Stomata

When we think about the parts of plants, we often thing about stems, leaves, seeds, or flowers. Many plants have these parts. However a plant does not need to have any of these parts to be considered a true plant. So, instead of talking about parts that all plants have, we’ll talk about parts that some plants have. Then, as we talk about different groups of plants, we’ll talk about which parts they do or do not have.

Many plants have a waxy layer called a cuticle. The cuticle helps keep water in the plant, and prevents water loss. However, the cuticle also keeps gases from entering or exiting the plant.

This is a pretty big problem, when you think about how important photosynthesis is in plants. Remember that in photosynthesis, carbon dioxide has to come in and oxygen has to go out. So, plants have small openings called stomata. Stomata can open when the weather is cool to allow gases in and out. When the weather is hot, stomata close up, conserving water and keeping it from escaping.

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Stomata are found on all land plants (except liverworts). Some have more stomata on the lower epidermis than the upper epidermis. In plants with floating leaves, stomata may be found only on the upper epidermis; submerged leaves may lack stomata entirely.

It may seem that pathogens can easily enter this “hole” in the leaf without any trouble. However, scientists have recently discovered that stomata are able to detect most (if not all) pathogens. A curious side note: in one experiment, the bacteria that was placed on the plant leaves released the chemical which forced the stomata open.

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