Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences
at the University of Oxford, and we're right in the middle of this very serious corona virus crisis right
now. And my students are all stuck at home and we want to keep them in touch with biology
and keep in touch with us. And so we're going to make a new series of videos and they're going to be called back garden
biology.
Hello and welcome to this episode of Back on Biology. It's high summer, the end
of July. My garden is starting to, well, kind of go over and look a bit shabby somehow.
And in this episode, I want to focus on some of the things that you can't see so easily.
Now, if you have a pond, I'm sure you're already very well aware that your pond teams with
life and some of it you can see easily. But of course, there's lots of things living in your pond that you can't
see easily. Now, what you need to reveal the unseen life in your pond is
a microscope. And I've got a small one here. This is what we call a dissecting microscope.
You look down it with two eyes, obviously two eyepieces, and it's not got really
high magnification, but it does enable you to see very small things, even single cells.
And in the past, a microscope by this, a good one, would have really cost you a lot of money. This microscope
is excellent, has really, really good quality optics. And it cost about 200 pounds.
So it's amazing how the price of those come down. And I'm going to show you some images that I took using
this microscope just with my mobile phone because the mobile phone struggles to focus through the
microscope. Those images are not brilliant quality. But most of the images I'm going to show you today, I took
on a different microscope in the teaching lab here at Oxford, where we have a camera attached to a microscope,
a proper camera. And those images are better quality. Now, there are lots of small things inside
ponds, and I could make all kinds of episodes about them. But what I want to focus on today
is to think about this. So here we have nice Greenleaf and we've seen before
and sets it back on biology. That leaves a green because they contain a molecule called chlorophyll
and chlorophyll can harness energy from the sun. And it uses that energy
to put carbon dioxide and water together to make sugar
and sugar, of course, as well. All life runs on. But the question is, what is that chlorophyll
contained in? And if you look at a leaf under a microscope, you would actually see lots of little
green dots. And those little green dots are called chloroplasts and they contain the chlorophyll.
And so we can ask, where did they come from, those chloroplasts? How did plants come to have
them? My answer is that they got them from my ancestors and the ancestors
of the land. Plants are a type of green algae, which you might well find in a pond.
You can also hang on. Why did the green algae get those chloroplast from? My answer
is that they got them from a type of bacteria, a special type of bacteria called
cyanobacteria. And those cyanobacteria are themselves often referred
to as a type of algae called a blue green algae. So the word algae is actually very confusing.
And that's one of the reasons biologists don't really like that word very much, because it's used as a bit of a basket term
to put all kinds of different organisms together aren't really that closely related.
So that's why I want to start this programme. What exactly is an algae?
OK. So what are algae? Well, this is something that's definitely an alga
and it's actually blanket weed. So sometimes in people's ponds you get these horrible mats
of green filamentous algae that can form sort of slimy clumps. And people
who have ponds often battle against it and spend a lot of money trying to get rid of it from their ponds.
But if we look at it under a microscope, we can see something that's really rather beautiful. We can see that each of these filaments
is made up of individual cells that are stuck together end to end to make a long
strand. I remember I said if it looked at a leaf under a microscope, you would see that it wasn't entirely
green, it would have green spots in it, and they would be the chloroplasts. And actually, it's difficult to put a whole
leaf under a microscope because they're too thick. But you can see that really beautifully here. And
those green spiral structures are the spiral chloroplasts in this
alga may give it its name. It's called Spierer GIRoA. So blanket wave of its rather
unsightly at our scale. If you look at the scale it lives at
the small scale, it's actually a really beautiful thing. Now here's a different
kind of filamentous alga, very, very similar. It's called Mujo here.
Each cell has just a single flat chloroplast in it. And it can
twist and turn and wrangle that chloroplast so that it can optimise the amount of light
that it gets. So algae can be pretty clever. Now, we also
asked, where did these chloroplast come from? Remember I said too? Well, algae got them from
cyanobacteria. And this is a filament of assigner bacteria.
