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  1. I

    A level Biology: Post your doubts here!

    As far as I know, if you mention 5 points out of 10, you'll get the full mark. But you have to make sure that all the points you mention are in a clear and logical order.
  2. I

    A level Biology: Post your doubts here!

    It secretes both times, and both matter (not only the second). Capillaries are destroyed in a patient with emphysema, so this is probably the reason why there is a greater 'resistance'.
  3. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    Insha2allah kheir. After 24 hours, you can post questions and I'll be glad to answer them. But since I didn't do the exam, please post the full question please.
  4. I

    A level Biology: Post your doubts here!

    So that the blood won't clot immediately which kills the host instantly. Plasmodium needs a host to survive. In emphysema patients, most of the elastic fibres are digested by white blood cells, so there is much greater resistance when the alveoli are trying to expand. A closed circulation system...
  5. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    Your exam is tomorrow??? Good luck people!!! Bitawfiq insha2allah! باتوفيق ان شاء الله! "A"الله ينجحكم و ان شاء الله ستحصلون ال Btw, when's your P1 exam? Just curious.
  6. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    Through glycosylation and phosphorylation. I'm not going to bother giving a detailed explanation, as I'm pretty sure they aren't included in the AS syllabus.
  7. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    Not really, to get an A, you gotta get questions right. It's as simple as that. Don't count on the threshold. If the threshold is low, then you can be sure that the exam was hard for the general population (which normally includes you as well) and that their marking is relatively strict.
  8. I

    A level Biology: Post your doubts here!

    I wouldn't say exactly that they have an advantage, but some organisms (like fish and earthworms) don't need the complexity of a double-circulation system. This is because their volumes are very small hence their energy requirements are low. Such requirements can be easily fulfilled by a...
  9. I

    A level Biology: Post your doubts here!

    Both are correct; I don't see any contradiction between the two explanations.
  10. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    From what I know, catalase DOES have a haem group. A haem group is just a group that contains iron. In RBCs, the haem group binds to oxygen, but in catalase, the haem group binds to hydrogen peroxide. EDIT: this is what I know from AP Biology; I'm not sure if it's included in the AS syllabus.
  11. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    As everyone said, herd immunity is vaccinating a large proportion of the population (ideally, 95%) When most people are vaccinated, the disease can only be transferred within the unvaccinated population (5%) Since the number of unvaccinated people are very low, the disease will eventually die...
  12. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    We know that people with SCA can't carry as much oxygen as they should. But the curve tells us that at low partial pressures of oxygen (like in tissues), they can release the oxygen they have more easily than those with normal RBCs. This is because the graph for SCA is "lower" than the normal...
  13. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    There's one crucial mistake: The bond between G and C is NOT a triple bond. It's three different HYDROGEN bonds. Same goes for the bonds between A and T/U.
  14. I

    A level Biology: Post your doubts here!

    Okay, if we look at cnidarians, we can easily see that they don't need a transport system. Cnidarians are organisms that live underwater and are only two cells thick (hence very high surface area to volume ratio). This means that any required nutrients or any wastes can easily pass in or out...
  15. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    From the word 'globular', it's a protein that folds into a 'globe'-like shape. So instead of being flat, it is folded into a 3-D shape.
  16. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    I don't really know how much you're supposed to know for the AS level. Our school offered an AP course last year, and here's what we took (I'll try to explain it as simply as possible). Cholesterol has a hydroxyl- group (-OH) which is hydrophilic, so this part interacts with the phospholipid...
  17. I

    A level Biology: Post your doubts here!

    In the endocrine system, the messengers are hormones (chemical messengers) while in the nervous system, the stimulus is transferred as impulses. Hormones reach their target organs (where it binds to the receptors on the cell membranes) by being circulated around the blood while the impulses...
  18. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    This is kinda hard to explain, so please bear with me. 1) You get a colony of bacteria to grow for many generations in a petri dish full of N15. So all the bacteria will have DNA that's made from N15. 2) For the next generation, breed those bacteria in a culture of N14. Remember that DNA has two...
  19. I

    AS LEVEL BIOLOGY... discuss here AS students only :)

    A mutualistic relationship is when both parties benefit from each other. For example, in legumes, you have nitrifying bacteria that can fix nitrogen (make nitrogen gas in the atmosphere to nitrate ions which plants can use), but they can't make their own food. Also, legumes can make their own...
  20. I

    A level Biology: Post your doubts here!

    Introductory notes: Sickle-cell anaemia (SCA) is a recessive genetic disease which causes haemoglobin (hence the RBC) to be shaped like a 'sickle' (crescent/moon-shaped) Since RBCs are deformed, they cannot carry oxygen as efficiently as normal RBCs can. People with SCA are immune to malaria...
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