Biological Molecules_115650.pdf

3.1 Biological Molecules Name: _Teacher Reflection on Outcomes  or  Target Explain what a monomer and polymer are Explain the concept of condensation and hydrolysis reactions in forming/breaking down polymers. Identify common monosaccharides and descri...

3.1 Biological Molecules Name: _Teacher Reflection on Outcomes  or  Target Explain what a monomer and polymer are Explain the concept of condensation and hydrolysis reactions in forming/breaking down polymers. Identify common monosaccharides and describe the monosaccharides from which lactose, maltose and sucrose are made. Explain what is meant by a glycosidic bond and how they form through condensation Describe and explain how polymerisation of α-glucose can form starch or glycogen and how this relates to their function and properties. Present the structure of α -glucose and β –glucose diagrammatically Explain why glycosidic bonds between β –glucose form cellulose and how this relates to its function and properties. Describe the structure of triglycerides and explain how triglycerides form Recognise, from diagrams, saturated and unsaturated fatty acids. Describe the structure of phospholipids and explain their properties. Contrast the different properties of triglycerides and phospholipids. Describe the general structure of an amino acid and how dipeptides form. Explain the variety of functions that proteins have and why they are so important to the body. Explain how dipeptides and polypeptides form Explain the hierarchical organisation of protein structure Describe the types of bonds involved in protein structure and the weakness of H bonds Relate the structure of proteins to the properties of proteins (required for proteins named throughout the spec) Describe the Biuret test, the emulsion test, reducing and non- reducing sugar and starch test and how they can be interpreted. Explain what is meant by qualitative testing and quantitative data. Describe how the Benedict’s test can be adapted to provide quantitative data Explain the usefulness of calibration curves or standards. Describe the properties that are important in water Explain the properties of water linked to the polar nature of the molecule Explain the significance of these properties to living organisms and processes Monomers and Polymers 2 Outcome:  Explain what a monomer and polymer are Definitions: Monomer: One of many small repeating molecules that combine to form a polymer Polymer: Large molecule made up of repeating smaller molecules Polymerisation: Process of producing a polymer Condensation: Addition of a monomer to another with the removal of water, forming a bond Hydrolysis: Splitting of the polymer into its monomers with the addition of water, breaking a bond Metabolism: All chemical processes that take place within the cells of an organism Biological Scientific name Monomer Polymer molecule Carbohydrate Saccharides Monosaccharide Polysaccharide Proteins Peptides Amino acids Protein/Polypeptide Nucleic acids Nucleotides Nucleotides Nucleotides Explain why are Lipids missing from the table? Cannot form polymer Made of two different monomers Outcome 3   Explain the concept of condensation and hydrolysis reactions in forming/breaking down polymers.  Identify common monosaccharides and describe the monosaccharides from which lactose, maltose and sucrose are made.  Present the structure of α -glucose and β –glucose diagrammatically Explain what is meant by a glycosidic bond and how they form through condensation Carbohydrates   Contain the elements C, H and O.  General formula (CH2O)n Carbohydrate name No. of C’s Triose 3 Pentose 5 Hexose 6 Monosaccharides Definition Isomer: _Same Chemical formula, different structural formula ___________________ Properties  Dissolve in water and are reducing sugars  The monosaccharide we have to study all have the same chemical formula C6H12O6 and are therefore isomers.  You need to know – Alpha glucose, beta glucose, fructose and galactose. Structure: Diagram of Alpha glucose Diagram of Beta glucose Exam tip: Can you write yourself a method to remember how to draw these hexose sugars? State the structural difference between alpha and beta glucose. Alpha H Above C1, Beta H Below C1 4 Disaccharides Properties:  Dissolve in water and can be reducing or non-reducing sugars  Made from two monomers joined by a condensation reaction  Forming a covalent bond called a glycosidic bond. Condensation reaction: Rules for drawing 1. Always show the groups involved 2. Always show water is released 3. Always circle and label the bond formed Structure: Formation of the disaccharide Maltose (a reducing sugar): + Formation of the disaccharide Sucrose (a non-reducing sugar): + Draw out the formation of lactose (a reducing sugar) using α-glucose and galactose. Exam tip: You do not need to remember this one for your exam but you might be asked to apply your knowledge to this example. 