Free Grade 12 Life Sciences practice questions covering all NSC topics with full explanations.
Life Sciences Grade 12 is broad — it spans from molecular genetics to population ecology, with plant and animal physiology, evolution, and environmental science in between. Tour practice set covers all four CAPS topic areas: Life at the Molecular and Cellular Level, Life Processes in Plants and Animals, Diversity, Change, and Continuity, and Environmental Studies. Questions reflect both Paper 1 and Paper 2 styles.
Pay close attention to the explanations for genetics and DNA questions — these are the areas where most marks are lost in the actual NSC exam, and they require precise sequential understanding rather than general knowledge.
Life Sciences consists of two 2.5-hour papers worth 150 marks each. Paper 2 covers genetics, which accounts for 40+ marks — master Punnett squares and inheritance first.
Priority: Genetics, DNA, and the nervous system are the highest-yield topics for Paper 2.
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Question 01 of 20
Which organelle produces ATP via aerobic respiration?
Explanation: Mitochondria: powerhouse of the cell. Aerobic respiration produces ~36-38 ATP per glucose.
Explanation: Active transport: moves substances AGAINST concentration gradient using ATP.
Question 15 of 20
What is a gene?
Explanation: Gene: specific DNA sequence that codes for a protein or functional RNA.
Question 16 of 20
Dominant allele is expressed?
Explanation: Dominant allele expressed in phenotype even when only one copy present.
Question 17 of 20
Function of stomata?
Explanation: Stomata: CO2 in, O2 out. Also regulate transpiration (water loss).
Question 18 of 20
What is transpiration?
Explanation: Transpiration: evaporation of water from leaves through stomata.
Question 19 of 20
Function of the nephron?
Explanation: Nephron: functional unit of kidney. Filters blood, produces urine.
Question 20 of 20
Aerobic respiration net ATP yield?
Explanation: Aerobic respiration produces approximately 36-38 ATP per glucose molecule.
Q21
What is the cell theory?
Explanation: Cell theory (Schleiden, Schwann, Virchow): 1) All living organisms are composed of cells, 2) The cell is the basic unit of structure and function, 3) All cells arise from pre-existing cells (biogenesis).
Q22
What is the difference between prokaryotic and eukaryotic cells?
Explanation: Prokaryotes: DNA in nucleoid region, no membrane-bound organelles, smaller (~1-10μm). Eukaryotes: nucleus, membrane-bound organelles (mitochondria, ER, Golgi), larger (~10-100μm). Eukaryotes evolved from prokaryotes.
Q23
What is osmosis?
Explanation: Osmosis: passive (no energy needed), water moves down its concentration gradient. Hypotonic (lower solute) → hypertonic (higher solute). Turgor pressure: water entering plant cells inflates them. Plasmolysis: water leaving causes wilting.
Q24
What is the difference between diffusion and active transport?
Explanation: Diffusion: passive, high → low concentration, no ATP needed. Examples: O₂ into cells, CO₂ out. Active transport: requires ATP, moves substances against gradient. Examples: Na⁺/K⁺ pump, mineral uptake by plant roots.
Q25
What are the phases of mitosis?
Explanation: PMAT: Prophase (chromosomes condense, spindle forms), Metaphase (chromosomes align at equator), Anaphase (chromatids pulled to poles), Telophase (nuclear envelopes reform). Then Cytokinesis (cytoplasm divides).
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Q26
What is the role of enzymes?
Explanation: Enzymes: specific (lock-and-key or induced-fit model), reusable, affected by temperature and pH. Active site binds substrate. Denaturation: enzyme loses shape (not function reversibly — wait, high temp causes irreversible denaturation above optimal).
Q27
What is genetic variation and why is it important?
Explanation: Genetic variation sources: mutation (random DNA changes), sexual reproduction (meiosis + fertilisation), crossing over (recombination). Variation provides raw material for natural selection. Without variation, species cannot adapt to environmental change.
Q28
What is the difference between genotype and phenotype?
Explanation: Genotype: Tt, AA, RrBb (allele combinations). Phenotype: tall, round seeds, blue eyes (expressed traits). Phenotype = genotype × environment. Example: genotype for height interacts with nutrition to produce final height.
Q29
What is a food web?
