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# AQA BIOL2 Biology Unit 2 Exam - 26th May 2011 watch

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1. (Original post by Limitless)
When it says explain. EXPLAIN!
When it says describe. DESCRIBE!
When it says use the data. USE THE DATA!
LOL
Explain = use your own lil brain

Remember, standard deviation:
more overlap = due to chance.
ETCCCCCCCC

urgh... =(
2. Can someone explain the gas exchange of insects to me please.
3. (Original post by EffKayy)
LOL
Explain = use your own lil brain

Remember, standard deviation:
more overlap = due to chance.
ETCCCCCCCC

urgh... =(
Er what? I thought overlap in standard deviation means there is not a significant difference
4. (Original post by Master.K)
Can someone explain the gas exchange of insects to me please.
This has to have been done atleast 5 times throughout the thread... just go through the pages dude
5. (Original post by ScienceGeek3)
Er what? I thought overlap in standard deviation means there is not a significant difference
it does
6. (Original post by EffKayy)
LOL
Explain = use your own lil brain

Remember, standard deviation:
more overlap = due to chance.
ETCCCCCCCC

urgh... =(
How you feeling about the exam then?
7. (Original post by Limitless)
I'm thinking the same.
:\ That's why I feel like revising a lot is pointless, so I'm not doing anymore.
8. (Original post by Limitless)
When it says explain. EXPLAIN!
When it says describe. DESCRIBE!
When it says use the data. USE THE DATA!
haha... -.- i know that...

i was hoping for more like 'don't panic' or 'read the questions thoroughly' or something like that....

also can some1 shed some light on COHESION-TENSION THEORY

thanks!!
9. (Original post by Master.K)
Can someone explain the gas exchange of insects to me please.
Insects have an waterproof exoskeleton made of chitin which prevents unwanted water loss.
They have tracheae which lead to holes in the surface of their exoskeleton called spiracles that can close to prevent evaporation of water when the insect is inactive. Branching off from the tracheae are tracheoles: the site of gas exchange in insects.

Smaller insects and inactive ones just use diffusion for gas exchange.

Larger insects during intense activity (e.g. flight) require more ATP so cells need more oxygen (because muscle contraction increases, so need for ATP increases, so rate of resp increases, so more oxygen is required to maintain rate of resp). Larger insects increase their oxygen supply by pumping their abdomen so more air moves in and out of the trachea

Water is withdrawn from the ends of the tracheoles during exercise because oxygen diffuses faster in air than in water, and to decrease the pressure so that air is pulled in faster.
10. (Original post by Sighrawr)
:\ That's why I feel like revising a lot is pointless, so I'm not doing anymore.
Same going to sleep in 10 minutes waking up early do some quick recap and check some mark schemes in the morning.
11. (Original post by Kishanpatel)
haha... -.- i know that...

i was hoping for more like 'don't panic' or 'read the questions thoroughly' or something like that....

also can some1 shed some light on COHESION-TENSION THEORY

thanks!!
The cohesion part is the attraction between individual water molecules, caused by the hydrogen bonds between them. It causes 'surface tension' and the 'meniscus' on the surface of water and, in the xylem of plants, causes each water molecule in a xylem vessel to be attracted to its neighbours.
Thus, if a water molecule is lost from the TOP of a plant, it will pull on its neighbour, which will pull on its neighbour, which wil....etc etc, all the way to the BOTTOM of the plant, where water will be attracted into a root hair.

The tensionpart refers to the water being PULLED UP the plant, as opposed to being PUSHED up the plant. The pressure inside each xylem vessel is thus negative (BUT positive inside the phloem, hence maple syrup and latex coming out when a tree is tapped), in just the same way as the pressure is negative inside a drinking straw when you suck.

This is the opposite of the situation inside domestic water pipes, where the pressure is poitive and water squirts out when you nail through a pipe!

So....water is lost from the leaves through evaporation,; it sucks water up the plant and the attraction between water molecules causes the water to be pulled all the way up the plant.
12. (Original post by Limitless)
Same going to sleep in 10 minutes waking up early do some quick recap and check some mark schemes in the morning.
Cool, good luck.
13. (Original post by lolo-x)
Insects have an waterproof exoskeleton made of chitin which prevents unwanted water loss.
They have tracheae which lead to holes in the surface of their exoskeleton called spiracles that can close to prevent evaporation of water when the insect is inactive. Branching off from the tracheae are tracheoles: the site of gas exchange in insects.

Smaller insects and inactive ones just use diffusion for gas exchange.

Larger insects during intense activity (e.g. flight) require more ATP so cells need more oxygen (because muscle contraction increases, so need for ATP increases, so rate of resp increases, so more oxygen is required to maintain rate of resp). Larger insects increase their oxygen supply by pumping their abdomen so more air moves in and out of the trachea

Water is withdrawn from the ends of the tracheoles during exercise because oxygen diffuses faster in air than in water, and to decrease the pressure so that air is pulled in faster.
Do they have waxy cuticles or is it just plants?
14. (Original post by al_habib)
cobra do you have revision notes for unit 4 & 5..
yes mate!

http://www.studentcreche.co.uk/resources/biol4.pdf

http://www.studentcreche.co.uk/resources/biol5.pdf
15. Just found out that a 6 mark question came up on fish exchange in June 2009, is it likely to come up tomorrow then?
16. (Original post by lolo-x)
Insects have an waterproof exoskeleton made of chitin which prevents unwanted water loss.
They have tracheae which lead to holes in the surface of their exoskeleton called spiracles that can close to prevent evaporation of water when the insect is inactive. Branching off from the tracheae are tracheoles: the site of gas exchange in insects.

Smaller insects and inactive ones just use diffusion for gas exchange.

Larger insects during intense activity (e.g. flight) require more ATP so cells need more oxygen (because muscle contraction increases, so need for ATP increases, so rate of resp increases, so more oxygen is required to maintain rate of resp). Larger insects increase their oxygen supply by pumping their abdomen so more air moves in and out of the trachea

Water is withdrawn from the ends of the tracheoles during exercise because oxygen diffuses faster in air than in water, and to decrease the pressure so that air is pulled in faster.
Thanks! +ve rep.
17. (Original post by heavencanwait_)
OMG I actually understand this now lol, thank you!
I'm really glad you do. You cheered me up by saying that.

Bonne chance!
18. (Original post by Kishanpatel)
haha... -.- i know that...

i was hoping for more like 'don't panic' or 'read the questions thoroughly' or something like that....

also can some1 shed some light on COHESION-TENSION THEORY

thanks!!
The water molecules have hydrogen bonds between each molecule so this causes them to stick to each other creating tension. You also have adhesive which causes it to stick to the walls of the stem. Cohesive is useful because it causes water to easily go up the stem when as it is pulled up by the others. Adhesive prevents the water falling back down the stem due to gravity.

So when water evaporates from the spongy mesophyll, the water potential is lowered. Mineral ions are pumped into the xylem through active transport to lower the water potential as well. Water goes up the stem. The cohesive forces cause it to pull up other water molecules and adhesive prevent it falling. Might also mention root pressure.
19. (Original post by ??????????????????)
Do they have waxy cuticles or is it just plants?
Put "waterproof coverings" for insects.
20. (Original post by Kandy_Kain_94)
Just found out that a 6 mark question came up on fish exchange in June 2009, is it likely to come up tomorrow then?
Probably not as a 6 marker then.
If it does, just mention counter currant system creates a concentration gradient allowing easier diffusion of oxygen into the blood. Stacked filaments and stacked lammele to increase surface area which also increases rate of respiration. Say it needs this because less oxygen in water than air.

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