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BSEH SS Biology study materials
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BSEH SS Biology practice questions

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Question 1Reproduction

In the human male reproductive system, which structure serves as the site of sperm maturation and storage before ejaculation?

  1. Prostate gland
  2. Epididymis Correct answer.
  3. Seminal vesicle
  4. Vas deferens

Explanation

Sperm produced in the seminiferous tubules are immature and immotile; they travel to the epididymis, where they undergo further maturation and are stored until ejaculation. The seminal vesicle and prostate are accessory glands that add fluid, while the vas deferens is a transport duct.

Question 2Reproduction

Which hormone surge directly triggers ovulation in the human menstrual cycle?

  1. Progesterone
  2. Follicle-stimulating hormone
  3. Luteinizing hormone Correct answer.
  4. Prolactin

Explanation

A sharp spike in luteinizing hormone, driven by rising estrogen from the mature follicle, causes the follicle to rupture and release the oocyte. This LH surge is the immediate trigger for ovulation.

Question 3Reproduction

Fertilization in humans normally occurs in which region of the female reproductive tract?

  1. Uterus
  2. Cervix
  3. Ovary
  4. Ampulla of the fallopian tube Correct answer.

Explanation

Sperm meet the secondary oocyte in the widened ampulla region of the fallopian tube, where fertilization typically takes place. The resulting zygote then travels to the uterus for implantation.

Question 4Reproduction

A structure that allows exchange of materials between the developing fetus and the maternal blood without direct mixing of the two bloods is the:

  1. Placenta Correct answer.
  2. Chorion
  3. Amnion
  4. Allantois

Explanation

The placenta brings fetal and maternal blood into close proximity, allowing diffusion of gases, nutrients, and wastes while keeping the two circulations separate. The amnion is a fluid-filled sac that cushions the fetus.

Question 5Reproduction

Which of the following correctly describes the chromosome number of a human zygote?

  1. Diploid, with 23 chromosomes
  2. Diploid, with 46 chromosomes Correct answer.
  3. Haploid, with 46 chromosomes
  4. Haploid, with 23 chromosomes

Explanation

A zygote forms when a haploid sperm (23 chromosomes) fuses with a haploid egg (23 chromosomes), restoring the diploid number of 46. Thus the zygote is diploid.

Question 6Reproduction

In flowering plants, the transfer of pollen from the anther to the stigma of the same flower is called:

  1. Self-pollination Correct answer.
  2. Cross-pollination
  3. Fertilization
  4. Germination

Explanation

Self-pollination occurs when pollen lands on the stigma of the same flower or another flower on the same plant. Cross-pollination involves transfer to a different plant, while fertilization is the later fusion of gametes.

Question 7Reproduction

Which process produces haploid gametes from diploid germ cells?

  1. Mitosis
  2. Budding
  3. Meiosis Correct answer.
  4. Binary fission

Explanation

Meiosis involves two divisions that halve the chromosome number, producing haploid gametes with genetic variation. Mitosis maintains the diploid number in body cells.

Question 8Reproduction

The primary function of the acrosome in a mammalian sperm cell is to:

  1. Detect chemical signals from the egg
  2. Release enzymes that help penetrate the egg Correct answer.
  3. Provide energy for swimming
  4. Carry the paternal chromosomes

Explanation

The acrosome is a cap-like vesicle at the sperm head containing hydrolytic enzymes. During the acrosome reaction these enzymes are released to digest the zona pellucida and allow the sperm to reach the oocyte membrane.

Question 9Reproduction

A woman's basal body temperature typically rises slightly at mid-cycle. This rise is best explained by the increased secretion of:

  1. Progesterone Correct answer.
  2. FSH
  3. Oxytocin
  4. Estrogen

Explanation

After ovulation, the corpus luteum secretes progesterone, which raises basal body temperature by a small but detectable amount. This thermal shift is used as a marker that ovulation has occurred.

Question 10Reproduction

A gardener wants to develop a new plant variety with desirable traits from two different parent plants. Which technique is most appropriate?

