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4.1Topic 4 · Biodiversity and Natural Resources

Biodiversity — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

30 min read 38 parts Lesson 2 of 22 2 quizzes

📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision
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Lesson summary

Biodiversity Edexcel A Level Biology SNAB notes: Define biodiversity and endemism and measure species richness, genetic diversity and index of diversity.Index of diversityD = N(N − 1) ÷ Σn(n − 1); no units; minimum value 1.Heterozygosity indexH = number of heterozygotes ÷ number …

  • Allele frequencies
  • Genotype frequencies
  • Hardy-Weinberg conditions
  • Natural selection
  • Classification is hierarchical
  • Sampling techniques

Section 1 of 38Biodiversity

Biodiversity can be compared between habitats using species richness (simple count) or the index of diversity, which also includes relative abundance (evenness).
Genetic diversity within a species can be assessed by the number of alleles or heterozygosity index; low genetic diversity reduces the ability to adapt to change (e.g. disease).
Each species occupies a niche; features that allow survival in that niche are adaptations — anatomical, physiological or behavioural.
Natural selection
Natural selection variation exists due to mutation; a selection pressure (predation, disease, competition, climate) acts; individuals with advantageous alleles survive and reproduce more; they pass alleles on; allele frequency increases over many generations.
Speciation occurs when populations are reproductively isolated (geographically or by behaviour/timing), experience different selection pressures and accumulate differences until they can no longer interbreed to produce fertile offspring.
The Hardy-Weinberg principle predicts that allele and genotype frequencies stay constant under ideal conditions; comparing real data with prediction shows whether selection or other factors are acting.
Classification is hierarchical
Classification is hierarchical domain, kingdom, phylum, class, order, family, genus, species; the binomial system names genus and species (e.g. Homo sapiens).
Carl Woese proposed three domains in 1990 using rRNA sequence data; Archaea differ from Bacteria in membrane lipids, cell wall (no peptidoglycan) and RNA polymerase, and are more similar to Eukarya in some genes.
New ideas are validated by the scientific community through publication in peer-reviewed journals, conferences and independent replication before being accepted.
Zoos
Zoos captive breeding programmes use studbooks to avoid inbreeding and maximise genetic diversity; reintroduction to the wild; research and education.
Seed banks store large numbers of genetically diverse seeds in a small space for long periods at low cost, protecting against extinction; but seeds may not reflect later evolution in the wild.
Endemic species are especially vulnerable because they exist in only one place, so habitat destruction there could cause extinction.
Sampling techniques
Plants and slow-moving organisms are sampled with quadrats placed at random grid coordinates.
  • Flying or long-grass insects are caught with a sweep net, ground-dwelling invertebrates with buried pitfall traps,
  • and stream invertebrates by kick-sampling upstream of a net.
  • Use the same method and many samples when comparing habitats.
Human threats to biodiversity
Biodiversity is reduced by habitat loss and fragmentation (small isolated populations suffer inbreeding), overexploitation such as overfishing and hunting, intensive agriculture (monocultures, hedgerow removal, pesticides killing non-target species, fertiliser run-off causing eutrophication) and climate change.
Inbreeding
In small or isolated populations related individuals breed, so more loci become homozygous and genetic diversity falls. Harmful recessive alleles are expressed more often, and the population is less able to adapt. H can be averaged over many loci to estimate diversity across the genome.
Isolating mechanisms
Reproductive isolation may be seasonal (breeding or flowering at different times), mechanical (reproductive structures no longer compatible) or behavioural (courtship signals no longer recognised).
  • It can follow geographical separation or arise from new mutations within one population.
Five kingdoms
Prokaryotaeno nucleus.
  • Protoctista: mostly single-celled eukaryotes, e.g. protozoa (no wall) and algae.
    • (cellulose wall, chloroplasts)
  • Fungi: chitin walls, saprotrophic, spores, hyphae.
  • Plantae: multicellular autotrophs with cellulose walls and chloroplasts.
  • Animalia: multicellular heterotrophs with no cell wall.
Competitive exclusion
If two species try to share one niche they compete for the same resources until one is outcompeted and either dies out locally or shifts to a slightly different niche. Similar species can coexist by partitioning resources, e.g. feeding at different heights in the same tree.
Seed bank limitations
Seeds lose viability over time, so samples must be grown periodically to collect fresh seed. Some species, e.g. cocoa and coffee, have seeds that cannot survive drying and freezing, so they are conserved as living plants or tissue cultures instead.
Reintroduction
Releasing captive-bred animals or plants restores wild populations and benefits species that depend on them. Risks: released organisms may carry new diseases into the habitat, and captive-raised animals may lack skills to find food, avoid predators or communicate with wild members.
Zoo limitations
Some species rarely breed in captivity, captive populations are small so genetic diversity can fall, enclosures may not meet specialised needs, and keeping animals raises ethical concerns. Animals may behave unnaturally, so research findings may not apply to wild populations.

