Edexcel GCE Biology Unit 4 6BI04 June 2013

how to calculate the efficiency of energy transfer between trophic levels?

Anyone have the topic test answers of Hodder Edexcel A Level BIOLOGY for A2?
Where can I get them?

hey do we have to know about gram staining?

Know that gram staining can be used to differentiate between gram-positive and gram-negative bacteria.
Result with gram-positive: Positive, bacteria appear purple in colour
Result with gram-negative: Negative, bacteria appear red in colour

I'm not sure whether we have to know the structural differences between gram-positive and gram-negative though

accuracy depends on the appratus u use.
Reliability depends on how many times u've repeated the experiment and got the same average mean value

Validity = accuracy plus reliabitily

for example, u might be given a data or a graph and asked to suggest if the data is valid or not. in that case, u check the variation between the mean values, or the error bars. the more difference is there there less valid it is

would someone please explain what is genetic drift and founder effect? when do we use them?

Genetic drift is when the allele frequency of a particular allele increases or decreases within a gene pool. This may result in the loss of a trait or the spread of a trait within a population. However, genetic drift is not due selection pressures resulting in mutations, creating beneficial alleles etc ( at least to my knowledge )
Now the founder effect, is when uncommon alleles increase in frequency, or when number of different alleles decrease in frequency, within a new population.
So, in a way, the founder effect may also cause genetic drift within a population (since allele frequencies get changed)

We could use these concepts to explain loss of genetic variatoin in a population, or speciation.

Hope I am right, and hope you understand

What is clonal selection??
I'm finding it hard to put in words

well clonal selection is the stage of antibodies and killing of pathogen . B effector cells differntiate to produce plasma cells (at this stage there are more RER and golgi body produced) Plasma cells produce large amount of anitbodies and release into blood.
correct me if im wrong

What is clonal selection??
I'm finding it hard to put in words

hey im struggling with succession!! can someone please help me out?