Cellular respiration
Releasing energy
Respiration releases energy – it is an exothermicReaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases. process.
Photosynthesis is the process by which plants, and some bacteria, synthesise food molecules – which they then use, in addition to other things, for respiration. The process of photosynthesis requires energy – it is endothermicReaction in which energy is taken in..
Don't confuse respiration with breathing, which is ventilationBreathing in and out.. Respiration happens in cells.
Why organisms need energy
All organisms need energy to live. This energy is used:
- to drive the chemical reactions needed to keep organisms alive – the reactions to build complex carbohydrateFood belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis., proteinOrganic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair. and lipidFat or oils, composed of fatty acids and glycerol. from the products of photosynthesisA chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. in plants, and the products of digestionThe breakdown of large insoluble food molecules to smaller soluble ones. in animals, require energy
- movement – in animals, energy is needed to make muscles contract, while in plants, it is needed for transport of substances in the phloemThe tissue in plants that transports the products of photosynthesis, including sugars and amino acids.
Respiration is only around 40 per cent efficient. As animals respire, heat is also released. In birds and mammals, this heat is distributed around the body by the blood. It keeps these animals warm and helps to keep a constant internal temperature.
Energy is also used:
- for cell division
- to maintain constant conditions in cells and the body – homeostasisThe maintenance of steady conditions. The ability of the body to maintain a constant internal environment, eg temperature and blood glucose concentration.
- to move molecules against concentration gradients inactive transportThe transport of molecules against their concentration gradient from a region of low concentration to a region of high concentration.
- for the transmission of nerve impulsesElectrical signals that travel along the nerve fibre from one end of the nerve cell to the other.