Cell: The Unit of Life

Flashcards for key vocabulary related to cell structure and function.

Biology

The study of living organisms.

Cell Theory

Emphasized the unity underlying the diversity of life forms through cellular organization.

Reductionist Biology

Physico-chemical approach to study and understand living organisms.

Unicellular Organisms

Organisms composed of a single cell capable of independent existence and performing essential functions.

Multicellular Organisms

Organisms composed of many cells.

Cell

The fundamental structural and functional unit of all living organisms.

Plasma Membrane

Thin outer layer of animal cells.

Cell Wall

Unique characteristic of plant cells; outer boundary of plant cells.

Cell Theory

All living organisms are composed of cells and products of cells; all cells arise from pre-existing cells.

Eukaryotic Cells

Cells that have membrane-bound nuclei.

Prokaryotic Cells

Cells that lack a membrane-bound nucleus.

Cytoplasm

Semi-fluid matrix that occupies the volume of the cell; the main arena of cellular activities.

Organelles

Membrane-bound distinct structures within eukaryotic cells (e.g., endoplasmic reticulum, Golgi complex, lysosomes, mitochondria).

Ribosomes

Non-membrane bound organelles found in all cells, site of protein synthesis.

Mycoplasmas

Smallest cells, about 0.3 µm in length.

Prokaryotic Cells

Represented by bacteria, blue-green algae, mycoplasma, and PPLO; generally smaller and multiply more rapidly than eukaryotic cells.

Plasmids

Small circular DNA outside the genomic DNA in bacteria; confers unique phenotypic characters like antibiotic resistance.

Mesosome

Specialized differentiated form of cell membrane in prokaryotes; infoldings of cell membrane.

Cell Envelope

In prokaryotic cells, a chemically complex, tightly bound three-layered structure (glycocalyx, cell wall, plasma membrane).

Gram-positive Bacteria

Bacteria that take up the gram stain.

Gram-negative Bacteria

Bacteria that do not take up the gram stain.

Glycocalyx

Outermost layer of the cell envelope in bacteria; can be a slime layer or a capsule.

Flagella

Thin filamentous extensions from the cell wall in motile bacteria.

Pili and Fimbriae

Surface structures of bacteria that do not play a role in motility; involved in attachment.

Polyribosomes or Polysome

Chain of several ribosomes attached to a single mRNA, translating the mRNA into proteins.

Inclusion Bodies

Reserve material in prokaryotic cells stored in the cytoplasm.

Eukaryotes

Include all protists, plants, animals, and fungi; cells possess an organized nucleus with a nuclear envelope.

Cell Membrane

Composed mainly of lipids and proteins, with lipids arranged in a bilayer.

Fluid Mosaic Model

The model proposed by Singer and Nicolson (1972) widely accepted as structure of cell membrane.

Passive Transport

Movement of molecules across the membrane without any requirement of energy.

Osmosis

Movement of water by diffusion.

Active Transport

Energy-dependent process in which ATP is utilized to transport molecules against their concentration gradient.

Cell Wall

Non-living rigid structure forming an outer covering for the plasma membrane of fungi and plants.

Endomembrane System

Includes endoplasmic reticulum (ER), Golgi complex, lysosomes, and vacuoles; functions are coordinated.

Endoplasmic Reticulum (ER)

Network of tiny tubular structures scattered in the cytoplasm of eukaryotic cells.

Rough Endoplasmic Reticulum (RER)

ER with ribosomes attached to their outer surface; involved in protein synthesis and secretion.

Smooth Endoplasmic Reticulum (SER)

ER without ribosomes; major site for synthesis of lipid.

Golgi Apparatus

Performs the function of packaging materials to be delivered either to the intra-cellular targets or secreted outside the cell.

Lysosomes

Membrane-bound vesicular structures formed by packaging in the Golgi apparatus.

Vacuoles

Membrane-bound space found in the cytoplasm; contains water, sap, excretory product, and other materials not useful for the cell.

Tonoplast

Single membrane that bounds the vacuole.

Mitochondria

Sites of aerobic respiration; produce cellular energy in the form of ATP; ‘power houses’ of the cell.

Cristae

Infoldings of the inner membrane of the mitochondria; increase the surface area.

Plastids

Found in all plant cells and euglenoides; bear some specific pigments, thus imparting specific colours to the plants.

Chloroplasts

Contain chlorophyll and carotenoid pigments; responsible for trapping light energy essential for photosynthesis.

Chromoplasts

Contain fat soluble carotenoid pigments like carotene, xanthophylls and others; gives the part of the plant a yellow, orange or red colour.

Leucoplasts

Colourless plastids of varied shapes and sizes with stored nutrients.

Grana

Stacks of thylakoids in the chloroplasts.

Stroma

The space limited by the inner membrane of the chloroplast.

Ribosomes

Granular structures composed of ribonucleic acid (RNA) and proteins; not surrounded by any membrane.

Cytoskeleton

Elaborate network of filamentous proteinaceous structures consisting of microtubules, microfilaments and intermediate filaments present in the cytoplasm.

Cilia and Flagella

Hair-like outgrowths of the cell membrane; involved in movement.

Axoneme

Core of cilia and flagella; possesses a number of microtubules running parallel to the long axis.

Centrosome

Organelle usually containing two cylindrical structures called centrioles.

Nucleus

Cell organelle that contains chromatin, nuclear matrix and one or more spherical bodies called nucleoli.

Chromatin

Material of the nucleus stained by the basic dyes.

Nuclear Envelope

Consists of two parallel membranes with a space between; forms a barrier between the materials present inside the nucleus and that of the cytoplasm.

Nuclear Pores

Passages through which movement of RNA and protein molecules takes place in both directions between the nucleus and the cytoplasm.

Nucleoli

Spherical structures present in the nucleoplasm; site for active ribosomal RNA synthesis.

Chromosomes

Structured forms of chromatin visible during cell division.

Centromere

Primary constriction on the chromosome that holds two chromatids.

Kinetochores

Disc shaped structures on the sides of centromere.

Microbodies

Many membrane bound minute vesicles that contain various enzymes; present in both plant and animal cells.