5 Hydrolysis reactions: Rules for drawing 1. Always show the groups involved 2. Always show where water is added 3. Always circle and label the bond broken 4. Name the monomers formed. Disaccharides can be broken down by a hydrolysis reaction. In the space below draw out the hydrolysis reaction of Maltose. How does the structure of alpha and beta glucose change the bonding? Every other B-glucose molecule is upside down. Exam questions: Q1.(a) What is a monomer? (a) (a monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made; Reject atoms / elements / ’building blocks’ for units / molecules Ignore examples (b) Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose. Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose. Similarity 1. Both contain galactose / a glycosidic bond; Ignore references to hydrolysis and / or condensation Difference. Lactulose contains fructose, whereas lactose contains glucose; Ignore alpha / beta prefix for glucose Difference must be stated, not implied 6 Q2.Lactose is a disaccharide found in milk. In the human small intestine, the enzyme lactase catalyses the hydrolysis of lactose to the monosaccharides, galactose and glucose. These monosaccharides are then absorbed into the blood. Complete the diagram to show the hydrolysis of lactose to galactose and glucose. use of water; must be above arrowhead OH drawn correctly in place of glycosidic bond on each monosaccharide; Q3.(a) Name the monosaccharides of which the following disaccharides are composed. (i) Sucrose monosaccharides Glucose and fructose (ii) Lactose monosaccharides Glucose and galactose1 7 Outcomes:  Describe and explain how polymerisation of α-glucose can form starch or glycogen and how this relates to their function and properties.  Explain why glycosidic bonds between β –glucose form cellulose and how this relates to its function and properties. Polysaccharides 1.StarchStructure:  Polysaccharide of a-glucose  1-4 and 1-6 glycosidic bonds  Branches and coiled shape held by H bonds within the molecule 2.Glycogen  Structure: Polysaccharide of a-glucose  1-4 and 1-6 glycosidic bonds  Branched and coiled shape held by H bonds within the molecule Function/property of Starch and Glycogen: Main role is as energy storage compound. Starch is in plants only, glycogen is in animals only. Describe Explain Insoluble Doesn’t affect WP Branched Compact/Can fit many in a small space Polymer of a-glucose Provides glucose for respiration Branched Many ends for enzymes to attach and hydrolyse Large Cannot leave cell. Contrast Starch and Glycogen structure: Starch structure Glycogen structure Less 1-6 glycosidic bonds More 1-6 glycosidic bonds 8  More branched. Less branched 3.Cellulose  Structure: Polysaccharide of B-glucose  Every other B--glucose upside down  1-4 glycosidic bonds only  Molecule form long and straight chains  Many H bonds between chains forming microfibrils. Function/property of cellulose: Describe Explain Long straight chains Provides rigidity/strength to plant cell wall Many H bonds forming microfibrils Exam tip: Most polysaccharide exam question asking you to compare and contrast the functions or structures of the 3 polysaccharides. Compare and contrast questions should ALWAYS be done as a table. Complete the revision poster below using the information about polysaccharides. Add information from your memory first to see what you can remember. Change colour and add information that you had forgotten, 9 Exam questions: Q1. Starch and cellulose are two important plant polysaccharides. The following diagram shows part of a starch molecule and part of a cellulose molecule. (a) Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above. 1. Starch formed from α-glucose but cellulose formed from β-glucose; 2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted. (b) Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function. Explain one way in which starch molecules are adapted for their function in plant cells. 1. Insoluble; 2. Don’t affect water potential; OR 3. Helical; Accept form spirals 4. Compact; OR 5. Large molecule; 6. Cannot leave cell. (c) Explain how cellulose molecules are adapted for their function in plant cells. 1. Long and straight chains; 2. Become linked together by many hydrogen bonds to form fibrils; 3. Provide strength (to cell wall).3 These are more challenging application and skills questions. Q2.Scientists investigated the hydrolysis of sucrose in growing plant cells by an enzyme called SPS. (a) Name the products of the hydrolysis of sucrose. 