Its name is not stock. And you can see it's also a long, thin filament, actually, with much smaller
cells than the than the Spierer GI Rahab and the algae had. Now,
how does an Al Gore get hold of the Sino bacteria? Well, most sign
about teret don't grow in filaments like that. They're just single cells. And what we think it
was happening is that some original cell and golfed a single cell
sign, a bacterium. Perhaps it was eating them and then it gradually enslaved it.
And so instead of eating it and digesting it, it kept it inside itself, puts it to
work. We think that probably happens at least a billion years ago and says
cyanobacteria were enslaved by algae and put to work. Perhaps
that's not the right way of thinking about it. Perhaps we could say that they've been domesticated. Well, perhaps
we can even say that Sinar bacteria enslaved an algal host because they would have
a protected environment in which to live. It doesn't really matter. The two live together
now in such an intimate way. But it's no longer a free living organism that chloroplasts
couldn't just leave and resume its free living existence. It's totally dependent
on the algal cell and we call that kind of event a symbiosis, a very
special kind of symbiosis called an end symbiosis, because it's actually ended
up one organism has ended up living inside another. And that event
gave rise to algae and gave rise to all of the land plants. To cyanobacteria
are the inventors of photosynthesis. They're the only inventors of it. It's such an incredible
piece of technology, but no other organism ever reinvented it. But like all great
tech, they just stole it. And if we look harder at some algae, we can see other
interesting features of them as well as these chloroplasts. We can see that most
algal cells actually live alone as single cells. These are corella just means tiny green
thing. And you can always find those in pond or some little green photosynthetic cells.
We've also seen that some algae gang up together to form these long filaments.
And if we not really, really hard at the side of bacterial strand, we see something interesting happening.
So most of the sounds of these little tiny square cells. But every now man is a little round
cell called a heterosexist. So this complexity forming within that strand
with different cells looking different and taking on different roles. We'll find out a bit
more about that in a minute. Sometimes you can find these really incredible algal
cells. This thing, all types of allegations say this is not a single cell. This little green football
that's slowly whirling around here. It's a group of algal cells. They are
acting as a multicellular being. The same that you are or I am
or a whole planet is not just a single cell. And so you've got the beginnings
here of more complex beings. Now we have to ask ourselves, how does
that happen? For most of the Earth's history, cells just lived alone. They reproduce.
They let their own independent lives and they died. But at some point in the earth's
history, cells started to form these larger structures. And that means that
cells. Start cooperating, they have to start taking on different tasks. And that's a huge
question in evolutionary biology. And to find out a little bit more about it, I went to speak to my colleague,
Stuart West, who works in the Department of Zoology here at Oxford.
So when people think about cooperative societies, they normally tend to think of
like meerkats on television or some group of birds going around and some family group.
But there's actually amazing cooperation within the microbial world. And one of the amazing things
about that is that we're actually the product of that. The human body is actually
an amazing co-operative society in itself. We are composed of billions of cells
that are all cooperating and acting together in unison to help us acquire resources
and survive and reproduce. And so you can think of most of the cells in your body,
still in your nose or your liver, sort of behaving altruistically to help the reproductive
cells get passed on to the next generation. Now, if you want to think about how
that evolved, we are quite a complex derived case. So we're not good for looking at.
And instead, what you what is more useful to do is go in the microorganisms that are still at
that transition stage between single celled and multi celled living. So,
for example, some algae like Lorella, we'll spend a lot of our time as little single
cells living sort of in the water, doing nothing, wandering around photosynthesising.
But then sometimes they will come together for multicellular groups or clumps and they do
it when predators around. And so there's no advantage to them to forming a sort of co-operative defensive
group that's harder to be eaten by predators. If we look at different micro organisms, a lot of
them do live in these kind of multicellular groups. But some of them have taken it even
further and they've got division of labour within those groups. So, for example, cyanobacteria
have some cells which give up, can't reproduce. They're not like sort of their average normal
cells, but all they do is they fix nitrogen and they supply nitrogen for the other cells.
And the reason they do that is that the enzyme that is needed to make nitrogen
is really messed up by having oxygen around. So what you end, you get these. They live in strands
and you'll have a collection of cells. Most of them will be normal photosynthesising reproducing cells.
