hey everyone, ive just started revision for unit 2 :L and im resiting unit 1 :L any tips and do you think ts do-able if i work hard but i do have three other subjects aswell which may be softer but require allot of work time and effort..

my second question is to all the other biology students can anyone remember any of the questions that came up in the empa/isa unit 3 task 3 (the actual exam part) on the agar jelly and surface area to ratio one! i cant remember most of the questions if anyone could help it would be very helpful!! ( the reason asking is so i can figure out what may be my result i think ive messed it up)

its off topic but related to biology apologies though :biggrin:

Reply 285

Scienceisgood

Can someone please help me on this - completely forgotten how to do this sort of question. =l

Reply 286

ryanj18

Original post by Scienceisgood

Can someone please help me on this - completely forgotten how to do this sort of question. =l

N: total numberof organisms of all species in area
n: total numberof organisms of each species in area

so:
11(11-1) = 110
6(6-1)= 30
5(5-1) = 20

Keep doing that for all of them.

Then add them all up e.g) 110 + 30 + 20 etc etc….. until youget a total and that total is E n(n-1).

N is the total number of all organisms. So 36.
N(N-1) = 36 x 35
36 x 35 = 1260

So it will 1260 divided by the total for E n(n-1).
And that gives you d. your answer.
hope its of assistance :smile:

Reply 287

Sophie1994

Does anyone want to start a bit of revision with me by exchanging questions? :smile:

I'll start...

Explain how frequent usage of antibiotics can lead to a species of bacteria becoming resistant? (3 marks)

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Reply 288

Omar Raza

Original post by Sophie1994

Does anyone want to start a bit of revision with me by exchanging questions? :smile:

I'll start...

Explain how frequent usage of antibiotics can lead to a species of bacteria becoming resistant? (3 marks)

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Yh Sure.

Ans - Antibiotic resistance can be passed down by one of two ways.
1. Vertical gene transfer - where the cell reproduces asexually to produce identical clones - passing down its genetic information and hence also the mutated gene for antibiotic resistance.
2. Horizontal gene transfer (between different species) - The plasmid containing the gene for antibiotic resistance is passed from one bacteria to another via a cytoplasmic bridge that joins the two. Hence making the other bacteria antibiotic resistance too.
Antibiotic resistance prevails because of natural selection. As more antibiotics are used they kill the non-resistant bacteria while the resistance survive therefore reducing competition for them hence they are able to pass on their genes.

Q. Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf? (3 marks) :smile:

Reply 289

username504651

I'm so screwed for this exam but more so my EMPA in two weeks...

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Reply 290

username951826

should i be worried about Unit 2 if I didn't do fantastically in Unit 1?

Reply 291

Sophie1994

Original post by Omar Raza

Yh Sure.

but make sure you put pilus conjugation tube in your answer to ensure you get all the marks.

Q. Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf? (3 marks) :smile:

Reply 292

Omar Raza

Original post by Sophie1994

Ans:

CO2 from the external air diffuses into the plant cell through the open stomata and CO2 then moves into the mesophyll cells where gas exchange happens. In the mesophyll cells there are many air spaces which allows easy movement of CO2 to reach the chloroplasts in the mesophyll cells for photosynthesis to take place.

Great! 3/3 Marks. There was another mark available for saying diffusion in the air space "DOWN a diffusion gradient" as CO2 is constantly being used up, and stomata are open by "Guard Cells".

Q: Describe the formation of tissue fluids (4 marks)

Tissue fluid is formed from blood plasma at the capillaries by the following method.
Blood at the atrial end is at a higher hydrostatic pressure than the fluid outside the vessel therefore blood plasma is forced out of the vessel, forming tissue fluid. This is done by ultra-filtration as only small molecules pass through, big molecules such as proteins too big to pass through the cell membrane. Hence tissue fluid is less dense than blood plasma.
At venous end of capillary bed, the blood plasma in vessel = low pressure due to loss of all the blood plasma, hence the tissue fluid outside moves back into the vessel via diffusion.