Section 2 of 38Process & sequence

1
Seed bank: collect seeds from many individuals across the range to capture genetic diversity.
2
Clean and dry the seeds to low water content, then test a sample for viability by germination.
3
Store seeds at low temperature (e.g. −20 °C) and low humidity to slow metabolism and extend viability.
4
Periodically germinate samples to check viability; grow plants to produce fresh seed when viability falls.
5
Use stored seeds for research, restoring habitats or reintroducing species to the wild.

Natural selection leading to adaptationwrite these steps in this order; each step is a marking point.

1
Random mutation produces new alleles, giving variation in the population
2
A selection pressure acts on the population
3
Individuals with an advantageous allele are more likely to survive and reproduce
4
They pass the advantageous allele on to their offspring
5
Allele frequency increases in the gene pool over many generations

Section 3 of 38Compare

Types of adaptation
TypeDefinitionExample
AnatomicalStructural feature of the bodyThick fur and small ears in arctic fox
PhysiologicalProcess inside the bodyConcentrated urine in desert rodents
BehaviouralWay an organism actsNocturnal feeding to avoid heat
In situ vs ex situ conservation
FeatureIn situEx situ
WhereIn natural habitatOutside natural habitat
ExamplesNational parks, reserves, marine protected areasZoos, botanic gardens, seed banks
AdvantagesProtects whole ecosystem; natural behaviour and selection continueProtects from poaching/habitat loss; captive breeding; gene pool stored
DisadvantagesHard to control poaching, disease, climateSmall populations, inbreeding, loss of natural behaviour; reintroduction difficult

Section 4 of 38Worked examples

Worked examples
A pond contains 10 species A, 5 species B and 5 species C. Calculate the index of diversity.
  • N = 20.
    • N(N − 1) = 20 × 19 = 380.
    • Σn(n − 1) = 10×9 + 5×4 + 5×4 = 90 + 20 + 20 = 130.
    • D = 380 ÷ 130 = 2.92 (3 s.f.).
In a population, 16% of people show a recessive phenotype. Calculate the frequency of heterozygotes.
  • q2 = 0.16, q = √0.16 = 0.4. p = 1 − 0.4 = 0.6. 2pq = 2 × 0.6 × 0.4 = 0.48, so 48% are heterozygous.
In a sample of 80 animals, 28 were heterozygous at a locus. Calculate H.
  • H = heterozygotes ÷ total = 28 ÷ 80 = 0.35.

Section 5 of 38Keep going

Biodiversity Edexcel A Level Biology SNAB: what to do next

These Biodiversity Edexcel A Level Biology SNAB notes covered the key ideas, worked examples and exam technique for this topic. Check your Biodiversity Edexcel A Level Biology SNAB understanding with the practice questions below, then reread any Biodiversity Edexcel A Level Biology SNAB point you were unsure about before moving on.