Explanation: Food web: more realistic than single food chain. Producers (plants) → Primary consumers (herbivores) → Secondary consumers → Tertiary consumers → Decomposers. Energy lost at each level (~90% as heat) — explains why food chains are short.
Q30
What is biodiversity?
Explanation: Biodiversity: genetic (variation within species), species (number of species in an area), ecosystem (variety of habitats). South Africa is megadiverse — 3rd most biodiverse country. Threats: habitat destruction, pollution, invasive species, climate change.
Q31
What is the carbon cycle?
Explanation: Carbon cycle: plants fix CO₂ via photosynthesis → animals eat plants (carbon moves up food chain) → respiration releases CO₂ → decomposition releases CO₂ → fossil fuels (long-term storage) → combustion releases stored carbon. Human activity is disrupting balance.
Explanation: Homeostasis examples: thermoregulation (37°C body temperature), blood glucose (insulin/glucagon), blood pH, osmoregulation (water balance). Negative feedback: deviation from set point triggers response that reverses the change.
Q34
What is the difference between aerobic and anaerobic respiration?
Explanation: Aerobic: glucose + O₂ → CO₂ + H₂O + ~38 ATP. Occurs in mitochondria. Anaerobic (lactic acid fermentation): glucose → lactic acid + 2 ATP. Anaerobic (alcoholic fermentation): glucose → ethanol + CO₂ + 2 ATP. Anaerobic used when O₂ is limited.
Q35
What is the structure of a neuron?
Explanation: Neuron: Dendrites receive signals → cell body processes → axon conducts electrical impulse → synaptic terminals release neurotransmitters across synapse to next neuron. Myelin speeds conduction. Nodes of Ranvier: gaps in myelin.
Q36
What is transpiration?
Explanation: Transpiration: water vapour exits through stomata. Transpiration pull: creates tension that pulls water up xylem. Factors increasing transpiration: high temperature, low humidity, wind, high light intensity. Guard cells regulate stomatal opening.
Q37
What is the immune response?
Explanation: Immune response: First line (skin, mucus). Second line (inflammation, phagocytosis, NK cells). Third line (specific): B-lymphocytes produce antibodies (humoral), T-lymphocytes destroy infected cells (cellular). Memory cells: faster response on re-exposure (basis of vaccination).
Q38
What is the role of the kidneys in excretion?
Explanation: Kidney filtration: 180L filtered daily, 1.5L urine produced. Glomerular filtration → tubular reabsorption (glucose, amino acids, water) → tubular secretion → urine. ADH controls water reabsorption. Urea: formed in liver from ammonia.
Q39
What are the parts of the digestive system in order?
Explanation: Genetic engineering: recombinant DNA technology — cut desired gene (restriction enzymes), insert into vector (plasmid), introduce to host. Applications: insulin production (bacteria), GM crops (pest resistance), gene therapy. Concerns: safety, ethics, biodiversity.
Q43
What is ecological succession?
Explanation: Primary succession: bare rock → pioneer species (lichens) → soil formation → grassland → shrubland → forest. Secondary succession: after disturbance where soil remains. Climax community: stable, self-sustaining. SA example: fynbos post-fire succession.
Q44
What is the nitrogen cycle?
Explanation: Nitrogen cycle: N₂ fixation (Rhizobium bacteria in legume roots → NH₃), Nitrification (NH₃ → NO₂ → NO₃ by bacteria), Plant uptake, Animal consumption, Decomposition (organic N → NH₃), Denitrification (NO₃ → N₂). Disrupted by fertiliser runoff.
Q45
What is HIV/AIDS?
Explanation: HIV transmission: unprotected sexual contact, blood (sharing needles, transfusion), mother-to-child (birth, breastfeeding). CD4 count: healthy >500. AIDS diagnosis: <200 CD4 cells/μL. ARVs (antiretrovirals) allow near-normal lifespan.
Q46
What is the water cycle?
Explanation: Water cycle: Solar energy → Evaporation (water→vapour) + Transpiration → Condensation (clouds form) → Precipitation (rain, snow) → Surface runoff → Infiltration (groundwater) → Taken up by plants → Repeat. Also: sublimation, freezing, melting.
