|Biology||A Level||£24 /hr|
Karen (Parent) February 17 2016
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Helen (Parent) March 20 2017
The process of diffusion is extremely important for the uptake of substances into cells. These substances can be very important for a whole range of cellular processes. Its also useful in reomoving waste products produced by cells themselves.
Diffusion is particularly during gas exchange. In respiring cells, oxygen must be taken up into cells to be used in respiration whilst carbon dioxide must be removed as a waste product. However, in photosynthesising plant cells, the opposite also occurs also as carbon dioxide must be taken up into the cell and oxygen should be expelled as a product.
Other important substances to be absorbed are nutrients such as amino acids glucose and most importantly, watersee more
The polymerase chain reaction (or PCR) is extremely useful at copying fragments of DNA so by the end of it you have a much bigger sample than what you started with. This is particularly useful for example, in forensics when collecting DNA samples from the scene of a crime.
There are essentially 3 steps to this process but each one follows the other automatically inside a piece of equipment called a thermocycler. Firstly, the 2 strands in your double stranded DNA are separated. This is done at temperatures of around 95 degrees Celsius which is enough to break the hydrogen bonds between the two strands.
Secondly, the mixture is cooled to 55 degrees C and primers are added. Primers are short sequences of nucleotides which are complimentary to a set of bases at one end of each DNA fragment. This process of "annealing" provides the starting point for the third stage in PCR...
Finally, the temperature is increased to 72 degrees C which is the optimum temperature for DNA polymerase to extend these primer sequences to make the complimentary strand of DNA by joining complimentary nucleotides (which are also in your reaction mixture). It will continue to do so until it reaches the end of the chain.
So the end result is double the amount of DNA you started with. You can do the reaction again to get quadruple the amount and so on until you have a large enough DNA sample to work with.see more
Some animals contain haemoglobin molecules which are structured in way which allows them to have a high affinity for oxygen whilst some are the complete reverse. The reason for this is all to do with the environment in which that organism lives.
For example, if an animal lives in a high altitude environment where there is little oxygen available, it would be an advantage to have a haemoglobin type which has a high affinity with oxygen so it can absorb as much as possible from the little there is available.
On the opposite end of the spectrum, an animal with a high metabolic rate such as a rodent requires a lot of oxygen to use in cellular respiration. This provides it with enough energy to carry out its daily routine. Therefore in this case, a haemoglobin type which has a high affinity for oxygen isn't advantageous. Instead, rodents have more haemoglobin which dissociate with oxygen more regularly, releasing it into tissues. Provided, there's enough oxygen in the organisms environment, its far better off having a haemoglobin which releases oxygen more easily than one which takes it up easily.see more