A2.1 Origin of Cells + A2.2 Cell Structure + A2.3 Viruses

A2.1 Origin of Cells (HL only) A2.2 Cell Structure (SL + HL) A2.3 Viruses (HL only)

Cell Theory

All living things are composed of cells; the cell is the basic unit of structure and function; all cells arise from preexisting cells.

Homeostasis

Maintenance of stable internal conditions within a narrow range.

Metabolism

All chemical reactions occurring within a cell or organism.

Nutrition

Process of obtaining and using nutrients for energy and growth.

Movement

Changing position of the whole organism or internal structures.

Excretion

Removal of metabolic waste products from the cell or organism.

Growth

Increase in size or mass of a cell or organism.

Response to Stimuli

Ability to detect and respond to changes in the environment.

Reproduction

Production of offspring; can be asexual or sexual.

Plasma Membrane

Phospholipid bilayer controlling what enters and exits the cell.

Cytoplasm

Water-based internal fluid where metabolism occurs.

DNA

Genetic material containing information for cell growth and development.

Ribosomes

Cellular structures responsible for protein synthesis.

Prokaryotic Cell

Cell without a nucleus; DNA in nucleoid region; no membrane-bound organelles.

Eukaryotic Cell

Cell with a nucleus and membrane-bound organelles.

Nucleoid Region

Region in prokaryotic cells containing circular naked DNA.

70S Ribosome

Smaller ribosomes found in prokaryotes.

80S Ribosome

Larger ribosomes found in eukaryotes.

Cell Wall

Provides strength and support to cells; composition differs (peptidoglycan in bacteria, cellulose in plants, chitin in fungi).

Flagellum

Long whip-like structure used for locomotion.

Pili

Short projections allowing bacterial adhesion and genetic exchange.

Endosymbiotic Theory

Eukaryotic organelles (mitochondria/chloroplasts) originated as engulfed prokaryotes.

Mitochondria

Organelle producing ATP by aerobic respiration.

Chloroplast

Plant organelle carrying out photosynthesis.

Rough Endoplasmic Reticulum

Membrane network with ribosomes for protein synthesis and transport.

Smooth Endoplasmic Reticulum

Membrane network without ribosomes for lipid synthesis and detoxification.

Golgi Apparatus

Modifies and packages proteins for secretion.

Lysosome

Vesicle containing digestive enzymes to break down macromolecules.

Vacuole

Storage organelle; large central vacuole in plants, small in animals.

Cytoskeleton

Network of protein filaments maintaining cell shape, enabling movement, and aiding cell division.

Centrioles

Animal cell structures organizing microtubules during cell division.

Plastids

Plant cell organelles including chloroplasts, chromoplasts, and amyloplasts.

Aseptate Fungal Hyphae

Fungal filaments without cross walls, forming a multinucleate cell.

Skeletal Muscle Cell

Multinucleate elongated cell responsible for movement.

Red Blood Cell (Erythrocyte)

Animal cell lacking a nucleus, specialized for oxygen transport.

Phloem Sieve Tube Element

Plant transport cell lacking a nucleus, supported by companion cells.

Light Microscope

Uses light and lenses to magnify specimens; lower resolution than electron microscopes.

Electron Microscope

Uses electrons for high-resolution images of cell ultrastructure.

Resolution

Ability to distinguish two separate points in an image.

Magnification

How many times larger an image appears compared to its actual size.

Eyepiece Graticule

A scale in the microscope eyepiece used to measure specimen size.

Cryogenic Electron Microscopy

Images biomolecules at very low temperatures without crystallizing them.

Freeze-Fracture Electron Microscopy

Technique splitting frozen cells to reveal membrane structures and integral proteins.

Immunofluorescence

Use of fluorescently labeled antibodies to visualize specific proteins in cells.

Virus

Submicroscopic infectious agent consisting of nucleic acid and a protein coat; obligate parasite.

Capsid

Protein coat surrounding viral genetic material.

Lytic Cycle

Viral replication cycle causing immediate production of new viruses and lysis of the host cell.

Lysogenic Cycle

Viral DNA integrates into host genome as a prophage and replicates with the host before induction to lytic cycle.

Prophage

Viral DNA integrated into a bacterial chromosome.

Obligate Parasite

Organism/agent that can reproduce only inside a host cell.

Bacteriophage

Large complex virus infecting bacteria (e.g., Lambda phage).

Antigen

Any molecule that triggers an immune response; parts of viral capsids often act as antigens.

Antibody

Protein produced by immune system that binds to antigens.

Antigenic Drift

Gradual accumulation of mutations changing viral antigens over time.

Antigenic Shift

Sudden major change in viral antigens due to gene recombination between strains.

LUCA (Last Universal Common Ancestor)

Hypothetical most recent ancestor of all living organisms on Earth.

Prebiotic Earth

Early Earth environment lacking oxygen, rich in CO2, methane, and UV light.

Miller-Urey Experiment

Laboratory simulation of early Earth conditions that produced amino acids spontaneously.

RNA World Hypothesis

Hypothesis that RNA was the first genetic material capable of catalysis and self-replication.

Hydrothermal Vent

Deep-sea environment rich in chemicals; proposed site for origin of life and LUCA evolution.

Vesicle

Membrane-bound compartment formed spontaneously by amphipathic molecules such as fatty acids.

Ribozyme

RNA molecule with catalytic activity.

Thermophiles

Heat-loving microorganisms; evidence LUCA evolved in high-temperature environments.