AQA BIOL2 Biology Unit 2 Exam - 26th May 2011

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Water is withdrawn from the ends of the tracheoles during exercise because oxygen diffuses faster in air than in water, and to decrease the pressure so that air is pulled in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.

cobra do you have revision notes for unit 4 & 5..

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Water is withdrawn from the ends of the tracheoles during exercise because oxygen diffuses faster in air than in water, and to decrease the pressure so that air is pulled in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.

OMG I actually understand this now lol, thank you!

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!!

Do they have waxy cuticles or is it just plants?

Just found out that a 6 mark question came up on fish exchange in June 2009, is it likely to come up tomorrow then?

Arghhh, this is bad i'm still getting confused is transpiration..

A- evaporation of water vapour from plants
or
B- Uptake of water through a plant or tree

??

Arghhh, this is bad i'm still getting confused is transpiration..

A- evaporation of water vapour from plants
or
B- Uptake of water through a plant or tree

??

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.

Arghhh, this is bad i'm still getting confused is transpiration..

A- evaporation of water vapour from plants
or
B- Uptake of water through a plant or tree

??

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.

A. B is transpiration pull.

Arghhh, this is bad i'm still getting confused is transpiration..

A- evaporation of water vapour from plants
or
B- Uptake of water through a plant or tree

??

Just got 71/85 on June 2010 mock... think I marked it fairly

Now im gonna do Core2 Math papers for my exam in morning tomorrow instead

Happy with that lol, good luck everyone x

I think thats cohesion which causes water molecules to stick together, and tension which pulls more water in to the leaf

I said that. Maybe poorly worded. The water is bonded with hydrogen bonds that cause them to stick to each other so when one is pulled they are also pulled with it. However tension is also created cos it's a bond. If you have a tug of war, there is tension due to the pulling.