; clipboard, pen and
paper for records; appropriate keys to iden3fy plants; camera or smartphone to record specimens and grid
loca3ons; results table prepared for records
At the site
- Use a range of sampling techniques and modify random sampling if the habitat is not homogeneous
- Use opportunis3c/stra3fied sampling by moving some of the sample sites into areas that look different
- Consider the effect your presence has on the habitat and cause as liUle disturbance as possible
Sampling plants
- Iden3fy and count large plants individually
- For small plants calculate a value of percentage ground cover occupied by each species
Using random quadrats
, - Quadrat = square frame used to define the size of the sample area, oYen 50cm/1m per side
- Random sampling -> generate random numbers and use them as coordinates to place quadrats in a habitat
- Use a tape measure or count even paces to place at the correct loca3on
-
- Iden3fy plants inside quadrat + calculate % cover for abundance, using the smaller divisions of 100 squares
to es3mate more accurately
- Point frame = frame of long needles lowered into the quadrat, count plants touching the needles, do 100
readings so each plant touching = 1% cover
- Record bare ground too
- 300-400% is possible as one plant can touch mul3ple needles
- Place at regular intervals within quadrat to remove bias -> systema3c sampling
Using a transect
- Transect = line of string or tape measure taken across a habitat, samples taken along it
- Use a line transect in large habitats and record plants touching line at set intervals across
- Can use quadrat at set intervals along line – an interrupted belt transect – providing quan3ta3ve data
- Con3nuous belt transect = quadrat placed beside the line and moved along to study band/belt in detail
3. Sampling animals
Sampling animals by observa<on
- Hard to collect quan3ta3ve data: large ones can detect human presence and hide, small ones hide and
move too fast to count accurately
- Presence can be iden3fied from footprints/droppings/own pellets/rabbits’ burrows/deer damage on trees
- Popula3on size can be es3mated by using DNA sequencing of droppings to dis3nguish between individuals
Collec<ng samples of live animals
- Plan by bringing appropriate apparatus for chosen sampling technique
Catching invertebrates
- Low vegeta3on (not too woody) or water: Sweep nefng = walking through habitat with stout net,
sweeping through vegeta3on in wide arcs to catch small animals e.g. insects, and empty onto a white
sheet to iden3fy them -> a pooter can be used to collect animals before they fly away
- Trees: spread out a white sheet under a branch and knock the branch with a stout s3ck -> small animals
get dislodged and fall onto sheet (again may crawl/fly away)
- Pihall trap = trap set in soil to catch small animals, small container buried in the soil with rim below surface
-> animals moving through plants/leaf liUer fall into trap, some water/paper stop animals crawling out,
shelter from rain so doesn’t fill up
- Tullgren funnel = collects small animals from leaf liUer, leaf liUer placed in funnel -> light above liUer drives
animals downwards as liUer dries and warms -> fall through mesh screen -> collected in jar below
- Light trap = collects flying insects at night using UV light to aUract insects -> alcohol-containing vessel
under light catches insects
Trapping small animals
- Technique depends on habitat and type of animal, a licence is needed to trap some animals, and should
never harm the animal
- Longworth trap used for small mammals – humane so no harm, must be monitored regularly to release
trapped animals, popula3on size can be calculated with mark-and-recapture:
1. Capture sample of animals + mark each individual in some way to cause no harm = C1
2. Release marked animals + leave traps for another period of 3me
3. Number captured again = C2 + number of second capture with original markings = C3
4. Total popula3on = (C1 x C2) / C3
- Can calculate size of some insect popula3ons by this technique
- Bird popula3on can be es3mated by using a ringing technique to iden3fy individuals, larger mammals can
be tagged -> both require skill + experience so only done with permit from relevant authori3es
4. Calcula<ng biodiversity
Es<ma<ng biodiversity
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