And then every odd cell of these cells called Heat-resistant, which are just fixing nitrogen and supply
it to those other cells. So in many ways, these headrests, these nitrogen fixing cells
are really analogous to the sort of sterile workers you get in social insects. And so
with some of these these multicellular groupings, these cooperative groupings you see in microbes
like algae, sometimes that facultative like the Lorella example where they just come
together and compline these predators around other times, that single celled for the other species,
that obligatory multicellular, that always living as an as a multicellular group. An
amazing example, those Volvox. And so you get some Volvox species where
you get a clump of cells. And within that clump some cells of these really big ones which are just reproducing.
And then you also get lots of these tiny little cells which are basically just doing all the swimming work and keeping
the colony afloat. High up in the water stream so that they
can get good light. And so, again, this is a really nice example of how you've got this co-operative
group in this division of labour, in these sort of reproductive and then these sterile
helpers again, which again, just like this or sterile sort of work. And you are doing
all the work to keep the colony afloat. Well, thanks, Stuart. So you can see
that multicellularity, complex beings haven't evolved that many times
in the history of life. And that's because there's lots of barriers to overcome. And one of those crucial
barriers is this idea about cooperation. How do you persuade some cells to give up
their own reproductive success in order to help other cells to do so?
And we think one of the most important aspects is if those cells are genetically identical.
So all of cells in your body and all of the cells in the Volvox body are genetically
identical to each other. They all are raised from a process of cell division that began
with a single foundings cell. And if you want to get that kind of stable cooperation to evolve,
that seems to be a very important factor. Now, looking down a microscope
is such a fascinating thing today, partly because it allows you to think about all kinds
of really deep questions around the history of life and how multicellular things got
going. And but I also love it because I love to watch the movement and the way things
move. Things are very small. And in that world, it's a very different place
to being a macroscopic organism like us. We're very influenced by gravity, but actually small
things barely feel gravity's pull. They're much more influenced by forces of surface tension.
And here's some really just cool things that I saw in the pond. So this is a die at home gliding
along. Now it's also photosynthetic and it enslaved a single celled
alga. So a single celled alga. Cyanobacteria. And then was itself enslaved
by a diatom. And that's happened several times over the history of life. And this diet on
glides along by secreting a kind of mucilage like a snail would. And so you see them
gliding along on the bottom of the microscope slide. May come in lots of different shapes and sizes. They have
beautiful glass skeletons that can be sculpted in all kinds of wonderful geometric
shapes. This is affiliated pre-tests so as a large
single celled organism. And the cilia are like hairs that cover up your organism
and they beat together in coordinated waves. And they allow this thing to whiz and spiral
around at very high speed as it chases around after prey. And finally,
I managed to find these little Vawter challa, and they are also silicates. I hope you can
see this on a big screen. It might if you watch this on your face, out over the. You will build. See this. But they attach themselves
down. And then they use their cilia to create a currents of water and pull
in particles. And that's called filter feeding. So you just pull in the water and you filter
out any good stuff that comes to you. And it's amazing that you can see these little things that whizzing
away and creating that water currents. And then if there's nothing much in the area they are, they can just pop themselves
off and swim off somewhere else and either go somewhere else. So if you do have a chance to look down a microscope,
then worry that you don't know what everything is. I don't think that matters. You can really enjoy looking
at it all. And there's always an amazing variety to see. And one of the great things is you never know
what you're going to see. Every time you put pond water under a microscope, you see something different.
But it's always a fascinating thing today. Well, a huge thank you to Stuart West
for appearing in this programme and also huge thank you to my colleague Stephen Harris, who is a mine
of information about all this stuff and helped me to identify a lot of the organisms that we've seen in
this programme when going on holiday. Now, for a couple of weeks, when I get back, I'll be doing a programme still
in looking at ponds, looking at frogs and toads, and also some of the reptiles
that some of them, of course, like the grass snake, also can be seen in garden ponds. So if you're
going on holiday, I hope you have a nice time.