Chapter 1: Humans in the World of Biology - Structured Study Notes

Living Things: Characteristics and Organization

Key Characteristics of Living Things

Living organisms share several fundamental characteristics that distinguish them from non-living matter. Understanding these traits is essential for studying biology and the human body.

• Contain nucleic acids, proteins, carbohydrates, and lipids: These are the four major classes of biological molecules essential for life. Nucleic acids (DNA and RNA) store genetic information; proteins perform structural and enzymatic functions; carbohydrates provide energy and structural support; lipids are important for energy storage and membrane structure.

• Composed of cells: The cell is the smallest unit of life. All living things are made up of one or more cells.

• Grow and reproduce: Living organisms increase in size and produce offspring, ensuring the continuation of their species.

• Use energy and raw materials: Organisms require energy (often from food or sunlight) and materials to carry out life processes.

• Respond to their environment: Living things can detect and react to changes in their surroundings.

• Maintain homeostasis: Homeostasis is the process of maintaining a stable internal environment despite external changes.

• Have adaptive traits and evolve: Over generations, organisms develop traits that help them survive and reproduce in their environment. This leads to evolution.

Example:

Humans, as living organisms, exhibit all these characteristics. For example, we use energy from food, maintain body temperature (homeostasis), and reproduce.

Biological Classification: Domain Systems

Domains of Life

All living organisms are classified into three major domains based on their cellular structure and genetic makeup.

• Bacteria: Single-celled prokaryotes with simple cell structure.

• Archaea: Single-celled prokaryotes, often found in extreme environments, genetically distinct from bacteria.

• Eukarya: Organisms with complex cells containing a nucleus and organelles. Includes animals, plants, fungi, and protists.

Humans belong to the domain Eukarya and are further classified as vertebrates within the animal kingdom.

Levels of Biological Organization

Hierarchy of Structure

Biological systems are organized in a hierarchical manner, from the simplest to the most complex.

• Atom: The smallest unit of matter that cannot be further broken down by chemical means.

• Molecule: Chemical components of cells, formed by atoms bonded together.

• Organelle: Specialized structures within cells that perform specific functions (e.g., mitochondria, nucleus).

• Cell: The basic unit of life, composed of molecules and organelles.

• Tissue: A group of similar cells that perform the same function (e.g., muscle tissue).

• Organ: A structure composed of two or more tissues working together (e.g., heart, liver).

• Organ system: Two or more organs working together to perform major body functions (e.g., digestive system).

• Individual: A single organism.

• Ecosystem: A community of organisms and their environment, interacting as a system.

Example:

The human body is organized from atoms (such as carbon and hydrogen) to molecules (like glucose), organelles (mitochondria), cells (muscle cells), tissues (muscle tissue), organs (heart), organ systems (cardiovascular system), and finally the individual (a person).

Summary Table: Levels of Biological Organization

Level	Description	Example
Atom	Smallest unit of matter	Carbon (C), Hydrogen (H)
Molecule	Group of atoms bonded together	Glucose (C6H12O6)
Organelle	Structure within a cell	Mitochondria, Nucleus
Cell	Basic unit of life	Muscle cell
Tissue	Group of similar cells	Muscle tissue
Organ	Structure with two or more tissues	Heart
Organ System	Two or more organs working together	Cardiovascular system
Individual	Single organism	Human
Ecosystem	Community and its environment	Forest ecosystem

Additional info: Expanded definitions and examples were added for clarity and completeness. The table was inferred and structured for academic context.