Biology: 7.3 Cell Transport: Osmosis and Diffusion

List three major types of active transport.

1. Protein pumps 2. Endocytosis 3. Exocytosis

Define active transport

Active transport is the movement of materials against a concentration difference is known as active transport. Active transport requires energy. (Example (i.c.): The removal of water by means of a contractile vacuole is one example of active transport).

Diffusion depends on what __ particle movements.

Diffusion depends on random particle movements. Therefore, substances diffuse across membranes without requiring the cell to use additional energy.

Define endocytosis

Endocytosis is the process of taking material into the cell by means of infoldings, or pockets, of the cell membrane. The pocket that results breaks loose from the outer portion of the cell membrane and forms a vehicle or vacuole within the cytoplasm. Large molecules, clumps of food, even whole cells can be taken up in this way.

Define exocytosis

Exocytosis is the process of many cells releasing large amounts of material. During exocytosis, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

Define the prefix homeo

Homeo means the same

The Effects of Osmosis on Animal and Plant Cells

Isotonic: The concentration of solutes is the same inside and outside the cell. Water molecules move equally in both directions. Hypertonic:: The solution has a higher solute concentration than the cell. A net movement of water molecules out the cell causes it to shrink. Hypotonic: The solution has a lower solute concentration than the cell. A net movement of water molecules into the cell causes it to swell.

Aquaporins

Many cells contain aquaporins are water channel proteins that allow water to pass through them.

What are examples of active transport across the cell membrane?

Osmosis and Diffusion

Define osmosis

Osmosis is a form of facilitated diffusion. It is the diffusion of water through a selectively permeable membrane. In osmosis, as in other forms of diffusion, molecules move from on area of higher concentration to an area of lower concentration. The only difference is that the molecules that move in the case of osmosis are water molecules, not solute molecules.

Define osmotic pressure

Osmotic pressure is driven by differences in solute concentration, the net movement of water out of or into a cell produces a force known as osmotic pressure.

Define passive transport

Passive transport ( including diffusion and osmosis) is the movement of materials across the cell membrane without using cellular energy.

Define the prefix phago

Phago means to eat

Define phagocytosis

Phagocytosis is a type of endocytosis, in which extensions of cytoplasm surround a particle and package it within a food vacuole.

Define the prefix pino

Pino means to drink

What does diffusion have to do with the cell membrane?

Suppose a substance is present in unequal concentrations on either side of the cell membrane. If the substance can cross the cell membrane, its particles will tend to move toward the area where it is less concentrated until it is evenly distributed. Once the concentration of the substance on both sides of the cell membrane is the same, equilibrium is reached. Even when equilibrium is reached, particles of a solution continue to move across the membrane in both directions. However, because almost equal numbers of particles move in each direction, there is no further net change in the concentration on either side.

How does osmosis work?

The barrier is permeable to water but not to sugar. This means water can cross the barrier in both directions, but sugar cannot. To start, there are more sugar molecules on the right side of the barrier than on the left side. Therefore, the concentration of water is lower on the right, where more of the solution is made of sugar. Although water molecules move in both directions across the membrane, there is a net movement of water toward the concentrated sugar solution. Water will tend to move across the membrane until equilibrium is reached. At that point, the concentrations of water and sugar will be the same on both sides of the membrane. When this happens, the two solutions will be isotonic.

Define hypertonic

The higher strength concentration on one side of the membrane.

Define hypotonic

The lower "below" strength concentration one side of the membrane

What is the role of the nucleus?

The nucleus contains nearly all the cell's DNA and, with it, the coded instructions for making proteins and other important molecules.

Define diffusion

The process by which particles move from an area of high concentration to an area of lower concentration. It is the driving force behind the movement of many substances across the cell membrane.

Define facilitated diffusion

The process in which molecules that cannot directly diffuse across the membrane pass through special protein channels. Although vacillated diffusion is fast and specific, it is still diffusion, so it does not require any additional use of the cell's energy.

Define isotonic

The same strength concentration on both sides of the membrane.

True of False: Every living cell exists in a liquid environment.

True

True of False: One of the most important functions of the cell membrane is to keep the cell's internal conditions relatively constant by regulating the movement of molecules from one side of the membrane to the other.

True

True of False: Substances diffuse across membranes without requiring the cell to use additional energy.

True