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Angola 12th Grade Biology National Exam study materials
Angola 12th Grade Biology National Exam study resources

Angola 12th Grade Biology National Exam practice questions

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Question 1Cell Biology

Which organelle is the main site of ATP synthesis in a eukaryotic cell?

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

Explanation

ATP is produced mainly by oxidative phosphorylation, a process carried out by the electron transport chain located on the inner mitochondrial membrane. Other organelles perform different specialised functions.

Question 2Cell Biology

A solution is described as hypertonic to a cell. What happens when the cell is placed in it?

  1. Water enters the cell and the cell swells
  2. The cell neither gains nor loses water
  3. Water leaves the cell and the cell shrinks Correct answer.
  4. Solutes move out of the cell by diffusion

Explanation

A hypertonic solution has a lower water potential than the cell contents, so water moves out by osmosis across the membrane. Loss of water reduces cell volume.

Question 3Cell Biology

Which molecule carries the genetic instructions from the nucleus to the ribosome?

  1. mRNA Correct answer.
  2. DNA polymerase
  3. tRNA
  4. rRNA

Explanation

Messenger RNA is transcribed from DNA in the nucleus and transports the coded message to ribosomes for translation. The other molecules have different roles in gene expression.

Question 4Cell Biology

Which structure controls the movement of substances into and out of a cell?

  1. Cell membrane Correct answer.
  2. Cell wall
  3. Cytoskeleton
  4. Nuclear envelope

Explanation

The cell membrane is a selectively permeable phospholipid bilayer that regulates exchange of materials. It is the boundary that determines what enters and leaves.

Question 5Cell Biology

Which process produces two genetically identical daughter cells?

  1. Mitosis Correct answer.
  2. Crossing over
  3. Meiosis
  4. Fertilisation

Explanation

Mitosis is a division in which chromosomes are copied and distributed so that each daughter cell receives an identical set. This maintains genetic constancy in body cells.

Question 6Cell Biology

Which part of the cell contains the chromosomes in a eukaryotic cell?

  1. Nucleus Correct answer.
  2. Centriole
  3. Vacuole
  4. Golgi apparatus

Explanation

Chromosomes are located within the nucleus, which encloses the genetic material. The other structures listed do not house the chromosomes.

Question 7Cell Biology

What is the basic unit of structure and function in all living organisms?

  1. The cell Correct answer.
  2. The organelle
  3. The organ
  4. The tissue

Explanation

Cell theory states that the cell is the fundamental structural and functional unit of life. Tissues, organs and organelles are either composed of cells or are parts of cells.

Question 8Cell Biology

Which type of transport requires energy from ATP?

  1. Simple diffusion
  2. Facilitated diffusion
  3. Osmosis
  4. Active transport Correct answer.

Explanation

Active transport moves substances against their concentration gradient and therefore requires metabolic energy in the form of ATP. Passive processes rely on the gradient itself.

Question 9Cell Biology

During which stage of the cell cycle does DNA replication occur?

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

Explanation

DNA is replicated during the S phase of interphase, before the cell enters division. This ensures each daughter cell receives a complete set of chromosomes.

Question 10Cell Biology

A plant cell is placed in pure water. What is the most likely result?

  1. Water leaves and the cell plasmolyses
  2. Water enters and the cell becomes turgid Correct answer.
  3. The cell bursts because it lacks a wall
  4. No water moves because the cell is isotonic

Explanation

Pure water has a higher water potential than the cell sap, so water enters by osmosis. The rigid cell wall resists expansion, producing turgor rather than bursting.

Question 11Cell Biology

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Prokaryotes lack ribosomes
  2. Prokaryotes lack a cell membrane
  3. Prokaryotes lack genetic material
  4. Prokaryotes lack a membrane-bound nucleus Correct answer.

Explanation

Prokaryotes have no nuclear envelope, so their DNA lies free in the cytoplasm. They still possess ribosomes, a cell membrane and genetic material.

Question 12Cell Biology

An enzyme catalyses a reaction. What happens to the enzyme after the reaction is complete?

  1. It is permanently broken down into amino acids
  2. It is converted into a substrate
  3. It becomes part of the product
  4. It is released unchanged and can catalyse again Correct answer.