1. Glucose; 2. Fructose; 10 (b) The scientists grew plant cells in a culture for 12 days. At the start, there were only a few cells in the culture. Each day, they determined the mass of sucrose hydrolysed by SPS in the plant cells in 1 hour. The following table shows their results. Mass of sucrose Rate of hydrolysis of sucrose Day hydrolysed by SPS by SPS in 1 hour / μg 0 0.07 2 0.09 4 0.11 6 0.15 8 0.20 10 0.24 12 0.24 For each day, calculate the rate per minute of the reaction catalysed by SPS. Record the rates in standard form and plot a suitable graph of your processed data. 1. Line graph with rate on y axis and days/time in days on x axis and linear scales; Correct answers × 10−3 1.17, 1.50, 1.83, 2.50, 3.33, 4.00, 4.00 (accept to 1DP) 2. Correct units of μg min−1/per minute/minute−1 × 10−3; Reject m−1 Reject if put 10−3 on axis for each point ‘/’ means separating units from what goes before i.e. accept sucrose hydrolysis per min / μgx10−3 3. Rates correctly calculated and plotted, with line connecting points/line of best fit and no extrapolation; Do not accept a ruled straight line of best fit Accept y axis starting at 1 (3) 11  (c) What can you conclude about the growth of the plant cells from these data? Explain how you reached your conclusions. 1. Sucrose hydrolysis linked to some aspect of growth; Accept ‘breakdown 2. Greater the rate of/faster hydrolysis/more SPS activity as plant grows/cells divide (up to 8/10 days); Accept ‘breakdown Accept converse of greater rate of growth, greater rate of hydrolysis Reject ‘sucrose broken down’ 3. Growth/division remains the same/slows after 8/10 days (because SPS activity is levelling off); Accept after 8 days/at 10 days growth rate maximum/growth stops Q3.In mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells in the lining of the uterus. At this stage, there is a high concentration of glycogen in cells lining the uterus. (a) Describe the structure of glycogen. 1. Polysaccharide of α-glucose; OR polymer of α-glucose; 2. (Joined by) glycosidic bonds OR Branched structure; 2 max (b) During early pregnancy, the glycogen in the cells lining the uterus is an important energy source for the embryo.Suggest how glycogen acts as a source of energy. Do not include transport across membranes in your answer. 1. Hydrolysed (to glucose); 2. Glucose used in respiration; 1. Ignore ‘Broken down’ 2. ‘Energy produced’ disqualifies mp2 12 (c) Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients. ) 1. Membrane folded so increased / large surface area; OR Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport; 2. Large number of protein channels / carriers (in membrane) for facilitated diffusion; 3. Large number of protein carriers (in membrane) for active transport; 4. Large number of protein (channels / carriers in membrane) for co-transport; 1. Accept ‘microvilli to increase surface area’ 1. Reject reference to villi. Note feature and function required for each marking point and reference to large / many / more. List rule applies. (d) In humans, after the gametes join at fertilisation, every cell of the developing embryo undergoes mitotic divisions before the embryo attaches to the uterus lining. The first cell division takes 24 hours. The subsequent divisions each take 8 hours. After 3 days, the embryo has a total volume of 4.2 × 10−3 mm3. What is the mean volume of each cell after 3 days? Express your answer in standard form. Show your working. 3.3 × 10−5 OR 3.28 × 10−5 OR 3.281 × 10−5; 1 mark for Evidence of 128 (cells) Correct numerical calculation but not in standard form gains 1 mark (0.00003281 OR 0.0000328 OR 0.000033); Accept any number of−5significant figures as long as rounding correct (3.28125 × 10 scores 2 marks) 13  Answer = ____________________ mm3 (2) Outcomes:  Describe the structure of triglycerides and explain how triglycerides form.  Recognise, from diagrams, saturated and unsaturated fatty acids.  Contain C, H, O  Insoluble in water/non-polar  Main groups of lipids are: - Triglycerides - also known as fats (solid at room temperature) and oils (liquid at room temperature). - Phospholipids – main component of plasma membranes. Triglyceride Structure Draw a molecule of glycerol and a fatty acid. Draw the condensation of a triglyceride. 14 Saturated and unsaturated Fatty acids Definition: Saturated: Single C-C bonds in the hydrocarbon chain ______ Unsaturated: Double C=C bonds in the hydrocarbon chain cause kinks in the chain _______ Saturated – Unsaturated- Circle and label the carboxyl group. Circle and label the double C bonds. Triglyceride Function: Property Function/Explanation Energy store Many C and H’s so more energy per g then carbohydrates Large, insoluble and non-polar Doesn’t affect WP of cell molecules Storage below dermis of the skin in Insulation adipose tissue Metabolic source of water From respiration due to high ratio of H’s to O 15 Buoyancy Low density Exam questions: 1. The figure below shows a phospholipid. X Y (b) The part of the phospholipid labelled A is formed from a particular molecule. Name this molecule. Glycerol. 