B6

• An individual's characteristics are determined by both the genes they inherit, and the environment they're exposed to. This means that both contribute to the variation between organisms. Often the genes and environment will interact to create further variation. 
• A gene pool is all the alleles present in a population at any given time. The frequency of these alleles determines how likely it is for them to be passed on to offspring. If there are many copies of a particular allele then this increases its chances of being inherited.
• What does the phrase 'survival of the fittest' mean?


  The individuals with the most favourable characteristics are most likely to survive
• Evolution is the process by which the inherited characteristics of a population change over time due to natural selection. In some cases this may result in the formation of a new species.
• What provides evidence for the theory of evolution?

  Fossils

  The spread of antibiotic resistance
• Describe a series of events that might result in zebras evolving to run more quickly.

  There is variation among the zebra population so that some can run faster than others 

  A mutation arises that allows some zebras to run faster

  Those zebras that can run fastest are more likely to survive and are therefore more likely to reproduce and pass on their advantageous alleles 

  This repeats over multiple generations 

  So the advantageous allele spreads throughout the population, until the species has 'evolved' to run faster
• Speciation is the evolutionary process by which populations evolve to become distinct species.
• Species

  A group of genetically similar organisms that are able to interbreed and produce fertile offspring.
• Speciation

  This can happen when different populations of the same species become so different that they are unable to interbreed and produce fertile offspring anymore, at which point they are considered different species and we say speciation has occurred.
• Explain how two different species of rabbit could have developed from a common ancestor.

  Two populations became geographically isolated from each other.

  These populations had different gene pools / developed different mutations as each population was exposed to different environmental conditions. These two populations pass down their genetic mutations onto their offspring which cannot be shared between populations. Eventually, the two populations become so genetically different they cannot interbreed to produce fertile offspring and are considered two different species.
• Why is the fossil record incomplete?

  Some fossils formed long ago may have been destroyed since

  Some organisms are soft-bodied so do not fossilise well
• Fossil formation

  Hard body parts, such as bones and shells, which decay very slowly, are gradually replaced by minerals, forming rock-like substances. Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock. Some parts of organisms may not decay at all. For example, dead animals and plants can be preserved in amber, peat bogs, tar pits, or in ice.
• Why might a dead animal be preserved in a tar pit, rather than decay?

  Not enough oxygen for decay to take place
• Reasons a species may become extinct


  A catastrophic event such as an asteroid

  Spread of a new disease

  Lack of resources such as habitat or food
• What effect does selective breeding usually have on variation within a population?

  Decreases variation
• What are the drawbacks of inbreeding?

  It reduces that size of the gene pool 

  Rare inherited diseases are more likely to appear

  The population as a whole will be more at risk of disease
• Describe how the process of selective breeding could be used to increase milk production in a population of cows. 

  Due to variation and random genetic mutation, some cows produce more milk than others. The cows that produce the most milk are selected and bred together. This process in then repeated with the offspring of those cows which inherited the gene and again for multiple more generations.
• Which type of reproduction allows an organism to colonise a new area most quickly?

  Asexual
• Which type of reproduction leads to more genetic variation in the population?

  Sexual
• Downsides of asexual reproduction.

  Low genetic variation means that offspring are more susceptible to disease 

  The population would have a smaller chance of adapting to new conditions 
• Discuss the pros and cons of sexual reproduction.

  Pros - Larger amount of variation, population is less likely to be wiped out by a disease, species can adapt to changing conditions via evolution

  Cons - Requires two parents, organisms may spend lots of time and energy trying to find a mate, many species spend resources impressing their mates even though it doesn't aid survival
• What is the advantage of using a binomial system to name species?

  It lets scientists discuss individual species

  Each species has a unique name
• Linnean classification system

  kingdom, phylum, class, order, family, genus, species.
• Carl Woese developed the three domain system to classify organisms. What are the three domains?

  Eukaryotes 

  Archaea

  Bacteria
• Eukaryotes

  Animals

  Plants

  Fungi

  Protoctists
• What do evolutionary trees show?

  The evolutionary relationship between the organisms being studied
• What do the branch points show on an evolutionary tree?

  The divergence of a single population/species into two separate populations/species 
• What is biodiversity? 


  The variety of living things on earth, or within a particular ecosystem
• Give three reasons high biodiversity is important


  It increases the stability of the ecosystem, so that changes are less likely to have adverse affects

  Many species provide specific services, such as pollination

  Many of our medicinal drugs come from wild species
• Two impacts of rapid growth in the human population.

  More resources are being used

  More waste is being produced
• Substances that contribute most to water pollution?


  Sewage from cities

  Fertiliser from agriculture
• Substances that contribute most to air pollution?


  Smoke from combustion 

  Acidic gases from burning fossil fuels 
• Substances that contribute most to land pollution?

  Landfill

  Nuclear waste
• How do field margins and hedgerows in agriculture help increase biodiversity? 

  They provide extra habitats and food sources so that a wider range of species can survive. 
• How can the government encourage businesses (including farmers) to reduce damage to biodiversity


  Set laws prohibiting or requiring certain things

  Pay businesses for carrying out certain practices (like planting hedgerows)
• Which human activities have a positive impact on biodiversity?

  Recycling waste

  Setting limits on co2 emissions

  Creating marine protected areas
• What are the 2 key features of food security?


  Sustainable for the planet into the future

  Access enough safe and nutritious food to meet their requirements for a healthy life
• Methods for producing food to achieve food security must be sustainable.

  What does this mean?

  We must meet the demand for food today without affecting the ability to meet the demand for food in the future.
• Factors affecting food security


  Rising populations - More people to feed

  New pests and pathogens can kill crops or livestock, which may lead to famine.

  Environmental changes due to climate change, such as higher temperatures or reduced rainfall, can decrease food yields.

  Agricultural inputs can be expensive. Fuels, pesticides, fertilisers, animal feed etc are all expensive and these costs are often passed onto the consumer, which means food becomes more expensive
• Give 2 ways in which changing diets could negatively affect food security.


  Increased consumption of resource intense foods such as meat

  Increased consumption of foods that have to be transported long distances across the world