Inheritance and Variation

• Cut a small piece of plant tissue, an explant, from the tips of stems, and sterilise them to remove microorganisms. Place the explants in a petri dish that contains agar jelly with growth hormones and nutrients like glucose and mineral ions. Once they grow a bit into calluses, transfer them to soil so they can grow into plantlets. Finally transfer them to their own pot. Ensure that the whole process is done at a reasonable temperature and that the plants get enough light and water.
• Three main ways fossils can form

  footprints / bones / sediment / decay / amber / minerals / casts

  1. Hard body parts, such as bones and shells, which decay very slowly, are gradually replaced by minerals, forming rock-like substances.
  2. Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock.
  3. 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 is the fossil record incomplete?

  Some organisms are soft-bodied so do not fossilise well

  Some fossils formed long ago may have been destroyed since
• Suggest three ways a species may become extinct.

  Rapid environment change such as an increase in temperature

  Reduction in habitat as it could reduce food and living space

  Increase hunting as individuals are directly killed 

  The spread of a new disease 

  Introduction of a new competitor or predator 

  A catastrophic event, such as an asteroid strike 
• Explain how two different species of rabbit could have developed from a common ancestor.

  Two populations became separated/isolation (by a geographical barrier like a river or mountain)

  These populations had different gene pools / developed different mutations 

  Each population was exposed to different environmental conditions (e.g. weather, water levels etc)

  Natural selection occurs in the two populations...

  ...which favours the alleles that best suit each environment

  So the two populations become genetically different 

  Eventually they cannot interbreed to produce fertile offspring
• Describe in detail how antibiotic resistance arises.

  A population of bacteria infect somebody

  That person takes antibiotics to kill the bacteria

  Some bacteria have (or get) a random mutation that makes them less susceptible to the antibiotic than others (or completely resistant to it)

  The antibiotics kill all the bacteria except those that are resistant

  The resistance strains of bacteria now have more resources to grow and multiply 

  More mutations may arise, leading to greater resistance

  There is now a strain of bacteria that can't be killed by antibiotics, which we call antibiotic resistance
• Give 3 reasons antibiotic resistance is becoming more common.

  Doctors often prescribe antibiotics in cases where they aren't necessary. For example, mild or viral infections

  Many people don't take the full course of antibiotics, so not all the bacteria are killed

  Huge amounts of antibiotics are given to farm animals in order to make them grow faster
• Why is the spread of antibiotic resistance a problem?

  If more bacteria are resistant to antibiotics, we won't be able to treat those infections 

  This means more people will die of bacterial infections 
• What is a species?

  Group of genetically similar organisms that can interbreed (mate with each other) to produce fertile offspring
• Explain how two different species of rabbit could have developed from a common ancestor

  Two populations became separated/isolated (by a geographical barrier like a river or mountain)

  These populations had different gene pools / developed different mutations 

  Each population was exposed to different environmental conditions (e.g. weather, water levels etc)

  Natural selection occurs in the two populations...

  ...which favours the alleles that best suit each environment

  So the two populations become genetically different 

  Eventually they cannot interbreed to produce fertile offspring
• Give three traits that could have been altered by genetic engineering in crops. 

  Increased yield e.g. bigger fruit 

  Increase quality e.g. better taste 

  Resistance to disease 

  Resistance to insects  

  Resistance to herbicides  

  Resistance to droughts  
• What are the drawbacks of genetic engineering? 

   There is a small risk that genetically modified food could negatively affect our health 

  If the crops breed with wild plants they could spread the new genes and affect the gene pool