Mod 1: Cells 1.1.2 Cell Membranes

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What are the roles of membranes within cells?
Seperate compartments of a cell, making functions more efficient e.g. substances for respiration kept in the mitochondria. Some are folded to increase S/A, to make chemical reactions faster. To form vesicles for transporting substances within cell.
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What are the roles of membranes at the surface of cells?
Plasma membranes- control what enters/leaves the cell. Substances can move across membrane via osmosis, diffusion or active transport. Allows recognition by other cells and cell communication
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What is meant by a partially permeable membrane?
Partially permeable- (only lets certain molecules through).
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Describe the structure of the fluid mosaic model.
Phospholipid molecules form continuous 'fluid' bilayer (constantly moving). Contains cholesterol, protein molecules, some proteins and lipids with polysaccharide (carbohydrate) chains attatched form glycoproteins and glycolipids.
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What are the roles of phospholipids in a cell membrane?
Form a barrier to dissolved substances. Hydrophilic head and hydrophobic tail. Heads face out towards water, eitherside of membrane. Tails form centre of bilayer- doesn't allow water-soluable substances (ions) through.
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What is the role of cholesterol within the cell membrane?
Gives membrane stability. Type of lipid- present in all cell membranes except bacteria. Fit inbetween phospholipids. Bind to hydrophobic tails to make membrane less fluid and more rigid.
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What are the roles of proteins in the cell membrane?
2 types. Protein channels- allow small/charged particles through. Carrier proteins- transport molecules and ions across membrane via active transport & facilitated diffusion. Both act as receptors for molecules in cell signalling.
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What are the main roles of glycoproteins and glycolipids?
Stabalise the membrane by forming hydrogen bonds with surrounding water molecules.Sites where drugs, hormones & antibodies bind. Also antigens (involved in immune responses).
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What is the effect of changing temperature on membrane structure and permeability?
Temp below 0- no energy, rigid membrane. Channel/carrier proteins denature, increases permeability (ice crystals). Temp above 45- bilayer melts (breaks down), more permeable. Water expands inside=pressure on membrane. Cannel/carrier proteins denature
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Explain the term cell signalling.
How cells communicate with each other to control processes or respond to changes in environment. One cell releases a messenger molecule, it travels to another cell, is detected by that cell by binding to that cells receptor.
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What is the role of membrane-bound receptors as sites where hormones and drugs can bind?
To trigger a response in cell, or block the receptor and prevent it functioning. E.g. Antihistamines. Receptor proteins have specific shapes for messenger molecules with a complementary shape- target cells.
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What is meant by passive transport?
Diffusion- net movement of particles from high conct to low conct. Particles will continue to move until they are evenly distributed on either side (liquid/gas). Particles always move down concentration gradient. No energy is required.
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What is facilitated diffusion and its role in membrane proteins?
No energy, uses proteins to carry larger molecules across membrane. Carrier-large molecule attatches to carrier protein, protein changes shape, releases molecule on otherside of membrane. Channel- form pores for charged particles to diffuse through.
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What is the role of active transport in membranes?
Moves substances against concentration gradient. Carrier proteins- same process as facilitated diffusion but requires energy (ATP)
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What is Endocytosis?
Much larger molecules are engulfed by a section of the cells plasma membrane, then pinches off to form a vesicle around the ingested substance so that it can be transported within the cell e.g. phagocytes.
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What is Exocytosis?
Cells secrete substances, vesicles containing a substance pinch off from sacs of Golgi, move to plasma membrane. Vesicle fuses with membrane and releases it's contents outside. Some used within the plasma membrane.
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Explain what is meant by osmosis, in terms of water potential.
The likelihood of water molecules to diffuse in/out a solution. The diffusion (net movement) of water molecules across partially permeable membranes, from area of higher water potential to area of lower wate potential. Pure water=0%
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What effects can solutions of various water potentials have upon animal cells?
Hypotonic solution (higher water P), water moves into cell, cell bursts. Isotonic solution- equal water potential, cell stays same. Hypertonic solution- (lower water P) water moves out of cell, cell shrinks becomes plasmolysed.
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What effects can solutions of various water potentials have upon plant cells?
Hypotonic solution- water moves into cell, vacuole swells, cytoplasm pushes against cell wall, cell becomes trugid. Isotonic solution- equal, cell stays same. Hypertonic solution- water moves out of cell, cell becomes flaccid, plasmolysis.
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Card 2

Front

What are the roles of membranes at the surface of cells?

Back

Plasma membranes- control what enters/leaves the cell. Substances can move across membrane via osmosis, diffusion or active transport. Allows recognition by other cells and cell communication

Card 3

Front

What is meant by a partially permeable membrane?

Back

Preview of the front of card 3

Card 4

Front

Describe the structure of the fluid mosaic model.

Back

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Card 5

Front

What are the roles of phospholipids in a cell membrane?

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Preview of the front of card 5
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