Visit 10--Pollination. Background

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1 Background Regardless of the shape or form of flowers, pollination is required for flowering plants to reproduce. Pollination takes place when a pollen grain lands on the stigma, the sticky topmost surface of the flower s pistil (female part). The pollen grain then grows a tube that extends through the style of the pistil and ends inside the ovary. The sperm cells travel through this tube into the ovary and combine with the ovule cells. This process of pollen and ovule combining is called fertilization and the product of this process is a seed. When ovules have been fertilized to form seeds, the ovary of the flower swells and becomes the fruit, the plant structure that protects (and eventually distributes) seeds. Fertilization and pollination are two separate but related activities that lead to the production of seeds: first, the male pollen is transported to the female pistil through pollination; then the pollen tube allows the male pollen cells to fertilize ovules so that seeds can begin to mature. Animals pollinate most fruit, vegetable, and seed crops. Animal pollinators may be insects (for example, bees, wasps, beetles.), birds, or bats. Honeybees play a key role in agriculture because they not only pollinate many food crops for humans but also many crops grown as food for livestock. However not all flowers are pollinated by animals. The size and shape of the flower provide a clue about whether animals play a role. Plants that have conspicuous and scented flowers are generally animal pollinated. However, some important food crops, specifically grasses and grains (such as wheat, corn, and rice) have tiny flowers that are pollinated by the wind. Corn is an excellent example of this. Corn has male and female flowers located on different parts of the plant. The tiny male flowers form in tassels at the top of the plant. Pollen grains produced in these flowers are carried by the wind to the silky threads that protrude from young ears of corn (that contain the cluster of female corn flowers). Each silky thread is a stigma and style that connects to a corn ovule. One grain of pollen needs to land on the end of each fiber of corn silk to make a good ear of corn. Sometimes farmers who have large fields of corn will hire a helicopter to fly around over their fields to create "wind" so that enough pollen will be blown around and pollinate all the corn silks. 1

2 Cross-Section of a Perfect Flower Petals Usually colorful to attract pollinators, can also Q&A Pollination serve as landing pads. anther pollenproducing male part of flower Stigma sticky opening of tube leading to ovary Filament holds up anther Stamen male part of flower; made up of filament and anther Pistil female part of flower, includes stigma and Ovary Female part of plant that contains ovules Nectary produces sugary nectar that attracts insects Ovules develop seeds when fertilized with pollen Stem provides support for flower and transports nutrients and water Sepal outer protective covering of flower bud 2

3 Pollination Q&A What is pollination? Pollination is the sexual reproduction of some plants that brings together pollen (male reproductive cells) and stigma (the female part of the plant) in flowering plants. Without pollination most plant fruits will not develop. Without fruits, there are no new seeds so the plant cannot continue to reproduce (make baby plants). What plants flower, fruit, and produce seeds? Most of our garden plants flower, fruit, and produce seeds (although some flower without producing fruits). This is obvious when we eat the fruits or seeds of the plant (as we do with berries cucumbers, tomatoes, squash, and peas), but a little more difficult to see when we harvest the plant before it has fruited for its stems or leaves (as we do with celery, rhubarb, spinach, kale, and lettuce), the roots (as we do with potatoes, onions, or garlic), or the flower or bud (as we do with broccoli and cauliflower). If we let all these plants grow without harvesting them, they will flower and bloom and produce seeds, often in seedpods. Have you ever seen kale or broccoli flower? How does pollination occur? Pollination occurs when the pollen grains (male reproductive cells) from one plant are transferred by wind, birds, bees, or other animals to the stigma (the female part of plant). Often pollen from one plant travels to another plant. This is called cross-pollination. Many plants require cross-pollination to produce fruit and seeds. Once pollination has occurred, new seeds begin to develop and fruits grow around the seeds to help protect them. Which foods require pollination? Over 70% of our food crops are dependent on pollinators. We wouldn t be able to eat these foods if we didn't have bees or other insects to pollinate these crops. Fruits like watermelons, cantaloupes, strawberries, blueberries, blackberries, raspberries, apples, cherries, oranges, peaches, and kiwifruit are all dependent on pollination. Almonds, which are a seed, require more bees than any other crop in the United States. Without enough bees they will not make good fruit. Cucumbers, squash, and some varieties of peas and beans must also have bees to produce well. Okra, tomatoes, peppers, eggplant, will produce vegetables without bees, but to get the best quality vegetables, they still need bees. Without bee pollination, the plants would not produce as many fruits and the fruits would not be as high quality. Many leaf crops (like greens) will produce a good harvest without bees, but the bees are necessary to get seeds. Cabbage, cauliflower, Brussels sprouts, collards, mustard, all require bees for making seeds. Believe it or not, our meat and dairy foods are also indirectly dependent upon pollination. Clover and alfalfa, which make up about one third of the diet of cows, need bees to make seeds. Bees, then, are a very important part in our supply of beef, milk, cheese, and other 3

