Continuous and discontinuous variationOxford AQA IGCSE Biology: Flashcards

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Define variation in the context of biology.

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Define variation in the context of biology.: Variation is the differences that exist between individuals of the same species. These differences can be genetic, environmental or both.
Distinguish between continuous and discontinuous variation, giving an example of each.: Continuous variation: characteristics that show a range of values with no distinct categories (e.g. height, mass, skin colour). Discontinuous variation: characteristics with distinct categories with no intermediates (e.g. blood type, presence/absence of horns).
Name the three causes of variation between individuals.: Genetic variation (differences in DNA/alleles) Environmental variation (differences in conditions/factors during development) Combined variation (interaction of both genetic and environmental factors)
Define natural selection.: Natural selection is the mechanism for evolution where organisms with advantageous traits are more likely to survive, reproduce and pass on their alleles to the next generation.
Describe the process of natural selection using the phrase 'survival of the fittest'.: Variation exists within a population → selection pressure acts on the population → organisms with advantageous traits survive better → survivors reproduce → advantageous alleles are passed to offspring → frequency of advantageous alleles increases over generations → evolution occurs.
Explain how natural selection leads to evolution over many generations.: As advantageous alleles increase in frequency across generations due to survival and reproduction of fit organisms, the characteristics of the population change. Eventually, the population becomes better adapted to its environment. Over very long periods, this leads to significant evolutionary change.
Name three pieces of evidence for evolution.: Fossil record: shows sequences of life forms and transitions between species over time Antibiotic resistance in bacteria: demonstrates rapid evolution in response to selection pressure Selective breeding: shows how artificial selection can produce significant changes in organisms
What is the significance of the fossil record as evidence for evolution?: The fossil record shows a sequence of life forms across different geological time periods, revealing intermediate forms and transitions between species. This demonstrates that species have changed over time and that life has a common ancestry.
Describe how antibiotic resistance in bacteria provides evidence for evolution.: Bacteria show genetic variation in antibiotic resistance. When antibiotics are used, resistant bacteria survive (selection pressure) and reproduce, increasing the frequency of resistance alleles. Within a short time period, the population becomes predominantly resistant, demonstrating evolution in action.
Describe Darwin's theory of evolution and explain how it was initially received.: Darwin proposed that evolution occurs through natural selection: organisms with advantageous traits survive and reproduce, passing traits to offspring. It was controversial when published because it contradicted religious beliefs about creation and suggested humans evolved from other animals.
Define speciation (Higher Tier).: Speciation is the development of a new species when populations become reproductively isolated. If populations cannot breed together, genetic differences accumulate over generations until they become separate species.
Explain how selective breeding is used to produce organisms with desirable characteristics.: Organisms showing desirable traits are selected and bred together. Their offspring, which inherit the desirable traits, are selected for the next breeding. This process is repeated over many generations, increasing the frequency of desirable alleles and creating new varieties with enhanced characteristics.
Describe the process of genetic engineering, naming the key enzymes and components used (Higher Tier).: Restriction enzymes cut DNA at specific sequences. Ligase joins DNA fragments together. Vectors (plasmids or viruses) carry the desired gene into target cells. The recombinant plasmid enters the host cell, which is then called a transformed organism. This produces new combinations of genes not found in nature.
Evaluate the benefits and risks of genetic engineering in agriculture (Higher Tier).: Benefits: increased crop yield, pest/disease resistance, improved nutritional content, reduced pesticide use. Risks: reduced genetic diversity, unintended effects on ecosystems, gene escape to wild populations, potential allergenic or toxic effects, unknown long-term consequences.
Evaluate the benefits and risks of genetic engineering in medicine (Higher Tier).: Benefits: production of medicines (insulin), potential cures for genetic diseases, personalised treatments. Risks: ethical concerns about germline therapy, off-target genetic effects, unknown long-term health effects, accessibility and cost issues, potential misuse of technology.
Describe two cloning techniques: embryo splitting and nuclear transfer (Higher Tier).: Embryo splitting: early embryo is divided into separate cells, each developing into an identical organism. Nuclear transfer (somatic cell nuclear transfer): nucleus from body cell is inserted into an enucleated egg cell, which then develops into a clone genetically identical to the donor.