Cell Transport Mechanisms and the Cell Cycle

Physical (Passive) Mechanisms

Do not require cellular energy (ATP) and include diffusion, osmosis, facilitated diffusion, and filtration.

Diffusion

Movement of atoms, molecules, or ions, from region of higher concentration to region of lower concentration, occurring due to constant motion of atoms, molecules, ions.

Example of Diffusion

A sugar cube dissolving in water.

Equilibrium in Diffusion

Solutes and water can diffuse across a membrane that is permeable to both of them until they reach equilibrium; at that point, the concentrations of water and the solute are equal in both compartments.

Osmosis

Movement of water across a selectively permeable membrane from region of higher water concentration to region of lower water concentration, often called 'diffusion of water'.

Passive Process of Osmosis

Water moves into a region containing higher impermeant solute concentration without requiring ATP.

Osmotic Pressure

Ability of osmosis to generate enough pressure to lift a volume of water, which increases as the concentration of impermeant solutes increases in a solution.

Tonicity

Ability of a solution outside cell to alter water volume inside cell.

Isotonic Solution

A solution with the same osmotic pressure; cells in an isotonic solution have no net gain or loss of water.

Hypertonic Solution

A solution with higher osmotic pressure; cells in a hypertonic solution lose water.

Hypotonic Solution

A solution with lower osmotic pressure; cells in a hypotonic solution gain water.

Active Mechanisms

Require ATP to move substances across cell membrane

Active Transport

Movement of substances across a membrane from region of lower concentration to region of higher concentration (against concentration gradient)

Carrier Molecules

Molecules in cell membrane, often called 'pumps', that facilitate active transport

Endocytosis

Process by which cells internalize substances from their external environment

Exocytosis

Process by which cells expel substances to the external environment

Transcytosis

Process that involves the transport of substances across a cell

Secondary Active Transport

A carrier protein uses a Na+ gradient to transport another substance across a cell membrane; this process does not require ATP energy

Cell Cycle

Series of changes a cell undergoes from the time it forms until the time it divides

Interphase

Growth of cell, maintenance of normal functions, and preparation for mitosis and cytokinesis

Mitosis

Division of the nucleus via karyokinesis

Cytokinesis

Division of the cytoplasm

S Phase

Phase of interphase where DNA is replicated

G1 and G2 Phases

Phases of interphase where structures and other molecules are duplicated

Prophase

Chromatin condenses to form chromosomes, centrioles move to opposite sides of cytoplasm, nuclear envelope and nucleolus disperse

Metaphase

Spindle fibers from centrioles attach to chromosomes and align them midway between centrioles

Anaphase

Chromosomes separate and move in opposite directions toward centrioles as the spindle fibers shorten

Telophase

Chromosomes return to chromatin structure, nuclear envelope forms around each chromosome set, and nucleoli become visible

Cytoplasmic Division

Cytokinesis, which begins during anaphase and continues through telophase

Contractile Ring

Structure of actin filaments that pinches cytoplasm in half during cytokinesis

Cleavage Furrow

Constriction formed during cytokinesis as the contractile ring pinches the cytoplasm

Daughter Cells

Newly formed cells that will have identical DNA, may have slightly different size and number of organelles