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Key Facts: NEB Class 12 Biology Exam

75

Theory Marks

25

Practical Examination Marks

3 hours

Theory Paper Duration

35%

Minimum Theory Score

NEB

Conducting Board

The NEB Class 12 Biology examination is conducted by the National Examinations Board (NEB) of Nepal. It consists of a 75-mark written theory paper (3 hours) plus 25 marks of practical examination, and students need at least 35% in theory to avoid a Non-Graded (NG) result. OpenExamPrep offers free independent practice questions on botany and zoology. OpenExamPrep's questions are an independent English-language multiple-choice study adaptation of the curriculum topics. They are not an official translation of the board paper or a simulation of its written format.

Sample NEB Class 12 Biology Practice Questions

Try these sample questions to review concepts for the NEB Class 12 Biology exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1In the primary root anatomy of vascular plants, Casparian strips are band-like wall thickenings found in the endodermis that are primarily composed of which hydrophobic substance?
A.Suberin
B.Cellulose
C.Pectin
D.Lignin
Explanation: Casparian strips are specialized suberin-impregnated wall bands deposited in the radial and transverse walls of root endodermal cells. Suberin is a waxy, hydrophobic lipid material that blocks passive apoplastic water and solute transport into the vascular cylinder, forcing water to traverse selectively permeable living cell membranes via the symplastic pathway.
2According to Levitt's active potassium ion (K+) transport theory of stomatal movement, what primary physiological change occurs in the guard cells during daytime?
A.Active extrusion of K+ ions and accumulation of malic acid into subsidiary cells
B.Active influx of K+ ions and formation of potassium malate in guard cell vacuoles
C.Conversion of organic malate into insoluble starch leading to water exit from guard cells
D.Decrease in guard cell turgor pressure caused by passive loss of chloride ions
Explanation: During daytime, active proton pumps extrude H+ ions out of the guard cells, creating an electrical gradient that drives the active influx of K+ ions along with Cl- into guard cell vacuoles. These combine with malate anions to form potassium malate, significantly lowering osmotic and water potential, causing endosmosis of water, increasing guard cell turgor, and opening the stomatal pore.
3In the Calvin cycle (C3 pathway) of photosynthesis, what is the primary acceptor molecule of atmospheric carbon dioxide?
A.Phosphoenolpyruvate (PEP)
B.3-Phosphoglyceric acid (3-PGA)
C.Ribulose-1,5-bisphosphate (RuBP)
D.Oxaloacetic acid (OAA)
Explanation: In the C3 photosynthetic pathway, atmospheric CO2 is accepted by the 5-carbon phosphorylated sugar ribulose-1,5-bisphosphate (RuBP). This carboxylation reaction is catalyzed by the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) to yield an unstable 6-carbon intermediate that immediately cleaves into two molecules of 3-phosphoglycerate (3-PGA).
4In C4 plants such as maize (Zea mays) and sugarcane, what are the primary CO2 acceptor in mesophyll cells and the first stable product formed, respectively?
A.RuBP and 3-Phosphoglyceric acid (3-PGA)
B.Pyruvate and Malate
C.Phosphoglyceraldehyde (PGAL) and Citrate
D.Phosphoenolpyruvate (PEP) and Oxaloacetate (OAA)
Explanation: In C4 plant leaves, primary carboxylation occurs in the cytoplasm of mesophyll cells where the 3-carbon compound phosphoenolpyruvate (PEP) accepts bicarbonate/CO2 catalyzed by PEP carboxylase. This reaction produces oxaloacetate (OAA), a 4-carbon dicarboxylic acid, as the first stable product of the pathway.
5Which structural and anatomical feature specifically characterizes the Kranz anatomy found in the leaves of C4 plants?
A.Prominent bundle sheath cells with agranal chloroplasts and radially arranged mesophyll cells
B.Mesophyll differentiated into distinct palisade and spongy layers with identical chloroplasts
C.Bundle sheath cells with thin cellulosic walls, large intercellular spaces, and granal chloroplasts
D.Absence of bundle sheath cells around vascular bundles to promote rapid gas diffusion
Explanation: Kranz anatomy (from the German word 'Kranz' meaning wreath) is characterized by a distinctive wreath-like ring of enlarged bundle sheath cells surrounding the vascular bundles, enveloped by concentric layers of mesophyll cells. Furthermore, C4 plants display chloroplast dimorphism: bundle sheath chloroplasts are large and agranal (lacking grana, specialized for the Calvin cycle), whereas mesophyll chloroplasts possess well-developed grana.
6The cohesion-tension theory, which provides the widely accepted physical mechanism for the ascent of sap in tall trees, was proposed by which scientists?
A.Sir J.C. Bose
B.Godlewski
C.Dixon and Joly
D.Stephen Hales
Explanation: The cohesion-tension theory (transpiration pull theory) was proposed by Henry Horatio Dixon and John Joly in 1894. It attributes the continuous upward movement of water in the xylem conduits to the strong cohesive forces between water molecules, adhesion of water molecules to hydrophilic tracheary walls, and the negative tension (transpirational pull) generated by evaporation at leaf surfaces.
7Loss of water in the form of liquid droplets along the margins or tips of uninjured herbaceous leaves is called guttation. Through which specialized structures does guttation occur?
A.Hydathodes
B.Lenticels
C.Pneumatophores
D.Bark fissures
Explanation: Guttation occurs through hydathodes (water stomata), which are permanently open pores located at the vein endings along leaf margins or tips. Beneath the hydathode pore lies a mass of loosely arranged, colorless, thin-walled parenchymatous cells called epithem, through which xylem sap is forced out under high root pressure when transpiration is suppressed.
8During the complete aerobic respiration of one molecule of glucose in a plant cell, how many net molecules of ATP are typically synthesized via substrate-level and oxidative phosphorylation?
A.2 ATP
B.12 to 14 ATP
C.686 ATP
D.36 to 38 ATP
Explanation: Complete aerobic oxidation of one glucose molecule yields a theoretical net total of 36 to 38 ATP molecules depending on the shuttle system used (glycolysis produces net 2 ATP + 2 NADH; link reaction produces 2 NADH; Krebs cycle produces 2 ATP/GTP + 6 NADH + 2 FADH2; reoxidation via the electron transport system produces 3 ATP per NADH and 2 ATP per FADH2).
9What is the respiratory quotient (RQ = volume of CO2 evolved / volume of O2 consumed) when malic acid, an organic acid, is used as the respiratory substrate?
A.1.0
B.1.33
C.0.7
D.0.9
Explanation: Organic acids such as malic acid are rich in oxygen, so they need less O2 than the CO2 they release. C4H6O5 + 3 O2 → 4 CO2 + 3 H2O, so RQ = 4/3 ≈ 1.33 (greater than 1).
10Which plant hormone is synthesized predominantly in the shoot apical meristem and maintains apical dominance by suppressing the growth of lateral axillary buds?
A.Auxin (Indole-3-acetic acid)
B.Gibberellic acid (GA3)
C.Cytokinin (Zeatin)
D.Abscisic acid (ABA)
Explanation: Auxin (primarily indole-3-acetic acid or IAA) is synthesized at the growing shoot apex and is transported basipetally through the stem. High apical auxin concentrations maintain apical dominance by inhibiting the outgrowth of lateral axillary buds, ensuring preferential primary upward growth.

