Overview
This lecture introduces the characteristics of life, emphasizing organization, energy and material requirements, reproduction, growth, and responses to stimuli, laying the foundation for further study in biology.
Characteristics of Life
- Living things share key characteristics: organization, energy/material input, reproduction, growth, development, response to stimuli, homeostasis, and adaptation.
- Organization is a major theme, from atoms to the biosphere.
- All living things require energy and materials to maintain life processes.
- Reproduction, growth, and development are essential for species continuation.
- Organisms respond to internal and external stimuli.
- Homeostasis involves maintaining a stable internal environment.
- Adaptation allows organisms to survive and thrive in changing environments.
Levels of Biological Organization
- Atoms combine to form molecules, which form cells (the basic unit of life).
- Cells group into tissues, tissues into organs, and organs into organ systems.
- Organ systems make up an organism.
- Organisms form populations (groups of the same species in an area).
- Multiple populations interact as a community.
- Ecosystems include communities plus their non-living environment.
- The biosphere includes all regions where life exists on Earth.
Energy and Metabolism
- Energy is the capacity to do work; all living things need energy.
- Metabolism is all chemical reactions in a cell, not just burning calories.
- Photosynthesizers (plants, algae) use sunlight to make food.
- Most life relies directly or indirectly on energy from sunlight.
- Food energy flows from producers to consumers, with energy lost as heat.
- Decomposers recycle nutrients from dead organisms and waste.
Reproduction, Growth, and Development
- Life arises only from pre-existing life (biogenesis theory).
- DNA contains hereditary information that determines species traits and behaviors.
- Single-celled organisms mainly reproduce asexually; some also reproduce sexually under certain conditions.
- Multicellular organisms primarily reproduce sexually, though some use asexual reproduction.
- Growth: increase in size and cell number.
- Development: all changes from conception through the life span.
Response to Stimuli
- Organisms detect and respond to internal and external stimuli to survive.
- Examples: feeling hunger, reacting to pain.
Key Terms & Definitions
- Organization — structured levels from atoms to biosphere in living things.
- Metabolism — all chemical reactions occurring in a cell.
- Photosynthesizer — organism that produces food using sunlight.
- Population — group of same-species organisms in one area.
- Community — multiple interacting populations in one area.
- Ecosystem — community plus its non-living environment.
- Biosphere — all environments on Earth supporting life.
- Homeostasis — maintenance of a stable internal environment.
- Biogenesis — theory that life comes from pre-existing life.
- Stimulus — any detectable change in the environment.
Action Items / Next Steps
- Review chapter 1 on characteristics of life.
- Preview chapters 2, 4, 6, 7, 8, 23–27, and 33 for deeper dives into organization, metabolism, genetics, and ecology.