For this question:
If two chromosomes of a species are the same length and have similar centromere placements and yet are not homologous what is different about them.
- They have different centromere placements?They do not have the same gene sequence?.
Homologous chromosomes are chromosomes with the same sequence of genes, thus these chromosomes might not be homologous if they have posses different genes to one another. Note that saying they have different centromere placements is incorrect as this it if specified in the question stem that the chromosomes have similar centromere placements.
Also
Why might different cells of the same organism have cell cycles of different durations.
Could I say
- Different cells have specialised functions in an organism and are therefore needed for different durations.
There a multiple factors that go into cell's lifespans, but a main component is the workload/stress they endure. As you have said, cell's are specialized and carry out different roles - some rolls endure high amounts of stress like those forming the lining of your gastrointestinal tract and those in your skin. These cells experience a fair amount of wear and tear and thus need to be replaced frequently compared to some cells (like some muscle cells) which are exposed to so much stress. As hinted upon though, this isn't the whole story and there are likely other factors at play here - such as the idea that a reason why neurons don't divide much being due to the fact that cell replication may affect the precises wiring of the brain.
Your answer is pretty much correct, although (depending on mark allocation) its probably best to elaborate some more and use some examples if you can.
For the question how does the photolysis of water benefit the biosphere.
Would this be a sufficient answer
Photolysis is necessary for photosynthesis to occur. Water molecules must be broken down so they can react with co2. Photolysis of water releases oxygen as a byproduct.
You have correctly identified that photosynthesis does allow the splitting of water to form oxygen gas, however you have not answered the question by stating how this benefits the biosphere. Why is the production of O2 important?
You might also want to comment on how Photolysis facilitates photosynthesis and thus enables the production of carbohydrates (another very important thing that benefits the biosphere).
While you clearly do have the right idea, its really important to break down the question and actually identify what it wants you to say- in this case it not only wants you to explain what photosynthesis does, but more importantly *how* it benefits other life.