Flowering Plants

Not only are flowering plants beautiful; they provide us with most of the fruits we are familiar with. Oranges, bananas, persimmons, strawberries, peaches, plums, mangoes... yummy! Let's take a quick look at how this all works.

The most important thing to remember about flowering plants is that the flower serves a very important purpose. The flower contains the reproductive organs. Have a look at the picture below to see the structure of these organs.

You may notice that the flower contains both male and female reproductive organs. The anther is the male reproductive organ. The anther is where you will find the pollen. When pollen from the anther is carried to the stigma. This process is called pollination. When the pollen lands on the stigma (part of the female reproductive system), a tube begins to grow down through the style until it reaches an ovule. This tube is called a pollen tube. Sperm then travel down the pollen tube until they reach an ovule. Inside the ovule is an ova, or egg. The sperm fertilizes the egg. Remember that the egg is haploid (it contains half the number of chromosomes as the rest of the cells in the plant) and the sperm are haploid. When the sperm fertilizes the egg, it's chromosomes fuse with the chromosomes in the egg, creating a diploid cell (a cell with the "normal" number of chromosomes.)

The fertilized eggs remain inside of the ovary. Eventually, they become seeds. Meanwhile, the ovary begins to grow and becomes the fruit. Remember that the fruit grows because its cells are reproducing using mitosis. Eventually, the fruit ripens and the seeds are released. If the seeds find a suitable home, they will sprout and grow into a new plant and the process will begin over again. This cycle is shown in the picture below:

There are a few things that you should know about pollination. Some plants are able to self-pollinate. That is, the pollen from one flower on the plant is able to fertilize the same flower or another flower on the same plant. Other plants require cross-pollination. That means that the pollen from a flower on one plant needs to be carried to the stigma of a flower on a different plant. Sometimes the wind carries the pollen from one plant to another. Other times, insects carry the pollen from one plant to another. Many flowers are "designed" to attract these insects. For example, the sweet nectar inside many flowers attracts bees. When the bees go down into the flower to get the nectar, pollen sticks to their fur. When they fly into another flower, some of that pollen falls off onto the stigma.

Plants have also developed different strategies for spreading their seeds. Have you ever blown air onto a dandelion? Dandelions depend on wind to carry their seeds. Other plants have seeds with burrs that get stuck to the fur of animals. Animals also eat the fruits that plants produce. The seeds inside of the fruit pass through the digestive system of the animal and are excreted.

What you should know.

You should be able to explain how fertilization occurs in a flowering plant. You should know the names of the reproductive organs contained in the flower. You should know which part of the flower turns into a seed and which part turns into a fruit. You should know that a fruit grows because its cells are undergoing mitosis. You should know that some plants are self-pollinators and that others require cross-pollination. Finally, you should know some of the strategies that plants use to spread their seeds.