Q. The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why? (3 marks) --- Good Luck :smile:

Also - something I don't understand ----- How does over use of antibiotics cause bacteria to become resistant. I know its due to mutations which perhaps change the shape of a site on the bacteria BUT aren't mutations always RANDOM? so why do they SPECIFICALLY prevent the drug (antibiotic) from functioning ? ALSO - how does an antibiotic cause mutation ?
--- It'll be great if you or anyone could explain that! :smile:

Reply 293

kiyubi

Mean num of stomata Standard deviation
18. 2
15.2. 1.3
14.3. 1.6

what do your results show of the number of stomata in your field of view?2marks

What is standard deviation?2marks

(edited 11 years ago)

Reply 294

Sophie1994

Original post by Omar Raza

Q. The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why? (3 marks) --- Good Luck :smile:

Raising the bar arnt you? haha :excited:

Well... I'm not too sure but here's what I came up... :tongue:

The aorta is an artery which transports blood to the whole body and because blood is directly pumped from the left ventricle it travels at very high pressure to the aorta. So during systole, the thick elastic layer of the aorta is stretched at each beat of the heart, decreasing its thickness and during diastole when the heart relaxes, the elastic layer recoils back to normal hence returning to its normal thickness. The stretching and recoiling action helps the aorta to maintain high pressure and smoothes pressure surges.

How does over use of antibiotics cause bacteria to become resistant. BUT aren't mutations always RANDOM? - Yep, you are right in saying that mutations are random and it is but don’t forget that mutation is linked to natural selection. Due to over exposing bacteria to antibiotics they become resistant through the process of natural selection. This is one of the reasons why some scientist say evolution takes a long time but I mean if the bacteria are being consistently exposed to antibiotics, they ARE going find a way and survive. For example, over time, some bacteria in a population will develop an allele (through mutation) that gives them resistance to an antibiotic so when exposed to that antibiotic, they survive whilst others die since they don’t have the antibiotic resistant gene. Bacteria that survive can then pass on their genes through reproduction and populate the population.

so why do they SPECIFICALLY prevent the drug (antibiotic) from functioning ?

I’ll try and explain with the little knowledge I have on biology, it won't be 100% correct, sorry :tongue:

Bacteria can prevent antibiotics from working by changing the permeability of their membrane or by reducing the number of channels available for the drug to diffuse through. So osmotic lysis cannot occur or is reduced therefore bacterial cell not burst -> survive.

Another way is mutations in the bacterial DNA, for example, Methicillin is an antibiotic that inhibits an enzyme involved in the cell wall formation but some bacteria have developed resistance to Methicillin because the gene has mutated. The mutated gene produces an altered enzyme that Methicillin no longer recognises and so cannot inhibit. Bacteria cell survives and go on to reproduction.

Finally my turn, your last question was evil!

Q: What would happen when air enters the xylem vessels in a plant during day time (3 marks)

(edited 11 years ago)

Reply 295

FutureMedic1009

Hey guys anyone got a good website which has questions to do for each topic? Just trying to get as much practice as I can(trying to get other sources apart from past papers and Exam style q's)

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Reply 296

biology911

Original post by FutureMedic1009

You could do worse than look at some of AQA’s Human Biology past papers. Some are an excellent ‘fit’ and others obviously not!

Even the exercise of assessing which ones are suitable, is good for your own spatial map of the subject. Have a go and then next week ask your teacher to look at your choices.

Good luck

(edited 11 years ago)

Reply 297

Jessie-x

Could someone please explain to me about root pressure and the two pathways water can take through plant cells?

Reply 298

Tplox

For meiosis, can someone tell me what happens in
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1

Prophase 2
Metaphase 2
Anaphase 2
Telophase 2

Thanks

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Reply 299

shonalee01

i was wondering if anyone could be help me with meiosis i don't understand what a homologous pair is as in the textbook it says 'the fusion of the egg and sperm, each contributes a set of chromosones to the offspring. therefore one each pair is derived from the chromosone is provided by the mother in the egg and the fathers in the sperm.'
does that mean that their are 23 chromosones in the egg and sperm and that from each chromosone of the mothers egg donates a chromatid and matches with the fathers chromatid for the same gene?
really confused???