DP Biology (first assessment 2025)

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Question 23M.2.HL.TZ2.6

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Date May 2023 Marks available [Maximum mark: 15] Reference code 23M.2.HL.TZ2.6
Level HL Paper 2 Time zone TZ2
Command term Describe, Explain, Outline Question number 6 Adapted from N/A
6.
[Maximum mark: 15]
23M.2.HL.TZ2.6

Many biological processes are cyclical. Examples of cycles can be found at the level of the cell, the organism and the ecosystem.

(a)

Explain how changes to the cell cycle can result in tumour formation.

[4]

Markscheme
  1. cell cycle is (repeated) sequence of cytokinesis/cell division, (then) interphase(then) mitosis / cell cycle includes the sequence of interphase, mitosis and cytokinesis/cell division (to form new cells which repeat the cycle)
  2. cyclins control/regulate this cycle / ensure the cell moves on to the next stage of the cycle when it is appropriate
  3. extra cells produced when they are needed
  4. tumour formation is the result of uncontrolled cell division/ cells growing and dividing endlessly
  5. repeated mitoses/high mitotic index
  6. due to mutations in oncogenes / oncogenes may become active and contribute to the development of a cancer cell
  7. carcinogens/radiation/mutagenic chemicals/mutagens/smoking cause mutations/tumours;

 

(b)

Outline the role of the right atrium in the cardiac cycle.

[4]

Markscheme
  1. right atrium collects (deoxygenated) blood from the body;
  2. blood drains into atrium through/from the vena cava;
  3. deoxygenated blood present in vena cava/right atrium/right ventricle;
  4. right atrium pumps blood into the right ventricle;
  5. during atrial systole/ventricular diastole/at the start of the cardiac cycle;
  6. sinoatrial node is in the right atrium/sinoatrial node acts as the (natural) pacemaker / sinoatrial node initiates the heartbeat;
  7. SA node sends out electrical signal to stimulate contraction in the (walls of the) atria/then propagated to the AV node / (walls of the) ventricles;

 

(c)

Describe processes in the carbon cycle that produce or use carbon dioxide.

[7]

Markscheme
  1. photosynthesis uses carbon dioxide / reduces carbon dioxide concentration of the atmosphere;
  2. autotrophs/plants/cyanobacteria convert/fix carbon dioxide into carbon/organic compounds;
  3. cell respiration produces/releases carbon dioxide;
  4. glucose/carbon/organic compounds oxidised/broken down to produce/release carbon dioxide;
  5. carbon dioxide released from aerobic (cell) respiration AND anaerobic respiration in yeast/plants (but not animals);
  6. carbon dioxide released from saprotrophs/detritivores/decomposers from dead organic matter / during decay/decomposition/respiration;
  7. (partially) decomposed organic matter can lead to the formation of peat /fossilized organic matter (coal/oil/natural gas)
  8. carbon dioxide released when carbon/organic compounds burn / during combustion (of biomass/fossil fuels) / forest fires;
  9. carbon dioxide dissolves in aquatic ecosystems / can form carbonic acid/hydrogen carbonate ions;
  10. reef-building corals/molluscs use calcium carbonate to make/build shells/exoskeletons or other body parts;
  11. hard parts/shells/exoskeletons / precipitation of calcium carbonate to form limestone/tufa;

Clear annotated diagrams with correct direction of arrows are accepted.

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