16  (c) Name the type of bond between A and fatty acid X. Ester (d) Which of the fatty acids, X or Y, in the figure above is unsaturated? Explain your answer. Y (no mark) Contains double bond between (adjacent) carbon atoms in hydrocarbon chain. Scientists investigated the percentages of different types of lipid in plasma membranes from different types of cell. The table shows some of their results. Type of lipid Percentage of lipid in plasma membrane by mass Cell lining ileum of Red blood cell of The bacterium mammal mammal Escherichia coli Cholesterol 17 23 0 Glycolipid 7 3 0 Phospholipid 54 60 70 Others 22 14 30 (e) The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values. 1. Divide mass of each lipid by total mass of all lipids (in that type of cell); 2. Multiply answer by 100. Q2.(a) A triglyceride is one type of lipid. The diagram shows the structure of a triglyceride molecule. (i) A triglyceride molecule is formed by condensation. From how many molecules is 17  this triglyceride formed? (1) 4 / four; (ii) Use the diagram to explain what is meant by an unsaturated fatty acid. 1. Double bonds (present) / some / two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen; Answer refers to unsaturated unless otherwise clearly indicated. May be shown in appropriate diagram. 2. In (fatty acid) C / 3; Q3.(a) Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? (a) Double bond(s); (Bonds) between carbon; C=C bond(s) = 2 marks ‘No’ C=C bond(s) disqualifies 1 mark only Accept: does not contain maximum number of H for 1 mark Neutral: contains C=O bonds (b) Scientists investigated the relationship between the amount of omega-3 fatty acids eaten per day and the risk of coronary heart disease. The graph shows their results. Do the data show that eating omega-3 fatty acids prevents coronary heart disease? Explain your answer. Graph shows negative correlation / description given; Correlation does not mean causation / prevention / shows lower risk not prevention; May be due to another factor / example given; Neutral: refs. to methodology e.g. sample size / line of best fit 18  (c) Olestra is an artificial lipid. It is made by attaching fatty acids, by condensation, to a sucrose molecule. The diagram shows the structure of olestra. The letter R shows where a fatty acid molecule has attached. (i) Name bond X. Glycosidic; Reject: ester bond (ii) A triglyceride does not contain sucrose or bond X. Give one other way in which the structure of a triglyceride is different to olestra. Contains glycerol / three fatty acids / forms three ester bonds; Neutral: contains less fatty acids Answers must refer to a triglyceride Neutral: olestra has eight fatty acids / R groups Reject: contains three glycerols (iii) Starting with separate molecules of glucose, fructose and fatty acids, how many molecules of water would be produced when one molecule of olestra is formed? (iii) 9; Q4.Omega-3 fatty acids are found in cows milk. Scientists investigated changes in the concentration ’ of omega-3 fatty acids in milk when cows were moved from eating grass in fields to eating corn in cattle sheds. The following figure shows the results of one investigation. 19  (a) The concentration of omega-3 fatty acids in milk changed when cows were fed on corn instead of grass. Describe how. (a) (Omega-3 concentration) falls more rapidly at first; Levels out at 140 days / concentration of 0.4%; (b) (i) Calculate the rate of decrease in the mean omega-3 fatty acid concentration between 0 and 40 days.Show your working. Two marks for correct answer of 0.04 or 0.043;; One mark for incorrect answer which clearly identifies total fall of 1.7; Outcome:  Describe the structure of phospholipids and explain their properties.  