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IGCSEBiologyCambridge (CIE)Flashcards18. Variation & SelectionVariation & Natural Selection

Variation & Natural Selection (Cambridge (CIE) IGCSE Biology)

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  • FrontVariation in Biology

    Define the term variation.

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  • Define the term variation.

    Variation refers to the differences between individuals of the same species.

  • True or False?

    Continuous variation results in a limited number of phenotypes with no intermediate values.

    False.

    It is discontinuous variation that results in a limited number of phenotypes with no intermediate values.

    Continuous variation results in a range of phenotypes.

  • What are some examples of continuous variation?

    Examples of continuous variation include:

    • body length

    • body mass

  • What are some examples of discontinuous variation?

    Examples of discontinuous variation include:

    • ABO blood group

    • pea seed shape

    • pea seed colour

  • Define the term environmental variation.

    The term environmental variation refers to differences in traits caused by factors in the environment, e.g.

    • Events that cause physical trauma

    • Stress

    • Culture

    • Lifestyle

  • True or False?

    Many characteristics are caused by a combination of genetic and environmental factors.

    True.

    Genetic and environmental factors interact with each other to produce observable traits in individuals, e.g. body mass is affected by diet and lifestyle, but there is also a large genetic component.

  • True or False?

    Continuous variation is caused by genetic factors alone.

    False.

    Continuous variation is caused by a combination of genetic factors and environmental factors.

  • True or False?

    Discontinuous variation is usually caused by genetic factors alone.

    True.

    Traits that show discontinuous variation are usually caused by genetic factors and not environmental factors.

  • In an investigation into variation in student height, what type of graph would be used to show the results?

    The results of an investigation into student height variation would be plotted on a histogram; a graph with bars that touch each other and that would show a bell-shaped curve. This is because height is an example of continuous variation.

  • Define the term mutation.

    Mutations are changes to the genetic material.

  • True or False?

    Mutations can lead to the formation of new alleles.

    True.

    Mutations can result in new alleles.

  • What are some factors that increase the rate of mutation?

    Factors that increase the rate of mutation include:

    • ionising radiation

    • exposure to some chemicals

  • True or False?

    Mutations are random changes to the shape of a DNA molecule. (Extended Tier Only)

    False.

    Mutations are random changes to the base sequence of a DNA molecule.

  • What are the sources of genetic variation in a population? (Extended Tier Only)

    Sources of genetic variation in populations include:

    • mutation

    • meiosis

    • random mating

    • random fertilisation

  • What is an adaptive feature?

    An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment.

  • What are some adaptive features of the animal shown in the image?

    Illustration of a dolphin with a curved body, depicted in muted gray and teal colors, showing its streamlined shape, dorsal fin, and flippers against a white background.

    Adaptive features of the dolphin include:

    • streamlined body shape to allow easy forward movement through the water

    • flippers and tail fins to propel the dolphin forwards

    • the ability to hold its breath for prolonged periods under water

    • blubber under the skin provides insulation

    Illustration of a dolphin with a curved body, depicted in muted gray and teal colors, showing its streamlined shape, dorsal fin, and flippers against a white background.

  • What are some adaptive features of the venus flytrap shown in the image?

    Illustration of a Venus flytrap plant with green leaves and a reddish trap, featuring sharp spikes along the edges, on a white background.

    Adaptive features of a venus flytrap include:

    • spines on leaves that prevent flies escaping

    • red colour that attracts flies

    • sensitivity to movement that allows them to close when a fly lands

    • the ability to produce digestive juices to break down the bodies of flies

    Illustration of a Venus flytrap plant with green leaves and a reddish trap, featuring sharp spikes along the edges, on a white background.

  • Define the term hydrophyte. (Extended Tier Only)

    Hydrophytes are plants adapted to live in very wet environments, e.g. aquatic plants.

  • What are some hydrophytic adaptations of the plant shown in the image? (Extended Tier Only)

    Illustration of a water lily plant with three long green stems, each bearing large green leaves, and visible brown roots at the bottom.

    Hydrophyte adaptations of the water lily include:

    • stomata on the upper leaf surface, allowing gas exchange with the air

    • large air spaces in the leaves, allowing them to float

    • a reduced root system due to the high availability of water

    Illustration of a water lily plant with three long green stems, each bearing large green leaves, and visible brown roots at the bottom.

  • Define the term xerophyte. (Extended Tier Only)

    Xerophytes are plants that are adapted to live in very dry environments.

  • What are some xerophytic adaptations shown by the plant in the image? (Extended Tier Only)

    Illustration of a green cactus with three arms and visible underground roots in brown soil against a white background.

