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What is the main function of carbohydrates in the cell membrane?

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What is the main function of carbohydrates in the cell membrane?

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The Fluid Mosaic Model describes membranes as a fluid lipid bi-layer with floating proteins and carbohydrates.

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Protein changes shape when denatured. Pepsin, the enzyme that breaks down protein in the stomach, only operates at a very low pH.
Jasmine Hart

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the material or protoplasm within a living cell, excluding the nucleus.
-Ricardo Cordova P1

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How are proteins able to move around the cell if they're completely surrounded by phospholipids?

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How are proteins able to move around the cell if they're completely surrounded by phospholipids?

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The cell membrane around the cell is relatively fluid which allows the transport proteins to freely move around the cells. The cell needs cholesterol which makes the membrane less fluid but this still allows proteins to move laterally across the cell

Michael Morales

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The glycocalyx or Carbohydrate Chains of a cell has multiple uses. The Glycocalyx provides cushioning and protection for the plasma membrane. It can also be used  for cell recognition. Based on the structure of the glycocalyx, your body is capable of identifying cells and recognize that cells proper placement. Glycocalyx can as well act as an adhesive to attach multiple cells together.

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How many proteins are in the cell membrane?

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How many proteins are in the cell membrane?

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proteins are free to move within the lipid bilayer as a result of its fluidity so their is no number of proteins.

Angel Duran

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What is the function of proteins in a cell membrane?

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What is the function of proteins in a cell membrane?

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Proteins in cell membranes can be and act as an enzyme and speed up chemical reactions, trigger sensory nerves, and move materials through the cell membrane.
by Kylie Barroso

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Do all cells have a protein channel or only some cells?

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Do all cells have a protein channel or only some cells?

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These protein channels have been found in plant, animal, and bacteria cells.

-Dustin Stringer, P1

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How do carbohydrate chains help with cell regulation?

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How do carbohydrate chains help with cell regulation?

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The carbohydrate chains form a structure called glycocalyx, which is used as a form of protection for the cell membrane. It creates this biofilms which are very tough and resistant to harmful factors. Gavin Doyle P1

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Complete this GOOGLE form when you are done. 

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Complete this GOOGLE form when you are done. 

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Exploring Cellular Transport Grading Criteria

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Instructions for Exploring Cellular Transport 

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ATis a nucleotide

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How much energy does a cell use durring active trasport?  -Lucas M p1

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How much energy does a cell use durring active trasport?  -Lucas M p1

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A cell will use around 1 molocule of atp per use of active transport on average, bigger transports take more. On average our body uses enough body atp to double thier body weight eveyday,but our body reuses.

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Where does passive transport take place?

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Where does passive transport take place?

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Passive transport takes place in the plasma membrane.
Kayla Ireland

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Why does active transport require energy?

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Why does active transport require energy?

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To move substances against concentration, the cell must use energy to maintain the right concentration of molecules in the living cell. Therefore, active transport requires energy to maintain the concentration of molecules.

Rilee Andrews

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is it possible for passive transport to use energy ?

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is it possible for passive transport to use energy ?

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Passive Transport - Taking the Easy Road. While active transport requires energy and work, passive transport does not. There are several different types of this easy movement of molecules. It could be as simple as molecules moving freely such as osmosis or diffusion.
by claudia malfavon

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Why doesn't passive transport require energy?

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Why doesn't passive transport require energy?

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Passive transport doesn't need energy because there isn't an order or anything guiding the particles that are going in and out of the cell. Active transport requires the different particles to go at specific times and guides them where they need to go. Passive transport also works through diffusion and osmosis, which doesn't require energy.
Tori Johnston

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Written by tutor Megan E.

In order to survive, a cell must maintain a careful balance of nutrients, electrolytes, water, and metabolites in its cytoplasm at all times. Many of these required nutrients are supplied to cells by the bloodstream (multicellular organisms) or extracellular fluid (single-celled organisms), and thus the cell must have ways to get these substances into its cytoplasm through its membrane. Also, cells must be able to excrete waste products into the extracellular space so the cytoplasm does not accumulate toxic and harmful products. In addition, an exact gradient of electrolytes must be maintained across the cell membrane in order for cells to perform normal functions like movement, signaling, and both anabolic and catabolic activities. Thus the cell has complex systems of transport to move these substances both in and out of the cell.

Passive transport is the name for a class of transport processes that do not require energy from the cell for the transport to take place. In the terms of thermodynamics, these processes of transport occur spontaneously or have a net negative Gibbs free energy (exergonic reaction). Active transport is the other class of transport systems that do require energy from the cell, usually in the form of ATP, do not occur spontaneously (endergonic reaction). Diffusion, osmosis, and facilitated diffusion are all types of passive transport.

A molecule will undergo passive transport when it flows down its electrochemical gradient, a combination of its chemical and electrical gradients. When the concentration of a solute is higher on one side of the membrane, this is called a chemical gradient. Molecules flow randomly and spontaneously towards areas of lower concentration of that molecule, a process called diffusion ("to spread out").

