biology4alevel600

1 Organisms must do work to stay alive. The energy input necessary for this work is either light, for photosynthesis, or the chemical potential energy of organic molecules. Work includes anabolic reactions, active transport and movement. Some organisms, such as mammals and birds, use thermal energy released from metabolic reactions to maintain their body temperature.   2 Reactions that release energy must be harnessed to energy-requiring reactions. Th is ‘harnessing’ involves an intermediary molecule, ATP. Th is can be synthesised from ADP and phosphate using energy, and hydrolysed to ADP and phosphate to release energy. ATP therefore acts as an energy currency in all living organisms.   3 Respiration is the sequence of enzyme-controlled steps by which an organic molecule, usually glucose, is broken down so that its chemical potential energy can be used to make the energy currency, ATP.   4 In aerobic respiration, the sequence involves four main stages: gly...

A respirometer is a device used to measure the rate of respiration of a living organism by measuring its rate of exchange of oxygen and/or carbon dioxide . They allow investigation into how factors such as age, chemicals or the effect of light affect the rate of respiration. There are various different types of respirometer. One type is shown in the diagram. 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 contact of the soda lime with the organisms. Coloured fluid is poured into the reservoir of each manometer and allowed to flow into the capillary tube. It is essential that there are no air bubbles. You must end up with exactly the same quantity of fluid in the two manometers. Two rubber bungs are now taken, fitted with tubes as shown in the diagram. Close the spring clips...

There are many varieties of rice and they differ in their water requirements. Most of the rice in south-east Asia is grown in unusual conditions for a cereal plant. It is grown partly submerged in water in paddy fields. The fields are flooded and then ploughed. Young rice plants are planted in the rich mud formed in these paddy fields. The oxygen concentration of this mud fails rapidly after the paddy field has been flooded. The top ten centimetres or so retains some oxygen because it is able to diffuse in but below this depth anaerobic conditions exist and there is little or no oxygen present. Rice plants have a number of adaptations which enable them to grow well in these conditions. Rice  stems  contain a large number of air spaces   (hollow aerenchyma ) running the length of the stem and into the roots. This allows oxygen (some formed in the plant from photosynthesis) to penetrate through to the roots which are submerged in water, supplying oxygen for aerobic res...

The mitochondrion is a power plant and industrial park of the cell where energy stored in the bonds of carbohydrates is converted to a form more useful to the cell (ATP) and certain essential biochemical conversions of amino acids and fatty acids occur. 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 highly permeable to small solutes, but it blocks passage of proteins and other macromolecules Inner membrane is convoluted and contains embedded enzymes that are involved in cellular respiration. The membrane' have many infoldings called cristae which increase the surface area available for these reactions to occur. The inner and outer membranes of mitochondria divide it into two internal compartments: inntermembrane space is the narrow region between the inner and outer ...

A respiratory substrate is a molecule from which energy can be liberated to produce ATP in a living cell. Glucose is not the only respiratory substrate. All carbohydrates, lipids and proteins can also be used as respiratory substrates. Many cells in the human body are able to use a range of different respiratory substrates. However, brain cells can only use glucose. Heart muscle preferentially uses fatty acids. 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 ACoA and fed into the Krebs cycle. Amino acids  are deaminated and their carbon–hydrogen skeletons converted into pyruvate or into ACoA.  The energy values of these different substrates are not the same. Energy values of respiratory substrates Most of the energy released in respiration co...

Only small amounts of ATP are produced when one glucose molecule undergoes anaerobic respiration . This is because only glycolysis is completed. The Krebs cycle and oxidative phosphorylation, which produce most ATP do not take place. The precise number of molecules of ATP produced in aerobic respiratlon of one glucose molecule varies between different organisms and different cells, but is usually between 30 and 32 molecules. Syllabus:  12.2 Respiration j) distinguish between respiration in aerobic  and anaerobic conditions in mammalian tissue and in yeast cells, contrasting the relative energy released by each  (a detailed account of the total yield of ATP from the aerobic  respiration of glucose is not required)

Anaerobic respiration is a type of respiration that does not use oxygen. It is used when there is not enough oxygen for aerobic respiration. In the absence of free oxygen: Oxidative phosphorylation cannot take place, as there is nothing to accept the electrons and protons at the end of the electron transport chain.  Hydrogen cannot be used up by combining it with oxygen to give water, so reduced NAD cannot be recycled to NAD in this way to allow glycolysis to continue.  The mitochondrion quickly runs out of NAD or FAD that can accept hydrogens from the Krebs cycle reactions. The Krebs cycle and the link reaction therefore come to a halt.  Glycolysis, however, can still continue, so long as the pyruvate produced at the end of it can be removed and the reduced NAD can be converted back to NAD.  Two other pathways allow the recycling of reduced NAD formed during glycolysis: • Ethanol pathway: conversion of pyruvate to ethanol in alcoholic fermentation, e.g. by yeast...