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Lesson Video: Types of Nutrition Biology

In this video, we will learn how to identify and compare between autotrophic and heterotrophic nutrition.

13:54

Video Transcript

In this video, we will learn what nutrition is and some examples of organisms which carry out different processes to obtain their nutrition. These processes broadly fall into the categories of autotrophs that make their own food and heterotrophs that consume other organisms to gain their nutrition. We will learn how to identify these different types of nutrition from descriptions and how to compare them.

All living things require some form of nutrition. Nutrition is the assimilation of food materials by living organisms. Nutrition provides many organisms with sugars that can be broken down to release energy they require to carry out many essential life processes, such as movement and reproduction. This energy is released in the cells of all living things via a process called cellular respiration. Nutrition also provides organisms with a source of proteins, which can be used for growth and repair, particularly to build muscles. The fats that are obtained through nutrition are often used for insulation and protection and can also be used to store energy.

Nutrition also provides organisms with a source of vitamins and minerals, which organisms can use for multitudes of different functions. For example, in humans, vitamins and minerals help support our immune system, our nervous system, and even play a role in our muscle contractions. Animals like us, humans, often obtain these essential nutrients from the food we eat. But other living organisms have adopted a diverse range of different methods.

There are two broad classifications of the methods of nutrition: autotrophic nutrition and heterotrophic nutrition. The suffix -trophic means food, describing how these different organisms obtain their nutrition. The prefix auto- means self. This describes how autotrophic organisms are able to synthesize their own food from simple inorganic materials. Plants, for example, are autotrophs as they use sunlight and simple inorganic materials like water and carbon dioxide molecules to build up bigger sugars as their method of nutrition.

The prefix hetero- means different. This describes how heterotrophic organisms obtain their food by consuming other different living organisms or the organic matter from once-living organisms. For example, this honeybee is a heterotroph as it gains its nutrition by consuming pollen that has been produced by this plant, a different organism.

Let’s explore autotrophic nutrition in some more detail by looking at some different types of autotrophs. This plant can be described more precisely as a photoautotroph. The prefix photo- means light. Photoautotrophs like green algae, some bacteria, and plants like this sunflower all obtain their nutrition by converting small inorganic molecules and light energy, usually from the Sun, into chemical energy in the form of sugars, like glucose. They do this through a process called photosynthesis. Photoautotrophs still need to obtain other nutrients, such as water and mineral ions, which plants usually absorb from soil through their roots. And they gain the carbon dioxide they need for photosynthesis primarily through their leaves.

Another example of autotrophic nutrition occurs in organisms called chemoautotrophs. The prefix chemo- means chemical, which describes how these organisms gain their nutrition by converting one chemical into another. There are bacteria that live inside other organisms called tube worms, deep under the sea in areas called hydrothermal vents. There is basically no light in these vents. They’re extremely hot, under incredibly high pressures, and full of chemicals, like hydrogen sulfide, that would be toxic to most organisms.

In spite of this, these bacteria still manage to obtain their nutrition by actually using these toxic chemicals like hydrogen sulfide and dissolved carbon dioxide in the seawater to produce sugars, in a process called chemosynthesis. The sugars do not only provide the bacteria with a source of energy, but they also provide nutrition for larger organisms which cohabit the hydrothermal vents, like the tube worms that the bacteria live in. Interestingly, as the tube worms obtain their nutrition from a different organism, the bacteria that symbiotically live within them, the tube worms are heterotrophic organisms. So let’s have a look at this type of nutrition next.

Heterotrophic organisms are sometimes known as heterotrophs. Remember, heterotrophs gain their food by consuming different living or once-living organisms, which differs from autotrophs who make their own food. There are three main types of heterotrophs: parasites, saprophytes, and holozoic organisms. Let’s discover some more information about parasites first. Parasitic organisms live on or inside the body of another organism called the host organism. Parasites obtain their nutrition from or at the expense of its host.

For example, some mosquitoes like this one can act as vessels for microscopic parasitic protists called Plasmodium falciparum, which you can see here magnified in amongst red blood cells found in the mosquito’s gut. When an infected mosquito feeds on the blood of a human, it transfers some of these protists into the human’s bloodstream, where it infects their red blood cells, leeching away their nutrients. This causes a disease called malaria, which is supremely dangerous for humans and causes more than 400,000 deaths every year.

While parasites are often associated with microbes and human disease, plants can also be parasitic. For example, mistletoe is a parasitic plant, and this is its host plant, a tree. The mistletoe attaches to the tree and absorbs water and nutrients from this host in order to obtain its nutrition. While this process does not kill the tree like Plasmodium tends to do to humans, it does significantly weaken the tree as it will have fewer nutrients for its own essential life processes.

Let’s look at saprophytes next, which carry out saprophytic nutrition. Saprophytic organisms acquire their nutrients by absorbing usually dead and decaying material. Saprophytes are usually fungi like this mushroom, though some bacteria fall into this category too. Saprophytes do not have an internal digestive system usually. But fungi, for example, do possess extensive systems of strands called hyphae. The extensive massive hyphae form a mycelium, usually underground, that extends out into the surrounding environment to seek out dead and decaying material, like this plant leaf.