Q47
What are the adaptations of desert plants?
Explanation: Desert plant adaptations: succulents (store water in tissues), reduced/absent leaves (spines in cacti), waxy cuticle, deep taproots OR shallow spreading roots, CAM photosynthesis (stomata open at night), dormancy during drought.
Q48
What is the difference between a parasite and a mutualist?
Explanation: Ecological relationships: Mutualism (+/+): both benefit (clownfish/anemone, bees/flowers). Commensalism (+/0): one benefits, other unaffected. Parasitism (+/-): parasite benefits, host harmed (tapeworm, mosquito). Predation: predator kills prey.
Q49
What is biotic vs abiotic?
Explanation: Biotic factors: plants, animals, fungi, bacteria, dead organic matter. Abiotic factors: sunlight (photosynthesis energy), temperature (enzyme activity), water (photosynthesis, transport), soil composition, pH, wind, fire. Both shape ecosystems.
Q50
What is the function of leaves?
Explanation: Leaves: large surface area for light capture, thin (short CO₂ diffusion path), chloroplasts (photosynthesis), stomata (gas exchange, transpiration), vascular tissue (xylem brings water, phloem removes sugar), waxy cuticle (reduce water loss).
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Q51
What is the cell theory?
Explanation: Cell theory (Schleiden, Schwann, Virchow): 1) All living organisms are composed of cells, 2) The cell is the basic unit of structure and function, 3) All cells arise from pre-existing cells (biogenesis).
Q52
What is the difference between prokaryotic and eukaryotic cells?
Explanation: Prokaryotes: DNA in nucleoid region, no membrane-bound organelles, smaller (~1-10μm). Eukaryotes: nucleus, membrane-bound organelles (mitochondria, ER, Golgi), larger (~10-100μm). Eukaryotes evolved from prokaryotes.
Q53
What is osmosis?
Explanation: Osmosis: passive (no energy needed), water moves down its concentration gradient. Hypotonic (lower solute) → hypertonic (higher solute). Turgor pressure: water entering plant cells inflates them. Plasmolysis: water leaving causes wilting.
Q54
What is the difference between diffusion and active transport?
Explanation: Diffusion: passive, high → low concentration, no ATP needed. Examples: O₂ into cells, CO₂ out. Active transport: requires ATP, moves substances against gradient. Examples: Na⁺/K⁺ pump, mineral uptake by plant roots.
Q55
What are the phases of mitosis?
Explanation: PMAT: Prophase (chromosomes condense, spindle forms), Metaphase (chromosomes align at equator), Anaphase (chromatids pulled to poles), Telophase (nuclear envelopes reform). Then Cytokinesis (cytoplasm divides).
Q56
What is the role of enzymes?
Explanation: Enzymes: specific (lock-and-key or induced-fit model), reusable, affected by temperature and pH. Active site binds substrate. Denaturation: enzyme loses shape (not function reversibly — wait, high temp causes irreversible denaturation above optimal).
Q57
What is genetic variation and why is it important?
Explanation: Genetic variation sources: mutation (random DNA changes), sexual reproduction (meiosis + fertilisation), crossing over (recombination). Variation provides raw material for natural selection. Without variation, species cannot adapt to environmental change.
Q58
What is the difference between genotype and phenotype?
Explanation: Genotype: Tt, AA, RrBb (allele combinations). Phenotype: tall, round seeds, blue eyes (expressed traits). Phenotype = genotype × environment. Example: genotype for height interacts with nutrition to produce final height.
Q59
What is a food web?
Explanation: Food web: more realistic than single food chain. Producers (plants) → Primary consumers (herbivores) → Secondary consumers → Tertiary consumers → Decomposers. Energy lost at each level (~90% as heat) — explains why food chains are short.
Q60
What is biodiversity?
Explanation: Biodiversity: genetic (variation within species), species (number of species in an area), ecosystem (variety of habitats). South Africa is megadiverse — 3rd most biodiverse country. Threats: habitat destruction, pollution, invasive species, climate change.
Q61
What is the carbon cycle?
Explanation: Carbon cycle: plants fix CO₂ via photosynthesis → animals eat plants (carbon moves up food chain) → respiration releases CO₂ → decomposition releases CO₂ → fossil fuels (long-term storage) → combustion releases stored carbon. Human activity is disrupting balance.
