1 00:00:00,330 --> 00:00:05,640 Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences 2 00:00:05,640 --> 00:00:10,770 at the University of Oxford, and we're right in the middle of this very serious corona virus crisis right 3 00:00:10,770 --> 00:00:15,820 now. And my students are all stuck at home and we want to keep them in touch with biology 4 00:00:15,820 --> 00:00:21,240 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 5 00:00:21,240 --> 00:00:47,020 biology. 6 00:00:47,020 --> 00:00:52,090 Hello and welcome to this episode of Back on Biology. It's high summer, the end 7 00:00:52,090 --> 00:00:57,130 of July. My garden is starting to, well, kind of go over and look a bit shabby somehow. 8 00:00:57,130 --> 00:01:03,010 And in this episode, I want to focus on some of the things that you can't see so easily. 9 00:01:03,010 --> 00:01:08,020 Now, if you have a pond, I'm sure you're already very well aware that your pond teams with 10 00:01:08,020 --> 00:01:13,210 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 11 00:01:13,210 --> 00:01:18,340 see easily. Now, what you need to reveal the unseen life in your pond is 12 00:01:18,340 --> 00:01:24,580 a microscope. And I've got a small one here. This is what we call a dissecting microscope. 13 00:01:24,580 --> 00:01:30,130 You look down it with two eyes, obviously two eyepieces, and it's not got really 14 00:01:30,130 --> 00:01:35,690 high magnification, but it does enable you to see very small things, even single cells. 15 00:01:35,690 --> 00:01:41,290 And in the past, a microscope by this, a good one, would have really cost you a lot of money. This microscope 16 00:01:41,290 --> 00:01:46,420 is excellent, has really, really good quality optics. And it cost about 200 pounds. 17 00:01:46,420 --> 00:01:51,700 So it's amazing how the price of those come down. And I'm going to show you some images that I took using 18 00:01:51,700 --> 00:01:56,770 this microscope just with my mobile phone because the mobile phone struggles to focus through the 19 00:01:56,770 --> 00:02:02,170 microscope. Those images are not brilliant quality. But most of the images I'm going to show you today, I took 20 00:02:02,170 --> 00:02:07,420 on a different microscope in the teaching lab here at Oxford, where we have a camera attached to a microscope, 21 00:02:07,420 --> 00:02:12,730 a proper camera. And those images are better quality. Now, there are lots of small things inside 22 00:02:12,730 --> 00:02:17,920 ponds, and I could make all kinds of episodes about them. But what I want to focus on today 23 00:02:17,920 --> 00:02:23,290 is to think about this. So here we have nice Greenleaf and we've seen before 24 00:02:23,290 --> 00:02:29,410 and sets it back on biology. That leaves a green because they contain a molecule called chlorophyll 25 00:02:29,410 --> 00:02:34,600 and chlorophyll can harness energy from the sun. And it uses that energy 26 00:02:34,600 --> 00:02:39,670 to put carbon dioxide and water together to make sugar 27 00:02:39,670 --> 00:02:45,100 and sugar, of course, as well. All life runs on. But the question is, what is that chlorophyll 28 00:02:45,100 --> 00:02:50,290 contained in? And if you look at a leaf under a microscope, you would actually see lots of little 29 00:02:50,290 --> 00:02:56,530 green dots. And those little green dots are called chloroplasts and they contain the chlorophyll. 30 00:02:56,530 --> 00:03:01,660 And so we can ask, where did they come from, those chloroplasts? How did plants come to have 31 00:03:01,660 --> 00:03:07,000 them? My answer is that they got them from my ancestors and the ancestors 32 00:03:07,000 --> 00:03:13,120 of the land. Plants are a type of green algae, which you might well find in a pond. 33 00:03:13,120 --> 00:03:18,280 You can also hang on. Why did the green algae get those chloroplast from? My answer 34 00:03:18,280 --> 00:03:23,340 is that they got them from a type of bacteria, a special type of bacteria called 35 00:03:23,340 --> 00:03:28,450 cyanobacteria. And those cyanobacteria are themselves often referred 36 00:03:28,450 --> 00:03:34,180 to as a type of algae called a blue green algae. So the word algae is actually very confusing. 