Characteristics of Living Organisms

The Seven Characteristics of Life

Living organisms share a set of fundamental characteristics that distinguish them from non-living matter. These characteristics are essential for defining life in biological terms.

• Cellular Organization: All living things are composed of one or more cells, which are considered the basic units of life.

• Metabolism: Living organisms carry out various chemical reactions to obtain and use energy for growth, repair, and maintenance. This includes processes such as respiration and photosynthesis.

• Homeostasis: The ability to maintain a stable internal environment despite changes in external conditions.

• Growth and Development: All living things grow and develop according to specific instructions coded in their DNA.

• Reproduction: The ability to produce new individuals, either sexually or asexually, ensuring the continuation of the species.

• Response to Stimuli: Living organisms can detect and respond to environmental changes (stimuli), such as light, temperature, or touch.

• Evolutionary Adaptation: Populations of living organisms evolve over generations through changes in genetic makeup, allowing adaptation to their environment.

Example: A plant (such as Arabidopsis thaliana) grows towards light (response to stimuli), uses sunlight for photosynthesis (metabolism), and produces seeds (reproduction).

Levels of Biological Organization

Hierarchy from Simplest to Most Complex

Biological organization refers to the structured levels of complexity in living systems, from the smallest chemical building blocks to the entire biosphere.

• Atom

• Molecule

• Organelle

• Cell

• Tissue

• Organ

• Organ System

• Organism

• Population

• Community

• Ecosystem

• Biosphere

Example: The human body is an organism composed of organ systems (e.g., circulatory system), which are made of organs (e.g., heart), which are made of tissues, and so on down to atoms.

The Scientific Method

Six Elements of the Scientific Method

The scientific method is a systematic approach used by scientists to investigate natural phenomena, acquire new knowledge, or correct and integrate previous knowledge.

• Observation: Gathering information about a phenomenon or group of phenomena.

• Question: Formulating a question based on the observation.

• Hypothesis: Proposing a tentative explanation or prediction that can be tested.

• Experiment: Designing and conducting experiments to test the hypothesis.

• Data Collection and Analysis: Gathering and analyzing data from the experiment.

• Conclusion: Drawing conclusions based on the data; the hypothesis is either supported or refuted.

Example: Francesco Redi's experiment tested the hypothesis that maggots come from flies, not spontaneously from meat, by using covered and uncovered jars of meat.

Francesco Redi's Experiment

Application of the Scientific Method

Francesco Redi's experiment is a classic example of the scientific method in action, demonstrating that life (maggots) does not arise spontaneously but from pre-existing life (flies).

• Observation: Maggots appear on decaying meat.

• Question: Do maggots arise spontaneously from meat or from flies?

• Hypothesis: Maggots come from flies, not from the meat itself.

• Experiment: Placing meat in jars, some covered and some uncovered.

• Data Collection: Observing whether maggots appear in covered versus uncovered jars.

• Conclusion: Maggots only appeared in uncovered jars, supporting the hypothesis that they come from flies.

Additional info: Redi's experiment was foundational in disproving the theory of spontaneous generation.

Comparison: Living vs. Non-Living Things

Applying the Characteristics of Life

To determine if something is alive, all seven characteristics of life must be present. Non-living things may exhibit some characteristics (e.g., crystals grow, fire consumes energy), but do not meet all criteria.

• Example: A rock does not reproduce, respond to stimuli, or maintain homeostasis, and thus is not considered alive.

• Example: A virus can reproduce (inside a host) and evolve, but lacks metabolism and cellular structure, so its status as 'alive' is debated.

Additional info: The comparison and contrast of living and non-living things is a foundational exercise in biology to clarify the definition of life.