Biology digestion flash cards

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  • Created by: I.m
  • Created on: 29-10-12 19:34
What is digestion?
Digestion is the process in which large, insoluble molecules are hydrolysed by enzymes into small, soluble molecules.
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What is amylase?
Amylase is a digestive enzyme that helps break down glycogen, carbohydrates and starches into simple sugars in the digestive system.
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Which two glands produce amylase?
Salivary glands and pancreas
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In humans, in which two stages does digestion take place?
Physical digestion and Chemcial digestion
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Explain physical digestion.
Phsyical digestion is carried out by the mouth. Chewing reduces large chunks of food into smaller pieces. This makes it easier to digest and also increases the total surface area of the food so enzymes have a greater surface area on which to act.
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Explain chemical digestion.
This breaks down large, insoluble moloecule into smaller soluble ones. It is carried out by enzymes. All digestive enzymes function by hydrolysis (splitting of molecules by adding water).
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What is assimilation?
Once large food molecules have been hydolysed they're absorbed into the blood through small intestine. Once inside the bloodstream the simple food molecules can be built up into large molecules to make cells/cell components or broken down for energy.
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How many naturally occurring amino acids are there?
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What elements do all amino acids contain?
All amino acids contain the elements carbon, hydrogen, oxygen and nitrogen. 2 contain the element sulfur.
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What defines an amino acid?
Its R group.
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What is the simplest amino acid and what is its R group?
The simplest amino acid is glycine and the R group is just a single hydrogen atom.
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What do amino acid monomers combine to form?
A dipeptide.
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What type of reaction is the formation of a dipeptide?
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Why is the formation of a dipeptide a condensation reaction?
In the process water is removed.
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What are proteins?
Proteins are polymers made up of amino acid monomers joined by peptide bonds
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What forms the primary structure of any protein?
The sequence of amino acids in a polypeptide chain form the primary structure of the protein.
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What bonds are involved in the primary structure?
Peptide bonds.
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What is the shape of the secondary structure?
The polypeptide chains can coil into an alpha helix or fold into a beta pleated sheet.
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In the secondary structure what is the shape maintained by?
Hydrogen bonds.
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What bonds is the tertiary structure maintained by?
Disulfide bonds (disulphide bridges) – strong bonds, ionic bonds –weak bonds (not involved in forming peptide bonds) and hydrogen bonds - weak interactions which are easily broken by heating.
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What does the quaternary structure consist of?
The quaternary structure is made up of 2 or more polypeptide chains that are linked in various ways and associated non-protein (prosthetic) groups to form a large, complex protein molecule.
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Give two examples of a quaternary structure?
Haemoglobin has a quaternary structure. It consists of 4 polypeptide chains and a prosthetic group (iron containing haem group). Collagen (a fibrous protein) which consist of 3 polypeptide chains that are coiled to from a rope like structure.
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Name the three bonds holding the tertiary structure?
Ionic bonds, disulfide bonds and hydrogen bonds.
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What does a purple colour indicate in a Biuret test?
The presence of peptide bonds.
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What does it mean if the colour of a solution remains blue in a Biuret test?
There are no peptide bonds present.
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What is denaturation?
The loss of the 3D structure of the protein. It results from the breaking of the bonds that maintain the tertiary structure.
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What are the causes of denaturation?
Heat - breaks hydrogen bonds due to the increased energy supply to the molecule (which causes vibrations). Strong acids & alkalis - break ionic bonds. Detergents & solvents - break hydrogen bonds.
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What happens if a protein loses its tertiary structure?
Once a protein loses its tertiary structure it loses its function - this is particularly important in enzymes when the sahpe of the active site is altered and the substrate will no longer fit.
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What structure does a fibrous protein have?
Fibrous proteins are made up of long chains running parallel to each other. The chains are linked by cross bridges and form very stable molecules.
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Give two examples of fibrous proteins.
Collagen and keratin
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Is a fibrous protein soluble or insoluble?
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What kind of function/role does a fibrous protein have?
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What structure is a globular protein?
