The life sciences are changing in ways that have important implications for high school biology. Many of these changes concern
our understanding of the largest and the smallest living systems. Molecular biology continues to produce new insights into how
living systems work and how they are connected with one another, as well as new technologies, such as recombinant DNA, that
have profound implications for our health, our lifestyles, and our political and economic systems. Equally important are changes
in ecology, a traditional biological discipline which plays a key role in the emerging interdisciplinary field of environmental science.
Ecologists are working together with oceanographers, atmospheric scientists, and social scientists to study the coupled human
and natural systems that support all life on earth, and to understand how those systems are changing in response to growing
human populations and our technologies. Our students will need to understand these changing fields in order to be healthy
and responsible citizens and productive workers.
An understanding of biology begins with appreciation of the diversity and the structures of living systems. The structure
of living systems directly influences how they carry out their life functions. Reasoning about living systems often involves
relating different levels of organization, from the molecule to the biosphere, and understanding how living systems are
structured at each level. Life processes in a cell are based on molecular interactions which keep the internal environment
relatively constant. Cells are composed of highly organized structures called organelles. Cells are the smallest unit of life
that can assimilate energy, reproduce, and react to the environment. A collection of cells with a common function forms a
tissue and several kinds of tissues form an organ. Together many organs form an organ system such as the digestive system.
A multicellular organism is the composite of cells, tissues, and organs. All organisms are interconnected in populations,
communities, and ecosystems.
All living systems function in ways that are consistent with basic physical laws, including conservation of matter and
energy. Transformations of matter and energy are crucial to the functions of every living system, from the molecular
to the global level. The food-making process of photosynthesis generates the energy source, in the form of organic
compounds, for all living things. Organic compounds transfer matter and energy through ecosystems via food chains and
webs. The energy found in organic chemical bonds is changed to usable cellular energy through the process of cellular
respiration. Photosynthesis and cellular respiration are key processes through which living systems exchange matter and
energy with the non-living environment, participating in biogeochemical cycles that are being altered in unprecedented
ways by human populations and human technologies.
In addition to transforming matter and energy, living systems have a unique ability to maintain their complex organization
over time. The information that enables them to do this is stored in the genomes of every living cell. Genetic information
is passed from parent to offspring in the form of gametes. Fertilization unites the genetic information from both parents
creating a unique individual. Organisms within a species are generally similar because they posses very similar genetic
material. However, genetic mixing and occasional mutation result in differences among individuals. Over time, changes in
genetic information can affect the size, diversity, and genetic composition of populations, a process called biological evolution.
It is widely accepted that Earth’s present day life forms have evolved from common ancestors by processes that include
natural selection. In the scientific community, evolution has been a unifying principle that provides a framework for
organizing most of biological knowledge into a coherent picture. It has been accepted by the scientific community that
evidence for evolution is found in the fossil record and is indicated by anatomical and chemical similarities evident within the
diversity of existing organisms.