Cells and movement in and out of them

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  • Created by: r98
  • Created on: 09-05-16 15:53
Why can light microscopes only distinguish between two objects if they are 0.2 micrometres, or further, apart?
Because the wavelengths of light are long.
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Why can an electron microscope distinguish between two objects that are as close together as 0.1 nanometres, but a light microscope can't?
Because electron microscopes use beams of electrons instead of light rays, and the beam of electrons has a shorter wavelength.
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What is the material that's put under a microscope referred to as?
The object.
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What is the appearance of the material when viewed under a microscope referred to as?
The image.
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What is the magnification of an object?
How many times bigger the image is when compared to the object.
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What is the equation for calculating magnification?
magnification = size of image / size of object
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What is the resolution, or resolving power, of a microscope?
The minimum distance apart that two objects can be in order for them to appear as separate items.
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Will increasing the magnification increase the size of an image or increase the resolution?
It will increase the size of the image but not always the resolution, as every microscope has a limit of resolution.
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What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out.
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What is the tissue placed in before cell fractionation begins?
Cold, isotonic, buffered solution.
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Why is the tissue placed in cold solution before cell fractionation?
To reduce enzyme activity that might break down the organelles.
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Why is the tissue placed in isotonic solution before cell fractionation?
To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
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What is an isotonic solution?
A solution that has the same water potential as the original tissue.
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Why is the tissue placed in buffered solution before cell fractionation?
To maintain constant pH.
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What are the 2 stages of cell fractionation?
Homogenation & ultracentrifugation.
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What happens to cells during homogenation?
Cells are broken up by a homogeniser (blender). This releases the organelles from the cell.
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What is the resultant fluid of homogenation called?
Homogenate.
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What happens to the fluid (homogenate) that was the result of the cells being homogenised?
The homogenate is filtered to remove any complete cells and large pieces of debris.
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What happens to the filtered homogenate during ultracentrifugation?
The fragments in the filtered homogenate are separated in a machine called an ultracentrifuge.
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What does an ultracentrifuge do?
It spins tubes of homogenate at very high speed in order to create a centrifugal force
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During ultracentrifugation, are the heaviest or lightest organelles the first to form a thin sediment or pellet at the bottom of the tube? Give an example of this type of organelle.
The heaviest organelles; the nuclei.
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What is the fluid at the top of the tube, that has been placed in a ultracentrifuge, called?
Supernatant.
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What happens to the supernatant after it has been removed from the tube?
It is transferred to another tube and spun in the ultracentrifuge at a faster speed than before.
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After the nuclei, what is the next heaviest organelles?
The mitochondria.
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After the mitochondria, what is the next heaviest organelles?
Lysosomes.
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After lysosomes, what is the next heaviest organelles?
Ribosomes.
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What are the two main advantages of the electron microscope?
Electron beam has a very short wavelength, the microscope can therefore resolve objects well. & as electrons are negatively charged the beam can be focused using electromagnets.
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What has to be created within the chamber of an electron microscope in order for it to work efficiently? Why?
A near-vacuum has to be created, because electrons are absorbed by the molecules in air.
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What are the 2 types of electron microscope?
Transmission electron microscope (TEM) & scanning electron microscope (SEM).
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In a transmission electron microscope, what produces the beam of electrons?
The electron gun.
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In a TEM, how is the beam of electrons focused onto the specimen?
By a condenser electromagnet
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In a TEM, what does the beam of electrons pass through? Why do some parts of the image appear dark and other parts appear bright?
The beam passes through a thin section of the specimen. Parts of this specimen absorb electrons and appear dark. Other parts of the specimen allow electrons to pass through and so appear bright.
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What is the resolving power of a TEM?
0.1 nm.
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What are the 4 main limitations of the TEM?
Whole system must be in a vacuum, so living specimens can't be observed. A complex 'staining' process is required but the image is only in black & white. Specimen must be extremely thin. Image may contain arterfacts.
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In a TEM, why does the specimen have to be extremely thin? Is the resulting image 2-D or 3-D?