Tertiary structure which contains alpha helix and beta pleated sheet (it is deeply folded).
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Give three examples of globular proteins.
Enzymes, hormones and antibodies.
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Is a globular protein soluble or insoluble?
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What kind of function/role does a globular protein have?
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What are enzymes?
Enzymes are biological catalysts that speed up the rate of reactions in living organisms without being used up in the reaction themselves.
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What are enzymes made up of?
Enzymes are made up of protein. Enzymes have a complex globular shape with a cleft or depression that usually complements just one substrate or set of substrates. This cleft or depression is called the active site.
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How do enzymes speed up the chemical reactions?
Enzymes speed up chemical reactions by lowering the activation energy. This means that they reduce the amount of energy needed to get the reaction going.
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Why do enzymes increase the rate of reaction?
Enzymes acts as catalysts that lower the activation energy through the formation of enzyme-substrate complexes.
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What are the two things the rate of enzyme controlled reaction measured by?
Amount of product formed or amount of substrate changed.
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What are the main variables that affect the rate of enzyme catalysed rate for reactions?
Temperature, pH, substrate concentration, enzyme concentration and enzyme inhibition.
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Explain what happens during a reaction if the temperature is above the optimum temperature.
Increase in kinetic energy causes enzyme molecules to vibrate= hydrogen bonds break, tertiary structure is destroyed, the enzyme is denatured. Active site changes shape and substrate no longer fits. Fewer enzyme-substrate complexes form --- less prod
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What are buffer solutions used for?
To keep the pH constant during an experiment.
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How does buffer solution keep the pH constant?
It maintains the pH of a solution by absorbing H+ ions if the solution becomes more acidic and releasing H+ ions when the solution become more alkaline.
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What is an enzyme’s maximum turn-over rate in a substrate concentration reaction?
The point where rate of reaction cannot increase any more as all active sites are in use (have become full – saturated).
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What is the limiting factor in a substrate concentration reaction?
The concentration of the enzyme.
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Explain the rate of reaction in substrate concentration.
The rate of reaction is directly proportional to the substrate concentration UNTIL all the enzymes are working at maximum speed.
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Explain the rate of reaction in enzyme concentration.
The rate of reaction is proportional to enzyme concentration if the substrate is in excess.
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If the substrate was not in excess in an enzyme concentration reaction and started to be used up what would happen to the rate of reaction?
It would decrease as there are less substrates and therefore less successful collisions.
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Explain what a competitive inhibitor does.
Competitive inhibitors have a similar shape to substrate.Inhibitor competes with substrate for active site.Inhibitor binds to active site so substrate can no longer fit as active site blocked.Less enzyme-substrate complexes form=rate of reaction less
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What is likely to happen with a low concentration of inhibitor?
Enzyme-substrate complex is still likely to form.
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What is likely to happen with a high concentration of inhibitor?
Enzyme-inhibitor complex is likely to form.
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How can you overcome competitive inhibition?
Inhibition can be overcome by increasing the concentration of the substrate.
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Explain what a non-competitive inhibitor does.
Non-competitive inhibitors bind to the allosteric site of an enzyme causing the active site of the enzyme to change shape so that the substrate can no longer fit. Fewer enzyme-substrate complexes are formed=rate of reaction is reduced.
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What is cyanide?
Cyanide is a non-competitive inhibitor.
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What does cyanide do?
Cyanide attaches to the copper prosthetic group of cytochrome oxidase (involved in respiration) – thereby inhibiting respiration.
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What are non-competitive inhibitors produced from?
Non-competitive inhibitors are often substance produced by a series of chemical reactions inside cells.
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Explain end-product inhibition.
Non-competitive inhibitors are substances produced by a series of chemical reactions inside cells.Each reaction is catalysed by a different enzyme.When enough product formed,it inhibits enzymes at the beginning of the process to slow/stop production.
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What is the advantage of end-product inhibition being non-competitive rather than competitive?
An increase in substrate concentration does not effect the level of end product.
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How many number of sugar units does a monosaccharide have? Give three examples of them.
One and glucose, fructose, galactose.
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How many number of sugar units does a disaccharide have? Give three examples of them.