37 00:03:34,180 --> 00:03:39,910 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 38 00:03:39,910 --> 00:03:45,310 to put all kinds of different organisms together aren't really that closely related. 39 00:03:45,310 --> 00:03:54,230 So that's why I want to start this programme. What exactly is an algae? 40 00:03:54,230 --> 00:03:59,560 OK. So what are algae? Well, this is something that's definitely an alga 41 00:03:59,560 --> 00:04:05,190 and it's actually blanket weed. So sometimes in people's ponds you get these horrible mats 42 00:04:05,190 --> 00:04:10,290 of green filamentous algae that can form sort of slimy clumps. And people 43 00:04:10,290 --> 00:04:16,200 who have ponds often battle against it and spend a lot of money trying to get rid of it from their ponds. 44 00:04:16,200 --> 00:04:21,990 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 45 00:04:21,990 --> 00:04:27,210 is made up of individual cells that are stuck together end to end to make a long 46 00:04:27,210 --> 00:04:32,370 strand. I remember I said if it looked at a leaf under a microscope, you would see that it wasn't entirely 47 00:04:32,370 --> 00:04:37,530 green, it would have green spots in it, and they would be the chloroplasts. And actually, it's difficult to put a whole 48 00:04:37,530 --> 00:04:42,540 leaf under a microscope because they're too thick. But you can see that really beautifully here. And 49 00:04:42,540 --> 00:04:47,830 those green spiral structures are the spiral chloroplasts in this 50 00:04:47,830 --> 00:04:52,920 alga may give it its name. It's called Spierer GIRoA. So blanket wave of its rather 51 00:04:52,920 --> 00:04:58,090 unsightly at our scale. If you look at the scale it lives at 52 00:04:58,090 --> 00:05:03,270 the small scale, it's actually a really beautiful thing. Now here's a different 53 00:05:03,270 --> 00:05:09,240 kind of filamentous alga, very, very similar. It's called Mujo here. 54 00:05:09,240 --> 00:05:14,250 Each cell has just a single flat chloroplast in it. And it can 55 00:05:14,250 --> 00:05:19,320 twist and turn and wrangle that chloroplast so that it can optimise the amount of light 56 00:05:19,320 --> 00:05:24,510 that it gets. So algae can be pretty clever. Now, we also 57 00:05:24,510 --> 00:05:29,790 asked, where did these chloroplast come from? Remember I said too? Well, algae got them from 58 00:05:29,790 --> 00:05:35,040 cyanobacteria. And this is a filament of assigner bacteria. 59 00:05:35,040 --> 00:05:40,560 Its name is not stock. And you can see it's also a long, thin filament, actually, with much smaller 60 00:05:40,560 --> 00:05:45,600 cells than the than the Spierer GI Rahab and the algae had. Now, 61 00:05:45,600 --> 00:05:50,760 how does an Al Gore get hold of the Sino bacteria? Well, most sign 62 00:05:50,760 --> 00:05:55,800 about teret don't grow in filaments like that. They're just single cells. And what we think it 63 00:05:55,800 --> 00:06:00,910 was happening is that some original cell and golfed a single cell 64 00:06:00,910 --> 00:06:06,360 sign, a bacterium. Perhaps it was eating them and then it gradually enslaved it. 65 00:06:06,360 --> 00:06:11,370 And so instead of eating it and digesting it, it kept it inside itself, puts it to 66 00:06:11,370 --> 00:06:16,530 work. We think that probably happens at least a billion years ago and says 67 00:06:16,530 --> 00:06:21,660 cyanobacteria were enslaved by algae and put to work. Perhaps 68 00:06:21,660 --> 00:06:26,670 that's not the right way of thinking about it. Perhaps we could say that they've been domesticated. Well, perhaps 69 00:06:26,670 --> 00:06:31,710 we can even say that Sinar bacteria enslaved an algal host because they would have 70 00:06:31,710 --> 00:06:36,960 a protected environment in which to live. It doesn't really matter. The two live together 71 00:06:36,960 --> 00:06:42,090 now in such an intimate way. But it's no longer a free living organism that chloroplasts 72 00:06:42,090 --> 00:06:47,400 couldn't just leave and resume its free living existence. It's totally dependent 73 00:06:47,400 --> 00:06:52,560 on the algal cell and we call that kind of event a symbiosis, a very 74 00:06:52,560 --> 00:06:57,750 special kind of symbiosis called an end symbiosis, because it's actually ended 75 00:06:57,750 --> 00:07:02,910 up one organism has ended up living inside another. And