Explanation

Enzymes are biological catalysts; they lower activation energy without being consumed. The enzyme is released unchanged and may act repeatedly.

Question 13Cell Biology

Which process describes the movement of water across a selectively permeable membrane from a dilute to a concentrated solution?

  1. Osmosis Correct answer.
  2. Diffusion of solutes
  3. Active transport
  4. Phagocytosis

Explanation

Osmosis is the net movement of water molecules through a selectively permeable membrane down a water potential gradient. It specifically concerns water, not solutes.

Question 14Cell Biology

In a cell, a mutation changes the active site of an enzyme. What is the most direct consequence?

  1. The substrate can no longer bind efficiently Correct answer.
  2. The enzyme will catalyse more reactions
  3. The enzyme is transported to the nucleus
  4. The enzyme becomes a different type of molecule

Explanation

Enzyme action depends on the complementary fit between the substrate and the active site. Altering the active site reduces or prevents substrate binding, lowering catalytic activity.

Question 15Cell Biology

Which statement correctly describes the fluid mosaic model of the cell membrane?

  1. The membrane is a rigid layer of protein with no lipids
  2. Proteins are embedded in or attached to a fluid phospholipid bilayer Correct answer.
  3. The membrane consists only of a single layer of phospholipids
  4. Carbohydrates form the main permeability barrier

Explanation

The fluid mosaic model describes a bilayer of phospholipids in which proteins float or are anchored, with carbohydrates attached to some components. The arrangement is dynamic rather than fixed.

Question 16Cell Biology

Which sequence correctly describes the stages of mitosis?

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

Explanation

Mitosis proceeds through prophase, metaphase, anaphase and telophase, followed by cytokinesis. In metaphase chromosomes align at the equator before chromatids separate in anaphase.

Question 17Cell Biology

A cell is treated with a drug that prevents the formation of spindle fibres. Which stage of mitosis is most directly affected?

  1. Formation of the nuclear envelope
  2. Movement of chromatids to the poles Correct answer.
  3. Replication of DNA
  4. Condensation of chromatin

Explanation

Spindle fibres attach to chromosomes and pull chromatids to opposite poles during anaphase. Without them, chromosome segregation cannot occur normally.

Question 18Cell Biology

Which molecule is the universal energy currency used to drive cellular reactions?

  1. ATP Correct answer.
  2. Pyruvate
  3. Glucose
  4. NADH

Explanation

ATP releases usable energy when its terminal phosphate bond is hydrolysed, and this energy drives many cellular processes. It is regenerated continuously by respiration.

Question 19Cell Biology

Which organelle contains hydrolytic enzymes and digests worn-out cell components?

  1. Chloroplast
  2. Ribosome
  3. Lysosome Correct answer.
  4. Smooth endoplasmic reticulum

Explanation

Lysosomes are membrane-bound vesicles containing hydrolytic enzymes that break down macromolecules and damaged organelles. Their acidic interior supports enzyme activity.

Question 20Cell Biology

A red blood cell is placed in distilled water. Which observation is expected?

  1. It swells and may burst Correct answer.
  2. It forms a cell wall
  3. It stays the same size
  4. It shrinks and becomes crenated

Explanation

Distilled water is hypotonic to the cytoplasm, so water enters by osmosis. Lacking a cell wall, the red blood cell can swell and eventually burst through haemolysis.

Question 21Cell Biology

A cell is observed to have a large central vacuole, chloroplasts and a cellulose cell wall. What type of cell is this?

  1. A fungal cell
  2. A plant cell Correct answer.
  3. A bacterial cell
  4. An animal cell

Explanation

A large central vacuole, chloroplasts and a cellulose wall are characteristic features of plant cells. Animal and bacterial cells lack these combined features.

Question 22Cell Biology

Which statement best explains why the rate of diffusion increases when the temperature rises?

  1. The concentration gradient always increases
  2. Particles gain kinetic energy and move faster Correct answer.
  3. The membrane becomes fully permeable
  4. Particles become larger and collide more

Explanation

Higher temperature increases the kinetic energy of particles, so they move more rapidly and diffuse faster. The gradient itself is not necessarily changed by heating.

