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40 Cards in this Set
- Front
- Back
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What is magnification and resolution?
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Magnification of an object is how many times bigger the image is when compared to the objects
Resolution is the minimum distance apart that two objects can be in order for them to appear as separate items. |
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What is cell fractionation?
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The process where cells are broken up and the different organelles they contain are separated out.
Before cell fractionation can begin the cell is placed in cold, isotonic and buffered solution. |
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How does ultracentrifugation work?
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Before ultracentrifugation the cells are broken up by a homogeniser (blender). This releases the organelles from the cell and the resultant fluid is called homogenate.
Ultracentrifugation is a process by which the fragments in the filtered homogenate are separated by a machine called an ultracentrifuge. Process is as follows: 1) The tube with filtered homogenate is placed in an ultracentrifuge and is spun slowly, the heaviest organelle falls to the bottom and leave the fluid with other organelles at the top (supernatant). 2) The supernatant is removed and can be spun again at a faster speed and the next heaviest organelle fall to the bottom. The process can be continued to separate out all the organelles. |
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How do electron microscopes work?
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Two types of electron microscope SEM and TEM.
Electron microscopes use a beam of electrons instead of light and the advantages of this are that the electron beam has a very short wavelength and the microscope can therefore resolve objects well. As electrons are negatively charged the beam can be focused using electromagnets. Best electron microscopes can resolve objects just 0.1 nm apart. |
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What are the differences between a transmission electron microscope and a scanning electron microspore.
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SEM creates a 3D image and the specimen does not need to be really thin as electrons do not penetrate it. SEM has a lower resolution than TEM.
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What are the limitations of the transmission and scanning electron microscopes?
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- The whole system must be in a vacuum, as air absorbs electrons, and therefore no living specimen can be observed.
- Complex staining process - For TEM the specimen must be extremely thin - The image may contain artefacts |
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What is the structure and function of the nucleus?
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Includes:
- The nuclear envelope; double membrane that surrounds the nucleus, which controls the entry and exit of materials. - Nuclear pores; allow the passage of large molecules - Nucleoplasm; granular, jelly-like material that makes up the bulk of the nucleus. - Chromatin; the DNA found within the nucleoplasm in the form when cell is not dividing. - The nucleolus small spherical body within nucleoplasm which manufactures ribosomal RNA and assembles ribosomes. Functions: - Act as a control centre of the cell (production of mRNA and protein) - Retain the genetic material of the cell (DNA or chromosomes) - Manufacture ribosomal RNA and ribosomes. |
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What is the structure and function of mitochondria?
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Includes:
- A double membrane which surrounds the organelle. The outer one controls the entry and exit of material and inner one is folded into cristae. - Cristae are shelf like extensions of the inner membrane which provide a large surface areas for the attachment of enzymes involved in respiration. - The matrix is a semi-rigid material containing protein, lipids and traces of DNA so it can control the production of their own proteins. Enzymes involved in respirations are also found there. Functions: - Sites of certain stages of respiration therefore responsible for the production of ATP from carbohydrates |
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What is the structure and function of rough endoplasmic reticulum?
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3D system of sheet-like membranes spreading through the cytoplasm of the cell. It is continuous with the outer nuclear membrane, the membranes enclose flattened sacs called cisternae.
Rough ER has ribosomes present on the outer surface of the membranes and it - Provides a large surface area for the synthesis of proteins and glycoproteins. - Provides a pathway for the transport of materials, especially proteins, throughout the cell. Smooth ER lacks ribosomes on its surface area and is often more tubular in appearance, it - Synthesises, stores and transports lipids and carbohydrates. |
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What is the structure and function of the Golgi apparatus?
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Similar to SER in structure but more compact. It consists of a stack of membranes that make up cisternae with small rounded hollowed structures called vesicles.
Functions: - Add carbohydrate to proteins to form glycoproteins - Produce secretory enzymes, such as those secreted by the pancreas - Secrete carbohydrates such as those used in making cell walls in plants - Transport, modify and store lipids - Form lysosomes |
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What is the structure and function of lysosomes?
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Lysosomes are formed when the vesicle from Golgi apparatus contains an enzyme. Lysosomes isolate the potentially harmful enzymes from the rest of the cell.
