To help students understand the different types of symmetry, ask them to classify a number of familiar items as having either radial or bilateral symmetry. For example: what type of symmetry does each of the following show: a baseball bat (radial); a garbage pail (radial); a chair (bilateral) and a spoon (bilateral).
Students often think of an ecosystem in terms of the living or biotic components. They must appreciate the significance of the abiotic components as well.
Each ecosystem has a particular set of abiotic factors. These influence the biotic factors that exist in an ecosystem. Abiotic factors include: temperature, water, atmosphere and wind, fire, gravity, topography, and geological substrate and soil. Discuss with the students how each factor affects the biotic factors. For example, most species of organisms are limited in the range of temperatures in which they can survive. Water is one of the most important factors because it is essential to living things. The carbon dioxide required for photosynthesis and the oxygen required for respiration come from the atmosphere. Fire can be destructive, but it can also rejuvenate an aging forest. Many structural adaptations of plants and animal are related to overcoming the pull of gravity.
To help students understand the difference between an organism and a population and between an organism and a community you may wish to present the students with the following:
In nearly any natural ecosystem that is not disturbed by human activities,
only slight changes occur with the passage of time. Year after year, about
the same number of frogs live in a woodland pond, and about the same number of flowers bloom nearby. The number and kinds of insects and
soil microorganisms also remain about the same.
The life of an individual organism is a striking contrast to this stable life.
An individual exists as part of a population, and a population exists as part
of a community. Often, the individual organism goes through a complex growth pattern during which its activities may vary tremendously. (You may wish to refer to the frog that the students observed in the For You To Do section.) It matures and produces young. Eventually the organism dies, but
the community continues to exist. The stability of the natural community is the result of the interactions of individual organisms in the community with each other and with the environment. At this point students are introduced to the consideration of humankind and its relationship with the environment. Your students are part of a society that is going to have to continue to come to grips with such problems as air and water pollution, overpopulation, living space, and food production. As future voters they must have a certain understanding of these problems if they are to help set a healthy destiny for humankind in the future. Their Chapter Challenge to provide booklets for voters is actually an invitation to educate themselves about environmental issues that will affect their futures and their future votes.
Humans today rely very heavily on only a few species of plants for food. Tropical rainforests are being destroyed to grow food crops. What makes the matter even worse, is that the soil in tropical rainforests is not well suited for monocultures (growing a single species of plant to the exclusion of others). These soils need the renewal of decomposed material to keep an adequate level of nitrogen and phosphorus. A few seasons after planting, the soil will no longer support the growth of crops.
The greatest biodiversity exists in rainforests and many species are yet to be classified. All these organisms are being destroyed. However, students must also take into consideration the people who live in these areas. Many grow the cereal grains to feed their families and sustain an income. |