GETTING STARTED

Diffusion and Osmosis AP Bio Lab

Preparing for the Investigation

What is kinetic energy, and how does it differ from potential energy?

Kinetic energy – energy of movement it has a magnitude, but not a direction, is always positive

Potential energy – energy stored in an object, This energy has the potential to do work. Gravity gives potential energy to an object. This potential energy is a result of gravity pulling downwards.

What environmental factors affect kinetic energy and potential energy?

Several factors affect how fast a molecule will diffuse

Kinetic energy of the molecule, measured as the temperature of the system.

Size of the molecule also affects how rapidly it

will diffuse.

Charges on the molecule (positive or negative)

Nature of the material that the molecules are moving through

Temperature Molecules in a system at a higher temperature will have

more energy and will move faster, and hence diffuse faster, than molecules of the same type in a low-temperature system.

Size of the molecule At the same temperature, smaller molecules will move

more rapidly than larger molecules because it takes more energy to get the larger molecule moving

Charges on the molecule Negative or positive ions usually move through some

type of transport proteinNature of the material

Hypoosmotic – solution has a lower osmotic pressure than a second solution

Hyperosmotic – solution has a higher osmotic pressure than a second solution

Isoosmotic – solution has an equal osmotic pressure to a second solution

Osmotic pressure and tonicity often are confusing to people

Osmotic pressure is the pressure of a solution against a semipermeable membrane to prevent water from flowing inward across the membrane

Tonicity is the measure of this pressure

If the concentration of solutes on both sides of the membrane is equal, then there is no tendency for water to move across the membrane and no osmotic pressure.

How and why do these factors affect rates?

Warmth speeds up movement across a membrane

Large molecules need energy and transport proteins to transport molecules across a membrane

Negative and positive charges require transport membranes to move across a membrane

Large molecules require energy and the processes exocytosis and endocytosis

Why are gradients important in diffusion and osmosis?

Why are gradients important in diffusion and osmosis?

Diffusion and osmosis generally occur as passive transport (using no energy) moving from a high to a low concentration gradient

Moving solutes from a low to high concentration gradient requires energy from ATP

What is the explanation for the fact that most cells are small and have cell membranes with many convolutions?

Most cells are smallMany convolutions

Large surface area

Most cells are relatively small due to reliance on diffusion of substances in and out of cells

Organism made of many small cells has an advantage over an organism composed of fewer, larger cells

As a cell’s size increases, its volume increases much more rapidly than its surface area

Rate of diffusion affected by

Surface area available Temperature Concentration gradient Distance

Will water move into or out of a plant cell if the cell has a higher water potential than the surrounding environment?

Water will move into the cell because distilled water has a higher water potential than the plant cell itself

When the plant cell’s central vacuole fills with water, then it will push back out on the water surrounding the cell

Plant cell doesn’t burst due to this pressure because it has a cell wall. An animal cell in the same situation would burst. When the pressure exerted outward on the water surrounding the plant cell is equal to the osmotic potential of the solution in the cell, the water potential of the cell will be equal to zero.

What would happen if you applied saltwater to a plant?

plant cell would undergo plasmolysis – shrinking of the cell because of water flowing out of the cell

http://www.youtube.com/watch?v=GOxouJUtEhE

How does a plant cell control its internal (turgor) pressure?

When a plant receives adequate amounts of water central vacuoles of its cells swell as the liquid collects

within creating a high level of turgor pressure