Unit 1- Section 3 Cell Structure And Membranes Flashcards
0
Q
What’s the difference between prokaryotic cells and eukaryotic?
A
Eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are simpler, for example, bacteria
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Q
What are the two types of cells?
A
Prokaryotic cells and eukaryotic cells
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Q
What are organelles?
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They are part of cells and each one has a specific function.
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Q
How can you see organelles?
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Through an electron microscope. You can see the organelles and the internal structure of most of them
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Q
Describe a plasma membrane
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It’s the membrane found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells. They’re made up of mainly lipids and proteins
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Q
What’s the function of plasma membrane?
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It regulates the movement of substances into and out of the cell. It also has receptor molecules on it that allow it to respond to chemicals like hormones
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Q
Describe microvilli
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They are folds in the plasma membrane,
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Q
What’s the function of microvilli?
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They are found on cells involved in the process like absorption, such as epithelial cells in the small intestine. They increase the surface area of the plasma membrane
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Q
Describe the nucleus
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It is a large organelle that is surrounded by a nuclear envelope(double membrane) which contains many pores. The nucleus contains chromatin and often a structure called the nucleolus
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Q
What’s the function of a nucleus?
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Chromatin is made from proteins and DNA, (DNA controls the cells activities) the pores allow substances to move between the nucleus and cytoplasm p, the nucleolus makes ribosomes
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Q
Describe lysosomes
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A round organelle that is surrounded by a membrane, it has my clear internal structure
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Q
What is the function of lysosomes?
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It contains digestive enzymes, these are kept separate from the cytoplasm by the surrounding membrane, it can be used to digest invading cells or to break down worn out components of the cell
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Q
Describe a ribosome
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A very small organelle that floats free in the cytoplasm or is attached to the rough endoplasmic reticulum
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Q
What is the function of ribosomes?
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Protein synthesis
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Q
Describe the endoplasmic reticulum
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There are two types:
Smooth: it’s a system of membranes enclosing a fluid filled space
Rough: it is similar but is covered in ribosomes
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Q
What are the functions of endoplasmic reticulum?
A
Smooth: it synthesises and processes lipids
Rough: folds and process proteins that have been made at the ribosomes
16
Q
Describe Golgi apparatus
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Group of fluid filled flattened sacs
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Q
What is the function of Golgi apparatus?
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It processes and packages new lipids and proteins, which are transported elsewhere by vesicles (membrane bound sacs) it also makes lysosomes
18
Q
Describe mitochondrion
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They’re usually oval shaped and have a double membrane. The inner one is folded to form the structures called cristae. Inside the matrix, which contains enzymes involved in respiration
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Q
What’s the function of mitochondrion?
A
The site of aerobic respiration, which produces ATP. A common energy source in the cell. Mitochondria are found in large numbers in cells and are very active which means they require a lot of energy
20
Q
Cell function and organelles of an epithelial cells
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The walls of the small intestine have lots of villi to increase surface area
The cells on the surface if the villi have microvilli to increase the surface area more
They also have lots of mitochondria to provide energy for the transport of digested food molecules into the cell
21
Q
Cells function and organelles of red blood cells
A
They are adapted to carry oxygen around the body, they have no nucleus to make more room for haemoglobin that carries oxygen
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Q
Cell function and organelles of sperm cells
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Lots of mitochondria to provide large amounts of energy to propel themselves towards the egg
23
Q
What’s the equation to work out magnification of a cell?
A
Magnification= length of image%length of specimen
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When calculating magnification what must you ensure?
All lengths are in the same units (all in mm)
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What is a micrometre (um) in mm?
0.001mm so you would divide it by 1000 to get it into mm
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What is a nanometre (nm) in mm?
0.000001 so you would divide it by 1,000,000
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What is the resoluton?
It is how detailed the image is, it's how well a microscope distinguishes between two points that are close together. If a microscope lens can't separate two objects, then increasing the magnification will not help
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What is a light microscope?
They use light
Have a lower resolution then electron microscopes. They have a maximum resolution of about 0.2 micrometers. The maximum useful magnification of a light microscope is about X 1500
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What is an electron microscope?
They use electrons instead of light to form an image.
