Academic Bio Chapter 5 Review: Homeostasis & Cell Transport

Homeostasis Definition: the maintenance of a stable level of internal conditions even though environmental conditions are constantly changing Homeostasis: the goal that drives an organism to undergo most of its reactions and processes

Equilibrium Definition: amount of materials, substances, charges, etc. is equal throughout a given area For our purposes, the concentration of molecules is the same throughout the space the molecules occupy

Concentration Gradient Concentration: amount of material, substance, charge, etc. in a given area, location, or volume Gradient: difference in the amount of a material, substance, charge, height, etc. across a distance

1. Diffusion Definition: movement of molecules from an area of higher concentration to an area of lower concentration in order to reach equilibrium Energy: driven by the molecules’ own kinetic energy – does not require additional energy input (with/down gradient) Membrane: no membrane required

Passive Transport Definition: simple diffusion of molecules across the cell membrane without an input of energy by the cell Energy: no energy from the cell required (with/down gradient) Membrane: yes, refers to processes that involve a membrane

Diffusion Across Membranes Definition: molecules can diffuse across membranes either: – 1) by dissolving in the phospholipid bilayer – OR – – 2) by passing through pores in the membrane

2. Osmosis Definition: diffusion of water molecules across a membrane from higher to lower concentration Energy: no energy from the cell required (with/down gradient) Membrane: yes, only called osmosis when an membrane is involved

Solutions Definition: mixture in which one or more substances is distributed in another – Solute: substance which is dissolved in the solvent – Solvent: substance in which the solute is dissolved

General Direction of Osmosis Definition: the net movement of water depends on the relative concentrations of solutes on the two sides of a membrane – the water follows the solute

Hypotonic Solution Definition: the relative concentration of solute molecules outside the cell is lower than the concentration of solute inside the cell Movement: water moves into the cell to try and dilute the solute there until equilibrium is reached Results: the cell expands

Hypertonic Solution Definition: the relative concentration of solute molecules outside the cell is higher than the concentration of solute inside the cell Movement: water moves out of the cell to try and dilute the solute there until equilibrium is reached Results: the cell shrinks

Isotonic Solution Definition: the relative concentrations of solutes outside and inside the cell are equal Movement: water diffuses into and out of the cell at equal rates (water is still moving, just no net movement) Results: the cell stays as it is

Cytolysis

3. Facilitated Diffusion Definition: diffusion of molecules across the cell membrane when they are too large or too charged to pass through membrane pores Energy: no energy from the cell required (with/down gradient) Membrane: yes, and the molecules are assisted by carrier proteins in the membrane

Facilitated Diffusion – the Process 1.A molecule bind to a specific carrier protein 2.Carrier protein changes shape to shield molecule from the hydrophobic interior of the plasma membrane 3.Molecule is transported through and released on the other side 4.Carrier protein regains shape and is reset to work again

4. Active Transport Definition: movement of materials from an area of lower concentration to an area of higher concentration, against the concentration gradient Energy: YES energy from the cell is required – it comes from ATP Membrane: yes, and the molecules are assisted by carrier proteins or channels

Sodium-Potassium Pump Definition: most common example of a cell membrane pump, moves 3 Na+ ions out of cell while moving 2 K+ ions into the cell Energy: YES energy from the cell is required – it comes from ATP Membrane: yes, and sets up a charge gradient across the membrane

Movement in Vesicles Definition: when molecules are too large to pass through the cell membrane by any other process, they are moved into or out of the cell with the help of transport vesicles Energy: YES energy from the cell is required Membrane: yes, in fact the vesicle is a piece of membrane

Endocytosis Definition: the process by which a cell ingests external fluids, macromolecules, and large particles (including other cells, bacteria, etc.) Energy: YES energy from the cell is required Membrane: yes, external materials are enclosed in a pouch of membrane which pinches off to capture the material in a vesicle

Endocytosis

Types of Endocytosis Pinocytosis: endocytosis involving the transport of liquids Phagocytosis: endocytosis involving large, solid particles

Exocytosis Definition: process by which a substance is released from the cell through a vesicle Energy: YES energy from the cell is required Membrane: yes, the vesicle carries the material to the membrane, fuses with the membrane, and releases the material to the external environment

Exocytosis