When one side of the membrane is positively or negatively charged compared to the other side, this is called an electrical gradient or potential. Positive ions will be attracted to negative ions and thus they will spontaneously move toward each other until neutrality across the membrane is reached. Basically, it is thermodynamically favorable for a molecule to move to the side of the membrane where the electrochemical gradient is lowered, or where there are less molecules like itself. Active transport occurs when a solute moves "uphill" or against its electrochemical gradient because energy is required to concentrate a molecule in an area.

Generally, small nonpolar molecules, such as cholesterol, CO2 and O2, diffuse rapidly across the lipid bilayer because they are hydrophobic and dissolve readily in the membrane. Some small polar molecules such as water or urea can also diffuse directly through the plasma membrane but the process is slow for these molecules. The plasma membrane is impermeable to large or charged molecules. Diffusion is the simplest type of passive transport and requires no proteins to occur. The diffusion of water across a semi-permeable membrane, of which the lipid bilayer is an example, is called osmosis, another type of passive transport. Water diffuses toward the side of the membrane that has more solutes so it can effectively lower their concentration and minimize the electrochemical gradient. Maintaining the correct electrochemical gradient requires osmosis, and if the normal electrochemical gradient is disturbed, osmosis can also cause the cell to shrivel or burst.

Because diffusion is a slow process for many important molecules, a process called facilitated diffusion is used by the cells to rapidly transport molecules across the membrane. Facilitated diffusion occurs when proteins, specific for the transported molecule, are used to move the molecule across the membrane. Channel proteins transport molecules down their electrochemical gradient and can be thought of as a tunnel through the plasma membrane that is specific for a certain type of molecule.

Channels bind weakly to the molecule they transport and are either simply closed or open to movement. Aquaporins are channels specific for water that allow diffusion of water to occur at a much higher rate than diffusion directly through the plasma membrane.

Transporter or carrier proteins are also specific for the molecule they transport, but now the carrier protein actually binds the molecule to be transported and changes conformations in order to move the molecule into or out of the cell. Rather than being simply open or closed, transporters change shape (conformations) when the solute binds and change shape again when the solute is released to the other side of the membrane. This process is relatively fast compared to diffusion, but slow compared to the movement of molecules through channels. Transporter proteins used in passive transport are also called permeases because they make the membrane permeable to a certain substance. Transporter proteins that are used for active transport are often called pumps because work is done and energy expended by the cell to move the molecule from one place to another. More information can be found in our lesson on facilitated diffusion.

It should be noted that transport occurs across all the lipid bilayers in eukaryotic cells, like those around other cellular organelles, in addition to the plasma membrane. The abundance and the specific types of transporter proteins vary in each membrane as each compartment of the cell maintains a particular milieu of substances.

Quiz Questions

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In order to survive, a cell must maintain a careful balance of nutrients, electrolytes, water, and metabolites in its cytoplasm at all times. Many of these required nutrients are supplied to cells by the bloodstream (multicellular organisms) or extracellular fluid (single-celled organisms), and thus the cell must have ways to get these substances into its cytoplasm through its membrane.

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How much energy is used during Endocytosis?

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How much energy is used during Endocytosis?

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Endocytosis requires ATP (a measurement of energy ) but how much energy does one ATP molecule  use, after some research i found out that it uses only 10^-19 J (J represents joule a universal unit for energy)
-Emilio Rebollozo P1

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How do passive and active transport help each other out?

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How do passive and active transport help each other out?

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They both use ion channels to move ion across the cell membrane, in and out of the cell
Yasmine Lazaro p1

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Which type of active transport uses the least amount of energy

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Which type of active transport uses the least amount of energy

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First of all, there are two types of active transport, Primary and Secondary. Primary uses ATP directly while secondary uses electrochemical gradient generated by active transport and doesn't need ATP directly.
In the end, they are use the same amount of energy, just different sources of energy.
Jose Vega P.1

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What happens if there is no cell membrane?

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What happens if there is no cell membrane?

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The nucleus would or wouldn't be needed because most likely it would float away, but if that didn't happen it would possibly not be able to work the cell with every other organelle floating away, or it would be infected because without a cell membrane stuff could get in freely and infect the nucleus
-Yoanna Gracia

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Without proteins what would happen to our cell membrane?

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Without proteins what would happen to our cell membrane?

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Our cell membranes wouldn't stay clean and their health depends on proteins so our cell would be dirty. Plus our cell membrane wouldn't be able to keep a high nutrient.
By: Mia Vidales

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Why would cell membranes help us from death

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Why would cell membranes help us from death

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ATP is a nucleotide with three phosphate groups and it loses on of those groups when it transfers energy to a protein pump.
-Eliot

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What would be the effects if the cell was not selectively permeable?

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What would be the effects if the cell was not selectively permeable?

