Biodiversity (Edexcel A Level Biology (A) SNAB): Flashcards
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- FrontThe Variety of Life
Define biodiversity.
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Define biodiversity.
Biodiversity is the range and variety of genes, species and habitats within a particular region.
At what three levels can biodiversity be assessed?
The range of ecosystems/habitats.
The number and abundance of species.
The genetic variation within each species.
Why are ecosystems with high species diversity usually more stable?
They are more resilient to environmental change.
If one species is lost, others can help maintain the ecosystem.
Define endemic species.
An endemic species is one that occurs naturally in only one particular area of the world and nowhere else.
Why are endemic species particularly at risk of extinction?
They have a limited range.
A threat to that one area could wipe out the whole species.
Why is genetic diversity important for a species?
It helps the population adapt to and survive environmental change.
More alleles mean a greater chance some individuals can cope with new conditions.
Why do small, isolated populations have low genetic diversity?
Inbreeding makes many individuals homozygous for many genes.
This also makes recessive genetic diseases more common.
Give three human activities that threaten biodiversity.
Any three of:
Habitat destruction and deforestation
Overexploitation and hunting
Agriculture (monoculture) or climate change
How does monoculture reduce biodiversity?
Growing a single crop supports far fewer species than a natural habitat.
Fewer plant types means fewer insects, birds and other animals.
How does climate change threaten marine biodiversity?
Dissolved CO₂ causes ocean acidification, harming shell- and coral-forming organisms.
Warmer seas cause coral bleaching, killing reefs and the species that depend on them.
When a habitat is divided into small separated areas by human activity, this is called habitat .
When a habitat is divided into small separated areas by human activity, this is called habitat fragmentation.
True or False?
A large sandy desert typically has high biodiversity.
False.
A desert has low biodiversity because conditions are similar throughout, supporting few habitats and species.
Define species richness.
Species richness is the number of different species within a community.
Define species abundance.
Species abundance is the relative number of individuals of each species within a given area.
Why can species richness alone be a misleading measure of diversity?
It counts only the number of species.
It ignores the abundance of each, so two areas can have equal richness but very different diversity.
Define quadrat.
A quadrat is a square frame placed on the ground to sample the abundance or percentage cover of plants in an area.
Why must quadrats be placed randomly?
To avoid sampling bias.
Random placement (e.g. using a grid and random numbers) makes the sample representative.
Why is random sampling used instead of counting every organism?
In large, complex habitats it is impossible to find and count every organism.
Samples are used to estimate the total for the whole habitat.
Name a technique for sampling flying insects and one for ground-dwelling invertebrates.
Sweep nets catch flying insects in long grass.
Pitfall traps catch ground-dwelling invertebrates.
Why must the same sampling method be used when comparing two habitats?
So the comparison is valid.
Different methods would introduce another variable and make results unfair to compare.
Define heterozygosity index.
The heterozygosity index (H) is a measure of genetic diversity: the proportion of individuals in a population that are heterozygous at a locus.
In a population of 620 pea plants, 350 are heterozygous (Rr) at the seed-shape locus. Calculate the heterozygosity index.
H = number of heterozygotes ÷ number of individuals
= 350 ÷ 620 = 0.56
What does a higher heterozygosity index tell you about a population?
It has a greater genetic diversity.
A higher proportion of individuals carry two different alleles.
The number of individuals of a species in an area is its abundance, while how it is spread out is its .
The number of individuals of a species in an area is its abundance, while how it is spread out is its distribution.
Define index of diversity.
An index of diversity is a measure that describes the relationship between the number of species present and the number of individuals in each.
What two things does the index of diversity take into account?
The number of species (richness).
The abundance of individuals across those species (evenness).
What does a larger index of diversity value indicate?
A higher level of biodiversity in that area.
In the diversity formula, what do N and n represent?
N is the total number of organisms in the community.
n is the total number of organisms of a single species.
Why is the index of diversity preferred over species richness alone?
It also accounts for species evenness (abundance).
This gives a fuller picture of diversity than counting species alone.
Why is it useful to calculate a diversity index for different habitats?
It allows the biodiversity of habitats to be compared fairly.
It can also show how a habitat changes over time.
A community has N = 202 and Σn(n−1) = 6884. Using D = N(N−1) ÷ Σn(n−1), calculate the index of diversity.
D = 202 × 201 ÷ 6884
= 40602 ÷ 6884 = 5.90
Do you need to memorise the index of diversity formula for the exam?
No — the formula is provided.
But you must be able to use it and interpret the values.
The the index of diversity value, the greater the biodiversity of the area.
The higher the index of diversity value, the greater the biodiversity of the area.
True or False?
Two areas with the same species richness always have the same index of diversity.
False.
If one area is dominated by a single species, its abundance is uneven, so its index of diversity is lower.
What does Σ mean in the index of diversity formula?
