The Plants & The Bees: Plant Reproduction - CrashCourse Biology #38

Key Takeaways

a couple of weeks ago I talked about a strategy for reproduction that the very first plants came up with called alternation of generation a strategy that nonvascular plants still use today hopefully this is coming back to you a plant can take two different forms that alternate back and forth between Generations the first form the spor ofite has diploid cells two sets of chromosomes and the second form the gapy has hpid cells just one set of chromosomes well a lot can happen in 470 million years today vascular plants still use the basic alternation of generations model but they've tricked it out so that it works a whole lot different than it did back in the OR division swamps where PL Hood got its start compared with their small damp nonvascular Brethren vascular plants with all their cones and flowers and other flashy accessories look like a bunch of drag queens at a Carmen Miranda conference and Samba dance off which might seem like Overkill but we rely on these crazy Cs and their upstart reproductive strategies for well pretty much for our everything the food we eat the air we breathe the bouquet that we send to our wives and girlfriends when they're mad at us physically what I'm saying is that we need vascular plans to have [Music] sex so as you'll recall the alternation of generations in nonvascular plants is pretty straightforward a gapy produces either sperm or eggs which find each other if it's wet enough for the sperm to swim to the nearest egg once the egg is fertilized the gapy creates the sporify which is a little capsule on a St that has a bunch of spores in it the spores are released into the air they land in a moist Place germinate and Bam a new gapy generation is born but nonvascular plants are what you call gapy dominant what you're looking at when you look at a moss or a horn wart or a liver wart is the gapy it's the form that has only one set of chromosomes for them the sporophytes are tiny and tucked away inside the gyes which they rely on for food water and protection but in vascular plants it's the opposite they're sporify dominant when you look at a fern or a pine your morning glory you're looking at the sporify generation and the gites are the teeny tiny sex making materials that has stashed away in special parts so yes all vascular plants are spor ofite dominant but that does not mean that they all reproduce in the same way no sir the simplest form of vascular plants are the ferns which reproduce a lot like nonvascular plants and that they have spores that grow on the underside of the frond or Fern Leaf which are released into the wild blue yonder to find a nice soggy patch of ground to germinate on the Spore then makes a tiny gamify which is only a few centimeters wide and has both male and female reproductive organs on the underside of its leaves if it's moist enough the sperm on the boy side of the gight will find the egg on the girl side and it will create a sporify which is what we recognize as a fern there's a lot of fossil evidence to suggest that at one point there probably were ferns that produced seeds and then all the Fancy Pants vascular plants that do have seeds and flowers evolved from them but those seed bearing ferns are all extinct now so we can just gaze longingly at their fossils and wonder what their alternate a of generations looked like but there are other groups of plants that are more complex than Ferns and what they all have in common is that they reproduce by creating pollen which contains the male gapy and the female gyes or ovules which are fertilized by the pollen the complete fertilized cell grows into a seed which ripens and can produce a complete adult plant so reiterating in your more advanced vascular plants that's how the alternation generation works the sporify generation grows from a seed and produces tiny gamify either pollen or ovules they then combine to form another seed which produces another sporify this evolutionary change from spores to seeds was a big deal and it began with the gymnosperms their single serving plant making packages cut out the middleman by allowing an adult plant to grow immediately from a seed rather than having to wait for a spor to go through that intermediate gamify stage it also means in most cases that there doesn't have to be water present in order to reproduce today gymnosperms include conifers genos and tropical palm-like plants called psyched and none of them produce flowers because they evolved Before Flowers were invented instead their reproductive structures are cones and you've seen a few of these in your day in fact their name gymnosperm means naked seed and that comes from the fact that their ovules develop Exposed on the surface of the cone scales now what we think of as cones are the spiky Woody things that boy scouts are throwing at each other at Camp right but those things are actually female cones which house the ovules the male cones are smaller and kind of spongy and their job is to crank out pollen all this pollen is car it on the wind and some of it might find its way to a female cone where it fertilizes the ovule located at the base of each of the scales of the female cone as the fertilized embryo matures inside the cone it makes a seed containing enough nutrients to sustain it for a while after it germinates this seed has a tough shiny casing to protect it from the elements and once it's mature the scales of the female cone just peel back and the seed falls to the ground and makes a new tree but some gyos sperms have evolved the need for special conditions in order to reproduce take the LOD pull Pine to super tough tree that evolved in a pretty dry climate where there's lots of lightning storms that regularly start fires that