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If the cell was fully permeable (ie. not selectively permeable) any molecule would be able to gain access to cell. This therefore would cause many molecules, some toxic, to access the cell interior and in the case of toxins it would harm and or kill the cell. If this happened your cells wouldn't be able to repair themselves in time and you would die quite quickly.
Matthew Cataline P2
https://www.enotes.com/homework-help/what-would-happen-cell-membrane-were-fully-208581

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What is active transport and what does active transport require?

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What is active transport and what does active transport require?

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Active transport is when the cell uses cellular energy(ATP)to move molecules to where they are needed.
*Against the concentration gradient
*Movement from an area of low concentration to an area of high concentration
Yes active transport does require energy to move substances.

Ivan Cabrera

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How fast is the process of Passive transport to Active transport?

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How fast is the process of Passive transport to Active transport?

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Active transport is much more faster but can change under different circumstances. During Active transport most is based on thermal energy alone, at a normal temperature of 20' Celsius (68' Fahrenheit) Active transport will pass at a speed of 1400 Mph( miles per hour)
-Source

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The cell membrane is semipermeable because it has to let certain things into the cell. The cell membrane only allows what it needs into the cell. Whatever it doesn't need or want it repels.
Emilee Goettig P

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What makes up the structure of the cell membrane?

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What makes up the structure of the cell membrane?

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The stucture of the cell membrane is composed of four components.
1.

1. Phospholipids

2. cholesterol
3.Proteins
4. Carbohydrates

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What are 2 functions of the cell membrane?

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What are 2 functions of the cell membrane?

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2 functions of the cell membrane are (1) to control what enters and exits the cell and (2) to protect and support the cell.
Amia Stults

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which type of active transport uses the most amount of energy 

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which type of active transport uses the most amount of energy 

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There are two types of active transport primary and secondary.  primary transport Involves the direct use of metabolic energy (Atp) to mediate transport. secondary transport Involves coupling the molecule with another moving along an electrochemical gradient

but they both use the same amount of energy just different types . Isaiah Sheldon P2

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Because some of the particles are to big to just go through the membrane so they need help.

Wyatt Mahan

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how does the cell membrane know what to let pass through?

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how does the cell membrane know what to let pass through?

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the protein channels have a shape only certain molecules can fit in, so if the molecule does have to correct shape then it cant pass through
Oscar Vega

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What tells the cell membrane what is okay to pass through and what is not?

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What tells the cell membrane what is okay to pass through and what is not?

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The Plasma membrane has these things called protein channels they basically are like a mold for molecules whatever fits goes in whatever doesn't fit doesn't go in. This makes it easier for water and nutrients to pass through. Some small nutrients might sneak in without even needing recognition because they're so small there able to pass through the membrane wall.
By: Courtney Williams

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What makes cell membranes selectively permeable?

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What makes cell membranes selectively permeable?

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The phospholipid bilayer, which has a hydrophobic interior, allows only certain substances to pass through. Charged atoms and polar molecules are repelled by this hydrophobic center, while lipids or other smaller non-polar molecules aren't.

Jeannie Acuna

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Cellular energy (ATP) moves molecules to where they are needed, cellular energy moves molecules from an area of low concentration to an area of high concentration.
Titus Mitchell

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what is a cell membrane? What does it do?

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what is a cell membrane? What does it do?

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The semipermeable membrane surrounding the cytoplasm of a cell.

It consists of a lipid bilayer  with embedded proteins. The basic function of the cell membrane is to protect the cell from its surroundings. The cell membrane controls the movement of substances in and out of cells and organelles. In this way, it is selectively permeable to ions and organic molecules.
Adrian G. Per:2

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Why do cell membrane use diffusion if they use facilitated diffusion?

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Why do cell membrane use diffusion if they use facilitated diffusion?

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How can high temperatures damage the cell membrane 

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How can high temperatures damage the cell membrane 

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High heat could break down protein in the cell membrane -Mia U

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what is the simplest form of passive transport

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what is the simplest form of passive transport

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the simplest form of passive transport is equilibrium/diffusion.

by, Hunter Gardner P.2

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Adenosine Triphosphate

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For transport protein, what type of molecule passes through each channel?

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For transport protein, what type of molecule passes through each channel?

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They allow various polar molecules such as ions, sugars, amino acids, nucleotides, and many other cell metabolites.
Albert Cuellar P.2

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The process that allows selective movement in and out of the cell membrane. The proteins are making it easy to got though.
Salvador Estrada

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It has one or more

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What is the protein pump and what does it do

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What is the protein pump and what does it do

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Permeability is conferred by two classes of membrane proteins, pumps and channels. Pumps use a source of free energy such as ATP or light to drive the thermodynamic-ally uphill transport of ions or molecules. Pump action is an example of active transport.

By: Arturo Gonzalez

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Changes shape.
ATP. Energy to change shape

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How are protein pumps important to Active Transport?

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How are protein pumps important to Active Transport?

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Active transport is the process of moving substances through membranes, and protein pumps will control what will go in and out inside the cell.
-Nicolas Esparza

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What does protein pumps have to do with active transport?

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What does protein pumps have to do with active transport?

