Notes

Action potentials

Myelin: specialized cells called Schwann cells wrapped along the axon. - Schwann cells are made of lipids and proteins - many Schwann cells form the myelin sheath  affects the speed of conduction of electrical impulses Transmission of nerve impulses: -...

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Control and co-ordination in mammals, the nervous system

Coordination In multicellular organisms, such as plants and animals, it is essential that cells can communicate with each other. This allows them to coordinate their activities appropriately. Organisms have specialised cells or molecules, called receptors, which are...

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Homeostasis in plants

Abscisic acid and stomatal closure Abscisic acid (ABA) is a stress hormone that is secreted in response to difficult environmental conditions such as very high temperatures or much reduced water supplies. ABA triggers the closure of stomata to reduce transpiration and...

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Control of blood glucose – glucagon

Insulin and glucagon work together as part of a negative feedback system. As a result of glucagon secretion, the liverreleases extra glucose to increase the concentration in the blood. Muscle cells do not have receptors for glucagon and so do not respond to it. This...

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The control of blood glucose

Blood glucose concentration should remain at a fairly constant value of about 100 mg glucose per 100 cm3 of blood.  If blood glucose concentration falls well below this level, the person is said to be hypoglycaemic. Cells do not have enough glucose to carry out...

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Osmoregulation

  Osmoregulation is the control of the water content of body fluids. It is part of homeostasis, the maintenance of a constant internal environment. It is important that cells are surrounded by tissue fluid of a similar water potential to their own contents, to...

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Excretion and structure of Kidneys

 CO2 produced by aerobic respiration. CO2 dissolves in H2O to produce a weak acid, so if too much builds up in body fluids the pH drops, which can damage cells and disrupt metabolism. CO2 is transported to the lungs dissolved in blood plasma and excreted in expired...

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Thermoregulation – The control of body temperature

Ectotherms - Animals that have a variable body temperature. - Use behavioural mechanisms (e.g. lying in the sun when cold, moving into shade when hot). Such mechanisms can be very effective, particularly when coupled with internal mechanisms to ensure that the...

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Homeostasis in mammals

VIDEO: Feedback loops https://www.youtube.com/watch?v=pR12XGWcn0U Negative feedback control of temperature https://www.youtube.com/watch?v=RgjKRJxvG-k Negative Feedback Control of Blood Pressure https://www.youtube.com/watch?v=YQMgV9pkwwA      ...

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Summary of Photosynthesis

4 ATP and reduced NADP are the two main products of the light-dependent reactions of photosynthesis, and they then pass to the light-independent reactions. 5 In the light-independent reactions, carbon dioxide is trapped by combination with a 5C compound, RuBP, which...

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Limiting factors in photosynthesis

Usually, only one of these factors will be the limiting factor in a plant at a certain time. This is the factor which is the furthest from its optimum level at a particular point in time. If we change the limiting factor the rate of photosynthesis will change but...

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The light-dependent reactions, Photophosphorilation

Chlorophyll molecules in photosystern I (PSI) and photosystern II (PSII) absorb light energy. The energy excites electrons, raising their energy level so that they leave the chlorophyll. The chlorophyll is said to be photo-activated. PSII contains an enzyme that...

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Photosynthetic Pigments

  An absorption spectrum is a graph showing the percentage of light absorbed by pigments, for each wavelength of light. An example is the absorption spectrum of chlorophyll a and b.  The best absorption is seen with violet-blue light.  There is also good...

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Using respirometers

Using a respirometer to measure the rate of uptake of oxygen The organisms to be investigated are placed in one tube, and non-living material of the same mass in the other tube. Soda lime is placed in each tube, to absorb all carbon dioxide. Cotton wool prevents...

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Structure and function of the mitochondrion

Structure Mitochondria is about 1 mm in diameter and 1-10 mm in length. Mitochondria have dynamic structures that move, change their shape and divide.  Enclosed by two membranes that have proteins embedded in phospholipid bilayers  Outer membrane is smooth and...

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7 Respiratory substrates, Respiratory quotions

Glucose is an essential fuel for some cells, e.g. brain cells, red blood cells and lymphocytes, but some cells, e.g. liver cells, also oxidise lipids and excess amino acids.  The fatty acid components of lipids are important: carbon atoms are detached in pairs as...

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Oxidative phosphorylation and Electron transport chain

Hydrogens from reduced FAD and reduced NAD first pass to hydrogen carriers in the inner membrane and are then split are split into protons (H+) and electrons (e-). The electrons pass along a series of electron carriers on the ETC of the inner membrane of the...

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The Krebs cycle

The Krebs cycle is a series of steps catalysed by enzymes in the matrix: • A 2-carbon atoms Acetyl CoA enters the cycle and combines with a 4- carbon compound (oxaloacetate) to give a 6-carbon compound (citrate/citric acid). Coenzyme A is reformed. Cycle turns twice...

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Energy and ATP

All living organisms need a continuous supply of energy to maintain their metabolism. They must absorb either light energy in photosynthesis or chemical potential energy to do the work necessary to stay alive. Such work includes: • Anabolic reactions: the synthesis of...

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