How Cells Exchange Molecules Active and Passive Transport

Diffusion and Osmosis Diffusion is the random movement of molecules from an area of higher concentration to an area of lower concentration. WHY? All molecules are in constant motion; they move and collide as they spread out into the available space.

Even though molecules are moving about randomly in all directions, there is a net movement of molecules from and area of higher concentration to an area of lower concentration. Question: What happens at equilibrium?

Diffusion and Osmosis Osmosis is the diffusion of water across a membrane. A concentration gradient is a difference in concentration across a distance. Molecules only diffuse down a concentration gradient. This does not require any energy. Moving molecules against a concentration gradient requires energy. Diffusion is a main mechanism for cells to receive nutrients and remove wastes.

Diffusion and Osmosis What determines the rate of diffusion? Difference in concentration (concentration gradient) Bigger difference in concentration means faster diffusion Temperature Higher temperature means faster diffusion because molecules have more energy and are moving faster.

Passive and Active Transport Cell membranes are barriers to the diffusion of some substances. A selectively permeable membrane allows some substances to cross the membrane more easily than others, and blocks others. Passive transport does not require any energy to move molecules across a membrane. Examples: diffusion, osmosis, facilitated diffusion

Oxygen (O2), carbon dioxide (CO2) and water (H2O) can diffuse easily across the cell membrane. Glucose (C6H12O6), amino acids, and ions cannot diffuse through membranes. They need to use special protein channels called transport proteins. Transport proteins move substances down their concentration gradient, which does not require any energy.

Active Tranport Sometimes cells need to move substances against their concentration gradient. This requires energy and is called active transport During active transport, a specific transport protein pumps a solute across a membrane, against the concentration gradient Examples: moving Sodium and Potassium ions in animal cells; Nitrogen, phosphorus, potassium, and calcium in plant cells. The mitochondria supplies the energy for active transport in the form of ATP.

Active Transport

Process & Procedure When salt solution was added to the outside environment of red onion cells, the concentration of water molecules was __lower__________ in the solution than in the cells. Molecules move from a region of _high________ concentration to a region of _low___________ concentration. A cell model that contains a 10% sugar solution is placed in a beaker with a 40% sugar solution. Water molecules will _diffuse________ from the _cell_________ into the __beaker____.

Process and Procedure #3 The “cell model” contains a higher concentration of solutes than the external environment. (The cell model is hypertonic compared to the external environment). Even though there was random movement of glucose molecules both into and out of the cell model, there was a net movement of glucose molecules from the inside of the cell model to the external environment. glucose

Process & Procedure #5 Lipids (fats and oils) are non-polar, which means they are hydrophobic. The polar heads of a phospholipid associate themselves with water while the nonpolar (fatty acid) tails arrange themselves to exclude water.

Reflect & Connect 1. Sketch or describe what happens to ions and molecules when they are in balance inside and outside the cell. Molecules are always in motion. Once equilibrium is reached, molecules will continue to move into and out of the cell at equal rates in both directions.

Reflect & Connect 2. Membranes regulate the movement of molecules into and out of cells. To show what you know about how membranes regulate movement, fill out a T-table with the headings “Ions or Molecules” and “How They Move Through Membranes” Oxygen and carbon dioxide Water Glucose and amino acids Nitrogen, Phosphorous, Potassium, and Calcium in plant cells Sodium and Potassium in animal cells

Reflect & Connect Molecule or Ion How it moves through membranes Transport type? Energy? Oxygen, CO2 Small enough to move directly through the membrane Diffusion Passive Transport (no energy) Water Osmosis Glucose Too big to move directly through the cell membrane, needs a transport protein Facilitated Diffusion Nitrogen, Phosphorus, Potassium, Calcium (plant cells) Moving against the concentration gradient. Transport protein (pump) Active Transport (energy) Sodium & Potassium (animal cells) Charged ions can’t go directly through the cell membrane. Also, moving against the concentration gradient. Active transport (energy)

Reflect & Connect Why is it a bad idea to drink seawater if you are stranded on a boat in the ocean? What do you think would happen to your cells? Seawater is hypertonic compared to your cells because seawater contains more solute (salt). Therefore, water would move through osmosis out of your cells, reducing the concentration of water in your cells. This would lead to dehydration

Cell Division Begin on page 297. Read the introduction paragraph. Follow the Process and Procedure (#1-3) Answer all questions in complete sentences Take notes on the reading, make sure you sketch each phase of mitosis in your notebook. Answer Reflect & Connect #1-3 p. 303