Biodiversity Edexcel A Level Biology SNAB: revision checklist

1
Revise the main Biodiversity Edexcel A Level Biology SNAB definitions until you can write them from memory.
2
Practise Biodiversity Edexcel A Level Biology SNAB exam questions under timed conditions.
3
Link each Biodiversity Edexcel A Level Biology SNAB idea to a diagram or a worked example.
4
List the common Biodiversity Edexcel A Level Biology SNAB mistakes and how to avoid them.
5
Explain one Biodiversity Edexcel A Level Biology SNAB idea out loud as if teaching a friend.
6
Summarise Biodiversity Edexcel A Level Biology SNAB in five key points on a revision card.
7
Check which command words appear most often in Biodiversity Edexcel A Level Biology SNAB questions.
1
Practice: Biodiversity Edexcel A Level Biology SNAB practice questions
2
Previous lesson: 3.4 Differentiation & Variation — 9BI0 Notes
3
Next lesson: 4.2 Resources from Plants — 9BI0 Notes
4
Course: Edexcel A Level Biology A (snab) 9BI0 — all units
5
Official syllabus: Pearson Edexcel A Levels

Section 6 of 38What biodiversity is

Biodiversity is the variety and variation of life: all the variation that exists within and between all forms of life. It covers the range of genes, species and habitats in a region and is assessed at three levels: habitat (ecosystem) diversity (the range of habitats), species diversity (the number of species and their abundance) and genetic diversity (the variety of alleles and genes within each species).

Section 7 of 38Diversity and stability; genetic diversity

Ecosystems with high species diversity are usually more stable than those with lower diversity because they are more resilient to environmental change.

1
For example, in the pine forests of Florida the ecosystem is dominated by one or two tree species.
2
If a pathogen targets one of the dominant species, the whole population could be wiped out and the ecosystem might collapse.
3
The genetic diversity within a species is the diversity of alleles and genes in its genome.
4
Individuals of the same species have the same genes but not necessarily the same alleles.
5
Genetic diversity can be measured by the proportion of genes that have more than one allele and how many alleles each gene has.

Section 8 of 38Human activity and biodiversity

Evolution by natural selection has increased the variety of life over time, but human activities have recently threatened many species with extinction.

Human activity and biodiversity
The global human population has grown exponentially for the last 150 years.
Reasons include improved technology giving abundant food (increasing birth rate), improved medicine and sanitation (lower death rate and higher life expectancy).
A conflict therefore exists between human needs and the conservation of biodiversity.

The main factors affecting biodiversity today are habitat loss, overexploitation, pollution, climate change, intensive agriculture and introduced species.

Habitat loss
Many human needs lead to natural environments being destroyed: land cleared for agriculture, industry, energy production, housing, transport, leisure facilities, waste disposal and water storage results in habitat loss, in which plants and animals completely lose their habitats.
Habitat fragmentation also isolates populations, reducing gene flow and genetic diversity.

Section 9 of 38Why biodiversity matters

There are ecological, economic and ethical reasons.

1
Ecologically, each species has a role in nutrient cycling, pollination and food webs.
2
Economically, wild species provide medicines (about a quarter of prescribed drugs derive from plants), crop varieties for breeding, timber, fisheries and tourism.
3
Ethically, many believe all species have a right to exist and that we have a duty to future generations.
4
Measures of biodiversity help monitor the health of an environment over time.

Section 10 of 38Worked examples

  1. Define genetic diversity. [1]1 mark

  2. Explain why an ecosystem with more species is more stable. [3]3 marks

  3. Give two reasons for human population growth. [2]2 marks

Section 11 of 38Overexploitation and modern farming

Overexploitation means taking organisms from the wild faster than they can reproduce, such as hunting animals for bush meat in developing countries (including primates such as monkeys and chimpanzees, and other mammal and reptile species).

Overexploitation and modern farming
After the Second World War there was a massive change in how food was produced: more food was needed, at a quicker rate,
  • and modern farming practices began.
These include monoculture (large fields of one crop), removal of hedgerows to make larger fields, drainage of wetlands,
  • and use of pesticides, herbicides and artificial fertilisers.
Each reduces the habitats and food sources available to wild species, harming pollinators and other insects and thus the species that feed on them; fertiliser runoff causes eutrophication;
  • and the loss of genetic variety in crops and livestock reduces genetic diversity.

