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.