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
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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
Part 1 of 8Key ideas
Key ideas
Index of diversity
D = N(N − 1) ÷ Σn(n − 1); no units; minimum value 1.
Heterozygosity index
H = number of heterozygotes ÷ number of individuals.
Allele frequencies
Allele frequencies p + q = 1.
Genotype frequencies
Genotype frequencies p2 (homozygous dominant) + 2pq (heterozygous) + q2 (homozygous recessive) = 1.
q2 = frequency of individuals showing the recessive phenotype, so q = √(q2).
Hardy-Weinberg conditions
Hardy-Weinberg conditions large population, random mating, no mutation, no migration, no selection.
If observed genotype frequencies differ from Hardy-Weinberg predictions, allele frequencies are changing (evolution is happening).
Molecular phylogeny compares DNA base sequences or protein amino acid sequences: more differences = more distantly related.
Part 2 of 8Learning objectives
1
Define biodiversity and endemism and measure species richness, genetic diversity and index of diversity.
2
Explain how adaptations to a niche arise by natural selection and use the Hardy-Weinberg equation.
3
Describe the three-domain classification and the role of the scientific community in validating it.
4
Evaluate in situ and ex situ conservation, including zoos and seed banks.
Part 3 of 8Essential knowledge
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.
Part 4 of 8Process & 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
Part 5 of 8Worked 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.
Part 6 of 8Summary
1
Biodiversity includes species richness, genetic diversity and ecosystem diversity.
2
D = N(N − 1) ÷ Σn(n − 1) measures species diversity; H measures genetic diversity.
3
Species evolve by natural selection of adaptations to fit their niche.
4
p2 + 2pq + q2 = 1 tests whether allele frequencies are changing.
5
Classification uses the three-domain system, confirmed by scientific peer review.
Part 7 of 8Keep 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.
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
Part 8 of 8Compare: Compare
| Type | Definition | Example |
|---|---|---|
| Anatomical | Structural feature of the body | Thick fur and small ears in arctic fox |
| Physiological | Process inside the body | Concentrated urine in desert rodents |
| Behavioural | Way an organism acts | Nocturnal feeding to avoid heat |
| Feature | In situ | Ex situ |
|---|---|---|
| Where | In natural habitat | Outside natural habitat |
| Examples | National parks, reserves, marine protected areas | Zoos, botanic gardens, seed banks |
| Advantages | Protects whole ecosystem; natural behaviour and selection continue | Protects from poaching/habitat loss; captive breeding; gene pool stored |
| Disadvantages | Hard to control poaching, disease, climate | Small populations, inbreeding, loss of natural behaviour; reintroduction difficult |
Key terms
Command 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.
Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Biodiversity · Species · Species richness · Genetic diversity · Heterozygosity index · Index of diversity (D) · Endemism · Niche · Adaptation · Natural selection · Gene pool · Allele frequency · Hardy-Weinberg equation · Three-domain system
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
1
Use specification keywords exactly (e.g. enzyme–substrate complex, active site, complementary).
2Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
3Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
4
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
5Avoid vague words
“it”, “stuff”, “goes up”, “energy is made”. Name the substance and the process.
6
Extended (6-mark) responses are marked on content AND a logical, linked line of reasoning.
Words to avoid
1
the organism adapts in order to surviveindividuals with advantageous alleles are more likely to survive and reproduce
2
the mutation was caused by the environment to help itmutations arise randomly; the environment selects
3
the gene becomes more commonthe frequency of the advantageous allele increases in the gene pool
4
biodiversity is the number of speciesspecies richness is the number of species; biodiversity also includes genetic and ecosystem diversity
5
in the Hardy-Weinberg equation p2 is the dominant phenotypep2 is the homozygous dominant genotype frequency; dominant phenotype = p2 + 2pq
Marked practiceQuizzes for this lesson
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