burn through a forest every few years not only do launch bus have no problem withstanding a good low-intensity forest fire their female cones are serotinous so they will only open and drop their seeds when exposed to extreme heat now this sounds kind of crazy but really it's super smart because the lodge poles have evolved to take advantage of forest fires they know that the forest fire will probably get rid of a lot of pesky underbrush that would crowd out their babies and maybe even it would kill some adult Lodge P Pine so they just wait for the competition to be removed before they expose their seeds so now I'm fixing to pull out the big guns the angiosperms because angiosperms are the winners of the all Invitational plant division of things that live on Earth at least for the past 140 million years or so the they're rookies really but they know what they're doing for starters they have seeds like gymnosperms but they also have flowers and flowers are awesome because they don't have to rely on the Wind to carry their pollen to another flower like gymnosperms do with their cones for the most part flowers put animals to work toing their pollen from one flower to another in fact angiosperms and flying insects probably evolve together or co-evolved the flowers providing food for the insects in the form of nectar and the insects providing transportation for the pollen to another flower's female reproductive parts this my friends is what we call mutualism the interaction of two organisms which mutually benefits both angiosperms reproduced by making flowers that contain the gyes in this case the sporify is made up of the stem and The Roots and the leaves and even the flowers all of the other parts of the plant except the pollen and the ovom which are the actual gyes some flowers contain both male and female gites these are called perfect flowers no pressure to other flowers other flowers have both male and female sex organs on the same plant but in different flowers and some have male and female flowers on entirely different plants there are no rules with angiosperms they're just winging it to see how flowers work let's take a look at a perfect flower as an example because a lot of the garden flowers you see have both male and female reproductive parts starting from the bottom up a flower has seil which look like leaves or petals but they're usually green tissue that covered the flower when it was a little bud the petals are usually colored to attract a certain kind of pollinator like like a flag the male parts of flowers consists of an anther which produces the pollen and sits on the end of a long filament attached to the base of the flour this whole male reproductive setup like this is called the statement now when it comes to Lady Parts in contrast to gymnosperms angiosperms don't leave their eggs hanging out all exposed they lock their ovules down in an ovary at the bottom of a vase likee structure which also has a neck called a style and an opening at the top called a stigma now all that's left is to get the male gametes packaged up in their gapy the pollen and have them carried to the female gapy the ovule to fertilize them this is pollination and flowers do it by luring animals with smells colors and food and in return the animals mix and match the pollen with different individual flowers bees are the most famously successful at this but lots of other insects do it too as well as birds like hummingbirds and even some bats so no matter who does it after fertilization happens the ovule starts to swell and the ovule wall starts to toughen up because it's going to become a seed the ovary meanwhile starts to grow around it and become the fruit now there are a bunch of different types of fruit fruit is defined as anything that the ovary the production around the seed turns into so anything that contains a seed is a fruit and that's a lot of different things including many many things that we think of as not a fruit to test your fruit skills how about a round of fruit and not a fruit so which one of these is the fruit and which one of them is the NAT a fruit one a sandspur you get while rocking around at the beach or a carrot answer a sand spur the little annoying thing that attaches to your pants is actually the swen up ovary of a flower a carrot is the root of a plant a stock of celery or a piece of dandelion fluff fluff fluff that little piece of fluff is attached to a dry little fruit that contains the seed celery is the actual stock of a celery plant a strawberry or a zucchini the zucchini a strawberry is actually the swollen end of the stem of the strawberry flower so it doesn't contain the seed it actually has the seeds on the outside it's one of the hard little things on the outside of the strawberry those are the fruit some people argue about this because what seems more fruity than a strawberry but zucchinis well they're definitely fruits because they contain seeds fruits are important to angiosperms because they like to get their seeds as far away from themselves as possible so that they're not competing with their own offspring so some fruits can be carried Away by the wind While others move around by being totally delicious so that they can be eaten by an elephant and pooped out in an elephant turd far far away so that's the steamy sex lives of vascular plant oh that is good thank you for watching this episode of Crash Course biology I really is like a perfect nectarine thanks to everyone who helped put this episode together including this nectarine and if you want to go and check out any of the angiosperm mess that is the sex Li of vascular plants there's a table of contents over there if you have questions for us we're on Facebook we're on Twitter and we're always in the comments below and we'll see you next time