NEET 2025 Zoology Paper Solutions
Detailed Analysis with Conceptual Explanations
Exam Date: May 4, 2025
Paper Overview & Analysis
The Zoology section of NEET 2025 was moderately difficult with a mix of direct and application-based questions. A total of 45 questions were asked from the Zoology section, carrying 180 marks. Based on our analysis, the paper focused heavily on human physiology, with significant representation from evolutionary biology and animal diversity.
Difficulty Level
65% of questions were of moderate difficulty, 20% easy, and 15% difficult.
Topic Distribution
- Human Physiology 40%
- Animal Diversity 20%
- Genetics & Evolution 15%
- Reproductive Health 12%
- Others 13%
Key Observations
- More emphasis on conceptual understanding than factual recall
- Several questions featured diagrams requiring accurate identification
- Multiple integrative questions connecting different biological concepts
- Increased focus on evolutionary relationships compared to previous years
- Several questions were NCERT-based but required application of concepts
Key Questions & Solutions
Question 1: Match the salivary glands in Column I with their locations in Column II:
| Column I (Salivary Gland) | Column II (Their Location) |
|---|---|
| Parotids | I. Below tongue |
| Submandibular/Submaxillary | II. Lower jaw |
| Sublinguals | III. Cheek |
a) a(i), b(ii), c(iii)
b) a(ii), b(i), c(iii)
c) a(i), b(iii), c(ii)
d) a(iii), b(ii), c(i)
Solution: Option d) a(iii), b(ii), c(i)
The correct mapping of the salivary glands to their locations is:
- Parotid glands are located in the cheek area, anterior and inferior to the ear.
- Submandibular (submaxillary) glands are found on the lower jaw in the floor of the mouth.
- Sublingual glands are located below the tongue in the floor of the mouth.
Concept Note:
There are three pairs of major salivary glands in humans: parotid, submandibular, and sublingual. Together, they secrete about 1-1.5 liters of saliva per day. Saliva contains salivary amylase (ptyalin), which begins carbohydrate digestion in the mouth by converting starch into maltose.
Question 2: Identify the correct order of heart chambers through which deoxygenated blood flows in a human:
a) Left atrium → Left ventricle → Right ventricle → Right atrium
b) Right atrium → Right ventricle → Left ventricle → Left atrium
c) Right atrium → Right ventricle → Pulmonary artery → Lungs
d) Left ventricle → Aorta → Body tissues → Right atrium
Solution: Option c) Right atrium → Right ventricle → Pulmonary artery → Lungs
The deoxygenated blood flow pathway in the human heart is:
- Deoxygenated blood from the body enters the heart through the superior and inferior vena cava into the right atrium.
- From the right atrium, blood passes through the tricuspid valve into the right ventricle.
- The right ventricle pumps deoxygenated blood through the pulmonary valve into the pulmonary artery.
- The pulmonary artery carries deoxygenated blood to the lungs where carbon dioxide is released and oxygen is absorbed.
Concept Note:
Humans have a double circulation system with a four-chambered heart that keeps oxygenated and deoxygenated blood separate. The right side of the heart handles deoxygenated blood (pulmonary circulation), while the left side handles oxygenated blood (systemic circulation). This separation allows for efficient oxygen delivery to tissues and is characteristic of birds and mammals.