Higher resolution than light microscopes so give a more detailed image
They have a much higher magnification
Produce black and white images, these are often coloured using a computer
The images can sometimes contain artefacts left over from preparing the specimen so they can affect the clarity and reliability of the image
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What is a transmission electron microscope? (TEM's)
They use electromagnets to focus a beam of electrons, which is then transmitted through the specimen. Denser parts of the specimen absorb more electrons which make them look darker on the image
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Positives about transmission electron microscopes
High resolution image so you can look and smaller objects
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Disadvantages of transmission electron microscope
Got to view the specimen in a vacuum so you cannot look at living organisms. Only work on thin specimens
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What is a scanning electron microscope? (SEMs)
Scan a beam of electrons across the specims, this knocks off electrons from the specimen which are gathered in a cathode ray tube to form an image.
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Advantages of scanning electron microscope
Images can be 3D
| Used on thick specimens
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Disadvantages of scanning electron microscope
Lower resolution image and still can't be used on living organisms
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What is homogenisation?
It is the breaking down of cells. It can be done in several ways, vibrating the cells or grinding them up in a blender. This breaks up the plasma membrane and releases the organelles into a solution
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Why does the solution for homogenisation have to be kept ice cold?
Reduce the activity of enzymes that may break down the organelles
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Why does the solution for homogenisation have to be isotonic?
Same concentration of chemicals as the cells being broken down. it's prevents the organelles bursting of shrivelling due to osmosis
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What three processes are involved in cell fractionation?
1) homogenisation
2) filtration
3) ultracentrifugation
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What is involved during filtration?
Next the homogenised cell solution is filtered through a gauze to separate any large cell debris or tissue debris, like connective tissue, from the organelles.
The organelles are much smaller than the debris, so they pass through the gauze
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What is involved in ultracentrifugation?
The cell fragments are poured into a tube, it's put into a centrifuge and is spun at a low speed. The heaviest organelles, like nuclei, get flung to the bottom of the tube by the centrifuge. They form a thick sediment at the bottom, the pellet. The rest of the organelles stay suspended in the fluid above the sediment.
The supernatant is drained off and poured into another tube, it's spun in the centrifuge at a higher speed. Heavier organelles like mitochondria sink to the bottom. It's them drained and spun at a much higher speed
This process is repeated at higher and higher speeds until all of the organelles are separated
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What is the order of the ultracentrifugation?
Nuclei, mitochondria, lysosomes, endoplasmic reticulum and then ribosomes.
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What are the functions of the plasma membrane?
Control what substances that enter and leave the cell. The membrane also plays an important role in cell communication and recognition
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What's the structure of the plasma membrane?
Composed of phospholipids, proteins and carbohydrates
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What is the bilayer?
The phospholipids from a continuous double layer (bilayer). This layer is fluid because the phospholipids are constantly moving. Protein molecules are scattered through the layer, like tiles in a mosaic
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In a phospholipid what is the head and tail
Head is hydrophilic and the tail is hydrophobic
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How does the fluid mosaic model controls entry and exits of a cell?
Some proteins in the membrane allow the passage of large of charged water-soluble substances that would otherwise find it difficult to cross the membrane. Different cells have different proteins to carry out this function eg. The membrane of a nerve cell has sodium-potassium carrier proteins (help to conduct nerve impulses) and muscle cells have calcium protein channels which are needed for muscle contraction
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How does the bilayer form a barrier against water-soluble substances?
Phospholipid molecules have a head and a tail, the head is hydrophilic and it attracts water. The tail is hydrophobic and repels water
The molecules automatically arrange themselves into a bilayer, the heads face out wards and tails inwards, the centre of the bilayer is hydrophobic so the membrane does not allow water-soluble substances through so it creates a barrier to water-soluble substances
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How does the bilayer allow cell communication?
Membranes contain receptor proteins, these allow the cell to detect chemicals released from other cells. The chemicals signal to the cell to respond in some way. For example, the hormone insulin binds to receptors in the membranes the liver cells, this tells the liver cells to absorb the glucose. This communication is vital for the body to function properly, different cells have different receptors present in their membranes
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How does the bilayer allow cell regonition?
Some proteins and lipids in the plasma membrane have short carbohydrate chains attached to them. They're called glycoproteins and glycolipids. These molecules tell white blood cells that the cell is their own. White blood cells only attack cells that they don't recognise as itsself
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Why is the bilayer fluid?
