A level Biology: Post your doubts here!

[gary221]

answer mine MCQs :O

39) A
The percentage transfer between the Sun and producers is 1% n between the producers and primary consumers is 10%.

 

[Malik777]

B
Since uracil replaces thymine in RNA, column C must be thymine. With adenine and thymine pairing up in DNA, column B must represent adenine.

didn't get you? :O

 

[gary221]

didn't get you? :O

i dunno hw 2 make it clearer, but u know thr r 4 bases, right??
adenine (A), thymine(T), guanine (G) n cytosine (C)... A pairs up with T n G pairs up wth C, okay? now ths 4 bases r in the DNA molecule.
In RNA, u hv urasil (U) instead of T....so U pairs wth A n G wth C..
In option 3, we see tht U = 25 n option C = nil.....so this means tht column C is thymine...
n since T pairs wth A, it follows tht A n T shud be roughly equal in no.
Thus column B is adenine
Hope i helped!!

 

[Amy Bloom]

Quick question
When answering questions that say with reference to a fig and there is a graph do we always hav to quote values when explaining the trend?

If you quote values, you'll have one mark more. ^^

 

[Malik777]

What is antigenic concealment ?

 

[Amy Bloom]

What is antigenic concealment ?

Antigenic concealment occurs when the pathogen hides itself inside cells (somatic or body cells) to avoid being attacked (detected via the antigens that they have) by defense cells of the body. you get it?

 

[dornam]

how can I prepare for paper 5? I know about past papers, but is there anything else?

 

[gary221]

how can I prepare for paper 5? I know about past papers, but is there anything else?

u should know all abt statistics (t-test, standard deviation. etc)
also abt common lab apparatuses

 

[Malik777]

yup

Antigenic concealment occurs when the pathogen hides itself inside cells (somatic or body cells) to avoid being attacked (detected via the antigens that they have) by defense cells of the body. you get it?

 

[aloha]

thnx a

You were told a sample is taken at each hour for 20 hours. It means that, at the end of the 20th hour, you will have 20 samples for each culture system.
Now, you understand that you will have 20 samples for pH 4.0 and 20 samples for pH 5.2.
So, degrees of freedom, v = 20 + 20 - 2 = 38
Hope this helped and good luck

thnx so much!!!

 

[Thampi4]

yes just once or twice

thanks

 

[Amy Bloom]

thnx a

thnx so much!!!

Welcome

 

[Amy Bloom]

how can I prepare for paper 5? I know about past papers, but is there anything else?

- review your practicals at school
- read about things like photosynthesis, factors affecting rate of P/s, respirometer, gen. crosses and so on... All A2 expts.
- statistics in biology: chi-squared test, t-test
- do all paper5 2007-2012

 

[Amy Bloom]

While cleaning up my pen drive, i saw this, it may help you (PhyZac) and other peeps here.
I know they are short but they are very concise.
Notes on Selection and Evolution
This is on

• Variation: www.s-cool.co.uk/a-level/biology/evolution/revise-it/variation
• Natural selection: http://www.s-cool.co.uk/a-level/biology/evolution/revise-it/natural-selection
• Antibiotic resistance as an evidence for evolution: http://www.s-cool.co.uk/a-level/biology/evolution/revise-it/evolution-in-action
• Evolution by speciation: http://www.s-cool.co.uk/a-level/biology/evolution/revise-it/evolution-by-speciation

 

[dornam]

Amy Bloom, thanks.

Can someone help me with this point in the syllabus?

"Outline the need for communication systems within mammals to respond to changes in the internal and external environment"

 

[Amy Bloom]

dornam
I didn't have notes on this dear, but i've put something out of my mind, i hope it helps. If you don't understand something, do tell.

Outline the need for communication systems within mammals to respond to changes in the internal and external environment

Homeostasis is the maintenance of constant body environment. It is important to keep some factors, like discussed below, constant to allow proper functioning of the body.

1. The body temperature. The body needs to be at a temperature of 37 degrees celsius so that enzymes, being proteins, work best. If temperature was allowed t0 rise out of control, the protein structure would be affected and lead to diseases.
2. The amount of water in the body. The levels of water should be appropriate because it affects metabolism and osmosis.
3. The amount of glucose in the body. If the amount of glucose is not regulated, the osmotic balance of the cells and the rate of cellular respiration may be affected, on either side (whether the amount of glucose in blood increases or decreases).
4. The amount of nitrogenous wastes. If the nitrogenous wastes like urine is not discarded from the body, the latter can become toxic to somatic cells and damage vital organs.

 

[dornam]

Thanks man!! Can you tell me where I can get some infos about drawing those tables for paper 3?

 

[Amy Bloom]

Thanks man!! Can you tell me where I can get some infos about drawing those tables for paper 3?

Drawing tables for practicals depends on the question itself. Here is a general rule what you are investigating (dependent variable), put that heading on the right side and the independent variable (e.g. different temperatures n concentration of R, for instance) put that on the left of your table. Else, its more of common sense and your logic.
P.S : I have edited the post above, please read.

 

[dornam]

I see. What about errors and ways of improvements?

 

[Amy Bloom]

I see. What about errors and ways of improvements?

Again, it depends on which experiment.
For e.g. errors can be:

• The number of concentrations of E used is not enough. Its improvement would be use wider concentrations of E.
• The experiment is conducted only once. Its improvement would be: do 3 experiments and obtain an average value.

It depends on the experiment, otherwise.