[Biology Class Notes] on Angiosperms Pdf

The kingdom Plantae consists of a diverse and varied group of plants that have been discovered and classified to date. It includes trees, shrubs, conifers, and even moss. This group is further subdivided into Angiosperms, gymnosperms, pteridophytes, bryophytes, and algae. This classification has been done based on external and internal features, such as morphology, anatomy, structure, phytochemistry, and so on.

Hence, considering the vast scope of this topic, we will limit our discussion to angiosperms only. 

So, what are Angiosperms?

Angiosperms are a type of vascular plant that bears both flowers and fruits. These types of plants also contain ovules enclosed in an ovary. The ovule, once fertilized, develops into seeds, which then mature into fruits.

The flowers in plants of these species help in pollination and protect the ovaries and the embryos, whereas fruits aid in seed dispersal. 

If you were to imagine any type of flower, you are almost certainly imagining an angiosperm. Even though gymnosperms biologically also have flowers, the angiosperms have a much broader diversity of more obvious flowering structures. Although angiosperm plants demonstrate an incredible diversity of flowers, the basic structure of a flower remains the same, regardless of species. 

Angiosperms have evolved the ability to manipulate other organisms to carry pollen to the right place. These pollinating animals include insects, birds, and bats that carry pollen to the right place by chance. Many flower petals even have stripes that act like a runaway to direct pollinating insects to their centers and some of these runaways are only visible in the UV spectrum, which is visible to most insects.

Gymnosperms have separate male and female cones, whereas angiosperms have both male and female reproductive organs in the same flower structure. The method of double fertilization generates a diploid zygote that will become the new sporophyte. Then, the second sperm cell fuses with two extra cell nuclei that accompany the egg cell. An endosperm is created from this triploid structure, and it is this endosperm that becomes the seed. It provides nutrition for the zygote as it grows into an embryo. 

The ovary surrounding the zygote swells to form a protective coating called the pericarp, which we are familiar with as a fruit after double fertilization generates the zygote and endosperm. This is the major difference from the naked seeds of gymnosperms. The fruits of angiosperm come in a huge variety of shapes and sizes. Usually, the shape of the seed is designed to fit the type of seed dispersal the plant relies on. For instance, bright red berries will attract the attention of birds, who will then ingest the berries and carry the seed for miles before depositing them with their fecal material. 

Other angiosperm pericarps become tough nuts that squirrels will bury in the ground. Some angiosperm fruits even grow with lots of hooks on the outside. The significant thing these different fruits have in common is that they protect the seeds inside them while helping move the seed to a new location.  There are an estimated 250,000 species of flowering plants in the world, of which trees, shrubs, and herbaceous plants are there. Angiosperms are a diverse group of plants with over 250,000 species recorded.