IGCSE Biology Paper-3: Specimen Questions with Answers 233 - 235 of 358

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Passage

shows part of the human gas exchange system.

Structure of Organ P

Question 233 (3 of 4 Based on Passage)

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State three features of an efficient gas exchange surface.

Explanation

Features of an Efficient Gas Exchange Surface

  • Wall of the alveolus is thin (a single layer of cells) to allow gases to diffuse across them quickly;
  • They are moist to prevent the cells from drying and to allow gases to dissolve;
  • They have a large surface area, so that a lot of gas can diffuse across at the same time;
  • They have a high concentration gradient - maintained by the movement of air & blood.

Question 234 (4 of 4 Based on Passage)

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Organ P on Fig. 12.1 is not part of the gas exchange system.

State the name of the organ system to which organ P belongs.

Explanation

Organ P Heart

The Mediastinum is a Division

The mediastinum is a division of the thoracic cavity; it contains the heart, thymus gland, portions of the esophagus and trachea, and other structures.

Passage

Fig. shows a species of bacterium, Lactobacillus bulgaricus.

Bacteria from Other Groups

Question 235 (1 of 5 Based on Passage)

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The curve shown in Fig. A. is a sigmoid population growth curve.

Define the term growth.

Number of Living Bacterial Cells

Explanation

The increase in mass and increase in the number of individuals are twin characteristics of growth. The multi-cellular organisms grow by cell division. The animals grow up to a certain age, whereas the plants grow throughout their life. The cell division also occurs to replace lost cells. The unicellular organisms also grow by cell division but there it is a type of reproduction. In multicellular organisms, whether animals or plants, the growth and reproduction are mutually exclusive events. Though the non-livings, like mountains, sand mounds and snow also grow, if we consider the increase in body mass as criterion, but this growth is by accumulation of material on the surface, and not from inside as we see in animals. So, growth alone cannot be considered as a defining property of living organisms until and unless it is well specified.

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