Question 23Cell Biology

In an experiment, a cell is placed in a solution and its mass decreases over time. Which conclusion is best supported?

  1. The external solution is hypotonic to the cell
  2. The external solution is hypertonic to the cell Correct answer.
  3. The cell is carrying out active transport of water
  4. The cell wall is digesting itself

Explanation

Loss of mass indicates net water loss by osmosis, which occurs when the surrounding solution has a lower water potential than the cell. Such a solution is hypertonic to the cell.

Question 24Cell Biology

A cell is unable to produce functional ribosomes. Which cellular process is most immediately disrupted?

  1. Translation of mRNA into protein Correct answer.
  2. Formation of the phospholipid bilayer
  3. Transcription of DNA into mRNA
  4. Replication of DNA

Explanation

Ribosomes are the site of translation, where mRNA is decoded into a polypeptide chain. Without functional ribosomes, protein synthesis stops even if transcription continues.

Question 25Cell Biology

During meiosis, crossing over between homologous chromosomes occurs. What is the main genetic consequence?

  1. Daughter cells become identical to the parent
  2. New combinations of alleles are produced Correct answer.
  3. DNA replication is prevented
  4. The chromosome number is doubled

Explanation

Crossing over exchanges segments between homologous chromosomes, generating new allele combinations in the gametes. This increases genetic variation among offspring.

Question 26Cell Biology

Which process produces the greatest number of ATP molecules from one molecule of glucose in a eukaryotic cell?

  1. Oxidative phosphorylation in the mitochondria Correct answer.
  2. Lactic acid fermentation
  3. Glycolysis in the cytoplasm
  4. The Krebs cycle alone

Explanation

Most ATP is generated when electrons from reduced coenzymes pass along the electron transport chain, creating a proton gradient that drives ATP synthase. Glycolysis and the Krebs cycle yield only small amounts of ATP directly, and fermentation yields very little.

Question 27Cell Biology

A student examines a tissue and finds cells with no nucleus and no membrane-bound organelles, surrounded by a cell wall. Which conclusion is best supported?

  1. The cells are prokaryotic, such as bacteria Correct answer.
  2. The cells are plant cells lacking a vacuole
  3. The cells are animal cells that have lost their nuclei
  4. The cells are fungal cells with chitin walls

Explanation

Prokaryotic cells lack a membrane-bound nucleus and organelles, and many have a cell wall. Plant, animal and fungal cells are eukaryotic and would show a nucleus and membrane-bound organelles.

Question 28Cell Biology

In an experiment, a strip of potato is placed in a concentrated sugar solution. After one hour the strip is shorter and stiffer. Which explanation best accounts for this observation?

  1. Water left the potato cells by osmosis, reducing their turgor Correct answer.
  2. The sugar solution dissolved part of the potato cell walls
  3. Water entered the potato cells and increased their turgor
  4. Sugar entered the potato cells and increased their volume

Explanation

The external solution has a lower water potential than the cell contents, so water moves out of the cells across the partially permeable membrane. Loss of water reduces turgor pressure, making the tissue shorter and less firm.

Question 29Cell Biology

A cell is exposed to a substance that blocks the synthesis of ATP in the mitochondria. Which process would continue unaffected for a short time?

  1. Movement of chromosomes by spindle fibres during anaphase
  2. Diffusion of oxygen across the cell membrane Correct answer.
  3. Synthesis of proteins on the ribosomes
  4. Active transport of ions against a concentration gradient

Explanation

Diffusion is a passive process driven by a concentration gradient and does not require ATP. Active transport, spindle activity and protein synthesis all depend on energy supplied by ATP.

Question 30Cell Biology

A mutation changes a single base in a gene so that one codon becomes a stop codon. Which effect on the resulting protein is most likely?

  1. The reading frame is shifted along the whole sequence
  2. The polypeptide chain is shortened and may lose its function Correct answer.
  3. The protein is produced normally because the genetic code is degenerate
  4. One amino acid is replaced but the chain length is unchanged

Explanation

A premature stop codon causes translation to end early, producing a truncated polypeptide that often cannot fold or function correctly. Degeneracy protects against some substitutions but cannot compensate for a codon turned into a stop signal.