Question 3: Match the heart valves with their functions:
| Valve | Function |
|---|---|
| I. Aortic valve | A. Prevents blood from going backward from the pulmonary artery to the right ventricle |
| II. Mitral valve | B. Prevents blood from flowing backward from the right ventricle to the right atrium |
| III. Pulmonic valve | C. Prevents backward flow from the aorta into the left ventricle |
| IV. Tricuspid valve | D. Prevents backward flow from the left ventricle to the left atrium |
a) I-A, II-B, III-C, IV-D
b) I-B, II-C, III-A, IV-D
c) I-C, II-D, III-A, IV-B
d) I-D, II-A, III-B, IV-C
Solution: Option c) I-C, II-D, III-A, IV-B
The correct matching of heart valves to their functions is:
- Aortic valve (I) – C: Prevents backward flow from the aorta into the left ventricle
- Mitral valve (II) – D: Prevents backward flow from the left ventricle to the left atrium
- Pulmonic valve (III) – A: Prevents blood from going backward from the pulmonary artery to the right ventricle
- Tricuspid valve (IV) – B: Prevents blood from flowing backward from the right ventricle to the right atrium
Concept Note:
The human heart has four valves that ensure unidirectional blood flow. The two atrioventricular (AV) valves (tricuspid and mitral/bicuspid) prevent backflow from ventricles to atria during ventricular contraction. The two semilunar valves (pulmonary and aortic) prevent backflow from the arteries into the ventricles during ventricular relaxation. Valve disorders can lead to conditions such as regurgitation (backflow) or stenosis (narrowing).
Question 4: The diagram below represents the cell cycle. Match the phases marked A, B, C, and D with their correct descriptions:
Column A:
A – Phase 1
B – Phase 2
C – Phase 3
D – Phase 4
Column B:
a) Organization of cellular contents and further cell growth
b) Leads to formation of two daughter cells
c) Cell grows physically and increases volume, proteins, organelles
d) Synthesis and replication of DNA
Which option correctly matches Column A with Column B?
Solution: A-c, B-d, C-a, D-b
Assuming the diagram shows the standard cell cycle with G1, S, G2, and M phases in order, the correct matches are:
- A (G1 phase) – c: Cell grows physically and increases volume, proteins, organelles
- B (S phase) – d: Synthesis and replication of DNA
- C (G2 phase) – a: Organization of cellular contents and further cell growth
- D (M phase) – b: Leads to formation of two daughter cells
Concept Note:
The cell cycle consists of interphase (G1, S, G2) and M phase (mitosis and cytokinesis):
- G1 (Gap 1): Cell increases in size, synthesizes proteins and organelles
- S (Synthesis): DNA replication occurs, chromosomes are duplicated
- G2 (Gap 2): Final preparations for mitosis, organization of cellular contents
- M (Mitosis): Nuclear division followed by cytokinesis resulting in two daughter cells
Cell cycle regulation involves cyclins and cyclin-dependent kinases (CDKs), with multiple checkpoints ensuring proper progression. Dysregulation can lead to cancer.
Question 5: Which of the following statements about Cockroaches is incorrect?
a) Malpighian tubules help in excretion
b) The nervous system consists of segmentally arranged ganglia joined by paired longitudinal connectives
c) The food is ground by mandibles and gizzard
d) Oxygen is transported by blood to the tissues
Solution: Option d) Oxygen is transported by blood to the tissues
In cockroaches, oxygen is NOT transported by blood to the tissues. Instead:
- Cockroaches have a highly specialized respiratory system consisting of a network of tracheal tubes.
- Oxygen reaches tissues directly through these tubes through diffusion.
- Air enters through spiracles (small openings on the body surface) and travels through increasingly finer branched tubes (tracheoles) that directly supply oxygen to cells.
- This is why the statement “oxygen is transported by blood to tissues” is incorrect for cockroaches.
All other statements are correct:
- Malpighian tubules are excretory structures that remove nitrogenous wastes from the hemolymph.
- The nervous system has segmentally arranged ganglia joined by paired connectives.
- Food is indeed ground by mandibles (externally) and then by the gizzard (internally).
Concept Note:
Insects like cockroaches have an open circulatory system where blood (hemolymph) flows freely in the body cavity (hemocoel). However, unlike vertebrates, their blood does NOT transport oxygen. The tracheal system handles respiratory gas exchange independently of the circulatory system. This direct oxygen delivery system is highly efficient for small organisms and is one of the adaptations that has contributed to the success of insects as a group.
Question 6: A substance known as “Smack” has the following properties:
- Known as Diacetylmorphine
- Possessing a white color
- Devoid of any odor
- Crystal compound with a bitter taste
- Obtained by extracting from the latex of the poppy plant
The above statements/information are correct for:
a) Cannabis
b) Heroin
c) Cocaine
d) LSD
Solution: Option b) Heroin
The substance described in the question is Heroin:
- Heroin is chemically known as diacetylmorphine.