To allow electrons to penetrate. Resulting in a flat, 2-D image.
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How is a 3-D image built upfrom photomicrographs using a TEM?
By takihg a series of sections through a specimen. The 3-D image can then be produced by looking at a series of photomicrographs.
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What is the limitation that applies to the TEM but not to the SEM? Why does it not apply to the SEM?
The specimens need not be extremely thin in an SEM because electrons don't penetrate.
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In an SEM, where is the beam of electrons directed to?
On to the surface ofthe specimen from above. The beam is then passed back and forth across a portion of the specimen in a regular pattern.
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What happens to the electrons as they pass over the specimen?
The electrons are scattered by the specimen and the pattern of this specimen depends on the contours of the specimen surface.
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In a SEM, what can be built up by computer analysis of the pattern of scattered electrons secondary electrons produced?
A 3-D image.
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What is the resolving power of a basic SEM?
20 nm.
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Which has a higher resolving power, the TEM or the SEM?
The TEM.
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What does the ultrastructure of a cell refer to?
The internal structure of a cell that suits it for its job.
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Are epithelial cells eukaryotic or prokaryotic cells?
Epithelial cells are eukaryotic cells.
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Do eukaryotic or prokaryotic cells have a distinct nucleus and possess membrane-bounded organelles?
Eukaryotic cells.
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What is the function of epithelial cells?
To absorb and secrete.
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What does the nucleus contain? What is its role? What is its diameter?
It contains the organism's heredutary material and it controls the activities of the cell. It's between 10-20 micrometres in diameter.
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What are the parts that make up a nucleus?
Nuclear envelope, nuclear pores, nucleoplasm, chromatin & the nucleolus.
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What is the structure of the nuclear envelope? What is its role?
It's a double membrane that surrounds the nucleus. It controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it.
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What part of the nucleus allows the passage of large molecules out of the nucleus? What is their dimeter?
Nuclear pores, each 40-100 nm in diameter.
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What is the nucleoplasm?
The granular, jelly-like material that makes up the bulk of the nucleus.
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What is the diffuse form that chromosomes take up when the cell is not dividing?
Chromatin.
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What is chromatin? Where's it found?
It's the DNA found within the nucleoplasm.
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What is the small spherical body within the nucleoplasm? What is its role?
The nucleolus. It manufactures ribosomal RNA and assembles the ribosomes.
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What are the functions of the nucleus?
To act as a control centre of the cell through production of mRNA and hence protein synthesis. Retain the genetic materiaa of the cell in the form of DNA or chromosome. Manufacture ribosomal RNA & ribosomes.
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Whatis the shape and length of mitochondria?
They're rod-shaped and 1-10 micrometres in length.
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What structures make up mitochondria?
A double membrane, cristae, & the matrix.
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What is the function of the double membrane?
The outer membrane controls the entry and exit of material. The inner membrane is folded to form extensions known as cristae.
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What are cristae? What is their role?
They're shelf-like extensions of the inner membrane. These provide a large surface area for the attachment of enzymes involved in respiration.
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What is the matrix of mitochondria? What enzymes are found in the matrix?
It's a semi-rigid material containing protein, lipids and traces of DNA that allows the mitochondria to control the production of their own proteins. The enzymes involved in respiration are found in the matrix.
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What do mitochondria produce? From what do they produce this product?
The energy-carrier molecule, ATP. Produced from carbohydrates.
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What is the endoplasmic reticulum (ER)? Is it separate or continuous to the outer nuclear membrane?
A system of sheet-like membranes, spreading through the cytoplasm of the cells. It's continuous with the outer nuclear membrane
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What do the membranes of the ER enclose?
Flattened sacs called cisternae.
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What are the 2 types of ER?
Rough endoplasmic reticulum (RER) & smooth endoplasmic reticulum (SER).
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What does the RER have on the surface of its membrane?
Ribosomes.
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What are the functions of the RER?