Let’s look a bit more closely at what these fungal hyphae look like when invading the plant cells in this leaf. The fungal cells shown here in blue protrude into the plant cells by producing extensions of their hyphae. The fungi secretes extracellular enzymes out to these hyphae into the plant cells to break down the dead or decaying matter in the leaf. After this extracellular digestion has occurred, the smaller food particles are absorbed back into the hyphae to be used as required by the saprophyte.

The final group of heterotrophs are called holozoic organisms. Holozoic nutrition is a type of heterotrophic nutrition characterized by the ingestion and internal digestion of gaseous, liquid, or solid food particles. This differs from saprophytic nutrition as holozoic organisms ingest and internally digest their food, whereas saprophytes release extracellular enzymes to digest food externally to their body.

There are three main classifications of organisms that carry out holozoic nutrition: carnivores, herbivores, and omnivores. Carnivores, such as this orca, lion, snakes, and even spiders, gain their nutrition from consuming animal matter only. Herbivores, such as this koala, elephants, and mice, gain their nutrition from consuming plant matter only. Omnivores, such as this raccoon, most humans, and dogs, gain their nutrition by consuming both plant and animal matter. Let’s look at a really simple example of an organism that primarily carries out holozoic nutrition: a single-celled organism called an amoeba.

The amoeba first ingests food particles. The food is then digested internally into smaller particles by enzymes. The smaller molecules, which might, for example, be a simple sugar like glucose, are then assimilated into other larger molecules that are useful to the amoeba. Any waste products that are not useful to the amoeba will then be excreted and egested from the cell. Though amoebas are much smaller than other holozoic organisms, we all follow the same basic process of ingestion, internal digestion, assimilation, and egestion. Let’s review what we’ve learned about the different types of nutrition by having a go at a practice question.

Leeches, shown in the picture, attach to the body of another organism and obtain their nutrition by consuming some of that organism’s blood. What classification of heterotrophic organisms do they belong to?

Let’s start off by defining some of the key terms in the question to figure out how to answer it. We’re told that leeches are heterotrophic organisms, but what does this term actually mean? Heterotrophic organisms obtain their food by consuming and ingesting other living or once-living organisms. For example, we, humans, are heterotrophs as we consume animal, plant, and sometimes fungal matter to obtain our nutrition, all of which are living or once-living organisms. Let’s find out what kind of heterotroph this leech is by comparing the three main classifications of heterotrophic organisms in a table. The three different groups of heterotrophs are parasites, saprophytes, and holozoic organisms.

Let’s look at the characteristics of how these groups typically obtain their food, starting with parasites. Parasites tend to live inside or on the surface of the body of another living organism, called the host. And they tend to obtain their nutrition at the host’s expense, just like how this parasitic vine absorbs nutrients from its host tree. Saprophytes, on the other hand, tend to obtain their nutrition from dead or decaying organisms rather than a living host. Saprophytes like this fungus can do this by releasing extracellular enzymes out of their body and onto rotting organisms to break down their large nutrients into smaller food molecules. The smaller molecules are then absorbed into the saprophyte cells to be used as required.

Holozoic organisms do not tend to be fussy about whether their host is living or dead. And rather than releasing enzymes onto their food, they ingest solid, liquid, or gas food particles into their body first. Once their food has been ingested, the food particles are digested with enzymes inside the holozoic organism’s body before the smaller nutrients are absorbed into their cells to be used as required.

Let’s take a look back at our question to discover which classification of heterotrophs the leech belongs to. The question tells us that the leech attaches to the body of another organism. This suggests that the leech might be a parasite which lives on or in the body of its host. We are also told that the leech consumes the organism’s blood to obtain its nutrition. This reflects the other key feature of parasites that they obtain their nutrition at the host’s expense. Losing blood would definitely be detrimental to the leech’s host’s health, and possibly survival. Therefore, we can conclude that the leech can be classified as a parasite.

Let’s review some of the key points that we’ve addressed in this video. We’ve learned how all living organisms need some form of nutrition so that they can release energy among the other benefits that nutrition provides. There are several different forms through which organisms can obtain their nutrition, such as autotrophs, who make their own food. Plants are photoautotrophic as they convert light energy and simple inorganic molecules into chemical energy, for example, in the form of glucose. And many bacteria are chemoautotrophic as they obtain their nutrition by converting one chemical into another to release their energy.

Heterotrophic nutrition is the other main grouping, which includes all organisms that obtain their nutrition from other living or once-living organisms. Heterotrophs can be further classified according to how they obtain this nutrition from other organisms. While parasites live in or on a host and obtain their nutrition at the host’s expense, saprophytes release extracellular enzymes that break down dead or decaying organisms before these smaller nutrients are absorbed. And holozoic organisms like humans ingest food material before internally digesting it with enzymes within our bodies or cells.

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