- It is commonly called “Smack” in drug slang terminology.
- Heroin is a white, odorless, bitter crystalline compound.
- It is derived from morphine, which is extracted from the latex (sap) of opium poppy plants (Papaver somniferum).
Other options:
- Cannabis: Derived from Cannabis sativa plant, not poppy; has a characteristic odor.
- Cocaine: Extracted from coca leaves (Erythroxylum coca), not poppy.
- LSD (Lysergic acid diethylamide): Semi-synthetic compound derived from ergot fungus, not poppy.
Concept Note:
Heroin is a highly addictive opioid drug that acts on opioid receptors in the brain, producing intense feelings of euphoria followed by drowsiness. It rapidly enters the brain due to its high lipid solubility. Regular use leads to physical and psychological dependence. Heroin is classified as a Schedule I controlled substance due to its high potential for abuse and lack of accepted medical use. This is an important topic in the section on “Drugs and Alcohol Abuse” in the NEET syllabus.
Question 7: The increase in the concentration of the toxicant at successive trophic levels of a food chain is referred to as:
a) Biomagnification
b) Biogeochemical cycling
c) Bioaccumulation
d) Bioremediation
Solution: Option a) Biomagnification
Biomagnification (also called biological magnification) refers to the progressive increase in the concentration of non-biodegradable substances (like pesticides, heavy metals) at successive trophic levels in a food chain.
For example, if a water body is contaminated with DDT (a persistent pesticide), the concentration might be:
- Water: 0.003 ppm
- Phytoplankton: 0.04 ppm
- Zooplankton: 0.5 ppm
- Small fish: 2 ppm
- Large fish: 25 ppm
- Fish-eating birds: 100 ppm
This happens because:
- These substances are not metabolized or excreted
- They accumulate in the fatty tissues
- Each organism consumes many individuals from the lower trophic level
Other options:
- Biogeochemical cycling: The movement and cycling of elements (like carbon, nitrogen) between living organisms and the physical environment
- Bioaccumulation: The gradual buildup of substances in an individual organism (not across trophic levels)
- Bioremediation: The use of living organisms to clean up environmental pollutants
Concept Note:
Biomagnification has serious ecological consequences. Top predators like birds of prey, polar bears, and large fish often suffer the most significant effects from biomagnification, leading to reproductive failures, birth defects, and population declines. Classic examples include DDT affecting birds (causing eggshell thinning) and mercury contamination in aquatic food chains. This concept is important in understanding ecological impacts of pollution and is a significant topic in environmental biology in the NEET syllabus.
Question 8: Which of the following is NOT a function of the placenta?
a) Production of estrogen
b) Facilitation of gas exchange
c) Secretion of oxytocin during labor
d) Providing nutrition to the embryo
Solution: Option c) Secretion of oxytocin during labor
The placenta does NOT secrete oxytocin during labor. Oxytocin is released by the posterior pituitary gland (neurohypophysis) during labor to stimulate uterine contractions and after delivery to stimulate milk ejection from the mammary glands.
Functions of the placenta include:
- Hormone production: The placenta produces several hormones including estrogen, progesterone, human chorionic gonadotropin (hCG), human placental lactogen (hPL)
- Gas exchange: It allows oxygen and carbon dioxide transfer between maternal and fetal blood
- Nutrient transfer: It facilitates the transfer of nutrients from mother to fetus
- Waste removal: It removes waste products from the fetal blood
- Protection: It acts as a barrier against some microorganisms and harmful substances
Concept Note:
The placenta is a temporary organ that develops during pregnancy to connect the developing fetus to the uterine wall. It’s a unique organ as it’s formed from both maternal and fetal tissues. The placenta contains villi that project into maternal blood sinuses, allowing close contact between maternal and fetal circulation without actual mixing of blood. The placental barrier becomes increasingly thin as pregnancy progresses, allowing greater exchange. After delivery, the placenta is expelled as the “afterbirth.” Understanding placental function is crucial for the reproductive health section of the NEET syllabus.
