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Key Facts: Bac D Niger Exam

Coefficient 5

Mathematics, Physical Sciences and SVT each carry coefficient 5 in Série D

OBEECS 2025 Baccalauréat paper headers

3 parts

The 2025 Série D SVT paper covered genetic information, reproductive function and immunity

OBEECS Banque de sujets (2025)

89,158

Candidates registered for the 2026 Baccalauréat session across 41 series and filières

Ministère de l'Enseignement Supérieur, reported by ActuNiger and Le Sahel (July 2026)

Written second group

OBEECS publishes written second-group papers for candidates not admitted after the first group

OBEECS Banque de sujets (2025)

Free independent practice for Niger's Baccalauréat Série D (OBEECS): English-language MCQs on genetics, immunity, nerve physiology, reproduction, functions and probability, mechanics, radioactivity, acid–base and organic chemistry, philosophy, French and English. Use it alongside past OBEECS papers, since the official exam is written in French.

Sample Bac D Niger Practice Questions

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

1In a monohybrid cross between two heterozygous garden pea plants (Pisum sativum) with round seeds (Rr x Rr), where the round seed allele (R) is completely dominant over the wrinkled seed allele (r), what is the expected phenotypic ratio among the resulting progeny?
A.1 round : 2 intermediate : 1 wrinkled (25% round, 50% intermediate, 25% wrinkled)
B.1 round : 1 wrinkled (50% round, 50% wrinkled)
C.All round seeds (100% round)
D.3 round : 1 wrinkled (75% round, 25% wrinkled)
Explanation: A monohybrid cross between two heterozygotes (Rr x Rr) produces a genotypic ratio of 1/4 RR, 1/2 Rr, and 1/4 rr. Because the R allele is completely dominant over r, both RR and Rr genotypes display the round seed phenotype (1/4 + 2/4 = 3/4 or 75%), whereas only the homozygous recessive genotype rr expresses wrinkled seeds (1/4 or 25%). This produces Mendel's classic 3:1 phenotypic segregation ratio.
2In four o'clock flowers (Mirabilis jalapa), flower color is governed by an incomplete dominance system where the homozygous allele pair C^R C^R produces red flowers and C^W C^W produces white flowers. When two heterozygous pink-flowered plants (C^R C^W) are crossed, what phenotypic proportions are expected in the F2 generation?
A.1 red : 2 pink : 1 white (25% red, 50% pink, 25% white)
B.9 red : 3 pink : 3 white : 1 variegated
C.3 red : 1 white (75% red, 25% white)
D.All pink (100% pink)
Explanation: Under incomplete dominance, the heterozygous genotype C^R C^W expresses an intermediate pink phenotype because neither allele is fully dominant over the other. Crossing two pink heterozygotes (C^R C^W x C^R C^W) produces the genotypic distribution 1/4 C^R C^R (red), 2/4 C^R C^W (pink), and 1/4 C^W C^W (white). Because each distinct genotype directly corresponds to a unique phenotype, the phenotypic ratio matches the genotypic ratio: 1 red : 2 pink : 1 white (25% : 50% : 25%).
3In mice, the yellow coat allele (Y) is dominant over the agouti allele (y) for coat color, but the homozygous dominant condition (YY) causes embryonic death during early gestation. If two yellow mice (Yy) are crossed, what phenotypic ratio is expected among the surviving live-born offspring?
A.1 yellow : 2 agouti : 1 albino
B.3 yellow : 1 agouti (75% yellow, 25% agouti)
C.1 yellow : 1 agouti (50% yellow, 50% agouti)
D.2 yellow : 1 agouti (67% yellow, 33% agouti)
Explanation: Crossing two heterozygous yellow mice (Yy x Yy) yields the initial zygotic genotypic ratio 1/4 YY, 2/4 Yy, and 1/4 yy. Because the YY homozygotes die in utero, they do not appear among live-born progeny. The surviving offspring consist of 2/3 heterozygous yellow (Yy) and 1/3 homozygous agouti (yy), resulting in a characteristic modified Mendelian phenotypic ratio of 2:1 (approximately 66.7% yellow to 33.3% agouti).
4In pea plants, the genes controlling seed shape (R round / r wrinkled) and seed color (Y yellow / y green) assort independently. In a cross between two double heterozygotes (RrYy x RrYy), what is the theoretical probability of obtaining an offspring that produces round, green seeds?
A.9/16 (56.25%)
B.6/16 (37.50%)
C.3/16 (18.75%)
D.1/16 (6.25%)
Explanation: According to Mendel's law of independent assortment, the two gene pairs segregate independently. For seed shape, the probability of obtaining the dominant round phenotype (R-) from Rr x Rr is 3/4. For seed color, the probability of obtaining the recessive green phenotype (yy) from Yy x Yy is 1/4. Applying the multiplication rule for independent events gives P(round and green) = P(R-) * P(yy) = (3/4) * (1/4) = 3/16 (18.75%).
5A testcross is performed between a female Drosophila melanogaster heterozygous for two linked autosomal genes in coupling phase (AB/ab) and a homozygous recessive male (ab/ab). The cross produces 1,000 offspring with the following counts: 415 [AB], 405 [ab], 92 [Ab], and 88 [aB]. What is the genetic distance between gene loci A and B?