The phospholipids in the plasma membrane make the bilayer quite fluid. Cholesterol molecules fit in between the phospholipids and reduce membrane fluidity. The more cholesterol molecules there are, the less fluid the membrane becomes. Cholesterol is important as it makes the cell membrane more rigid and prevents it from breaking up
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What are the five properties of the bilayer?
1) controls entry and exit of cells
2) forms a barrier against water-soluble substances
3) allow cell communication
4) allows cell recognition
5) is a fluid
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What are triglycerides?
One molecule of glycerol with three fatty acids attached to it. Fatty acid molecules have long tails made of hydrocarbons. The tails are hydrophobic (repel water) these tails make lipids insoluble in water
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What is the basic structure of fatty acids?
Carbon atom links fatty acid to glycerol. Variable R group hydrocarbon tail
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What is the difference in two fatty acids?
Hydrocarbon tails
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What is a saturated fatty acid?
They do not have any double bonds between their carbon atoms, the fatty acid is saturated with hydrogen
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What is a unsaturated fatty acid?
They have double bonds between carbon atoms which cause the chain to kink. Have an unsaturated hydrocarbon tail
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What is the formation of triglycerides?
They are formed by a condensation reaction. An ester bond is formed between the two molecules, releasing a molecule of water. This happens twice more to form a triglyceride
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What is a phospholipid?
The lipids in plasma membranes are mainly phospholipids. Phospholipids are pretty similar to triglycerides except one of the fatty acid molecules is replaces by a phosphate group. The phosphate group is hydrophilic and the fatty acid tails are hydrophobic tails. This is important in a plasma membrane
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What is the emulsion test for?
Lipids
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What happens during the emulsion test?
Shake the test substance with ethanol for about a minute then pour the solution into the water
Any lipid will show out as a milky emulsion, the more lipid that is present the more noticeable the milky colour will be
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What is diffusion?
Diffusion is the net movement of particles, from a higher concentration to an area of lower concentration. Particles move down the concentration gradient
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What process is diffusion?
Passive diffusion. No energy is needed for it to happen. Particles can diffuse across plasma membranes as long as they can move freely through the membrane
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What are the factors affecting the rate of diffusion?
Concentration gradient, the higher it is the faster the rate of diffusion
The thickness of the exchange surface- the thinner the exchange surface the faster the rate of diffusion
The surface area- the larger the surface area the faster the rate of diffusion
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What is osmosis?
Diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential.
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What is water potential?
It's the potential of water molecules to diffuse out of or into a solution
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What does the partially permeable membrane do?
Allows some molecules through it but not all of them
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What is the plasma membrane?
It is partially permeable, water molecules are small and can diffuse easily through the plasma membrane but large solute molecules cannot
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What water potential does pure water have?
0
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Adding salutes to pure water........ The water potential
Lowers the water potential so the water potential is always negative
The more negative the water potential, the stronger the concentration of solutes in the solutions
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If two solutions have the same water potential, what are they?
Isotonic
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Will cells in a isotonic solution gain or lose water?
They won't do any because there is no net movement of water molecules because there is no difference in water potential between the cell and the surrounding solution
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What happens if a cell is placed in a solution that has a higher water potential?
It will swell as water moves into it by osmosis, solutions with a higher water potential compared with the inside of the cell are called hypotonic
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What happens if a cell is placed in a solution that has a lower water potential
It may shrink as water moves out of it by osmosis, solutions with a lower water potential Then the cell is called hypertonic
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What is facilitated diffusion?
Some larger molecules and charged atoms can't diffuse directly through the phospholipid bilayer of the cell membrane. Instead they diffuse through proteins in the cell membrane
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How is facilitated diffusion similar to diffusion?
It moves particles down a concentration gradient, from a higher concentration to the lower concentration. It's also a passive process, it does not use energy. There are two types of protein involved, carrier proteins and protein channels
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What are carrier proteins?
They move large molecules into or out of the cell down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules.
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How does carrier proteins work?
A large molecule attaches to a carrier protein in the cell membrane. Then the protein changes shape. This releases the molecule on the opposite side of the membrane
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What are protein channels?
They form pores in the membrane for charged particles to diffuse through, down their concentration gradient. Different protein channels facilitate the diffusion of different charger particles
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What is active transport?
Active transport uses energy to move molecules and ions across plasma membranes, against the concentration gradient. Carrier proteins and co-transporters are involved in active transport
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How are carrier proteins used in active transport?
