AQA AS Unit 1 Biology - Unofficial Markscheme

1)Pancreas and small intestine (2m)
a.Maltase has a specific tertiary (3D) structure and so forms a unique active site, only which a complementary substrate can enter – Maltose. Forming Enzyme-substrate complexes. (3m)

2)Ribosomes, golgi apparatus and mitochondria. (3m)
a.Magnification of 2000 (1/100)/5x10^-6) = 2000. (2m)

3)Lactose (disaccharide) hydrolysed into glucose and galactose which are both reducing sugars > whilst lactose remains undigested and so tastes less sweet. (2m)
i. Large surface area, and so increases exposure of the lactase enzyme to the lactose.
ii. Prevents contamination of the milk, doesn't contain lactase enzymes.
iii. (3m)

4)[Fish question]
a.Conclusions:
i.People who didn’t eat fish are more likely to suffer from asthma [data]
ii.Can’t remember x2 (3m)
b.Test for lipids: grind the fish up, add ethanol and water and mix. A cloudy white colour/emulsion if form oils are present as they’re lipids. (3m)

5)[Whooping cough]
i. Number of cases decreases, elaborated that point.
ii. Religious, ethical, medical objects and so more people reject vaccinations. (2m)

The peaks) This is all about the Secondary response, on initial exposure B-memory cells are made for the antigens of the pathogen. After every peak, the cases decreases as people produce more antibodies and at a faster rate. [Spoke about primary and secondary response] (2m?)

Last part) Herd Immunity, majority of population are vaccinated in a given time period and so the number of cases is minimal this reduces the transmission of Whooping cough as no-one virtually is infected by it. (2m)

6)[Honey thing] Water potential decreases and so water moves in by osmosis from an area of higher WP to an an area of lower WP, down the concentration gradient. I went onto speaking about osmositc lysis which is apparently incorrect. (3m?)

7)Heartbeat question - the range was like 71 - 53, can't entirely remember for 100%.(1m)
i. The percentage decrease for women = 13.6%.(2m)
ii. Stroke volume increases due to deeper contractions of the Heart Muscle, greater surge of blood per contraction. (2m)

8)Antigens/bacteria which antibodies are required for. (1m)
a.Facilitated diffusion, molecules bind onto the carrier proteins which causes them to change in shape and release to the opposite side – down the concentration gradient [high concentration to a lower concentration] from the blood – liver cells I think. (2m)

Reducing risk of CHD) less deposits of fatty substances such as LDL cholesterol and so likelihood of atheroma's developing is minimal and so reduces the risk of aneurysms and thrombosis. (3m?)

9)Cell fractionation separates organelles in order of mass.
a.Animals cells placed in cold, isotonic and buffered solution – reduce enzyme activity, prevent osmotic movement (cells bursting or shrinking) and maintain contain pH, respectively.
b.Cells broken down in a Homogeniser which releases the organelles.
c.Resultant fluid, homogenate, filtered to remove whole cells and debris.
d.Homogenate spun in tubes in a Centrifuge. Nuclei sets at the bottom (heaviest organelle) as sediment. The reminisce known as supernatant which is removed and spun once more at a faster speed – Mitochondria sets at the bottom – sediment. (5m)

10)TEM has the highest resolving power and magnification, as it uses a beam of electrons which has a short wavelength and so diffraction is considerably lower.
a.TEM works by penetrating electrons through the specimen, some regions absorb the electrons appearing darker whilst other regions allow electrons to directly penetrate through, appearing brighter – onscreen image produced.
b.Limitations: black and white, 2D imagine [EXPLAIN]
c.Complex staining process – artefacts + specimen needs to be thin [EXPLAIN]
(5m)

Misc questions:
-Asthma = muscles surrounding the bronchioles constrict. (1m)
Total-60m

Pretty sure when they asked you why the peaks were reducing between 1980 & 1990, part of Q5, you were meant to notice and discuss that the percentage of infants being vaccinated rose from like 45% to 81% (if I remember correctly) so an increasing proportion of the population had immunity to it and hence the total number of recorded cases in each outbreak (peak) would decrease. Or thats what I wrote ... I didn't write anything about a B-Cell response and don't think it was what it was asking for?

Pretty sure when they asked you why the peaks were reducing between 1980 & 1990, part of Q5, you were meant to notice and discuss that the percentage of infants being vaccinated rose from like 45% to 81% (if I remember correctly) so an increasing proportion of the population had immunity to it and hence the total number of recorded cases in each outbreak (peak) would decrease. Or thats what I wrote ... I didn't write anything about a B-Cell response and don't think it was what it was asking for?

9. a) was endocytosis : "LDL particles in the bloodstream bind to these extracellular LDL receptors. The clathrin-coated pits then form vesicles that are endocytosed into the cell." - wikipedia page for LDL

for limitations of the tem surely there are more points you could have put. i put like 6 limitations.

For the beeds questions: more suggestions?

-if not doing beed method the lactose maybe too large to be absorbed and broken down (1)?
-more faster thus efficient (1)?

4) [Fish question]
a. Conclusions:
i. People who didn’t eat fish are more likely to suffer from asthma [data]

You probably get a mark for saying correlation doesn't mean causation/there may be another factor also

Meh I put facilitated diffusion too like many others because it mentioned binding

The question asked "what does figure 5 tell you" or something along those lines, so they'd want you to explicitly mention figure 5 and what it means, not what it doesn't mean.

Though, I could be wrong, but that's just my take on it.