C1.2 Cell Respiration PDF

## C1.2 Cell respiration ### 1. Properties of ATP - Every cell needs to distribute energy like a country distributes money. - The basic energy currency in all cells is the substance ATP (adenosine triphosphate) - a nucleotide with adenine, ribose and three phosphate groups. ATP has the followin...

## C1.2 Cell respiration ### 1. Properties of ATP - Every cell needs to distribute energy like a country distributes money. - The basic energy currency in all cells is the substance ATP (adenosine triphosphate) - a nucleotide with adenine, ribose and three phosphate groups. ATP has the following characteristics: - **Chemically stable** at neutral pH levels typical of cells, so ATP doesn't break down and prematurely release energy. - **Soluble in water** so ATP can diffuse freely in cytoplasm, reaching any part of the cell in a fraction of a second. - **Unable to diffuse through the phospholipid bilayers** of membranes so ATP's movement within cells can be controlled and there is no leakage out of cells. - ATP can release a quantity of energy (by removal of the third phosphate group) that is sufficient for a wide range of tasks within the cell, but with a little extra that is wasted by transformation to heat. - ATP can be easily regenerated by adding a third phosphate group to ADP (adenosine diphosphate). ### 2. Cellular processes requiring ATP - Active transport across membranes - Synthesis of macromolecules (anabolism) - Movement of cell components such as chromosomes moving during mitosis and meiosis. - Movement of the whole cell (cell motility) ### 3. Converting between ATP and ADP - ATP and ADP are endlessly interconvertible. - Energy is released when ATP is converted to ADP. - Energy has to be invested to convert ADP to ATP. - This energy can come from a variety of sources including sunlight, oxidation of foods (sugar and fat), and transfer of a phosphate group from other compounds in the cell to ADP. - ADP + phosphate + energy → ATP + H2O (condensation/phosphorylation reaction) - This is also a condensation reaction as water is produced, whereas conversion of ATP to ADP requires a water molecule to be split so it is a hydrolysis reaction. ### 4. Cell respiration as a system for producing ATP - Respiration is the part of metabolism in which carbon compounds are oxidized to release energy in the form of ATP. - It happens inside every living cell. - Glucose and fatty acids are the principal substrates used in respiration, but a wide range of other carbon compounds can be used, including amino acids. - Cell respiration is different from ventilation and gas exchange: - Ventilation (breathing) is moving air in and out of the lungs. - Gas exchange is swapping one gas for another at a surface where a cell or organism is in contact with its environment. ### 5. Comparing anaerobic and aerobic cell respiration in humans Cell respiration can be carried out aerobically or anaerobically: | Characteristic | Aerobic | Anaerobic | |---|---|---| | Is oxygen used? | Yes | No | | What substrates can be used? | Sugars or lipids | Glucose and other sugars | | How much ATP is produced per glucose? | 30- 32 (a large yield) | 2 (a small yield) | | What are the waste products? | Carbon dioxide + H2O | Lactate (lactic acid) | | In a human cell, where do the reactions occur? | Cytoplasm + mitochondria | Cytoplasm only | Simple word equations can be used to show the substrates and end products of respiration in humans using glucose: - **Aerobic respiration:** glucose + oxygen → carbon dioxide + water + energy - **Anaerobic respiration:** glucose → lactate + energy ### 6. Investigating the rate of cell respiration - Any device that measures the rate of cell respiration is a respirometer. - A sample is put into the apparatus, where it can absorb oxygen from and excrete CO2 into the air around it. - An alkali such as potassium hydroxide absorbs all the CO2 excreted, so changes in air pressure or volume inside the respirometer are due to oxygen consumption. - The decrease in pH of the alkali can be used to deduce the amount of CO2 produced. - The diagram shows a respirometer used to measure the respiration rate of soil microorganisms. - O2 uptake is calculated from the decrease in air pressure. - CO2 release is calculated from the decrease in pH of the potassium hydroxide solution. - Temperature changes affect air pressure so it is essential to prevent the respirometer heating up or cooling down. - Respiration rate is O2 uptake or CO2 release per unit time.