AQA AS Biology Unit 1 Unofficial Mark Scheme

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Reply 80

sconter

Original post by Blob2491

55 for 100ums?

probably something like that.

Reply 81

mulac1

Q1) a) Name Organelle Y - golgi body/apparatus (1)
b) What two features of this cell make it eukaryotic?
- nucleus
- mitochondria (1) ... may have been multiple answers
c) Function of X (1) - (aerobic) respiration/produce ATP/release energy
d) Why use TEM? (2)
-high resolution
- detailed image, can look at organelles, ameoba small?
- uses electron beam, shorter wavelength

Q2) a) describe effect of alcohol consumption on risk of HD in exp. A (2) From 0-3 (i think) risk decreases. From 3-6 risk increases
b) experiment C used only volunteers aged 40-50. This made the exp. better. Why? (1) Age may affect risk of HD. Ensures that only alcohol consumption affects results.
c) Newspaper claim 'alcohol is good for you' Evaluate. (3)
- for) neg. correlation between 0-3
against) - +ve correlation after 3 drinks
- correlation doesn't mean causation
- other factors
- investigation only looked at risk of HD (not overall health)

Q3) a) What is a pathogen? (1) A disease-causing micro-organism
b) Describe phagocytosis (4)
- pathogen releases chemicals which attract phagocyte
- phagocyte engulfs pathogen
- in vesicle/phagosome ...
- lysosomes fuse with phagosome
- release hydrolytic enzymes
- digest and destroy pathogen
c) Soemthing to do with antibofy being specific to one pathogen... (2)
- Unique primary and tertiary structure
- unique binding site
-comp. to only one antigen
- found on surface of the specific pathogen

Q4) a) How does diaphragm bring about the changes from A to B (or whatever it was) (2)
- muscles contract
- diaphragm flattens
b) How do these changes bring in air to lungs (3)
-increase volume
-decrease pressure
- air moves in down pressure gradient
c) how does O2 move from air in alveoli into blood (2)
- through alveolar epithelium
- through capillary epithelium

Q5) a) the rate question (i did % change - what an idiot!) (2) 10-4/30 = 0.2
b) describe the affect of cyanide on uptake of CN ions (2)
- possibly one mark for an general decrease
- then maybe rate of uptake = 0 after 'x' secs.
c) cyanide affects respiration. explain why cyanide has the affect on uptake of Na+ ions. (3) the nasty one... i'm not sure so ill put my answer..
- no resp, no ATP/ energy released
- for AT of Na+ ions out of epithelial cells into blood in Na+K+ pump
- reduced diffusion gradient between solution and E. cells
- reduced diffusion of Na+ into cells (co-transport with glucose??)

Q6) How would you test for a reducing sugar? (3)
- add benedicts reagent
- heat
- positive result = brick red colour
b) explain why vol of solution is greater in B (3)
- amylase not denatured
- starch digested into maltose/glucose by hydrolysis
- lowers water potential
- water moves into tube through ppm by osmosis
c) why can the student not conclude ph8 is optimum (1)
- she didn't experiment on any other ph's

Q7) a) type of reaction when polyp are digested into peptides? (1) hydrolysis
b) why cant peptides move into E cells by FD? (tnot sure but)... (3)
- peptides are too large
- to bind to carrier proteins
- to pass through protein channels
c) Why does coeliac disease reduce the uptake of the products of digestion (3)
- microvilli damaged
- reduced SA
- less diffusion
d) Why does gluten cause an immune response (1)
Contains antigens that stimulate B cells/ causes production of ABs
e) two factors that should be considered before given to patients: (2)
- side effects
- (i put) .. whether the drug was actually successful (but not sure!)
i think other suggestions include other health issues of volunteers in trial, age, gender etc...

8) a) -SAN initiates heartbeat.acts as pacemaker/myogenic
- SAN sends impulses across atria causing atria to contract
- AVN delays
- allowing atria to empty before ventricles contract (or ventricles to contract after filled)
- AVN sends wave down bundle of His/ Purkyne fibres
- causing ventricular systole/ ventricles to contract

(5)

b) Hmm... hasn't been a long answer question before
Here's a few things that might get marks..
- high blood cholesterol level/LDLs
- atheroma
- thrombosis
- aneurysm
- artery walls weakened/damaged
- salt and alcohol
- increase blood pressure
- talk about a MI
- antioxidants??

will be interesting to see how this matches up to the real thing....

