Fertilization in Flowering Plants Happens Through a Process Called Pollination
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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. After pollen grains land on the stigma, a Sperm cells inside the pollen grain travel pollen tube grows from the pollen grain, down the pollen tube and into the ovary through the style, and into the ovary. which contains the ovules. • Fertilization occurs when one of the sperm 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. 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. not associate with being fruits. • As the fruit develops, it swells and ripens. • For example, a green bean is the • The function of a fruit is to fruit of the green hold and protect the seeds. 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 many seeds. Most of the “fruit” of an apple is Germination actually formed by the stem surrounding the ovary. • Once the fruit and • If you slice an apple in seeds are fully half, you can see the developed, the plant bdbboundary between t he embryo inside of the ovary wall and the seed goes into a stem. dormant (inactive) 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. • 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. dropped into an environment with • Fruits have evolved many ways to aid in suitable conditions. seed dispersal. Many seeds are dispersed directly into Milkweed seeds have a tiny “umbrella” the air and rely on the wind to carry that allows them to drift over long them. distances. • Maple trees have winged fruits that carry their seeds from the parent plant. Coconuts are encased in a leathery fruit Fruits like grapes, strawberries, and that floats over great distances on the raspberries have sweet, fleshy fruits ocean. that are eaten by animals. • 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.