bio

Done by: Amr Jaber Grade 10B Heterotrophs A heterotroph is an organism that eats other plants or animals for energy and nutrients. The term stems from the Greek words hetero for “other” and trophe for “nourishment.” Organisms are characterized into two broad categories based upon how they obtain their energy and nutrients: autotrophs and heterotrophs. Autotrophs are known as producers because they can make their own food from raw materials and energy. Examples include plants, algae, and some types of bacteria. Heterotrophs are known as consumers because they consume producers or other consumers. Dogs, birds, fish, and humans are all examples of heterotrophs. Heterotrophs occupy the second and third levels in a food chain, a sequence of organisms that provide energy and nutrients for other organisms. Each food chain consists of three trophic levels, which describe an organism’s role in an ecosystem. Occupying the first trophic level are autotrophs, such as plants and algae. Herbivores—organisms that eat plants—occupy the second level. Carnivores (organisms that eat meat) and omnivores (organisms that eat plants and meat) occupy the third level. Both primary (herbivores) and secondary (carnivores and omnivores) consumers are heterotrophs, while primary producers are autotrophs. A third type of heterotrophic consumer is a detritivore. These organisms obtain food by feeding on the remains of plants and animals as well as fecal matter. Detritivores play an important role in maintaining a healthy ecosystem by recycling waste. Examples of detritivores include fungi, worms, and insects. There are two subcategories of heterotrophs: photoheterotrophs and chemoheterotrophs. Photoheterotrophs are organisms that get their energy from light, but must still consume carbon from other organisms, as they cannot utilize carbon dioxide from the air. Chemoheterotrophs, by contrast, get both their energy and carbon from other organisms.  A major difference between autotrophs and heterotrophs is that the former can make their own food by photosynthesis whereas the latter cannot. Photosynthesis is a process that involves making glucose (a sugar) and oxygen from water and carbon dioxide using energy from sunlight. Autotrophs can manufacture energy from the sun, but heterotrophs must rely on other organisms for energy. Another major difference between autotrophs and heterotrophs is that autotrophs have an important pigment called chlorophyll, which enables them to capture the energy of sunlight during photosynthesis, whereas heterotrophs do not. Without this pigment, photosynthesis could not occur.  Heterotrophs benefit from photosynthesis in a variety of ways. They depend on the process for oxygen, which is produced as a byproduct during photosynthesis. Moreover, photosynthesis sustains the autotrophs that heterotrophs depend on to survive. While meat-eating carnivores may not directly depend on photosynthetic plants to survive, they do depend on other animals that consume photosynthetic plants as a food source.  Examples of Heterotroph Herbivores 287718560579000Heterotrophs that eat plants to obtain their nutrition are called herbivores, or primary consumers. During photosynthesis, complex organic molecules (carbon dioxide) are converted into energy (ATP) through cellular respiration. The ATP is often in the form of simple carbohydrates (monosaccharaides), such as glucose, and more complex carbohydrates (polysaccharides), such as starch and cellulose. Starch is easily broken down by most animals, due to the presence of an enzyme secreted from the salivary glands and pancreas called amylase. Cellulose, which is a major component of plant cell walls and an abundant carbohydrate, converted from inorganic carbon, is harder to digest for many animals. Most herbivores have a symbiotic gut organism, which breaks down the cellulose into a usable form of energy. Examples of herbivores include cows, sheep, deer and other ruminant animals, which ferment plant material in special chambers containing the symbiotic organisms, within their stomachs. Animals that eat only fruit, such as birds, bats and monkeys, are also herbivores, although they are called frugivores. Most plant material consists mostly of hard-to-digest cellulose, although plant nectar consists of mostly simple sugars, and is eaten by herbivores called nectarivores, such as hummingbirds, bees, butterflies and moths. Carnivores The energy that is transferred through the food chain, initially from the inorganic compounds, converted to organic compounds that are used as energy by autotrophs, is stored within the body of the heterotrophs called primary consumers. The energy carnivores can use as energy mainly comes from lipids (fats) that the herbivore has stored within its body. Small amounts of glycogen (a polysaccharide of glucose which serves as form of long term energy storage) is stored within 345016664240800the liver and in the muscles and can be used for energy intake by carnivores, although the supply is not abundant. Carnivores are usually predators, such as secondary consumers: heterotrophs which eat herbivores, such as snakes, birds and frogs (often insectivores) and marine organisms which consume zooplankton such as small fish, crabs and jellyfish. They may also be tertiary consumers, predators that eat other carnivores, such as lions, hawks, sharks, and wolves. Carnivores may also be scavengers, animals such as vultures or cockroaches, which eat animals which are already dead; often this is the carrion (meat) of animals that has been left over from the kill of a predator. Fungi Fungi are heterotrophic organisms, although they do not ingest their food as other animals do, but feed by absorption. Fungi have root-like structures called hyphae, that grow and form a network through the substrate on which the fungi is feeding. These hyphae secrete digestive enzymes, which break down the substrate, making digestion of the nutrients possible. 280225587185500Fungi feed on a variety of different substrates, such as wood, cheese or flesh, although most of them specialize on a restricted range of food sources; some fungi are highly specialized, and are only able to obtain nutrition from a single species. Many fungi are parasitic, which means they feed on a host without killing it. Although, most fungi are saprobic, meaning they feed from already dead or decaying material, such as leaf litter, animal carcasses and other debris. The saprobic fungi recycle the nutrients from the dead or decaying material, which becomes available as nutrients for animals that eat fungi. The role of decomposers that fungi have as recyclers at all trophic levels of the nutrient cycle is extremely important within ecosystems, although they are also highly valuable to humans economically. Many fungi are responsible for production of human food, such as yeast (Saccharomyces cerevisiae), which is used to make bread, beer and cheese. Fungi are also used as medicines, such as penicillin.