  1. Grafting
  2. Vegetative propagation
  3. Tissue culture
  4. Cross-pollination Correct answer.

Explanation

Cross-pollination combines gametes from two genetically different parents, producing offspring with new combinations of traits. The other methods are asexual and yield clones of a single parent.

Question 11Reproduction

During the ovarian cycle, the corpus luteum forms from:

  1. The ruptured follicle after ovulation Correct answer.
  2. The cervical mucus glands
  3. The primary oocyte before meiosis
  4. The endometrium after implantation

Explanation

After the mature follicle releases its oocyte, the remaining follicular cells transform into the corpus luteum. This structure secretes progesterone to support the endometrium.

Question 12Reproduction

Which feature of the human male urethra distinguishes it from the female urethra?

  1. It serves both the urinary and reproductive systems Correct answer.
  2. It opens directly into the uterus
  3. It carries only urine
  4. It is shorter in length

Explanation

In males, the urethra is a shared passage that conducts both urine and semen. In females, the urethra carries only urine and is separate from the reproductive tract.

Question 13Reproduction

In the double fertilization of angiosperms, one sperm nucleus fuses with the egg and the other fuses with:

  1. A synergid nucleus
  2. Two polar nuclei to form endosperm Correct answer.
  3. The antipodal cells
  4. The tube nucleus

Explanation

Double fertilization involves one sperm fertilizing the egg to form the zygote and the second sperm fusing with two polar nuclei to form a triploid endosperm. The endosperm nourishes the developing embryo.

Question 14Reproduction

A couple is undergoing in vitro fertilization. Oocytes are collected and fertilized outside the body, and the resulting embryo is placed in the uterus. This procedure bypasses which normal step?

  1. Cleavage of the zygote
  2. Development of the placenta
  3. Fertilization in the ampulla of the fallopian tube Correct answer.
  4. Implantation of the blastocyst

Explanation

IVF performs fertilization in the laboratory, so the normal meeting of sperm and egg in the ampulla of the fallopian tube is bypassed. Cleavage, implantation, and placental development still occur afterward.

Question 15Reproduction

Which statement best explains why sexual reproduction generates more genetic variation than asexual reproduction?

  1. It produces more offspring per event
  2. It always produces identical offspring
  3. It requires fewer resources
  4. It involves crossing over and independent assortment during meiosis Correct answer.

Explanation

Meiosis introduces variation through crossing over in prophase I and independent assortment of homologous chromosomes in metaphase I, and random fertilization adds further combinations. Asexual reproduction typically yields genetically identical clones.

Question 16Reproduction

The hormone human chorionic gonadotropin (hCG) is secreted by the developing embryo and has which effect?

  1. It stimulates milk production
  2. It initiates labor contractions
  3. It triggers ovulation
  4. It maintains the corpus luteum so progesterone continues to be produced Correct answer.

Explanation

hCG from the early embryo prevents degeneration of the corpus luteum, which continues secreting progesterone to maintain the endometrium. This is the basis of many pregnancy tests.

Question 17Reproduction

In a flowering plant, the structure that develops into the fruit after fertilization is the:

  1. Ovary Correct answer.
  2. Stigma
  3. Receptacle
  4. Ovule

Explanation

After fertilization, the ovary wall thickens and develops into the fruit, which encloses and protects the seeds. The ovule develops into the seed.

Question 18Reproduction

A mutation prevents the formation of the zona pellucida around a mammalian oocyte. Which outcome is most directly expected?

  1. The egg would not be released from the ovary
  2. Multiple sperm could fuse with a single egg, causing polyspermy Correct answer.
  3. The corpus luteum would fail to form
  4. The oocyte would not undergo meiosis

Explanation

The zona pellucida is a protective coat that, after the first sperm enters, undergoes changes that block additional sperm. Without it, the block to polyspermy is impaired and multiple sperm may fuse with the egg.

Question 19Reproduction

Which structure in the human female reproductive system is the site where the fetus normally develops?

  1. Vagina
  2. Fallopian tube
  3. Cervix
  4. Uterus Correct answer.

Explanation

After implantation, the embryo develops within the muscular wall of the uterus, which expands to accommodate the growing fetus. The fallopian tube is the site of fertilization, not normal fetal development.

