AQA A-level Biology Unit 1 26th May 2016

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I feel like the the Heart, Lungs, Immunity and Mitochondria questions were nice. The others not so much. Did everyone else say stronger cardiac muscle on the left side causes higher blood pressure in left ventricle?

Thicker muscular walls so more forceful contractions

Reply 181

A9M4D

A = 12
B = 10
C = 8
D = 6

init

Reply 182

Anam

Okay for the tryglyceride one i put all of its been hydrolyesed/broken down and also the lipase enzymes active site is occupied/saturated and that no more enzyme-substrate complexes can form

Reply 183

haegrey

The magnification already had units written for us

Reply 184

username1084917

For the question about drawing the curve:

It started the same as other curve but it went straight for a bit longer than decreased a bit later until it is similar level as other curve?

Reply 185

A9M4D

Original post by Kira Yagami

Why was lactose give in morning?

High metabolic rate?

More active in morning?

It's the first consumable the volunteer will drink that day = if they get symptoms it will only be as a result of the milk?!?!!?

Reply 186

turtle294

Original post by A9M4D

A = 12
B = 10
C = 8
D = 6

init

Hahaha we wish

Reply 187

turtle294

Would i get penalised for not adding units for the magnification question??!!

Reply 188

Ordo

Original post by Louisss

what were the possible reasons for the mitochondria having been evolved from a prokaryote?

Posted from TSR Mobile

There is circular DNA in mitochondrion diagram so it must be evolved from prokaryotic cell.

Reply 189

mordin1428

Is posting unofficial mark schemes allowed?

Reply 190

username1194172

Original post by turtle294

Would i get penalised for not adding units for the magnification question??!!

the units were already given next to it

Reply 191

EmmaHarvard

Original post by mordin1428

Is posting unofficial mark schemes allowed?

Yeh can someone please post 1?

Reply 192

maggie43

Original post by TWeeks

i did

Reply 193

franpavis

The last 5 marker was awful!! Will be lucky if i scored any of the marks :frown:

Reply 194

piggywag1

Original post by Kira Yagami

Why was lactose give in morning?

High metabolic rate?

More active in morning?

You can't record symptoms when you're asleep

Reply 195

EmmaHarvard

Original post by turtle294

Would i get penalised for not adding units for the magnification question??!!

No as units were given..

Reply 196

turtle294

Original post by Louisss

the units were already given next to it

Thank god for that - Thank you!!

Reply 197

mordin1428

So, DRAFT unofficial mark scheme (only what I remember, feel free to add and/or correct)
Q 1.
a) White blood cell has a cell membrane and a nucleus, no cell wall

Bacterial cell has a cell wall and cell membrane, no nucleus

b) actual size = image size/magnification, so (image size in mm)x10^3/30000, mine was 2.86

c) evidence for mitochondria - its own looped molecule of DNA, looks similar to bacterial cell

d) advantage of mitochondria - aerobic respiration? produces ATP for metabolic processes in the cell, cell growth and repair, active transport etc.

Q2
a) oxygenated blood away from the heart - aorta, C

deoxygenated blood to the heart - vena cava, A

b) Ventricle has a thicker wall, so a thicker muscle layer. Thicker muscle layer means more forceful contraction and higher blood pressure

c) hole between two ventricles - deoxygenated and oxygenated blood mixes, stroke remains the same volume, so instead of a full stroke of oxygenated blood, a mixture of deox. and ox. is pumped into the body --> less oxygen to cells

Q3
a) Ph meter gives a precise value, ph indicator gives a range

b) triglycerides get broken down into glycerol and fatty acids by lipase. Fatty acids lower the ph.

c) ph is constant because all triglycerides have been broken down so no more fatty acids formed, so their conversation remains constant --> no change in ph

d) curve's gotta start from the same ph and decease less rapidly, taking no longer to reach the same ph level as the first curve in the end

Q4

a) rough endoplasmic reticulum/ribosome

b) not active inside the cell: trypsin is a protease - many vital proteins present within the cell, like channel proteins, that facilitate active transport, structural support etc. - if protease activates within the cell, it can break them down

c) peptide bond breaks

d) competitive inhibitor=shape similar to substrate - binds to active site - doesn't get broken down, so stays there - enzyme can no longer form E-S complexes - rendered useless

Q5

a) Diaphragm relaxes and curves upwards - thorax and lungs collapse inwards and down - less volume in lungs so air pressure rises (above atmospheric) - air moves from area of high pressure to area of low pressure, which is outside of the body

b) FEV1 of non-smokers went up by 0.05 after a year, whereas FEV1 of smokers went down by 0.05 after a year. Then FEV1 of non-smokers decreased by 0.12 after the increase and FEV1 of smokers decreased by 0.25 after the first decrease.

c) scar tissue formation - loss of lung elasticity tar in cigarettes causes release of proteases - digests elastin, so less recoil and breakdown of alveoli

Q6

a) milk treated with lactase to break down lactose

b) first thing in the morning - nothing else in digestive tract, so provides a benchmark OR in the morning, not before sleep - can consciously become aware of the symptoms and record them

c) dietary guidelines - don't eat any other dairy, foods that will cause bloating or any other symptoms (beans/peas), or lactase supplements

the part about conclusions from results I put none of the symptoms are severe or even moderately severe, all of them scoring less than 2, so it may be safe for lactose intolerant people to drink small quantities of milk. Then bloating was more likely to be experienced when drinking untreated milk, whereas diarrhoea - when drinking lactose-free milk. Both untreated and lactose-free milk scored roughly equally on stomach ache.

results may be unreliable because the respondents may have been biased about symptoms, not answered truthfully, not a quantitative analysis and no long-term effects studied

Q7

a) No receptor protein - virus can't enter cell, so can't replicate and its RNA can't be transcribed, so it can't start harming the cells or make cells produce harmful substances and also is quickly destroyed by white blood cells (phagocytes) if it remains in the blood

b) increase in plasma cells: a macrophage presenting antigens meets T-helper cell with a complimentary receptor to that antigen, cytokines activate, among others, B-cells (their proliferation and speciation) and after clonal selection many clone B-plasma cells are produced to produce antibodies to combat the viruses

c) plasma transfusion: people who have been recently infected still have specific plasma cells active (that produce antibodies specific to Ebola antigen) and soluble antigens, so a transfusion will introduce those into the sufferer's blood, so that the antigens can bind to Ebola viruses

d) high mutation rate=high antigen variability. A vaccine exposes a person to one set of Ebola virus antigens - highly specific antibodies and memory cells formed will only respond/are complementary to the same set of antigens. A new strain of Ebola virus can have completely different antigens, rendering the memory cells useless - primary immune response all over again

Q8

a) glucose enters small intestine epithelial cells via facilitated diffusion through a carrier protein by co-transport with sodium. 1 Na+ and 1 glucose have to bind for carrier protein to change shape and release Na+ and glucose inside the cell. A concentration gradient of Na+ has to be maintained since it's facilitated diffusion (passive process). This is achieved by Na+/K+ pump that actively pumps Na+ out of cell (K+ into the cell), so there is always a higher concentration of Na+ outside of the cell, so it binds to a carrier protein again and glucose can enter the cell.

b) Plasma membrane=phospholipid bilayer arranged in a fluid mosaic (fluid mosaic makes diffusion possible). Only lipid soluble or very small molecules/atoms (that can be polar) can diffuse across. Oxygen is a small non-charged molecule, so can diffuse down its conc. gradient. Chloride is strongly (negatively) charged and not lipid-soluble, so needs a channel/carrier protein.