7/22/2009 Fertilization in flowering plants happens through a - PDF document

7/22/2009 Fertilization in flowering plants happens through a process called pollination. • Pollination occurs when pollen grains Fertilization in Flowering Plants from the anther land on a stigma. Flowering plants generate pollen, ovules, seeds, and fruit. Sperm cells inside the pollen grain travel After pollen grains land on the stigma, a down the pollen tube and into the ovary pollen tube grows from the pollen grain, which contains the ovules. through the style, and into the ovary. • Fertilization occurs when one of the sperm p cells fuses with the egg inside of an ovule. After fertilization occurs, each ovule develops into a seed. • Each seed contains a tiny, undeveloped Let’s look at Bill Nye’s view on flower plant called an fertilization. fertilization. embryo. • The ovary surrounding the ovules develops into a fruit that contains one or more seeds. 1

7/22/2009 Fertilization When you think of fruit, you may first A fruit is defined as a ripened ovary think of oranges, grapes, and that contains angiosperm seeds. strawberries. • The ovary develops into a • But there are other fruit at the same time the examples you may ovules develop into seeds. p not associate with not associate with • As the fruit develops, it being fruits. swells and ripens. • For example, a • The function of a fruit is to green bean is the hold and protect the seeds. fruit of the green bean plant. The simplest fruits consist of a single Each kernel of corn on a cob is actually seed enclosed in a single ovary. an individual fruit! • Grains like corn and • In nuts like acorns and chestnuts, the ovary wheat fit this hardens into a protective shell. description. • In many grains, the ovary walls are so thin that they fuse with the seed. 2

7/22/2009 In fruits like peaches and cherries, the Grapes with seeds and tomatoes are fruits are soft and fleshy and contain a examples. single, stony seed. • Legumes like beans and peas produce a • Ovaries that contain fruit called a pod that contains many seeds. many ovules produce a single fruit with f many seeds. Most of the “fruit” of an apple is Germination actually formed by the stem surrounding the ovary. • Once the fruit and seeds are fully • If you slice an apple in developed, the plant half, you can see the embryo inside of the embryo inside of the b boundary between the d b h seed goes into a ovary wall and the dormant (inactive) stem. state. Dormant seeds can often survive Germination is the various harsh conditions like freezing process of a seed temperatures and drought. sprouting and its • Some seeds require growth into a young extreme conditions to plant. break their dormancy break their dormancy. • Forest fires for example, burn the seed coats of some plant species and allow them to germinate . 3

7/22/2009 Seed dispersal —the scattering of seeds, Because plants cannot move, they is an important part of a seed plant’s life depend on other forces to help seeds cycle. find the right conditions. • In order to germinate, a • These forces may include wind, water, or seed needs to be animals animals. dropped into an • Fruits have evolved many ways to aid in environment with seed dispersal. suitable conditions. Milkweed seeds have a tiny “umbrella” Many seeds are dispersed directly into that allows them to drift over long the air and rely on the wind to carry distances. them. • Maple trees have winged fruits that g carry their seeds from the parent plant. Fruits like grapes, strawberries, and Coconuts are encased in a leathery fruit raspberries have sweet, fleshy fruits that floats over great distances on the that are eaten by animals. ocean. • The seeds pass, unharmed, through the animal’s digestive system and are deposited in a new location. 4

7/22/2009 Flower to Fruit 5