Autotrophs & heterotrophs (nutrition modes) | Life processes | Biology | Khan Academy

Autotrophs & heterotrophs (nutrition modes) | Life processes | Biology | Khan Academy

September 15, 2019 1 By Ewald Bahringer


– Why do these plants on
my balcony need sunlight? Why is this apple rotting? And why does my head itch so much? To answer this seemingly random questions we need to figure out
the modes of nutrition. Basically what are the
different ways of getting food. That’s what we’re doing in this video. So, based on how different
living things get their food, we can classify them in to two categories; producers, and consumers. So, producers, as the names suggests, they are the ones who can
produce their own food. Most examples involve the
green trees and plants and all the green stuff around you, and some bacteria as well. And how do they make their own food? Well, they do that by
using the energy of living from their surrounding. For example, plants and
all the green things can use the energy from
the sunlight to make their own food, and you
may have heard of this process called photosynthesis
which we’ll talk about in more detail in future videos but, that is the reason why I
need to expose these plants to sunlight, because that’s
from that’s how they make their own food. And you and I are not producers, because we can’t make
our own food like that. So what are we? Well, if you’re not a
producer you are a consumer. Consumers as the name suggests, are the ones that consume others, that eat others for food. You and I are consumer, my friend, and most animals and insects
that you are familiar with and even most bacterias,
they’re all consumers. Either we eat vegetables and fruits, or we eat others animals,
like chicken or fish, or maybe eggs. So anyways, producers make their own food, consumers eat others. Now, before we proceed,
let me tell you their biological names, right we
need to give, in biology everything has a technical name, right? So, the technical name,
or the biological name of producers is autotrophs. The word auto means self, and trophs mean nourish. So this means they can
self-nourish, right? They can make their own food, they can feed themselves, self-nourish. On the other hand, consumers, their biological name is heterotrophs. The word hetero means others, trophs means again, nourish. So, like the name says, they can’t self-nourish, they relies on others
to nourish themselves. You and I and donkeys are heterotrophs. Insects and most bacterias, heterotrophs. Now, guess what? Based on how heterotrophs
eat, we can further classify them in to three categories; holozoic, saprotrophs, and parasites. Again, lets look at each one in detail. Holozoic are consumers
which digest their food inside of their body, you are a holozoic. I am also holozoic, most
animals and insects, we are all holozoic
because, we eat and then the food digested inside our body. And we are called so
because, the word holo means whole, in the
sense we eat whole food. Okay, what does that mean. Take an example of an
apple, it doesn’t say that you have to eat the whole apple, but even you take a slice of an apple, then that apple can have
some constituents, right? Like, it has, for example,
sugars, then it has some proteins, maybe, it
also has some vitamins, and so many other constituent. These dots just represent
constituents, okay? Now, when you eat this slice of apple you take in all the constituents
inside your mouth, right? That’s that’s the whole
that’s the meaning of whole. That’s the meaning holo,
you’re eating this whole thing. And then, once it goes
into your body then, your digestion system breaks it into it’s constituent particles, right? That’s the whole idea behind holozoic. These are are the animals
that digest their food inside their body. Now in order to be a holozoic, you need to have pretty
good digestion system so that you can break down
whatever you eat inside your body. But, what if you don’t have
a good digestion system, Then what happens? Well, then you become a saprotroph. Saprotrophs are the ones
that don’t have a good digestions system, and as a result, they digest the food
outside of their body, and then eat it. And as we will see, it’s
these guys who are responsible for rotting and decaying things, and they include most
bacteria and mushrooms, well, mushrooms is a
very specific example. In general, these are fungus, right? So, bacteria and fungi, fungi is plural, fungus is singular, so, bacteria and fungi are the saprotrophs, they digest the food outside of their body. And they’re there everywhere, okay? I mean, if you take that piece of apple, and let’s just leave it
outside, don’t eat it, then, pretty soon you find
these bacteria and fungi will start attacking it, so, let’s say these
bacteria start attacking it, now, since they can not digest
the food inside their body, because they don’t have a
very good digestion system, what they do is they try
to digest the food outside. How do they do that? They spit all the enzymes,
or the acids needed to break down the food, right? So, as they spit these enzymes and acid, chemical reactions take place, and the food gets digested then and there. And so this apple start getting broken into it’s constituents and
then, once it’s broken, then these bacteria will start
absorbing these constituents. Okay but, why does it
rot and start smelling? Well, that’s because, whenever
digestion is happening, whenever chemical reactions are happening, some byproduct is created, right? And it’s these byproducts
that start making things rot. And that’s what makes the
whole thing smell as well, and because of that, more
