3 cells and movement in and out of them

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  • Created by: Naana
  • Created on: 07-04-15 12:39
What is cell fractionation?
The process where cells are broken up and the different organelles contained in the cell is separated out
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Before cell fractionation can begin, why is the tissue placed in a cold, isotonic and buffered solution?
Cold-to reduce enzyme activity that might break down the organelles. Isotonic- to prevent organelles bursting or shrinking due to osmotic gain or loss of water. Buffered- to maintain constant pH
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How are organelles released from the cell?
Cells are broken up by a homogeniser (blender) which releases the cells organelle. This resultant fluid called the homogenate is created
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Why is the homogenate filtered?
To remove any complete cells or large piece of debris
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What is ultracentrifugation?
The process by which fragments in a filtered homogenate are separated in a machine called an ultracentrifuge. The tubes of homogenate are spun at a very high speed in order to create a centrifugal force
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Why are organelles able to be separated by the ultracentrifuge?
Because they have different densities therefore different speeds of centrifugational force
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What is magnification?
How many times bigger the image is compared to the object
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What is resolution?
Resolution refers to the ability of a microscope to distinguish two separate points
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Why is the electron microscope better than the light microscope?
The light microscope has a long wavelength of light- poor resolution. Whereas the electron beam has a short wavelength – good resolution, and because electrons are negatively charged the beam can be focused using electromagnets
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How does a transmission electron microscope (TEM) work?
TEM’s use electromagnets to focus a beam of electrons, which is then transmitted through the specimen. Denser parts of the specimen absorbs more electrons, which make them look darker on the image produced on the screen
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How does a scanning electron microscope (SEM) work?
SEM’s scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. The image shows the surface of the specimen and can be 3D. SEM’s can be used on thick specime
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What are the disadvantages of TEM’s?
The whole system has to be in a vacuum so living organisms can’t be observed. The image is black and white and 2D- even after a complex staining process. The specimen must be really thin. The preparation of the specimen might result in the image cont
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What are disadvantages of SEM’s?
It has a lower resolution than a TEM and can only be used on non-living specimens
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What is the function of the nucleus?
It controls the activities of the cell through the production of mRNA and hence protein synthesis. It retains genetic information on the form of DNA or chromosomes. The nucleolus makes ribosomal RNA and ribosomes.
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What is the structure of the nucleus?
Nuclear envelope is the double membrane that surround the nucleus- controls the entry and exit of material in and out of the nucleus and contains reactions. Nuclear pores- allow passage of large molecules e.g. mRNA out. Chromatin- the DNA found withi
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What is the function of the mitochondria?
The site of aerobic respiration (with oxygen). They produce ATP (energy) by aerobic respiration. They are found in large numbers in cells that are very active and require a lot of energy
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What is the structure of the mitochondria?
Double membrane- outer -controls the entry and exit of material. Inner- folded to form extensions known as cristae. Cristae-provide large surface area for the attachment of enzymes involved in respiration. Matrix- contains proteins, lipids and traces
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What is the function and structure of rough endoplasmic reticulum?
It has ribosomes studded on its membranes. It provides a large surface area for the synthesis of proteins and glycoproteins. And it provides a pathway for the transport of materials esp proteins throughout the cell
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What is the function and structure of smooth endoplasmic reticulum?
Doesn’t have ribosomes studded and is more tubular. It synthesises, stores and transports lipids and carbohydrates
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What is the function and structure of Golgi apparatus?
A group of fluid- filled flattened sacs. It adds carbohydrates to proteins to form glycoproteins, it produces secretory enzymes, it secretes carbohydrates, it transports/modifies/stores lipids, and it forms lysosomes
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When do lysosomes form and what is its function?
They are formed when the vesicle produced by the Golgi apparatus contains enzymes such as proteases or lipases. Since lysosomes contain digestive enzymes they break down invading cells, digest worn out organelles, and release enzymes to outside of th
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What is the structure and function of microvilli?
They are finger like projections of the epithelial cell that increase its surface area to allow more efficient absorption
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How are triglycerides formed?
When three fatty acids combine with a glycerol molecule. Each fatty acid forms a ester bond with glycerol in a condensation reaction
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How can fatty acids vary?
It can either be saturated – with single carbon- carbon bonds, or it can be unsaturated with one double bond (mono-unsaturated) or more than one double bond (poly-unsaturated)
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How are phospholipids formed, and where is this lipid found?
When two fatty acids and one phosphate molecule combine with a glycerol molecule by condensation reactions. Fatty acids form ester bond with glycerol, whereas phosphate molecule forms a phosphoester bond with glycerol. Phospholipids are found in plas
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How is the presence of a lipid identified?
Using the emulsion test. Add 2 cm3 of the sample being tested into a test tube. And then add 5 cm3 ethanol and shake the test tube to dissolve any lipids. Add 5 cm3 of water and shake. A cloudy white colour indicates presence of lipid
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What are the components of a phospholipid?
