Biology Paper 2

• Genes


  Code for particular sequences of amino acids, which are put together to make specific proteins
• How DNA bases in a gene code for a specific chain of amino acids

  Each sequence of three bases codes for one specific amino acid, so the order of the bases in the gene decides the order of the amino acids in the chain
• How DNA can be used in the synthesis of proteins when it is unable to leave the nucleus

  A molecule called mRNA is made by copying the code from the DNA. The mRNA carries the code from the DNA to the site of protein synthesis
• Process that takes place at the site of protein synthesis to produce chains of amino acids

  Carrier molecules bring the amino acids coded for by the mRNA to the site of protein synthesis in the correct order
• What happens to a chain of amino acids once it has been assembled

  It folds up into a unique shape, which allows the protein to perform the task it is meant to do
• Process of selective breeding to increase milk production in a population of cows

  The cows that produce the most milk are selected and bred together. This process is then repeated with the offspring of those cows and again for multiple generations
• Lamarck's theory of evolution: how giraffes have long necks

  1. Giraffes started with very short necks adapted to lower vegetation. 2) They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime. 3) This acquired longer neck trait was passed to offspring, and successive generations have longer necks for reaching higher branches
• Darwin and Wallace's theories of evolution: how giraffes have long necks

  1. Some giraffes had longer necks than others, due to variation within the species. 2) Giraffes with longer necks were better adapted to their environment, as they could eat leaves from taller trees. 3) Giraffes with longer necks had a higher chance of surviving and reproducing, and passed the trait of long necks to their offspring. 4) Over many generations, this process produced modern giraffes with very long necks
• Importance of knowledge of the human genome

  1. It helps us understand how genetic diseases work so preventative steps can be taken. 2) It aids the diagnosis and treatment of inherited disorders by letting us quickly identify fault genes. 3) It enables us to trace human migration patterns from the past
• Drawbacks of genetic screening

  1. Learning about genetic risks can cause stress and mental health issues for some people. 2) Genetic discrimination may lead to unfair treatment in jobs and insurance for those with certain gene variants. 3) There are concerns about the misuse of genetic data by employers and insurers
• Stages involved in a course of in vitro fertilisation


  The mother is given FSH and LH to stimulate the maturation of many eggs. 2) Several eggs are collected from the mother and fertilised by sperm from the father in a laboratory. 3) The fertilised eggs are grown into embryos in the laboratory. 4) At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus
• Disadvantages of in vitro fertilisation

  1. The treatment may not work, so repeated attempts are needed which could be upsetting/stressful for the couple and expensive. 2) It could result in multiple births which can be a risk to the mother's health. 3) The mother may have a strong reaction to the hormones (e.g. pain, vomiting)
• Why the length of food chains is limited

  Energy is lost at each level of a food chain. After about five levels, the amount of energy being passed on is not sufficient to support another level of organisms
• How the brain obtains information about the body's core temperature and skin temperature

  The thermoregulatory centre in the brain contains receptors that monitor the temperature of blood flowing through the brain. It also receives impulses from temperature receptors in the skin, giving information about skin temperature
• How a dialysis machine works

  The person's blood flows between partially permeable membranes. The dialysis fluid contains the same concentration of glucose and dissolved ions as healthy blood, which ensures that glucose and other useful ions are not lost. Waste products/urea and excess ions and water are able to diffuse out of the blood into the dialysis fluid
• Path taken by a nervous impulse in a reflex

  The impulse travels along a sensory neurone to the central nervous system/spinal chord. When the impulse reaches a synapse between the sensory neurone and a relay neurone, it triggers chemicals to be released. These chemicals cause impulses to be sent along the relay neurone. When the impulse reaches a synapse between the relay neurone and a motor neurone, it triggers chemicals to be released again which cause impulses to be sent along the motor neurone. The impulse then reaches the muscle which contracts
• Pros and cons of sexual reproduction

  Pros: 1) Leads to genetically unique offspring, increasing variation. 2) Reduces chance of population being wiped out by single event. 3) Allows evolution to take place. Cons: 1) Individuals spend time and energy searching for mates. 2) May have adaptations only useful for impressing mates
• Process of micropropagation to clone plants

  Cut a small piece of plant tissues, an explant, from the tips of stems, and sterilise them to remove microorganisms. 2) Place the explants in a petri dish that contains agar jelly with growth hormones and nutrients like glucose and mineral ions. 3) Once they grow into calluses, transfer them to soil so they can grow into plantlets. 4) 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
• Nutrients to add to agar medium for plant micropropagation

  • Nitrates for amino acids/proteins/DNA/genetic material
  • Phosphates for DNA/genetic material/cell membranes
  • Glucose or sucrose for energy/respiration
  • Magnesium for chlorophyll/chloroplasts
• Advantages of producing cows with desirable characteristics via embryo cloning, rather than via selective breeding

  1. All offspring are identical/no variation. 2) It is faster. 3) More offspring are produced. 4) There is no need for natural mating/no need to keep two parents
• Potential risk of using cloning methods to produce plants

  Disease could wipe out an entire plant population because the reduced gene pool resulting from cloning reduces the chance of there being an allele in the population that gives the plants resistance to a new disease
• How animals can be cloned via embryo transplants

