I85PREP
⌘ K
Kerala SSLC Biology study materials
Kerala SSLC Biology study resources

Kerala SSLC Biology practice questions

One question at a time. Build your Kerala SSLC Biology understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Cell Biology and Cell Division

Which cell organelle is described as the control centre of the cell because it contains the genetic material DNA?

  1. Golgi apparatus
  2. Ribosome
  3. Nucleus Correct answer.
  4. Lysosome

Explanation

The nucleus encloses the chromosomes, which are made of DNA, and it directs all cellular activities through the instructions coded in that DNA. Ribosomes, Golgi bodies and lysosomes carry out protein synthesis, packaging and digestion rather than storing genetic information.

Question 2Cell Biology and Cell Division

A student observes a cell with a rigid cellulose wall, a large central vacuole and chloroplasts. This cell most probably belongs to which group of organisms?

  1. Bacteria
  2. Animals
  3. Fungi
  4. Green plants Correct answer.

Explanation

Cellulose walls, a prominent central vacuole and chloroplasts are together characteristic of plant cells, which photosynthesise and need turgor support. Animal cells lack walls and chloroplasts, bacterial walls are not cellulosic, and fungal walls are chiefly chitin.

Question 3Cell Biology and Cell Division

Which of the following is the correct sequence of stages in mitosis?

  1. Anaphase, telophase, prophase, metaphase
  2. Prophase, anaphase, metaphase, telophase
  3. Metaphase, prophase, telophase, anaphase
  4. Prophase, metaphase, anaphase, telophase Correct answer.

Explanation

Mitosis proceeds through prophase, when chromosomes condense; metaphase, when they align at the equator; anaphase, when chromatids move to the poles; and telophase, when nuclei reform. Any other order places chromosome alignment after separation, which cannot occur.

Question 4Cell Biology and Cell Division

The fluid-filled jelly-like substance in which the cell organelles are suspended is called the:

  1. Nucleoplasm
  2. Stroma of the chloroplast
  3. Cytoplasm Correct answer.
  4. Matrix of the mitochondrion

Explanation

The cytoplasm is the ground substance of the cell between the plasma membrane and the nucleus, and it holds the organelles in position. Nucleoplasm, mitochondrial matrix and chloroplast stroma are each confined inside a specific organelle.

Question 5Cell Biology and Cell Division

How many chromosomes are present in a normal human somatic (body) cell?

  1. 92
  2. 46 Correct answer.
  3. 23
  4. 22

Explanation

Human body cells are diploid, carrying 23 pairs of chromosomes, which gives a total of 46. The number 23 is the haploid count found in gametes, and 92 would appear only after DNA replication in a dividing cell.

Question 6Cell Biology and Cell Division

Which organelle is known as the powerhouse of the cell because it releases energy through aerobic respiration?

  1. Mitochondrion Correct answer.
  2. Nucleolus
  3. Endoplasmic reticulum
  4. Vacuole

Explanation

Mitochondria carry out the later stages of aerobic respiration and produce ATP, the energy currency of the cell, so they are called the powerhouse. The endoplasmic reticulum transports materials, the nucleolus makes ribosomal subunits and the vacuole stores substances.

Question 7Cell Biology and Cell Division

Which of these structures is present in a prokaryotic cell such as a bacterium?

  1. Ribosome Correct answer.
  2. Membrane-bound nucleus
  3. Mitochondrion
  4. Golgi apparatus

Explanation

Prokaryotic cells have no membrane-bound organelles, but they do contain ribosomes, which are the non-membranous sites of protein synthesis. Nucleus, mitochondria and Golgi bodies are all membrane-bound structures found only in eukaryotes.

Question 8Cell Biology and Cell Division

During which phase of the cell cycle does DNA replication take place?

  1. M phase
  2. G2 phase
  3. S phase Correct answer.
  4. G1 phase

Explanation

DNA synthesis occurs in the S phase, the middle part of interphase, when each chromosome is copied into two sister chromatids. G1 and G2 are growth phases, and M phase is when the copied chromosomes are separated and distributed.

Question 9Cell Biology and Cell Division

A cell with 20 chromosomes undergoes mitosis. What will be the chromosome number in each daughter cell produced?