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Active transport usually happens across the cell membrane. ... Many times, proteins have to work against a concentration gradient. That term means they are pumping something (usually ions) from areas of lower to higher concentration.
Makayla Martin

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How does a cell create a pocket inside of itself for exocytosis?

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How does a cell create a pocket inside of itself for exocytosis?

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The golgi apparatus clips off a  piece of itself that contains bacteria or harmful organism and sends it out of the cell.
Ezra Hernandez.

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What does Diffusion transport? What elements?

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What does Diffusion transport? What elements?

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Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. More specifically diffusion transports O2, CO2, and small uncharged particles.
Haileigh Anderson P1

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How does cholesterol help maintain the cell membrane rigid?

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How does cholesterol help maintain the cell membrane rigid?

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Cholesterol is a steroid! With it's 4 fused rings, it is more "rigid" than the fatty acid tails. So, it helps keep the membrane rigid.

Example, by Ms. Gallegos

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1.3 Application: Cholesterol in animal cell membranes

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What are the Similarities and Differences of Water and Other Particles in the Way that They are Transported?

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What are the Similarities and Differences of Water and Other Particles in the Way that They are Transported?

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Tanner Cox- Per. 4, 24.10.
Osmosis - Transportation of water through a semipermeable membrane, allowing water to freely pass.
Facilitated Diffusion- Transportation of particles through transport proteins found in the cell membrane.

Difference in Transportation:

1. Water can pass freely, Particles must go through protein channels.

2. Water takes place through semipermeable membrane, Facilitated doesn't require.

3. The process of osmosis is only for liquids, The process of diffusion can take place in all the three states of matter

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What are the three types of active transport?Describe

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What are the three types of active transport?Describe

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Protein pumps-pump ions from area of lower to higher concentration.
endocytosis-brings materials in.
exocytosis-puts materials out.
-Troyce Mitchell

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Active Transport takes place while digestion is occurring. Carbs are broken into simple sugars like glucose which is then absorbed into the villi(absorption hairs) and spread through the blood stream.
-Devin Laws

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BBC - GCSE Bitesize: Active transport - Higher tier

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A secondary school revision resource for OCR 21st Century Additional GCSE Science about enzymes, processes of life and processes of plants

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Why do plants and animal cells have a cell membrane?

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Why do plants and animal cells have a cell membrane?

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Plants and animal cells have a cell membrane because the cell membrane controls what enters and what leaves the cell to maintain  the balance called, homeostasis. The cell membrane also provides protection and support for the cell.
-Elissa Leos

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How Does Passive Transport Not Require Energy?

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How Does Passive Transport Not Require Energy?

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Passive Transport does not require energy because it follows the contration gradients from high to low

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osmosis can occur in other liquids, and even gases. The water molecules pass through the cell membrane from an area of low to high concentration.
~Sadie O'Dea P.5

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What is the function of the carbohydrate chains attached to the proteins in the cell membrane?

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What is the function of the carbohydrate chains attached to the proteins in the cell membrane?

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These "tails" trailing out of the proteins in the cell form hydrogen bonds with surrounding water molecules. This stabilizes the cell membrane, keeping its structure in place, almost as if it were tethered down.- Johnathan Ballejos

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All living cells have something known as a cell membrane. This selectively-permeable membrane controls the exchange of materials, receives hormone messages and is very thin. It can be described as a phospholipid bi-layer - meaning that it's made from phospholipid molecules and has two layers.

The phospholipid bi-layer is so thin it can barely even be seen by an electron microscope - a x100,000 magnification is required, and only shows a double black line around 7 nm wide. Since we cannot properly see the membrane, we have to take what we know about it and create a model - in this case known as a fluid mosaic model.

A diagram of the fluid mosaic model can be seen below.

Features of the fluid mosaic model;

The membrane primarily consists of a bilayer of phospholipid molecules. These molecules can move about by diffusion in their own layer.

Width is about 7 nm on average

Some of the phospholipids are saturated and some are unsaturated. This affects the fluidity of the membrane, a heavily unsaturated membrane means a more fluid membrane. This is due to the kink in unsaturated tails causing the molecules to not sit closely together.

Phospholipid tails point inwards, facing each other, meaning that inside the membrane it is non-polar hydrophobic.

The protein molecules within the structure can move around although some are fixed to structures inside the cell and do not move. Also, some of them span the width of the membrane, some are only on the inner layer and some on the outer layer.

Many proteins and lipids have short carbohydrate chains attached to them, forming glycoproteins and glycolipids.

Contains cholesterol.

The previous section spoke about several components that may be new to you, their structures and roles are below.

You may remember phospholipids from chapter two. It was stated that they have hydrophilic heads and hydrophobic tails, the importance of which should be becoming clear. A phospholipid bi-layer forms the body of the membrane, creating a hydrophobic interior and isolating the cell from the outside environment. Do not forget that organelles within a cell are also often surrounded by a membrane, and this too is a phospholipid membrane.

