Double fertilization is a distinctive feature of angiosperms. The male gametocyte delivers two sperm to an ovule. One sperm fertilizes the egg and the other fertilizes a cell that gives rise to endosperm that supports the embryo.
This animation (Audio - Important) is an introduction to double fertilization that we will discuss in the last lecture.
The aboveground parts of plants (also called shoots) consist of stems, leaves, and flowers. Stems are frameworks for upright growth and display of flowers. Photosynthetic cells in leaves are exposed to light. Flowers are displayed to pollinators.
The plant's descending parts, called roots, usually grow below ground. They anchor and support the plant. They penetrate the soil and absorb water and dissolved minerals and conduct them upward. They also store food.
This animation (Audio - Important) describes the structure of plants.
There are two classes of flowering plants:
Monocot seeds have one cotyledon ("seed leaf") and dicot seeds have two. Monocots have their flower parts in threes or multiples of three. Dicots have their flower parts in fours (or multiples) or fives (or multiples). There are also differences in the structures of stems, leaves, and roots.
This animation (Audio - Important) compares monocots and dicots.