About the NEB Class 12 Biology Exam

The NEB Class 12 Biology examination is the national board examination for Grade 12 Science students in Nepal who take Biology, based on the Curriculum Development Centre (CDC) curriculum. It covers botany (plant anatomy and physiology, genetics and biotechnology) and zoology (human physiology, development, animal behaviour and evolution). OpenExamPrep's questions are an independent English-language multiple-choice study adaptation of the curriculum topics. They are not an official translation of the board paper or a simulation of its written format.

Exam sponsor: National Examinations Board (NEB), Sanothimi, Bhaktapur, Nepal. The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

Written board examination: a 75-mark written theory paper (3 hours) plus 25 marks of practical examination.

Time Limit

3 hours (theory paper)

Passing Score

At least 35% in the theory paper (below that: Non-Graded, NG)

Exam / Certification Fees

Set annually by NEB; paid through the school

Exam sponsor website

Reported exam pass rate: Not published by subject. Under NEB's letter-grading rules, a theory score below 35% is recorded as Non-Graded (NG) for that subject. Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

25% of practice bank

Botany: Plant Anatomy & Physiology

Plant tissues and anatomy, photosynthesis, respiration, and water relations.

25% of practice bank

Botany: Genetics, Molecular Biology & Biotechnology

Mendelian and molecular genetics, gene expression, and biotechnology.

25% of practice bank

Zoology: Human Physiology & Organ Systems

Digestion, circulation, respiration, excretion, and nervous and endocrine control.

25% of practice bank

Zoology: Developmental Biology, Animal Behaviour & Evolution

Gametogenesis and development, animal behaviour, and evolution.

Preparing for the NEB Class 12 Biology Exam

What You Need to Know

  • Passing score: At least 35% in the theory paper (below that: Non-Graded, NG)
  • Assessment: Written board examination: a 75-mark written theory paper (3 hours) plus 25 marks of practical examination.
  • Time limit: 3 hours (theory paper)
  • Exam / certification fees: Set annually by NEB; paid through the school Official sources

Using Our Practice Resources

  • Work through all 100 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

NEB Class 12 Biology: Suggested Study Strategy

1Practice drawing and labeling biological diagrams such as the internal structure of dicot/monocot stems, nephron, heart, reflex arc, and embryonic gastrula.
2Master biochemical pathways and word equations, including the Calvin cycle, C4 pathway, glycolysis, Krebs cycle, and electron transport chain.
3Work through genetic crosses, Punnett squares, and pedigree charts to ensure confidence in Mendelian genetics and sex-linked inheritance calculations.
4Time yourself when answering multiple-choice questions to build speed and accuracy before tackling subjective short and long-answer sections.

Frequently Asked Questions

What is the format of the NEB Class 12 Biology examination?

The official assessment is a 75-mark written theory paper (3 hours) plus 25 marks of practical examination. It is a written board examination, not a multiple-choice test.

What score is needed to pass NEB Class 12 Biology?

Under NEB's letter-grading rules, students need at least 35% of the theory marks. A lower theory score is recorded as Non-Graded (NG) for the subject.

What happens if a student is Non-Graded (NG) in Biology?

Students who are NG in up to two subjects can sit the grade-increment (supplementary) examination announced by NEB after the results; others take the subject again in a later regular examination.

Are these practice questions official NEB papers?

No. OpenExamPrep's questions are an independent English-language multiple-choice study adaptation of the curriculum topics. They are not an official translation of the board paper or a simulation of its written format. OpenExamPrep is independent and is not affiliated with or endorsed by NEB or the Curriculum Development Centre (CDC).