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Read the following passage… (Class 12 Biology 2024, Q29)

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BiologyCBSE Class 12 · Board exam 2024, set 57/1/1 · 4 marks · Case-based

CBSE Class 12 Biology 2024: question 29

Set in the CBSE Class 12 board exam of 2024, paper 57/1/1, section D, question 29, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q29 · 4 marks · Case-basedCompetency-basedBiodiversity and Conservation

Read the following passage and answer the questions that follow.
Isn't it incredible that India's land area is only 2·4 per cent of the world's total land area whereas its share of the global species diversity is an impressive 8·1 per cent ! However, in these estimates of species, prokaryotes do not figure anywhere.

Biologists are always keen on collecting data with respect to species diversity observed in different regions of the world. The data collected based on the survey conducted for species richness of groups of mammals in three different regions of the world is shown in the bar graph given below :

  1. (a)

    Why is the species richness maximum in Region III in the bar graph ?

    1 mark

  2. OR

    (a)

    Why is the species richness minimum in Region I in the bar graph ?

    1 mark
  3. (b)

    Plants and animals do not have uniform diversity in the world but show rather uneven distribution. Mention what this kind of diversity is referred to as.

    1 mark
  4. (c)

    Why is it that prokaryotes do not have an estimated number of their species diversity as seen in plants and animals ? Explain.

    2 marks

Figure in the paper: Bar graph: y-axis 'Taxonomic Richness', x-axis with Region I, Region II, Region III. Bars increase in height: Region I lowest, Region II medium, Region III highest. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/1/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Think of how species diversity changes from the equator to the poles.

Hint 2

Ecologists give three explanations for tropical richness: time, environmental stability and energy.

Hint 3

How do taxonomists normally identify species, and would that work for bacteria?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (a) [First alternative] Region III represents tropical latitudes, so species richness is maximum there. These regions have remained relatively undisturbed for millions of years and had a long evolutionary time for species diversification. They are also less seasonal, with a more constant and predictable environment, and receive more solar energy, which gives higher productivity.

    1 mark

  2. (a) [Second alternative] Region I represents temperate (higher-latitude) regions, so species richness is minimum there. These regions were subjected to frequent glaciations in the past and got less evolutionary time for diversification. They are more seasonal and less predictable, and receive less solar energy, so productivity and diversity are lower.

    1 mark

  3. (b) This uneven distribution is called the latitudinal gradient in diversity: species diversity decreases from the equator towards the poles.

    1 mark

  4. (c) Conventional taxonomic methods are based on morphology. They are not suitable for identifying microbial (prokaryotic) species, which look alike.

    1 mark

  5. (c) Many prokaryotic species cannot be cultured under laboratory conditions, so they cannot be studied and counted. Their diversity is therefore not estimated, though biochemical and molecular methods suggest it may run into millions.

    1 mark

Answer: (a) Region III – tropics: long undisturbed evolutionary time, constant environment, more solar energy; Region I – temperate: glaciations, seasonal, less solar energy; (b) Latitudinal gradient; (c) conventional taxonomy unsuitable for microbes and many are not culturable

Where the marks are

  • Reason for maximum richness in Region III (tropics) (1 mark)
  • Reason for minimum richness in Region I (temperate) (1 mark)
  • Latitudinal gradient (1 mark)
  • Conventional taxonomic methods unsuitable for microbes (1 mark)
  • Many species not culturable in the laboratory (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biodiversity and Conservation, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 57/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.