What's the deal with plant reproduction?
Welcome to the alternation of generations! Let’s start with the most complicated version first, because it’s how over 90% of plant species reproduce:
Ah, it’s that time of year, you know the one. Your eyes are itchy and you can’t stop sneezing. Yes, love is in the air. Plants are producing tiny plants, which are having tiny plant sex and turning into seeds. … what do you mean I lost you? Alright, I’ll back up.
So most plants are flowering plants. They make flowers, those flowers get pollinated, and then the flowers make seeds. Simple enough, right? YOU WOULD BE WRONG. We have to start even further back.
The plants we see (usually) have two pairs of chromosomes. One set is from its mother, and one from its father. This means the plant is diploid. So, this plant (with two sets of chromosomes) makes a flower. This flower has both male and female parts. Inside the female part, cells mix up their chromosomes and divide into two diploid cells, and then divide again into two cells with only one set of chromosomes. Cells with only one set of chromosomes are called haploid.
Now, for animals, this is where the process stops. you have an egg, and that egg gets fertilized by a sperm, and a baby results. Could plants do this? No. Plants have to be all kinds of extra.
So over on the female side of things: Those haploid cells start dividing and making more of themselves, and soon there’s a tiny plant, usually microscopic, held by its parent plant inside the flower bud. The little red things? That’s them.
Those little plants contain seven cells. The three greens in the back won’t be useful until later, the two purples in the middle join together and become diploid, the blue one to the front is the egg, and the two oranges on either side of the egg just tell the sperm where to go.
Over to the male side of things, where everything is a lot simpler: The process is pretty much the same. The parent plant cells divide into cells that only have half the chromosomes of the parent plant. These cells only divide in two, though, with a protective covering. That’s as big as they ever get before they’re released from the parent plant. This stuff is what makes you miserable when the seasons change. Two cells covered in a tough shell just trying to find a lady of their own species to get with - Referring back to the picture of the flower, imagine those little orange fellows are hundreds of thousands of horny dudes. They get blown away to fly through the air and ultimately into your eyes and up your nose. “This isn’t a lady” they remark as they’re shredded and consumed by your immune cells.
So, finally, the pollen flies off into the suneset and somehow (probably with the aid of a bee), find a flower’s lady bits. Like so:
It then uses one of its cells to make a tube for its sperm to go down to one of those red gals,and the other to make two sperm.One sperm goes down and creates an embryo out of the tiny ladyplant’s egg, (two sets of chromosomes again!) and the other fertilizes the giant cell in the middle so that the embryo has something to eat while it’s trapped as a seed in the earth. The original diploid plant (A.K.A. the flower) feeds nutrients to what is now a seed until the embryo has enough of a food source with it that it can bust through the ground once it’s planted.
And that’s how big plants make tiny plants, that make seeds that make big plants.