Question 20Reproduction

In the context of the menstrual cycle, menstruation occurs when:

  1. hCG levels rise after implantation
  2. Progesterone and estrogen levels fall as the corpus luteum degenerates Correct answer.
  3. FSH levels rise to stimulate a new follicle
  4. LH levels peak and trigger ovulation

Explanation

If no pregnancy occurs, the corpus luteum degenerates, causing progesterone and estrogen levels to drop. This withdrawal of hormonal support causes the endometrium to shed as menstruation.

Question 21Reproduction

Which of the following is a secondary sexual characteristic in human males that results from testosterone during puberty?

  1. Development of breast tissue
  2. Onset of menstruation
  3. Deepening of the voice Correct answer.
  4. Widening of the hips

Explanation

Testosterone drives male secondary sexual characteristics, including deepening of the voice due to growth of the larynx and vocal cords. Breast development, menstruation, and hip widening are female characteristics.

Question 22Reproduction

A researcher observes that a certain plant species produces seeds only when insects visit its flowers. Which conclusion is best supported?

  1. The plant reproduces only asexually
  2. The plant self-pollinates without vectors
  3. The plant reproduces by vegetative propagation
  4. The plant depends on insect-mediated pollination for sexual reproduction Correct answer.

Explanation

If seed production requires insect visits, the insects are likely transferring pollen between flowers, making the plant dependent on animal pollination for sexual reproduction. Seeds form only after fertilization, which requires successful pollination.

Question 23Reproduction

Which comparison of oogenesis and spermatogenesis in humans is correct?

  1. Both begin before birth and pause at puberty
  2. Spermatogenesis produces one functional sperm and polar bodies
  3. Oogenesis produces one functional ovum and polar bodies, while spermatogenesis produces four sperm Correct answer.
  4. Both produce four gametes from each starting cell

Explanation

In oogenesis, meiosis yields one large functional ovum and smaller polar bodies that degenerate, conserving cytoplasm for the egg. Spermatogenesis yields four functional sperm from each primary spermatocyte.

Question 24Reproduction

A woman has a blocked fallopian tube on one side. Which statement best explains why she may still conceive naturally?

  1. The ovary on the blocked side cannot release eggs
  2. Sperm cannot survive in the uterus
  3. Fertilization can occur directly in the uterus
  4. The other fallopian tube can capture an oocyte and support fertilization Correct answer.

Explanation

Each ovary is not strictly tied to the adjacent tube, and the remaining patent tube can capture an oocyte and serve as the site of fertilization. Conception is therefore still possible, though fertility may be reduced.

Question 25Reproduction

In a cross between two heterozygous pea plants (Tt x Tt) for a single trait, what fraction of the offspring is expected to show the recessive phenotype?

  1. 0
  2. 3/4
  3. 1/4 Correct answer.
  4. 1/2

Explanation

A Tt x Tt cross yields genotypes in a 1 TT : 2 Tt : 1 tt ratio. Only the tt genotype expresses the recessive phenotype, so one quarter of the offspring are expected to show it.

Question 26Reproduction

In the human male reproductive system, which structure serves as the site of sperm maturation and storage?

  1. Vas deferens
  2. Epididymis Correct answer.
  3. Prostate gland
  4. Seminal vesicle

Explanation

The epididymis is a coiled tube where sperm undergo final maturation and are stored until ejaculation. The seminal vesicle and prostate gland produce seminal fluid, while the vas deferens transports sperm.

Question 27Reproduction

Which event directly triggers ovulation in the human menstrual cycle?

  1. A surge in luteinizing hormone (LH) Correct answer.
  2. An increase in human chorionic gonadotropin (hCG)
  3. A rise in progesterone
  4. A decrease in follicle-stimulating hormone (FSH)

Explanation

Ovulation is induced by a sharp surge in LH that occurs around mid-cycle. This surge causes the mature follicle to rupture and release the oocyte.

Question 28Reproduction

A plant species has separate male and female individuals. Which term describes this condition?

