IB Biology: Cell Origins, Cell Structure, Viruses, and Membrane Transport

Comprehensive vocabulary flashcards covering the pre-biotic origin of cells, cell structure and microscopy, atypical cells, endosymbiosis, stem cells, viral biology, and membrane transport based on the lecture notes.

Prebiotic chemistry

Chemical reactions that occurred before life existed, in which simple inorganic substances reacted to form organic carbon compounds without the involvement of living organisms.

Abiotic synthesis

The formation of organic molecules from simpler inorganic substances without the presence or involvement of living organisms.

Cell

The smallest basic structural and functional unit that can independently perform all essential processes of self-sustaining life.

Miller–Urey experiment (1953)

An experiment that simulated proposed early Earth conditions using heat, gases representing the early atmosphere, and electrical sparks to demonstrate the abiotic synthesis of organic compounds, including amino acids.

Amphipathic molecules

Molecules that contain both a hydrophilic region that interacts with water and a hydrophobic region that avoids water, such as phospholipids and fatty acids.

Vesicle

A small membrane-bound compartment containing an aqueous interior formed by the spontaneous arrangement of amphipathic lipid bilayers in water.

Protocells

Primitive, non-living cell-like structures formed by lipid vesicles enclosing organic molecules that provide a possible starting point for early cellular evolution.

RNA world hypothesis

The hypothesis proposing that RNA was the first important genetic material before DNA and proteins evolved, because RNA can both store genetic information and catalyse chemical reactions.

Ribozymes

RNA molecules that function as biological catalysts, such as the RNA in ribosomes that catalyses peptide bond formation during protein synthesis.

LUCA (Last Universal Common Ancestor)

The ancestral population of organisms from which all currently living cellular life forms on Earth descended.

Stromatolites

Layered rock structures formed over geological time through the mineral-trapping activity of ancient microbial communities.

Half-life

The time required for half of the radioactive parent isotope in a sample to decay into its daughter isotope, used in radiometric dating.

Molecular clock

A technique that estimates evolutionary divergence times between species by comparing the number of accumulated differences in DNA or protein sequences.

Hydrothermal vents

Fissures on the ocean floor releasing hot, mineral-rich, reduced fluids, providing chemical energy gradients, mineral catalysts, and microscopic compartments proposed as an environment for early evolution.

Cell theory

A fundamental biological theory stating that all living organisms consist of one or more cells, the cell is the basic structural and functional unit of life, and all cells arise from pre-existing cells by division.

Magnification

The ratio that describes how many times larger an image is compared to the actual size of the specimen, calculated as $\text{Magnification} = \frac{\text{image size}}{\text{actual size}}$.

Resolution

The ability of a microscope or imaging system to distinguish two closely spaced points as separate entities.

Ultrastructure

The fine, detailed biological structures of cells and organelles that can be observed and resolved only using electron microscopy.

Cryo-electron microscopy

An electron microscopy technique using rapidly frozen specimens to preserve biological structures and molecular complexes in a near-native hydrated state.

Nucleoid

The irregularly shaped region inside a prokaryotic cell containing the main circular chromosome without a surrounding membrane.

Plasmids

Small, autonomous circular DNA molecules in prokaryotes that carry accessory genes (such as antibiotic resistance) and can be transferred between cells.

Endosymbiotic theory

The evolutionary theory proposing that eukaryotic mitochondria and chloroplasts evolved from free-living aerobic and photosynthetic prokaryotes engulfed by ancestral cells.

Cell differentiation

The developmental process by which unspecialized cells express different sets of genes from the same genome to develop specialized structures and functions.

Stem cells

Undifferentiated biological cells that retain the ability to divide continuously and differentiate into specialized cell types.

Totipotent stem cells

Stem cells with the capacity to develop into any cell type of an entire organism as well as extraembryonic tissues.

Pluripotent stem cells

Stem cells capable of giving rise to almost any body cell type, but not extraembryonic tissues.

Multipotent stem cells

Stem cells that can develop into a limited range of related specialized cell types within a particular tissue or lineage.

Colony

A group of individual unicellular organisms living together without permanent cellular specialization or complete mutual dependence.

Viruses

Acellular infectious particles containing either DNA or RNA surrounded by a protein coat that can replicate only within living host cells.

Capsid

The external protein shell surrounding and protecting the genetic material of a virus, composed of repeating protein subunits called capsomeres.

Viral envelope

A host-derived lipid bilayer containing viral glycoproteins that encases the protein capsid of certain viruses, aiding in host attachment and entry.

Reverse transcriptase

A viral enzyme found in retroviruses that catalyses the synthesis of a complementary DNA molecule from an RNA template.

Lytic cycle

A viral replication cycle in which the host-cell machinery rapidly produces new viral genomes and proteins, culminating in host cell lysis and death.

Lysogenic cycle

A viral life cycle in which the viral genome integrates stably into the host cell chromosome and replicates alongside host division without immediately killing the cell.

Prophage

The latent form of a bacteriophage genome integrated into the circular bacterial chromosome.

Reassortment

The exchange of whole genome segments that occurs when two related segmented viruses infect the same host cell, leading to novel genetic variants.

Simple diffusion

The passive net movement of solute particles down a concentration gradient directly across the hydrophobic core of the phospholipid bilayer without requiring transport proteins or ATP.

Integral proteins

Membrane proteins permanently embedded within the hydrophobic core of the phospholipid bilayer, frequently spanning the entire membrane as transmembrane proteins.

Peripheral proteins

Proteins that are loosely attached to the hydrophilic exterior surfaces of the membrane rather than embedded in the hydrophobic interior.

Osmosis

The net passive movement of water molecules across a selectively permeable membrane from an area of higher water potential to an area of lower water potential.

Water potential ($\Psi$)

A measure of the potential energy of water per unit volume relative to pure water under standard conditions, calculated as $\Psi = \Psi_s + \Psi_p$.

Aquaporins

Integral channel proteins that selectively and rapidly facilitate the passive movement of water molecules across cell membranes.

Channel proteins

Transmembrane proteins with hydrophilic pores that permit specific ions or molecules to diffuse passively across the membrane down an electrochemical gradient.

Pump proteins

Transmembrane carrier proteins that consume metabolic energy, typically from ATP hydrolysis, to move solutes across a membrane against their concentration or electrochemical gradient.

Glycocalyx

A carbohydrate-rich protective coating on the outer surface of animal cell membranes formed by the carbohydrate chains of glycoproteins and glycolipids.

Fluid mosaic model

A structural model describing cell membranes as dynamic, flexible two-dimensional fluids of laterally diffusing phospholipids embedded with a mosaic of diverse proteins and lipids.

Cholesterol (membrane fluidity buffer)

An amphipathic lipid interspersed among phospholipids in animal membranes that restricts phospholipid motion at high temperatures and prevents tight tail packing at low temperatures.