insects get attracted, and now you can’t eat this. And this sounds very disgusting, right? But what’s interesting is,
a similar digestion process happening in our bellies as well, even when we digest food,
all this stuff happening but, because it’s inside our
body, we don’t smell it but, if you throw up, if you vomit then, you can smell it, I know
it’s pretty disgusting, sorry for that. But, when you vomit basically, you are vomiting out digested food with all these byproducts, and you know, even that smells, right? So, we digest the food inside but, these saprotrophs digest the food outside, and that causes things to rot, and that’s the same reason
why this apple is rotting, it’s being digested by these saprotrophs. Another example is, you may have seen, if you keep bread outside for some time, then they will start growing
this fungus over here. The fungus are digesting it outside now, and your teeth also gets
decayed for the same reason, There are a lot of bacteria in our mouth, and when we eat food, the
food gets stuck in the teeth, and then, they start getting
digested by the saprotrophs. And that’s why I always brush
my teeth twice every day. And, just a small thing, okay? After learning this, I used
to feel they are so annoying. I mean, if they were not there, I wouldn’t have to brush my teeth, things wouldn’t rot at all,
wouldn’t that be awesome? No, because, guess what? They also feed on the dead,
they are the ones that make sure to decompose all the dead stuff, right? So, if they were not there,
then all the dead things like, the dead animal and plants
and everything would just pile up, you can not
imagine what earth would be. So, thanks to them, they decompose all the dead stuff as well and
recycle all the nutrients, make sure they go back into
the nature, which can be re-absorbed by the plants,
re-used to make more food, they are super essential
for our environment. And the word sapro itself means rotting, that’s why they’re called
saprotrophs because, they eat on the dead, and
decay, and make them rot. Okay, and finally, what if
you can’t digest food at all, Whether inside or outside, then what? Then, you become a parasite. Parasites hardly digest any food. Then how do they get their nutrients? Well, they depend on a host, meaning another living organism. For example, this leech is a parasite, it gets stuck to my leg, let’s say, and then it starts sucking my blood. Now, my blood already contains
digested food, and so, it just starts getting nutrients
from my blood directly. So you see, they don’t
have to digest anything, so, in that case, since
they are depending on me, I am their host. Similarly, my head is scratch,
I have to scratch my head so much because there are
some parasites on my head. Lices are examples of parasites as well, they also suck on the blood
from the scalp, again, I am their host. So parasites can either live
on the surface of their hosts, like leeches and lices, or they can live inside them as well. For example, tapeworms and roundworms
live inside intestines. So, even though you may be healthy, you have these inside
you intestines, okay? And guess why are they there? Well, because again, intestine where most
food already digested, and so, they can just eat that. And so, the word para
kind of means alongside, in the sense that eating
alongside it’s host, so, whatever I eat, they
goes to these guys as well. Now, an important about
parasites is I should think they’re trying to kill me
but, no, they are not trying to kill me, they want me to
be alive so that I can keep on feeding them for their entire life. So, parasites don’t try
to kill their hosts but, they end up harming their hosts. For example, when this leech
starts sucking on my blood, they rupture the skin,
because of these lices, I am getting, my head is getting itchy, tapeworms and roundworms can
cause my stomach to ache. So they are definitely
no trying to kill us but, they end up harming us. And again, I should think
parasites are pretty useless, and many scientists
usually think as well but, recently we realize, even they are useful. For example, some scientists
believe that the worms in our intestines actually help in boosting our immunity over there. Another example, some leeches
are useful in removing infected blood from our body, and would you be surprised if
I told you that fifty percent of all the species of
living things on our planet are parasites? That’s right, there are a lot
of parasites on our planet. Almost every living thing
has a parasite inside, or on top of it. Anyways, that’s pretty much it so, let’s quickly look at what we learned. There are two basic
kinds of living beings; autotrophs, who generate
the food themselves using the energy from the surrounding, and the heterotrophs, who
can’t produce their own food so they eat others, and based
on how we digest the food, heterotrophs can be further classified as holozoic, if you take
the whole food inside, and digest it inside your body, most animals and insects
come under this category, and you need a pretty good
digestion system for that. But, if you don’t have a great
digest system, no worries, you become a saphrotrope,
then you just digest the food outside of your body, and
then you must make things rot, they are the decomposers,
they are the ones who eat on the dead and the decaying animals, most bacteria and fungi. And finally, if you can’t even do that, then you just become a parasite, just stick yourself to a
host or live inside of them, and then you get free digested food. They might harm you but, most of them have no
intentions of killing you.