  1. Dichogamous
  2. Hermaphroditic
  3. Dioecious Correct answer.
  4. Monoecious

Explanation

Dioecious plants have male and female reproductive structures on separate individual plants. Monoecious plants have both male and female flowers on the same individual.

Question 29Reproduction

A woman takes a contraceptive pill that contains estrogen and progestin. Which mechanism best explains its contraceptive effect?

  1. It thickens the uterine lining to prevent implantation.
  2. It blocks the fallopian tubes to prevent fertilization.
  3. It prevents ovulation by inhibiting FSH and LH secretion. Correct answer.
  4. It directly kills sperm in the vagina.

Explanation

Combined oral contraceptives contain estrogen and progestin, which exert negative feedback on the hypothalamus and pituitary. This suppresses FSH and LH secretion, thereby preventing follicular development and ovulation.

Question 30Reproduction

In a flowering plant, which process results in the formation of a diploid zygote?

  1. Fusion of one sperm nucleus with the egg cell Correct answer.
  2. Germination of the pollen grain on the stigma
  3. Fusion of one sperm nucleus with two polar nuclei
  4. Division of the generative cell

Explanation

Double fertilization in angiosperms involves two fusion events. One sperm nucleus fuses with the egg cell to form a diploid zygote, while the other fuses with two polar nuclei to form triploid endosperm.

Question 31Reproduction

A researcher treats a culture of human sperm with a compound that blocks the acrosomal reaction. Which outcome is most directly expected?

  1. Sperm cannot undergo capacitation in the female tract.
  2. Sperm cannot swim toward the oocyte.
  3. Sperm cannot penetrate the zona pellucida of the oocyte. Correct answer.
  4. Sperm cannot fuse with the oocyte plasma membrane.

Explanation

The acrosomal reaction releases enzymes that digest a path through the zona pellucida, allowing the sperm to reach the oocyte membrane. If this reaction is blocked, the sperm cannot penetrate the zona pellucida.

Question 32Reproduction

In humans, oogenesis and spermatogenesis differ in several key aspects. Which comparison is accurate?

  1. Oogenesis begins at puberty, while spermatogenesis begins before birth.
  2. Oogenesis produces four functional ova, while spermatogenesis produces one functional sperm.
  3. Oogenesis occurs continuously throughout life, while spermatogenesis stops after puberty.
  4. Oogenesis produces one functional ovum and three polar bodies, while spermatogenesis produces four functional sperm. Correct answer.

Explanation

During oogenesis, meiosis produces one large ovum and three smaller polar bodies that degenerate. In contrast, spermatogenesis yields four functional sperm cells from each primary spermatocyte.

Question 33Genetics and Evolution

In a population of insects, a single gene controls body color with two alleles: B (black) and b (brown). If the frequency of the B allele is 0.7 and the population is in Hardy–Weinberg equilibrium, what is the expected frequency of heterozygotes?

  1. 0.49
  2. 0.21
  3. 0.09
  4. 0.42 Correct answer.

Explanation

Under Hardy–Weinberg equilibrium, genotype frequencies are p² + 2pq + q². With p = 0.7 and q = 0.3, the heterozygote frequency is 2pq = 2(0.7)(0.3) = 0.42.

Question 34Genetics and Evolution

Which process produces new combinations of alleles on a single chromosome and therefore increases genetic variation in gametes?

  1. Crossing over during prophase I Correct answer.
  2. Formation of the spindle apparatus
  3. DNA replication during S phase
  4. Cytokinesis following telophase

Explanation

Crossing over exchanges corresponding segments between homologous chromosomes during prophase I of meiosis, creating recombinant chromatids with new allele combinations. Replication, cytokinesis, and spindle formation do not recombine alleles.

Question 35Genetics and Evolution

A mutation changes a single DNA base but the amino acid sequence of the encoded protein remains unchanged. This mutation is best described as:

  1. a silent mutation Correct answer.
  2. a nonsense mutation
  3. a frameshift mutation
  4. a missense mutation

Explanation

A silent mutation alters a codon but, because the genetic code is degenerate, still specifies the same amino acid, leaving the protein sequence unchanged. Missense and nonsense mutations change the amino acid or create a stop codon, and frameshifts shift the reading frame.