2 and maltose, sucrose, lactose.
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How many number of sugar units does a polysaccharide have?Give three examples of them.
Many and starch, glycogen, cellulose.
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What does the name of a monosaccharide depend on?
The name monosaccharides are given depends on the number of carbon atoms in their structure.
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Name three monosaccharides.
Glucose, fuctose and galactose.
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What is the name of the monosaccharides that have 3,5 and 6 carbon atoms in their structure?
3= trioses, 5= pentoses and 6= hexoses.
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What are all monosaccharides?
All monosaccharides are reducing sugars.
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Which two forms does glucose exists as?
a-glucose and B-glucose.
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In which medical conditions is it important to test the blood/urine glucose levels?
Diabetes and pregnancy.
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What is used to measure the level of glucose in blood/urine and what kind of test is this?
Clinistix (a glucose *****) which is a qualitative test.
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What is Benedict’s reagent?
Benedict’s reagent is an alkaline solution of copper (II) sulphate. When a reducing sugar is heated with Benedict’s reagent it forms a precipitate of copper (I) oxide
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What is the test for a reducing sugar?
Add Benedict’s reagent to the solution and heat. A negative result is a blue solution and a positive result is the solution turns red.
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How is a disaccharide formed?
Two monosaccharides can combine to form a disaccharide.
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What type of reaction is the formation of a disaccharide?
It is a condensation reaction because a molecule of water is removed.
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What is the bond that is formed when a disaccharide is formed?
The bond that is formed is called a glycosidic bond (C-O-C).
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When does a hydrolysis reaction occur on a disaccharide?
A hydrolysis reaction occurs when energy and water is used to break the glycosidic bond in a disaccharide.
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Name three disaccharides.
Maltose, lactose and sucrose.
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What is the general formula for all disaccharides?
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Which two monosaccharides make the disaccharide maltose?
Glucose and glucose.
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Where is maltose found?
Seeds e.g. wheat or barley.
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Which two monosaccharides make the disaccharide lactose?
Galactose and glucose.
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Where is lactose found?
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Which two monosaccharides make the disaccharide sucrose?
Glucose and fructose.
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Where is sucrose found?
Fruit, sugar cane and sugar beet.
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Which disaccharide is a reducing sugar?
Which disaccharide is not a reducing sugar? Sucrose.
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What is the test for a non-reducing sugar?
To be carried out after a neg result from reducing sugar test. Add HCl to sample of solution in test tube.Heat test tube.Add sodium hydrogencarbonate to neutralise the acid then add Benedict's reagent + heat.Positive result =red.Negative result=blue
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How could you tell if a solution had both reducing and non-reducing sugars present?
Carry out each reducing sugar test and non-reducing sugar test. If the solution is a mixture, both tests will be positive but the non-reducing sugar test will be a darker red. Measure on a colorimeter. (Depth of colour of the precipitate).
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Suggest a way other than comparing colour changes in which different concentrations of reducing sugars could be estimated.
Dry the precipitate in each sample and weigh it. The heavier the precipitate, the more reducing sugar present.
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Explain why it is not possible to distinguish between very concentrated samples of reducing sugars, even though there concentrations are different.
Once all the copper (II) sulphate has been reduced to copper (I) oxide, further amounts of reducing sugar cannot make a difference.
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What are polysaccharides?
Polysaccharides are polymers formed by combining together many monosaccharide molecules.
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What are the three polysaccharides?
Starch, glycogen and cellulose.
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What are the three polysaccharides (starch,glycogen and cellcuose) made up of?
They are all polymers formed from hundreds of glucose units.
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Are polysaccharides soluble or insoluble?
As polysaccharides are very large molecules, they are insoluble.
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What does the insolubility of polysaccharides make them suitable for?
As many polysaccharides are large molecules, they are insoluble. This feature makes them more suitable for storage.
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Which polysaccharide is not used for storage but gives structural support?
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What is the main polysaccharide in our diet?
Starch is the main storage compound in plants and so is the main polysaccharide in our diet.
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What four things do storage compounds need to be?
Storage compounds need to be insoluble, compact, osmotically inactive and easily converted to energy.