It means the sum of — you calculate n(n−1) for each species and add them together.
Why does an ecosystem dominated by one species have a low diversity index?
Most individuals belong to one species.
The uneven abundance gives a low index, even if several species are present.
Define habitat.
A habitat is the place where a species lives within an ecosystem.
Define niche.
A niche is the role a species plays within its habitat, including its biotic and abiotic interactions.
Why can only one species occupy a particular niche?
Two species in the same niche would compete for the same resources.
One would out-compete the other, forcing it to move niche or go extinct.
How do the three North American warbler species avoid competition?
They live in the same trees but feed at different heights.
This gives each a slightly different niche, letting them coexist.
Define adaptation.
An adaptation is a feature that increases an organism's chances of surviving and reproducing in its habitat.
Name the three types of adaptation.
Anatomical (structural).
Behavioural.
Physiological.
What is an anatomical adaptation? Give an example.
A structural feature, such as claws, horns or feathers.
It increases the organism's chance of survival.
What is a physiological adaptation? Give an example.
An internal body process, such as venom production or the ability to digest cellulose.
What is a behavioural adaptation? Give an example.
A behaviour that aids survival, such as courtship displays or defensive behaviours.
The role a species plays within its habitat is its , which is unique to that species.
The role a species plays within its habitat is its niche, which is unique to that species.
True or False?
Two species can occupy exactly the same niche in the same habitat indefinitely.
False.
They would compete, and one would out-compete the other — only one species can occupy a niche.
Why must a species be adapted to both biotic and abiotic factors?
To exploit its habitat in a way no other species can.
This lets it occupy its own unique niche.
Define natural selection.
Natural selection is the process by which individuals with advantageous alleles are more likely to survive and reproduce, increasing those alleles' frequency over time.
Define selection pressure.
A selection pressure is an environmental factor that affects an organism's chance of survival, such as predation, disease or competition.
What is the original source of new alleles in a population?
Random mutations.
These introduce new alleles and so new phenotypes.
Describe how natural selection changes allele frequencies over time.
Individuals with advantageous phenotypes survive and reproduce more.
They pass on the advantageous alleles, so these increase in frequency over generations.
What happens to non-advantageous alleles over time?
Individuals carrying them are less likely to survive and reproduce.
So these alleles decrease in frequency in the population.
What does natural selection acting over many generations ultimately lead to?
Evolution — a change in the allele frequencies of a population over time.
Give three examples of selection pressures.
Predation, disease and competition.
Who first proposed the theory of evolution by natural selection?
Charles Darwin.
What is a well-known example of natural selection leading to evolution?
The peppered moth, whose colour frequencies changed with pollution levels.
Natural selection increases the frequency of alleles in a population over time.
Natural selection increases the frequency of advantageous alleles in a population over time.
True or False?
Natural selection creates new alleles in a population.
False.
New alleles arise from mutation; natural selection changes their frequency.
Define variation.
Variation is the differences between individuals — either between species (interspecific) or within a species (intraspecific).
What does the Hardy-Weinberg principle state?
That the allele frequencies of a gene in a population will not change between generations, if certain conditions are met.
State the conditions required for the Hardy-Weinberg principle to hold.
Random mating and an infinitely large population.
No migration, mutation or natural selection.
What do p and q represent in the Hardy-Weinberg equations?
p is the frequency of the dominant allele.
q is the frequency of the recessive allele.
State the Hardy-Weinberg allele frequency equation.
p + q = 1
State the Hardy-Weinberg genotype frequency equation.
p² + 2pq + q² = 1
What does each term p², 2pq and q² represent?
p² = frequency of homozygous dominant.
2pq = frequency of heterozygous.
q² = frequency of homozygous recessive.
Which genotype frequency should you always start a Hardy-Weinberg calculation from, and why?
The homozygous recessive frequency (q²).
It is the only genotype you can identify directly, from the recessive phenotype.
In a population, 10% show the recessive phenotype. Calculate q and then p.
q² = 0.10, so q = √0.10 = 0.32
p = 1 − q = 1 − 0.32 = 0.68
What does it mean if allele frequencies in a population do change over time?
The Hardy-Weinberg conditions are not met.
Something such as migration, mutation or natural selection must be occurring.
In the Hardy-Weinberg equations, the frequency of heterozygous individuals is given by .
In the Hardy-Weinberg equations, the frequency of heterozygous individuals is given by 2pq.
True or False?
The dominant phenotype includes both homozygous dominant and heterozygous individuals.
True.
Both p² (homozygous dominant) and 2pq (heterozygous) individuals show the dominant phenotype.
What is the difference between the Hardy-Weinberg principle and the equations?
The principle states allele frequencies stay in equilibrium between generations.
The equations are used to estimate allele and genotype frequencies.
Define reproductive isolation.
