Unit 5 Biology Essay Questions

Previous IB Exam Essay Questions: Unit 5

Use these model essay question responses to prepare for essay questions on your in class tests, as well as the IB Examination, Paper 2. These questions have appeared on recent IB examinations, exactly as shown below. Following each question is the markscheme answer which was used to evaluate student answers on the examination paper.
1. Outline the process of glycylosis. 5 marks
  • occurs in cytoplasm;
  • hexose is phosphorylated using ATP;
  • hexose phosphate is split into two triose phosphates;
  • oxidation by removal of hydrogen; (do not accept hydrogen ions/protons)
  • conversion of NAD to NADH (+H+);
  • net gain of two ATP / two ATP used and four ATP produced;
  • pyruvate produced at the end of glycolysis;
Accept glucose/fructose/6C sugar instead of hexose.Accept 3C sugar/glyceraldehyde instead of triose.

2. Draw the structure of a mitochondrion as seen in an electron microscope.5 marks

Award 1 mark for each of the following structures clearly drawn and labelled correctly.

  • outer membrane
  • intermembrane space / outer compartment
  • inner membrane
  • matrix
  • cristae
  • ribosome
  • naked / circular DNA
  • ATP synthase
Do not accept plasma membrane.

3. Explain how the structure of the mitochondrion allows it to carry out its function efficiently.8 marks

  • membranes to compartmentalise / separate from processes in the cytoplasm
  • small size gives large surface are to volume ratio
  • large surface area to volume ratio allows rapid uptake / release of materials
  • matrix contains enzymes of the Krebs cycle / matrix carries out Krebs cycle
  • inner membrane invaginated / infolded / forms cristae to increase the surface area
  • large surface area gives more space for electron transport chain / oxidative phosphorylation
  • inner membrane contains ATP synthetase / ATPase / stalked particles that make ATP
  • (narrow) gap between inner and outer membranes / intermembrane space ( must be stated or labeled)
  • pH / H+ / proton concentration gradient rapidly established / steeper
  • chemiosmosis therefore more efficient / chemiosmosis can occur
  • inner membrane contains the electron transport pathway
  • DNA present to act as genetic material
  • ribosomes for protein synthesis
  • some proteins do not need to be imported

4. Explain the reactions that occur in the matrix of the mitochondrion that are part of aerobic respiration. 8 marks

  • pyruvate is decarboxylated/ CO2 removed
  • link reaction/ pyruvate combined with CoA/ ethanoyl/acetyl CoA formed
  • pyruvate is oxidized/ hydrogen removed
  • reduction of NAD/ formation of NADH + H+
  • whole coversion called oxidative decarboxylation
  • Krebs cycle
  • C2 + C4 ---> C6
  • C6 ---> C5 giving off CO2
  • C5 ---> C4 giving off CO2
  • hydrogen atoms removed collected by hydrogen-carrying molecules (NADH, FADH2)
  • ATP formed by substrate level phosphorylation
  • oxygen accepts electrons/ oxygen combines with hydrogen
  • total yield perturn of Krebs cycle = 2 CO2,, 3 NADH + H+, 1 FADH2, 1 ATP (directly produced)

5. Explain the process of aerobic respiration. 8 marks

  • by glycolysis, glucose is broken down into pyruvate (two molecules) in the cytoplasm
  • with a small yield of ATP/ net yield of 2 ATP
  • and NADH + H+/ NADH
  • aerobic respiration in the presence of oxygen
  • pyruvate converted to acetyl CoA
  • by oxidative decarboxylation / NADH and CO2 formed
  • fatty acids / lipids converted to acetyl CoA
  • acetyl groups enter the Krebs cycle (accept acetyl CoA)
  • Krebs cycle yields a small amount of ATP/ one ATP per cycle
  • and FADH2/ FADH + H+/ NADH /NADH + H+/ reduced compounds/ electron collecting molecules
  • these molecules pass electrons to electron transport chain (reject donates H+)
  • oxygen is final electron acceptor/ water produced
  • electron transport chain linked to creation of an electrochemical gradient
  • electrochemical gradient/ chemiosmosis pwers creation of ATP
  • through ATPase/synthase/synthetase
Accept any appropriate terminology for NAD and FAD.

6. Outline the role of oxygen in providing cells with energy.6 marks

(Award 1 mark for any of the below; up to 6 marks max.)