Topic-wise Analysis
Human Physiology
| Subtopic | No. of Questions | Difficulty Level |
|---|---|---|
| Digestive System | 4 | Moderate |
| Circulatory System | 5 | Moderate to Difficult |
| Respiratory System | 3 | Easy to Moderate |
| Nervous & Endocrine | 4 | Difficult |
| Excretory System | 2 | Moderate |
Animal Diversity
| Subtopic | No. of Questions | Difficulty Level |
|---|---|---|
| Classification | 3 | Easy |
| Non-chordates | 4 | Moderate |
| Chordates | 2 | Difficult |
Genetics & Evolution
| Subtopic | No. of Questions | Difficulty Level |
|---|---|---|
| Mendelian Genetics | 2 | Moderate |
| Molecular Basis | 3 | Difficult |
| Evolution | 2 | Moderate |
Reproduction & Development
| Subtopic | No. of Questions | Difficulty Level |
|---|---|---|
| Human Reproduction | 3 | Moderate |
| Reproductive Health | 2 | Easy |
| Development | 1 | Difficult |
Key Takeaways & Preparation Strategies
Focus Areas for Future NEET Aspirants
- Human Physiology continues to dominate the zoology section, especially the circulatory and nervous systems
- Questions on animal diversity require clear understanding of distinctive features of various phyla
- Increased emphasis on integration of concepts across different systems
- Application-based questions that connect theory to real-life scenarios
- Strong emphasis on NCERT content with additional depth required for higher level questions
Most Important Chapters
- Human Physiology (especially Circulatory, Digestive, and Nervous Systems)
- Animal Diversity and Classification
- Human Reproduction and Reproductive Health
- Cell Biology (Cell Cycle and Division)
- Genetics and Its Molecular Basis
- Evolutionary Biology
- Ecological Concepts and Environmental Biology
Effective Study Strategies
Content Mastery
- Focus on NCERT textbooks as the primary source for concept clarity
- Create concise notes highlighting key mechanisms and processes
- Use diagrams and flowcharts to understand complex physiological processes
- Connect related concepts across different chapters and systems
- Study comparative aspects of animal groups to understand evolutionary relationships
Practice & Revision
- Solve previous years’ NEET question papers to understand pattern and difficulty level
- Focus on application-based MCQs rather than just factual recall
- Practice diagrams and their labeling for important systems
- Take regular mock tests under timed conditions
- Create a revision schedule that allows multiple revisions of high-yield topics
Common Mistakes to Avoid
- Neglecting diagrams: Many questions in the Zoology section are diagram-based, requiring clear visualization of structures and processes
- Memorizing without understanding: NEET increasingly tests application and integration of concepts rather than rote memorization
- Ignoring NCERT examples: Many questions are directly based on examples discussed in NCERT textbooks
- Skipping small topics: Even seemingly minor topics can become sources of questions in the exam
- Poor time management: Spending too much time on difficult questions at the expense of easier ones
Conclusion
The NEET 2025 Zoology section maintained a moderate difficulty level overall, with a strong emphasis on human physiology, particularly the circulatory and nervous systems. The paper featured a good mix of direct recall questions and those requiring application of concepts, in line with the trend of recent years.
Animal diversity questions focused on distinctive features of different phyla, while questions on cell biology emphasized understanding the cell cycle and division processes. The genetics and evolution questions were more concept-based than calculation-intensive.
A thorough understanding of NCERT content remains crucial for success in NEET, but the increasing trend of application-based questions suggests that aspirants should focus on conceptual clarity rather than mere memorization. The integration of concepts across different systems and topics was notable in this year’s paper.
For future aspirants, a strategic approach focusing on high-yield topics, regular practice with previous years’ questions, and timed mock tests will be essential for success. With proper preparation and concept clarity, the Zoology section presents an excellent opportunity to score well in the NEET examination.