OSMOSIS READING COMPREHENSION

(1)

Gen rahsport is the movement of substances across the cell membrane. Cells transport substances

in and out of the cell to maintain homeostasis. Homeostasis is the state of stable internal conditions

maintained by organisms. Homeostasis is a condition of optimal functioning, and cells must maintain many

variables including the balance of fluids. Maintaininga balance of water inside the cell's internal environment

and its external environment helps the cell take in nutrients and release waste, therefore keeping the cell and organism healthy.

(2) The cell membrane is selectively permeable, meaning that some substances can pass through it

while others cannot. Substances move through the cell membrane either by diffusion, osmosis, or active

transport. Active transport requires cellular energy to move substances through the cell membrane.

Diffusion and osmosis are types of passive transport, meaning that the cell does not use energy to move

substances across the membrane. In both diffusion and osmosis, substances move through the cell

membrane from an area of higher concentration to an area of lower concentration.

OSMOSIS

(3)

The diffusion of water molecules through a selectively permeable

membrane is called osmosis. Like diffusion, molecules move from an area

of higher concentration to an area of lower concentration. Osmosis only

refers to water molecules, not solute molecules. Osmosis is important to

Aquaporins facilitate the

cells because cels cannot function properly without adequate water.

movement of water through

Osmosis facilitates the transport of nutrients and waste across the cell

the cell membrane from a

membrane and stabilizes the internal environment by maintaining the

high to low concentration.

balance of water and intercellular fluid levels.

(4) Water molecules can directly move through the cell membrane, but to increase the rate of diffusion,

water may also move through channel proteins called aquaporins. When water moves through aquaporins,

it is called facilitated diffusion because the aquaporins help to facilitate the movement of water through the cell membrane. Aquaporins allow water to easily pass through the cell membrane from a high to low concentration.

(5) Water tends to move across the cell membrane until equilibrium is reached, meaning that both sides of the membrane contain the same concentration of water and solute molecules. Observe the experimental

set up below. The selectively permeable barrier of the U-tube apparatus allows water to pass through, but not solute molecules. In diagram A, the concentration of solute is higher on the right side, than on the left

side of the barrier. Water moves through the barrier from a higher to lower concentration until the concentration of solute on both sides of the tube is equal.

(6) TONICITY Tonicity is the capability of an extracellular solution to modify the volume of cells by making water

move into or out of a cell by osmosis. The movement of water into or out of a cell can lead to isotonicity,

nypotonicity, or hypertonicity. Due to the difference in solute concentration, the movement of water into or

Out of a cell produces a force known as osmotic pressure. This force causes cells to swell or shrink in size.

(7)

As you observed in the U-tube apparatus experiment, water tends to move across the membrane

until equilibrium is reached. At that point, the concentration of water and solutes will be the same on each

side of the membrane barrier. When this occurs, the solution is said to be isotonic. The prefix iso refers to

things that are the same. In isotonic conditions, the concentration of solutes is the same inside and outside

of the cell, and water molecules move equally in both directions.

(8) When a solution outside the cell has a higher solute concentration than inside the cell, the solution is

hypertonic. The prefix hyper means above strength. If a cell is placed in a hypertonic solution, there will be

a net movement of water out of the cell, causing the cell to lose volume and shrink.

(9) When a solution outside the cell has a lower solute concentration than inside the cell, the solution is

hypotonic. The prefix hypo means below strength. If a cell s placed in a hypotonic solution, there will be a

net movement of water into the cell, causing the cell to Swell. If a cell swells over its maximum volume, it

may burst or lyse.

0SMOSIS IN PLANT CELLS

(10) Animal cells thrive in isotonic conditions. However, in the case of a plant cell, hypotonic conditions

ideal. Unlike animal cells, plant cells have a cell wall that surrounds their cell membrane. In hypotonic

conditions, the rigid cell wall prevents the cell from bursting or lysing. Water will enter a plant cell until its

internal pressure, called turgor pressure, prevents a further influx of water. The pressure of the cytoplasm

against the cell wall prevents the plant from wilting and losing its shape.

(11) The balance of water and solutes is crucial to the health of a plant. Ifa plant does not obtain enough

water, the extracellular fluid will become hypertonic or isotonic, causing water to leave the plant's cells by

osmosis. This results in a loss of turgor pressure, which causes a plant cel to become flaccid (soft) and to

wilt. In hypertonic conditions, a plant's cell membrane may detach from the cell wall and constrict the

cytoplasm, in a process called plasmolysis.

Hypertonie Solution

Have you ever poured salt on a snail or slug in your yard, and then watched as it seemed to melt before your eyes?

Adding the salt caused the cells of the slug to be suOunded by a hypertonic solution. Hypertonie means that the

Solution outside the cell membrane contains less water and more solute than the solution insde the cell membrane

"Water rushes out of the cell through the cell membrane, and the cell shrivels up. This movement of water out of the

cells makes it looks as if the slug is melting.

Hypertonie Solution

Have you ever poured salt on a snail or slug in your yard and then watched as it seemed to melt before your eyes?

Adding the salt caused the cells of the slug to be surrounded by a hypertonic solution. Hypertonie means that the

Solution outside the cell membrane contains less water and more solute than the solution inside the cell membrane

"Water rushes out of the cell through the cell membrane, and the cell shrivels up. This movement of water out of the

cells make it look as if the slug is melting.

Isotonic Solution

Isotonic means that the solution on the outside of the cell membrane

has the same concentration as the solution on the inside of the

membrane, so there is no net movement of water molecules across the

membrane.

A prokaryote is a unicellular organism that lacks a membrane-bound nucleus.

Bacteria are prokaryotes that fall into two major categories: The Kingdom Eubacteria and the Kingdom Archaebacteria. Eubacteria are common types that occur all around us, usually they are on surfaces and in the soil. You can only find Archaebacteria in extreme environments, like hot sulfur springs. Archaebacteria are thought to be some of the oldest life forms on earth. Most bacteria don't make their own food. That means they must rely on other organisms to provide them with food. These bacteria break down, or decompose, other living things to obtain energy. When most people hear the word bacteria, they think of something that is bad for you. In fact, very few bacteria cause illnesses. Somne bacteria actually help you! Bacteria are used to make food, such as cheese and yogurt, and they can also help us break down harmful substances in the environment. Scientists created a type of bacteria that could gobble up oil from oil spills.

Some bacteria live inside the guts of animals and help them to digest food.