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AQA Biology AS New Spec - 26th May and 7th June

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Reply 540

sgill23

How are people feeling for this exam?

Reply 541

Enderbat1999

Original post by Wisteria_xo

Can someone please simply explain the formation and return of tissue fluid?

OK so what happens is at the arteriole end of the capillary there is a high hydrostatic pressure due to large amount of proteins and substances and also the large amount of water( refer to this as fluid). Due to the high hydrostatic pressure in the capillary there is a pressure difference, in which there is a high pressure inside the capillary than outside, because of this the is a difference and so due to outwards pressure small fluids are pushed out of the capillary including water.

Now at this point in the capillary blood plasma and large proteins cannot leave the capillary so water potential is extremely negative (low) inside the capillary and so osmotic pressure is also low, hence water moves back via osmosis into the capillary which increases osmotic pressure, leaving the other fluids to be drains of into the lymph and returned back into the blood stream

Reply 542

Wisteria_xo

On a question it asked how the reduced elasticity of the lungs causes breathing difficulties, and one of the marking points was that lungs cannot fully inflate (reduced lung capacity)- which I understand.
However the other marking but was that breathing out would no longer be passive? Which i don't understand at all

Reply 543

Wisteria_xo

Original post by Enderbat1999

Thank you so much !

Reply 544

LoyaltyAb0veAll

Original post by SANTR

Does anyone know what is exactly meant by 'mass transport'?

Mass transport Hypothesis

Active transport is used to actively load solutes ( such as sucrose ) from companion cells into the sieve tubes of the phloem at the source.
This - Lowers the water potential inside the sieve tubes so water enters the tubes by osmosis via the Xylem vessels and companion cells
- creating high pressure inside the sieve tube elements at the source end

At the sink end, solutes are removed from the phloem to be used.
This - Increases water potential inside the sieve tubes, which means water leaves the sieve tubes by osmosis
- thus lowering the pressure inside the sieve tubes

This Pressure Gradient from the source end to the sink end pushes solutes along the sieve tubes towards the sink - where they are used up ( in respiration or stored as starch)

(edited 7 years ago)

Reply 545

Sparky2016

What do we need to know about the aphid experiment

Reply 546

Sparky2016

Also I don't remember being taught about what happens with the capillary bed??

Reply 547

Productivity

Just a few quick questions about the upcoming exam:

1. Do we need to know statistical tests? Even though it came up on the last paper, it could come up again, where for the last paper I had absolutely no clue about them and hadn't heard of most of them before.

2. Do we need to remember details of practicals such as the ringing experiment, the potometer, and different dissections?

3. Do we need to know details on all of the lung diseases listed in the CGP revision guide (emphysema, asthma, TB, fibrosis)? It came up on the specimen paper so i'm a bit weary.

Reply 548

RKM21

Original post by Sparky2016

What do we need to know about the aphid experiment

What aphid experiment?

Reply 549

RKM21

Original post by SANTR

1.) Unlikely
2.) Yes
3.) No, those diseases are not mentioned in the spec.

Actually you may be wrong.
1) Yes - they could come up as they could relate it to another situation e/g probability values
2. Yes - but they are not required
3. Yes - because it mentions lung disease somewhere on the spec and we were told to learn it.

Reply 550

RKM21

Original post by SANTR

It's not an experiment as such but I think OP is referring to the fact that Aphids can be used to extract sucrose from the Phloem, to measure the sucrose concentrations.

Oh, did you get taught it?

Reply 551

shivanisinha1998

Original post by RKM21

I was taught that you need to be aware of the lung diseases but in questions they will give you the information on them?

Reply 552

RKM21

Original post by shivanisinha1998

I was taught that you need to be aware of the lung diseases but in questions they will give you the information on them?

Tbh idek anymore. :frown:

Reply 553

boredom07

Original post by RKM21

I don't think we're supposed to learn it because on the spec it only tells us to be able to:
- interpret information relating to the effects of lung diseases on gas exchange and/or ventilation
- interpret data relating to the effects of pollution and smoking on the incidence of lung disease
- analyse and interpret data associated with specific risk factors and the incidence of lung disease

They'll give the information you need on lung diseases in the question in order to answer. We don't have to learn them.

Reply 554

shivanisinha1998

Original post by RKM21

Tbh idek anymore. :frown:

I'm goning read over them before the exam I think. The CPG guide is also really specific on cardiovascular diseases that we didn't cover in class.

Reply 555

Lola1244

Original post by RKM21

What aphid experiment?

Basically, aphids have these sucker things they inject into the phloem of plants to obtain sucrose as their food. We can analyse the contents of these suckers to find that they indeed do contain organic substances. This shows organic substances are transported in the phloem not the xylem. Also, when the sucker thing is injected into the phloem, the sap oozes out showing that the contents of the phloem are under pressure. Also, you can show that the contents of the phloem ooze out more quickly near the leaves than the roots. This shows the contents of the phloem are moving down a hydrostatic pressure gradient

Reply 556

The Panic Queen

For set 2 paper 2
could someone explain how to do Q3.4??? I don't understand why it is -0.34

(edited 7 years ago)

Reply 557

Lola1244

Original post by Enderbat1999

can someone go over the ringing experimet and the patomter with me pls

The ringing experiment is used to show that organic substances are transported in the phloem. A ring of bark is removed from a tree. This is the phloem tissue and the xylem tissue is left intact. After a few hours you find that above the ringing, there is a bulge and below the ring tissue has died. This shows that the organic substances were transported in the phloem.

The potometer:

you assemble the apparatus underwater, cut the shoot underwater and insert the shoot into the apparatus underwater. This is to prevent any air bubbles entering the xylem vessels which would prevent a continuous column of water being pulled up, affecting rate of transpiration which is what you are measuring. The plant should be cut at a slant for maximum surface area for absorption of water. Take the apparatus out of the water. Dry the leaves. Allow time for the plant to acclimatize. Introduce an air bubble into the capillary tubing by lifting it up from the beaker. Measure the distance traveled by the air bubble in a given time.

Repeat, calculate reliable mean