crashcourse
Plant Anatomy & Physiology: Plants Are Hardcore: Crash Course Biology #42
YouTube: | https://youtube.com/watch?v=pvVvCt6Kdp8 |
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View count: | 41,659 |
Likes: | 1,612 |
Comments: | 28 |
Duration: | 13:05 |
Uploaded: | 2024-05-07 |
Last sync: | 2024-12-23 14:30 |
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Citation formatting is not guaranteed to be accurate. | |
MLA Full: | "Plant Anatomy & Physiology: Plants Are Hardcore: Crash Course Biology #42." YouTube, uploaded by CrashCourse, 7 May 2024, www.youtube.com/watch?v=pvVvCt6Kdp8. |
MLA Inline: | (CrashCourse, 2024) |
APA Full: | CrashCourse. (2024, May 7). Plant Anatomy & Physiology: Plants Are Hardcore: Crash Course Biology #42 [Video]. YouTube. https://youtube.com/watch?v=pvVvCt6Kdp8 |
APA Inline: | (CrashCourse, 2024) |
Chicago Full: |
CrashCourse, "Plant Anatomy & Physiology: Plants Are Hardcore: Crash Course Biology #42.", May 7, 2024, YouTube, 13:05, https://youtube.com/watch?v=pvVvCt6Kdp8. |
Plants may not seem like they’re doing much, but if you look closer, you’ll find a whole world just lurking beyond the surface. We’re talking chemical defenses, highways, and even ways to change the weather. In this episode, we’ll learn how plants get resources, get rid of waste, stay defended, govern themselves, and much more.
Introduction: How Plants Work 00:00
Meet the angiosperms 00:58
How plants transport nutrients 02:04
How plants eliminate waste 05:28
Plant defenses 08:05
Plant Communication and Reproduction 09:55
Review & Credits 11:47
This series was produced in collaboration with HHMI BioInteractive, committed to empowering educators and inspiring students with engaging, accessible, and quality classroom resources. Visit https://BioInteractive.org/CrashCourse for more information.
Are you an educator looking for what NGSS Standards are covered in this episode? Check out our Educator Standards Database for Biology here: https://www.thecrashcourse.com/biologystandards
Check out our Biology playlist here: https://www.youtube.com/playlist?list=PL8dPuuaLjXtPW_ofbxdHNciuLoTRLPMgB
Watch this series in Spanish on our Crash Course en Español channel here: https://www.youtube.com/playlist?list=PLkcbA0DkuFjWQZzjwF6w_gUrE_5_d3vd3
Sources: https://docs.google.com/document/d/1GLDtAXE6ekg4Chk2qN3TYbNt0pJbyaHqTqRd6QY8pd4/edit?usp=sharing
***
Crash Course is on Patreon! You can support us directly by signing up at http://www.patreon.com/crashcourse
Thanks to the following patrons for their generous monthly contributions that help keep Crash Course free for everyone forever:
Leah H., David Fanska, Andrew Woods, DL Singfield, Ken Davidian, Stephen Akuffo, Toni Miles, Steve Segreto, Kyle & Katherine Callahan, Laurel Stevens, Burt Humburg, Perry Joyce, Scott Harrison, Mark & Susan Billian, Alan Bridgeman, Breanna Bosso, Matt Curls, Jennifer Killen, Jon Allen, Sarah & Nathan Catchings, team dorsey, Bernardo Garza, Trevin Beattie, Eric Koslow, Indija-ka Siriwardena, Jason Rostoker, Siobhán, Ken Penttinen, Nathan Taylor, Barrett & Laura Nuzum, Les Aker, William McGraw, Vaso, ClareG, Rizwan Kassim, Constance Urist, Alex Hackman, Pineapples of Solidarity, Katie Dean, Stephen McCandless, Wai Jack Sin, Ian Dundore, Caleb Weeks
__
Want to find Crash Course elsewhere on the internet?
