What Do Pollen Grains Contain?
A pollen grain is what develops from an immature male gametophyte. A gametophyte is the stage in the life cycle of a plant that produces gametes which are egg and sperm. The pollen grain of a flowering plant and that of a conifer have different contents. A flowering plant is one that produces flowers for sexual reproduction. On the other hand, conifers are woody plants that have cones which produce seeds. Does this Spark an idea?
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Distinct Parts
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The pollen grain consists of a thick wall with at least two layers known as the intine and the exine. The intine is the inner layer and is made up of cellulose and pectins. The outer layer is known as the exine and is made of a chemical called sporopollenin which is decay-resistant. Within the exine there are pores which are thinner areas. Pollen tubes grow out of these thinner areas. The inner part is where cytoplasm is located as well as the nuclei.
Flowering Plants
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A pollen grain in flowering plants consists of two cells surrounded by an outer wall. The generative cell forms two nonflagellated male gametes after dividing by mitosis. The male gametes are known as sperm cells. The second cell is known as the tube cell and forms the pollen tube. The pollen tube is the structure through which sperm cells travel to reach the ovule. The ovule is the structure that later produces an egg cell.
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Conifers
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A pollen grain of a conifer contains four cells. Only two of these cells are involved in reproduction: the generative and the tube cell. The other two cells are not as specialized. Each pollen grain also has two large air sacs.
Benefits of Contents
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The air sacs in conifer pollen grains allow them to be carried large distances for wind dissemination. Wind currents can therefore carry the grains to the female cones. In flowering plants, the pollen tube grows into the ovary to become germinated. The contents of the pollen grain contain the genetic code to produce a new plant which is required for the continuation of the plants life.
Size
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Pollen grains vary greatly in size depending on the type of plant they come from. With a few exceptions, the size can range from 10 to 100 micrometers.
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References
- Photo Credit pollen image by asb from Fotolia.com Bee on flower with pollen image by Tanya Reddin from Fotolia.com pollen image by photlook from Fotolia.com