Provide a large S.A. for the synthesis of proteins and glycoproteins. Provide a pathway for the transport of materials, espcially proteins, throughout the cell.
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Does the smooth endoplasmic reticulum (SER) have ribosomes on its surface?
No.
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What are the functions of the SER?
Synthesise, store and transport lipids. Synthesise, store and transport carbohydrates.
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Why do cells such as liver cells and secretory cells have a very extensive ER?
Because these cells need to manufacture and store large quantities of carbohydrates, proteins and lipids.
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What other organelle is the Golgi apparatus similar to in structure?
The SER, except that it's more compact.
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What does the Golgi apparatus consist of?
A stackof membranes that make up flattened sacs, or cisternae, with small rounded hollow structures called vesicles.
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What happens to the proteins and lipids produced by the ER? What does the Golgi apparatus do to them?
They're passed through the Golgi apparatus in strict sequence . Thr Golgi modifies these proteins often adding non-protein components (e.g. carbohydrates) to them.
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Apart from modifying proteins and lipids, what else does the Golgi apparatus do to them?
It 'labels' them, allowing them to be accurately sorted and sent to their correct destinations.
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What happens to the lipids and proteins in the Golgi after they have been sorted?
They are transported in vesicles which are regularly pinched off from the ends of the Golgi cisternae. These vesicles move to the cell surface, where they fuse with the membrane & release their contents to the outside.
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What are the functions of the Golgi apparatus?
To add carbohydrates to proteins to form glycoproteins, to produce secretory enzymes, to secrete carbohydrates, to transport modify snd store lipids, to form lysosomes.
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Whar are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases?
Lysosomes.
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What is the role of lysosomes?
They isolate potentially harjful enzymes from the rest of the cell before releasing them to the outside or into a phagocytic vesicle within the cell.
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What are the functions of lysosomes?
To break down material ingested by phagocytic cells (e.g. white blood cells), to release enzymes to the outdide of the cell in order to destroy material around the cell, to digest worn out organelles, to completely break down cells after they've died
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What are ribosomes?
Small cytoplasmic granules in all cells.
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Where is the 80S type of ribosome found?
In eukaryotic cells.
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Where is the 70S type of ribosome found?
In prokaryotic cells.
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What do both the subunits of a ribosome contain? What process are ribosomes involved in?
They contain ribosomal RNA and protein. Ribosomes are important in protein synthesis.
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What are microvilli? Where are microvilli found? What is their role?
They're finger-like projections of the epithelial cell that increase its surface area to allow more efficient absorption.
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How is it possible to deduce the role of a cell?
By looking at the number and size of the organelles it contains.
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Are lipids soluble or insoluble in water?
They're insoluble in water.
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Are lipids soluble or insoluble in organic solvents (e.g. alcohols)?
Soluble.
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What are the 3 main groups of lipids?
Triglycerides (fats and oils), phospholipids, and waxes.
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What is the role of phospholipids in the plasma membrane?
They contribute to the flexibility of the membrane & the transfer of lipid-soluble substances across them.
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What are 4 roles of lipids?
An energy source, waterproofing, insulation, & protection.
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How many fatty acid(s) and glycerol(s) make up a triglyceride?
3 fatty acids combined wwith glycerol.
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Do the fatty acids form bonds with glycerol via condensation reactions or hydrolysis?
Condensation reactions.
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What does hydrolysis of a triglyceride produce?
Glycerol and 3 fatty acids.
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If the fatty acid hydrocarbon chain has no carbon-carbon double bonds, is it saturated or unsaturated?
Saturated.
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If the fatty acid hydrocarbon chain has carbon-carbon double bonds, is it saturated or unsaturated?
Unsaturated.
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Are fats generally made of saturated or unsaturated fatty acids?
Saturated fatty acids.
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Are oils generally made of saturated or unsaturated fatty acids?
Unsaturated fatty acids.
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What two parts make up a phospholipid?
A hydrophilic 'head' which is attracted to water but not fat, & a hydrophobic 'tail' which interacts with fat but not water.
