UNIT II: Cells

Living Things

All living things are composed of cells, which are the basic unit of structure and function in life.

Cell Theory

The cell is the smallest unit of living material that can carry out all activities necessary for life.

Specialization

Cells must maintain a high surface area-to-volume ratio to allow for efficient cellular exchanges across the membrane.

Prokaryotic Cells

Simple, smaller cells found in the domains Bacteria and Archaea, lacking a nucleus and membrane-bound organelles.

Eukaryotic Cells

More complex cells with organized structures called organelles and a nucleus containing DNA.

Plasma Membrane

The outer envelope of the cell, composed of a phospholipid bilayer that regulates movement in and out of the cell.

Fluid-Mosaic Model

Describes the plasma membrane structure, where proteins and carbohydrates are embedded within the lipid bilayer.

Nucleus

The largest organelle that directs cell activities and houses hereditary information (DNA).

Ribosomes

Sites of protein synthesis, composed of RNA and proteins, can be free-floating or attached to the endoplasmic reticulum.

Endoplasmic Reticulum (ER)

A continuous channel involved in lipid and protein synthesis; includes rough ER (with ribosomes) and smooth ER (without ribosomes).

Golgi Bodies

Organelles that process, modify, and package proteins for distribution within or outside the cell.

Mitochondria

Known as the "powerhouse of the cell," responsible for converting energy from organic molecules into ATP.

Lysosomes

Organelles that contain digestive enzymes to break down waste and old organelles.

Centrioles

Structures involved in cellular division, producing microtubules to separate chromosomes.

Vacuoles

Fluid-filled sacs that store substances like water, food, and waste; larger in plant cells.

Cytoskeleton

A network of fibers that maintain cell shape and are involved in movement.

Cilia and Flagella

Structures that enable motion in single-celled organisms and assist in moving substances across cell surfaces.

Extracellular Matrix

A network of molecules secreted by cells that provides structural and biochemical support.

Tonicity

Describes the osmotic gradients affecting cell water movement; includes isotonic, hypertonic, and hypotonic solutions.

Active Transport

The movement of substances against their concentration gradient, requiring energy.

Endocytosis

The process of engulfing large particles or liquids into the cell via membrane invagination.

Exocytosis

The process of transporting large particles out of the cell by vesicle fusion with the plasma membrane.

Cell Junctions

Structures that allow communication and nutrient flow between neighboring cells, including desmosomes, gap junctions, and tight junctions.

Signal Transduction

The process by which an external signal is transmitted to the inside of a cell, involving reception, transduction, and response.

Apoptosis

Programmed cell death, essential for development and maintenance in multicellular organisms.

G-Protein Coupled Receptors

A large family of cell-surface receptors that work with G proteins to transmit signals into the cell.

Quorum Sensing

A process by which unicellular organisms communicate their population density to each other.