0:00:00.000,0:00:03.960 To us modern folk, we tend to take for granted the existence of cells 0:00:03.960,0:00:06.500 and the idea that all living things are made up of cells 0:00:07.000,0:00:11.000 that we as human beings, as living organisms, we are made up of many, many, many cells 0:00:11.220,0:00:19.380 the estimates of the cells, of the human body, are around the order of 37 trillion cells! 0:00:19.440,0:00:23.200 But, if we were to rewind, even 400 years ago to the 1600's 0:00:23.260,0:00:25.000 this wasn't so obvious. 0:00:25.000,0:00:26.920 and that is because people really didn't have the tools 0:00:26.920,0:00:30.960 to make direct observations of cells. They didn't know that these cells were around. 0:00:30.960,0:00:34.040 They didn't know that things, even like unicellular organisms, even existed! 0:00:34.540,0:00:37.340 But, all of that began to change, with Robert Hooke. 0:00:38.920,0:00:43.500 Robert Hooke, was able to leverage a primitive microscope 0:00:43.560,0:00:45.400 and this is a picture of his microscope 0:00:45.400,0:00:46.980 and when you see this, you appreciate how 0:00:47.000,0:00:48.720 at least relative, to what we have today, how primitive it was. 0:00:48.720,0:00:51.660 He had lenses here, that would provide some magnification, 0:00:51.660,0:00:56.280 but he had to use -- this right over here -- this is a flame, and he is able to channel that light 0:00:56.280,0:00:59.420 so that it gets reflected over whatever he is observing. 0:00:59.420,0:01:03.840 And in, 1665, he publishes the "Micrographia". 0:01:03.840,0:01:07.340 I am probably not pronouncing it right. 0:01:07.340,0:01:11.740 So, this is 1665, Robert Hooke publishes this 0:01:11.780,0:01:14.760 and in this, he describes and he draws a lot 0:01:14.760,0:01:18.680 of his observations, using his microscope. 0:01:18.680,0:01:21.320 He has some fascinating drawings, he was actually quite a good artist, 0:01:21.320,0:01:23.720 where he was able to draw pictures 0:01:23.720,0:01:26.940 of his observations, of things like lice, and fleas. 0:01:26.940,0:01:30.580 But, it's not just lice and fleas that he is able to observe. 0:01:30.580,0:01:36.880 He actually takes a look at some corks or what he just sees as "cork" 0:01:36.880,0:01:49.160 and when he makes that observation, he says, "Hey look, you know there are these little squares over here, and this kind of seems to be somehow kind of a basic unit of this cork. " 0:01:49.160,0:01:56.160 And he says, " Well, this kinda reminds me of these little rooms that monks live in and spend their time in, which we call cells". 0:01:56.160,0:01:58.040 So he calls these cells. 0:01:58.040,0:02:00.220 And, that is where the word comes from. 0:02:00.280,0:02:02.060 He calls them cells, in "Micrographia". 0:02:03.100,0:02:04.020 That is a cell. 0:02:04.020,0:02:07.140 Now unfortunately for us, he was a great artist 0:02:07.140,0:02:09.780 and he was really good at drawing things 0:02:09.780,0:02:13.580 and he drew a lot in his "Micrographia", but we don't have any pictures of Robert Hooke anymore. 0:02:13.580,0:02:16.880 And it's a fascinating story. Most theories are that 0:02:17.080,0:02:22.920 actually, it was Isaac Newton, who burned the only original painting, that we have of Robert Hooke. 0:02:22.920,0:02:26.320 And, that is another intriguing story, that we can talk about, at a future date. 0:02:26.320,0:02:31.800 But, what Robert Hooke — he coined these things "cells" — but he was looking at dead tissue, and actually he was 0:02:31.800,0:02:37.040 looking at the remnants of cells. And what he saw was really just the cell wall remnants. 0:02:37.040,0:02:41.920 He wasn't actually able to observe, directly, "living cells". And he didn't have enough to go on 0:02:41.920,0:02:46.140 to think , "Hey maybe, this is a building block of all life and maybe, cells themselves reproduce." 0:02:46.140,0:02:52.520 "And, all cells come from other cells. " And that doesn't start to get developed, until we get further on into history. 0:02:52.620,0:02:57.320 You go a few years later, we get to Antonie von Leeuwenhoek. 0:02:57.320,0:02:59.320 I know I'm not probably pronouncing it right. 0:03:00.280,0:03:03.640 But he was a Dutch lense crafter, and he was inspired 0:03:03.640,0:03:09.940 by Hooke's work , and he says "Hey, I can craft lenses, maybe I can use that to make better microscopes, and make better observations. " 0:03:10.120,0:03:13.240 And he was able to do that, and doing that he was able to directly observe 0:03:13.240,0:03:17.040 living cells and living unicellular organisms. 0:03:17.040,0:03:19.920 So, he was able to directly observe sperm. 0:03:19.920,0:03:23.340 He said, "Hey this thing looks like it's alive!" 0:03:23.340,0:03:30.960 He was able to directly observe protists — so these unicellular, eukaryotic... 0:03:31.060,0:03:34.780 ... they have cell walls, these things that look like unicellular animals. 0:03:34.780,0:03:37.780 And he called them, actually, "animalcules". 