Question 31Genetics and Heredity

Which molecule carries the genetic information from the nucleus to the ribosome during protein synthesis?

  1. Ribosomal RNA
  2. Deoxyribonucleic acid
  3. Messenger RNA Correct answer.
  4. Transfer RNA

Explanation

Messenger RNA is transcribed from DNA in the nucleus and carries the coded sequence of bases to the ribosome, where it is translated into a polypeptide. The other nucleic acids serve different roles in the cell.

Question 32Genetics and Heredity

In a monohybrid cross between two heterozygous individuals (Aa x Aa), what proportion of the offspring is expected to show the recessive phenotype?

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

Explanation

Each heterozygous parent produces A and a gametes in equal numbers, giving a 1 AA : 2 Aa : 1 aa ratio. Only the aa genotype expresses the recessive phenotype, which is one quarter of the offspring.

Question 33Genetics and Heredity

A human somatic cell normally contains how many chromosomes?

  1. 46 Correct answer.
  2. 44
  3. 92
  4. 23

Explanation

Human somatic cells are diploid, carrying 23 pairs of homologous chromosomes for a total of 46. Gametes are haploid and carry only 23.

Question 34Genetics and Heredity

What is the base sequence of the DNA strand complementary to the sequence 5'-ATGCC-3'?

  1. 5'-TACGG-3'
  2. 3'-TACGG-5' Correct answer.
  3. 3'-ATGCC-5'
  4. 5'-GGCAT-3'

Explanation

Complementary base pairing joins A with T and G with C, and the two strands are antiparallel. The complement of ATGCC read in matching order is TACGG, written antiparallel as 3'-TACGG-5'.

Question 35Genetics and Heredity

A cross between a red-flowered plant and a white-flowered plant produces only pink offspring. This result is best explained by

  1. sex linkage
  2. complete dominance
  3. incomplete dominance Correct answer.
  4. codominance

Explanation

In incomplete dominance the heterozygote shows an intermediate phenotype because neither allele fully masks the other, producing a blend such as pink from red and white. Codominance would instead show both parental phenotypes distinctly in the same individual.

Question 36Genetics and Heredity

Which of the following best describes the genotype of an organism?

  1. The environment in which it develops
  2. The visible physical traits it expresses
  3. The number of chromosomes in its cells
  4. The set of alleles it carries for a gene Correct answer.

Explanation

Genotype refers to the combination of alleles present in an organism for a given gene, such as AA, Aa or aa. Phenotype, by contrast, is the observable expression of those alleles.

Question 37Genetics and Heredity

A man with blood group A (genotype IA i) and a woman with blood group B (genotype IB i) have a child. What is the probability that the child has blood group O?

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

Explanation

Each parent can pass on either the i allele or their dominant allele. Group O requires genotype ii, which occurs only when both parents transmit i, giving a probability of 1/2 x 1/2 = 1/4.

Question 38Genetics and Heredity

During which stage of meiosis does crossing over occur?

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

Explanation

Crossing over takes place during prophase I, when homologous chromosomes pair as bivalents and exchange segments at the chiasmata. This recombination increases genetic variation among the resulting gametes.

Question 39Genetics and Heredity

A colour-blind man (X^b Y) marries a woman who is homozygous for normal colour vision (X^B X^B). What is expected for their children?

  1. All sons are colour-blind
  2. All daughters are carriers Correct answer.
  3. Half of the daughters are colour-blind
  4. All children are colour-blind

Explanation

Daughters receive X^B from the mother and X^b from the father, so all are heterozygous carriers with normal vision. Sons receive Y from the father and X^B from the mother, so all have normal colour vision.

Question 40Genetics and Heredity

Which of the following is a source of genetic variation produced during sexual reproduction?

  1. Replication of DNA in somatic cells
  2. Independent assortment of chromosomes Correct answer.
  3. Active transport across membranes
  4. Formation of the cell plate in plant cells

Explanation

Independent assortment during meiosis randomly distributes maternal and paternal homologues to gametes, creating many allele combinations. Together with crossing over and random fertilisation, it generates variation in offspring.