Contrast the different properties of triglycerides and phospholipids. Phospholipids Structure Definition: Amphipathic: Have polar and non-polar regions Fatty acids repel water and are referred to as being hydrophobic Phosphate group is attracted to water and is referred to as being hydrophilic On the diagram label the hydrophilic phosphate head, the hydrophobic fatty acid tail and circle the C=C double bond. Hydrophilic phosphate head 20  Hydrophobic fatty acid tail Add details to the diagrams below showing how phospholipids arrange themselves when interacting with water. When placed in water the phospholipid molecules arrange themselves either: Phospholipid function: Form a bilayer within a cell surface membrane so hydrophobic barrier formed between the inside and 21 outside of cell Forms membranes inside the cell e.g. mitochondria, to isolate metabolic reactions. Controls exchange of substances Compare and contrast triglycerides and phospholipids Triglyceride Phospholipid Ester Bonds (S) 3 2 Glycerol (S) Yes Yes Fatty acid structure (S) Saturated and unsaturated Saturated and unsaturated Fatty acid number (s) 3 2 Elements (S) C,H,O C,H,O,P Solubility (F) Hydrophobic Hydrophilic head, phobic tail Bilayer (F) No Yes Exam tip: ALWAYS do contrast questions as a table to get fully marks. Examiners notes always say “must be directly comparative statements, on the same line/same sentence”. Exam questions: (b) Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids. Compare and contrast the structure and properties of triglycerides and phospholipids. 1. Both contain ester bonds (between glycerol and fatty acid); 2. Both contain glycerol; 3. Fatty acids on both may be saturated or unsaturated; 4. Both are insoluble in water; 5. Both contain C, H and O but phospholipids also contain P; Must relate to element. 6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group; 7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region; 8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t; Outcome: 22   Describe the general structure of an amino acid and how dipeptides form.  Explain the variety of functions that proteins have and why they are so important to the body.  Explain how dipeptides and polypeptides form Proteins Property:  Contains C, H, O, N and sometimes S Amino20 naturally  Acidsoccurring amino acids  Same 20 amino acids found in almost all living organisms.  Proteins can be: o Globular - spherical and soluble. Have a metabolic function e.g. haemoglobin, insulin, enzymes. o Fibrous – long, thin and insoluble. Have structural function e.g. collagen, keratin Structure: All amino acids have:  An amine group = -NH2  A carboxyl group = -COOH  A hydrogen atom = -H  R group (side chain) = differs in all amino acids Draw and label General Amino Acid Dipeptides  Structure: Polypeptides formed by condensation reactions  Bond formed is called a peptide bond  Forms between amine group of one amino acid and carboxyl group of the other Draw and label General Dipeptide here. Outcome: 23   Explain the hierarchical organisation of protein structure  Describe the types of bonds involved in protein structure and the weakness of H bonds Hierarchical  protein structure Proteins can consist of a single polypeptide chain e.g. most enzymes, or 2 or more polypeptides e.g. haemoglobin, collagen. Primary Structure Definition: Polymer of amino acids joined by condensation reaction in a specific order of amino acids in a polypeptide chain. Bond: Peptide Secondary Structure Definition: Polypeptide chain folds into either: - α-helix - β – pleated sheets Bond: H bonds Tertiary Structure Definition: Polypeptide folds further to produce a specific 3D structure. Bonds: H bonds – between the polar R-groups of the amino acids. Easily broken by temperature and pH changes Ionic bonds – between an amino acid with a positive charge and an amino acid with a negative charge if close enough. Easily broken by pH changes, Disulphide bridges – between amino acids that contain Sulphur in the R-group. Strong covalent bonds but broken by reducing agents. Tertiary structure is determined by where these bonds form which is determined by sequence of amino acids. Tertiary structure determines 3D shape and function of th t i Quaternary Structure Definition: More than one polypeptide chain. Bonds: Same as Tertiary 24 Exam questions: Q1. (a) Draw the general structure of an amino acid. Accept other correct representations. (1) Q2. (a) Glycine, an amino acid. In the space below, draw a diagram to show the dipeptide produced when two molecules of glycine are joined together. (c) 1. Peptide bond shown correctly; 2. Rest of dipeptide structure shown correctly; (b) Name the other molecule formed when two molecules of glycine are joined together. Water Q3. the structure of proteins. 1. Polymer of amino acids; 2. Joined by peptide bonds; 3. Formed by condensation; 4. Primary structure is order of amino acids; 5. Secondary structure is folding of polypeptide chain due to hydrogen bonding; Accept alpha helix / pleated sheet 6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds; 7. Quaternary structure is two or more polypeptide chains. 5 max 25 Outcomes:  Describe the Biuret test, the emulsion test, reducing and non-reducing sugar and starch test and how they can be interpreted.  Explain what is meant by qualitative testing and quantitative data.  