Instagram - https://www.instagram.com/thecrashcourse/
Facebook - http://www.facebook.com/YouTubeCrashCourse
Twitter - http://www.twitter.com/TheCrashCourse
CC Kids: http://www.youtube.com/crashcoursekids
Introduction: How Plants Work 00:00
Meet the angiosperms 00:58
How plants transport nutrients 02:04
How plants eliminate waste 05:28
Plant defenses 08:05
Plant Communication and Reproduction 09:55
Review & Credits 11:47
This series was produced in collaboration with HHMI BioInteractive, committed to empowering educators and inspiring students with engaging, accessible, and quality classroom resources. Visit https://BioInteractive.org/CrashCourse for more information.
Are you an educator looking for what NGSS Standards are covered in this episode? Check out our Educator Standards Database for Biology here: https://www.thecrashcourse.com/biologystandards
Check out our Biology playlist here: https://www.youtube.com/playlist?list=PL8dPuuaLjXtPW_ofbxdHNciuLoTRLPMgB
Watch this series in Spanish on our Crash Course en Español channel here: https://www.youtube.com/playlist?list=PLkcbA0DkuFjWQZzjwF6w_gUrE_5_d3vd3
Sources: https://docs.google.com/document/d/1GLDtAXE6ekg4Chk2qN3TYbNt0pJbyaHqTqRd6QY8pd4/edit?usp=sharing
***
Crash Course is on Patreon! You can support us directly by signing up at http://www.patreon.com/crashcourse
Thanks to the following patrons for their generous monthly contributions that help keep Crash Course free for everyone forever:
Leah H., David Fanska, Andrew Woods, DL Singfield, Ken Davidian, Stephen Akuffo, Toni Miles, Steve Segreto, Kyle & Katherine Callahan, Laurel Stevens, Burt Humburg, Perry Joyce, Scott Harrison, Mark & Susan Billian, Alan Bridgeman, Breanna Bosso, Matt Curls, Jennifer Killen, Jon Allen, Sarah & Nathan Catchings, team dorsey, Bernardo Garza, Trevin Beattie, Eric Koslow, Indija-ka Siriwardena, Jason Rostoker, Siobhán, Ken Penttinen, Nathan Taylor, Barrett & Laura Nuzum, Les Aker, William McGraw, Vaso, ClareG, Rizwan Kassim, Constance Urist, Alex Hackman, Pineapples of Solidarity, Katie Dean, Stephen McCandless, Wai Jack Sin, Ian Dundore, Caleb Weeks
__
Want to find Crash Course elsewhere on the internet?
Instagram - https://www.instagram.com/thecrashcourse/
Facebook - http://www.facebook.com/YouTubeCrashCourse
Twitter - http://www.twitter.com/TheCrashCourse
CC Kids: http://www.youtube.com/crashcoursekids
Meet Barbacenia.
Plants that grow between a rock and a hard place… literally. They’ve got hairy roots that ooze rock-dissolving acids, letting them chisel their way into Brazilian mountaintops.
So, instead of getting nutrients from the soil like most plants, they’re busy carving into boulders. Now, the petunias in your grandma’s yard aren’t out there dissolving stones to make a living. But the rest of the plant world is no less hardcore.
Plants transport water against gravity, defend themselves against predators, and all-in-all function through super-specialized, interlocking systems in their bodies. Basically, the closer you look at plants, the more mind-blowing they become. Hi, I’m Dr.
Sammy, your friendly neighborhood entomologist, and this is Crash Course Biology. Speaking of mindblowers, Callieeeeeeeee, drop that theme music, please! We’re dropping theme music, not our manners. [THEME MUSIC] Plants are wildly diverse—there are nearly 400 thousand species, and that’s just the ones we know of. So, today, we’re zooming in on one category: angiosperms, which grow flowers and fruits.
But don’t worry, you can go check out Crash Course Botany to learn about our other plant friends. I may be biased, but I highly recommend it. And sorry, ferns, we still love you. You see, angiosperms are the dominant plant life on Earth.
Almost every plant you would recognize is an angiosperm, whether it’s a tomato, oak tree, or wildflower. And they grow basically everywhere on Earth, including the Arctic tundra. Now, just like our bodies need systems to help them eat, breathe, poop, fight germs, and so on, plants rely on integrated systems in their bodies.