  Sperm cells could be taken from the male animal with the desired characteristics and egg cells could be taken from the female animal with the desired characteristics. 2) The sperm would be used to artificially fertilise an egg cell. 3) The embryo that develops could then be split many times to form clones before any of the cells become specialised. 4) These cloned embryos could then be implanted into lots of female animals, where they could develop into identical clones
• How animal cell cloning can be used to clone an animal


  An unfertilised animal egg cell would have its nucleus removed. 2) An adult body cell would then be taken from the animal being cloned and its nucleus would be removed. 3) The nucleus from the adult body cell would then be inserted into the empty egg cell. 4) The egg cell would then be stimulated by an electric shock to make it divide like a normal embryo. 5) When the embryo was a ball of cells, it would be implanted into the womb of an adult female animal, where it would develop into a genetically identical clone
• What is a species

  A group of organisms that are genetically similar and are able to interbreed and produce fertile offspring
• How two different species could have developed from a common ancestor

  1. Two populations became separated/isolated (by a geographical barrier like a river or mountain). 2) These populations had different gene pools/developed different mutations. 3) Each population was exposed to different environmental conditions (e.g. weather, water levels etc.). 4) Natural selection occurs in the two populations, which favours the alleles that best suit each environment. 5) So the two populations become genetically different. 6) Eventually they cannot interbreed to produce fertile offspring
• Factors that can cause a species to become extinct


  • The environment changes too quickly
  • A new predator kills them all
  • A new disease kills them all
  • They can't compete with another new species for food
  • A catastrophic event occurs that kills them all
• How a species of hare evolved to have smaller ears than others than hares that live in a warmer climate

  Species show a wide variation in their characteristics because of differences in their alleles/genes. In this case, hares with smaller ears have more suitable characteristics for a cold environment because they will lose less heat, so are more likely to survive and successfully reproduce and pass on the genes controlling smaller ears to the next generation/their offspring. Over time, these genes will have become more common in the species, causing the hares to evolve
• Traits that can be improved by genetic modification

  • Increased yield
  • Increased drought resistance
  • Herbicide tolerance
  • Virus resistance
  • Production of specific proteins
  • Pesticide resistance
  • Increased nutrients
  • Flood resistance
• Reasons why maintaining high biodiversity is important

  • It increases the stability of the ecosystem, so that changes are less likely to have adverse effects
  • Many species provide specific services, such as pollination
  • Many of our medicinal drugs come from wild species
• Reasons for deforestation


  • To clear land for agriculture (planting crops or grazing cattle)
  • Mining
  • Logging for wood
• How draining peat bogs contributes to global warming

  The draining of water allows air (and oxygen) to return to the soil. This allows microorganisms to carry out aerobic respiration and decay the organic matter. This releases CO2 which acts as a greenhouse gas, and contributes to global warming
• Reasons why only ~10% of the energy & biomass is passed on at each stage in a food chain

  • Organisms don't normally eat every part of their food (e.g. rabbits may not eat the roots of the grass they eat)
  • Some of the material they eat may not be absorbed (e.g. rabbits may not be able to digest all the cellulose in grass)
  • Most of the biomass/energy that is absorbed is used to release energy (via respiration) for movement etc.
• Role of decomposers and how they carry it out

  Decomposers break down/recycle any dead plant or animal matter in the environment. They do this by secreting enzymes which break down the dead material into small soluble molecules. They take up these molecules by diffusion
• Stable community


  Where all the species and environmental factors are in balance so that the population size remains fairly constant
• How respiration affects the amount of biomass that is transferred from one trophic level to the next

  Glucose is used in respiration to provide energy, rather than to make biomass. Also, respiration produces carbon dioxide and water as waste products which are lost from the body and therefore not passed on as biomass
• How producers produce biomass for the rest of the food chain

  They produce glucose by carrying out photosynthesis. They then use this glucose to make biological molecules that make up the plant's biomass
• Discoveries made after Mendel's work that built on his discovery of 'hereditary units' and led to our current understanding of genes


  In the late 1800s, scientists were able to observe how chromosomes behaved during cell division. Then in the early 20th century, scientists realised that there were striking similarities in the way that chromosomes and Mendel's 'hereditary units' acted. Based on this, it was proposed that the 'units' were found on chromosomes, and we now know these 'units' as genes. In the mid-20th century, the structure of DNA was determined. This allowed scientists to go on and find out exactly how genes work
• Explain how a mutation could lead to a rapid change in a species.


  The mutation could lead to a new phenotype. If the environment changes, the new phenotype could make the individual more suited to the new environment. It could then become common throughout the species relatively quickly by natural selection.
• Explain how antibiotic-resistant strains of bacteria develop and spread.

  Bacteria develop random mutations in their DNA, some of which lead to the bacteria becoming less affected by antibiotics. These bacteria are better able to survive and reproduce in hosts undergoing antibiotic treatment, meaning that the gene becomes more common in the population, forming antibiotic-resistant strains. As there is no effective treatment for these strains, they can spread very easily between individuals.
• Explain why patients prescribed a course of antibiotics should always complete the full course.

  To ensure all bacteria are killed and none can survive to mutate and form resistant strains.