ISC Class 12 Biology Answer Key 2025 and Question Papers, Download PDF All SETs

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The ISC Class 12 Biology 2025 exam was conducted March 21, 2025. The exam lasted for 3 hours, was conducted from 2 PM to 5 PM, with an additional 15 minutes for reading the question paper.

Here we are providing a detailed analysis of student responses, expert opinions and the difficulty level of the paper including expected good scores, time-consuming section and longest question.

We have shared the ISC Class 12 Biology question paper 2025 PDF and answer key to help students check their answers and evaluate their performance.

👉 ISC Class 12 Biology Question Paper 2025, Download FREE PDF

ISC Class 12 Biology Exam Analysis 2025

Based on initial feedback from students and subject experts, the ISC Biology paper was moderate to slightly challenging.

Student Reactions:

Many students felt the paper was moderate, with a few challenging questions in Section C & D.
Diagram-based questions were straightforward and scoring, making them a relief for students.
Some students found the application-based and assertion-reasoning questions slightly tricky.
Those who practiced previous years' papers found the exam manageable and well within expectations.

Expert Review:

Biology experts reviewed the paper and confirmed that it was well-structured, aligned with the ISC syllabus, and tested both theoretical knowledge and analytical skills.
The question paper had a balanced mix of conceptual, application-based, and critical thinking question.

Overall, students and teachers were satisfied with the level of questions in the ISC Class 12 Biology exam 2025, with many agreeing that the paper was fair and well-balanced in difficulty.

Class 12 ISC Biology Answer Key 2025

The test takers waiting to know the Class 12 ISC Biology answers can check their performance level in the exam. Check out the Class 12 ISC Biology unofficial answer key for the short questions here.

Section A: 1-2 Mark Questions

Question Number	Correct Answers
Q1 (i) A sportsperson quenched his thirst by drinking some tender coconut water. Name the part of the fruit from where the liquid content is derived.	The liquid content is derived from the endosperm of the coconut fruit.
Q1 (ii) In a particular ecosystem, there were 1000 species at a given time. After 5 years, 200 more species were added. Calculate the growth rate of the population.	The growth rate of the population is 20% (200/1000).
Q1 (iii) Rachel attained puberty at the age of fourteen years. She conceived for the first time at the age of thirty years. How many primary oocytes did she lose till the time of conception?	Rachel lost approximately 620-630 primary oocytes till the time of conception (assuming 1-2 oocytes lost per month from puberty to conception).
Q1 (iv) How many nuclei are present in the central cell of the mature embryo sac of angiosperms before fertilisation?	There are 2 polar nuclei present in the central cell of the mature embryo sac of angiosperms before fertilisation.
Q1 (v) (v) A woman's first child suffered from Down's syndrome. During her second pregnancy, she wanted to find out whether her second child would be normal or not. Which method will the gynaecologist adopt to test the genetic abnormality in the embryo?	The gynaecologist will adopt Amniocentesis to test the genetic abnormality in the embryo.
Q1 (vi) Derive a name for a restriction endonuclease that was extracted in the 5th order from the RY13 strain of E. coli.	The name of the restriction endonuclease would be EcoRY13I, where "Eco" represents E. coli, "RY13" represents the strain, and "I" indicates it's the 5th enzyme extracted (Roman numeral for 5 would be "V", but restriction enzymes usually use "I", "II", "III", etc.).
Q1 (vii) A pistillate flower of a tetraploid angiosperm is pollinated by a pollen grain from a staminate flower of a diploid plant. What would be the level of the ploidy in the endosperm of seeds thus formed?	The ploidy level of the endosperm would be pentaploid (5n), as it results from the fusion of a diploid (2n) sperm and two tetraploid (4n) polar nuclei.
Q1 (viii) Observe the relationship between the first two words / terms and then fill in the fourth word/ term. Lipase: Candida lipolytica :: Taq polymerase: ________.	The answer is Thermus aquaticus. The relationship is that the first word is an enzyme, and the second word is the organism from which it is obtained.
Q1 (ix) The capacitation of sperms plays a significant role in the process of fertilisation in humans. Which of the following events are associated with the process of capacitation? I. Large quantity of Cat ⁺²ions enter the sperm to enhance the permeability of the acrosome. II. Antifertilisin reacts with the fertilisin protein. III. Membrane covering the sperm head and acrosome gets removed. (a) I and II only (b) I and III only (c) II and III only (d) I, II, and III	(b) I and III only
Q1 (x) What is the purpose of the Red Data Book? (a) To list the endangered species (b) To promote sustainable development (c) To check the growth of the animal species (d) To identify areas for conservation	(a) To list the endangered species
Q1 (xi) Given below are two statements marked Assertion and Reason. Read both the statements carefully and choose the correct option. Assertion: The eyes of octopus and horse are evidence of convergent evolution. Reason: Eyes of both the organisms have the same structure and serve the same function. (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion. (b) Both Assertion and Reason are true but Reason is not the correct explanation for Assertion. (c) Assertion is true and Reason is false. (d) Both Assertion and Reason are false.	(c) Assertion is true and Reason is false.
Q1 (xii) Given below are two statements marked Assertion and Reason. Read both the statements carefully and choose the correct option. Assertion: In a pond ecosystem, pyramid of biomass shows a sharp decrease in the biomass at higher trophic levels. Reason: Primary producers convert only 10% of the energy of sunlight into net primary productivity. (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion. (b) Both Assertion and Reason are true but Reason is not the correct explanation for Assertion. (c) Assertion is true and Reason is false. (d) Both Assertion and Reason are false.	(c) Assertion is true and Reason is false.
Q1 (xiii) A forest has a GPP of 20,000 kcal/m²/year, and 40% of this energy is used for respiration. Calculate the amount of energy available as NPP.	NPP = 12,000 kcal/m²/year.
Q1 (xiv) Ryan used a synthetic hair dye to colour his hair. Within a day of dyeing, red rashes appeared on his face causing constant itching. What condition do these symptoms indicate?	Allergic contact dermatitis
Q1 (xv) Answer the following questions. (a) Name the scientist who is considered the Father of Indian Ecology. (b) Expand the abbreviation SSBP.	(a) Dr. Ramdeo Misra (b) Solid State Biochemistry
Q1 (xvi) A transformed bacterial cell contains a transgene that can produce one molecule of protein 'X' per cell. This bacterium duplicates every 20 minutes. It is cultured in a nutrient medium for 3 hours. How many molecules of protein 'X' will be produced by the end of the culture?	X = 512
Q1 (xvii) Which drug is extracted from the leaves shown in the image shown below?	Cannabis
Q1 (xviii) Give a reason for the following. (a) The period of lactational amenorrhoea is marked by the absence of menstruation.	(a) Breastfeeding delays the resumption