Like, you might have heard of photosynthesis, the process plants use to turn sunshine, carbon dioxide from the air, and water from the soil, into sugars for the plant’s food and basic building material. But it’s not a one-and-done: photosynthesize and chill. Plants then need to move those sugars throughout their bodies to keep things running smoothly. [Chapter 3 - How plants transport nutrients] For this, angiosperms use veins called phloem.
You can actually see phloem in those stringy things on peeled bananas. Though in most cases, they’re inside the plant where you can’t see them, like here in this redwood tree. The phloem moves sugars from the leaves to the rest of the plant.
This can happen either through diffusion, where molecules passively spread into an area where there aren’t a lot of them. Or, through active transport, where the plant uses energy and special proteins to drag molecules to where they need to go, even if there’s already a bunch there. But let’s back up a second.
For photosynthesis to even begin, plants need to move stuff in a totally different, way more impressive direction. You see, they have to suck water from the soil, into the roots, and upwards to get to the leaves, where photosynthesis happens. That means plants are working against gravity.
Now, this isn’t a huge issue for a low-lying plant like a moss. But for an angiosperm like a 100-meter-tall redwood? It has to get that water all the way to the leaves at the very top.
I don’t know about you, but I’ve never seen a waterfall go in reverse. Keeping those sky-high leaves hydrated is a bit of a journey, and it begins at the roots. Roots, by the way, are one of the main types of plant organs, along with stems and leaves.
An organ is just a structure made of tissues working together to do a job. And tissues are just groups of cells working together, so organs are like a system of teams. Plants —and animals for that matter — are all pretty much organized into these kinds of systems.
But back to defying gravity. Roots need to absorb lots of water, so most angiosperm roots have a bunch of little hairs to suck up as much as possible through many different entryways. Again, this transportation happens through diffusion: If there’s more water in the soil than the roots, the H2O will passively travel into the plant.
Meanwhile, nutrients like salts and nitrogen may get into the roots through either diffusion or through active transport, which requires energy. But that just gets us as far as the roots! From there, the solution of water and minerals heads to another type of plant vein, called xylem, which will carry everything to the rest of the plant.
But again, that usually means going up. So, how does that work? The first thing to know is that water may not be immune to gravity, but it is sticky.
On the molecular level, water molecules are slightly attracted to each other, so they tend to group up like the cliques in a teen movie. That’s called cohesion. And when water molecules are gently attracted to other things — like, say, the walls of xylem — that’s adhesion.
The second thing to know? Water may come into a plant through the roots, but if it’s not used for photosynthesis, it leaves through… well, the leaves in the form of water vapor. That’s called transpiration, and it’s yet another process powered by diffusion.
When you put cohesion, adhesion, and transpiration together, it’s a more magical trio than peanut butter, jelly, and bread. [Sammy sings “Peanut Butter Jelly”] Sorry. Ahem. As water - in the form of vapor - transpires out of the leaves, those sticky water molecules pull on the molecules behind them.
And those molecules pull on the ones behind them. And suddenly, there’s this giant conga line that drags water all the way from the soil to the roots to the leaves at the tops of the tallest trees. Take that, gravity!
So, that was a quick and dirty tour of some of plants’ resource acquisition and nutrient transport systems. But, just like us, plants don’t only need to eat stuff and move those nutrients around. They also need to get rid of stuff.
And no, I’m not saying plants poop. I’m just saying, plants… expel waste products. Which, yes, sounds like a fancy phrase for poop, but it’s not!
Like, take transpiration again. A huge amount of water that’s no longer needed can actually leave a plant through transpiration. We’re talking enough water for a forest to create its own weather.
See, in the Amazon rainforest, it rains. A lot. Typically, rainy seasons are caused by seasonal winds carrying moist ocean air inland.
But the rainy season in the Amazon actually starts two to three months before that — thanks to local trees. Scientists estimate there are nearly 400 billion trees in the Amazon — about 50 for every person on Earth! — and all of them are releasing water from their leaves on a daily basis. Enough that it collects in the atmosphere and condenses to form rain clouds!