A phosphate head which is hydrophilic (water loving) and a fatty acid tail which is hydrophobic (water hating). They form a phospholipid bilayer.
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What substances does the plasma membrane allow to pass through?
Non polar, small and lipid soluble
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What is the difference between extrinsic and intrinsic proteins?
Extrinsic proteins are only partly embedded in the phospholipid bilayer, whereas intrinsic proteins completely span the phospholipid bilayer from one side to the other
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Why is the plasma membrane describes as a fluid mosaic model?
Fluid- because the individual phospholipids can move relative to one another and are constantly moving. Mosaic-because the proteins embedded vary in shape, size and pattern
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What is the role of cholesterol in the plasma membrane?
It made the plasma membrane more rigid and less fluid and so prevents the plasma membrane from breaking up
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What are the functions of the proteins in the membrane?
To provide structural support, to act as carriers, to allow active transport across the membrane, to form recognition sites by identifying cells and to act as receptors
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What is diffusion?
The net movement of molecules or ions from an area of higher concentration to an area of lower concentration (down a concentration gradient)
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What factors affect the rate of diffusion?
Concentration gradient- the greater in the difference in concentration of molecules on either side of the exchange surface, the faster the rate of diffusion. Surface area-the larger the surface area, the faster the rate of diffusion. Thickness of exc
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What is facilitated diffusion?
The diffusion of large, charged or water soluble molecules using carrier or channel proteins
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What does 'diffusion is passive' mean?
It means that the energy comes from the natural inbuilt motion of particles rather than an external source
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What is osmosis?
The passage of water across a partially permeable membrane from an area of higher water potential to an area of lower water potential (down a water potential gradient)
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What is the water potential of pure water?
The water potential of water is zero. Pure water has the highest water potential
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How does adding a solute to pure water affects its water potential?
Adding a solute to pure water will lower the pure water's water potential. The water potential will become more negative as the amount of solute added increases.
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What is the result of placing an animal cells into pure water?
Animal cells have a lower water potential than pure water, as they contain a variety of dissolved solutes, so water will move in by osmosis. The movement of water into the cell will cause the cell to burst and release its contents as the cell surfac
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What is the result of placing an animal cell into a solution with a lower water potential?
Water will leave the cell by osmosis and cause the cell to shrink and become shrivelled
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What is the result of placing a plant into pure water?
Plant cells have a lower water potential than pure water so water will move in by osmosis. The movement of water into the cell will cause the plant cell to swell up. The protoplast will be pushed up against the cell wall however the rigid cellulose
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What is active transport?
The movement of molecules or ions into or out of a cell from an area of lower concentration to an area of higher concentration (against a concentration gradient)
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What is needed in order for active transport to take place?
Metabolic energy in the from of ATP is needed. Carrier proteins which act as pumps are needed.
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What properties do villi and microvilli have which allow them to increase the efficiency of absorption?
They increase the surface area for diffusion, they are very thin walled-short pathway to diffusion, they are able to move so they help maintain a steep concentration gradient, they are well supplied with blood vessels so the blood can carry away abso
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How is the cholera bacterium able transmitted?
It is transmitted by the ingestion of water that has been contaminated with faecal material containing the pathogen
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How is the cholera bacterium able to produce a toxin?
Almost all of the cholera bacterium ingested by humans are killed by the acidic condition of the stomach. However, when the surviving bacteria reach the small intestine they are able to propel themselves through the mucus lining of the intestinal wal
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How does the toxin produced by the cholera bacterium cause the water potential in the lumen to lower?
The toxin enters the epithelial cell. This causes the chloride ion channels of the cell surface membrane to open. This causes the chloride ions to move from the epithelial cell into the lumen of the small intestine, which lowers the water potential o
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How does the loss of chloride ions from the epithelial cells cause diarrhoea and dehydration?
The loss of chloride ions causes from the epithelial cells, causes the epithelial cell to have a higher water potential than the lumen so water moves into the lumen by osmosis. Also, water moves into the epithelial cell from the blood by osmosis as a
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What is an oral rehydration therapy?
This is when a patient is given an oral rehydration solution which is a drink that contains water, glucose, chloride ion, sodium ions and potassium ions.
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Other cards in this set

Card 2

Front

Before cell fractionation can begin, why is the tissue placed in a cold, isotonic and buffered solution?

Back

Cold-to reduce enzyme activity that might break down the organelles. Isotonic- to prevent organelles bursting or shrinking due to osmotic gain or loss of water. Buffered- to maintain constant pH

Card 3

Front

How are organelles released from the cell?

Back

Preview of the front of card 3

Card 4

Front

Why is the homogenate filtered?

Back

Preview of the front of card 4

Card 5

Front

What is ultracentrifugation?

Back

Preview of the front of card 5
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