If you are attacked, it makes sense to call for help. Plants do this, too. When caterpillars begin to chew on the leaves of corn, cotton, or some other plant species, the plants synthesize chemical signals and release them into the atmosphere. These substances attract other insects that feed on the caterpillars.
Caterpillars and other herbivores aren't the only challenges plants face, however. The environment teems with organisms that cause plant diseases. We know of more than a hundred diseases that can kill a tomato plant, each of them caused by a different pathogen (including various bacteria, fungi, protists, and viruses). Like animals, plants have a variety of defenses against pathogens. Like the defenses of our own bodies, these mechanisms are not perfect, but they generally keep the plant world in competitive balance with its pathogens.
Environmental challenges to plants are not limited to herbivores and pathogens. Some physical conditions pose substantial problems for plants and thus limit the places where plants can live. The most challenging physical environments include those that are very dry (deserts), that are water-saturated, that are dangerously salty, that contain high concentrations of toxic substances such as heavy metals, and that are very hot or very cold.
This chapter focuses on how plants meet the myriad challenges presented by their biological and physical environments. We will begin by examining interactions between plants and pathogens, then go on to consider interactions between plants and herbivores. Finally, we will discuss some of the adaptations different types of plants have made to their physical environments.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.