  1. 40
  2. 20 Correct answer.
  3. 5
  4. 10

Explanation

Mitosis is an equational division, so each daughter cell receives the same chromosome number as the parent cell. A parent with 20 chromosomes therefore yields two daughter cells, each with 20 chromosomes.

Question 10Cell Biology and Cell Division

Which event is characteristic of anaphase of mitosis?

  1. Chromosomes line up along the equatorial plane
  2. Chromosomes condense and become visible
  3. Sister chromatids separate and move towards opposite poles Correct answer.
  4. Nuclear membrane reforms around each group of chromosomes

Explanation

In anaphase the centromeres split, sister chromatids are pulled apart and travel along the spindle fibres towards opposite poles. Nuclear reformation, chromosome condensation and equatorial alignment belong to telophase, prophase and metaphase respectively.

Question 11Cell Biology and Cell Division

Which of the following best explains why meiosis is essential for sexual reproduction?

  1. It produces gametes with half the chromosome number so that fusion restores the diploid number Correct answer.
  2. It replaces worn-out cells in body tissues
  3. It produces genetically identical daughter cells for growth
  4. It doubles the chromosome number before fertilisation

Explanation

Meiosis is a reduction division that halves the chromosome number, so gametes are haploid. When two gametes fuse at fertilisation the diploid number is restored and the species number stays constant across generations.

Question 12Cell Biology and Cell Division

A plant cell placed in a strongly hypertonic solution will most likely show:

  1. Plasmolysis, with the protoplast shrinking away from the wall Correct answer.
  2. Swelling due to endosmosis
  3. No change in the vacuole
  4. Bursting of the cell

Explanation

In a hypertonic solution water leaves the cell by exosmosis, so the vacuole and protoplast shrink and pull away from the cell wall, a condition called plasmolysis. Because a plant cell has a rigid wall it does not burst, and swelling happens only in a hypotonic medium.

Question 13Cell Biology and Cell Division

Which statement correctly distinguishes rough endoplasmic reticulum from smooth endoplasmic reticulum?

  1. Rough ER stores starch while smooth ER stores protein
  2. Rough ER lacks ribosomes while smooth ER carries them
  3. Rough ER bears ribosomes and synthesises proteins while smooth ER synthesises lipids Correct answer.
  4. Rough ER is found only in prokaryotes while smooth ER is found in eukaryotes

Explanation

Rough ER is studded with ribosomes and is the site of synthesis of proteins destined for secretion or membranes. Smooth ER has no ribosomes and is associated with lipid and steroid synthesis and detoxification.

Question 14Cell Biology and Cell Division

In a section of onion root tip, cells showing chromosomes lined up at the centre of the cell belong to which stage?

  1. Anaphase
  2. Prophase
  3. Telophase
  4. Metaphase Correct answer.

Explanation

Metaphase is identified by chromosomes arranged along the equatorial plate of the spindle. Prophase shows scattered condensed chromosomes, anaphase shows separating chromatids and telophase shows two reforming nuclei.

Question 15Cell Biology and Cell Division

Which of the following is a function of the cell membrane?

  1. Digestion of worn-out organelles
  2. Synthesis of ribosomal RNA
  3. Formation of spindle fibres
  4. Selective transport of substances into and out of the cell Correct answer.

Explanation

The plasma membrane is selectively permeable and controls which substances enter or leave the cell, largely through its protein channels and pumps. rRNA synthesis, organelle digestion and spindle formation belong to the nucleolus, lysosomes and centrioles respectively.

Question 16Cell Biology and Cell Division

A cell is treated with a drug that prevents the formation of the spindle apparatus. Which process will be most directly blocked?

  1. Formation of the cell plate in plant cells
  2. Movement of chromatids to the poles during mitosis Correct answer.
  3. Replication of DNA during S phase
  4. Synthesis of proteins on ribosomes

Explanation

Spindle fibres attach to centromeres and pull sister chromatids to opposite poles during anaphase, so their absence blocks that movement and the cell cannot complete division. DNA replication, cell-plate formation and ribosomal protein synthesis do not depend on the spindle.

Question 17Cell Biology and Cell Division

Which pair of organelles is directly involved in the synthesis and secretion of an enzyme from a gland cell?