Reproductive isolation is when changes in alleles or phenotypes prevent some individuals in a population from successfully breeding with others.
Define species.
A species is a group of organisms with similar characteristics that can breed to produce fertile offspring.
Name three types of change that can cause reproductive isolation.
Seasonal changes (different mating or flowering times).
Mechanical changes (mismatched reproductive parts).
Behavioural changes (different courtship behaviours).
Define speciation.
Speciation is the formation of a new species from an existing one, often when populations become reproductively isolated.
Describe how geographical isolation can lead to speciation.
A barrier separates two populations, so no gene exchange occurs.
Different selection pressures and mutations change each gene pool until they can no longer interbreed.
Give two examples of geographical barriers that can cause isolation.
A natural barrier such as a body of water or a mountain range.
A man-made barrier such as a motorway.
Why does no gene exchange occur between geographically isolated populations?
The barrier physically separates them.
They cannot meet to interbreed, so alleles are not shared between the populations.
What two processes change the gene pools of separated populations?
Different selection pressures acting on each population.
Random mutations producing new alleles in each.
Two populations of a species separated by a barrier are said to be isolated.
Two populations of a species separated by a barrier are said to be geographically isolated.
True or False?
Speciation usually happens rapidly, over a few generations.
False.
Speciation takes a very long time, as enough genetic differences must accumulate to reproductively isolate the populations.
How do you know two similar-looking populations have become separate species?
They can no longer interbreed to produce fertile offspring.
What is an example of a behavioural change causing reproductive isolation?
A change in courtship behaviour.
Individuals can no longer attract mates of the opposite sex.
Define classification.
Classification (taxonomy) is the arrangement of organisms into groups based on their evolutionary relationships.
List the taxonomic ranks from domain to species.
Domain, kingdom, phylum, class, order, family, genus, species.
Define taxon.
A taxon is any group within the hierarchical classification system, such as a genus or a family.
What is the binomial system?
A naming system giving each species a two-part Latin name: its genus then its species.
For example, Homo sapiens.
How is a binomial name written correctly?
The genus is capitalised and the species is lower case.
Both are italicised (or underlined when handwritten).
Why are binomial names useful to scientists?
They allow species to be universally identified.
The same name is used for a species across the whole world.
Name the five kingdoms.
Prokaryotae, Protoctista, Fungi, Plantae and Animalia.
How do the cell walls of fungi and plants differ?
Fungi have cell walls of chitin.
Plants have cell walls of cellulose.
Why did classification move from using physical features to molecular methods?
Physical appearance can be misleading, as unrelated species may look alike.
DNA sequencing reveals the true evolutionary relationships.
Name the three domains.
Archaea, Bacteria and Eukarya.
What evidence led to the three-domain classification system?
Molecular analysis of RNA genes.
It showed that prokaryotes fall into two distinct groups — Archaea and Bacteria.
Define molecular phylogeny.
Molecular phylogeny uses similarities and differences in molecules such as DNA, RNA or proteins to work out how closely related organisms are.
True or False?
The more similar two organisms' DNA, the more recent their common ancestor.
True.
Greater molecular similarity indicates a more recent shared ancestor.
Define conservation.
Conservation is the protection and management of species and habitats for future generations.
Define endangered species.
An endangered species is one that is being threatened with extinction.
Why is conserving a species in its natural habitat usually preferred?
All the support systems the species needs already exist there.
Examples include national parks and marine parks.
How does a seed bank conserve plant diversity?
Seeds are dried and stored in a temperature-controlled environment.
If a plant goes extinct, the stored seeds can be grown again.
Why are seeds of the same species collected from different sites for a seed bank?
To maintain genetic diversity.
Seeds from many sites carry a wider range of alleles.
How can zoos contribute to conservation?
Through captive breeding programmes to increase numbers.
Offspring can be released into the wild, and zoos support research and education.
Give two problems with using zoos for conservation.
Captive breeding of small populations can reduce genetic diversity.
Some species will not breed in captivity, and there are ethical concerns about keeping animals captive.
Why might data from zoo-based studies be unreliable?
Animals in captivity may not behave as they would in the wild.
This limits how well the findings apply to wild populations.
Give one benefit and one risk of reintroducing species to the wild.
Benefit: it helps prevent extinction and restores degraded habitats.
Risk: reintroduced organisms may carry new diseases or struggle to find food.
Breeding animals in captivity so their offspring can be released into the wild is called breeding.
Breeding animals in captivity so their offspring can be released into the wild is called captive breeding.
True or False?
All plant seeds can be successfully frozen and stored in seed banks.
False.
Some seeds, such as coffee and cocoa, cannot be frozen, so their plants must be grown on or kept as tissue cultures.
Besides preserving species, give one wider benefit of seed banks and zoos.
They support scientific research and educate the public.
This increases public engagement with conservation.
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