TRANSPORT ACROSS THE CELL MEMBRANE PASSIVE TRANSPORT

First, some terminology… Concentration: the amount of a substance in a given volume. Concentration Gradient: the distribution of particles across a space from high to low concentration. High Concentration Low Concentration Concentration Gradient Semi-permeable membrane: a thin, film-like structure that allows some substances through but not others to pass through. ATP: the super important molecule that supplies energy for many biochemical cellular processes.

The process of diffusion Diffusion: the process by which particles move down their concentration gradient – they go from high concentration to low concentration. This does not require a cell membrane. Particles are constantly in motion Particles “spread out” to fill a container or space Even when the concentration through a space is equal, the particles are still moving Examples?

Water & Dye Demo Drop one or two drops of food colouring into a beaker of water. Do not stir or shake the beaker. Check the status of the beaker every few minutes. Observations? Explain your observations using proper scientific vocabulary. __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Diffusion of Dye in Water Random Dispersal Dispersing Time 0 Time 1 Time 2 Steep Concentration Gradient Reduced Concentration Gradient No Concentration Gradient

Transport Processes Movement across the cell membrane Passive Transport Active Transport Substances move from high concentration to low concentration. No energy input required 3 Types: Simple Diffusion Facilitated Diffusion Osmosis Substances move from low concentration to high concentration. Energy input required 3 Types: Protein Assisted Endocytosis Exocytosis

PASSIVE TRANSPORT 1. Simple Diffusion A form of transport across a semi-permeable membrane Particles cross directly through the membrane Particles move from high concentration to low concentration (with concentration gradient) Does not require energy Particles small, uncharged particles (water, oxygen, carbon dioxide) small lipid molecules (hydrophobic)

PASSIVE TRANSPORT 2. Facilitated Diffusion A form of transport across a semi- permeable membrane Particles cross through the membrane with the help of proteins Protein channels: provide a tunnel through the phospholipid bilayer. Particles: ions (charged particles) like chloride and sodium. Carrier proteins: certain proteins bind to a particle, transport it across the membrane, and release it. Particles: large polar molecules like glucose. Does not require energy

SIMPLE & FACILITATED DIFFUSION OVERVIEW

PASSIVE TRANSPORT 3. Osmosis the diffusion of water across a semi-permeable membrane the direction of water movement tends to equalize the concentration of water and dissolved substances on both sides of the membrane. dissolved substances cannot cross the membrane – only water water is always moving across the membrane, but there is a net (overall) movement of water: from high water concentration to low water concentration from low solute concentration to high solute concentration Net movement of water

TONICITY A way to compare the concentrations of two different solutions on different sides of a membrane – based on water 3 Types Isotonic – the solution has the same solute concentration as the comparative solution. Hypertonic – the solution has a greater concentration of solutes than the comparative solution. Hypotonic – the solution has a lesser concentration of solutes than the comparative solution. The surrounding solution is hypotonic to the inside of the cell. The inside of the cell is hypertonic to the surrounding solution. The surrounding solution is isotonic to the inside of the cell. The inside of the cell is isotonic to the surrounding solution. The surrounding solution is hypertonic to the inside of the cell. The inside of the cell is isotonic to the surrounding solution.

TONICITY AND CELLS Cells in Isotonic Surroundings Water moves in and out of cells at equal rates There is no net movement of water Animal cells: healthy & normal shape. Plant cells: healthy, normal shape, but lack firmness. Plant cells in isotonic solution Magnified 100X. Notice the vacuole. Red blood cells in isotonic solution Magnified 400X. Notice the shape.

TONICITY AND CELLS Cells in Hypertonic Surroundings Net movement of water out of cells. Decrease in water pressure inside cells causes them to shrivel. Animal cells: Shrivel. Plant cells: Cytoplasm shrinks, cell membrane pulls away from the cell wall. Red blood cells in hypertonic solution. Magnified 450X. Notice them shrivelling. Plant cells in hypotonic solution. Magnified 100X. Notice the membrane pulling away from the cell wall.

TONICITY AND CELLS Cells in Hypotonic Surroundings Net movement of water into cells. Increase in water pressure inside cells causes them to swell. Animal cells: Swollen and may burst. Plant cells: Firm. Plant cells in hypotonic solution. Magnified 100X. Notice you that you can’t see the vacuoles anymore – they are so inflated that their membranes are squashed up against the cell membrane. Red blood cells in hypotonic solution. Magnified 450X. Notice them bursting.

Lettuce Demo One iceberg lettuce leaf has been soaking in salt water and the other in filtered water. Examine the two samples and answer the following questions. ______________________________________________________ The __________ container contained the salt water. The ________________ container contained the filtered water. Compare the two leave and describe your observations. __________________________________________________________________________________________________________________________________________________________________ b) Was the salt water hypertonic or hypotonic to the leaf? _____________________________

c) Was the filtered water hypertonic or hypotonic to the leaf? ____________________________ d) Through osmosis, water naturally moves from areas of _________ solute concentration to ____________ solute concentration. e) Explain your observations from part a). ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ f) Switch the two samples and observe the outcome.

PENICILLIN: OSMOSIS AT WORK Penicillin is an antibiotic. Extracted from mould  grows naturally on stale food and rotting vegetation. Antibiotic: “Anti” = against, “Biotic” = life Medication that destroys or slows down the growth of bacteria. Antibiotics DO NOT affect viruses, like the flu! Bacteria have cell walls similar to plants, and thrive in hypotonic environments like plant cells. Penicillin prevents reactions that repair the cell wall of certain harmful bacteria  cell wall becomes weaker. In the hypotonic environment, water enters the bacterial cell, cell swells and bursts, killing the bacteria.