As the clouds dump rain onto the forest, this raises the humidity, which in turn warms up the atmosphere just a little. This causes air to rise and start circulating, like the bubbles at the bottom of a teapot. This circulation then causes the local wind patterns to change and starts dragging in wet air from the ocean and kicking off the rainy season months in advance.
It goes to show how big of a deal transpiration is — and how adding or removing trees from an area can do more than just shape the obvious parts of an ecosystem: On a big enough scale, it can even change the weather. So, leftover water transpires out of plants through pores in their leaves called stomata. But the stomata are also where carbon dioxide and oxygen enter and leave the plant.
You guessed it, through diffusion. And for plants, as for people, maintaining the right balance of stuff we need vs. stuff we don’t can be tricky. For every molecule of carbon dioxide a plant takes in through its stomata, it can lose around 400 water molecules that it may want to hang onto.
It needs that water not only for photosynthesis, but because water helps plants keep their structure and shape. So, to maintain the right balance, plants have evolved strategies for how to take in air through their stomata without losing too much water. For example, cacti only open their stomata at night when the air is cool; if they opened them in the daytime, they would lose a lot more water in the heat.
OK, we’ve seen lots of interlocking systems at this point. Plant systems are taking in resources, moving ‘em around, and getting rid of waste. Check, check, and check.
But how do plants get rid of other things… like predators? Yes, you adorable bunny you, you are a threat to my strawberry plants. Rooted in just one spot, plants can’t just up and book it when lil thumper comes wiggling his little nose in their direction.
So to fight against local predators, plants might have stabby thorns on their stems, or fuzzy hairs that make it harder for very hungry caterpillars to reach a leaf. Some plants even use chemical weapons — special compounds that make them taste awful, or that make them poisonous to would-be diners. And they ramp up production of those nasty compounds when they sense plant-eaters are around.
Plants can warn each other of danger, too. For instance, when a giraffe checks into the Acacia tree buffet, the tree releases chemicals on the wind that warns its buddies that leaf-eaters are in the area. Any Acacia that gets the message starts producing gross compounds.
So, ultimately, giraffes have to go upwind to find tasty trees that haven’t gotten the memo. And they can even call for help. Some plants, like tomatoes, detect compounds from the saliva of a caterpillar and release a chemical signal which summons the caterpillar’s worst enemy: a parasitoid wasp.
This wasp stings the caterpillar paralyzing it and allows its babies to chow down on the nutritious meal. And when it comes to microscopic threats like bacteria, viruses, or fungal infections, plants have immune systems to keep themselves safe, too. Their cells have proteins and special molecules that can recognize and neutralize invaders.
So bacteria and bunnies don’t stand a chance, usually…there’s no fool-proof defense in the evolutionary arms race. As the armor grows thicker, the swords grow sharper still. Now, all of that said, for any of the systems we’ve mentioned to work, plant cells have to be communicating with each other: If each plant part were just vibing on its own, they wouldn’t know how to coordinate to take down a germ or make plant food.
Plant cells get information about the outside world from receptor proteins, which change in response to the plant’s environment. Like, a protein that’s sensitive to light will change shape when the sun comes up and when it goes down. And that can cause a chain reaction that leads to bigger changes in the plant — like, cueing a cactus that it’s safe to open its stomata.
Plants can also coordinate their bodies with hormones, just like humans do. These signaling molecules travel around and trigger responses in any cell they can bind to. And there are more varieties of hormones than there are flavors of jelly beans in one of those giant jugs you win in a raffle.
Some hormones, for example, help plants reproduce. Like, check out these strawberry plants. The flowers are their reproductive organs.
In fact, that’s true for all angiosperms! Which does make giving your crush a bouquet of roses a little weird…but at least they’re pretty. Anyway, when the plant is ready to reproduce, the hormone florigen lets flowers know they should start blooming.
That yellow, powdery stuff called pollen contains plant sperm cells, and the hormone auxin helps it develop. When that pollen hits an egg in another part of the flower, it’s only a matter of time until seeds and baby strawberry plants are on the way. But plants reproduce in other ways, too.
