Overview
This lecture introduces the definition of life in biology, outlining key characteristics shared by all living organisms and the hierarchical organization of life.
Definition and Basic Characteristics of Life
- Biology is the study of life and its interactions.
- All known living organisms are made of cells, the basic unit of life.
- Living things contain DNA, which stores genetic information and instructions for cell function.
Hierarchical Organization of Life
- Life is organized from atoms → molecules → organelles → cells → tissues → organs → organ systems → organism.
- Multiple organisms of the same type form a population; multiple populations and their environment form a community.
- A community plus its environment is an ecosystem; all ecosystems make up the biosphere.
- Emergent properties are new characteristics that arise at each higher level of organization.
Energy and Metabolism
- All life requires energy, with the Sun as the main source for most organisms.
- Producers (like plants) use photosynthesis; consumers eat producers; decomposers recycle nutrients.
Homeostasis
- Homeostasis is maintaining a stable internal environment.
- Feedback systems with sensors and effectors regulate conditions like temperature and hydration.
Growth, Reproduction, and Evolution
- Living organisms grow and reproduce.
- Asexual reproduction produces genetically identical offspring from one parent.
- Sexual reproduction involves two parents and produces genetically varied offspring.
- Sexual reproduction is advantageous in changing environments; asexual is efficient in stable ones.
- Life evolves over generations through genetic mutations and environmental pressures, leading to adaptations.
Determining Life
- To classify something as alive, check for cells and DNA.
- Definitions of life may change as new forms are discovered.
Key Terms & Definitions
- Cell — The basic structural and functional unit of all living organisms.
- DNA — Deoxyribonucleic acid; molecule carrying genetic instructions for development and function.
- Homeostasis — The maintenance of a stable internal environment in an organism.
- Asexual Reproduction — Reproduction involving one parent, producing genetically identical offspring.
- Sexual Reproduction — Reproduction involving two parents, resulting in genetic diversity.
- Emergent Properties — Characteristics that arise from the interaction of simpler components at higher levels.
- Population — A group of organisms of the same species living together.
- Ecosystem — A community of living organisms and their physical environment.
- Biosphere — The sum of all ecosystems on Earth.
Action Items / Next Steps
- Review textbook images for examples of cell structures and organization.
- Read Chapter 2 for more details on atomic and molecular organization.