Nature of Science: Characteristics of Life (Unit 1 - Lesson 3)

Nature of Science

Scientific Inquiry and Investigation

Scientific inquiry is the process by which scientists ask questions, develop hypotheses, and conduct experiments to understand natural phenomena. This process is fundamental to biology and helps ensure that scientific knowledge is based on evidence.

• Ask and Investigate Scientific Questions: Scientists begin by observing the world and asking questions about what they see.

• Develop and Test Hypotheses: A hypothesis is a testable explanation for an observation. Experiments are designed to test these hypotheses.

• Understand Scientific Evidence and Measurement: Accurate measurement and data collection are essential for reliable results.

• Plan and Conduct Ethical Investigations: Ethical guidelines ensure that research is conducted responsibly and safely.

Characteristics of Life

Defining Life

Biologists define living things by a set of universal characteristics. To be considered alive, an organism must possess all of these traits. There are eight main characteristics shared by all living things.

• Cellular Organization: All living things are composed of cells, which are the basic units of life. Organisms may be unicellular (one cell) or multicellular (many cells).

• Reproduction: Living things reproduce to create new organisms. Reproduction can be asexual (one parent) or sexual (two parents).

• Metabolism (Obtaining and Using Energy): Organisms obtain energy from their environment and use it to carry out life processes. This includes processes such as photosynthesis and cellular respiration.

• Homeostasis: Living things maintain a stable internal environment, such as temperature, pH, and water balance, despite changes in the external environment.

• Heredity: Organisms have a universal genetic code (DNA) that carries instructions for traits and is passed from parents to offspring.

• Responsiveness: Living things respond to stimuli in their environment, such as light, temperature, and gravity.

• Growth and Development: Organisms grow and develop, increasing in size and/or changing in form and function over time.

• Adaptation Through Evolution: Populations of organisms change over generations through evolution, allowing them to better survive in their environments.

Example: Humans are multicellular organisms that reproduce sexually, maintain homeostasis (e.g., body temperature), respond to stimuli (e.g., pain), grow and develop from infancy to adulthood, and possess DNA inherited from their parents.

Cellular Organization

Cells are the smallest units capable of all life functions. Organisms can be classified based on their cellular structure:

• Prokaryotes: Simple cells without a nucleus (e.g., Bacteria and Archaea).

• Eukaryotes: Complex cells with a nucleus and organelles (e.g., Plants, Animals, Fungi, Protists).

Homeostasis and Metabolism

Homeostasis and metabolism are closely linked. Metabolism refers to all chemical reactions in an organism, while homeostasis ensures these reactions occur under optimal conditions.

• Homeostasis: Maintains constant internal conditions (e.g., temperature, water balance).

• Metabolism: Includes pathways such as photosynthesis and cellular respiration.

Equation (Cellular Respiration):

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy}$

Classification of Life

Organisms are classified into domains and kingdoms based on similarities and differences in cellular and biochemical characteristics.

• Three Domains: Archaea, Bacteria, Eukarya

• Six Kingdoms: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia

Table: Domains and Kingdoms of Life

Domain	Kingdom(s)	Cell Type	Example Organisms
Archaea	Archaebacteria	Prokaryotic	Halophiles, Thermophiles
Bacteria	Eubacteria	Prokaryotic	Escherichia coli, Streptococcus
Eukarya	Protista, Fungi, Plantae, Animalia	Eukaryotic	Amoeba, Mushrooms, Oak Tree, Human

Viruses vs. Living Organisms

Viruses share some characteristics with living organisms but lack others, leading to debate about whether they are truly alive.

• Similarities: Contain genetic material (DNA or RNA), can evolve.

• Differences: Not made of cells, cannot reproduce or carry out metabolism independently.

Example: Influenza virus requires a host cell to reproduce and does not maintain homeostasis.

Cell Theory

Cell theory is a fundamental concept in biology that describes the properties of cells.

• All living things are composed of cells.

• Cells are the basic units of structure and function in living things.

• All cells come from pre-existing cells.

Specialization and Multicellularity

In multicellular organisms, cells specialize to perform specific functions, leading to the development of tissues, organs, and organ systems.

• Specialization: Cells develop unique structures and functions (e.g., muscle cells, nerve cells).

• Organization: Specialized cells form tissues, which group into organs, and organs work together in organ systems.

Example: In humans, red blood cells transport oxygen, while neurons transmit signals.

Summary Table: Eight Characteristics of Life

Characteristic	Description
Cellular Organization	Made of one or more cells
Reproduction	Ability to produce offspring
Metabolism	Obtain and use energy
Homeostasis	Maintain stable internal conditions
Heredity	Universal genetic code (DNA)
Responsiveness	Respond to environmental stimuli
Growth and Development	Increase in size and/or change in form
Adaptation Through Evolution	Change over generations to better survive

Additional info: Some context and examples have been inferred and expanded for clarity and completeness.