Section 12 of 38Climate change and ocean acidification

Global warming reduces biodiversity as species must move or adapt to rising temperatures.

Some species, such as plants, may not be able to move or change their distributions fast enough and may go extinct.
Ocean acidification
Global warming and the human-produced CO2 that is its primary cause also threaten marine biodiversity: increasing atmospheric CO2 leads to more CO2 dissolving in seawater, lowering its pH (ocean acidification).
This negatively affects organisms that need calcium carbonate for shells and skeletons, such as plankton and coral polyps, damaging whole food webs.

Section 13 of 38Measuring biodiversity in a habitat

A habitat is the place where an organism lives; habitats vary in size, from very large (grasslands) to very small (a puddle). Species richness is the number of different species in a habitat. Species abundance is the number of individuals of each species.

Measuring biodiversity in a habitat
Species diversity takes both richness and abundance into account.
For example, two areas may have the same species richness but different abundance patterns; the area in which individuals are spread more evenly across the species has the higher species diversity,
  • whereas one where a single species dominates has lower diversity.

Measuring biodiversity can be difficult. It requires identifying and cataloguing all organisms present to build a species list and estimating the size of each population. Because habitats are usually too large to count everything, sampling is used, which must be random to avoid bias and large enough to be representative.

Section 14 of 38Evaluating the impact of farming

Intensive farming increases yield but at a cost to biodiversity. Fertiliser run-off causes eutrophication: algae bloom, block light, die, and are decomposed by bacteria which use up oxygen, killing fish. Pesticides can bioaccumulate in food chains. Agri-environment schemes aim to reduce these effects by leaving field margins, restoring hedgerows and rotating crops, balancing food production with conservation.

Section 15 of 38Worked examples

  1. Explain how ocean acidification affects coral. [3]3 marks

  2. Two habitats each have 5 species. Habitat A has 20 individuals of each; habitat B has 96 of one species and 1 of each of the other four. Which has higher diversity? [2]2 marks

  3. Give two ways modern farming reduces biodiversity. [2]2 marks

Section 16 of 38Quadrats and sampling bias

Quadrats measure the distribution and abundance of plants.

1
Quadrats of different sizes can be used depending on what is measured and the space available.
2
They must be placed randomly (for example with random coordinates from a random number generator) to avoid sampling bias.
3
In a quadrat you can record species frequency, number of individuals, or percentage cover.
4
Percentage cover is useful when counting individuals is difficult.
5
Because some squares may contain several species and some none, the total percentage cover may be over or under 100%.

Section 17 of 38Sampling animals

Quadrats are suitable for plants, but for many animals it is not possible to use them to measure abundance and distribution. Methods include a pitfall trap (a container sunk into the ground to catch ground-dwelling invertebrates), kick sampling in streams (disturbing the stream bed for a fixed time with a net held downstream and identifying what is caught), sweep nets for insects in vegetation, and mark-release-recapture for mobile animals.

Section 18 of 38Genetic diversity

The greater the allele variety within a species, the higher the genetic diversity.

1
Measuring genetic diversity is useful to investigate changes in a population over time or to compare two populations or species.
2
It can be considered through the phenotype (observable features), though DNA analysis is more direct,
  • and through the proportion of genes with more than one allele.
3
A heterozygosity index is: H = number of heterozygotes / number of individuals in the population.
4
This value can estimate the genetic diversity of the entire genome of the population.

Section 19 of 38Comparing species diversity: the index of diversity

Once the abundance of species has been recorded, species diversity can be calculated. It considers both the number of species and their abundance. Simpson's index of diversity is D = N(N - 1) / Σn(n - 1), where N is the total number of individuals of all species and n is the number of individuals of each species.

Comparing species diversity: the index of diversity
Calculate N(N - 1) to find value A.
For each species calculate n(n - 1), and add them to give value B.
Divide A by B to give D.