that event 76 00:07:02,910 --> 00:07:08,550 gave rise to algae and gave rise to all of the land plants. To cyanobacteria 77 00:07:08,550 --> 00:07:13,770 are the inventors of photosynthesis. They're the only inventors of it. It's such an incredible 78 00:07:13,770 --> 00:07:18,930 piece of technology, but no other organism ever reinvented it. But like all great 79 00:07:18,930 --> 00:07:24,090 tech, they just stole it. And if we look harder at some algae, we can see other 80 00:07:24,090 --> 00:07:29,250 interesting features of them as well as these chloroplasts. We can see that most 81 00:07:29,250 --> 00:07:34,470 algal cells actually live alone as single cells. These are corella just means tiny green 82 00:07:34,470 --> 00:07:39,720 thing. And you can always find those in pond or some little green photosynthetic cells. 83 00:07:39,720 --> 00:07:45,200 We've also seen that some algae gang up together to form these long filaments. 84 00:07:45,200 --> 00:07:50,280 And if we not really, really hard at the side of bacterial strand, we see something interesting happening. 85 00:07:50,280 --> 00:07:55,410 So most of the sounds of these little tiny square cells. But every now man is a little round 86 00:07:55,410 --> 00:08:00,840 cell called a heterosexist. So this complexity forming within that strand 87 00:08:00,840 --> 00:08:05,970 with different cells looking different and taking on different roles. We'll find out a bit 88 00:08:05,970 --> 00:08:11,130 more about that in a minute. Sometimes you can find these really incredible algal 89 00:08:11,130 --> 00:08:16,780 cells. This thing, all types of allegations say this is not a single cell. This little green football 90 00:08:16,780 --> 00:08:21,810 that's slowly whirling around here. It's a group of algal cells. They are 91 00:08:21,810 --> 00:08:26,880 acting as a multicellular being. The same that you are or I am 92 00:08:26,880 --> 00:08:32,160 or a whole planet is not just a single cell. And so you've got the beginnings 93 00:08:32,160 --> 00:08:37,170 here of more complex beings. Now we have to ask ourselves, how does 94 00:08:37,170 --> 00:08:42,960 that happen? For most of the Earth's history, cells just lived alone. They reproduce. 95 00:08:42,960 --> 00:08:48,090 They let their own independent lives and they died. But at some point in the earth's 96 00:08:48,090 --> 00:08:53,190 history, cells started to form these larger structures. And that means that 97 00:08:53,190 --> 00:08:58,230 cells. Start cooperating, they have to start taking on different tasks. And that's a huge 98 00:08:58,230 --> 00:09:03,270 question in evolutionary biology. And to find out a little bit more about it, I went to speak to my colleague, 99 00:09:03,270 --> 00:09:12,040 Stuart West, who works in the Department of Zoology here at Oxford. 100 00:09:12,040 --> 00:09:17,200 So when people think about cooperative societies, they normally tend to think of 101 00:09:17,200 --> 00:09:22,770 like meerkats on television or some group of birds going around and some family group. 102 00:09:22,770 --> 00:09:28,180 But there's actually amazing cooperation within the microbial world. And one of the amazing things 103 00:09:28,180 --> 00:09:33,190 about that is that we're actually the product of that. The human body is actually 104 00:09:33,190 --> 00:09:38,530 an amazing co-operative society in itself. We are composed of billions of cells 105 00:09:38,530 --> 00:09:44,440 that are all cooperating and acting together in unison to help us acquire resources 106 00:09:44,440 --> 00:09:49,480 and survive and reproduce. And so you can think of most of the cells in your body, 107 00:09:49,480 --> 00:09:54,580 still in your nose or your liver, sort of behaving altruistically to help the reproductive 108 00:09:54,580 --> 00:09:59,710 cells get passed on to the next generation. Now, if you want to think about how 109 00:09:59,710 --> 00:10:04,850 that evolved, we are quite a complex derived case. So we're not good for looking at. 110 00:10:04,850 --> 00:10:09,850 And instead, what you what is more useful to do is go in the microorganisms that are still at 111 00:10:09,850 --> 00:10:14,860 that transition stage between single celled and multi celled living. So, 112 00:10:14,860 --> 00:10:19,960 for example, some algae like Lorella, we'll spend a lot of our time as little single 113 00:10:19,960 --> 00:10:25,330 cells living sort of in the water, doing nothing, wandering around photosynthesising. 