Living things are both similar to and different from each other and from nonliving things.
Introduction: Living things are similar in that they rely on many of the same processes to stay alive, yet are different in the waysthat these processes are carried out.
Nonliving things lack certain features of living organisms, such as the ability to maintain a cellular organization,carry out metabolic processes while maintaining internal stability (homeostasis), and pass on hereditary information through reproduction.
In most biological respects, humans are like other living organisms. For instance, they are made up of cells likethose of other animals, have much the same chemical composition, have organ systems and physical characteristicslike many others, reproduce in a similar way, carry the same kind of genetic information system, and are part of afood web.
The components of living systems, from a single cell to an ecosystem, interact to maintain balance. Different organisms have different regulatory mechanisms that function to maintain the level of organization necessary for life.Diversity is evident and important at all levels of organizationÑfrom a single cell to a multicellular organism to anecosystem.
Key Idea 2:
Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring.
Introduction: Organisms from all kingdoms possess a set of instructions (genes) that determines their characteristics. Theseinstructions are passed from parents to offspring during reproduction. Students are familiar with simple mecha-nisms related to the inheritance of some physical traits in offspring. They are now able to begin to understand the molecular basis of heredity and how this set of instructions can be changed through recombination, mutation, and enetic engineering.
The inherited instructions that are passed from parent to offspring exist in the form of a code. This code is contained in DNA molecules. The DNA molecules must be accurately replicated before being passed on. Once the coded information is passed on, it is used by a cell to make proteins. The proteins that are made become cell parts and carry out most functions of the cell.
Throughout recorded history, humans have used selective breeding and other biotechnological methods to produce
products or organisms with desirable traits. Our current understanding of DNA extends this to the manipulation ofgenes leading to the development of new combinations of traits and new varieties of organisms.
Key Idea 3:
Individual organisms and species change over time.
Introduction:. Evolution is the change of species over time. This theory is the central unifying theme of biology. This change over time is well documented by extensive evidence from a wide variety of sources. Students need to know that in sexually reproducing organisms, only changes in the genes of sex cells can become the basis for evolutionary change and that these evolutionary changes may occur in structure, function, and behavior over time. Students need to be able to distinguish between evolutionary change and the changes that occur during the lifetime of an individual organism.
According to many scientists, biological evolution occurs through natural selection. Natural selection is the result of overproduction of offspring, variations among offspring, the struggle for survival, the adaptive value of certain variations, and the subsequent survival and increased reproduction of those best adapted to a particular environment.
Selection for individuals with a certain trait can result in changing the proportions of that trait in a population.
The diversity of life on Earth today is the result of natural selection occurring over a vast amount of geologic time for most organisms, but over a short amount of time for organisms with short reproductive cycles such as pathogens in an antibiotic environment and insects in a pesticide environment.
Key Idea 4:
The continuity of life is sustained through reproduction and development.
Introduction: Species transcend individual life spans through reproduction. Asexual reproduction produces genetically identical
offspring. Sexual reproduction produces offspring that have a combination of genes inherited from each parentís specialized sex cells (gametes). The processes of gamete production, fertilization, and development follow an orderly sequence of events. Zygotes contain all the information necessary for growth, development, and eventual reproduction of the organism. Development is a highly regulated process involving mitosis and differentiation.Reproduction and development are subject to environmental impact. Human development, birth, and aging should be viewed as a predictable pattern of events. Reproductive technology has medical, agricultural, and ecological applications.
Key Idea 5:
Organisms maintain a dynamic equilibrium that sustains life.
Introduction: Life is dependent upon availability of an energy source and raw materials that are used in the basic enzyme-controlled biochemical processes of living organisms. These biochemical processes occur within a narrow range of conditions. Because organisms are continually exposed to changes in their external and internal environments, they must continually monitor and respond to these changes. Responses to change can range in complexity from simple
activation of a cell chemical process to elaborate learned behavior. The result of these responses is called homeostasis, a "dynamic equilibrium" or "steady state" which keeps the internal environment within certain limits. Organisms have a diversity of homeostatic feedback mechanisms that detect deviations from the normal state and take corrective actions to return their systems to the normal range. These mechanisms maintain the physical and
chemical aspects of the internal environment within narrow limits that are favorable for cell activities. Failure of these control mechanisms can result in disease or even death.
Key Idea 6:
Plants and animals depend on each other and their physical environment.
Introduction: The fundamental concept of ecology is that living organisms interact with and are dependent on their environment and each other. These interactions result in a flow of energy and a cycling of materials that are essential for life.
Competition can occur between members of different species for an ecological niche. Competition can also occur within species. Competition may be for abiotic resources, such as space, water, air, and shelter, and for biotic resources such as food and mates. Students should be familiar with the concept of food chains and webs.
Key Idea 7:
Human decisions and activities have had a profound impact on the physical and living environment.
Introduction: and extinction of species, global warming, and alteration of the ozone shield. Some individuals believe that there
will be a technological fix for such problems. Others, concerned with the accelerating pace of change and the ecological concept of finite resources, are far less optimistic. What is certain, however, is that resolving these issues will
require increasing global awareness, cooperation, and action.
Since the students of today will be the elected officials and informed public of tomorrow, the teacher shouldencourage a diversity of activities that will allow students to explore, explain, and apply conceptual understandings and skills necessary to be environmentally literate.