The higher D is, the greater the biodiversity of the area. Example: a sample has 3 species with 10, 5 and 5 individuals; N = 20, A = 20 x 19 = 380; B = 10 x 9 + 5 x 4 + 5 x 4 = 90 + 20 + 20 = 130; D = 380 / 130 = 2.9. It is useful to calculate D for several habitats to compare them.

Section 20 of 38Worked examples

  1. Calculate D for a sample with 6, 3 and 1 individuals of three species. [3]3 marks

  2. Explain why quadrats must be positioned randomly. [2]2 marks

  3. There are 40 individuals, 12 heterozygous. Calculate the heterozygosity index. [1]1 mark

Section 21 of 38Niches and adaptations

The role a species plays in its habitat is its niche, including its biotic interactions (what it feeds on and what feeds on it) and its abiotic interactions (conditions it tolerates). Species that appear to share a niche usually differ slightly: several bird species feed on spruces and other conifers but spend their time eating in different parts of the trees, which reduces competition.

Adaptations are features that increase an organism's chances of surviving and reproducing: anatomical (structural features such as horns, claws, feathers), physiological (processes such as the ability to produce venom or to concentrate urine) and behavioural (such as courtship or defensive behaviour).

Section 22 of 38Natural selection

Variation exists within a speciesdifferences between individuals can be interspecific (between species) or intraspecific (within a species).

Natural selection: (1) variation exists, caused by mutation and sexual reproduction; (2) more offspring are produced than can survive; (3) selection pressures (predation, disease, competition) act on the population; (4) individuals with advantageous alleles are more likely to survive and reproduce; (5) they pass on those alleles to offspring so allele frequency changes over generations,
  • leading to adaptation and evolution.
Peppered moth
The peppered moth is a well-known example: before industrialisation pale moths were camouflaged on lichen-covered trees;
  • as soot darkened the trees, dark moths were better camouflaged, escaped predation and the frequency of the dark allele rose.

Section 23 of 38Hardy-Weinberg equations

The Hardy-Weinberg principle states that if certain conditions are met, the allele frequencies of a gene in a population will not change from one generation to the next.

Conditions: mating is random; no mutations; no selection; no migration (no gene flow); the population is large; and no genetic drift.
P + q = 1
With two alleles, with p = frequency of the dominant allele and q = frequency of the recessive allele: p + q = 1 and p2 + 2pq + q2 = 1.
The chance of being homozygous dominant is p2 (a dominant allele from both parents, p x p).
The chance of being heterozygous is 2pq (dominant from father and recessive from mother, or the reverse).
Homozygous recessive is q2.

Worked example

  • if q2 = 0.1024 (fff), then q = 0.32 and p = 1 - 0.32 = 0.68.
  • Then p2 = 0.68 x 0.68 = 0.46 (FF), 2pq = 2 x 0.68 x 0.32 = 0.44 (Ff), and q2 = 0.10.
  • Check: 0.46 + 0.44 + 0.10 = 1.

Section 24 of 38Applying natural selection to bacteria

The same principles explain antibiotic resistance: random mutation gives a few bacteria resistance; the antibiotic is a selection pressure; the resistant bacteria survive, reproduce and pass on the resistance allele, so its frequency rises. Note that the mutation exists before the antibiotic is used; the antibiotic does not cause it.

Section 25 of 38Worked examples

  1. In a population 1 in 2500 people has a recessive condition. Calculate q and the carrier frequency. [4]4 marks

  2. Explain how natural selection led to dark peppered moths becoming common. [4]4 marks

  3. State two conditions for the Hardy-Weinberg principle to apply. [2]2 marks

Section 26 of 38Reproductive isolation and speciation

Organisms of the same species share characteristics and can produce fertile offspring. Reproductive isolation occurs when changes in the alleles and phenotypes of some individuals in a population prevent them from successfully breeding with others.