A.18.0 centimorgans (cM)
B.82.0 centimorgans (cM)
C.9.0 centimorgans (cM)
D.36.0 centimorgans (cM)
Explanation: Recombinant offspring arise from homologous crossing-over between loci A and B during female meiosis. The recombinant phenotypes are [Ab] (92) and [aB] (88), totaling 92 + 88 = 180 recombinant flies out of 1,000. The recombination frequency is calculated as (180 / 1,000) * 100% = 18.0%. Since one percent recombination equals one map unit or centimorgan (cM), the genetic map distance between loci A and B is 18.0 cM.
6Red-green color blindness is an X-linked recessive condition (X^b) in humans. A woman with normal vision whose father was color-blind marries a man with normal vision. What is the probability that their first child will be a color-blind son?
A.50% (1/2)
B.12.5% (1/8)
C.100% (1)
D.25% (1/4)
Explanation: Because the woman's father was color-blind (X^b Y), she necessarily inherited his X^b chromosome and is a carrier (X^B X^b). The father has normal vision and has the genotype X^B Y. The offspring genotypes are: 1/4 X^B X^B (normal daughter), 1/4 X^B X^b (carrier daughter), 1/4 X^B Y (normal son), and 1/4 X^b Y (color-blind son). Therefore, the overall probability that their first child is a color-blind son is 1/4 or 25% (or 50% among sons specifically).
7In a human pedigree, cystic fibrosis is inherited as an autosomal recessive disorder (cc). In a family, a healthy couple (II-1 and II-2) are planning to have a child. Neither parent has the disease, but both had an affected sibling (cc), while their parents (generation I) were all phenotypically healthy. What is the probability that their unborn child will be affected with cystic fibrosis?
A.1/9 (approximately 11.1%)
B.1/16 (6.25%)
C.1/4 (25.0%)
D.2/3 (66.7%)
Explanation: Because both sets of grandparents had an affected child (cc), all four grandparents must be obligate heterozygotes (Cc). A healthy child of heterozygous parents has a 2/3 probability of being a carrier (Cc) because the homozygous recessive genotype (cc) is excluded. Thus, P(II-1 is Cc) = 2/3 and P(II-2 is Cc) = 2/3. If both parents are carriers, the probability of transmitting the recessive allele from each parent is 1/4. Therefore, P(affected child) = (2/3) * (2/3) * (1/4) = 4/36 = 1/9 (approximately 11.1%).
8When analyzing a human genealogical tree, which of the following transmission patterns definitively excludes an X-linked dominant mode of inheritance?
A.An affected father transmitting the condition to his son while having an unaffected daughter
B.Every affected individual having at least one affected parent across successive generations
C.A higher overall frequency of affected females compared to affected males
D.An affected female transmitting the trait to both her sons and daughters
Explanation: In humans, males transmit their single X chromosome exclusively to their daughters and pass only their Y chromosome to their sons. Under an X-linked dominant mode of inheritance, an affected father (X^D Y) must transmit his mutant X chromosome to 100% of his daughters (making them all affected) and never transmits it to his sons (Y chromosome). Therefore, the observation of father-to-son transmission or an unaffected daughter born to an affected father definitively refutes X-linked dominant inheritance.
9Chemical analysis of a double-stranded genomic DNA sample shows that 32% of its nitrogenous bases are adenine. According to Chargaff's rules of base pairing, what is the percentage of cytosine in this DNA sample?
A.32%
B.18%
C.64%
D.36%
Explanation: Chargaff's rules dictate that in double-stranded DNA, adenine pairs with thymine (A = T) via two hydrogen bonds, and guanine pairs with cytosine (G = C) via three hydrogen bonds. If adenine constitutes 32%, then thymine also constitutes 32%, giving A + T = 64%. The remaining bases must be guanine and cytosine, totaling G + C = 100% - 64% = 36%. Because G = C, the percentage of cytosine is 36% / 2 = 18%.
10During semi-conservative DNA replication in prokaryotes, what is the specific catalytic function of DNA ligase on the lagging strand?
A.Synthesizing a short complementary RNA primer with a free 3'-OH group to initiate synthesis
B.Excising incorrectly paired nucleotides via 3' to 5' exonuclease proofreading activity
C.Catalyzing phosphodiester bond formation between adjacent Okazaki fragments after primer replacement
D.Unwinding the double-stranded DNA helix ahead of the replication fork by breaking hydrogen bonds
Explanation: Discontinuous synthesis on the lagging strand yields short segments of newly synthesized DNA called Okazaki fragments, each originally preceded by an RNA primer. After DNA polymerase I removes the RNA primers and fills the gaps with deoxyribonucleotides, a nick remains between the adjacent 3'-OH and 5'-phosphate ends. DNA ligase seals this nick by catalyzing the formation of a covalent phosphodiester bond, thereby creating a continuous, intact DNA strand.

