Topic 1 questions

• Describe the function of DNA helicase [1]

  breaking H bonds
• Describe the function of DNA polymerase [1]

  joins nucleotides/forms phosphodiester bonde
• Contrast the structures of ATP and a nucleotide found in DNA to give two differences [2]

  1. ATP has three phosphate groups and DNA nucleotide has 1 phosphate

  2. ATP has ribose and DNA nucleotide has deoxyribose

  3. ATP - base always adenine and in DNA nucleotide base can be different
• State and explain the property of water that can help to buffer changes in temperature. [2]

  1. High (specific) heat capacity)

  2. Takes a lot of energy to change temperature
• Name the two products of ATP hydrolysis [2]

  1. Adenosine diphosphate (ADP)

  2. Inorganic phosphate
• What is a monomer? [1]

  1. unit from which polymers are made;
• Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose.

  
  

  Other than being disaccharides give one similarity and one difference between the structure of lactulose and lactose. [2]


  1. Both contain galactose/ a glycosidic bond;

  2. Lactulose contains fructose, whearas lactose contains glucose;
• Following digestion and absorption of food, the undigested remains are processed to form faces in the parts of the intestine below the ileum.

  
  

  The faeces of people with constipation are dry and hard. constipation can be treated by drinking lactulose. Lactulose is soluble, but not digested or absorbed in the human intestine.

  
  

  Use your knowledge of water potential to suggest why lactulose can be used to help people suffering from constipation. (2 marks)

  (Lactulose) lowers the water potential of faeces;

  Water enters (due to osmosis) and softens the faeces;
• Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA. [2]

  1. Circular/ non-linear (DNA);

  2. Not (associated) with proteins/ histones;

  3. No introns/ no non-coding DNA;
• Humans and grasshoppers have very similar percentages of each base in their DNA but

  they are very different organisms.

  Use your knowledge of DNA structure and function to explain how this is possible. [2]

  1. Have different genes;

  2. (So bases/triplets) are in a different sequence/ order;

  3. (So) different amino acid (sequence/ coded for)/ different protein/ different polypeptide/ different enzyme;
• The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how. (4)

  1. DNA replicated;

  2. (Involving) specific/ accurate/ complementary base-pairing;

  3. (Ref to) two identical/ sister chromatids;

  4. Each chromatid/ moves/ is seperated to (opposite) polrs/ ends of cell;
• The student cut thin sections of tissue to view with an optical microscope. Explain why it was important that the sections were thin. [2]

  1. To allow (more) light through;

  2. A single/ few layer(s) of cells to be viewed;
• The movement of the woodlice in low relative humidity is an advantage to their survival. Explain how [2]

  Low humidity results in more woodlice moving;

  So increased movement increased change of leaving dry/ unfavourable environment so reduce water loss/ reduce evaporation;
• Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells. [6]

  1. made from beta-glucose;

  2. joined by condensation/ glycosidic bond;

  3. 1:4 link specified or described;

  4. "fliiping over" of alternate molecules;

  5. hydrogen bonds linking chains / long straight chains;

  6. cellulose makes cell walls strong/ cellulose fibres are strong;

  7. can resist turgor pressure/ osmotic pressure/ pulling forces;

  8. bond difficult to break;

  9. resists digestion/ action of microorganisms/ enzymes;

  (max 4 marks for structural features)
• Describe the roles of calcium ions and ATP in the contraction of a myofibril. [6]

  1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;

  2. (Calcium ions) cause movement of tropomyosin (on actin);

  3. (This movement causes) exposure of the binding sites on the actin;

  4. Myosin heads attach to binding sites on actin;

  5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;

  6. (Bending) pulling actin molecules;

  7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites);
• ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use. [2]

  1. Releases relatively small amount of energy/ little energy lost as heat;

  2. Releases energy instantaneously;

  3. Phosphorylates other compounds, making them more reactive;

  4. Can be rapidly re-synthesised;

  5. Is not lost from/ does not leave cells;
• Give two ways in which the properties of ATP make it a suitable source of energy in biological processes. (2)

