The sex lives of nonvascular plants발음듣기
대기중
The sex lives of nonvascular plants
72문장
100% 한국어
번역 4명 참여
출처 : 칸아카데미
번역
0%
The plants that we see today probably evolved from a single species of algae that nudged itself on shore about 1.2 billion years ago and from that one little piece of algae, all of the the half million or so species of plants that we have today evolved.발음듣기
대기중
It wasn't until about 475 million years ago that the first plants started to evolve and they were very simple, didn't have a lot of different tissue types.발음듣기
대기중
They're the nonvascular plants, the liverworts, the hornworts, and everybody's best friend, the mosses. Mmm, fuzzy.발음듣기
대기중
Yeah, it's clear that these guys are less complicated than an orchid or an oak tree and if you said that they were less beautiful, you probably wouldn't get that much argument from me, but by now I think you've learned enough about biology to know that when it comes to the simplest things, sometimes they're the craziest of all.발음듣기
대기중
Because they evolved early in the scheme of things, they were sort of able to evolve their own set of rules, much like we saw with archea and protists and bacteria.발음듣기
대기중
Nonvascular plants have some bizarre features and some kooky habits that seem to us kind of just like, "What?" especially when it comes to their sex lives.발음듣기
대기중
The main thing to know about nonvascular plants is their reproductive cycle, which they inherited from algae, but perfected to the point where now it is used by all plants in one way or another.발음듣기
대기중
(upbeat rock music) Usually when we're talking about plants, we're really talking about vascular plants, which have stuff like roots and stems and leaves.발음듣기
대기중
Those roots and stems and leaves are actually tissues that transport water and nutrients from one part of the plant to another.발음듣기
대기중
The main defining trait of nonvascular plants is that they don't have specialized conductive tissues.발음듣기
대기중
Since they don't have roots and stems, they can't reach down into the soil to get water and nutrients.발음듣기
대기중
They have to take moisture in directly through their cell walls and move it around from cell to cell through osmosis, while they rely on diffusion to transport minerals.발음듣기
대기중
Another thing nonvascular plants have in common is limited growth potential, largely because they don't have tissues to move the good stuff around or woody tissue to support more mass.발음듣기
대기중
The way for them to win is to keep it simple and small, so small that when you look at one of these dudes you sometimes might not know what you're looking at.발음듣기
대기중
This is a bummer for them because it means that they can't really survive in dry places like a lot of vascular plants can, but I'll get back to that in a minute.발음듣기
대기중
They're multicellular, they have cell walls made of cellulose, and they use photosynthesis to make their food.발음듣기
대기중
All the nonvascular plants are collectively referred to as bryophytes and who knows how many different sorts there used to be back in the olden days, but we can currently meet three phyla of bryophytes in person.발음듣기
대기중
The mosses in phylum bryophyta, the liverworts in phylum hepatophyta, and the hornworts in phylum Anthocerotophyta.발음듣기
대기중
Take it together, there are over 24,000 species of bryophytes out there, about 15,000 are mosses, 9,000 are liverworts, and only about 100 are hornworts.발음듣기
대기중
Hornworts and liverworts, funny names, but are named after the shape of their leaf like structures.발음듣기
대기중
Horns for the hornworts and livers for the liverworts, with wort stuck on the end there, which just means "herb" and you know what mosses look like, though some things that are called moss, like Spanish moss in the southern United States and reindeer moss, up in the Alpine tundra of Alaska are impostors.발음듣기
대기중
The very oldest fossils of plant fragments look really similar to liverworts, but nobody really knows which of the bryophytes evolved first and which descended from which.발음듣기
대기중
We just know that something very bryophytic looking was the first plant to rear its leafy head back in the ordovician swamps.발음듣기
대기중
Now I've got these ultra old timey nonvascular plants to provide us with some clues as to how plants evolved and like I mentioned, the most important contribution to the kingdom plantae and everything that came after them is their wonderfully complex reproductive cycle.발음듣기
대기중
Plants, vascular and nonvascular, have way more complicated sexual life cycle than animals do.발음듣기
대기중
Two haploid gametes, one from the mom, one from the dad, come together to make a diploid cell that combines the genetic material from both parents.발음듣기
대기중
That diploid cell divides and divides and divides until, voila, the world is one marmot or grasshopper richer.발음듣기
대기중
