Osmosis, Diffusion and Active Transport

Osmosis and Active Transport

Multiple Choice

What is osmosis?

• The movement of water only from a region of low water potential to a region of higher water potential across a selectively permeable membrane until equilibrium.

• The movement of solute only from a region of high water potential to a region of lower water potential across a selectively permeable membrane until equilibrium.

• The movement of solute only from a region of low water potential to a region of higher water potential across a selectively permeable membrane until equilibrium.

• The movement of water only from a region of high water potential to a region of lower water potential across a selectively permeable membrane until equilibrium.

​​Substances Entering and Leaving Plants

​The cell membrane controls the movement of substances into and out of cells.

​The cell membrane therefore controls the chemical composition of the internal environment of the cell.

​The cell membrane controls movement in two ways:

1. ​Passive processes - in which the cell does not use energy.

2. ​Active processes - in which the cell does use energy.

Multiple Select

Therefore the cell membrance controls the...

• united states

• god of all

• tone of the poem

• chemical composition of the internal environment of the cell.

Multiple Select

How does the cell membrane control movements?

• action processes

• passive processes

• active processes

• passive voice

Multiple Choice

In which the cell does not use energy.

• passive processes

• active processes

Multiple Choice

In which the cell does use energy.

• active processes

• passive processes

​The Cell Membrane

​Cell membranes are selectively or partially permeable. This means that some molecules and ions can pass freely through them down concentration gradients but others cannot. Oxygen, carbon dioxide and water are examples of molecules which cross membranes easily, by diffusion. In a respiring muscle cell, for example, oxygen will pass into the muscle and carbon dioxide will pass out.

​Osmosis

​The cell membrane is partially permeable in that it allows some molecules to diffuse through rapidly but slows down the passage of others.

​The glucose molecules try to diffuse to the outside but cannot get through the membrane because the pores are too small. Water molecules diffuse through the pores down a concentration gradient.

​This membrane-controlled diffusion of water molecules is called osmosis. Osmosis can work both ways so that water can pass into to out of the cell.

Multiple Select

Select examples of molecules and ions that can pass freely through the cell membrane.

• glucose

• carbon dioxide

• water

• oxygen

• All of the above

Multiple Choice

Why can't glucose molecules diffuse through the cell membrane?

• it's too small

• it's too big

• a cell membrane only allows water through

• the glucose refuses to

Multiple Choice

You have a container filled with water and it contains a tubing full of sugar solution.

Will the water move into the tubing or out of?

• into

• out of

​In this case, it doesn't have to be until equilibrium, sometimes it's just until it can't take anymore water, but let's stick with the definition of osmosis.

Multiple Choice

Fresh potato was diced, surface dried and weighed in two separate batches. The batches were then treated in the following way: Batch A was placed in pure water. Batch B was placed in sugar solution. After 2 hours the batches were surfaced dried and re-weighed. Whose potato increased in size?

• Batch B

• Batch A

Osmosis In Plant Cells

Water flows from the less concentrated solution outside the cell, through the cell wall and cell membrane into the cytoplasm and into the vacuole. This increased pressure in the vacuole is called turgor pressure and it causes the cytoplasm to press up against the cell wall. When the cell contains as much water as it can hold, it is said to be fully turgid. Turgid cells do not burst because the cell wall is strong enough to withstand the turgor pressure.

​

​Turgidity allows the plant to stay upright and gives it support. When cells lose water they become flaccid and the plant droops or wilts.

Multiple Choice

A plant cell was placed in a strong sugar solution. It lost water osmotically. The plant cell is now ____.

• turgid

• flaccid

Multiple Choice

A plant cell was placed in water. It took in water osmotically. The plant cell is now ____.

• turgid

• flaccid

Multiple Choice

If a plant takes in a lot of water, what will happen?

• it will burst

• it will not burst

• a lot

​Plasmolysed

When water passes out of the cell. Water passes out of the vacuole, out of the cytoplasm, out through the cell membrane and cell wall and into the solution outside the cell. The pressure of the vacuole on the cytoplasm decreases until the cytoplasm pulls away from the cell wall, causing the cell to become flaccid. Cells in this condition are said to be plasmolysed.

​

​Sidenote: my teacher said when describing plant cells as turgid, we can say plasmolysed since animals cells can be turgid too.

Multiple Choice

What is a dilute solution?

• When there is more solvent than solute.

• When there is less solvent than solute.

• When there is an equal amount of solute and solvent.

• None of the above

Multiple Choice

What is a concentrated solution?

• One that has a relatively large amount of dissolved solvent.

• One that has a relatively large amount of solvent.

• One that has a relatively large amount of dissolved solute.

• None of thee above

Multiple Choice

An animal cell was placed in a dilute solution. Would water enter or leave the cell animal?

• enter

• leave

Multiple Choice

An animal cell was placed in a more concentrated solution. Would water enter or leave the animal cell?

• leave

• enter

Multiple Choice

When the animal cell shrinks, it is described as ____ because of its shape.

• nated

• mated

• cremated

• crenated

​Diffusion

​The movement of molecules of a substance along a concentration gradient from where the substance is highly concentrated to where it is in low concentration.

​Active Transport

​Sometimes substances move across the cell membrane and other membranes from a region where they are present in low concentration to a region where they are present in high concentration. That is, they move against a concentration gradient in the reverse direction to normal diffuse. Such movement is called active transport. It allows cells to build up stores of substances which otherwise would be spread out by diffusion. Active transport is an active process, which means that it requires energy, unlike diffusion which a passive process and does not require energy.

​Active Processes

• ​It is possible to transport substances across a cell membrane against a concentration gradient.

• ​​However, it does require energy to achieve this. This energy is derived from breaking down glucose molecules into adenosine triphosphate (ATP).

• ​​Using this energy, proteins can "pump" water molecules through a membrane against a concentration gradient.

• ​Active transport of glucose occurs in the cells of the gut lining in animals. Similarly, in plants, minerals are taken up by means of active transport.