Some essentially make clones of themselves, in a process known as asexual reproduction. And some plants do both! Like strawberry plants, for instance.
And there are pros and cons to both types of reproduction. Asexual reproduction is generally simpler: it doesn’t require the organism to find a mate. But sexual reproduction can also introduce genetic diversity into a population, which helps a strawberry patch survive long-term.
So, being able to reproduce both ways gives plants the best of both worlds. So, while it can seem like plants are just chilling, minding their own business… there’s a lot more going on than we realize. Our leafy green neighbors are constantly moving nutrients throughout their bodies, defending themselves against danger, and communicating within and among themselves to keep these overlapping systems functioning.
And in the end, plant life doesn’t just make our world more beautiful: It can shape the weather and climate, act as important sources of food and medicine, and reshape our world. Next time, we’ll be jumping into the amazingly complex world of animals, starting with how they get the stuff they need and get rid of the stuff they don’t. I’ll see you then.
Peace! This series was produced in collaboration with HHMI BioInteractive. If you’re an educator, visit BioInteractive.org/crashcourse for classroom resources and professional development related to the topics covered in this course.
Thanks for watching this episode of Crash Course Biology which was filmed at our studio in Indianapolis, Indiana, and was made with the help of all these nice people. If you want to help keep Crash Course free for everyone, forever, you can join our community on Patreon.
Plants that grow between a rock and a hard place… literally. They’ve got hairy roots that ooze rock-dissolving acids, letting them chisel their way into Brazilian mountaintops.
So, instead of getting nutrients from the soil like most plants, they’re busy carving into boulders. Now, the petunias in your grandma’s yard aren’t out there dissolving stones to make a living. But the rest of the plant world is no less hardcore.
Plants transport water against gravity, defend themselves against predators, and all-in-all function through super-specialized, interlocking systems in their bodies. Basically, the closer you look at plants, the more mind-blowing they become. Hi, I’m Dr.
Sammy, your friendly neighborhood entomologist, and this is Crash Course Biology. Speaking of mindblowers, Callieeeeeeeee, drop that theme music, please! We’re dropping theme music, not our manners. [THEME MUSIC] Plants are wildly diverse—there are nearly 400 thousand species, and that’s just the ones we know of. So, today, we’re zooming in on one category: angiosperms, which grow flowers and fruits.
But don’t worry, you can go check out Crash Course Botany to learn about our other plant friends. I may be biased, but I highly recommend it. And sorry, ferns, we still love you. You see, angiosperms are the dominant plant life on Earth.
Almost every plant you would recognize is an angiosperm, whether it’s a tomato, oak tree, or wildflower. And they grow basically everywhere on Earth, including the Arctic tundra. Now, just like our bodies need systems to help them eat, breathe, poop, fight germs, and so on, plants rely on integrated systems in their bodies.
Like, you might have heard of photosynthesis, the process plants use to turn sunshine, carbon dioxide from the air, and water from the soil, into sugars for the plant’s food and basic building material. But it’s not a one-and-done: photosynthesize and chill. Plants then need to move those sugars throughout their bodies to keep things running smoothly. [Chapter 3 - How plants transport nutrients] For this, angiosperms use veins called phloem.
You can actually see phloem in those stringy things on peeled bananas. Though in most cases, they’re inside the plant where you can’t see them, like here in this redwood tree. The phloem moves sugars from the leaves to the rest of the plant.
This can happen either through diffusion, where molecules passively spread into an area where there aren’t a lot of them. Or, through active transport, where the plant uses energy and special proteins to drag molecules to where they need to go, even if there’s already a bunch there. But let’s back up a second.
For photosynthesis to even begin, plants need to move stuff in a totally different, way more impressive direction. You see, they have to suck water from the soil, into the roots, and upwards to get to the leaves, where photosynthesis happens. That means plants are working against gravity.
Now, this isn’t a huge issue for a low-lying plant like a moss. But for an angiosperm like a 100-meter-tall redwood? It has to get that water all the way to the leaves at the very top.