Examples include changes that cause: different breeding seasons or times of day; different courtship behaviour; changes in the shape of reproductive organs;
  • and gametes that are incompatible.
Speciation
Reproductive isolation leads to speciation, the formation of new species.
Allopatric speciation
In allopatric speciation populations become geographically isolated (for example by a mountain or sea),
  • so no gene flow occurs;
    • different selection pressures and mutations cause allele frequencies to diverge;
    • eventually the populations can no longer interbreed, even if they meet again.
Speciation takes a very long time, as enough genetic differences must accumulate to isolate the populations.

Section 27 of 38Classification and taxonomy

Taxonomy is the practice of biological classification.

Classification and taxonomy
The phylogenetic classification system groups species based on their evolutionary origins and relationships.
Taxa
Grouping organisms into taxa makes them easier to understand and remember.
The hierarchy is Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
Higher ranks contain more organisms with less similarity; lower ranks contain fewer organisms with more similarity.
Many species with similar genotypes and phenotypes may be grouped in a genus, yet remain separate species because they cannot produce fertile offspring.

Section 28 of 38The five kingdoms

Prokaryotae (bacteria)
Prokaryotae (bacteria) prokaryotic cells with no nucleus; typically less than 5 µm in size.
Protoctista
Protoctista eukaryotic, mostly single-celled organisms such as algae and amoebae.
Fungi
Fungi eukaryotic, with chitin cell walls; some consist of long threads called hyphae that form the mycelium; larger fungi have fruiting bodies that release large numbers of spores; they feed saprotrophically.
Plantae
Plantae multicellular eukaryotes with cellulose cell walls, large, usually permanent, vacuoles for support, and chloroplasts for photosynthesis.
Animalia
Animalia multicellular eukaryotes without cell walls that feed heterotrophically and usually have nervous coordination and move.

Section 29 of 38Worked example: speciation of island birds

Suppose a population of finches reaches a group of islands and some individuals colonise a different island.

1
The islands have different seed types, so beaks of different shape are selected.
2
Over many generations different mutations accumulate in each population and allele frequencies diverge, with no gene flow.
3
If the populations meet again and cannot interbreed to produce fertile offspring, speciation is complete.
4
Note that interbreeding that produces infertile offspring, such as a mule, shows the parents are different species.

Section 30 of 38Worked examples

  1. Explain how geographical isolation can lead to speciation. [4]4 marks

  2. Define species. [1]1 mark

  3. Name the taxon below family. [1]1 mark

Section 31 of 38Binomial names and the three domains

A species is given a two-part Latin name, the binomial.

It is typed in italics or underlined when handwritten; the genus begins with a capital letter and the species name with a lower-case letter (e.g. Homo sapiens).
The four kingdoms of eukaryotes (Protoctista, Fungi, Plantae, Animalia) fall under the domain Eukarya.
Domains
A newer system places all organisms in three domains: Archaea (prokaryotes), Bacteria (prokaryotes) and Eukarya.
Molecular phylogeny
The system is based on molecular phylogeny: comparing the base sequences of DNA and rRNA,
  • and the amino acid sequences of proteins, shows how closely related organisms are.
Archaea differ from bacteria in their ribosomal RNA, membrane lipids and cell wall composition.
This is an example of how new data changes classification, and scientists critically evaluate and accept evidence through peer review.

Section 32 of 38Why conservation matters

When species go extinct there is a decrease in overall biodiversity. Many species have already gone extinct, and others are endangered, which means threatened with extinction. Reasons for conservation include ethical reasons, ecosystem stability, the potential for new medicines and crops, and economic value from tourism.

Section 33 of 38Seed banks

Seed banks store seeds of endangered and useful plants under cold, dry conditions.

Seed banks
Advantages of seed banks:
  • Large numbers of species and genetic variants can be stored in little space.
  • Seeds can be kept for decades and grown later.
  • They provide an opportunity to investigate how to grow plants from seeds.
  • They provide a stock of endangered plants that may be useful to humans (medicinal or crop plants), taking pressure off wild populations.
  • They educate people and increase interest in conservation.
  • Local people can be trained to set up community seed banks.
Limitations: data from seed banks may not be representative of wild populations because of the small, genetically limited sample size; some seeds do not survive freezing;
  • and seeds do not preserve the habitat.