Functions: - Break down material ingested by phagocytic cells. - Release enzymes to the outside of the cell in order to destroy material around the cell. - Digest worn out organelles so that the useful chemical they are made of can be re-used. - Completely break down cells after they have died. |
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What is the structure and function of microvilli?
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Microvilli are finger-like projections of the epithelial cell that increase its surface area to allow more efficient absorption.
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What can the ultrastructure of a cell indicate about its functions?
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As each organelle has its own function it is possible to deduce the role of the cell by looking at the number and size of the organelles it contains.
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How are triglycerides formed?
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They consist of three fatty acids combined with glycerol. Each fatty acid forms a bond with glycerol in a condensation reaction.
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How can fatty acids vary?
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There are over 70 fatty acids and all have a carboxyl group with a hydrocarbon chain attached. If this chain has no carbon-carbon double bond then it is described as saturated if there is a single double bond it is mono-unsaturated and if there is more than one double bond it is polyunsaturated.
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What is the structure of a phospholipid?
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Phospholipids are similar to lipids except one of the fatty acids is replaced by a phosphate molecule. A phospholipid is made up of a hydrophilic head and hydrophobic tail. the hydrophilic head interacts with water but not with fat whereas the hydrophobic tail interacts with fat but not water.
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How is the presence of a lipid identified?
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Test for Lipids:
1) Add the sample to be tested to alcohol. 2) Shake the tube thoroughly to dissolve any lipid in the sample. 3) Add water and shake gently. A cloudy-white colour indicates the presence of a lipid. |
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What is the structure of the cell surface membrane?
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The cell surface membrane has a bilayer of phospholipids, extrinsic proteins and intrinsic proteins. The hydrophobic tails of both layers of phospholipids point into the centre of the membrane protecting them from water.
Extrinsic proteins occur either on the surface of the bilayer of are partially embedded into it. They provide mechanical support. Intrinsic proteins completely span the phospholipid bilayer from one side to the other. Some act as carriers while others are enzymes. |
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What are the functions of the various components of the cell-surface membrane?
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Phospholipid functions:
- Allow lipid-soluble substances to enter and leave the cell - Prevent water-soluble substances entering and leaving cell - Make the membrane flexible Protein Functions: - 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 by identifying cells - Help cells adhere together - Act as receptors, e.g. hormones |
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What is the fluid-mosaic model?
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The way the molecules are combined to form the cell-surface membrane is called fluid-mosaic model because:
- Fluid as the individual phospholipid molecules can move relative to one another Mosaic as the proteins that are embedded in the phospholipid bilayer vary in shape size and patter. |
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What is diffusion and how does it occur?
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Diffusion is the net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower.
The particles collide randomly due to the kinetic energy they posses and after a short time the collisions cause the particles to spread out evenly. |
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What affects the rate of diffusion?
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Diffusion is affected by the:
- Concentration gradient - Area over which diffusion takes place - Thickness of the exchange surface |
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How does facilitated diffusion differ from diffusion?
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Like diffusion it occurs down a concentration gradient but it differs in that it occurs at specific points on the plasma membrane where there are special protein molecules.
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What is osmosis?
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It is 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?
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The water potential of pure water is 0.
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What is the effect of solutes on water potential?
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The addition of a solute to water will lower its water potential, the more solute added the lower (more negative) its water potential.
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How does water potential affect water movement?
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Water will move by osmosis from a region of higher water potential to one of lower water potential.
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What is the result of placing animal cells and plant cells into pure water?
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The water from the solution will move into the plant cell to try to balance the water potential and it will cause the animal cell to swell and finally burst open.
The water will move from the solution into the plant cell and will cause the protoplast to be pushed against the cell wall and the cell to become turgid, this cell however will not burst open as it has the cell wall which protects it from doing so. |
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What is active transport?
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The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using energy and carrier molecules.
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What does active transport require to take place?
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- It requires metabolic energy in form of ATP.
- Carrier protein molecules which act as pumps. |
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What part do villi and microvilli play in absorption?
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- They increase the surface area for diffusion.
