DP Biology (last assessment 2024)

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Question 22N.2.SL.TZ0.7

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Date November 2022 Marks available [Maximum mark: 15] Reference code 22N.2.SL.TZ0.7
Level SL Paper 2 Time zone TZ0
Command term Describe, Explain, Outline Question number 7 Adapted from N/A
7.
[Maximum mark: 15]
22N.2.SL.TZ0.7

Humans ingest food which provides energy and nutrients to carry out life processes.

(a)

Outline how starch in the diet is modified for absorption in humans.

[3]

Markscheme
  1. starch is broken down by the enzyme amylase;
  2. (amylase) secreted by the pancreas/salivary glands;
  3. acts in the duodenum/small intestine/mouth;
  4. starch is broken down into monomers/maltose/glucose;
  5. products of digestion are smaller/more soluble molecules for absorption
Examiners report

The average mark for 7(a) was over 2 out of 3. It was quite well known with most knowing that energy was lost as heat etc.

(b)

Describe how the small intestine is adapted for efficient absorption of nutrients.

[5]

Markscheme
  1. small intestine is very long;
  2. small intestine contains villi/microvilli;
  3. the epithelial cells of villi have microvilli;
  4. these increase the surface area for absorption;
  5. the cells of the small intestine contain (a large number of) mitochondria;
  6. these provide energy for active transport;
  7. the walls contain proteins for active transport/ facilitated diffusion;
  8. the villi have a rich blood supply/ lacteals;
  9. the walls of the villi are thin so less distance for diffusion;
Examiners report

In (b) most gained two marks for correctly mentioning villi and that they increase the SA. A common misconception was that the villi were sort of 'stuck on', rather than being foldings. There were a lot of vague answers about position of the rich blood supply and lacteals as being in the small intestines rather than in the villi themselves. The question was about efficient absorption, therefore references to the longitudinal and circular muscles were superfluous.

(c)

Blood transports nutrients to all tissues of the body. Explain the initiation of the heartbeat and how blood flow is controlled in the heart.

[7]

Markscheme
  1. the contraction of the heart is myogenic / heart beat initiates within the heart tissue itself;
  2. heart beat initiates in the sinoatrial node
    OR
    SA acts as a pacemaker;
  3. the SA node is located in the right atrium;
  4. electrical impulses pass over the atria then the ventricles;
  5. nerves from the medulla can control the rate of heart beat/ blood flow;
  6. epinephrine/adrenaline can increase the rate of the heart/blood flow;
  7. contraction of heart/cardiac muscle causes blood to flow;
  8. ventricles send blood to the organs/cells of the body;
  9. the direction of flow is controlled by valves/valves prevent backflow
    OR
    when the heart/named chamber contracts the valves/named valve open;
  10. AV valves prevent backflow from ventricles/into atria;
  11. semilunar valves prevent blood returning/backflow to the heart/ventricles;
Examiners report

Weaker candidates incorrectly took (c) to be 'write all you know about the blood system', rather than being about the heart. Perhaps they were confused by the first sentence, which set the scene. The myogenic nature of the contraction and the role of the SA node was well known. Everyone seemed to know that the blood flowed between the chambers, but few stated that the movement is due to muscle contractions pushing the blood. Also, most knew about the presence of valves, but their role in preventing backflow was poorly understood. Many included some quite proficient diagrams of the heart, but their use in answering the question was usually questionable.

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