About the Bac D Niger Exam

Série D is Niger's mathematics and natural-sciences baccalauréat, organized nationally by OBEECS, in which mathematics, physical sciences and SVT carry equal coefficients. This independent practice bank offers English-language multiple-choice questions on the Terminale D programme and on the philosophy, French and English papers. It is a study adaptation, not an official translation or a simulation of the written papers.

Exam sponsor: Office du Baccalauréat, des Équivalences et des Examens et Concours du Supérieur (OBEECS). The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

First-group written papers on the OBEECS 2025 paper headers: Mathematics (coeff. 5, 4 h), Physical Sciences (coeff. 5, 3 h), SVT (coeff. 5, 3 h; the 2025 paper covered genetic information, reproductive function and immunity), French (coeff. 3, 4 h), Philosophy (coeff. 2, 4 h, also set in Arabic), English (coeff. 2, 3 h) and Arabic (coeff. 2, 3 h); a Dessin-Couture paper (coeff. 1, 2 h) also appears in the paper bank. Candidates who are not admitted after the first group may sit a second group of written papers (History-Geography, for example, appears as a 3 h 30 second-group paper for series C and D in 2025).

Time Limit

Written papers of 3 to 4 hours each over several days; second-group papers of 2 to 3 h 30

Passing Score

Marked out of 20 on a coefficient-weighted average; the admission and second-group thresholds are not published on OBEECS's public pages

Exam / Certification Fees

Not published on OBEECS's public pages; fees are set for each session and paid during online pre-registration (officebacniger.com)

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.

30% of this local bank (30 questions)

Life Sciences (SVT)

Genetic information and its transmission, protein synthesis, meiosis and human genetics, nerve messages and glycaemia, the reproductive system and its regulation, and immunity

23% of this local bank (23 questions)

Mathematics

Functions, limits and derivatives, logarithms and exponentials, integrals, differential equations, sequences, combinatorics, probability and random variables

22% of this local bank (22 questions)

Physical Sciences

Kinematics and Newton's laws, satellites, oscillators, interference, Lorentz force and induction, radioactivity, acid–base chemistry, esters, amines and amino acids

25% of this local bank (25 questions)

Philosophy, French and English

Philosophy notions and authors of the Terminale programme (9), French text-analysis and dissertation skills and African literature (9), and English grammar, vocabulary and reading (7)

Preparing for the Bac D Niger Exam

What You Need to Know

  • Passing score: Marked out of 20 on a coefficient-weighted average; the admission and second-group thresholds are not published on OBEECS's public pages
  • Assessment: First-group written papers on the OBEECS 2025 paper headers: Mathematics (coeff. 5, 4 h), Physical Sciences (coeff. 5, 3 h), SVT (coeff. 5, 3 h; the 2025 paper covered genetic information, reproductive function and immunity), French (coeff. 3, 4 h), Philosophy (coeff. 2, 4 h, also set in Arabic), English (coeff. 2, 3 h) and Arabic (coeff. 2, 3 h); a Dessin-Couture paper (coeff. 1, 2 h) also appears in the paper bank. Candidates who are not admitted after the first group may sit a second group of written papers (History-Geography, for example, appears as a 3 h 30 second-group paper for series C and D in 2025).
  • Time limit: Written papers of 3 to 4 hours each over several days; second-group papers of 2 to 3 h 30
  • Exam / certification fees: Not published on OBEECS's public pages; fees are set for each session and paid during online pre-registration (officebacniger.com) 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

Bac D Niger: Suggested Study Strategy

1Practise recent OBEECS Série D papers from the official paper bank, especially SVT document-analysis questions.
2Give equal attention to mathematics, physical sciences and SVT, which each carry coefficient 5.
3In SVT, learn to read curves and pedigrees: DNA quantity during the cell cycle, hormone curves of the sexual cycle and primary versus secondary immune responses.
4In chemistry, revise acid–base titrations, buffers, esters, amines and the predominance diagram of amino acids.
5Practise the French contraction de texte and dissertation, which carry coefficient 3.

Frequently Asked Questions

Is the Niger Bac D a multiple-choice exam?

No. The OBEECS Série D papers are written exercises, document analyses and essays in French. This bank is an independent English-language MCQ study adaptation for revising concepts; it is not an official translation and does not reproduce the written format.

Which subjects weigh most in Série D?

On the OBEECS 2025 paper headers, Mathematics, Physical Sciences and SVT each carry coefficient 5, French coefficient 3, and Philosophy, English and Arabic coefficient 2 each.

Does the Série D SVT paper include geology?

Not in the current programme: the Terminale D SVT programme covers genetic information, physiology (nerve messages, glycaemia), reproduction, birth control and immunity, and the 2025 OBEECS SVT paper for series D had parts on genetic information, reproductive function and immunity.

Are Franco-Arabic Série D candidates covered?

Yes. OBEECS lists Série D Franco-Arabe as a registration option, and its paper bank shows those candidates taking the Série D science papers, with Philosophy and Arabic papers set in Arabic. This bank covers the shared Série D programme.