Angiosperms
Throughout Earth's history, there have been four periods of plant evolution. The fourth are angiosperms, ("contained seed"), or flowering plants. A flower has a complex reproductive structure that has seeds within protective chambers. This is different from naked seed plants, like pines.
There are 250,000 species of angiosperms, while there are only about 700 species of conifers and other gymnosperms. Angiosperms also supply nearly all our food and our fiber for textiles.
Flowers, Fruits, and the Angiosperm Life Style
Parts of a Flower
The structure of a flower is pretty straightforward. There are four major parts of an angiosperm. At the bottom of the flower are the sepals, which are usually green. They wrap the flower before it opens. Above the sepals are the petals, which are usually very colorful in an attempt to attract insects and other pollinators. The actual reproductive structures are multiple stamens and one or more carpels. Each stamen consists of a stalk- the filament, and a sac at the top, called the anther. That's where the pollen grains develop. The carpel or pistil consists of a stalk- the style- with an ovary at the base and a sticky tip known as the stigma, which traps pollen. The ovary is a protective chamber, containing one or more ovules, where the eggs develop.
Angiosperm Life Cycle
- An angiosperm begins as a sporophyte plant. The male gametophyte of angiosperms is the pollen grain. The female gametophyte of angiosperms is located within an ovule.
- A pollen grain attaches to the sticky stigma of a pistil and it extends down a tube to the ovule.
- The pollen deposits two sperm nuclei within the embryo sac. This double fertilization is a characteristic of an angiosperm. One sperm cells fertilizes an egg, while the other sperm cell fertilizes another gametophyte cell, which then develops into a nutrient-storing tissue called the endosperm.
- The zygote, created by a sperm cell fertilizing an egg, eventually becomes an embryo.
- The whole ovule eventually develops into a seed. Its enclosure within an ovary is what distinguishes angiosperms from gymnosperms.
A fruit is a ripened ovary of a flower. As seeds develop from ovules, the wall thickens, forming the fruit. The reason fruits taste good are because animals would eat the fruit, and it would destroy the outer, fleshy part of the fruit, but the seed would pass undisturbed through their digestive system, coming out unharmed, away from the original plant, and surrounded by their poop, a nutrient-rich natural fertilizer.
Angiosperms and Agriculture
Flowering plants, or angiosperms, produce nearly all of our food. In fact, all of our fruits and vegetables are angiosperms. Corn, rice, wheat, and other grains are grass fruits.
Types of Flowers
There are multiple ways to describe an angiosperm.
Perfect
It has both a carpel/pistil and a stamen, so it has both sexual organs.
Complete
It is perfect and it has both petals and sepals.