  1. Energy released in small/ suitable amounts;

  2. Soluble;

  3. Involves a single/ simple reaction;
• Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

  1. ATP cannot be stored/ is an immediate source of energy;

  2. ATP only releases a small amount of energy at a time;
• Describe the part played by the inner membrane of a mitochondrion in producing ATP. (3)

  1. Electrons transferred down electron transport chain;

  2. Provide energy to take protons/ H+ into space between membranes;

  3. Proton/ H+ pass back, through membrane/ into matrix/ through ATPase;

  4. Energy used to combine ADP and phosphate/ to produce ATP;
• In anaerobic respiration, what is the net yield of ATP molecules per molecule of glucose (1)

  1. 2 (molecules);
• Give two advantages of ATP as an energy-storage molecule within a cell. (2)

  1. Cannot pass out cell;

  2. Quickly/ easily broken down (hydrolysed)/ broken;

  3. immediate source of energy;

  4. Stores/ releases small amounts of energy;
• Describe how NAD is regenerated in anaerobic respiration in yeast cells. (1)

  Formed when reduced NAD used to reduce/ donate H+ ions to pyruvate/ convert pyruvate to ethanol;
• Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae. [2]

  (more cristae/ larger surface are) for electron transport chain/ more enzymes for ATP production/ oxidative phosphorylation;

  muscle cells use more ATP (than skin cells)(not just more respiration);
• Name the substance that muscles use as their immediate energy source. [1]

  1. ATP;
• At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this. [2]

  1. lactate/ lactic acid has built up/ been produced;

  2. oxygen used to break down lactate/ convert it back to pyruvate/ glucose/ glycogen;
• When glucose is respired what happens to the energy which is not incorporated into ATP? [1]

  1. released as heat;
• When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration. [1]

  1. Glucose only partly broken down/ only broken down to lactate;
• The Krebs cycle, which takes place in the matrix, releases hydrogen ions. These hydrogen ions provide a source of energy for the synthesis of ATP, using coenzymes and carrier proteins in the inner membrane of the mitochondrion.

  
  

  Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP. [3]


  1. NAD/ FAD reduced / hydrogen attached to NAD/ FAD;

  2. H+ ions/ electrons transferred from coenzyme to coenzyme/ carrier to carrier/ series of redox reactions;

  3. energy made available as electrons passed on;

  4. energy used to synthesis ATP from ADP and phosphate/ using ATPase;

  5. H+/ protons passed into intermembrane space;

  6. H+/ protons flow back through stalked particles/ enzyme;
• In the link reaction Substance X is converted to a substance with molecules effectively containing only two carbon atoms.

  
  

  Describe what happens in this process. [2]

  1. carbon dioxide formed/ decarboxylation;

  2. hydrogen released/ reduced NAD formed;

  3. acetyl coenzyme A produced;
• Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X has three carbon atoms. Name substance X. [1]

  1. pyruvate;
• E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why. [2]

  1. Cell unable to change shape;

  2. Cell has a cell wall;

  3. (wall is) rigid;
• The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different. [2]

  1. Double bond(s);

  2. (Bonds) between carbon;

  
  

  C=C bond(s) = 2 marks
• Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? [2]

  1. Double bond(s);

  2. (Bonds) between carbon;

  
  

  C=C bond(s) = 2 marks
• Hydrogen bonds are important in cellulose molecules. Explain why. [2]

  6. c i)

  Holds chains/ cellulose molecules together/ forms cross links between chains/ cellulose molecules/ forms microfibrils, providing strength/ rigidity (to cellulose/ cell wall);
• A starch molecule has a spiral shape. Explain why this shape is important to its function in cells. [1]

  Compact/ occupies small space/ tightly packed;
• COOH = carboxyl
• Unsaturated has double bond
• Lipids - add ethanol and water, cloudy emulsion if present
• How triglyceride is formed:

  • one glycerol and 3 fatty acid
  • condensation reaction removes 3 water molecules
  • ester bond formed
• ester Bond in phospholipid is formed by condensation between glycerol and fatty acid