Question 36Genetics and Evolution

In a dihybrid cross between two individuals heterozygous for both genes (AaBb × AaBb), assuming independent assortment, what fraction of offspring is expected to show both recessive phenotypes?

  1. 9/16
  2. 1/16 Correct answer.
  3. 3/16
  4. 1/4

Explanation

Each parent produces gametes with a 1/4 chance of carrying both recessive alleles. The probability of an offspring being aabb is (1/4)(1/4) = 1/16, which is the only genotype showing both recessive phenotypes.

Question 37Genetics and Evolution

Which structure in a eukaryotic cell contains the enzymes needed for transcription and is the site where mRNA is synthesized?

  1. The Golgi apparatus
  2. The ribosome
  3. The nucleus Correct answer.
  4. The lysosome

Explanation

In eukaryotes, transcription occurs in the nucleus, where RNA polymerase and associated factors synthesize mRNA from a DNA template. Ribosomes translate mRNA, while the Golgi and lysosomes handle protein modification and degradation.

Question 38Genetics and Evolution

Which of the following best defines a species under the biological species concept?

  1. A group of populations whose members can interbreed and produce fertile offspring Correct answer.
  2. A group of organisms with the same number of chromosomes
  3. A group of organisms that share identical physical characteristics
  4. A group of organisms living in the same geographic region

Explanation

The biological species concept defines a species as populations that can interbreed in nature and produce viable, fertile offspring, and that are reproductively isolated from other such groups. Physical similarity, shared habitat, and chromosome number are not the defining criteria.

Question 39Genetics and Evolution

In a pedigree, a trait appears in every generation and affects both males and females approximately equally. Which mode of inheritance is most consistent with this pattern?

  1. X-linked recessive
  2. Y-linked
  3. Autosomal dominant Correct answer.
  4. Autosomal recessive

Explanation

Autosomal dominant traits typically appear in every generation (vertical transmission) and affect males and females equally because the gene is on an autosome. X-linked recessive traits show a male bias and often skip generations, and Y-linked traits affect only males.

Question 40Genetics and Evolution

Which of the following is a source of genetic variation that arises during sexual reproduction rather than from mutation?

  1. Independent assortment of homologous chromosomes Correct answer.
  2. Errors during DNA replication
  3. A point mutation in a somatic cell
  4. Exposure to a chemical mutagen

Explanation

Independent assortment during metaphase I of meiosis randomly distributes maternal and paternal homologues into gametes, generating variation without any change in DNA sequence. The other options all involve changes to the DNA itself.

Question 41Genetics and Evolution

A population of beetles is exposed to an insecticide. After several generations, most beetles are resistant. Which mechanism best explains this change?

  1. Random genetic drift causing resistance alleles to appear
  2. Natural selection acting on pre-existing resistant alleles Correct answer.
  3. Directed mutation induced by the insecticide
  4. Inheritance of acquired resistance from exposed parents

Explanation

Resistance alleles already exist in the population; the insecticide acts as a selective pressure that favors resistant individuals, which survive and reproduce more. Mutations are not directed by the environment, and drift does not create new alleles.

Question 42Genetics and Evolution

In a certain plant, flower color shows incomplete dominance: RR produces red flowers, rr produces white flowers, and Rr produces pink flowers. If two pink-flowered plants are crossed, what phenotypic ratio is expected among the offspring?

  1. 2 pink : 1 red : 1 white
  2. 1 red : 1 white
  3. 3 red : 1 white
  4. 1 red : 2 pink : 1 white Correct answer.

Explanation

Crossing Rr × Rr yields genotypes in a 1 RR : 2 Rr : 1 rr ratio. Because heterozygotes are phenotypically distinct (pink), the phenotypic ratio is 1 red : 2 pink : 1 white.

Question 43Genetics and Evolution

A woman who is a carrier of an X-linked recessive disorder (X^A X^a) has children with an unaffected man (X^A Y). What is the probability that a son will be affected?