  1. Centriole and nucleolus
  2. Lysosome and vacuole
  3. Chloroplast and mitochondrion
  4. Ribosome and Golgi apparatus Correct answer.

Explanation

Secretory proteins are synthesised on ribosomes, passed into the endoplasmic reticulum, and then modified, packaged and dispatched by the Golgi apparatus. Lysosomes, chloroplasts, mitochondria and centrioles are not part of the secretory pathway.

Question 18Cell Biology and Cell Division

Which feature is common to both plant and animal cells?

  1. Presence of chloroplasts
  2. Presence of a nucleus enclosed by a nuclear membrane Correct answer.
  3. Presence of a cellulose cell wall
  4. Presence of a large permanent central vacuole

Explanation

Both plant and animal cells are eukaryotic, so both have a true nucleus bounded by a nuclear membrane along with other membrane-bound organelles. Cellulose walls, chloroplasts and a large central vacuole are plant features.

Question 19Cell Biology and Cell Division

Two cells, one from a leaf and one from a root, are compared. Which difference would you expect?

  1. Only the leaf cell has a nucleus
  2. The leaf cell has chloroplasts while the root cell generally lacks them Correct answer.
  3. The root cell has chloroplasts while the leaf cell lacks them
  4. Only the root cell has a cell wall

Explanation

Chloroplasts develop in cells exposed to light, so photosynthetic leaf cells contain them while root cells, being underground, normally do not. Both cell types are plant cells and therefore both have walls and nuclei.

Question 20Cell Biology and Cell Division

A cell has completed meiosis II. How many haploid daughter cells are produced from one parent cell, and what is their chromosome content?

  1. Four cells, each haploid Correct answer.
  2. Four cells, each diploid
  3. Two cells, each haploid
  4. Two cells, each diploid

Explanation

Meiosis consists of two successive divisions after a single replication, so one parent cell yields four daughter cells. Each of these is haploid, carrying one chromosome of each homologous pair.

Question 21Cell Biology and Cell Division

In a dihybrid cross between two plants heterozygous for both characters (RrYy x RrYy), what phenotypic ratio is expected in the offspring when the genes assort independently?

  1. 3:1
  2. 9:3:3:1 Correct answer.
  3. 1:2:1
  4. 1:1:1:1

Explanation

Independent assortment of two heterozygous gene pairs gives four phenotypic classes in the ratio 9:3:3:1, obtained by multiplying the two 3:1 monohybrid ratios. The 3:1 and 1:2:1 ratios describe single-gene crosses, and 1:1:1:1 arises from a test cross with a double recessive.

Question 22Cell Biology and Cell Division

Which statement about the behaviour of chromosomes during meiosis explains Mendel's law of segregation?

  1. Non-homologous chromosomes fuse during prophase I
  2. Chromosomes replicate again between meiosis I and meiosis II
  3. Homologous chromosomes pair and then separate into different gametes Correct answer.
  4. Sister chromatids remain together throughout both divisions

Explanation

During meiosis I the homologous chromosomes synapse and then move to opposite poles, so each gamete receives only one member of each pair. This separation of the two alleles of a gene is the physical basis of segregation.

Question 23Cell Biology and Cell Division

A cell in G2 phase is compared with the same cell in G1 phase. Which difference is expected?

  1. The G2 cell has half the DNA content of the G1 cell
  2. The G2 cell has twice the chromosome number and twice the DNA content
  3. The G2 cell has the same DNA content but double the chromosome number
  4. The G2 cell has twice the DNA content but the same chromosome number Correct answer.

Explanation

DNA replicates during S phase, so by G2 the DNA content is doubled, but the two copies remain attached at a common centromere and are still counted as one chromosome. The chromosome number therefore stays unchanged until anaphase.

Question 24Cell Biology and Cell Division

A mutation prevents the centromeres from splitting during mitosis. What is the most direct consequence?

  1. The nuclear membrane cannot break down
  2. Chromosomes fail to condense during prophase
  3. DNA replication cannot begin in the next cycle
  4. Sister chromatids cannot be pulled to opposite poles, so the daughter nuclei receive unequal or no chromatids Correct answer.

Explanation

Centromere splitting releases the sister chromatids so that spindle fibres can draw them to opposite poles. If it fails, the chromatids cannot separate and distribution of the genetic material between the daughter cells is disrupted.