Question 41Genetics and Heredity

A mutation that changes a single DNA base but does not alter the amino acid sequence of the protein is called

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

Explanation

A silent mutation changes a base without changing the encoded amino acid, because the genetic code is degenerate and several codons specify the same amino acid. The protein therefore remains unchanged.

Question 42Genetics and Heredity

In a pedigree, a trait appears in every generation and affects both males and females in roughly equal numbers. This pattern is most consistent with

  1. mitochondrial inheritance
  2. autosomal dominant inheritance Correct answer.
  3. X-linked recessive inheritance
  4. Y-linked inheritance

Explanation

Autosomal dominant traits appear in each generation because one copy of the allele is sufficient for expression, and they affect both sexes equally. X-linked recessive traits typically skip generations and affect males more often.

Question 43Genetics and Heredity

What is the role of DNA ligase in DNA replication?

  1. It unwinds the double helix
  2. It proofreads the new strand
  3. It adds free nucleotides to the primer
  4. It joins Okazaki fragments Correct answer.

Explanation

DNA ligase seals the sugar-phosphate backbone between adjacent fragments, joining the Okazaki fragments produced on the lagging strand into a continuous molecule. Helicase unwinds the helix and polymerase adds nucleotides.

Question 44Genetics and Heredity

A test cross is performed to determine whether a tall pea plant is homozygous or heterozygous. Which cross is used?

  1. With another tall plant of unknown genotype
  2. With a short homozygous recessive plant Correct answer.
  3. With a plant heterozygous for height
  4. With itself through self-pollination

Explanation

A test cross uses a homozygous recessive partner, so any recessive allele in the unknown parent will be revealed by short offspring. If all offspring are tall, the parent is likely homozygous dominant.

Question 45Genetics and Heredity

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

  1. A gene is a variant form of an allele
  2. An allele contains many genes
  3. A gene and an allele are the same structure
  4. An allele is a variant form of a gene Correct answer.

Explanation

A gene is a segment of DNA that codes for a trait, while alleles are the alternative versions of that gene that may exist in a population. An organism inherits one allele of each gene from each parent.

Question 46Genetics and Heredity

A woman who is a carrier of an X-linked recessive disorder (X^A X^a) has children with a man who is unaffected (X^A Y). What proportion of their sons is expected to be affected?

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

Explanation

Sons receive Y from the father and one of the mother's X chromosomes. Half the sons inherit X^a and are affected, while half inherit X^A and are unaffected.

Question 47Genetics and Heredity

The phenotype of an organism is determined by

  1. the number of chromosomes only
  2. its genotype interacting with the environment Correct answer.
  3. its genotype alone
  4. the type of mutation only

Explanation

Phenotype results from the expression of the genotype under the influence of environmental factors such as nutrition, temperature and light. Identical genotypes can therefore produce different phenotypes in different conditions.

Question 48Genetics and Heredity

Which of the following is an example of a chromosomal mutation rather than a gene mutation?

  1. Insertion of a single nucleotide
  2. Deletion of a whole chromosome segment Correct answer.
  3. Substitution of one base pair
  4. Inversion of a single codon

Explanation

Chromosomal mutations involve changes in the structure or number of whole chromosomes, such as the deletion of a segment containing many genes. Gene mutations affect only the base sequence of a single gene.

Question 49Genetics and Heredity

In humans, the sex of a child is determined by

  1. the age of the mother at conception
  2. the type of egg produced by the mother
  3. the number of autosomes in the zygote
  4. the type of sperm that fertilises the egg Correct answer.

Explanation

The mother produces only X-bearing eggs, while the father produces X-bearing and Y-bearing sperm. If a Y-bearing sperm fertilises the egg the child is male, and if an X-bearing sperm does so the child is female.

Question 50Genetics and Heredity

A pure-breeding black guinea pig is crossed with a pure-breeding white guinea pig, and all the offspring are black. If two of these black offspring are crossed, what phenotypic ratio is expected?

  1. 1 black : 3 white
  2. All black
  3. 1 black : 1 white
  4. 3 black : 1 white Correct answer.

Explanation

Since all the first-generation offspring are black, black is dominant and the parents were homozygous BB and bb. The F1 pigs are all Bb, and Bb x Bb gives a 3:1 ratio of black to white in the next generation.