Characteristics of Living Things

Introduction to Biology

Biology is the study of living things, known as organisms. All organisms considered "alive" share a set of basic characteristics. If an entity does not possess one of these qualities, it is not classified as a living organism. For example, a virus is not considered living, although it affects living things.

Eight General Characteristics of Living Things

All living things share the following eight fundamental characteristics:

1. Cellular Organization

   • All living things are made of cells, which are the basic units of life.

   • Cells form highly organized structures within organisms.

   • Organisms can be unicellular (one cell, e.g., bacteria) or multicellular (many cells, e.g., plants, animals).

   • In multicellular organisms, cells are organized into a hierarchy: organelles → cells → tissues → organs → organ systems → organism.

2. Metabolism (Energy Use)

   • Living things require energy to survive and maintain homeostasis.

   • Organisms obtain energy from their environment.

   • Autotrophs make their own food by absorbing energy (usually from the Sun) and using it to power their cells. Example: plants use photosynthesis.

   • Heterotrophs must consume other living organisms, digest them, and use their molecules for energy. Example: animals.

3. Response to Stimuli

   • Organisms must respond to changes in their environment (stimuli) to maintain homeostasis and survive.

   • Stimuli can include temperature, sound, pH, gravity, oxygen levels, and more.

   • Examples: Mammals sweat when temperature increases; teeth chatter when temperature decreases; Venus flytrap closes its trap in response to touch.

4. Reproduction

   • Living things reproduce to create offspring of their own kind.

   • Sexual reproduction involves two gametes (sperm and egg) from two parents, combining to form a zygote.

   • Asexual reproduction requires only one parent and produces genetically identical offspring.

   • Examples: Sperm and pollen are male gametes; eggs are female gametes.

5. Growth and Development

   • Growth and development are controlled by DNA inherited from parent(s).

   • Unicellular organisms grow by mitosis, a process where a cell duplicates its DNA and divides to form two identical cells.

   • Multicellular organisms develop by cell differentiation, where cells become specialized for different functions.

   • Specialized cells (e.g., neurons, muscle cells, skin cells) work together to maintain the organism's homeostasis.

   • Cells use different parts of their DNA to perform specific jobs.

6. Homeostasis

   • Homeostasis is the maintenance of a relatively stable internal environment.

   • Examples include regulation of body temperature, sugar concentration, carbon dioxide, sodium, potassium ions, and water balance.

   • Blood pressure is an example of homeostasis; hypertension (high blood pressure) can lead to medical conditions such as strokes.

7. Universal Genetic Code

   • All living things have genetic information coded in DNA.

   • DNA is a long, linear molecule made of two chains connected by pairs of bases: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

   • The DNA molecule twists into a double helix structure.

   • This universal code is found in all living things, from bacteria to elephants to trees.

8. Adaptation and Evolution

   • Species adapt to their environment through heritable traits that provide an advantage.

   • Evolution is the change over time in a population's genetic makeup.

   • Adaptations must be coded for in DNA to be passed from parent to offspring.

   • Individuals with advantageous traits have higher reproductive success, making those traits more common over generations.

   • Example: Rock pocket mice in the southwestern United States have fur color adaptations (dark or light) that provide camouflage depending on the environment (lava rock or golden sand).

   • Example: Peppered moths in Great Britain changed color frequency due to industrial soot, demonstrating natural selection.

Case Study: Peppered Moth Frequency

The frequency of light-colored and dark-colored peppered moths in Great Britain changed over time due to environmental changes caused by industrialization. This is an example of natural selection in action.

Industrial soot darkened the environment, favoring dark moths. Later, environmental regulations reduced soot, and light moths became more prevalent again.

Summary Table: Characteristics of Living Things

Key Terms and Definitions

• Organism: Any living thing.

• Cell: The basic unit of life.

• Homeostasis: The maintenance of stable internal conditions.

• Autotroph: An organism that produces its own food.

• Heterotroph: An organism that consumes other organisms for food.

• DNA: Deoxyribonucleic acid, the molecule that carries genetic information.

• Adaptation: A heritable trait that improves an organism's ability to survive and reproduce.

• Evolution: Change in the genetic makeup of a population over time.

Relevant Equations

• Mitosis: Cell division process

• Genetic Code Base Pairing:

Example Application: The adaptation of fur color in rock pocket mice and the color change in peppered moths are classic examples of natural selection and evolution in response to environmental changes.

Additional info: Academic context and definitions have been expanded for clarity and completeness. Tables have been reconstructed and summarized for study purposes.