Describe how the Benedict’s test can be adapted to provide quantitative data  Explain the usefulness of calibration curves or standards. Testing for Biological Molecules Biological molecule Method Result Protein Add Biuret Blue to Lilac Carbohydrates- Heat to 80c with Benedict’s Blue to Brick red Reducing sugar precipitate Carbohydrates- Non Follow Benedict method but solution stays blue. Blue to Brick red -reducing sugar Fresh sample precipitate Boil with acid then neutralise with alkali Heat to 80c with Benedict’s Lipids Shake with ethanol White/milky emulsion Then add water Starch Add iodine Yellow to blue black Testing for carbohydrates Give an example of an acid and an alkali you would use in the non-reducing test. Hydrochloric acid Explain why an acid is added in the non-reducing test Hydrolyse the glycosidic bond forming reducing sugars Explain why an alkali is added after the acid in the non-reducing test. Benedicts only works in alkaline conditions Definition: Quantitative data: Numerical measurement of a variable, can be statically analysed Qualitative data: Judgement, cannot be statically analysed 26  Describe the qualitative data Lighter colours have a lower conc of glucose, the darker colours have a higher conc of glucose Describe the method for quantitative a Benedict’s test: Producing a calibration curve Use distilled water and a stock solution of reducing sugar to produce a dilution series of different concentrations Add Benedict’s to a constant volume each solution Heat to 80oC in water bath Calibrate the colorimeter Measure and record the % absorption using the colorimeter Plot concentration on x-axis against absorbance on y-axis and draw a curve Sketch a graph showing the % absorption using a colorimeter Examiner Tip: LEARN THIS This method can be used to produce a calibration curve for known concentrations of different molecules. You can then work out the concentration of an unknown solution. You just need to replace the Benedict’s with a ‘detecting solution’ for the molecule being investigated. Describe how you could use this calibration curve to work out the glucose concentration of an unknown solution Use the same volumes of solutions in producing your calibration curve Add Benedict’s and heat to 80oC Read off the concentrations against absorbance obtained from the curve 27 Water Structure  Major component of cells  Made up of 2 atoms of hydrogen and 1 atom of oxygen  Hydrogens joined to oxygen by covalent bonds.  Electrons are not shared equally – oxygen atom has slight negative charge, hydrogen atoms have slight positive charge – polar- dipolar  Each water molecule is attracted to each other  Attractions called hydrogen bonds Property Explanation Advantage to organisms Polar molecule Universal solvent Transport ions around the body for faster reaction Universal solvent Water is polar allowing ions to dissolve Transport ions around the body for faster reaction Reactive Involved in hydrolysis/condensation Allows metabolic reactions to reactions occur High heat capacity Takes a lot of heat energy to break H External: Stable environment for bonds organisms eg fish Energy is used instead of changing Internal: Maintains stable temperature temperature for enzymes and Act as a buffer reactions. Latent heat of Takes a lot of heat energy to break H Heat energy is lost through vaporisation bonds. evaporation allowing animal to Energy is used to change liquid to gas cool down. when it evaporates carrying away the heat energy Cohesion Attraction between water molecules Column: Transport ions in plants 28  Water forms a column for support Surface tension: Habitat for Water has a high surface tension when in insects. contact with air Exam questions a) State and explain the property of water that can help to buffer changes in temperature. (a) 1. (water has a relatively) high (specific) heat capacity; Ignore numbers relating to heat capacity 2. Can gain / lose a lot of heat / energy without changing temperature; OR Takes a lot of heat / energy to change temperature; Accept due to H bonding between water molecules 2 Water and inorganic ions have important biological functions within cells. (a) Give two properties of water that are important in the cytoplasm of cells. For each property of water, explain its importance in the cytoplasm. (a) 1. Polar molecule; 2. Acts as a (universal) solvent; OR 3. (Universal) solvent; 4. (Metabolic) reactions occur faster in solution; OR 5. Reactive; 6. Takes place in hydrolysis / condensation / named reaction; Polar molecule so acts as (universal) solvent so (metabolic reactions are faster = 3 marks 29  Q3. The diagram below shows the structure of molecules found in organisms. (a) Complete the table below by putting the correct letter, A, B, C or D, in the box next to each statement. Each letter may be used once, more than once, or not at all. Letter Statement is a monomer in an enzyme’s active site is a monomer in cellulose is produced during photosynthesis and respiration forms a polymer that gives a positive result with a biuret test (4) Letter Statement B; is a monomer in an enzyme’s active site D; is a monomer in cellulose C; is produced during photosynthesis and respiration B; forms a polymer that gives a positive result with a biuret test Must be in correct order Q4. (a) Explain five properties that make water important for organisms. 