114 00:10:25,330 --> 00:10:30,430 But then sometimes they will come together for multicellular groups or clumps and they do 115 00:10:30,430 --> 00:10:35,890 it when predators around. And so there's no advantage to them to forming a sort of co-operative defensive 116 00:10:35,890 --> 00:10:40,960 group that's harder to be eaten by predators. If we look at different micro organisms, a lot of 117 00:10:40,960 --> 00:10:46,030 them do live in these kind of multicellular groups. But some of them have taken it even 118 00:10:46,030 --> 00:10:52,000 further and they've got division of labour within those groups. So, for example, cyanobacteria 119 00:10:52,000 --> 00:10:57,040 have some cells which give up, can't reproduce. They're not like sort of their average normal 120 00:10:57,040 --> 00:11:02,440 cells, but all they do is they fix nitrogen and they supply nitrogen for the other cells. 121 00:11:02,440 --> 00:11:07,630 And the reason they do that is that the enzyme that is needed to make nitrogen 122 00:11:07,630 --> 00:11:12,920 is really messed up by having oxygen around. So what you end, you get these. They live in strands 123 00:11:12,920 --> 00:11:18,160 and you'll have a collection of cells. Most of them will be normal photosynthesising reproducing cells. 124 00:11:18,160 --> 00:11:23,290 And then every odd cell of these cells called Heat-resistant, which are just fixing nitrogen and supply 125 00:11:23,290 --> 00:11:28,540 it to those other cells. So in many ways, these headrests, these nitrogen fixing cells 126 00:11:28,540 --> 00:11:33,670 are really analogous to the sort of sterile workers you get in social insects. And so 127 00:11:33,670 --> 00:11:39,070 with some of these these multicellular groupings, these cooperative groupings you see in microbes 128 00:11:39,070 --> 00:11:44,290 like algae, sometimes that facultative like the Lorella example where they just come 129 00:11:44,290 --> 00:11:49,540 together and compline these predators around other times, that single celled for the other species, 130 00:11:49,540 --> 00:11:54,700 that obligatory multicellular, that always living as an as a multicellular group. An 131 00:11:54,700 --> 00:12:00,970 amazing example, those Volvox. And so you get some Volvox species where 132 00:12:00,970 --> 00:12:07,540 you get a clump of cells. And within that clump some cells of these really big ones which are just reproducing. 133 00:12:07,540 --> 00:12:12,730 And then you also get lots of these tiny little cells which are basically just doing all the swimming work and keeping 134 00:12:12,730 --> 00:12:17,770 the colony afloat. High up in the water stream so that they 135 00:12:17,770 --> 00:12:22,900 can get good light. And so, again, this is a really nice example of how you've got this co-operative 136 00:12:22,900 --> 00:12:28,000 group in this division of labour, in these sort of reproductive and then these sterile 137 00:12:28,000 --> 00:12:33,040 helpers again, which again, just like this or sterile sort of work. And you are doing 138 00:12:33,040 --> 00:12:38,230 all the work to keep the colony afloat. Well, thanks, Stuart. So you can see 139 00:12:38,230 --> 00:12:43,390 that multicellularity, complex beings haven't evolved that many times 140 00:12:43,390 --> 00:12:48,790 in the history of life. And that's because there's lots of barriers to overcome. And one of those crucial 141 00:12:48,790 --> 00:12:54,070 barriers is this idea about cooperation. How do you persuade some cells to give up 142 00:12:54,070 --> 00:12:59,920 their own reproductive success in order to help other cells to do so? 143 00:12:59,920 --> 00:13:05,650 And we think one of the most important aspects is if those cells are genetically identical. 