Introduction to Life Sciences, Semester 2

The second semester of the Introduction to Life Sciences course introduces students (in grade 8, 9, or 10) to the concepts of ecosystems and the diversity of life. Within the course, there are two main organizing themes from which to develop standards-based learning cycle lessons:

• Diversity and interdependence
• Evolutionary theory

Diversity and Interdependence

• Matter and energy transformations occur when organisms react with one another and with their physical environment. Ecology is the study of these transformations and interactions.
• Populations consist of all the members of a species living in the same place at the same time. A community consists of all the populations in a given area.
• Living things interact with biotic and abiotic components of the environment. Biotic relationships are represented by interactions such as predation, competition, and mutualism. Examples of abiotic components are climate, weather, soil, and water. These biotic and abiotic components can act as limiting factors that impact the number of individuals in a given population.
• Food chains and food webs are models used to describe feeding relationships in a community and demonstrate how energy flows through a community. Energy is dispersed at each level of the food chain or web. The sun provides a constant source of energy. Matter is recycled through biogeochemical pathways such as the nitrogen and carbon cycles.
• Ecosystems have cyclic fluctuations that can change when climate changes, when one or more new species appear as the result of immigration, or when one or more species disappear. Carrying capacity is the number of individuals an environment can support.
• Human activities can deliberately or inadvertently alter an ecosystem. Changes in technology/biotechnology can affect, either positively or negatively, both science and society. Current issues include genetically modified food, stem cell research, genetic research, cloning, and natural resource depletion.

Evolutionary Theory

• Life on Earth began as simple, one-celled organisms somewhere between 3.5 and 4 billion years ago. In the 1920s, A. I. Oparin proposed the primordial soup model in which lightning and heat from volcanic eruptions were energy sources for the chemical reactions that led to the origin of these organisms. In 1986, Louis Lerman suggested these key chemical reactions took place not in a primordial soup, but within bubbles on the ocean’s surface.
• Significant contributions from such individuals as Lamarck, Darwin, and Mendel have shaped evolutionary thought.
• Natural selection and other evolutionary mechanisms (e.g., genetic drift, immigration, emigration, mutation), along with their consequences, provide a scientific explanation for the diversity and unity of past and present life-forms.
• During most of the Earth's history, only single-celled microorganisms existed. Once cells with nuclei developed (about one billion years ago), increasingly complex multicellular organisms evolved.
• Biologists classify organisms based on similarities and differences that reflect their evolutionary relationships. Organisms are classified into kingdoms and then further subdivided into phylum, class, order, family, genus, and species.