- They are very thin thus reduce the area over which diffusion takes place. - They are able to move and so help to maintain a diffusion gradient. - They are well supplied with blood vessels so that blood can carry away absorbed molecules and hence maintain a diffusion gradient. |
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How are the products of carbohydrate digestion absorbed in the small intestine?
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As carbohydrates are being digested continuously, there is normally a greater concentration of glucose within the small intestine than in the blood, therefore there is a concentration gradient down which glucose diffuses from the lumen of the small intestine into the blood. The blood is constantly circulated so the glucose is constantly removed and the concentration gradient is kept steep. Another way to maintain the gradient is the contractions of villi, they contain muscles that regularly contract and relax mixing the contents of the small intestine so a new, rich in glucose food replaces the food from which glucose was already absorbed.
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What are the roles of diffusion, active transport and co-transport in the process?
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At some point we will no longer be able to absorb glucose through diffusion as the concentrations inside the small intestine and outside will be equal so some glucose would be lost as we wouldn't absorb it. This is prevented by active-transport of glucose.
The actual mechanism is also an example of co-transport as glucose is absorbed along with another molecule. 1) Sodium are actively transported out of the epithelial cells by the sodium-potassium pump into the blood. 2) There is now a much higher concentration of the sodium ions in the lumen of the intestine than in the epithelial cells. 3) Now the sodium ions can diffuse back into the epithelial cell using a protein carrier but as they go through the protein carrier they couple with glucose so both molecules diffuse through. This way all the glucose in the lumen is absorbed. |
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What are prokaryotic cells?
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A cell of an organism belonging to the kingdom Prokaryotae that is characterised by lacking a nucleus and membrane-bound organelles. Examples include bacteria.
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How do prokaryotes differ from eukaryotes?
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- No true nucleus
- No nucleolus - Circular strands of DNA but no chromosomes - No membrane-bounded organelles - No chloroplasts - Ribosomes are smaller (70S) - No endoplasmic reticulum or associated Golgi apparatus or lysosomes - Cell wall made of peptidoglycan (in plants made out of cellulose) |
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What causes cholera and how does it produce the symptoms?
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Cholera is caused by a bacteria- vibrio cholera.
When the bacteria is ingested most of it is killed by acidic conditions in the stomach but some survive. These bacteria reach the small intestine where they use their flagella to propel through the mucus lining. Then they start producing a toxic protein which has two parts. One part binds to specific carbohydrate receptor (which are only present in the small intestine) and the other part enters the epithelial cells. This causes the ion channels of the cell-surface membrane to open and the chloride ions flood into the lumen of the intestine. This dramatically lowers the water potential of the lumen of the intestine so the water from the cells surrounding the intestine moves by osmosis into the lumen to balance out the water potential and this causes the diarrhoea and dehydration. |
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What is oral rehydration therapy and how does it work?
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Oral rehydration therapy is created in order to rehydrate the patient and replace any lost ions.
It consists of: - water; to rehydrate the tissues - sodium; to replace the lost sodium ions and to make the optimum use of sodium-glucose carrier proteins - glucose; to stimulate the uptake of sodium ions and to provide energy - potassium; to replace the lost potassium ions and stimulate appetite - other electrolytes- to prevent electrolyte imbalance |
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How have more effective rehydration solutions been developed?
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Early rehydration therapies lead to side effects especially in children (excess sodium), then new mixtures were tested and their limitations were improved each time until they came up with one which works best.
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What are the advantages of using starch in place of some glucose in rehydration solutions?
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Starch is large, insoluble molecule that consequently has no osmotic effect. It is however broken down steadily by amylase and maltase in the small intestine into its monomers- glucose. This allowed the glucose to be absorbed as it is produced without affecting the water potential.
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How do drug trials follow a regulated set of ethical procedures?
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1) A small number of usually healthy people are given a small amount of the drug to test for side-effects. The dose may be increased gradually.
2) The drug is given to a slightly bigger group of people with the condition the drug is designed to treat. This is to check if the drug works and if there are any side effects. 3) A large scale trial takes place, many are given a placebo and often a double-blind trial occurs (neither the patient or scientist know who is given a placebo). 4) If the drug passes all these stages it may granted a licence but its use and effects are still monitored over many years to check for any long term effects. |