144 00:13:05,650 --> 00:13:10,660 So all of cells in your body and all of the cells in the Volvox body are genetically 145 00:13:10,660 --> 00:13:15,850 identical to each other. They all are raised from a process of cell division that began 146 00:13:15,850 --> 00:13:21,100 with a single foundings cell. And if you want to get that kind of stable cooperation to evolve, 147 00:13:21,100 --> 00:13:26,740 that seems to be a very important factor. Now, looking down a microscope 148 00:13:26,740 --> 00:13:31,840 is such a fascinating thing today, partly because it allows you to think about all kinds 149 00:13:31,840 --> 00:13:37,000 of really deep questions around the history of life and how multicellular things got 150 00:13:37,000 --> 00:13:42,220 going. And but I also love it because I love to watch the movement and the way things 151 00:13:42,220 --> 00:13:47,440 move. Things are very small. And in that world, it's a very different place 152 00:13:47,440 --> 00:13:52,810 to being a macroscopic organism like us. We're very influenced by gravity, but actually small 153 00:13:52,810 --> 00:13:58,570 things barely feel gravity's pull. They're much more influenced by forces of surface tension. 154 00:13:58,570 --> 00:14:04,210 And here's some really just cool things that I saw in the pond. So this is a die at home gliding 155 00:14:04,210 --> 00:14:09,280 along. Now it's also photosynthetic and it enslaved a single celled 156 00:14:09,280 --> 00:14:14,290 alga. So a single celled alga. Cyanobacteria. And then was itself enslaved 157 00:14:14,290 --> 00:14:19,390 by a diatom. And that's happened several times over the history of life. And this diet on 158 00:14:19,390 --> 00:14:24,400 glides along by secreting a kind of mucilage like a snail would. And so you see them 159 00:14:24,400 --> 00:14:29,500 gliding along on the bottom of the microscope slide. May come in lots of different shapes and sizes. They have 160 00:14:29,500 --> 00:14:34,840 beautiful glass skeletons that can be sculpted in all kinds of wonderful geometric 161 00:14:34,840 --> 00:14:39,910 shapes. This is affiliated pre-tests so as a large 162 00:14:39,910 --> 00:14:45,010 single celled organism. And the cilia are like hairs that cover up your organism 163 00:14:45,010 --> 00:14:50,290 and they beat together in coordinated waves. And they allow this thing to whiz and spiral 164 00:14:50,290 --> 00:14:55,720 around at very high speed as it chases around after prey. And finally, 165 00:14:55,720 --> 00:15:00,760 I managed to find these little Vawter challa, and they are also silicates. I hope you can 166 00:15:00,760 --> 00:15:06,190 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 167 00:15:06,190 --> 00:15:11,410 down. And then they use their cilia to create a currents of water and pull 168 00:15:11,410 --> 00:15:16,570 in particles. And that's called filter feeding. So you just pull in the water and you filter 169 00:15:16,570 --> 00:15:21,670 out any good stuff that comes to you. And it's amazing that you can see these little things that whizzing 170 00:15:21,670 --> 00:15:26,710 away and creating that water currents. And then if there's nothing much in the area they are, they can just pop themselves 171 00:15:26,710 --> 00:15:32,620 off and swim off somewhere else and either go somewhere else. So if you do have a chance to look down a microscope, 172 00:15:32,620 --> 00:15:38,050 then worry that you don't know what everything is. I don't think that matters. You can really enjoy looking 173 00:15:38,050 --> 00:15:43,090 at it all. And there's always an amazing variety to see. And one of the great things is you never know 174 00:15:43,090 --> 00:15:48,340 what you're going to see. Every time you put pond water under a microscope, you see something different. 175 00:15:48,340 --> 00:15:53,440 But it's always a fascinating thing today. Well, a huge thank you to Stuart West 176 00:15:53,440 --> 00:15:58,570 for appearing in this programme and also huge thank you to my colleague Stephen Harris, who is a mine 177 00:15:58,570 --> 00:16:03,610 of information about all this stuff and helped me to identify a lot of the organisms that we've seen in 178 00:16:03,610 --> 00:16:08,860 this programme when going on holiday. Now, for a couple of weeks, when I get back, I'll be doing a programme still 179 00:16:08,860 --> 00:16:14,350 in looking at ponds, looking at frogs and toads, and also some of the reptiles 180 00:16:14,350 --> 00:16:19,360 that some of them, of course, like the grass snake, also can be seen in garden ponds. So if you're 181 00:16:19,360 --> 00:16:54,413 going on holiday, I hope you have a nice time.