Angiosperms and Flower Anatomy

Angiosperms

• Angiosperms are flowering plants that are highly successful and diverse.
• Many grasses, crops, and plants producing fruit are angiosperms.
• Fruits, by biological definition, develop from the ovary of a plant.
• Pumpkins, green beans, tomatoes, and squash are fruits because they develop from the ovary.

Vegetables aren't a true biology definition, they are leaves, stems, or plant products that are less sweet.

Flower Anatomy

Flowers can contain male and female parts, or only one part.

Flowers are the reproductive structures of angiosperms.

Stamen (Male Part)

• Stamen includes the filament and the anther.
• The filament is a stalk that supports the anther.
• The anther is a fluffy structure that produces pollen.

Pistil (Female Part)

• Pistil is made of three major parts: stigma, style, and ovary.
• Stigma is a sticky structure where pollen is supposed to stick.
• Style is the stalk that supports the stigma.
• The ovary is where fertilization occurs and seeds are formed; it ripens into a fruit.

Other Flower Parts

• Sepals protect a developing flower bud.
• Petals attract pollinators.

Pollination

• Pollinators, such as hummingbirds, butterflies, and bees, transfer pollen.
• Nectar, a sugary substance, attracts pollinators by providing carbohydrates and energy.
• Pollinators brush against the anthers and collect pollen on their bodies.
• Pollen is transferred to the sticky stigma, resulting in pollination.
• Pollination is not enough, sperm cell and egg must be fertilized

Pollen Grain Maturation

• Mature pollen grains consist of two types of cells: a tube cell and a generative cell.
• After landing on the stigma, the pollen grain uses the tube cell to burrow down a pollen tube from the stigma through the style to the inside area of the ovary.
• The generative cell divides to form two sperm cells.

Fertilization

• Two sperm cells target an ovule inside the ovary.
• Ovules have the potential to develop into a seed if fertilized.
• Ovules contain an egg cell and two polar nuclei.
• One sperm cell fertilizes the egg, forming a zygote (fertilized egg).
• The second sperm cell joins with the two polar nuclei, developing into the endosperm, which contains nutrients for the developing plant.

Double Fertilization

• Double fertilization is when sperm cells join two different things i.e. combines with the egg and the polar nuclei
• Double fertilization is an important event in angiosperms

Fruit Development

• The surrounding ovary ripens and develops into a fruit, which helps seeds travel away from the parent plant.
• Nonedible fruits can stick to animal fur or be carried by wind or water.
• Edible fruits are eaten by animals, and the seeds pass through the digestive system unharmed, traveling a great distance.

Preventing Self-Pollination

• Many angiosperm species will only accept pollen from other plants and not their own anthers.