Osmosis, Diffusion and Active Transport

Objectives 1.Define diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis. 2. List the factors that affect diffusion. 3. Give definitions for solvent, solute, osmotic pressure, osmolality (or osmolarity). 4. Explain (briefly) what would happen to a body cell placed in hypotonic, hypertonic or isotonic solutions.

Terminology Intrinsic Proteins: ‘Built- In’ Solute: Substance that is dissolved in a solvent Solvent: Substance that is capable of dissolving a solute Solution concentration: Number of molecules of solute in the solution Solvent Solute

Methods by which substances enter and leave cells All substances must travel through the cell membrane (which is ‘semi’ permeable) Four different processes for this: 1. Diffusion 2. Osmosis 3. Active Transport 4. Endocytosis and Exocytosis

Diffusion Movement of substances from a HIGH to a LOW concentration (i.e. DOWN the concentration gradient) Net diffusion The ‘overall’ direction of diffusion

Rate of Diffusion The rate of diffusion depends on: a) Concentration gradient b) Size and nature of different molecules c) Distance over which the diffusion takes place d) Surface area

Facilitated Diffusion There are intrinsic proteins in cell membranes. These proteins have receptor sites which recognize specific substances. The substance binds to the protein and the protein deposits the substance on the other side of the membrane. The process is reversible and passive.

Osmosis This is a specific form of diffusion Osmosis is the movement of water (i.e. the body's solvent) through a semi- permeable membrane from a region where it is in high concentration to a region where the concentration is lower This is also a passive process.

Osmotic pressure The pressure exerted by the flow of water through a semi-permeable membrane separating two solutions with different concentrations of solute

Osmolality and Osmolarity Osmolality: The concentration of osmotically active particles in solution (expressed in terms of osmoles of solute per kilogram of solvent) Osmolarity: The concentration of osmotically active particles in solution (expressed in terms of osmoles of solute per litre of solution)

Osmotic Effects Only water can pass through the semi permeable membrane Water will move down its own concentration gradient The volume of the compartment with more non diffusible particles will increase = Non diffusible particle

Concentration of solutions Isotonic solution Same concentration Hypotonic solution Less concentrated Hypertonic solution More concentrated

The Effect of osmosis on cells What will happen to the cells? Hypotonic Hypertonic Isotonic Cell will gain water and burst Cell will lose water and shrivel Water gained = water lost

Active Transport Active Transport = Transport that requires ENERGY Active transport is needed when substances are transported against their concentration gradient Active transport depends upon intrinsic proteins in the cell surface membrane - called protein pumps (Passive Transport = Transport that does not require energy)

Active Transport The process is not reversible Another example of active transport is the Na-K pump (important in nerve impulse transmission). Cells carrying out active transport tend to be metabolically active and contain lots of mitochondria

Movement of Large particles Endocytosis = Movement of substances into the cell (occurs when substances are too large to be moved into the cell's cytoplasm by protein pumps) Exocytosis = Movement of substances out of the cell (opposite of endocytosis)

Endocytosis and Exocytosis

Exocytosis

Mcq's A concentrated solution: a) will contain more molecules of solute b) will contain more molecules of solvent c) can also be referred to as a hypotonic solution d) can also be referred to as an isotonic solution The substance dissolved in a solution is called the: a) salt b) sugar c) solute d) solvent The substance within the body that acts as a solvent is: a) NaCl b) H2O c) H2SO4 d) H2CO3 Solutions of the same concentration are: a) Isotonic b) Hypotonic c) Hypertonic d) Osmotic

Mcq's A solution that is more concentrated than another is said to be: a) Isotonic b) Hypotonic c) Hypertonic s d) Osmotic A solution that is less concentrated than another is said to be: a) Isotonic b) Hypotonic c) Hypertonic d) Osmotic The 'overall' direction of movement of a substance is called: a) Net movement b) Gross movement c) Endocytosis d) Exocytosis Processes that do not require energy are termed: a) Active b) Passive c) Intrinsic d) Automatic

Mcq's Movement of water across a semi permeable membrane is: a) Diffusion b) Osmosis c) Active Transport d) Exocytosis Substances are transported against their concentration gradients via: a) Diffusion b) Osmosis c) Active Transport d) Facilitated diffusion Movement of a substance down its concentration gradient is: a) Diffusion b) Endocytosis c) Active Transport d) Exocytosis Large substances are moved out of the cell via: a) Diffusion b) Osmosis c) Endocytosis d) Exocytosis

Mcq's A concentrated solution: a) will contain more molecules of solute b) will contain more molecules of solvent c) can also be referred to as a hypotonic solution d) can also be referred to as an isotonic solution The substance dissolved in a solution is called the: a) salt b) sugar c) solute d) solvent The substance within the body that acts as a solvent is: a) NaCl b) H2O c) H2SO4 d) H2CO3 Solutions of the same concentration are: a) Isotonic b) Hypotonic c) Hypertonic d) Osmotic

Mcq's A solution that is more concentrated than another is said to be: a) Isotonic b) Hypotonic c) Hypertonic d) Osmotic A solution that is less concentrated than another is said to be: a) Isotonic b) Hypotonic c) Hypertonic d) Osmotic The 'overall' direction of movement of a substance is called: a) Net movement b) Gross movement c) Endocytosis d) Exocytosis Processes that do not require energy are termed: a) Active b) Passive c) Intrinsic d) Automatic

Mcq's Movement of water across a semi permeable membrane is: a) Diffusion b) Osmosis c) Active Transport d) Exocytosis Substances are transported against their concentration gradients via: a) Diffusion b) Osmosis c) Active Transport d) Facilitated diffusion Movement of a substance down its concentration gradient is: a) Diffusion b) Endocytosis c) Active Transport d) Exocytosis Large substances are moved out of the cell via: a) Diffusion b) Osmosis c) Endocytosis d) Exocytosis