    Xerophyte adaptations shown by the cactus include:

    • leaves are reduced to spines to reduce water loss by transpiration

    • thick waxy cuticle reduces water loss by evaporation

    • extensive roots maximise water absorption from the soil

    • a thickened stem allows water storage

    Illustration of a green cactus with three arms and visible underground roots in brown soil against a white background.

  • True or False?

    Natural selection can occur in a population of genetically identical individuals.

    False.

    Natural selection can only occur when genetic variation is present. This is why populations with no, or limited, genetic variation are unable to adapt to changes in their environment.

  • Describe the process of natural selection.

    The process of natural selection states that:

    • individuals within a species exhibit variation due to genetic differences

    • reproduction in populations produces many offspring

    • there is competition for resources within populations, resulting in a struggle for survival

    • those with advantageous traits are more likely to survive and reproduce, passing on their advantageous alleles to the next generation

  • Describe the process of adaptation. (Extended Tier Only)

    Adaptation is the process by which populations become more suited to their environment over many generations. It occurs as the result of natural selection.

  • What is antibiotic resistance? (Extended Tier Only)

    Antibiotic resistance is the ability of bacteria to withstand the effects of an antibiotic; bacteria with resistance to a particular antibiotic are more likely to survive when they are exposed to the drug.

  • True or False?

    Mutation can result in antibiotic resistance in bacteria. (Extended Tier Only)

    True.

    Random mutations in bacterial DNA can lead to antibiotic resistance, enabling some bacteria to survive antibiotic treatment.

  • How do antibiotic resistant strains of bacteria arise? (Extended Tier Only)

    Antibiotic resistant strains of bacteria can arise by natural selection as follows:

    • mutation gives rise to an allele that codes for antibiotic resistance in one individual

    • the resistant individual survives when treated with the antibiotic

    • the individual reproduces and passes on the resistance allele

    • this occurs over many generations until only resistant individuals remain

  • How does antibiotic use increase the probability that a resistant population of bacteria will arise? (Extended Tier Only)

    Antibiotic use can increase the probability that a resistant population of bacteria will arise because the antibiotics kill any non-resistant individuals, meaning that any randomly occurring alleles for resistance become advantageous. The resistance alleles are therefore more likely to be passed on.

  • How is selective breeding carried out?

    The selective breeding process involves:

    • the selection of individuals with characteristics that are desired by humans

    • crossing together individuals with desired characteristics

    • selection of offspring with desired characteristics and crossing them together

    • repetition of the process over many generations

  • What is the purpose of selective breeding?

    The purpose of selective breeding is to improve the yield from crops and domesticated animals.

  • What are some features that might be selectively bred for in plants?

    Features that might be selectively bred for in plants include:

    • increased yield

    • disease resistance

    • pest resistance

    • frost resistance

  • What are some features that might be selectively bred for in animals?

    Features that might be selectively bred for in animals include:

    • faster growth

    • disease resistance

    • gentle temperament

    • increased milk yield

  • How are natural and artificial selection different? (Extended Tier Only)

    Natural and artificial selection are different as follows:

    Natural selection

    Artificial selection

    Advantageous features are 'selected' by pressures in the environment

    Desired features are selected by humans

    Results in species that are better adapted to their environment

    Is likely to result in varieties that are less well adapted to survive in a natural environment

    Takes a long time

    Takes less time than natural selection as only offspring that show the desired features are allowed to breed

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    1. Topic 1

      Characteristics, Classification & Features of Organisms

    1. Topic 1

      Cell Structure & Size of Specimens

    1. Topic 1

      Diffusion, Osmosis & Active Transport

    1. Topic 1

      Biological Molecules

    1. Topic 1

      Enzymes

    1. Topic 1

      Photosynthesis & Leaf Structure

    1. Topic 1

      Human Diet & Digestion

    1. Topic 1

      Transport in Plants

    1. Topic 1

      Circulatory Systems, Heart & Blood Vessels

    1. Topic 1

      Diseases & Immunity

    1. Topic 1

      Gas Exchange in Humans

    1. Topic 1

      Respiration

    1. Topic 1

      Excretion in Humans

    1. Topic 1

      Coordination, Response & Homeostasis

    1. Topic 1

      Drugs in Medicine

    1. Topic 1

      Reproduction in Plants & Humans

    1. Topic 1

      Inheritance, Genes & Cell Division

    1. Topic 1

      Variation & Natural Selection

    1. Topic 1

      Energy & Feeding Relationships

    1. Topic 1

      Human Impact: Biodiversity, Pollution & Conservation

    1. Topic 1

      Biotechnology & Genetic Modification