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OCR AS Biology F211 - Unofficial Mark Scheme

This is not the official mark scheme, this is a collation from me and my friends, who are all A students. I will not have every point on here that gains credit. Post questions and I'll try to answer.

CELL STRUCTURE QUESTION

1a)i) Present in plant cells but not animal cells:
Chloroplasts, cell wall (2 marks)
ii) Present in animal cells but not plant cells:
Centrioles (1 mark)
1b) Description of what the cytoskeleton does:
Determines shape of cell; changes shape of cell; vesicles move down microtubules; RNA/other molecules move down microtubules (3 marks)
1c) Secretion of protease enzymes from pancreatic cells:
EXOCYTOSIS; mRNA moves out of nuclear pores to the ribosomes; ribosomes assemble the proteins;
vesicles move to Golgi body down microtubules; modified and repackaged; vesicles move to the cell surface membrane; fuse with membrane; deposit enzymes outside cell (5 marks, one for QWC)

VASCULAR TISSUES CROSS-SECTION LEAF QUESTION
-Xylem on top, phloem on bottom (DON'T label the middle, that's cambium) (1 mark)
-Vascular bundle (1 mark)

BALLOONS
The balloon expands because pulling the rubber sheet down increases the volume inside the bell jar, which decreases the pressure, so air is sucked into the balloons down the pressure gradient (2 marks)
Tidal volume: Volume of air moved in and out of the lungs from a 'normal' breath at rest (2 marks)
How to demonstrate it: Pull the rubber sheet down and release it (in tandem with a student's even breaths at rest?) (2 marks)
Vital capacity: Maximum volume of air that can be inspired + maximum volume of air that can be expired (2 marks)
How to demonstrate it: Pull the rubber sheet down as far as it can go without the balloons bursting (1 mark)

TISSUE FLUID/HAEMOGLOBIN/BOHR SHIFT
a) Why erythrocytes don't enter the tissue fluid:
They're too big, 7 micrometres, can't fit through the fenestrations of the capillary wall (2 marks)
b) Haemoglobin transporting oxygen:
High affinity for oxygen; 4 haem groups, each of which can bond to one oxygen molecule; transported around body in blood; oxygen released to tissues where there is a low O2 partial pressure (3 marks)
c) How hydrogencarbonate ions are made:
Carbonic anhydrase; reaction of water and carbon dioxide to make H2CO3; dissociation into H+ ions and hydrogencarbonate ions (4 marks)
d) Carbon dioxide reaction:
Bohr shift. The H+ ions produced due to the high partial pressures of carbon dioxide bind to haemoglobin and displace the oxygen atoms, so they diffuse out of the haemoglobin into the actively respiring tissue. (3 marks)

GREX
a) Mitosis (asexual reproduction) (1 mark)
b) 3 is where differentation starts (1 mark)
c) Cell signalling (1 mark)
d) There is cell signalling with the folic acid and bacteria; and the cAMP (specific complementary receptors...molecules...trigger response...) (2 marks)
e) They can be adapted to this by having specific, complementary receptors in their plasma membranes to the molecules folic acid and cAMP, e.g. glycoproteins (2 marks)
f) It takes 17 hours to form the grex (1 mark)

TRANSLOCATION
Observations:
2 and 3 means that charged particles (H+ ions) are transported out and then back into the companion cells, due to the changes in pH; against concentration gradient (2 marks)
4 means that the process is an active process requiring ATP from aerobic respiration. (1 mark)
Observations through electron microscope:
Large amount of mitochondria, transporter proteins in plasma membranes of companion cells
Gap fill:
Active transport, concentration, facilitated, diffusion, ARGH (amino acids is definitely correct; waiting for confirmation on glucose/fructose/maltose) (5 marks)

DEFINITIONS (1 mark each)
-Homologous pair (of chromosomes)
-Organ system
-Open circulatory system
-Apoplast pathway
-Ultrastructure
-Meiosis
-Exocytosis
(edited 9 years ago)

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Bump :smile:
Reply 2
Avatar for cuppa
cuppa
18
Thanks for this :smile:
I kinda panicked and put the labels X and P in the actual inside of them, rather than drawing a line and labelling it like you'd do in practicals. I wonder if that's gonna cost me LOL
Original post by paradoxicalme
Bump :smile:


for the last one i said exophagocytosis
Original post by Legal drugdealer
for the last one i said exophagocytosis


That'll work, because they're solid substances. :smile:
Original post by paradoxicalme
That'll work, because they're solid substances. :smile:


cool are they all the question?
Original post by Legal drugdealer
cool are they all the question?


I'm not entirely sure. I think so. I may have missed part of one out, but I'm sure someone will let me know if I have. In any case it's the vast majority of the questions. :smile:
You forgot the 'why does the balloon expand?' question, and the assimilates gap fill :smile:
Original post by cuppa
Thanks for this :smile:
I kinda panicked and put the labels X and P in the actual inside of them, rather than drawing a line and labelling it like you'd do in practicals. I wonder if that's gonna cost me LOL


Nope, that'll be fine :smile:
Reply 9
Avatar for ariman111
ariman111
will i lose the mark if I put the X and the P actually inside the diagram (not drawing a line)
Original post by Nandosfood
You forgot the 'why does the balloon expand?' question, and the assimilates gap fill :smile:


Fixed, thank you. :smile:
If you wrote that the stage for differentiation of the cells was interphase rather than a number, would that still be a mark? /:
Original post by ariman111
will i lose the mark if I put the X and the P actually inside the diagram (not drawing a line)


I don't think so! Everyone I've spoken to did that.
Ok, maybe I didn't do as badly as I first thought xD
Original post by Unknown Life
If you wrote that the stage for differentiation of the cells was interphase rather than a number, would that still be a mark? /:


Nope, don't think so :frown: I think you had to put the number. And 'interphase' is a little vague. Only one mark, though :smile:
Original post by ariman111
will i lose the mark if I put the X and the P actually inside the diagram (not drawing a line)


... I thought that was what you were meant to do?!
And also, for the question about how haemoglobin aids the transport of oxygen, could you write about how oxygen and haemoglobin bind reversibly in the erythrocytes, and travel to the resourcing tissues where they are needed, and then dissociate? Sorry /:


and for the question about what the structure was containing the xylem and phloem, was it okay if you wrote vein (vascular)?:frown:
(edited 9 years ago)
Original post by paradoxicalme
I'm not entirely sure. I think so. I may have missed part of one out, but I'm sure someone will let me know if I have. In any case it's the vast majority of the questions. :smile:


Oh also I said Bohr effect not shift, the microtubules move the organelles; keep the shape of the cell; and i didn't say release it afterwards for the balloon question
Reply 18
Avatar for Dave97
Dave97
2
Instead of homogenous pair of chromosomes I put alleles, is that still acceptable?
Original post by ResultInExcellence
... I thought that was what you were meant to do?!


same here

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