DIFFUSION, OSMOSIS, ACTIVE TRANSPORT AND SURFACE AREA TO VOLUME RATIO.

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  • Created by: _romaisa
  • Created on: 21-03-18 11:12
What is diffusion?/definition.
Diffusion is the net movement of ions or molecules from a region where they are in higher concentration to a region where they are in lower concentration, down the concentration gradient.
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Does diffusion require a membrane?
NO. No membrane is required for diffusion to take place.
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Why does diffusion happen?
It happens because of the random movement of individual particles.
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Why is diffusion important to living things?
It's important to living things as it explains how useful materials and wasteful products move into and out of cells.
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When does diffusion stop?
When the particles have evenly spread out./ When there is no concentration gradient existing and concentration is same everywhere.
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Which process is diffusion, active or passive?
It's a passive process(does not require energy.)
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Give some examples of diffusion.
Exchange of gases in lungs/RBCs and Exchange of gases in leaf.
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What's a solvent?
The liquid in which the solute dissolves to to form a solution. It's a liquid eg, water.
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What's a solute?
The dissolved substance in a solution. It's a solid. eg, sugar.
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What is osmosis?/definition.
Osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential,(down the water potential gradient), through a partially permeable membrane.
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What's a partially permeable membrane?
It's a selectively permeable or semi-permeable membrane which allows some substances to pass through but not the others. Cell surface membrane is a partially permeable membrane.
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Differentiate b/w a dilute solution and a concentrated solution.
A dilute solution contains a higher concentration of water molecules while a concentrated solution contains a low concentration of water molecules.
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What is water potential?
It is the measure of the tendency of water to move from one place to another. When two solutions of different water potential are separated by a partially permeable membrane, a water potential gradient is established.
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How does water move?
It always moves from higher water potential to lower water potential, down the concentration gradient.
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When are the terms: hypotonic, hypertonic and isotonic VALID/CAN BE USED?
These terms apply to animal cells only. These terms are "always" used in relation to pairs of solution. (there's no point of saying that a solution is hypotonic unless you have stated whom it is hypotonic to/with regard to?
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If solution X is less concentrated and has a higher water potential than solution Y, it is said to be_______________________________.
hypotonic with regard to solution Y.
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Solution Y, being more concentrated and having less water potential than solution X is said to be______________________________
hypertonic with regard to solution X.
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What does isotonic mean?
if two solutions are of equal concentrations, they are isotonic.
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Give an example statement where you use the terms hypotonic/hypertonic or isotonic.
the cytoplasm of the amoeba is a hypertonic solution relative to the water in which it is living, whilst the water is hypotonic to the cytoplasm of the amoeba.
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What happens when animal cell is placed in a solution with higher water potential?
Size of the cell starts to increase as water moves in by osmosis, down the WP gradient. Due to the absence of cell wall, cell bursts.
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What happens when a plant cell is placed in a solution w higher water potential?
Water enters the cell by osmosis so the size of vacuole starts to increase, and this water pushes cell contents against the cell wall. Cell wall prevents over expansion and stops cell from bursting, whilst maintaining its shape.
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What is turgidity or turgor pressure?
Turgor pressure is the pressure exerted outwards on the cell wall due to the WATER IN THE CELL. It gives the cell its firmness or turgidity. Turgor helps to support the soft tissues in plants.
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What happens when an animal cell is placed in a solution w lower water potential?/hypertonic sol.
Water will move out of the cell by osmosis,from higher wp to lower wp, down the water potential gradient, through a partially permeable membrane. Cell will form spikes & will shrink/aka the cell becomes crenated. Cell won't maintain shape/no cellwall
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What happens when a plant cell is placed in a solution w lower water potential?
Water will move out of the plant by osmosis. All cell organelles incl. cell membrane will move away frm cell wall but cell wall will maintain shape of cell. The cell becomes plasmolysed.
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What is crenation/What does a crenated cell mean?
Crenation means the shrinking of an animal cell by osmosis./when water moves out of the plant.
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What does plasmolysis mean?
The shrinkage of the cytoplasm away from the cell wall when plant cells are put in a low WP solution is called plasmolysis.
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What is a plasmolysed cell?
A plant cell that has lost water causing the cell membrane to be pulled away from the inside of the cell wall.
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Can a plasmolysed cell be restored to it's original state?
Yes, by placing it in water or a solution w higher water potential.
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What happens when an animal cell is placed in a solution w lower water potential?/hypertonic sol. (CONT)
An animal cell will become dehydrated when placed in a hypertonic solution and will eventually die.
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What is active transport./define.
Active transport is the process in which energy is used to move the particles of a substance against a concentration gradient, from a region where they are in lower concentration to a region where they are in higher concentration.
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Give examples of where active transport occurs?
-In the absorption of dissolved mineral salts by root hairs. - in the absorption of glucose and aminoacids by cells in the small intestine of humans.
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Where does active transport occur?
It only occurs in living cells because living cells respire and produce energy which is used for the process of active transport.
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Where does the energy come from which is used for the process of active transport?
The energy released by tissue repiration.
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How are mineral salts absorbed by root hair cells?
RHC's absorb mineral salts from soil by active transport, against the conc. gradient by using energy from resp.(salts can't go out of root hair cell as it's membrane doesnt allow/they only go in.)
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Explain the importance of turgidity.
-it maintains the shape of the plant and keeps the plant in an upright postion.-controls the opening and closing of stomata.-controls opening&closing of diff. flowers eg. touch me not plant.
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Surface area: volume rattio.
A small cell has a larger surface area to volume ratio than a large cell of the same shape.
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Surface area/Vol ratio: absorption.
Cells concerned w absorption of substances are modified to increase the surface are: volume ratio. Such modifications incl. long, narrow protrusions of root hair cells,microvilli in epithelial cells in small intest.&flattened biconcave shape of RBCs.
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Differences b/w diffusion and osmosis.
Diffusion: refers to any substance, gaseous or liquid whereas osmosis refers only to water(solvent molecules). Membrane not req. for diffusion whereas partially permeable membrane req. for osmosis.
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Similarities b/w diffusion and osmosis.
Both are passive processes, meaning that no respiratory energy required. Mov. of substances is down a concentration gradient.
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Active transport is a passive process or an active one?
It's an active process, meaning that it requires energy(from resp.
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Active transport occurs through____________ in ____________.
living membrane in living cells.
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Card 2

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Does diffusion require a membrane?

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NO. No membrane is required for diffusion to take place.

Card 3

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Why does diffusion happen?

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Preview of the front of card 3

Card 4

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Why is diffusion important to living things?

Back

Preview of the front of card 4

Card 5

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When does diffusion stop?

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