Biology Paper 2 Questions Selection

Q: Explain how plants meet the challenges of hot environments.

Rephrased to - 'what are the adaptations of plants in hot areas?'

• the rate of transpiration in hot, dry environments is faster, and so plants must work to conserve water. there is also low rainfall so they must work to get to water as well
• succulents and cacti are examples of plants in hot dry climates, and they store water in their stems and leaves
• thick waxy cuticles on the leaves and stems of plants help to prevent water loss through evaporation
• smaller surafce area of leaves will reduce water loss - so many have very small leaves, which may even resemble spines (like on cacti)
• to gain more water, many plants in hot areas have extensive root sytems which can be deep-reaching to get to underground water (aquifers) or very wide to cover a large area and absorb the maximum amount of water following rainfall

Q: 'Explain the importance of mitosis in growth and repair and meiosis in the production of gametes'

• mitosis is important as it produces exact copies (clones) of itself - this means that all muscle cells, for example, in one area are going to be the same as they must do the same job
• mitosis is good for repair as it means that the daughter cells which may replace other cells are genetically identical to the ones they replace, and so work the same way
• the production of identical daughter cells is important in growth - eg it occurs when a fertilised egg grows into an embryo
• meiosis is important for genetic variation as the daughter cells have random chromosomes, and are haploid (have 23 single chromosomes, not 23 pairs)
• if gametes were produced by mitosis, then each generation the number of chromosomes in a fertilised egg would double etc
• genetic variation (a result of meiosis) is essential for survival of a species, to overcome disease etc
• mutations in meiosis lead to evolution by natural selection - very important in the long term

Describe how quadrats should be used to estimate the number of dandelion plants in a field

REQUIRED PRACTICAL

• place the quadrats randomly by throwing it over your shoulder - this reduces bias, as you cannot choose the patch with the most dandelions etc 
• count the number of dandelions in the quadrat and record in a suitable table
• repeat this at least five times (perhaps more, depending on the size of the field) in different areas
• once done, the mean number of dandelions per quadrat can be calculated by adding up all the frequencies collected and then dividing by the number of quadrats you did
• a quadrat is 1 metre squared, so divide the area of the field by this and then multiply the value by the mean dandelion number

Q: Moose have distinct characteristics such as antlers. Decribe how moose may have evolved to have antlers

• through reproduction there are mutations in genes which cause different characteristics
• there is natural variation within a species caused by this (in sexual reproduction)
• this affects phenotype (outside characterics - physical)
• the phenotype most suited to the environment will survive to reproduce (eg they can outcompete other animals for food or will fight their own species better and win mates)
• non-mutated moose will die for various reasons (eg lack of food or mates) as they are more vulnerable than those with the antlers - so only the mutated genes are passed on
• gradually, the genes for large antlers are passed on through sexual reproduction until all or most of the population have them

Key Idea: mutations in genes can lead to evolution by natural selection as they can give animals an advantage over the others in that species

Q: Explain why mixing peat with air leads to the release of carbon dioxide

• peat bogs are acidic, waterlogged areas which have few microbes which cause decay
• this means that when plants die they do not decay, as the microbes are not present, so carbon dioxide is stored
• when peat is mixed with air (which has oxygen - the gas that many decay-microbes use to respire) deomposition can occur which releases carbon dioxide
• in oxygen-rich conditions and in the air, microbes causing decay are present and will use the peat as a reactant in respiration
• oxygen is abundant in the air

Q: How does the body respond if slightly too much insulin is injected into the body?

• insulin is the hormone designed to bring blood glucose levels down, so too much will result in a lower blood glucose level
• this is because the liver will convert too much glucose into glycogen to be stored
• the receptors in the pancreas will detect that the level is too low and it will release glucagon
• glucagon travels in the blood to stimulate the liver to convert glycogen into glucose and release it into the blood
• this is a negative feedback system as it does the opposite of what is detected orignially - the blood glucose level is brough up to normal, healthy levels

Q: The dead leaves fall and the carbon is recycled by the carbon cycle. Explain how the carbon is recycled into the growth of new leaves

• microorganisms or decomposers (eg fungi) in the soil recycle the carbon by breaking down the compounds in the lead leaves
• these microorganisms respire and release the carbon from the leaves as carbon dioxide into the air
• carbon dioxide is then taken in by leaves in living plants as it is used in the process of photosynthesis
• photosynthesis uses the reactants carbon dioxide and water to produce glucose and oxygen
• glucose is used in the growth of new leaves because it makes amino acids (proteins) and cellulose which are required for plant growth

Q: Explain how the cat which does not cause an allergic reaction to humans has been selectively bred

• selective breeding involves choosing two members of a species with desirable characteristics (in this case it's not causing allergic reactions)
• breed the two cats together and then choose the offspring with the characteristic - the kittens which don't cause allergic reactions
• breed these offspring together
• continue the process over several generations until the cat is completely without the gene that causes allergic reactions in humans

Note: care must be taken to ensure that the cats are healthy and avoid possible problems with selective breeding

Q: Compare how each type of diabetes is caused. Suggest how each one can be treated.

• Type 1 diabetes is caused when the body does not produce enough or any insulin, so blood glucose levels can increase to a potentially fatal level
• Type 2 diabetes is when the body becomes immune to its own insulin, and so the insulin is produced but loses its effect as the organs do not respond to it
• Type 1 diabetes can be inherited (genetically) or the body's immune system accidentally destroys insulin-making cells in the pancreas
• Type 2 diabetes is associated with risk factors such as high sugar and simple carbohydrate diet, and obesity

TREATMENT - only type 1 diabetes can be treated with insulin therapy, as type 2 is immune to insulin. Insulin therapy involves regular injections of insulin, especially after meals, which will bring down blood glucose levels. Both diabetes conditions can be treated with exercise (respiration involves using glucose so would reduce blood glucose levels) and monitored diets which must be low in sugars and simple carbohydrates