30 ) 1. A m e tabolite in conde ns ation/hydrolys is / photos ynthe s is /re s piration; 2. A s olve nt s o (m e tabolic) re actions can occur OR A s olve nt s o allowing trans port of s ubs tance s ; 3. H igh he at capacity s o buffers change s in tem pe rature; F or ‘ buffer ’ accept ‘ res is t’. 4. Large late nt he at of vaporis ation s o provide s a cooling effect (through e vaporation); 5. C ohe s ion (betwe e n wate r m ole cule s ) s o s upports colum ns of wate r (in plants ); F or ‘ colum ns of w ater ’ accept ‘ trans piration stream ’. D o not credit ‘ trans piration ’ alone but accept des cription of ‘ s tream ’. F or ‘ colum ns of w ater ’ accept ‘ cohes ion-tens ion (theory) ’. F or cohes ion accept hydrogen bonding 6. C ohe s ion (betwe e n wate r m ole cule s ) s o produce s s urface te ns ion s upporting (s m all) organis m s ; F or cohes ion accept hydrogen bonding Ignore reference to pH. A llow other s uitable properties but m ust have a valid explanation. F or exam ple ice floating s o m aintaining aquatic habitat beneath w ater trans parent s o allow ing light penetration for photos ynthes is (b) Describe the biochemical tests you would use to confirm the presence of lipid, non -reducing sugar and amylase in a sample. ___________________________________________________________________ 31  4 m ax if m arks gained from only 2 s ubstance tests. Lipid 1. A dd e thanol/alcohol th e n add wate r an d s hake/m ix OR A dd e thanol/alcohol an d s hake/m ix th e n pour into/add wate r; R eject heating em uls ion tes t. A ccept ‘ A dd S udan III and m ix ’. 2. W hite/m ilky e m uls ion OR e m uls ion te s t turns white /m ilky; Ignore cloudy. R eject precipitate. A ccept (for S udan III) top (layer) red. N on-re ducing s ugar 3. D o B e ne dict’ s te s t an d s tays blue /negative ; Ignore details of m ethod for B enedict’s tes t for this m p. 4. B oil with acid th e n ne utralis e with alkali; A ccept nam ed exam ples of acids /alkalis. 5. H e at with B e ne dict’ s an d be com e s re d/orange (pre cipitate); D o not credit m p5 if no attem pt at m p4. F or ‘ heat’ ignore ‘ w arm ’/’ heat gently ’/’ put in a w ater bath ’ but accept s tated tem peratures ≥ 60° C. H eat m us t be stated again, do not accept us ing res idual heat from m p4. A ccept ‘ do the B enedict’ s test’ if full correct m ethod given els ew here. A ccept ‘ s odium carbonate, s odium citrate and copper s ulfate s olution ’ for B enedict’s but m us t have all three if term ‘ B enedict’ s ’ not us ed. A m ylas e 6. A dd biuret (re age nt) an d be com e s purple /viole t/m auve /lilac; A ccept ‘ s odium or potass ium hydroxide and copper s ulfate s olution ’ for ‘ biuret’. R eject heating biuret test. 7. A dd s tarch, (le ave for a tim e ), te s t for re ducing s ugar/abs e nce of s tarch (5) (c) Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. Give two named examples of polymers and their associated monomers to illustrate your answer. (5) 32 1. A conde ns ation reaction joins m onom ers togethe r an d form s a (che m ical) bond an d re leas e s wate r; 2. A hydrolys is re action bre aks a (chem ical) bond be twe e n m onom e rs an d us e s wate r; 3. A s uitable e xam ple of polym e rs and the m onom e rs from which the y are m ade ; 3. and 4. P olym ers m ust contain m any m onom ers. 3. and 4: s uitable exam ples include am ino acid an d polypeptide, protein, enzym e, antibody or s pecific exam ple nucleotide an d polynucleotide, D N A or R N A A lpha glucos e an d s tarch/glycogen B eta glucos e an d cellulos e. If neither s pecific carbohydrate exam ple is given, allow m onos accharide/glucos e and polys accharide. 3. and 4. R eject (once) reference to triglycerides. 4. A s e cond s uitable e xam ple of polym e rs and the m onom e rs from which the y are m ade ; 5. R efe re nce to a corre ct bond within a nam ed polym e r; R eject reference to ester bond. 33 34 Polysaccharides Summary Sheet Name of Found in Found as Function/ Monomer Type of Type of Extra Notes Polysaccharide Role bond chain between formed monomer Starch Glycogen Cellulose Fibres