AS Level biology, Chapter 1: Cell structure

Cell Theory

-States that all living organisms are composed of cells, cells are the basic unit of structure and function, and all cells arise from pre-existing cells.

Light Microscope

-Uses visible light and glass lenses to magnify images of specimens up to ×1500 magnification and 200 nm resolution.

Electron Microscope

-Uses a beam of electrons instead of light for much higher magnification (up to ×1,000,000) and resolution (~0.1 nm).

Transmission Electron Microscope (TEM)

-An electron microscope that produces high-resolution 2D images by passing electrons through thin specimens.

Scanning Electron Microscope (SEM)

-Produces detailed 3D images of the specimen surface by scanning it with a focused beam of electrons.

Magnification

-The number of times larger the image is compared to the actual size of the object.

Formula

Image size ÷ Actual size.

Resolution

-The smallest distance between two points that can still be distinguished as separate entities.

Ultrastructure

-Fine detail of cell structures only visible with an electron microscope.

Nucleus

-Large organelle containing DNA, controls cell activities. Surrounded by a double membrane (nuclear envelope) with pores.

Nuclear Envelope

-Double membrane surrounding the nucleus, containing nuclear pores for exchange of materials.

Nucleolus

-Dense area in the nucleus involved in synthesis of ribosomal RNA (rRNA) and assembly of ribosomes.

Rough Endoplasmic Reticulum (RER)

-System of membranes with ribosomes on surface; synthesizes and transports proteins.

Smooth Endoplasmic Reticulum (SER)

-Lacks ribosomes; synthesizes lipids, steroids and detoxifies chemicals.

Golgi Apparatus

-Stack of flattened sacs that modifies, packages, and transports proteins and lipids from ER.

Vesicles

-Small membrane-bound sacs that transport substances around the cell.

Lysosomes

-Membrane bound vesicles containing digestive (hydrolytic) enzymes used for breaking down waste or cell components.

Ribosomes

-Tiny organelles (80S in eukaryotes, 70S in prokaryotes) that carry out protein synthesis. Made of RNA and protein.

Mitochondria

-Double-membraned organelle responsible for aerobic respiration and ATP production; contains circular DNA and 70S ribosomes.

Cristae

-Folds of the inner mitochondrial membrane, increasing surface area for ATP synthesis.

Matrix

-The fluid inside mitochondria containing enzymes for respiration and mitochondrial DNA.

Chloroplasts

-Double membraned organelles found in plant cells where photosynthesis occurs; contain chlorophyll, DNA, and 70S ribosomes.

thylakoids

-Flattened membrane sacs inside chloroplasts that contain chlorophyll and are the site of light-dependent reactions.

Grana

-Stacks of thylakoids in a chloroplast.

Stroma

-Fluid-filled space in chloroplasts where the Calvin cycle (light-independent reaction) takes place.

Vacuole (in plant cells)

-Large membrane-bound sac filled with cell sap; helps maintain turgor pressure in plant cells.

Tonoplast

-The membrane surrounding the plant cell vacuole.

Plasma Membrane (Cell Surface Membrane)

-Partially permeable phospholipid bilayer that controls the movement of substances into and out of the cell.

Centrioles

-Paired structures involved in organizing the spindle fibers during cell division in animal cells.

Cell Wall (Plant Cell)

-Rigid structure made of cellulose that supports and protects the cell and prevents osmotic bursting.

Middle Lamella

-Pectin rich layer that binds plant cells together.

Plasmodesmata

-Cytoplasmic channels through cell walls that connect adjacent plant cells.

Prokaryotic Cell

-A cell that lacks a nucleus and membrane-bound organelles; includes bacteria and archaea.

Eukaryotic Cell

-Cell that has a true nucleus and membrane-bound organelles; found in plants, animals, fungi, and protoctists.

Cell Surface Membrane (in both types)

-Controls entry and exit of substances; composed of a phospholipid bilayer with proteins.

Capsule (Prokaryotic)

-A slimy outer layer in some bacteria that provides protection from desiccation and immune attack.

Cell Wall (Prokaryotic)

-Made of peptidoglycan (murein); provides shape and prevents bursting.

Cytoplasm (Prokaryotic)

-Gel like substance containing enzymes, ribosomes, and genetic material.

Nucleoid Region

-in a prokaryotic cell where the circular DNA chromosome is located; not membrane-bound.

Plasmid

-Small, circular DNA molecule in prokaryotes; often carries genes for antibiotic resistance.

Pili (Singular: Pilus)

-Short protein appendages on bacteria used for attachment or DNA transfer during conjugation.

Flagellum (Prokaryotic)

-Long whip-like structure used for locomotion; rotates for movement.

70S Ribosomes

-Smaller ribosomes found in prokaryotes, mitochondria, and chloroplasts.

80S Ribosomes

-Larger ribosomes found in the cytoplasm of eukaryotic cells.

Mesosome (Artefact)

-Folded invaginations of plasma membrane once thought to be functional structures in prokaryotes; now considered artefacts from sample preparation.

Endosymbiotic Theory

-Proposes that mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic cells.

Differential Staining

-Use of specific dyes to distinguish between different cell components or types of cells under the microscope.

Micrometer (μm)

-A unit of length equal to one-millionth of a meter (1 μm = 10⁻⁶ m).

Nanometer (nm)

-A unit of length equal to one-billionth of a meter (1 nm = 10⁻⁹ m).

Artefact

-Structure seen in a microscope image that is not a true feature of the specimen but caused by preparation techniques.