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BIOLOGY EDEXCEL A LEVEL (TOPIC 4) EXAM QUESTIONS AND ANSWERS 2025( A+ GRADED 100% VERIFIED).
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BIOLOGY EDEXCEL A LEVEL (TOPIC 4) EXAM QUESTIONS AND ANSWERS 2025( A+ GRADED 100% VERIFIED).
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Biology Edexcel A Level (TOPIC 4)3.43: Describe the difference in structure between alpha glucose and beta glucose. - ANS- See
Diagram.
4.1: Explain how the variety of species has generally increased over time. - ANS- Variety of life
has become more extensive because species adapted to all environments in the world- even
extreme habitats.
4.10: List the 5 general points needed to explain the process of natural selection. - ANS- 1.
variety of alleles in a population
2. new alleles are produced as a result of mutations to DNA
3. a change in selection pressure means some individuals survive, others do not
4. survivors with the new allele reproduce and pass on their alleles to offspring
5. the alleles become more common in the population (change in allele frequency)
4.11: Explain the importance of meiosis to natural selection and evolution (mentioning genetic
variation.) - ANS- Meiosis is important because it creates genetic variation; this variation in the
species allows evolution to occur and means natural selection dos not wipe out an entire
population.
4.12: Define the term "gene pool" and how this relates to the amount of genetic diversity in a
population. - ANS- Gene Pool: the total of all the alleles of all the genes present in a particular
population at any give time.
large gene pool=more genetic diversity
4.13: Explain how reproductive isolation can lead to change in allele frequencies possibly
leading to the formation of a new species. - ANS- Reproductive isolation may lead to certain
alleles decreasing as the species become specialised to a new environment.
This may form a new species if the new ecosystem has extremely different environmental
conditions which organisms will adapt to.
4.14: Quote the equation for the Hardy-Weinberg calculation and use it to calculation and use it
to calculate the frequencies of alleles and genotypes in a population. - ANS- p² + 2pq + q² = 1
p²=homozygous dominant
2pq=heterozygous
q²=homozygous recessive
additionally p+q=1
, 4.15: List the assumptions that are made when working with the Hardy Weinberg equation. -
ANS- 1. Population is large
2. Mating is random amongst the males and females
3. There is no (natural) selection
4. There are no random mutations occuring
5. There is no migration into or out of the population (immigration/emigration)
4.16: State the two main components of biodiversity. - ANS- Genetic Diversity- gene pool;
which genes and alleles are present in the community
Species Diversity- which species are present in the community; how many individuals of each
species
4.17: Explain the benefit of greater genetic diversity in a population and state how is it measure
by calculating the heterozygous index. - ANS- -greater genetic diversity is good because it
allows the population to adapt
-heterozygous index (H)
= number of heterozygotes/number of individuals in the population
4.18: Describe what tends to happen to genetic diversity over time and explain why. - ANS-
-genetic diversity increases over time because: meiosis; random mutation to DNA
4.19: Explain the significance of a very low genetic diversity to humanity in terms of our
evolution history. - ANS- Humans are a relatively young species therefore out genetic diversity
is low; over time this genetic diversity will expand.
We are very vulnerable (e.g.: to diseases like HIV and the Black Death) and at risk.
4.2: Explain the negative impact that some human activities (give 3 examples) have on diversity
of species. - ANS- -Deforestation/loss of habitat leads to decrease in species richness
-Whole ecosystems are affected when species rapidly decline
-Leading to extinction or imbalance in a habitat
(deforestation, pollution, ozone damage)
4.20: State the two main sources of genetic diversity. - ANS- -meiosis [crossing over of
chromosomes, random assortment]
-random mutation to DNA
4.21: Define the terms biodiversity, species richness, endemism. - ANS- Biodiversity- genetic
diversity and species diversity.
Species Richness- a way of measuring biodiversity to count the number of species present in a
given habitat.
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