The process is pretty similar to facilitated diffusion, a molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane releasing it onto the other side. The only difference is that energy is used (ATP) to move the solute against the concentration gradient
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How are co-transporters used in active transport?
They are a type of carrier protein, they bind two molecules at a time. The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient.
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Describe diffusion
- net movement of particles from an area do higher concentration to an area of lower concentration
- passive process, does not require energy
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Describe osmosis
- movement of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
- passive process, does not require energy
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Describe facilitated diffusion.
- net movement of particles from an area do higher concentration to an area of lower concentration
- uses carrier proteins and protein channels to aid the diffusion of large molecules and charged atoms through the plasma membrane
- passive process, does not require energy
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Describe active transport
- movement of molecules against a concentration gradient
- uses carrier proteins and co-transporters to transport molecules
- active process, requires energy
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Example of these processes, absorption of glucose. What are the two stages?
Diffusion into the blood- when carbohydrates are first broken down, there is a higher concentration of glucose in the small intestine rather than the blood. There is a concentration gradient. Glucose then moves across the epithelial cells of the small intestine into the blood by diffusion. When the concentration in the lumen becomes lower than in the blood diffusion stops
Stage 2- active transport. The remaining glucose is absorbed by active transport with sodium ions
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Describe the 3 steps included on the active transport with the absorption of glucose
Step 1- sodium ions are actively transported out of the small intestine epithelial cells into the blood by the sodium-potassium pump. This creates a concentration gradient. There is now a higher concentration of sodium ions in the small intestine lumen than in the cell
Step 2- this causes sodium ions to diffuse from the small intestine lumen into the cell down their concentration gradient, they do this via the sodium-glucose co-transporter proteins. The co-transporter carries glucose into the cell with the sodium, as a result the concentration of glucose inside the cell increases
Step 3- glucose diffuses out of the cell, into the blood down the concentration gradient through a protein channel, by facilitated diffusion
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What is cholera?
It is a disease cause by the bacteria vibrio cholerae, a prokaryotic organism. The bacteria infect the small intestine and produce a toxin that disrupts osmosis in the intestinal cells. This results I'm watery diarrhoea and vomiting
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How is cholera spread?
Contaminated food and water, is common in developing countries where there are overcrowded populations and small places, poor sanitation.
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What is the prokaryotic cell structure?
Single celled organisms.
Plasma membrane made of lipids and proteins-controls entry and exit of cell
Cell wall- supports cell
Capsule- protect the bacteria from attack of immune system
Plasmids- small loops of DNA that aren't present in the chromosomes
COILED DNA- contains genes and is coiled up into a long strand
Flagellum- rotates bacteria
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How does the cholera toxin infect the body?
- toxin causes the chloride ion protein channels in the plasma membranes of the small intestine epithelial cells to open
- chloride ions move into the small intestine lumen, the build up of chloride ions lowers the water potential of the lumen
- water moves out of the blood across the epithelial cells and into the small intestine by osmosis
- the massive increase in water secretion into the intestine lumen leads to very bad diarrhoea causing the body to become extremely dehydrated
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How do you treat cholera?
People suffering from the disease need to replace the fluid that they have lost in the diarrhoea, the quickest way to do this is by inserting a drip into the versions vein. However not everywhere over the world has this access so oral rehydration solutions are used
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What is an oral rehydration solution?
It is a drink that contains large amounts of salts (sodium and chloride ions) and sugars (glucose and sucrose) dissolved In water.
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Why are sodium ions included in oral rehydration solutions?
Increase glucose absorption
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Why is getting the concentration of the ORS right essential?
Effective treatment
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Advantages of ORS
Very cheap
| Does not require much energy
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How do you test her oral rehydration solutions?
Scientists have to show that it is more effective that the old ORS And it is safe
This is done my clinical testing on humans, there are some ethical issues
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Who do the trials for ORS normally involve?
Children so parents need to decide if they take part. Because the child does not have his own choice so people think this is unethical. But scientists need to use this method
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What do clinical trials normally involve?
Blind trials, this is where some people are given the new drug and some the old. The patients do not know which one they have and some people think this is unethical
When a new ORS is first trialled there is no way of knowing if it will be better than the old one so there is a risk of the person dying from worse treatment in the process