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What is the structure of a phospholipid?
2 fatty acid molecules and one phosphate molecule.
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What is the test for lipids also known as?
The emulsion test.
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How do you carry out the test for lipids?
Place 2cm^3 of sample in a dry, grease-free test-tube & add 5cm^3 of ethanol. Shake the tube to dissolve any lipid in the sample. Add 5cm^3 of water and shake gently.
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What would be the observations for a positive result in a lipids test?
A cloudy-white colour indicates presence of a lipid.
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In the test for lipids, what is used as a control?
Repeat the procedure with water instead of the sample, and the final solution should remain clear.
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What are all the membranes around and within cells known as?
Plasma membranes.
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What do phospholipids forms in the plasma membrane?
A phospholipid bilayer.
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What is the arrangement of phospholipids in the bilayer in membranes?
One layer of phospholipids has its hydrophilic heads pointing inwards & interacts with water in cytoplasm. The other layer has its hydrophilic heads pointing outwards & interacts with water in surrounding cells. The hydrophobic tails point inwards.
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How do lipid-soluble molecules move through the plasma membrane?
Via the phospholipid bilayer.
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What are the functions of phospholipids in the membrane?
To allow lipid-soluble substances to enter & leave the cell, prevents water-soluble substances entering & leaving the cell, makes the membrane more flexible.
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What are the two main ways that proteins are embedded in the phospholipid bilayer?
Extrinsicly (extrinsic proteins) or instrinsicly (intrinsic proteins).
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In the phospholipid bilayer, what is the role of extrinsic proteins?
To give mechanical support to the membrane or, in conjuction with glycolipids, they act as cell receptors.
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In the phospholipid bilayer, what is the role of intrinsic proteins?
To act as carriers to transport water-soluble material across the membrane, and others are enzymes.
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What are the functions of he proteins in the plasma membrane?
To provide structural support, act as carriers transporting water-soluble substances across the membrane, allow active transport across the membrane by forming ion channels, form recognition sites, act as receptors, help cells adhere together.
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What is the arrangement of the molecules in the cell-surface membrane known as?
The fluid-mosaic model.
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Why is the arrangement of the molecules in the cell-surface membrane known as the fluid-mosaic model?
'Fluid' because the individual phospholipid molecules can move relative to one another. 'Mosaic' because the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern.
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What is the definition of diffusion?
The net movement of molecules or ions from a region of high concentration to a region of low concentration.
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What are the 3 factors that affect rate of diffusion?
Concentration gradient, area over which diffusion takes place (surface area), & thickness of exchange surface.
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What is the equation to express what diffusion is proportional to?
(surface area x difference in concentration) / length of diffusion path
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Is facilitated diffusion an active or passive process?
Passive process.
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How is facilitated diffusion similar to diffusion? How does it differ?
It occurs down a concentration gradient, but it differs in that it occurs at specific points on the plasma membrane where there are protein channels.
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What is the role of proteins in facilitated diffusion?
They form water-filled channels (protein channels) across the membrane, allowing only water-soluble ions to pass through. The channels are selective, each opening only in the presence of a specific ion.
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What does the alternative form of facilitated diffusion involve using? (the one that doesn't use protein channels). How does it work?
Uses carrier proteins that span the plasma membrane. A molecule specific to the protein binds to the protein and changes the protein's shape, allowing the molecule to be released to the inside.
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What is the definition of osmosis?
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a partially permeable membrane.
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What is the water potential of pure water?
0.
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Will the water potential of pure water increase or decrease when a solute is added to it?
Decrease; it will lower its water potential.
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What's the definition of active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of a higher concentration using energy and carrier molecules.
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What form of metabolic energy is needed for active transport to take place?
ATP.
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What 3 soluble products are absorbed in the small intestine?
Glucose, fructose & galactose.
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What are the villi lined with?
Epithelial cells on one side, and on the other side is a rich network of blood capillaries.
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What are the four ways that villi increase the efficiency of absorption?
