Characteristics of Living Things

Defining Life and Its Properties

Biologists use several key characteristics to define living things. These properties distinguish living organisms from non-living matter and are fundamental to the study of biology.

• Organism: The term that defines any individual living thing. Examples include a single bacterium, a tree, or a human.

• Unicellular vs. Multicellular: Organisms made up of only one cell are unicellular (e.g., bacteria), while those with many cells are multicellular (e.g., plants, animals).

• Growth and Development: Growth refers to an organism becoming larger, while development is the process of change and increased complexity over time.

• Response to Stimuli: A stimulus is a change in the environment that causes a reaction. The response is how the organism reacts to the stimulus.

• Adaptation and Homeostasis: Adaptation is a change that helps an organism survive in its environment. Homeostasis is the maintenance of stable internal conditions.

• Six Characteristics of Living Things: Living things obtain and use energy, grow and develop, reproduce, respond to their environment, are made of cells, and have a genetic code. Spontaneous generation is not a characteristic of living things.

Example: A plant growing toward sunlight demonstrates both growth and response to a stimulus.

Essential Needs and Biochemistry of Life

Basic Needs and Chemical Foundations

All living things require certain essential needs and are composed of key chemical substances that support life processes.

• Essential Needs: The four essential needs of living things are sunlight, water, air (carbon dioxide or oxygen), and living space.

• Water: The most common chemical in living things, providing the environment for most chemical reactions.

• Carbohydrates: Main energy source for cell activities.

• Proteins: Make up cell membranes and store energy long-term.

• Lipids: Used for building and repairing body parts; also store energy.

• Nucleic Acids: Contain genetic information (DNA/RNA).

Classification and Taxonomy

Organizing Life's Diversity

Classification helps biologists organize and understand the diversity of life. Taxonomy is the science of naming, describing, and classifying organisms.

• Taxonomy: The scientific study of how living things are classified.

• Species: A group of organisms that can mate and produce offspring that can also reproduce.

• Binomial Nomenclature: The two-part naming system for organisms, consisting of the genus and species name (e.g., Felis domesticus).

• Hierarchical Classification: The broadest level is Domain, followed by Kingdom, Phylum, Class, Order, Family, Genus, and Species.

• Most Closely Related: Organisms in the same species are most closely related.

• Domains of Life: The three domains are Bacteria, Archaea, and Eukarya.

• Dichotomous Key: A tool used to identify organisms by presenting a series of choices.

• Father of Taxonomy: Carolus Linnaeus developed the binomial nomenclature and hierarchical classification system.

Example: Felis domesticus is the correct scientific name for the domestic cat.

Evolution by Natural Selection

Mechanisms of Evolution

Evolution explains how species change over time. Natural selection is the primary mechanism by which evolution occurs.

• Natural Selection: The process by which species gradually change over time due to inherited traits that help them survive and reproduce.

• Adaptations: Inherited traits that help an organism survive and reproduce in its environment.

• Extinction: Occurs when a species can no longer adapt to changes in its environment.

• Charles Darwin: Developed the theory of natural selection.

Example: The development of antibiotic resistance in bacteria is an example of natural selection in action.

Ecology and Interactions

Levels of Organization and Energy Flow

Ecology is the study of how organisms interact with each other and their environment. It includes understanding the flow of energy and the cycling of matter.

• Biotic Factors: All the living parts of a habitat.

• Community: All the different populations that live together in an area.

• Ecosystem: Includes all the living (biotic) and non-living (abiotic) parts of an environment.

• Decomposer: An organism that breaks down wastes and dead organisms, returning raw materials to the environment (e.g., fungi, bacteria).

• Consumer: An organism that eats other organisms. Types include herbivores (eat plants), carnivores (eat animals), and omnivores (eat both).

• Producer: An organism that makes its own food, usually through photosynthesis (e.g., plants, algae).

• Energy Pyramid: The most energy is found at the base, which is made up of producers.

Example: In a forest ecosystem, trees are producers, deer are herbivores (primary consumers), wolves are carnivores (secondary consumers), and fungi are decomposers.

Short Answer Concepts

Key Definitions and Comparisons

• Heterotroph: An organism that cannot make its own food and must obtain energy by consuming other organisms. Example: Humans, bears, mushrooms.

• Domains of Life: Bacteria, Archaea, Eukarya.

• Food Chain vs. Food Web: A food chain shows a single, direct path of energy transfer; a food web shows complex, overlapping feeding relationships among many organisms.

• Stimulus and Response: Stimulus: A plant detecting sunlight. Response: The plant bending or growing toward the sunlight.