I don’t know about you, but I’ve never seen a waterfall go in reverse. Keeping those sky-high leaves hydrated is a bit of a journey, and it begins at the roots. Roots, by the way, are one of the main types of plant organs, along with stems and leaves.
An organ is just a structure made of tissues working together to do a job. And tissues are just groups of cells working together, so organs are like a system of teams. Plants —and animals for that matter — are all pretty much organized into these kinds of systems.
But back to defying gravity. Roots need to absorb lots of water, so most angiosperm roots have a bunch of little hairs to suck up as much as possible through many different entryways. Again, this transportation happens through diffusion: If there’s more water in the soil than the roots, the H2O will passively travel into the plant.
Meanwhile, nutrients like salts and nitrogen may get into the roots through either diffusion or through active transport, which requires energy. But that just gets us as far as the roots! From there, the solution of water and minerals heads to another type of plant vein, called xylem, which will carry everything to the rest of the plant.
But again, that usually means going up. So, how does that work? The first thing to know is that water may not be immune to gravity, but it is sticky.
On the molecular level, water molecules are slightly attracted to each other, so they tend to group up like the cliques in a teen movie. That’s called cohesion. And when water molecules are gently attracted to other things — like, say, the walls of xylem — that’s adhesion.
The second thing to know? Water may come into a plant through the roots, but if it’s not used for photosynthesis, it leaves through… well, the leaves in the form of water vapor. That’s called transpiration, and it’s yet another process powered by diffusion.
When you put cohesion, adhesion, and transpiration together, it’s a more magical trio than peanut butter, jelly, and bread. [Sammy sings “Peanut Butter Jelly”] Sorry. Ahem. As water - in the form of vapor - transpires out of the leaves, those sticky water molecules pull on the molecules behind them.
And those molecules pull on the ones behind them. And suddenly, there’s this giant conga line that drags water all the way from the soil to the roots to the leaves at the tops of the tallest trees. Take that, gravity!
So, that was a quick and dirty tour of some of plants’ resource acquisition and nutrient transport systems. But, just like us, plants don’t only need to eat stuff and move those nutrients around. They also need to get rid of stuff.
And no, I’m not saying plants poop. I’m just saying, plants… expel waste products. Which, yes, sounds like a fancy phrase for poop, but it’s not!
Like, take transpiration again. A huge amount of water that’s no longer needed can actually leave a plant through transpiration. We’re talking enough water for a forest to create its own weather.
See, in the Amazon rainforest, it rains. A lot. Typically, rainy seasons are caused by seasonal winds carrying moist ocean air inland.
But the rainy season in the Amazon actually starts two to three months before that — thanks to local trees. Scientists estimate there are nearly 400 billion trees in the Amazon — about 50 for every person on Earth! — and all of them are releasing water from their leaves on a daily basis. Enough that it collects in the atmosphere and condenses to form rain clouds!
As the clouds dump rain onto the forest, this raises the humidity, which in turn warms up the atmosphere just a little. This causes air to rise and start circulating, like the bubbles at the bottom of a teapot. This circulation then causes the local wind patterns to change and starts dragging in wet air from the ocean and kicking off the rainy season months in advance.
It goes to show how big of a deal transpiration is — and how adding or removing trees from an area can do more than just shape the obvious parts of an ecosystem: On a big enough scale, it can even change the weather. So, leftover water transpires out of plants through pores in their leaves called stomata. But the stomata are also where carbon dioxide and oxygen enter and leave the plant.
You guessed it, through diffusion. And for plants, as for people, maintaining the right balance of stuff we need vs. stuff we don’t can be tricky. For every molecule of carbon dioxide a plant takes in through its stomata, it can lose around 400 water molecules that it may want to hang onto.
It needs that water not only for photosynthesis, but because water helps plants keep their structure and shape. So, to maintain the right balance, plants have evolved strategies for how to take in air through their stomata without losing too much water. For example, cacti only open their stomata at night when the air is cool; if they opened them in the daytime, they would lose a lot more water in the heat.
OK, we’ve seen lots of interlocking systems at this point. Plant systems are taking in resources, moving ‘em around, and getting rid of waste. Check, check, and check.