They increase S.A., they're very thin walled (diffusion distance reduced), they're able to move & they're well supplied with blood vessels. (both maintain diffusion gradient).
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What's the difference between villi and microvilli?
Villi are 1mm projections of the wall of the small intestine while microvilli are 0.6 micrometre projections of the cell-surface membrane of the epithelial cells that line this wall.
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How does the villi mix the contents of the small intestine?
The villi contain muscles that regularly contract and relax, mixing the contents of the small intestine.
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As diffusion does not absorb all the glucose form the small intestine, by what other method is glucose absorbed?
By active transport (co-transport).
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What is the process of co-transport in the absorption of glucose from the small intestine?
The conc. of Na+ ions is higher in lumen of intestine than inside the epithelial cells (due to sodium-potassium pump), so Na+ ions, coupled with glucose, diffuse into epithelial cells down this conc. gradient through a different protein carrier.
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During co-transport, which out of Na+ ions and glucose molecules move down their conc, gradient, and which move up (against) their conc gradient?
Sodium ions move down their conc. gradient, & the glucose molecules move up their conc. gradient.
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What bacteria causes cholera?
Vibrio cholerae.
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How do prokaryotic cells differ from eukaryotic cells?
Prokaryotic cells have no true nucleus, only a diffuse area of nuclear material, no nucleolus, circular strands of DNA but no chromosomes, no chloroplasts or ER or Golgi or lysosomes, peptidoglycan cell wall, 70S ribosomes.
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What are the main structures found in a bacterial cell?
Cell wall, capsule, cell-surface membrane, flagellum, circular DNA, plasmid.
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What are the 2 main symptoms of cholera?
Diarrhoea and consequently dehydration.
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How is vibrio cholerae transmitted?
By the igestion of water, or more rarely food, that has been contaminated with faecal material containing this pathogen.
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Once in the small intestine, how does the vibrio cholerae bacteria cause movement of ions?
They use their flagella to propel themselves through the mucus lining of intestinal wall, produce toxic proteins, 1 part binds to specific carb receptors. The toxic part, enters epithelial cells causing ion channels to open, Cl- ions flood into lumen
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What does the loss of chloride ions from epithelial cells lead to? (referring to cholera)
Raises water potential of epithelial cells, water flows from cells into the lumen. Ions then diffuse from tissuees and blood into epithelial cells, causes water to move (osmosis) from blood & tissues to intestines, causing diarrhoea & dehydration.
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How is cholera treated?
By restoring the water and ions that have been lost using oral rehydration therapy.
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Why does the cholera toxin only affect the intestines?
Because only the epithelial cells of the small intestine have the specific carbohydrate receptors that the toxin binds to.
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When treating diarrhoeal diseases, why is just drinking water ineffective?
Water isn't being absorbed from the intestines. The drinking of water doesn't replace the electrolytes (ions) that are being lost from the epithelial cells of the intestine.
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How does oral rehydration therapy (ORT) work?
It uses the alternative Na+ carrier proteins, as sodium ions are obsorbed, the water potential of the cells falls & water enters the cells by osmosis.
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What does a rehydration solution need to contain?
Water, sodim, glucose, potassium, other electrolyte (e.g. chloride and citrate ions).
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Why is starch used in place of some glucose in rehydration solutions?
Starch is a large, insoluble molecule that consequently has no osmotic effect. It's broken down steadily by amylase and maltase to glucose, in the smal intestine.
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How have more effective rehydration solutions been developed?
By experimenting with different concs. of starch and sodium.
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How do drug trials follow a regulated set of ethical procedures?
First a small smaple of healthy people are given a tiny amount of the drug to test for side-effects. Then the drug is given to a larger number of people (with illness), checks drug works & looks at safety issues. Then double-blind trials + placebo.
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What 3 reasons that the results of drug trials published in a scientific journal, before being granted a licence?
To be considered worthy of publication, research must conform to scientific standards. Other scientists can critically review the results (peer review). The experiments/trials can be replicated by others to see if same results can be obtained.
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