  • needed for aerobic (but not anaerobic) resp./simple equation for aerobic resp.
  • used in oxidative phosphorylation
  • oxygen accepts electrons at the end of the ETC
  • also accepts protons to form water / water formed using oxygen
  • allows more electrons along the ETC
  • allows NAD to be regenerated / reduced NAD to be oxidised
  • allows ATP production
  • allows a high yield of ATP from glucose in respiration / 32-38 instead of 2

7. Explain how chemiosmosis assists in ATP production during oxidative phosphorylation.9 marks

  • occurs during aerobic respiration;
  • oxidative phosphorylation occurs during the electron transport chain;
  • hydrogen/electrons are passed between carriers;
  • releasing energy;
  • finally join with oxygen (to produce water);
  • occurs in cristae of mitochondria;
  • chemiosmosis is the movement of protons/hydrogen ions;
  • protons move/are moved against their concentration gradient;
  • into the space between the two membranes;
  • protons flow back to the matrix;
  • through the ATP synthase/synthetase (enzyme);
  • energy is released which produces more ATP/combines ADP and Pi;

8. Explain the similarities and differences in anaerobic and aerobic cellular respiration. 8 marks

Answers must include both similarities and differences to receive full marks.

  • aerobic requires oxygen and anaerobic does not utilize oxygen

similarities:3 max

  • both can start with glucose
  • both use glycolysis
  • both produce ATP/energy(heat)
  • both produce pyruvate
  • carbon dioxide is produced
  • (both start with glycolosis) aerobic leads to Krebs' cycle and anaerobic leads to fermentation

differences:5 max


  • (fermentation) produces lactic acid in humans
  • (fermentation) produces ethanol and CO2 in yeast
  • occurs in cytoplasm of the cell
  • recycles NADH (NAD+)

aerobic cellular respiration

  • pyruvate transported to mitochondria
  • further oxidized to CO2 and water (in Krebs cycle)
  • produces a larger amount of ATP (36-38 ATP)/anaerobic produces less ATP (2)
  • can use other compounds / lipids / amino acids for energy

9. Describe the central role of acetyl (ethanoyl) CoA in carbohydrate and fat metabolism. 5 marks

  • acetyl CoA enters Krebs cycle
  • glucose / carbohydrates converted to pyruvate in glycolysis
  • pyruvate enters mitochondria
  • pyruvate converted to acetly CoA
  • by oxidative decarboxylation / hydrogen and CO2 removed
  • fats enter mitochondria
  • fats oxidised to acetyl CoA / oxidation of fatty acids / fats converted to acetyl CoA

Essay titles


The process of diffusion and its importance inliving organisms.2.

The different ways in which organisms useATP (June 2002) OR ATP and its roles in livingorganisms.3.

The movement of substances within livingorganisms (Jan 2003) OR Transportmechanisms in living organisms.4.

Mutation and its consequences.5.

The properties of enzymes and theirimportance in living organisms OR The role of enzymes in living organisms.6.

The ways in which a mammal maintainsconstant conditions inside its body.7.

Negative feedback in living organisms (June2005)8.

Chemical coordination in organisms.9.

The production and elimination of metabolicwaste products in living organisms.10.

The biological importance of water (Jan 2003)OR The role of water in the lives of organisms.11.

The importance of proteins in livingorganisms.12.

How the structure of proteins is related totheir functions (Jan 2004).13.

The importance of lipids in living organisms.14.

The importance of carbohydrates in livingorganisms OR The structure and functions of carbohydrates (June 2003).15.

How the structure of cells is related to theirfunction (June 2002).16.

Natural selection and the effects of environmental change.17.

Gas exchange in animals and flowering plants.18.

The importance of molecular shape in livingorganisms.19.

The factors affecting the growth and size of populations.20.

Cycles in Biology (June 2003).21.

The causes of variation and its biologicalimportance (Jan 2004).22.

The process of osmosis and its importance toliving organisms (June 2004).23.

Energy transfers which take place inside livingorganisms (June 2004).24.

How microscopes have contributed to ourunderstanding of living organisms (Jan 2005).25.

Enzymes and their importance in plants andanimals (Jan 2005).26.

Mean temperatures are rising in many partsof the world. The rising temperatures mayresult in physiological and ecological effectson living organisms. Describe and explainthese effects. (June 2005)27.

The transfer of substances containing carbonbetween organisms and between organismsand the environment (June 2006).28.

Cells are easy to distinguish by their shape.How are the shapes of cells related to theirfunction? (June 2006)29.

Movements inside cells. (June 2007)30.

Transfers through ecosystems. (June 2007)31.

The part played by the movement of substances across cell membranes in thefunctioning of different organs and organssystems (June 2008).32.

The part played by enzymes in the functioningof different cells, tissues and organs (June2008)33.

Ions and Organisms (June 2009)34.

DNA and the transfer of information (June2009)35.

Carbon dioxide may affect organisms directlyor indirectly. Describe and explain theseeffects. (June 2010)36.

The causes of disease in humans (June 2010).37.

The role of carbon containing compounds inliving organisms.38.

The role of nitrogen containing compounds inliving organisms.39.

The roles of membranes in living organisms.40.

The role of DNA in living organisms.41.

Applications and implications of genetechnology.42.

Genetic variation and speciation.43.

Control of the internal environment in livingorganisms.44.

The movement of molecules and ions throughmembranes.45.

Roles of pigments in living organisms.46.

Light and life.47.

Support and movement in living organisms.48.

The chemical and biological control of insectpests.

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