There are two types of protein when discussing the cell membrane, those being intrinsic proteins and extrinsic proteins. Intrinsic proteins are proteins embedded in the cell membrane, extrinsic proteins being those not embedded within the cell. What decides whether a protein is intrinsic or extrinsic is the proteins charge - if the protein is completely charged then the protein will be extrinsic as it will be repelled by the non polar fatty acis tails. If the protein is partially charged or not charged at all then the protein will be intrinsic as it will be drawn towards the non polar fatty acid tails.

Lipid and proteins on the cell membrane surface often have short carbohydrate chains protruding out from the cell surface, known as glycolipids and glycoproteins. They form hydrogen bonds with the water molecules surrounding the cell and thus help to stabilize membrane structure. However, more importantly, they are used as receptor molecules, binding with hormones or neurotransmitters to trigger a series of chemical reactions within the cell itself. Using insulin as an example, only some cells within the body (liver, muscles), have receptors for insulin and as such, insulin can be released to the entire body without upsetting anything as any cell without an insulin receptor will not be affected.

Glycoproteins can also serve as antigens, which are used in allowing cells to recognize each other.

Cholesterol helps to regulate fluidity of the membrane and also to provide mechanical stability of the membranes - without it cells will burst open as their membranes break. Their hydrophobic regions help to prevent ions or polar molecules inadvertently passing through the membrane.

Transport across the phospholipid bi-layer is regulated, and it is an effective barrier - but exchange is necessary. Methods of exchange are discussed here.

Diffusion is defined as the net motion of a substance from an area of high concentration to an area of low concentration, 'down a concentration gradient'.

Factors which affect diffusion;

How steep the concentration gradient is. Concentration gradient is the ratio of molecules on one side of the membrane to the other, many on one side compared to few on the other will result in a faster net rate of diffusion

Temperature. High temperatures increase the kinetic energy of molecules and ions and thus they move around faster - net rate of diffusion goes up.

Surface area. A large surface area increases the amount of ions or molecules that can cross at one time, increasing the net rate of diffusion.

Type of molecule. Large molecules are slower to diffuse, non-polar molecules diffuse more easily through cell membranes as they are soluble.

Molecules and ions that are small enough can cross membranes easily, regardless of polarity, but large polar molecules such as glucose cannot diffuse through a cell membrane. They can only pass through hydrophilic protein channels - this process is known as facilitated diffusion. All the factors that affect diffusion affect facilitated diffusion, and an additional one - how many transport proteins are available.

Facilitated diffusion: [1]

Osmosis is best described as a special type of diffusion involving water molecules only.

The first diagram is the experiment just set up, the 'before diagram', and as you can see, water is moving from the more dilute substance to the less dilute solution, separated by a partially permeable membrane - down the concentration gradient. The second picture shows the substance after it has been left for a while - there is the same concentration of solute molecules and thus the same concentration of water molecules, this is known as equilibrium. The fact that this is the movement of water molecules alone that has brought about the equilibrium is characteristic of osmosis.

The propensity for water molecules to move from one place to another is known as the water potential, and the symbol for water potential is the Greek letter 'psi', Ψ. Water always moves from an area of high water potential to a low water potential area - equilibrium as mentioned before is the equaling of two adjacent (separated by a partially-permeable membrane) water potentials. Pure water has a water potential of 0, and any solutes make the water potential negative, the degree to which they do is called the solute potential.

Net movement of water from a high to low concentration gradient can be prevented or slowed by increasing the pressure in the low concentration gradient solution, since pressure increases the water potential.

Plants have cell walls, and thus pressure potential is especially important - if the volume of the cell increases as a result of water entering the cell via osmosis, the cell starts to push against the cell wall and pressure builds up rapidly. This pressure increases the water potential of the cell so that water stops entering it, creating a 'false-equilibrium' (in that pressure helps it) preventing it from bursting. When a cell is fully inflated it is described as turgid.

The opposite to turgidity is plasmolysis - when a cell is placed in a concentrated sucrose solution, the cell begins to shrink away from the cell wall, creating a pressure potential of 0, and so the water potential is equal to its solute potential. Eventually cytorrhysis - the complete collapse of the cell wall - can occur. There is no mechanism in plants to prevent excess water loss in the same way as excess water gain, but plasmolysis can be reversed if the cell is placed in a weaker solution . The equivalent process in animal cells is called crenation. The liquid content of the cell leaks out due to diffusion. Plasmolysis is extremely rare in nature.

In animal cells however, there is no cell wall, and so if the water potential of the solution around the cell is too high, the cell will swell and burst, but if it is too low, the cell shrinks. This is why it is important to keep a constant water potential inside animal bodies.

Active transport is defined as the energy-consuming transport of molecules or ions across a membrane against a concentration gradient, made possible by transferring energy from respiration. The energy is supplied by ATP, and is used to make the transport protein change its 3d shape, transferring the molecules or ions across the membrane in the process. Something to note is that cells that do a lot of active transport are likely to have many mitochondria to provide the energy for it.