Question 25Genetics and Heredity

Which term describes the observable characteristics of an organism, such as flower colour and seed shape?

  1. Phenotype Correct answer.
  2. Genotype
  3. Allele
  4. Karyotype

Explanation

Phenotype refers to the visible or measurable features expressed by an organism, which result from the interaction of its genotype with the environment. Genotype is the underlying allele combination, not the outward appearance.

Question 26Genetics and Heredity

Mendel crossed pure-breeding red-flowered and pure-breeding white-flowered plants and obtained only red-flowered plants in the F1 generation. Which conclusion follows from this result?

  1. Red and white alleles blend to give an intermediate pink colour
  2. Red is dominant over white and the F1 plants are heterozygous Correct answer.
  3. White is dominant over red and the F1 plants are heterozygous
  4. The F1 plants are homozygous for the red allele

Explanation

When two pure lines are crossed and only one parental trait appears in F1, that trait is dominant and the F1 individuals carry one allele from each parent, making them heterozygous. The recessive white allele is still present but not expressed.

Question 27Genetics and Heredity

A cross between two heterozygous tall pea plants (Tt x Tt) produces offspring. What is the expected phenotypic ratio of tall to dwarf plants?

  1. All tall
  2. 3 tall : 1 dwarf Correct answer.
  3. 1 tall : 1 dwarf
  4. 1 tall : 3 dwarf

Explanation

A Tt x Tt cross gives the genotypic ratio 1 TT : 2 Tt : 1 tt. Since T is dominant, both TT and Tt are tall, so three of the four combinations are tall and only tt is dwarf, giving 3:1.

Question 28Genetics and Heredity

Which statement correctly describes the relationship between a gene and an allele?

  1. A gene and an allele are identical structures with no functional difference
  2. An allele is one of the alternative forms of a gene occupying the same locus Correct answer.
  3. An allele is a complete chromosome carrying many genes
  4. A gene is one of the alternative forms of an allele occupying different loci

Explanation

A gene is a segment of DNA that codes for a trait, and its variant forms are called alleles. Alleles of the same gene occupy the same position, or locus, on homologous chromosomes.

Question 29Genetics and Heredity

In humans, which combination of sex chromosomes produces a male child?

  1. XY Correct answer.
  2. YY
  3. XO
  4. XX

Explanation

Human males normally have one X and one Y chromosome, while females have two X chromosomes. The father's sperm determines the sex of the child because it may carry either an X or a Y.

Question 30Genetics and Heredity

A colour-blind man marries a woman who is homozygous normal for colour vision. What is the expected status of their children with respect to colour blindness?

  1. All sons are colour-blind and all daughters are normal
  2. All daughters are carriers and all sons have normal vision Correct answer.
  3. All daughters are colour-blind and all sons are normal
  4. Both sons and daughters are colour-blind

Explanation

Colour blindness is X-linked recessive. The affected father passes his X bearing the recessive allele to every daughter, making them carriers, while his Y goes to every son, so sons receive a normal X from the mother and see colours normally.

Question 31Genetics and Heredity

Which of the following is a sex-linked genetic disorder in humans?

  1. Thalassaemia
  2. Phenylketonuria
  3. Sickle cell anaemia
  4. Haemophilia Correct answer.

Explanation

Haemophilia is caused by a recessive allele carried on the X chromosome, so it is described as sex-linked and is far more common in males. The other disorders listed are autosomal conditions.

Question 32Genetics and Heredity

A woman who is a carrier of an X-linked recessive disorder marries a man with normal vision. What is the probability that a son born to them will be affected by the disorder?

  1. 50% Correct answer.
  2. 25%
  3. 0%
  4. 100%

Explanation

A carrier mother has one normal X and one X carrying the recessive allele. Each son receives one of her X chromosomes with equal chance, so half of her sons inherit the affected allele and show the disorder.

Question 33Genetics and Heredity

What is the chromosomal basis of Down syndrome in humans?

  1. A missing X chromosome
  2. An extra Y chromosome
  3. An extra copy of chromosome 21 Correct answer.
  4. Deletion of a part of chromosome 4

Explanation

Down syndrome results from trisomy of chromosome 21, that is three copies instead of the usual two, usually due to failure of chromosomes to separate during meiosis. This produces the characteristic features of the condition.

