AQA AS Biology Unit 2 - 1 June 2015

Original post by benjenstark

Do yous think there'll be a lot of species diversity calculations on today? I always manage to get the wrong answer

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I hate them, one mistake and you almost lose all the marks,and they waste time too.Just make sure you get the correct denominator, thats 1 mark,and other one is for the correct answer to 1 decimal point.

Reply 1582

Bruno26

8

Original post by edward090

i am stressing out. can anyone prove that this is infact aqa website pack questions http://sciencemathsmaster.weebly.com/pack.html coz like the PP are aqa but not sure if the pack questions are?

Yes they are :smile:

Reply 1583

TheFinalExamDay

Original post by ThoughtIsFree

do we need to know this? (buccal cavity/operculum) stuff

Not really, but in terms of fish you will need to learn:
Gill lamellae provide a large surface area for the gills
Short diffusion pathway
The countercurrent principle: The flow of water over the gill lamellae and the flow of blood within them are in opposite directions which maintains a diffusion gradient. For example, blood with little or no oxygen passes water that's had most of it's oxygen removed. Therefore, oxygen moves from the water to the blood down a concentration gradient.

Reply 1584

Original post by Oiseaux

Gas exchange (diffusion) occurs through the stomata which is opened and closed via guard cells
There are air spaces next to mesophyll cells which the air spaces lose water to (evaporation)
The mesophyll cells have a low WP so water enters them via osmosis
WP gradient is maintained pushing water out of the xylem across the leaf mesophyll and into the atmosphere
Wind temperature and humidity affect the rate of water loss

I can only think of these 5 points but maybe one of the points could be worth two marks.

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For your first point,you could say gases diffuse into the stomata down the diffusion gradient.

Reply 1585

Oiseaux

10

Original post by Imtheish

What's the difference between horizontal and vertical transmission

Vertical: binary fission. Involves all the DNA in a cell being replicated. When the cell divides, each daughter cell receives resistant plasmids.
Horizontal: involves conjugation. Bacteria passes plasmids to other surrounding bacteria via a conjugation tube.

Reply 1586

persononinternet

16

Original post by TheFinalExamDay

Not really, but in terms of fish you will need to learn:
Gill lamellae provide a large surface area for the gills
Short diffusion pathway
The countercurrent principle: The flow of water over the gill lamellae and the flow of blood within them are in opposite directions which maintains a diffusion gradient. For example, blood with little or no oxygen passes water that's had most of it's oxygen removed. Therefore, oxygen moves from the water to the blood down a concentration gradient.

thankyou

Reply 1587

J.K

Original post by Kadak

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The water then has to go through the cell membrane via the symplast pathway , so this allows the cell to control the movement of substances like water.

Thank you! :smile:

Reply 1588

edward090

4

Original post by Bruno26

Yes they are :smile:

pls can u tell me how? coz it i cant see where it says it :frown:

Reply 1589

Original post by TheFinalExamDay

Not really, but in terms of fish you will need to learn:
Gill lamellae provide a large surface area for the gills
Short diffusion pathway
The countercurrent principle: The flow of water over the gill lamellae and the flow of blood within them are in opposite directions which maintains a diffusion gradient. For example, blood with little or no oxygen passes water that's had most of it's oxygen removed. Therefore, oxygen moves from the water to the blood down a concentration gradient.

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I think you also have to say the countercurrent system creates a steep concentration gradient which is maintained along the gills.

Reply 1590

ImNotReallyMe

15

Original post by Imtheish

What's the difference between horizontal and vertical transmission

horizontal gene transmission occurs between two bacteria of different species = by process of conjugation where plasmid dna is replicated and passed through the pilus to the other dna

Vertical gene transmission = between same species when a bacteria divides to give a genetically identical bacteria

Reply 1591

KommunistCake

12

Original post by Imtheish

What's the difference between horizontal and vertical transmission

Horizontal transmission is the transfer of genetic info between different species via conjugation tubes.Vertical transmission is transfer of genetic info between generations via cell replication.
At least that's what I've been taught :smile:

Reply 1592

frances98

19

Original post by benjenstark

Ikr! Might just leave it out and go back to it if I have any time at the end :P

I actually understand it now so I'll just do it as I come to it

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Reply 1593

cc262626

3

Original post by ThoughtIsFree

do we need to know this? (buccal cavity/operculum) stuff

yes im pretty sure its come up in past papers

Reply 1594

TheFinalExamDay

Original post by Kadak

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I think you also have to say the countercurrent system creates a steep concentration gradient which is maintained along the gills.

Sure, it really depends on how many marks they are asking for. I really hope it's not a 6 marker about gas exchange in fish!

Reply 1595

Original post by J.K

Thank you! :smile:

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Welcome :smile:

.

Reply 1596

Original post by TheFinalExamDay

Sure, it really depends on how many marks they are asking for. I really hope it's not a 6 marker about gas exchange in fish!

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I wouldn't mind.Prefer that to insects or leaves.

Reply 1597

edward090

4

someone explain the circulatory system of a mammal? and bacteria. many thanks

Reply 1598

J.K