Specification for B4, C4 and P4 in Additonal Science (OCR21stC)

I used this to revise for my B4. C4 and P4 exams.
i printed it out as a handout with 2 slides on a sheet,
i then highlighted and made notes around the handout.
It covers 'what you need to know' for the exam.
i hope its useful, let me know !! <3

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  • Created by: Manisha
  • Created on: 22-09-11 19:23

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Additional Revision
B4, C4, P4
B4 C4 P4…read more

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HOME…read more

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B4.1 What is homeostasis?
· 1. recall that homeostasis is the maintenance of a constant internal
· environment;
· 2. understand that automatic control systems throughout the body maintain
· a range of factors at steady levels, which are required for cells to function
· properly (limited to temperature and water);
· 3. understand that strenuous exercise, survival in hot or cold climates:
· scuba-diving and mountain climbing affect homeostasis (temperature,
· blood oxygen levels, hydration and salt levels);
· 4. understand how artificial systems, such as the temperature control
· system in an incubator, are similar to body control systems;
· 5. understand that artificial and body systems have:
· a. receptors to detect stimuli;
· b. processing centres to receive information and coordinate responses;
· c. effectors which produce the response automatically;
· 6. understand the principle of negative feedback;
· 7. recall that negative feedback between the effector and the receptor
· of a control system reverses any changes to the systems steady
· state;
· 8. understand that some effectors work antagonistically, which allows
· a more sensitive response.…read more

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B4.2 Why is homeostasis important for a cell?
· 1. understand that diffusion is the passive overall movement of molecules
· from a region of their high concentration to a region of their low
· concentration;
· 2. understand that osmosis (a specific case of diffusion) is the overall
· movement of water from a dilute to a more concentrated solution through
· a partially permeable membrane;
· 3. recall some examples of chemicals, such as O2, CO2 and dissolved food,
· which move in/out of cells by diffusion;
· 4. understand that some chemicals (for example, glucose) are also
· moved by active transport;
· 5. understand that if excess water moves into animal cells by osmosis
· the cell membrane may rupture and if too much water moves out of
· cells they are unable to function correctly;
· 6. recall that enzymes are proteins that speed up chemical reactions in
· cells;
· 7. recall that enzymes need a specific constant temperature to work at their
· optimum;
· 8. explain how, at low temperatures, small increases in temperature
· increase the frequency of collisions between an enzyme and other
· molecules, so the rate of reaction increases;
· 9. recall that at higher temperatures enzymes stop working (denature);
· 10. understand that only molecules with the correct shape can fit into the
· enzyme. This is known as the `lock and key' model;
· 11. recall that enzymes have a small part called the active site where
· certain molecules bind to the enzyme and the reaction occurs;
· 12. understand that the shape of the active site can be changed by
· heating above a certain temperature or altering the pH, so that the
· molecules can no longer fit and the reaction cannot happen.…read more

Slide 5

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B4.3 How is our body temperature kept constant?
· 1. recall that energy gain and loss must be balanced in order to maintain a
· constant body temperature;
· 2. recall that body extremities tend to be cooler than the core body
· temperature, and that energy is transferred from the blood to the tissues
· when blood reaches cooler parts;
· 3. recall that temperature receptors in the skin detect external
· 4. recall that temperature receptors in the brain (hypothalamus) detect
· temperature of the blood;
· 5. understand that the brain (hypothalamus) acts as a processing centre,
· receiving information from the temperature receptors, and triggering the
· effectors automatically;
· 6. recall that effectors include sweat glands and muscles;
· 7. understand that at high body temperatures:
· a. more sweat is produced by sweat glands which cools the body when it
· evaporates;
· b. blood vessels supplying the capillaries of the skin dilate
· (vasodilation) allowing more blood to flow through skin
· capillaries which increases energy loss;…read more

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8. recall that heat stroke is an uncontrolled increase in body temperature;
· 9. recall the common causes, symptoms and initial treatment of heat
· 10. explain how exposure to very hot temperatures produces increased
· sweating, and can produce dehydration, which may lead to reduced
· sweating and further increase of core body temperature;
· 11. understand that when core body temperature becomes too high the
· normal mechanisms for controlling body temperature break down;
· 12. understand that at low body temperatures:
· a. the increased rate of respiration stimulated when muscles contract
· rapidly (shivering) results in some of the energy transferred in
· respiration warming the surrounding tissues;
· b. blood vessels supplying the capillaries of the skin constrict
· (vasoconstriction) restricting blood flow through skin capillaries
· which reduces energy loss;
· 13. recall that hypothermia is when core body temperature falls below
· 14. recall the cause, symptoms and initial treatment of hypothermia;
· 15. understand that in hypothermia body heat cannot be replaced as fast
· it is being lost.…read more

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