It is particularly important in reabsorption in the kidneys where certain useful molecules must be reabsorbed into the blood after filtration. In plants it is used to load sugar from photosynthesizing cells into the phloem tissue for transport.

Bulk transport can be defined as the movement of large quantities of materials into or out of cells, endocytosis and exocytosis, respectively.

Exocytosis is the process by which materials are removed from cells - for example, the secretion of digestive enzymes, where vesicles from the Golgi apparatus carry the enzymes to the cell surface, bind to it, and release their contents. See: [4]

Endocytosis is the reverse of exocytosis and involves the engulfing of the material by the cell to form a small sac inside the cell. The most common form is phagocytosis, performed by phagocytes - an example of which would be white blood cells engulfing bacteria. The second form of endocytosis is pinocytosis, the bulk uptake of liquid, and the human egg cell takes up nutrients from cells that surround it by this method.

This relates to how substances move in and out of whole organisms, using two examples.

All mammals need a supply of oxygen to use in respiration - and in mammals the cells that require the oxygen are too far for diffusion to be effective and so they have a specialised gaseous exchange surface, where oxygen can diffuse into the body and carbon dioxide can diffuse out. In humans, this exchange surface is the alveoli in the lungs, and as you can see in the diagram below, each alveolus is tiny but collectively they have a huge surface area, totaling around 70m ² in an adult. This increases the net rate of diffusion. Alveoli also have extremely thin walls, no more than 0.5 μm thick, directly next to blood capillaries also with very thin cell membranes. This thinness allows diffusion to be extremely speedy.

Since diffusion only works down a concentration gradient, and the steeper said concentration gradient, the faster diffusion, the concentration gradient between the alveoli and the blood must be kept steep constantly to ensure speedy diffusion. Carbon dioxide is rapidly breathed out, meaning that carbon dioxide transported to the alveoli will be quickly transported into them and breathed out, and deoxygenated blood is constantly kept coming to the alveoli, meaning that oxygen diffuses into it quickly.

See picture: [5]

Root hairs of a flowering plant are also specialized exchange surfaces - they are extensions of the cells that make up the epidermis of a root, and are each around 200-250μm across, providing an enormous total surface area that is in contact with the soil surrounding the root. Both water and mineral ions are absorbed by diffusion and facilitated diffusion/active transport respectively.

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All living cells have something known as a cell membrane. This selectively-permeable membrane controls the exchange of materials, receives hormone messages and is very thin. It can be described as a phospholipid bi-layer - meaning that it's made from phospholipid molecules and has two layers.

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An important mechanism that allows exocytosis to occur is called a motor protein. This type of protein uses ATP energy to convert chemical energy into mechanical motion. They are crucial in exocytosis because these proteins direct the vesicles to the cell membrane, rather than simply allowing the vesicles to roam the cell freely.
PJ Noonan

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How do you identify whether a cell uses Passive transport or Active transport?

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How do you identify whether a cell uses Passive transport or Active transport?

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What Elements Are Pumped In and Out Of Protein Pumps?

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What Elements Are Pumped In and Out Of Protein Pumps?

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Protein pumps can pump elements such as sodium, potassium, and calcium. There's special type called a proton pump that pumps protons across cell membranes

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Passive transport gives an ion or molecule “room to breathe.” It goes from high concentration to low concentration.
-Julliett cheney, p5

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The different  of protein pump in the body.

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The different  of protein pump in the body.

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Aquaporins are the membrane's protein that work as channels that help transfer water and small molecules through the membrane.

-Bryanna Valera 5th

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if carbon dioxide was to stop moving across the cell membrane would not be as rich and blood would not travel as smoothly

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What is the difference between ndocytosis and exocytosis

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What is the difference between ndocytosis and exocytosis

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The difference between endocytosis and excytosis is that endocytosis is the process of capturing a particle from the outside by taking it with the cell membrane ,while exocytosis describes the process of the vesicles fusing with the plasma membrane ,also releasing the content outside of the cell.

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What would happen if the cell membrane breaks or snaps      

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What would happen if the cell membrane breaks or snaps      

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If the cell was to break or snap,what would happen is the cell energy production will start to slow down or stop working
Juan M P.5

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Aquaporins are "the plumbing system for cells". They selectively conduct the water molecules in and out of the cells,while that's happening their also trying to prevent the passage of ions and other solutes. It's also known as the water channel. Aquaporins are found in the vacuolar  membrane.
alisia deppel

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What are some functions of the cell membrane?

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What are some functions of the cell membrane?

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they keep toxic substances out of the cell, they have certain receptors that allow molecules such as ions to pass  between organelles and between the cell and the outside environment.
Edgar Solis

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All living cells have something known as a cell membrane. This selectively-permeable membrane controls the exchange of materials, receives hormone messages and is very thin. It can be described as a phospholipid bi-layer - meaning that it's made from phospholipid molecules and has two layers.

The phospholipid bi-layer is so thin it can barely even be seen by an electron microscope - a x100,000 magnification is required, and only shows a double black line around 7 nm wide. Since we cannot properly see the membrane, we have to take what we know about it and create a model - in this case known as a fluid mosaic model.

