Biology 103

2005 Final Paper

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Imagine you're a small insect buzzing about and a bright colored plant catches your eye. You fly towards it and softly land on the sticky portion of the plant. Unfortunately, this was a fatal mistake. The plant begins to close around you and no matter how you struggle you are trapped. You have just become the latest meal for a carnivorous plant also known as the Venus Fly Trap.
A plant that eats bugs, it seems like something out of a science fiction novel, but in fact carnivorous plants have existed for thousands of years and there are over 500 different types of these plants. The most famous is the Venus Fly Trap, Dionaea muscipula (1).

Although the Venus flytrap has captivated people across the world, the plant is confined to a very small geographic area (1). In the wild, they are found in a 700-mile region along the coast of North and South Carolina. Within this area, the plants are further limited to living in humid, wet and sunny bogs and wetland areas (3).

Flytraps actually get most of their sustenance like other plants do, through the process of photosynthesis. The plant uses energy from the sun and converts the carbon dioxide and water to sugar and oxygen. The sugar produced is then converted to energy in the form of ATP, through the same processes used by our bodies to process carbohydrates (1). However, in addition to synthesizing glucose, plants also need to make amino acids, vitamins and other cellular components to survive. In the bogs where the Venus flytrap is found the soil is poor and minerals and nutrients necessary for a plant's survival are scarce. Most plants can't even live in this habitat because they do not have the ability to produce these nutrients internally. The Venus Flytrap however, has adapted the capacity to thrive in the acidic soil found in the bogs by using an alternate means to acquire elements like nitrogen. Insects are rich in nitrogen as well as other key nutrients missing from the soil and so are a perfect means for the plant to gain these elements for survival (3).

Since insects are an important part of the flytraps' diet the plant must have the ability to trap its prey. The leaves of Venus' Flytrap open wide and on them are short, stiff hairs called trigger or sensitive hairs. When anything touches two or more of these hairs enough to bend them, the two lobes of the leaves snap shut trapping whatever is inside. The trap can shut in under a second. At first the trap only closes partially. This is thought to allow time for very small insects to escape because they would not provide enough nutrients. If the object isn't food the trap will reopen in about twelve hours and spit it out (2).

When the trap closes over food, the cilia. finger-like projections, keep larger insects inside. In a few minutes the trap will shut tightly and form an air-tight seal. Then glands on the leaf surface secrete several digestive enzymes that help to decompose the insect. Once the insect has been digested sufficiently, the leaf re-opens for another victim (2).

It is the act of trapping the insect that has fascinated biologists for years. How is it possible that a plant can react to the stimulus of touch? There have been many theories over the years about how and why the flytrap reacts in such a way. Even the most recent theory is not 100 percent clear and is only a collection of circumstantial evidence without direct links to demonstrate cause and effect. When the hairs are triggered a change occurs in the electrical potential this change sends a signal to the lower cells of the midrib. The next few steps occur so quickly that biologists are unsure what happens first. There is a substantial increase of the growth hormone IAA in the cells of the midrib. The energy potential caused from the response of the trigger hairs causes hydrogen ions to move rapidly into the cell walls.
The next steps are merely assumptions, but the most accepted theory is that "a proton (H+) pump moves H+ ions out of the midrib cells and into the cell wall spaces between the cells" (4). Hydrogen ions naturally make the area of the cell wall more acidic. These ions are able to loosen the cell walls by dissolving the calcium that holds the cellulose together. This reaction causes the lower side of the midrib to become limp. Calcium moving out of the cell wall increases inside the cells and the cells absorb water (4).

Once the calcium enters the cell there is a larger percentage of calcium and a smaller percentage of water on the inside of the cell than the outside. Water then enters the cells by osmosis. Since the cell walls have been broken down, they are able to expand as they take in water, and the cells grow (4).

This growth of the cells causes an expansion of the leaf and the closing action of the trap. This all occurs so quickly the trap is able to shut in less than a second (1). The cells remain at this larger size and the cellulose eventually increases to strengthen the walls. All of these steps merely take place to close the trap. In a few days it will have to re-open. Once the insect is digested, the cells on the upper surface of the midrib will grow, much more slowly, and the leaf will re-open. The plant is unable to grow so rapidly forever. That is why it is only able to close its trap about seven times during the life of a leaf (2).

The Venus flytrap in many ways remains a mystery. It is one of the most unique plants on Earth and it shows the power of adaptive evolution. The Venus flytrap is not near as dramatic as it is portrayed in TV and films but it is a bizarre organism worthy of our study.

1) http://science.howstuffworks.com/venus-flytrap6.htm


2) http://www.botany.org/bsa/misc/carn.html


3) http://www.botany.org/Carnivorous_Plants/


4) http://www.botany.org/Carnivorous_Plants/venus_flytrap.php


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