Question 213 marksShort AnswerSection A

Explain the terms:

(i) Speciation

(ii) Natural selection

Heredity
Speciation and Natural Selection

Official answer

  1. Speciation:
  • Definition: Speciation is the evolutionary process by which new, distinct biological species emerge from existing populations.
  • Mechanism: It occurs when a population of a species becomes split into sub-populations due to geographical isolation (like mountains, rivers). Over time, genetic drift, natural selection, and local environmental factors cause genetic variations to accumulate. Eventually, reproductive isolation is established, preventing the two groups from interbreeding even if they meet again.

  1. Natural Selection:
  • Definition: Natural selection is the process by which environmental factors select for individuals with favorable variations, allowing them to survive, reproduce, and pass on their traits to the next generation.
  • Mechanism: In any population, variations exist. As stated in the NCERT text, 'Selection of variants by environmental factors forms the basis for evolutionary processes.' For example, bacteria that can withstand heat will survive better during a heat wave, while others die. The surviving bacteria reproduce, passing on the heat-resistant trait, leading to an adaptation in the population.
Answer keywords:Speciationgeographical isolationreproductive isolationNatural selectionenvironmental factorssurvival of variants

Marking scheme

  1. 1.1.5 marks
  2. 2.1.5 marks

Hint

For speciation, focus on how a single species splits into two non-interbreeding groups. For natural selection, focus on how the environment selects the fittest variants.

Quick oral answer

What is the primary driver of speciation? Geographical isolation followed by genetic drift and natural selection, which leads to reproductive isolation.

Common mistakes

  1. 1.Thinking speciation happens in a single generation.
  2. 2.Confusing natural selection with artificial selection.
  3. 3.Not mentioning reproductive isolation as the final step of speciation.

Analysis and explanation

Speciation requires reproductive isolation so that two populations can no longer exchange genes. Natural selection is the mechanism driving adaptation within those isolated populations, as environmental pressures favor certain survival traits over others.

Interesting facts

Natural selection does not create new traits; it only selects for traits already present in the population or arising through random mutations and DNA copying inaccuracies.

Question details

Q21 of 36 questions

Board
CBSE
Class
Class 10
Subject
Science
Year
2011
Section
Section A
Marks
3
Type
Short Answer
Chapter
Heredity
Topic
Speciation and Natural Selection
Bloom's level
Understanding
Syllabus topic
Heredity; Evolution; Speciation; Natural Selection

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Frequently asked questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 3 marks in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Heredity" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Speciation and Natural Selection" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.