As I usually do with these classes, I started with an essential question. Why do plants make flowers? What are they for? I got back a range of answers. Some were "Ummm... because they are pretty?" and some were more, "So bees can have food." or "To make more plants!" Bingo!
Essentially, flowers are where the plant makes seeds. The point of a flower is reproduction. Many plants have flashy colorful petals to attract pollinators, but some have very unnoticeable flowers. They may rely on smell, wind or pollinators that don't fly.
I gave them a hand-out at this point and we went over the different things that pollenate plants and the different ways plants get those things to do that job for them.
First off, we have wind pollinated plants. This has a fancy name: anemophily. Most gymnosperms and a few angiosperms use this method. Many wind-pollinated plants are also allergens. Some common wind pollenated plants in our area are pines (that lovely yellow coating we get every Spring), birches, oaks, ragweed and grasses.
You'll notice that most of these have flowers that are not showy. There is no reason to spend energy on showy flowers if you are just counting on the wind to move the pollen around. Pollen from male cones or spikes needs to somehow get to the female cones or spikes in these cases, so that seeds can form. In some cases, both will be on the same plant, and in some cases there will be male plants and female plants.
Other kinds of plants have both male and female parts on each flower, and flowers can be self-pollenated or cross-pollenated.
Other than the wind, insects are the most common pollinators, and of these, bees and butterflies do 80% of the work. Bees are by far the most important insect when it comes to pollination, and we rely upon them for many of our crops.
The single largest pollination event in the world is in the California almond orchards, where about one million hives are trucked in each spring to do the job. New York's apple crop requires about 30,000 hives, and Maine's blueberry crop uses about 50,000 hives each year (from Wikipedia: Pollination).
Day pollinated flowers tend to be colorful and flashy. Many offer sugary nectar as a reward. In return, the insect unwittingly carries the pollen from flower to flower. Bees drink nectar but also gather pollen to feed their young and make honey with (which is food for getting through the winter). There are many types of bees. You many also find beetles or other bugs also feasting on what the plants have to offer.
Long tubular flowers can only be pollinated by things with long tongues, like hummingbirds. Hummingbirds also tend to like the color red, so many of these flowers are also red.
The rafflesia flower (Rafflesia arnoldii) is the largest in the world and it smells like rotting meat to attract flies.
The next part of the class involved going over the parts of a flower and doing a flower dissection. I handed out some little booklets I had made up for them. On the front was a flower diagram with the parts of the flower labeled. Inside was an unlabeled diagram. I gave them each a flower or two to pull apart and they were to find each flower part and label the inside diagram of the booklet. I asked them to also tape one of each part onto the inside as well.
They really enjoyed this, and I enjoyed the big pile of flowers all over the table.
While they did this, I explained that the pollen grain would go down the stigma to the ovary and then the seed could start forming once the pollen and egg had merged.The diagram they had had both "male" and "female" parts labeled on it. I also explained that flowers like sunflowers were actually multiple flowers in one.
For homework, they each got a flower parts sheet to color. This way, hopefully they would review the flower parts I had just given them. I got the sheet at Docstoc.com, which seems to have a good selection of materials. Here's the link.