Science Osmosis and Diffusion

Active transport

Active transport is the movement of materials through a cell membrane using cellular energy. Active transport requires the cell to use its own energy, while passive transport does not.

What is the difference between passive transport and active transport?

Active transport requires the cell to use its own energy, while passive transport does not.

What happens when you drop a sugar cube into a mug of hot tea?

After a period of time, the sugar will eventually dissolve fully and be evenly dispersed throughout the tea. Molecules are always moving. As they move, the molecules bump into one another. The more molecules there are in an area, the more collisions there will be. Collisions cause molecules to push away from one another. Over time, the molecules of a substance will continue to spread out. Eventually, they will be spread evenly throughout the area.

Why is osmosis important to cells?

Because cells cannot function properly without adequate water, many cellular processes depend on osmosis.

How do water molecules move through a cell membrane during osmosis?

Because osmosis only occurs with water molecules, only water is being passed through the cell membrane. It always goes from higher to lower concontration, and because the cell membrane is semi-permeable, the water is always allowed to pass through.

Diffusion

Diffusion is the main method by which small molecules move across the cell membrane. Diffusion (dih fyoo zhun) is the process by which molecules move from an area of higher concentration to an area of lower concentration.

What are transport proteins?

In one method, transport proteins in the cell membrane "pick up" molecules outside the cell and carry them in, using energy. Figure 10 illustrates this process. Transport proteins also carry molecules out of cells in a similar way. Some substances that are carried into and out of cells in this way include calcium, potassium, and sodium.

Osmosis

Osmosis is the diffusion of water molecules through a selectively permeable membrane. Because cells cannot function properly without adequate water, many cellular processes depend on osmosis.

How do most small molecules cross the cell membrane?

Substances that can move into and out of a cell do so by one of three methods: diffusion, osmosis, or active transport.

Selectively permiable

The cell membrane is selectively permeable, which means that some substances can pass through the membrane while others cannot.

Passive transport

The movement of dissolved materials through a cell membrane without using cellular energy is called passive transport.

A selectively permeable membrane separates solutions A and B. The concentration of water molecules in Solution B is higher than that in Solution A. Describe how the water molecules will move.

The water molecules will move from soloution B to soloution A. This is because water molecules move from an area of higher concentrartionb to an area of lower concontration.

Explain why transport proteins require energy to function in active transport.

Transport protiens have to "pick up" the molecules, and so as opposed to just letting them travel from higher to lower concontrations, they have to take them from lower to higher. This is like peadeling your bike up a hill.