But how do plants get rid of other things… like predators? Yes, you adorable bunny you, you are a threat to my strawberry plants. Rooted in just one spot, plants can’t just up and book it when lil thumper comes wiggling his little nose in their direction.
So to fight against local predators, plants might have stabby thorns on their stems, or fuzzy hairs that make it harder for very hungry caterpillars to reach a leaf. Some plants even use chemical weapons — special compounds that make them taste awful, or that make them poisonous to would-be diners. And they ramp up production of those nasty compounds when they sense plant-eaters are around.
Plants can warn each other of danger, too. For instance, when a giraffe checks into the Acacia tree buffet, the tree releases chemicals on the wind that warns its buddies that leaf-eaters are in the area. Any Acacia that gets the message starts producing gross compounds.
So, ultimately, giraffes have to go upwind to find tasty trees that haven’t gotten the memo. And they can even call for help. Some plants, like tomatoes, detect compounds from the saliva of a caterpillar and release a chemical signal which summons the caterpillar’s worst enemy: a parasitoid wasp.
This wasp stings the caterpillar paralyzing it and allows its babies to chow down on the nutritious meal. And when it comes to microscopic threats like bacteria, viruses, or fungal infections, plants have immune systems to keep themselves safe, too. Their cells have proteins and special molecules that can recognize and neutralize invaders.
So bacteria and bunnies don’t stand a chance, usually…there’s no fool-proof defense in the evolutionary arms race. As the armor grows thicker, the swords grow sharper still. Now, all of that said, for any of the systems we’ve mentioned to work, plant cells have to be communicating with each other: If each plant part were just vibing on its own, they wouldn’t know how to coordinate to take down a germ or make plant food.
Plant cells get information about the outside world from receptor proteins, which change in response to the plant’s environment. Like, a protein that’s sensitive to light will change shape when the sun comes up and when it goes down. And that can cause a chain reaction that leads to bigger changes in the plant — like, cueing a cactus that it’s safe to open its stomata.
Plants can also coordinate their bodies with hormones, just like humans do. These signaling molecules travel around and trigger responses in any cell they can bind to. And there are more varieties of hormones than there are flavors of jelly beans in one of those giant jugs you win in a raffle.
Some hormones, for example, help plants reproduce. Like, check out these strawberry plants. The flowers are their reproductive organs.
In fact, that’s true for all angiosperms! Which does make giving your crush a bouquet of roses a little weird…but at least they’re pretty. Anyway, when the plant is ready to reproduce, the hormone florigen lets flowers know they should start blooming.
That yellow, powdery stuff called pollen contains plant sperm cells, and the hormone auxin helps it develop. When that pollen hits an egg in another part of the flower, it’s only a matter of time until seeds and baby strawberry plants are on the way. But plants reproduce in other ways, too.
Some essentially make clones of themselves, in a process known as asexual reproduction. And some plants do both! Like strawberry plants, for instance.
And there are pros and cons to both types of reproduction. Asexual reproduction is generally simpler: it doesn’t require the organism to find a mate. But sexual reproduction can also introduce genetic diversity into a population, which helps a strawberry patch survive long-term.
So, being able to reproduce both ways gives plants the best of both worlds. So, while it can seem like plants are just chilling, minding their own business… there’s a lot more going on than we realize. Our leafy green neighbors are constantly moving nutrients throughout their bodies, defending themselves against danger, and communicating within and among themselves to keep these overlapping systems functioning.
And in the end, plant life doesn’t just make our world more beautiful: It can shape the weather and climate, act as important sources of food and medicine, and reshape our world. Next time, we’ll be jumping into the amazingly complex world of animals, starting with how they get the stuff they need and get rid of the stuff they don’t. I’ll see you then.
Peace! This series was produced in collaboration with HHMI BioInteractive. If you’re an educator, visit BioInteractive.org/crashcourse for classroom resources and professional development related to the topics covered in this course.
Thanks for watching this episode of Crash Course Biology which was filmed at our studio in Indianapolis, Indiana, and was made with the help of all these nice people. If you want to help keep Crash Course free for everyone, forever, you can join our community on Patreon.