AQA A level biology paper 1 7th June 2018 unofficial markscheme

please contribute

Please contribute

100% not anaphase it was prophase

1. Chromatin was condensed into chromosome; sister chromatids joined together by centromere in X shape

for lycxose and ATP i said without lyxcose it continued as normal then levelled off because the enzymes were saturated. Said with lyxcose it was a lower rate because it was a competitive inhibitor and blocked active site but then as concentration of ATP increased rate increased because the inhibitor had less of an effect.

But i was in such a panic I have a feeling I might have read the graph wrong

Answers I remember:

First Question: Why does the figure show mitosis? Because chromosomes were double-armed chromatids replicated previously from interphase. And the double-armed chromatids were condensed to be shorter and thicker and thus easily visible with staining. Mutlichoice question: the answer was prophase. Why were the cells placed in a solution with higher water potential? So water moves into the cells by osmosis, and this increases the volume of the cell so more space for the double-armed chromatids, so less likely to cross.

The answer to the Percentage Question involving the ratios was around 30%. You divide the value of the lower curve ration around 0.4 by the value of the upper curve ratio of around 1.35. This is because the 1.35 ratio is considered to be 100%.

Horses and rabbits question about blood was 2 marks. Horse because more blood (give the calculation so 350x13 compared to rabbit calculation) so more antibodies. Why were they given a vaccine after two weeks? Initially the vaccine induced a primary response = low number of antibodies produced but memory cells produced. Second vaccination induces a secondary immune response = much higher antibody production because memory cells are stimulated. This was a 3 marker.

Lyxcose and the ATP question. No idea.

Chi-squared question: the value given was much greater than the critical value. So result is significant = null hypothesis rejected. Some factor other than chance is affective the results.

Potato cube surface area 3 marker: you actually had to calculate the surface area. Totally looked passed this and lost 3 marks.

No idea how to do the proportion of 2n gametes table question. The question on directional selection was 3 marks. Directional selection is selection to one extreme phenotype in this case it is tetraploids. So more likely to survive as higher yield so a shift in the mean towards this extreme i.e. more 2n gametes over generations produce more tetraploids.

Bees Question. Ethical so make sure no harm to bees. Different species so make sure you identify different physical features. How would they improve their method? Random sampling but this only gives you 1 mark.

The amino acid table question. Drawing was 1 marker. Why does the change from glu amino acid to lys amino acid cause a change in one chain but no change in the other chain? The position of the substitution was different. This changed the tertiary structure and specific bonds formed here e.g. hydrogen/ionic/disulphide. So one chain had a change in tertiary structure but the other chain did not as there was no difference in the tertiary structure bonds. Something related to tertiary structure is the answer.

Breathing 6 marker. You can bullet point this. Inspiration = active process as contraction of external intercostal muscles and diaphragm increase volume of thorax decrease pressure of lungs so air forced into lungs. Oxygen in air diffuses from bronchioles into alveoli into capillaries. You can expand on alveoli I guess. Expiration = passive process as external intercostal muscles and diaphragm relax decreasing volume of thorax increase pressure in lungs so air forced out of the lings. I am assuming two marks for each inspiration, alveoli, expiration.

Triglycerides and Phospholipid comparison 5 marker. Both have glycerol. Both ester bonds. Both fatty acid chains. Both insoluble. Triglyceride three fatty acids. Phospholipid two fatty acids and phosphate. Phospholipid forms bilayer, Triglyceride forms insoluble droplets. Bullet points.

Lactose 4 marker glycoprotein. Lactose disaccharide with glycosidic bond. Monomers are glucose and galactose. Proteins modified in the Golgi apparatus and glycoprotein formed when a carbohydrate such as lactose is added to protein (the question asked how does a glycoprotein form not where are they glycoproteins located so not cell membrane).

Overall, much more difficult than previous papers. WAY MORE TIME NEEDED TO ANSWERS ALL THESE QUESTIONS. I DONE THE LAST 3 QUESTIONS IN AROUND 10 MINUTES. These answers are probably not in order, its just the way I remember them.

what did the was the y axis on the lyxcose graph?