Plants, on the other hand, along with algae and a handful of invertebrate animal species, have evolved a cycle in which they take on two different forms over the course of their lives, one form giving rise to the other form.발음듣기
대기중
This type of reproductive cycle is called alternation of generations and it evolved first in algae and many of them still use it today.발음듣기
대기중
However, the difference between algae and plants is that in algae, both generations look pretty much the same.발음듣기
대기중
While in land plants, all land plants, the alternating generations are fundamentally different from each other.발음듣기
대기중
One generation, called the gametophyte, reproduces sexually by producing gametes, eggs, and sperm, which you know are haploid cells that only carry one set of chromosomes and the bryophyte sperm is actually a lot like human sperm, except that they have two flagella instead of one and they're kind of coily shaped.발음듣기
대기중
When the sperm and the egg fuse, they give rise to the second generation, called the sporophyte generation, which is asexual.발음듣기
대기중
The sporophyte itself is diploid, so it already has two sets of chromosomes in each cell and it has a little capsule, called a sporangium, which produces haploid reproductive cells, called spores.발음듣기
대기중
During its life, the sporophyte remains attached to its parent gametophyte, which it relies on for water and nutrients.발음듣기
대기중
Once its spores disperse and germinate, they in turn, produce gametophytes, which turn around to produce another sporophyte generation and so on.발음듣기
대기중
This means that the nonvascular plants that we all recognize, the green, leafy, livery or horny parts of the moss, liverwort, or hornwort, are actually gametophytes.발음듣기
대기중
Sporophytes are only found tucked inside the females and they're super small and hard to see.발음듣기
대기중
The male makes sperm through mitosis in a feature called the antheridia, the male reproductive structure, while the female gametophyte makes the egg, also through mitosis, inside the female reproductive structures, which are called the archegonia.발음듣기
대기중
These two gametophytes might be hanging out right next to each other, sperm and eggs totally ready to go, but they can't do anything until water is introduced to the situation.발음듣기
대기중
By way of the water, the sperm finds its way to the female and then into the egg where the two gametes fuse to create a diploid zygote, which divides by mitosis and grows into a sporophyte.발음듣기
대기중
The sporophyte grows inside the mother until one day it cracks open and the sporophyte sends up a long stalk with a little cap on top, called the calyptra.발음듣기
대기중
This protective case is made out of the remaining piece of the mother gametophyte and under it a capsule forms, full of thousands of little diploid spores.발음듣기
대기중
If one lands on a basketball court or something, it will just die if it doesn't get water, but if it lands on moist ground, it germinates, producing a little filament called the protonema.발음듣기
대기중
That gives rise to buds, these eventually grow into a patch of moss, which is just a colony of haploid gametophytes.발음듣기
대기중
That generation will mate and make sporophytes and the generations will continue their alternation indefinitely.발음듣기
대기중
Now, because nonvascular plants are the least complex kind of plants, their alternation of generations process is about as simple as it gets, but with vascular plants, because they have all kinds of specialized tissues, things get a little more convoluted.발음듣기
대기중
For instance, plants that produce unprotected seeds, like conifers or ginkgo trees, are gymnosperms and it's at this level that we start to see pollen, which is just a male gamete that can float through the air.발음듣기
대기중
The pollen thing is taken to the next level with angiosperms, or flowering plants, which are the most diverse group of land plants and the most recently evolved.발음듣기
대기중
The main difference between the alternation of generations in vascular and nonvascular plants is that in bryophytes, you recognize the gametophyte as being the plant part, the moss or the liverwort or whatever, while the sporophyte is less recognizable and smaller, but as plants get more complicated, like with vascular plants, the sporophytes become the dominant phase, more prominent or recognizable.발음듣기
대기중
Now I maybe just stuck a spoon in all the stuff that you learned and stirred it up to confuse you more, but we'll get into this more when we talk about the reproduction of vascular plants.발음듣기
대기중
Whether they have a big, showy sporophyte like a flower or a little, damp gametophyte like a moss, all land plants came from the same, tiny, little, ancient nonvascular plant who just put their sperm out there hoping to find some lady gametophyte they could call their own and I think that's kind of sweet.발음듣기
대기중
칸아카데미 더보기더 보기
-
22문장 100%번역 좋아요4
번역하기 -
Cranach the Elder, Cupid complaining to Venus
35문장 100%번역 좋아요0
번역하기 -
Federalist Papers #10 (part 1)
68문장 100%번역 좋아요0
번역하기 -
47문장 100%번역 좋아요2
번역하기