  1. 3/4
  2. 1/2 Correct answer.
  3. 1/4
  4. 0

Explanation

Sons receive their X chromosome from the mother, who is heterozygous, so each son has a 1/2 chance of inheriting X^a and being affected. The father contributes a Y chromosome to sons and cannot pass his X-linked allele to them.

Question 44Genetics and Evolution

Which statement best describes the role of restriction enzymes in recombinant DNA technology?

  1. They cut DNA at specific recognition sequences, producing fragments that can be joined with other DNA. Correct answer.
  2. They separate DNA fragments according to size in a gel.
  3. They amplify a target sequence using thermal cycling.
  4. They join two DNA fragments by forming phosphodiester bonds.

Explanation

Restriction endonucleases recognize specific palindromic sequences and cleave DNA there, often leaving sticky ends that allow complementary fragments to be ligated. Ligation, amplification, and separation are performed by other tools.

Question 45Genetics and Evolution

A population of 500 individuals has 320 individuals with the dominant phenotype and 180 with the recessive phenotype. Assuming Hardy–Weinberg equilibrium, what is the approximate frequency of the recessive allele?

  1. 0.36
  2. 0.60 Correct answer.
  3. 0.40
  4. 0.64

Explanation

The recessive phenotype frequency is q² = 180/500 = 0.36, so q = √0.36 = 0.60. The dominant allele frequency p is therefore 0.40, and the heterozygote frequency is 2pq = 0.48.

Question 46Genetics and Evolution

Which of the following provides the strongest evidence that two species share a recent common ancestor?

  1. They have similar body size
  2. They share highly similar DNA sequences in conserved genes Correct answer.
  3. They live in the same geographic region
  4. They occupy similar ecological niches

Explanation

Molecular similarity in conserved genes reflects shared ancestry because mutations accumulate over time; closer sequences imply a more recent divergence. Ecological niche, body size, and geography can converge without common ancestry.

Question 47Genetics and Evolution

A frameshift mutation occurs near the beginning of a coding sequence. Which consequence is most likely?

  1. A single amino acid substitution with no other effects
  2. A longer protein due to extra nucleotides being added
  3. A completely different amino acid sequence downstream of the mutation Correct answer.
  4. No change in the protein because the code is degenerate

Explanation

Inserting or deleting a number of bases not divisible by three shifts the reading frame, so every downstream codon is read differently. This usually produces a nonfunctional protein, unlike a simple substitution.

Question 48Genetics and Evolution

In a cross between a homozygous dominant individual and a homozygous recessive individual, all F1 offspring show the dominant phenotype. When the F1 generation is self-crossed, what genotypic ratio is expected in the F2?

  1. 9 dominant : 3 : 3 : 1 recessive
  2. 1 heterozygous : 1 homozygous recessive
  3. 3 homozygous dominant : 1 homozygous recessive
  4. 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive Correct answer.

Explanation

The F1 individuals are all heterozygous (Aa). Crossing Aa × Aa yields genotypes in the ratio 1 AA : 2 Aa : 1 aa, which corresponds to a 3:1 phenotypic ratio.

Question 49Genetics and Evolution

Which event during meiosis is the primary cause of the independent assortment of genes located on different chromosomes?

  1. Formation of the nuclear envelope in telophase I
  2. Condensation of chromatin in prophase I
  3. Separation of sister chromatids at anaphase II
  4. Random orientation of homologous pairs at metaphase I Correct answer.

Explanation

At metaphase I, each homologous pair aligns independently of other pairs, so maternal and paternal chromosomes are distributed randomly to the poles. This random orientation underlies independent assortment; sister chromatid separation affects identical copies.

Question 50Genetics and Evolution

A gene for coat color in mice has two alleles: A (agouti) and a (black). In a population, the frequency of the A allele is 0.8. If mating is random and the population is large, what is the expected frequency of black mice?

  1. 0.04 Correct answer.
  2. 0.32
  3. 0.64
  4. 0.16

Explanation

Black mice have the aa genotype, whose expected frequency is q². With q = 0.2, q² = 0.04. The heterozygote frequency 2pq would be 0.32, and p² would be 0.64.