Question 34Genetics and Heredity

Which of the following best describes a mutation?

  1. The normal exchange of alleles during fertilisation
  2. The separation of homologous chromosomes during meiosis
  3. The random assortment of chromosomes into gametes
  4. A sudden change in the base sequence or structure of DNA Correct answer.

Explanation

A mutation is a heritable change in the genetic material, involving alteration of the base sequence of a gene or the structure and number of chromosomes. It is not a routine part of sexual reproduction.

Question 35Genetics and Heredity

A mutation that changes a single base pair in a gene is best described as which type of mutation?

  1. Point mutation Correct answer.
  2. Frameshift mutation
  3. Polyploidy
  4. Chromosomal deletion

Explanation

A point mutation is a change involving a single base pair, such as a substitution. It differs from changes in chromosome number or structure and from insertions or deletions that shift the reading frame.

Question 36Genetics and Heredity

Which of the following is an example of a hereditary variation that arises from sexual reproduction?

  1. Uniform height of all plants grown from cuttings
  2. Identical body weight of all members of a clone
  3. Differences among siblings produced by the same parents Correct answer.
  4. Constancy of traits in a pure-breeding line

Explanation

Sexual reproduction produces new allele combinations through crossing over and independent assortment, so siblings differ from one another. Asexual propagation and pure-breeding lines produce genetically uniform offspring.

Question 37Genetics and Heredity

In a dihybrid cross between plants heterozygous for both seed shape and seed colour (RrYy x RrYy), what phenotypic ratio is expected in the offspring?

  1. 9:3:3:1 Correct answer.
  2. 3:1
  3. 1:2:1
  4. 1:1:1:1

Explanation

When two genes on different chromosomes are considered together, each behaves independently, and the 3:1 ratio of each monohybrid cross multiplies to give 9:3:3:1. This is the classic outcome of independent assortment in a dihybrid cross.

Question 38Genetics and Heredity

What does the law of independent assortment state?

  1. Dominant alleles always mask recessive alleles in the heterozygote
  2. Alleles of different genes assort independently of one another during gamete formation Correct answer.
  3. Both alleles of a gene separate during gamete formation
  4. Genes on the same chromosome always segregate together

Explanation

Mendel's law of independent assortment states that the alleles of two or more different genes are distributed into gametes independently of one another. This holds for genes located on different chromosomes or far apart on the same chromosome.

Question 39Genetics and Heredity

Which process during meiosis produces new combinations of alleles on a single chromosome?

  1. Formation of the spindle apparatus
  2. Separation of sister chromatids
  3. Crossing over between homologous chromosomes Correct answer.
  4. Cytokinesis after telophase

Explanation

Crossing over involves exchange of segments between non-sister chromatids of homologous chromosomes during prophase I. This recombination creates new allele combinations on a chromosome and increases genetic variation.

Question 40Genetics and Heredity

A pure-breeding red-flowered plant crossed with a pure-breeding white-flowered plant gives F1 plants with pink flowers. When these F1 plants are self-pollinated, what phenotypic ratio appears in the F2 generation?

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

Explanation

This is incomplete dominance: the heterozygote shows an intermediate phenotype, so the genotypic ratio is visible directly. The F2 offspring are 1 homozygous red : 2 heterozygous pink : 1 homozygous white.

Question 41Genetics and Heredity

In humans, the ABO blood group is controlled by three alleles. What is this situation called?

  1. Pleiotropy
  2. Codominance between two alleles only
  3. Multiple allelism Correct answer.
  4. Polygenic inheritance

Explanation

Multiple allelism means that a gene exists in more than two allelic forms within a population, as with the IA, IB and i alleles of the ABO locus. Any individual still carries only two of these alleles.

Question 42Genetics and Heredity

A child has blood group AB. Which parental blood group combination is possible for this child?

  1. O and O
  2. A and B Correct answer.
  3. A and O
  4. B and O

Explanation

Blood group AB requires one IA allele and one IB allele, which must come from the two parents. A parent of group A can supply IA and a parent of group B can supply IB, giving an AB child.

Question 43Genetics and Heredity

Which of the following is an autosomal recessive disorder in humans?

