From Seed to Seed:
Plant Science for K-8 Educators
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From Seed to Seed: |
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Other Neat Adaptations Of course, the aforementioned adaptations for fulfilling the basic needs
are in vain if the plant is munched by a passing herbivore! As a result,
plants have also developed various means of protecting themselves. In
fact, some of the most fascinating adaptations to explore with your students
are those that help plants protect themselves-remember, they can't run
away from their predators!
A cactus has spines to protect its succulent stems, and thus its precious
water supply.
Many plants have fuzzy or hairy leaves-the hairs are actually specialized epidermal cells-that protect the plant from insect attack. (The fuzzy texture may also discourage grazing.) Perhaps the simplest example of physical protection is the bark of trees. Bark is made up of a thick layer of dead cells that form a barrier against water loss and invasion by insect or disease.A key component of physical protection is rapid wound healing. If a plant's epidermis is injured, water loss and invasion by insects and disease organisms can rapidly weaken the plant. Herbaceous plants respond to any break in the epidermis by collapsing the cells along the surface of the wound, effectively sealing it. Waxy substances are then deposited to further seal the wound. Woody tissues respond to injury by forming a callus, which consists of a mass of undifferentiated cells arising from cell division near the wound surface. Over time, cork encroaches from the area surrounding the wound, and may completely cover it. Recall that cork is the secondary tissue formed by the cork cambium. It is the part of the outer bark that replaces the epidermis in woody plant parts. Other plants use chemical protection. The ability of a plant to produce and retain toxic substances in its tissues gives it considerable evolutionary advantage over its less toxic relatives. Many poisons-as well as many useful pharmaceuticals-are derived from plants, including hemlock, strychnine, curare, digitalis, nicotine, and many hallucinogens. Some of these chemicals are extremely toxic, and can cause injury and even death in very small doses. Others have curative powers in small doses but are lethal at higher doses.In addition to producing toxic substances, some plants produce chemicals that make them taste bitter, sour, or otherwise unpalatable. However, this doesn't always prevent them from being eaten. Humans, in their fascinating and sometimes bizarre attraction to the shocking or unpleasant, take advantage of many plants' chemical deterrents. Witness the popularity of fiery hot peppers, astringent wines and teas, cigarettes and cigars, and caffeinated coffee! But these deterrents to would-be devourers aren't the only forms of chemical protection. Other plants use different tactics:
Since the daily activities of plants are so interconnected, it is difficult
to talk about any one metabolic process in isolation. You'll recall that
during our discussion on photosynthesis, we mentioned two other metabolic
processes; namely, transpiration and respiration. In the next two sections
we will examine these processes in more detail. Would you like to know more?
Relevant Books Charman, Andrew. 1997. I Wonder Why Trees Have Leaves. Kingfisher Books. ISBN: 0-7534-5094-1
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