Biology - Mr. Willets
Flowers
The plant kingdom is divided into several groups. The largest of these contains plants known as angiosperms. These are commonly called the "flowering plants" because they have (surprise!!) flowers.
Common plants that are NOT part of this group are mosses, ferns, and conifers (cone producing plants).
The flower is the reproductive part of the angiosperm. It produces sperm and egg cells. The sperm are in the form of pollen. Pollen is able to be carried through the air by wind or insects. This allows these plants to reproduce without water. Usually sperm have to swim to get to the egg cell. Unofficially, I like to call pollen-the flying sperm cells (good name for a rock band!!)
Some plants have flowers that are separate sexed but most flowers are hermaphroditic. The male part of the flower is called the stamen. On the top of the stamen is a structure called the anther. Pollen is produced in the anther.
The female part of the flower is called the pistil. The top of the pistil is called the stigma. It is usually sticky or has tiny hairs. The stickiness or the hairs hold onto the pollen grains if they land there. The bottom of the pistil is where the ovary is located. This is where the egg cells are produced.
There is usually only one pistil located in the center of the flower. Several stamens surround it.
When a pollen grain lands on the stigma, it starts to grow a pollen tube down into the ovary. The pollen tube contains a nucleus with a half set of DNA. This haploid nucleus is the sperm nucleus. When the tube reaches the ovary, the sperm nucleus fertilizes the egg cell to form a zygote. (A lot of other things happen here also but we will ignore them.) When the pollen of corn fertilizes the eggs, the pollen tubes remain. You know them as the stringy things you see when you remove the outer leaves from fresh corn. They are called corn silks (because someone thought they looked like silk) but they are pollen tubes.
If pollen from a different species of plant lands on the stigma, it will not grow a pollen tube. There are chemicals on the stigma to prevent this.
If a flower uses insects to carry pollen (insect pollination), the flower has brightly colored petals. The flower also has a sweet liquid called nectar that the insects feed on. Both the petals and the nectar attract the insects. Insect pollination has the advantage that the insect will very likely leave one flower and proceed to another of the same species where it will drop off the pollen. Pollen tends to stick to the insect body.
If a flower is wind pollinated, the flower has no petals or nectar. Because they are so drab looking, most people would not think of them as flowers. Because wind pollination is a hit or miss situation (the wind can blow the pollen anywhere, not always to another flower) it works best if huge amounts of pollen are produced. It also requires good air flow around the plants, the plants must be located near one another and it works best in dry weather. The rain can wash the pollen from the air.
Some plants use self-pollination and others use cross-pollination. Sometimes by looking at the flower, you can tell which is used. Obviously, if the plant has separate sex flowers, it must use cross-pollination.
Holly bushes are separate sexed. If you plant a female holly bush and want berries, you must have a male bush somewhere nearby.
When the egg cells in the ovary are fertilized, the zygote grows into an embryonic plant. It is surround by stored food and covered with a protective coat. This combination of plant embryo, food and a coat is called a seed. The ovary may contain several seeds or just one. Either way, the ovary develops into what we call a fruit.
Questions-
1) Angiosperms are known as the ____________________ plants. What types of plants are not in this group? _________________________________________________________
2) What is the general function of flowers? _________________________________
3) Pollen is essentially the same as _______________ except that it does not need ________________
to get to the egg cells.
4) What two methods might pollen use to get to an egg cell? ___________________________________
5) What is the male part of a flower called? ___________________ On the top of this is a structure called the _____________. What is produced here? ______________
6) The pistil is the ____________________ part of the flower. The top of the pistil is called the ________________ How is this designed to hold on to pollen grains that land there? ________________
_____________________________________________________________________________
What happens if the wrong kind of pollen lands there? _______________________________________
7) The lower part of the pistil is called the __________________ This is where ________ cells are produced.
8) How are the stamens and pistil arranged in a flower? _____________________________________
9) When it lands on the stigma, the pollen grows a ______________________ down into the ovary.
10) The pollen tube contains a _______________ nucleus. How much DNA does this nucleus contain? _____________________ What word describes this? _________________
11) Where have you seen pollen tubes? ____________________________________
12) What two things attract an insect to certain flowers? ____________________________________
13) After eating the nectar in one flower, the insect (with pollen sticking to it) is likely to go where? _____________________________ What will happen there? _____________________________
14) Are all flowers "pretty"? _________ Which ones are not? _______________________________
15) What four conditions would help the success of wind pollination? a) __________________________
b) __________________________ c) __________________________ d) _________________
16) Plants with separate sexed flowers must use _______________ pollination. Name such a plant_____________________. Because of this, when you plants these, you should be sure to have both a ____________ and a ____________ plant. If not, you won't get any _______________
17) A fertilized egg cell (also called a __________________) will develop into a plant _____________
This will be surround by stored _____________ and covered by a _______________________. This is called a _________. The ovary of the flower, where the seeds are growing, will become the ____________