A diagram of the fluid mosaic model can be seen below.

Features of the fluid mosaic model;

The membrane primarily consists of a bilayer of phospholipid molecules. These molecules can move about by diffusion in their own layer.

Width is about 7 nm on average

Some of the phospholipids are saturated and some are unsaturated. This affects the fluidity of the membrane, a heavily unsaturated membrane means a more fluid membrane. This is due to the kink in unsaturated tails causing the molecules to not sit closely together.

Phospholipid tails point inwards, facing each other, meaning that inside the membrane it is non-polar hydrophobic.

The protein molecules within the structure can move around although some are fixed to structures inside the cell and do not move. Also, some of them span the width of the membrane, some are only on the inner layer and some on the outer layer.

Many proteins and lipids have short carbohydrate chains attached to them, forming glycoproteins and glycolipids.

Contains cholesterol.

The previous section spoke about several components that may be new to you, their structures and roles are below.

You may remember phospholipids from chapter two. It was stated that they have hydrophilic heads and hydrophobic tails, the importance of which should be becoming clear. A phospholipid bi-layer forms the body of the membrane, creating a hydrophobic interior and isolating the cell from the outside environment. Do not forget that organelles within a cell are also often surrounded by a membrane, and this too is a phospholipid membrane.

There are two types of protein when discussing the cell membrane, those being intrinsic proteins and extrinsic proteins. Intrinsic proteins are proteins embedded in the cell membrane, extrinsic proteins being those not embedded within the cell. What decides whether a protein is intrinsic or extrinsic is the proteins charge - if the protein is completely charged then the protein will be extrinsic as it will be repelled by the non polar fatty acis tails. If the protein is partially charged or not charged at all then the protein will be intrinsic as it will be drawn towards the non polar fatty acid tails.

Lipid and proteins on the cell membrane surface often have short carbohydrate chains protruding out from the cell surface, known as glycolipids and glycoproteins. They form hydrogen bonds with the water molecules surrounding the cell and thus help to stabilize membrane structure. However, more importantly, they are used as receptor molecules, binding with hormones or neurotransmitters to trigger a series of chemical reactions within the cell itself. Using insulin as an example, only some cells within the body (liver, muscles), have receptors for insulin and as such, insulin can be released to the entire body without upsetting anything as any cell without an insulin receptor will not be affected.

Glycoproteins can also serve as antigens, which are used in allowing cells to recognize each other.

Cholesterol helps to regulate fluidity of the membrane and also to provide mechanical stability of the membranes - without it cells will burst open as their membranes break. Their hydrophobic regions help to prevent ions or polar molecules inadvertently passing through the membrane.

Transport across the phospholipid bi-layer is regulated, and it is an effective barrier - but exchange is necessary. Methods of exchange are discussed here.

Diffusion is defined as the net motion of a substance from an area of high concentration to an area of low concentration, 'down a concentration gradient'.

Factors which affect diffusion;

How steep the concentration gradient is. Concentration gradient is the ratio of molecules on one side of the membrane to the other, many on one side compared to few on the other will result in a faster net rate of diffusion

Temperature. High temperatures increase the kinetic energy of molecules and ions and thus they move around faster - net rate of diffusion goes up.

Surface area. A large surface area increases the amount of ions or molecules that can cross at one time, increasing the net rate of diffusion.

Type of molecule. Large molecules are slower to diffuse, non-polar molecules diffuse more easily through cell membranes as they are soluble.

Molecules and ions that are small enough can cross membranes easily, regardless of polarity, but large polar molecules such as glucose cannot diffuse through a cell membrane. They can only pass through hydrophilic protein channels - this process is known as facilitated diffusion. All the factors that affect diffusion affect facilitated diffusion, and an additional one - how many transport proteins are available.

Facilitated diffusion: [1]

Osmosis is best described as a special type of diffusion involving water molecules only.

The first diagram is the experiment just set up, the 'before diagram', and as you can see, water is moving from the more dilute substance to the less dilute solution, separated by a partially permeable membrane - down the concentration gradient. The second picture shows the substance after it has been left for a while - there is the same concentration of solute molecules and thus the same concentration of water molecules, this is known as equilibrium. The fact that this is the movement of water molecules alone that has brought about the equilibrium is characteristic of osmosis.

The propensity for water molecules to move from one place to another is known as the water potential, and the symbol for water potential is the Greek letter 'psi', Ψ. Water always moves from an area of high water potential to a low water potential area - equilibrium as mentioned before is the equaling of two adjacent (separated by a partially-permeable membrane) water potentials. Pure water has a water potential of 0, and any solutes make the water potential negative, the degree to which they do is called the solute potential.

Net movement of water from a high to low concentration gradient can be prevented or slowed by increasing the pressure in the low concentration gradient solution, since pressure increases the water potential.