4 milk products. Because so many of our foods depend on the bees to pollinate them, we need to learn what we can do to help protect them. Some grasses and grains need only wind to pollinate them. Corn pollen, for example, grows on the tassels that stick out the top of each ear of corn. One grain of pollen needs to land on the end of each fiber of corn silk to form each corn seed. Some farmers who have large fields of corn will hire a helicopter to fly around over their fields just to make "wind" so the pollen will be blown around and stick to the corn silks. Why do bees pollinate? Bees are drawn into brightly colored flowers by their pollen and sweet nectar. They collect pollen and nectar to feed to other bees in the hive. As bees fly into flowers, pollen sticks to a fuzzy part of their legs that we call pollen baskets. Some of the pollen will stick to the stigma of the next flower they fly into. This is how bees pollinate flowers. When bees return to the hive, they brush off the pollen and store it in cells in their hive as a source of protein to eat. Is that how bees make honey? Honey is not made from pollen. Honey is made from nectar, which is the sweet juice inside many (but not all) flowers. The nectar is sucked from the flower through a long, straw-like structure called a proboscis, mixed with natural chemicals inside the bee, and then stored in cells in the hive to age and ripen. Aaaa-Choo! Some people are allergic to different types of pollen. When these plants are in bloom, you may find yourself sneezing, itching, or coughing because the pollen is carried through the air by the wind. Although pollen looks soft and tiny to the naked eye, if you were to look at one grain of pollen under a microscope you could see that each grain is a very tiny very spiky ball. No wonder it irritates our noses! Afraid of bees? There are about 20,000 species of bees in the world. Some, like honeybees and bumble bees, are social animals and live together in big colonies where each bee has a special job. Some bees, however, are solitary and do not produce honey or beeswax. While many people fear bees because of their stingers, many species of bees cannot sting. Most honeybees and bumblebees only sting when threatened. Male honeybees and bumblebees do not have stingers at all. 4

5 Bee Aware **Note: This activity should be done when flowers are in bloom. Student learning outcomes: Students will be able to: -Observe, report, and note the value of pollinators in their environment -Explain why pollinator populations are under pressure Materials: -Descriptions of pollinators (can be found on the Pollination Canada Brochure, downloaded from -observation sheets -clipboards -pencils -magnifying glasses - a watch -field guides/id charts on insects and birds in your region -graph paper and pencil crayons (back in the classroom) Food for thought: Many plants require the assistance of a pollinator to reproduce. There are over 1000 species of pollinating insects in Canada! Procedure: Explain that bees are not the only animals that pollinate plants. Ask students to think about the insects or other animals they have seen around flowers. These might include beetles, butterflies and moths, and humming birds among others. Discuss why animals are attracted to flowers (primarily for their nectar; most are drawn by sweet smells and bright colours). Review why pollination is important (food production and plant reproduction) and discuss why some pollinators are at risk. Loss of habitat, loss of food sources, disease, and pesticides put pressures on pollinators. Look at pictures and descriptions of the following pollinating insect categories: bees, wasps, butterflies and moths, flies, and beetles. Short descriptions can be found on the Pollination Canada Brochure, downloaded from Take a pollinator walk through your neighborhood and tally the pollinators you see. You may want to use the observation sheets available at found on the following page. You can join volunteers from across Canada by signing up to report on the pollinators you see at Back in the classroom, create bar graphs to visually represent the numbers of different pollinators the class observed. 5

6 Pollinator Observation Sheet Names: Date: Start time: End Time: Total Time: Location: List the insects that are visiting flowers. If you don t know the name of the insect, describe it. Write the how many of each pollinator you observe. If you know the name of the flowers they are visiting, you may want to document that as well. Type of pollinator Insect Name (or description) Bees Ex. Honeybee Ex. Bumble bee How many observed? Butterflies and Moths Wasps Beetles Other Don t know 6