Biology - Diffusion, Osmosis, Active Transport
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Substances can MOVE IN AND OUT of CELLS by DIFFUSION, OSMOSIS and ACTIVE TRANSPORT. True or False.
TRUE.
Define DIFFUSION
THE NET (overall) MOVEMENT OF PARTICLES FROM AN AREA OF HIGHER CONCENTRATION TO LOWER CONCENTRATION but will ALSO spread evenly throughout liquid or gas and continue to move (think perfume diffusing through the air).
Give 2 examples of DIFFUSION.
• Spraying perfume. • Dropping ink into water.
Give 2 examples of DIFFUSION in living organisms.
• Products of digestion cross the wall of the small intestine. • Oxygen and carbon dioxide, dissolved in water, are exchanged by diffusion in the lungs.
Explain the term concentration.
The amount of substance in a certain volume of solution (e.g. salt, sugar). For understanding - When sucrose is dissolved in water, the solute is sucrose, and water is the solvent. Together they form a solution. The more sucrose particles there are in a certain volume of the solution, the more concentrated the solution is.
Watch this - https://www.bbc.co.uk/bitesize/guides/z9myxfr/revision/1
OSMOSIS involves what?
Water molecules.
Osmosis refers to the movement of many different molecules. True or False?
False. Osmosis refers to the movement of water molecules only.
Define OSMOSIS
The movement of WATER MOLECULES across a PARTIALLY PERMEABLE MEMBRANE From a LESS concentrated SOLUTION to a MORE concentrated SOLUTION
What is a partially permeable membrane?
A membrane with very small holes in it.
Give an example of a partially permeable membrane?
A cell membrane (remember the function of the cell membrane is to control what goes in and out).
Give 2 examples of where osmosis occurs?
• Plant cells • Animal cells • Dried fruit (soaking in water would cause the fruit to swell)
What is the function of a partially permeable membrane?
To allow small molecules to pass through the holes but to stop bigger molecules passing through.
Water molecules can only pass one way through a membrane during osmosis? True or False?
False. Water molecules can pass both ways through a membrane during osmosis (but remember it moves from a less concentrated solution (so more water molecules) to a more concentrated solution meaning less water molecules).
A DILUTE solution contains a high concentration of water molecules. True or False?
True.
A CONCENTRATED solution contains a LOW concentration of water molecules. True or False?
True.
When the concentration of water is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. True or False?
True. There will be no net movement of water molecules.
https://www.bbc.co.uk/bitesize/guides/z22vw6f/revision/1
What is the process for water moving in and out of cells called?
Osmosis. (Cells contain dilute solutions of ions, sugars and , amino acids. The cell membrane is partially permeable).
To help understand plant cells and osmosis. Isolated plant cells placed in a dilute solution or water will take in water by osmosis. If the soil is wet or moist then root hair cells will also take up water by osmosis. Leaf cells of land plants, unless it is raining or the humidity is high, will have a tendency to lose water. Plant cells have a strong cellulose cell wall, outside the cell membrane. The cell wall is fully permeable to all molecules. It supports the cell and stops it bursting when it gains water by osmosis. Under normal circumstances, the cells in all organisms live in a safe equilibrium. They have enough water to live but not too much. They also have the correct amount of salts and sugars. If individual cells are placed in different solutions, we can see how important it is that equilibrium is maintained in living organisms.
No answer, to help understand plant cells and osmosis.
ACTIVE TRANSPORT works in the SAME way to DIFFUSION. True or False?
False. Active Transport works in the OPPOSITE way to diffusion.
Describe ACTIVE TRANSPORT?
Active Transport is the MOVEMENT OF PARTICLES across a membrane from an area of LOWER CONCENTRATION to HIGHER CONCENTRATION.
Give 2 examples of where Active Transport occurs.
• Root hair cells in plants • Small intestine in humans
Active transport moves particles towards or against a CONCENTRATION GRADIENT?
Against. Active transport moves particles AGAINST a CONCENTRATION GRADIENT. Going from low to high concentration is going against the concentration gradient. (Think of going up a slide, against the gradient, active requires energy to go up the slide).