Plants have cell walls, and thus pressure potential is especially important - if the volume of the cell increases as a result of water entering the cell via osmosis, the cell starts to push against the cell wall and pressure builds up rapidly. This pressure increases the water potential of the cell so that water stops entering it, creating a 'false-equilibrium' (in that pressure helps it) preventing it from bursting. When a cell is fully inflated it is described as turgid.

The opposite to turgidity is plasmolysis - when a cell is placed in a concentrated sucrose solution, the cell begins to shrink away from the cell wall, creating a pressure potential of 0, and so the water potential is equal to its solute potential. Eventually cytorrhysis - the complete collapse of the cell wall - can occur. There is no mechanism in plants to prevent excess water loss in the same way as excess water gain, but plasmolysis can be reversed if the cell is placed in a weaker solution . The equivalent process in animal cells is called crenation. The liquid content of the cell leaks out due to diffusion. Plasmolysis is extremely rare in nature.

In animal cells however, there is no cell wall, and so if the water potential of the solution around the cell is too high, the cell will swell and burst, but if it is too low, the cell shrinks. This is why it is important to keep a constant water potential inside animal bodies.

Active transport is defined as the energy-consuming transport of molecules or ions across a membrane against a concentration gradient, made possible by transferring energy from respiration. The energy is supplied by ATP, and is used to make the transport protein change its 3d shape, transferring the molecules or ions across the membrane in the process. Something to note is that cells that do a lot of active transport are likely to have many mitochondria to provide the energy for it.

It is particularly important in reabsorption in the kidneys where certain useful molecules must be reabsorbed into the blood after filtration. In plants it is used to load sugar from photosynthesizing cells into the phloem tissue for transport.

Bulk transport can be defined as the movement of large quantities of materials into or out of cells, endocytosis and exocytosis, respectively.

Exocytosis is the process by which materials are removed from cells - for example, the secretion of digestive enzymes, where vesicles from the Golgi apparatus carry the enzymes to the cell surface, bind to it, and release their contents. See: [4]

Endocytosis is the reverse of exocytosis and involves the engulfing of the material by the cell to form a small sac inside the cell. The most common form is phagocytosis, performed by phagocytes - an example of which would be white blood cells engulfing bacteria. The second form of endocytosis is pinocytosis, the bulk uptake of liquid, and the human egg cell takes up nutrients from cells that surround it by this method.

This relates to how substances move in and out of whole organisms, using two examples.

All mammals need a supply of oxygen to use in respiration - and in mammals the cells that require the oxygen are too far for diffusion to be effective and so they have a specialised gaseous exchange surface, where oxygen can diffuse into the body and carbon dioxide can diffuse out. In humans, this exchange surface is the alveoli in the lungs, and as you can see in the diagram below, each alveolus is tiny but collectively they have a huge surface area, totaling around 70m ² in an adult. This increases the net rate of diffusion. Alveoli also have extremely thin walls, no more than 0.5 μm thick, directly next to blood capillaries also with very thin cell membranes. This thinness allows diffusion to be extremely speedy.

Since diffusion only works down a concentration gradient, and the steeper said concentration gradient, the faster diffusion, the concentration gradient between the alveoli and the blood must be kept steep constantly to ensure speedy diffusion. Carbon dioxide is rapidly breathed out, meaning that carbon dioxide transported to the alveoli will be quickly transported into them and breathed out, and deoxygenated blood is constantly kept coming to the alveoli, meaning that oxygen diffuses into it quickly.

See picture: [5]

Root hairs of a flowering plant are also specialized exchange surfaces - they are extensions of the cells that make up the epidermis of a root, and are each around 200-250μm across, providing an enormous total surface area that is in contact with the soil surrounding the root. Both water and mineral ions are absorbed by diffusion and facilitated diffusion/active transport respectively.

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All living cells have something known as a cell membrane. This selectively-permeable membrane controls the exchange of materials, receives hormone messages and is very thin. It can be described as a phospholipid bi-layer - meaning that it's made from phospholipid molecules and has two layers.

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what would happen if CO2 would stop moving across the cell membrane?

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what would happen if CO2 would stop moving across the cell membrane?

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the blood would not be as rich and also the blood would not flow easily.
Oscar velasquez

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there are 6 diff

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What dose cholesterol do for the cell membrane.

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What dose cholesterol do for the cell membrane.

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Cholesterol is abundant in the cell membrane. Cholesterol help stabilize  the and keep it ridged

by Isaac ferro

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What happens if the protein channel doesn't work?

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What happens if the protein channel doesn't work?

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When the protein channel doesn't work ATP will help and use energy to move the materials inside the protein channel.
Simon Martinez P.7

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What do molecules do during passive transport

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What do molecules do during passive transport

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Molecules spread out from an area of high to low concentration.

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What does active transport do in a cell membrane?

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What does active transport do in a cell membrane?

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They cross the membrane so one part is inside the cell and the other part is outside the cell. When they cross the bilayer, they move molecules and ions in and out of the cell.

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How do proteins act during facilitated diffusion

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How do proteins act during facilitated diffusion

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The proteins act as channels or carriers