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What two compounds is starch a mixture of?
Amylose and amylopectin.
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What type of chains does amylose consists of?
Amylose consists of single, unbranched chains of α glucose.
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What do the single, unbranched chains in amylose form and what is its purpose?
A helix which is a compact structure which allows lots of glucose to be stored in a small place.
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What type of chains does amylopectin consist of?
Amylopectin consists of branched chains of α-glucose molecules.
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What type of bonds does amylose and amylopectin have?
They both have 1,4 and 1,6 glycosidic bonds formed at branching points.
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Where is glucose released from in amylose and amylopectin?
The glucose in these compounds can only be released from the ends of the chains.
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How is glucose provided as a quick source of energy for respiration?
As amylopectin has many branches, glucose can be hydrolysed quickly, providing a quick source of chemical energy for respiration.
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Name the three properties of starch.
Insoluble – due to its large size, osmotically inactive (do not cause movement of water into cells) and compact – due to the spiral/branched structure of the molecule.
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What is the chemical test for starch?
And two drops of iodine solution to sample being tested and shake. A positive result is a blue-black solution and a negative result is a yellow solution.
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How many enzymes does it take to completely break down (digest) starch?
It take more than one enzyme.
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What is starch broken down to?
Starch is broken down to its monomer glucose.
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Which three parts of the digestive system help in starch digestion?
Mouth, pancreas and small intestine.
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How does the mouth help starch digestion?
Salivary amylase released in the mouth hydrolyes starch into maltose.
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How does the pancreas help starch digestion?
The pancreas produces pancreatic amylase which breaks down long starch molecules to maltose (smaller molecules).
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How does the small intestine help starch digestion?
Pancreatic amylase hydrolyses starch into maltose. The small intestine produces maltase which hydrolyses maltose to α-glucose.
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What are the two main regions the small intestine is divided into?
The duodenum and the ileum.
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What does the duodenum receive?
The duodenum receives secretions from the liver and pancreas.
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Which enzymes does the ileum secrete?
The epithelial cells lining the small intestine (ileum) secrete the enzymes maltase, sucrase and lactase.
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What are the end products of carbohydrate digestion?
The end products of carbohydrate digestion are all monosaccharides.
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What is absorbtion?
The end products of carbohydrate digestion are all monosaccharides which are taken into the cells and then into the blood stream. A process called absorption
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What do cells do with glucose, fructose and galactose?
Glucose, fructose and galactose are absorbed continuously by cells as they use them up during respiration to release energy.
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What is done to excess glucose,fructose and galactose?
Any excess is stored in the liver as glycogen or converted into fat. They can also be carried by the blood to tissues for assimilation (made into new products).
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What is lactose?
Lactose is a disaccharide formed by the condensation of a molecule of α-glucose and a molecule of galactose.
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What does lactose consist of?
Lactose or ‘milk sugar’ consists of a galactose molecule joined to an α-glucose molecule.
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How is lactose digested?
Lactose cannot pass through the epithelium of the small intestine into blood.Must be digested first.New born mammals produce enzyme lactase which hydrolyses lactose,producing α-glucose/galactose.So these 2 monosaccharides can be absorbed into blood.
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Why can’t adults digest lactose?
The genes that are responsible for producing lactase are switched off and no more lactase is produced to digest the lactose.
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Why are people described as lactose intolerant?
They cannot digest lactose because they do not produce the enzyme lactase.
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Why does lactose intolerance cause higher than normal levels of gas in the colon?
People with lactose intolerance cannot digest lactose so the undigested lactose passes along the gut to the colon where the gut bacteria ferment the lactose and produce a variety of smaller soluble substances and gases e.g. methane/carbon dioxide.
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Other cards in this set

Card 2


What is amylase?


Amylase is a digestive enzyme that helps break down glycogen, carbohydrates and starches into simple sugars in the digestive system.

Card 3


Which two glands produce amylase?


Preview of the front of card 3

Card 4


In humans, in which two stages does digestion take place?


Preview of the front of card 4

Card 5


Explain physical digestion.


Preview of the front of card 5
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