Reply 82

_tay

Hey everyone!

how did everyone find it and what do you think the grade boundaries gnna be like?

Reply 83

swiftylol

For the cyanide question:

Cyanide stops/inhibits respiration
Resp creates atp -> No atp for active transport
Thru carrier proteins that transport sodium
So no sodium uptake

Reply 84

mulac1

possibly .. i reckon my answers probably overcomplicated! Only thing is, i'm pretty sure that Na+ move into E.cells by diffusion with glucose molecules (and not by AT) .. but i may be wrong.

Reply 85

sconter

Original post by mulac1

possibly .. i reckon my answers probably overcomplicated! Only thing is, i'm pretty sure that Na+ move into E.cells by diffusion with glucose molecules (and not by AT) .. but i may be wrong.

you are. na and glucose are co-transported not diffused.

glucose is diffused initially. but when there is no longer a gradient. co-transport goes against the gradient of glucose and with the gradient of sodium. sodium is kept low by the KNa pump

Reply 86

W4L1Y

Ffs aqa nobheads always do these slug missions bollox

Reply 87

swiftylol

Original post by mulac1

possibly .. i reckon my answers probably overcomplicated! Only thing is, i'm pretty sure that Na+ move into E.cells by diffusion with glucose molecules (and not by AT) .. but i may be wrong.

You're probabley right, I think I overcomplicated it because I was thinking in terms of higher processes. Kinda forgor this was for unit 1, your answer is perfect :biggrin:

Reply 88

The Assassin

One of the past mark schemes says 'Sodium removed (from epithelial cell) by active transport/sodium-potassium pump.' So I'm hoping that's the case here, haha.

Reply 89

etta

Was it hydrolysis or condensation ?

Reply 90

Jakez123

Hmm, for the diaphragm question is said that the:

Diaphragms muscles contract
causing it to flatten
increasing the volume in the thorax
thus air moves in.

Would i get 3 marks for that?

Reply 91

MediterraneanX

Original post by etta

Was it hydrolysis or condensation ?

hydrolysis

Reply 92

sconter

Original post by Jakez123

Hmm, for the diaphragm question is said that the:

Diaphragms muscles contract
causing it to flatten
increasing the volume in the thorax
thus air moves in.

Would i get 3 marks for that?

from my experience, you get full marks just for using the word 'thus'

you will get 2/3

Reply 93

etta

Original post by MediterraneanX

hydrolysis

Yesss got it right !!!

Reply 94

Jakez123

Original post by sconter

from my experience, you get full marks just for using the word 'thus'

you will get 2/3

ah that's a shame,

what about for he co-transport question with cyanide:

i said:

As NA ions are not taken up glucose and NA+ do not undergo co transport
therefore less glucose reaches the blood
glucose is used in respiration (resipration = glucose + 02)
therefore respiratory problems

(as it said what was the "effect" of the lack of NA+ ions in animal tissues)

Reply 95

swiftylol

Original post by Jakez123

But didn't the question mention/imply that cyanide caused sodium uptake to stop?

Reply 96

Chicken Bacon

Here's a little something to make those of us who feel they could have done better laugh.

Exam meme.png

Reply 97

Jakez123

Original post by swiftylol

But didn't the question mention/imply that cyanide caused sodium uptake to stop?

which lead to respiration problems, yea i know but that was the only logical thought process i though of in the exam, + other around me talked about co-transport also.

Reply 98

Hippokrates

Do you think it was a hard or easy paper, what do you think the grade boundaries will be?

Reply 99

swiftylol

Original post by Jakez123

which lead to respiration problems, yea i know but that was the only logical thought process i though of in the exam, + other around me talked about co-transport also.

Hmm, I thought the question was asking

Cyanide > respiration problems > which causes a lack of sodium

rather than

Cyanide > Lack of sodium > effects on respiration

They may just accept both.