(a) Explain how the proteins control the 'characteristics' in an organism with the help of an example of 'tallness' trait in pea plant.

(b) Name the section of DNA that controls the 'characteristics' in an organism.

Heredity

Molecular basis of trait expression

Official Answer

(a) Proteins control characteristics by regulating the biochemical processes that produce the trait. Cellular DNA is the information source for making proteins, and a section of DNA that codes for one particular protein is called the gene for that protein. For the tallness trait in a pea plant, plant height depends on the amount of a particular plant growth hormone present. The amount of this hormone made depends on how efficiently an enzyme (a protein) carries out the process of making it. If the gene for that enzyme makes an efficient form of the enzyme, a large amount of hormone is produced and the plant grows tall. If the gene has an alteration that makes the enzyme less efficient, less hormone is made and the plant remains short. Thus, by controlling the efficiency of the enzyme (protein), the gene ultimately controls the visible trait — tallness or shortness — in the pea plant.

(b) The section of DNA that provides information for making one protein, and which thereby controls a characteristic, is called a gene.

geneproteinenzymehormoneefficiencytallness

Marking Scheme

11 mark for correctly explaining the gene $\rightarrow$ enzyme $\rightarrow$ hormone $\rightarrow$ tallness pathway with reference to enzyme efficiency
21 mark for correctly naming 'gene' as the DNA section controlling the characteristic

Hint

Think of the pathway: gene $\rightarrow$ enzyme $\rightarrow$ hormone $\rightarrow$ height.

Quick Oral Answer

Genes are sections of DNA that code for proteins; in pea plants, the gene for an enzyme controlling hormone synthesis determines how much growth hormone is made, and this amount determines whether the plant is tall or short.

Analysis & Explanation

This question directly tests the NCERT explanation in the section 'How do these Traits get Expressed?'. The chapter explicitly states: 'A section of DNA that provides information for one protein is called the gene for that protein... Consider now an enzyme that is important for this process. If this enzyme works efficiently, a lot of hormone will be made, and the plant will be tall. If the gene for that enzyme has an alteration that makes the enzyme less efficient, the amount of hormone will be less, and the plant will be short. Thus, genes control characteristics, or traits.' Part (a) requires tracing this causal chain: gene $\rightarrow$ protein (enzyme) $\rightarrow$ efficiency of hormone synthesis $\rightarrow$ amount of hormone $\rightarrow$ height. Part (b) requires the precise NCERT terminology 'gene' as the DNA section controlling a characteristic — not 'chromosome' or 'allele', which are distinct concepts introduced elsewhere in the chapter.

Common Mistakes

1Saying 'chromosome' instead of 'gene' as the DNA section controlling a trait
2Stating that the hormone itself is the protein, instead of identifying the enzyme (protein) that controls hormone synthesis
3Omitting the causal chain and just saying 'genes control traits' without explaining the mechanism via enzyme efficiency

Interesting Facts

A single gene alteration (mutation) affecting enzyme efficiency, rather than a completely non-functional enzyme, is often enough to shift a plant from tall to short — showing traits can arise from quantitative, not just on/off, differences in protein activity.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2025?

This question carries 2 marks in the CBSE Class 10 Science 2025 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 "Molecular basis of trait expression" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2025 paper?

This is a Very Short Answer question from Section B in the CBSE Class 10 Science 2025 paper.