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Cellular Transport

Miss. Burriesci OLH

October 2018

Passive Transport: The movement of substances across the cell membrane without any input of energy by the cell.

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Passive Transport

Types of Passive Transport Diffusion Movement of molecules from high to low (concentration) § till dynamic equilibrium is reached. § It does not require the cell to use energy § Driven by the concentration gradient §  Spreads out evenly.

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Question Corner How would the movement of solute particles be

different if if the initial area of high concentration had been on the inside of the cell

instead of outside the cell?

If the concentration of solute particles had been higher on the inside of the cell, than more solute particles would have moved out of the cell and then

back into the cell.

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Facilitated Diffusion: § Cell membranes are built around lipid bilayers, the molecules that pass through

them most easily are small and uncharged. §  But many ions, such as Chlorine, are larger molecules. § How do these large molecules pass easily? §  PROTEINS act as carriers or channels, making it easy to cross the cell membrane. §  These MEMBRANE channels facilitate or “HELP” with diffusion across the

membrane. §  Facilitated Diffusion= is the process in which molecules that cannot directly

diffuse across the membrane pass through special protein channels. It does NOT require any additional energy.

Osmosis: An example of facilitated diffusion Meaning= the diffusion of water through a selectively permeable membrane.

-Being that part of the cell membrane is hydrophobic (“water-hating”), water molecules have a hard time passing through. Thus many cells will have water channel proteins called Aquaporins, which allow water to pass right through them.

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Question Corner? Does Osmosis require the cell to use

energy? Yes or no? Why?

Osmosis is a form of Facilitated diffusion, therefore it doesn't’t need any energy.

How Osmosis Works? A solution may be one of the following: (compared to a cell) §  Isotonic solution: same amount of water and solute §  Hypotonic solution: lower amount of solute, a lot of water §  Hypertonic solution: higher amount of solute, less water § Osmotic Pressure= driven by differences in solute concentration, the net movement of water out of or into a cell, which produces a force.

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Isotonic Solution (Red Blood Cells)

A solution is isotonic to a cell if it has the same concentration of solutes as the cell. Equal amounts of water enter and exit the cell, so its size stays constant.

Hypotonic Solution (Red Blood Cells)

A hypotonic solution has fewer solutes than a cell. Overall, more water enters a cell in a hypotonic

solution, causing the cell to expand and even burst.

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Hypertonic Solution (Red Blood Cells)

A hypertonic solution has more solutes than a cell. Overall, more water exits a cell in a hypertonic solution, causing the cell to shrivel and even die.

** If the solution outside the cell is hypotonic, then inside the cell is hypertonic and vice versa ** Water tends to diffuse from hypotonic to hypertonic.

Outside the Cell Inside the Cell Net Movement

Isotonic Isotonic None

Hypotonic Hypertonic Into the Cell

Hypertonic Hypotonic Out of the Cell

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Question Corner?

What would happen to the cells of a saltwater plant if the plant were

placed into fresh water?

The cell would become rigid and push up against the cell wall causing damage to the

plant cells, which could eventually burst (lyse).

Cytolysis Cell bursts due to water entering the cell

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Plasmolysis Cells shrink when turgor pressure (also referred to as water pressure inside a plant) is lost. §  The reason plants wilt.

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Review Questions:

§ Question #1: What is Passive Transport?

The movement of materials across the cell membrane without having

to use cellular energy.

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Active Transport: § The movement of materials AGAINTS a concentration difference

(gradient). § Energy is REQUIRED. § Small molecules or ions are carried out by transport proteins or “protein

pumps” that are found in the cell membrane.

§ Other types of Active Transport are (BULK TRANSPORT):

§ Endocytosis 1.  Phagocytosis

2.  Pinocytosis § Exocytosis

Active Transport: 1)  Endocytosis= is the process of taking material into the cell

by means of infoldings, or pockets of the cell membrane. § Phagocytosis= is a type of Endocytosis in which extensions

of the cytoplasm surround a particle and package it within a food vacuole. The cell then “engulfs” the food vacuole!

§ Pinocytosis= when tiny pockets form along the cell membrane , fill up with liquid, and pinch off to form vacuoles within the cell.

1)  Exocytosis=when the membrane of a vacuole fuses with

the cell membrane, forcing content out of the cell.

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Review Questions: § Question #1: What is Active Transport?

The movement of materials against a concentration difference, which

requires cellular energy.

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Question Corner?

§ What are the similarities and differences between facilitated diffusion and active transport by protein pump?

ANSWER -Facilitated diffusion and active transport by protein pumps are similar because they both make use of protein carriers to get materials across the cell membrane. -They differ because facilitated diffusion acts in the direction of the concentration gradient and does not use energy; while active transport requires energy to go against the concentration gradient.

How do these cells communicate? § Cells in a large organism communicate by means of chemical signals

that are passed from one cell to another. § These signal either speed up or slow down cellular activity. § Cells form “junctions” to neighboring cells. (Ex. Gap Junctions, Tight Junctions, etc.) § Receptor= where a signaling molecule can bind. A structure that

responds to a stimulus.

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