  1. Sickle cell anaemia Correct answer.
  2. Haemophilia
  3. Colour blindness
  4. Huntington's disease

Explanation

Sickle cell anaemia is caused by a recessive allele on an autosome and appears only in homozygotes. The other conditions listed are either X-linked recessive or dominant.

Question 44Genetics and Heredity

A carrier of a recessive genetic disorder is best described as a person who

  1. has one recessive allele but shows no symptoms of the disorder Correct answer.
  2. has two recessive alleles and shows the disorder
  3. has two dominant alleles and cannot pass the disorder to offspring
  4. has a chromosomal abnormality affecting many genes

Explanation

A carrier is heterozygous for a recessive allele, so the dominant normal allele prevents expression of the disorder. However, the carrier can pass the recessive allele to offspring, who may be affected if the partner also contributes one.

Question 45Genetics and Heredity

Two parents who are both carriers of an autosomal recessive disorder have a child. What is the probability that the child will be affected?

  1. 25% Correct answer.
  2. 75%
  3. 100%
  4. 50%

Explanation

Crossing two heterozygotes gives a genotypic ratio of 1 homozygous dominant : 2 heterozygous carriers : 1 homozygous recessive. Only the homozygous recessive combination shows the disorder, so the chance is one in four.

Question 46Genetics and Heredity

Which of the following observations from Mendel's work provides the strongest evidence for the law of segregation?

  1. The F2 generation shows a 3:1 ratio of dominant to recessive traits
  2. The recessive trait reappears in the F2 generation after being absent in F1 Correct answer.
  3. The F1 generation shows only the dominant trait
  4. Pea plants can be self-pollinated easily

Explanation

The reappearance of the recessive trait in F2 shows that the recessive allele was not lost but remained hidden in F1 and separated again during gamete formation. This separation of paired alleles is exactly what the law of segregation describes.

Question 47Genetics and Heredity

Why do the offspring of a cross between two pure-breeding lines show genetic variation when the parents are crossed with each other over several generations?

  1. The alleles of the parents change their chemical structure during fertilisation
  2. New allele combinations arise through segregation, independent assortment and crossing over Correct answer.
  3. Dominant alleles are converted into recessive alleles in each generation
  4. The number of chromosomes doubles in every generation

Explanation

Genetic variation in sexual reproduction arises because alleles separate, assort independently and recombine by crossing over during meiosis, producing gametes with many different combinations. Fusion of such gametes yields offspring that differ from each other and from the parents.

Question 48Genetics and Heredity

In a cross between a heterozygous tall pea plant (Tt) and a short pea plant (tt), what proportion of the offspring is expected to be short?

  1. One half Correct answer.
  2. Three quarters
  3. One quarter
  4. All of them

Explanation

The heterozygous parent Tt produces two kinds of gametes, T and t, in equal numbers, while the short parent tt produces only t gametes. Combining them gives Tt (tall) and tt (short) in a 1:1 ratio, so half the offspring are short. This is a test cross, and the appearance of short offspring shows that the tall parent carried the recessive allele.

Question 49Physiology of Plants and Animals

In the human digestive system, which enzyme begins the chemical digestion of starch, and where is it secreted?

  1. Lipase, secreted by the liver into the duodenum
  2. Trypsin, secreted by the pancreas into the small intestine
  3. Pepsin, secreted by the gastric glands into the stomach
  4. Salivary amylase, secreted by the salivary glands into the mouth Correct answer.

Explanation

Starch digestion starts in the mouth, where salivary amylase (ptyalin) hydrolyses starch into maltose at a slightly alkaline pH. Pepsin acts on proteins in the stomach, trypsin on proteins and peptides in the small intestine, and lipase on fats.

Question 50Physiology of Plants and Animals

Which blood vessel carries oxygenated blood from the lungs to the heart?

  1. Aorta
  2. Vena cava
  3. Pulmonary artery
  4. Pulmonary vein Correct answer.

Explanation

The pulmonary vein is the exception to the rule that veins carry deoxygenated blood: it returns oxygenated blood from the lungs to the left atrium. The pulmonary artery carries deoxygenated blood to the lungs, the vena cava brings body blood to the right atrium, and the aorta carries blood away from the left ventricle.