Biology Chapter: Cell Theory and Organization

Cell Theory

• Living things are composed of one or more cells
• The cell is the basic unit of life
• New cells arise only from existing cells

Exceptions to Cell Theory

• Viruses: Not considered cells; composed of protein and nucleic acid, not protoplasm, only active when infecting a host cell
• Mitochondria & Chloroplasts: Organelles with their own DNA, reproducing independently of the host cell; mitochondrial DNA inherited only from the mother

Levels of Biological Organization

• Chemical Level: Atoms form molecules (e.g., water, DNA, carbohydrates)
• Cellular Level: Cells are the smallest unit of life, enclosed by a membrane or cell wall, performing specialized functions
• Tissue Level: Tissues are groups of similar cells working together
• Organ Level: Organs are made of two or more tissue types with a specific function (e.g., stomach, heart, brain)
• Organ System Level: Organ systems consist of a group of organs functioning together (e.g., digestive, circulatory, nervous systems)
• Organismal Level: Organism has multiple organ systems working together

The Cell

• A cell is the smallest unit of a living organism
• All cell components are called protoplasm
• Living organisms with one cell (bacteria) or many (human) are called organisms
• Cells are the fundamental building blocks of all organisms

Components of a Cell

• Nucleus: Control center, contains chromosomes (DNA), regulates reproduction and other cellular activities. Surrounded by the nuclear membrane (envelope)
• Cytoplasm: Gel-like fluid outside the nucleus; where organelles are located
• Cell Membrane: Thin membrane surrounding the cell, enclosing the protoplasm

Cell Size & Architecture

• Most cells are microscopic, measuring 1-100 micrometers
• Smaller parts of a cell are called organelles
• Organelle structure often requires an electron microscope

Organelles

• Nucleolus: Located inside the nucleus; responsible for ribosome production
• Ribosomes: Minute granules; involved in protein synthesis; may be free-floating or attached to endoplasmic reticulum
• Endoplasmic Reticulum (ER): Interconnected membranes; smooth (SER) synthesizes carbohydrates, lipids, and steroid hormones; detoxifies medications and poisons; involved in calcium storage. Rough (RER) synthesizes proteins, modifes proteins and transports proteins to the Golgi; studded with ribosomes, connected to the nuclear envelope
• Golgi Apparatus: Flattened membranes; sorts, tags, packages, and distributes lipids and proteins
• Lysosomes: Digest food materials and destroy pathogens
• Mitochondria: "Powerhouses of the cell"; produce energy (ATP) by converting glucose through aerobic cellular respiration; have double membranes for increased surface area; muscle and liver cells have many mitochondria
• Cytoskeleton: Network of microtubules and filaments providing internal support, anchoring internal structures, and important for cell movement and division
• Vacuoles: Storage sacs, large in plant cells for water storage (cell sap)

Prokaryotic vs Eukaryotic Cells

• Prokaryotic: No nucleus, lacks membrane-bound organelles (e.g., bacteria)
• Eukaryotic: Has a nucleus and membrane-bound organelles (e.g., protists, plants, fungi, animals)

Plant vs Animal Cells

• Plant: Rigid cell wall, chloroplasts (photosynthesis), large central vacuole, contain chlorophyll
• Animal: No cell wall, no chloroplasts, smaller vacuoles, do not contain chlorophyll

Types of Cells

• Nerve, Muscle, Bone, Gland, Blood, Reproductive

Cell Examples

• Free-living Protozoa (e.g., Euglena, Paramecium, Ameba): Display diverse structures and methods of nutrition; have similar basic cellular components

Explore the fundamental concepts of cell theory and the various levels of biological organization in this quiz. Understand the basic unit of life, exceptions to cell theory, and how cells form tissues, organs, and systems. Test your knowledge of these essential biological principles.