0:03:41.320,0:03:47.240 Saying, "Hey, look, these look like these little mini-animals going on here. " 0:03:47.300,0:03:51.060 And so he started to say, well maybe this is some form of a basis of life, or at least started to say, 0:03:51.060,0:03:54.300 at this very small scale, you actually have life. 0:03:55.140,0:04:03.040 But, a fully, modern theory of the cell, doesn't really start to emerge until we get another 100-150 years, into the future. 0:04:03.140,0:04:05.480 And, we get into the early 1800's. 0:04:05.840,0:04:13.620 So, if we fast-forward, to the 1830's , these two gentlemen, Matthias Schleiden and Theodor Schwann, come into the picture. 0:04:13.620,0:04:16.360 And, they are the one's that start laying the foundation 0:04:16.360,0:04:19.240 of what we can call, "modern cell theory". 0:04:19.240,0:04:22.320 So, modern cell theory 0:04:22.320,0:04:26.720 And using their observations and kind of what they are able to deduce 0:04:26.720,0:04:30.480 they said, "Hey maybe, all living things 0:04:30.480,0:04:42.360 all life, is composed of one or more cells." 0:04:42.360,0:04:45.660 And today, we kind of take this for granted, but this wasn't obvious. 0:04:45.660,0:04:51.600 It wasn't obvious that all things, that this was somehow a building block for life, one or more cells. 0:04:51.600,0:04:54.100 And then, following that if all life is composed of one or more cells, 0:04:54.100,0:04:58.740 you can also say, that a cell, is the basic unit of life. 0:04:58.740,0:05:07.480 Cell is basic unit of life 0:05:07.480,0:05:09.680 And these are strong statements, that all life, if you were to get down small enough, 0:05:09.680,0:05:14.820 you are going to come to cells, living cells, that make up that life. 0:05:15.240,0:05:20.840 Now, this isn't our full, complete cell theory and both of these gentlemen, they knew that cells could come from other cells. 0:05:20.900,0:05:25.320 They were able to observe cells reproducing, but, it still 0:05:25.320,0:05:30.820 was an open question, "Hey, maybe some cells come from other cells? While others, maybe they somehow get spontaneously created .... 0:05:30.820,0:05:36.700 ... if you have the right elements and the right amount of conditions. Maybe they somehow just emerge out of nothing. " 0:05:36.780,0:05:46.580 And, it wasn't until this kind of third tenet of modern cell theory, it wasn't until the mid 1800's that we get our third tenet of modern cell theory that gets established. 0:05:46.580,0:05:51.300 And this is this idea that all cells come from other cells. 0:05:51.300,0:05:56.340 All cells from other cells 0:05:56.340,0:05:59.960 And the real father of this idea, the one that really established this, 0:05:59.960,0:06:02.800 is this gentleman, right here, Robert Remak. 0:06:02.800,0:06:09.200 Now sometimes, the credit for this goes to, Rudolph Virchow, right over here, but it turns out that 0:06:09.380,0:06:17.840 he plagiarized Remak's work, so it's really Remak who deserves the bulk of the credit 0:06:17.840,0:06:20.060 for this tenant, that all cells come from other cells. 0:06:20.060,0:06:23.980 And once again, he wasn't the first person to say, "Hey, maybe, we will observe that some cells.. 0:06:23.980,0:06:31.560 .. come from other cells." But he said, "This is a fundamental thing, all cells, this is how they actually come about they aren't just somehow, spontaneously emerged". 0:06:31.560,0:06:34.780 Now whenever, even in today's world, people 0:06:34.780,0:06:37.020 see this last thing, all cells come from other cells, 0:06:37.020,0:06:42.740 there is a natural question, " Well, there must have been a first cell or an initial set of "proto-cells ?". 0:06:43.100,0:06:47.100 And, people aren't a hundred percent sure, but when we 0:06:47.100,0:06:53.320 look back, at the evolution of life on earth, we think the first cells emerged about three and a half billion years ago. 0:06:53.320,0:06:57.480 And we are not a hundred percent sure about how they emerged, but there are some theories. 0:06:57.560,0:07:00.600 For example, we have videos on, phospholipids, 0:07:00.740,0:07:09.460 and it turns out that, phospholipids, naturally form bi-layers 0:07:10.040,0:07:15.500 and they can actually form, spherical membranes, that have phospholipid bi-layers. 0:07:15.500,0:07:19.320 So, that kinda gets you a start, so that can spontaneously form. 0:07:19.320,0:07:24.700 And, there is also, theories that maybe in the information, the machinery of cells 0:07:24.700,0:07:28.520 maybe their ancestors, if we were to go three and a half billion years or longer ago, 0:07:28.520,0:07:34.840 that it might have been self-replicating RNA molecules or maybe it was somehow, self-replicating proteins 0:07:34.840,0:07:39.820 that over time, over very large, large time scales, 0:07:39.880,0:07:44.820 were able to, start replicating themselves, have more sophisticated machinery, 0:07:44.960,0:07:50.500 the ones that had or were approaching our modern cells, were able to reproduce more, 0:07:50.500,0:07:54.340 were able to take advantage of more of the energy, the resources in an environment. 0:07:54.340,0:08:00.540 So, that we eventually get to our modern cells. But, this is a fascinating question, and is still an area of research.