Section 34 of 38Zoos and captive breeding

Zoos contribute to research on the behavioural, physiological and nutritional needs of species, which aids conservation in the wild.

Zoos and captive breeding
Captive breeding programmes have helped some species: the oryx, an antelope-like species, was saved from extinction and reintroduced into the wild in Africa.
By contrast pandas have been in captive breeding for over 60 years and none has been reintroduced.
Problems of reintroduction include that released organisms may carry new diseases that harm other organisms in the habitat; reintroduced animals may lack the ability to find food or communicate with members of their species; captive populations have small gene pools,
  • reducing genetic diversity;
  • and the original cause of decline must be addressed.
    • (such as habitat loss)

Section 35 of 38Worked examples

  1. Write the binomial for the lion, Panthera leo, correctly. [1]1 mark

  2. Evaluate seed banks as a way of conserving plant species. [4]4 marks

  3. Give two problems of reintroducing zoo-bred animals. [2]2 marks

Section 36 of 38Key terms

TermMeaning
BiodiversityVariety of life: genes, species and habitats.
Species diversityNumber of species and their relative abundance.
Genetic diversityVariety of alleles within a species.
Habitat lossDestruction of the place where organisms live.
TermMeaning
Species richnessNumber of species in a habitat.
Species abundanceNumber of individuals of a species.
Ocean acidificationFall in seawater pH due to dissolved CO2.
OverexploitationHarvesting faster than a population can recover.
MonocultureGrowing a single crop species over a large area.
TermMeaning
QuadratSquare frame used to sample organisms in a small area.
Percentage coverProportion of a quadrat covered by a species.
Pitfall trapContainer sunk in soil to catch ground invertebrates.
Index of diversityMeasure of species diversity that takes richness and abundance into account.
Heterozygosity indexProportion of individuals that are heterozygous.
TermMeaning
NicheRole of a species in its habitat.
AdaptationFeature that increases survival and reproduction.
Natural selectionDifferential survival and reproduction of individuals with favourable alleles.
Allele frequencyProportion of an allele in a population.
Hardy-Weinberg principleAllele frequencies stay constant if conditions are met.
TermMeaning
SpeciationEvolution of new species.
Reproductive isolationInability of populations to interbreed successfully.
TaxonomyScience of classifying organisms.
TaxonA group in the classification hierarchy.
HyphaeThreads that make up a fungal mycelium.
TermMeaning
BinomialTwo-part Latin name: genus then species.
DomainHighest level in the three-domain classification.
Molecular phylogenyUsing DNA and protein comparison to work out evolutionary relationships.
Endangered speciesSpecies threatened with extinction.
Seed bankFacility storing seeds for conservation.

Section 37 of 38Command terms

Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.

Section 38 of 38Exam technique

1
Treating biodiversity as the same as the number of species — it has three levels.
2
Saying a forest dominated by one species is biodiverse.
3
Saying that a large number of individuals means high biodiversity — it also needs many different species and alleles.
4
Thinking genetic diversity means the same as the number of species.
1
Equating species richness and diversity.
2
Saying CO2 raises seawater pH.
3
Saying farming only reduces biodiversity through habitat loss — pesticides and fertilisers also harm species.
4
Writing that global warming changes pH of the sea directly — it is dissolved CO2 that does so.
Avoid these mistakes
Using n squared rather than n(n - 1).
Saying a higher D means lower diversity.
Placing quadrats where there are more plants.
Avoid these mistakes
Taking the square root of the frequency of the dominant phenotype to find p.
Forgetting that p + q = 1.
Saying individuals evolve — populations evolve.
1
Saying speciation is rapid.
2
Saying animals of different species cannot mate — they may, but not produce fertile offspring.
3
Saying that two species can never mate — they sometimes can, but not produce fertile offspring.
4
Stating that classification is only based on appearance — phylogenetic classification uses evolutionary relationships.
Avoid these mistakes
Writing the genus in lower case.
Saying archaea are eukaryotes.
Using 'Species' as the capitalised word — the genus has the capital letter, species does not.

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