Cell – The Fundamental Unit of Life

Vocabulary flashcards covering key terms, organelles, cell types, and historical scientists from the lecture on cells as the fundamental unit of life.

Cell

Basic structural and functional unit of all living organisms.

Cell Theory

Concept stating that all living things are made of cells, cells arise from pre-existing cells, and the cell is the basic unit of structure and function.

Unicellular Organism

Living being composed of a single cell (e.g., Euglena, Paramecium, Yeast).

Multicellular Organism

Living being composed of more than one cell (e.g., plants, animals, fungi).

Micrometer (μm)

Unit used to measure cell size; 1 μm = 1/1000 mm.

Mycoplasma

Bacterium representing the smallest known cell (~0.1 μm).

Ostrich Egg

Example of the largest single cell (about 18 cm in diameter).

Sperm Cell

Smallest human cell (~5 μm).

Ovum

Largest human cell (~120 μm).

Nerve Cell

Longest human cell, extending up to 1 m in length.

Plasma Membrane

Thin, living, semi-permeable lipid bilayer that encloses the cytoplasm and regulates molecule passage.

Cell Wall

Rigid, non-living outer covering made of cellulose, hemicellulose, and pectin in plants (and peptidoglycan in bacteria).

Nucleus

Membrane-bound organelle containing chromatin; controls metabolism and heredity.

Nuclear Membrane

Double membrane around the nucleus, perforated by pores (~80–100 nm).

Nucleolus

Dense region within the nucleus that synthesizes ribosomal RNA.

Chromatin

DNA-protein complex (with histones) that condenses into chromosomes during cell division.

Gene

Functional segment of DNA that transmits hereditary information.

Cytoplasm

Jelly-like matrix (cytosol + organelles) between plasma membrane and nucleus.

Cytosol

Liquid portion of the cytoplasm containing dissolved molecules and ions.

Endoplasmic Reticulum (ER)

Network of membrane-bound tubules; connects nuclear and plasma membranes.

Rough ER (RER)

ER studded with ribosomes; synthesizes secretory and membrane proteins.

Smooth ER (SER)

ER lacking ribosomes; synthesizes lipids, detoxifies drugs, stores Ca²⁺ in muscle cells.

Golgi Body

Stack of flattened cisternae that modifies, sorts, and packages cell products; forms vesicles and lysosomes.

Lysosome

Single-membrane sac filled with hydrolytic enzymes for intracellular digestion and recycling.

Vacuole

Membrane-bound sac (tonoplast) storing water, ions, and wastes; large and permanent in plants, small and temporary in animals.

Mitochondrion

Double-membrane organelle with cristae and matrix; site of aerobic respiration and ATP synthesis.

Cristae

Inward folds of the mitochondrial inner membrane increasing surface area for respiration enzymes.

ATP (Adenosine Triphosphate)

Energy-rich molecule produced mainly in mitochondria; powers cellular activities.

Plastid

Double-membrane organelle in plants/algae involved in food production or storage.

Chloroplast

Green plastid with thylakoid grana and stroma; conducts photosynthesis.

Chromoplast

Plastid containing carotenoid pigments (e.g., carotene, xanthophyll, lycopene) that color fruits and flowers.

Leucoplast

Colorless plastid that stores starch, proteins, or oils (amyloplast, proteoplast, elaioplast).

Thylakoid

Membrane-bound disc within chloroplast grana holding chlorophyll molecules.

Centrosome

Organelle near nucleus containing a pair of centrioles; organizes spindle fibers.

Centriole

Cylindrical microtubule structure arranged at right angles; helps form cilia, flagella, and spindle apparatus.

Cytoskeleton

Framework of microtubules (tubulin) and microfilaments (actin) giving shape, strength, and mobility to cells.

Prokaryotic Cell

Cell lacking a true nucleus and membrane-bound organelles; size 0.5–5 μm (e.g., bacteria, cyanobacteria).

Eukaryotic Cell

Cell with a well-defined nucleus and membrane-bound organelles; size 5–100 μm.

Animal Cell

Eukaryotic cell without a cell wall or plastids; contains small vacuoles and centrioles.

Plant Cell

Eukaryotic cell with cell wall, plastids, large vacuoles, and no centrioles.

Robert Hooke

Scientist who discovered cells in 1665 using cork slices.

Anton van Leeuwenhoek

Observed living cells (protozoa, bacteria) in 1674 with a single-lens microscope.

Robert Brown

Discovered the cell nucleus in 1833.

Matthias Schleiden

Proposed (1838) that all plants are composed of cells.

Theodor Schwann

Proposed (1839) that all animals are composed of cells, co-founding cell theory.

Rudolf Virchow

Stated (1855) “Omnis cellula e cellula”: all cells arise from pre-existing cells.