Explanation: Homeostasis examples: thermoregulation (37°C body temperature), blood glucose (insulin/glucagon), blood pH, osmoregulation (water balance). Negative feedback: deviation from set point triggers response that reverses the change.
Q64
What is the difference between aerobic and anaerobic respiration?
Explanation: Aerobic: glucose + O₂ → CO₂ + H₂O + ~38 ATP. Occurs in mitochondria. Anaerobic (lactic acid fermentation): glucose → lactic acid + 2 ATP. Anaerobic (alcoholic fermentation): glucose → ethanol + CO₂ + 2 ATP. Anaerobic used when O₂ is limited.
Q65
What is the structure of a neuron?
Explanation: Neuron: Dendrites receive signals → cell body processes → axon conducts electrical impulse → synaptic terminals release neurotransmitters across synapse to next neuron. Myelin speeds conduction. Nodes of Ranvier: gaps in myelin.
Q66
What is transpiration?
Explanation: Transpiration: water vapour exits through stomata. Transpiration pull: creates tension that pulls water up xylem. Factors increasing transpiration: high temperature, low humidity, wind, high light intensity. Guard cells regulate stomatal opening.
Q67
What is the immune response?
Explanation: Immune response: First line (skin, mucus). Second line (inflammation, phagocytosis, NK cells). Third line (specific): B-lymphocytes produce antibodies (humoral), T-lymphocytes destroy infected cells (cellular). Memory cells: faster response on re-exposure (basis of vaccination).
Q68
What is the role of the kidneys in excretion?
Explanation: Kidney filtration: 180L filtered daily, 1.5L urine produced. Glomerular filtration → tubular reabsorption (glucose, amino acids, water) → tubular secretion → urine. ADH controls water reabsorption. Urea: formed in liver from ammonia.
Q69
What are the parts of the digestive system in order?
Explanation: Genetic engineering: recombinant DNA technology — cut desired gene (restriction enzymes), insert into vector (plasmid), introduce to host. Applications: insulin production (bacteria), GM crops (pest resistance), gene therapy. Concerns: safety, ethics, biodiversity.
Q73
What is ecological succession?
Explanation: Primary succession: bare rock → pioneer species (lichens) → soil formation → grassland → shrubland → forest. Secondary succession: after disturbance where soil remains. Climax community: stable, self-sustaining. SA example: fynbos post-fire succession.
Q74
What is the nitrogen cycle?
Explanation: Nitrogen cycle: N₂ fixation (Rhizobium bacteria in legume roots → NH₃), Nitrification (NH₃ → NO₂ → NO₃ by bacteria), Plant uptake, Animal consumption, Decomposition (organic N → NH₃), Denitrification (NO₃ → N₂). Disrupted by fertiliser runoff.
Q75
What is HIV/AIDS?
Explanation: HIV transmission: unprotected sexual contact, blood (sharing needles, transfusion), mother-to-child (birth, breastfeeding). CD4 count: healthy >500. AIDS diagnosis: <200 CD4 cells/μL. ARVs (antiretrovirals) allow near-normal lifespan.
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Q76
What is the water cycle?
Explanation: Water cycle: Solar energy → Evaporation (water→vapour) + Transpiration → Condensation (clouds form) → Precipitation (rain, snow) → Surface runoff → Infiltration (groundwater) → Taken up by plants → Repeat. Also: sublimation, freezing, melting.
Q77
What are the adaptations of desert plants?
Explanation: Desert plant adaptations: succulents (store water in tissues), reduced/absent leaves (spines in cacti), waxy cuticle, deep taproots OR shallow spreading roots, CAM photosynthesis (stomata open at night), dormancy during drought.
Q78
What is the difference between a parasite and a mutualist?
Explanation: Ecological relationships: Mutualism (+/+): both benefit (clownfish/anemone, bees/flowers). Commensalism (+/0): one benefits, other unaffected. Parasitism (+/-): parasite benefits, host harmed (tapeworm, mosquito). Predation: predator kills prey.
Q79
What is biotic vs abiotic?
Explanation: Biotic factors: plants, animals, fungi, bacteria, dead organic matter. Abiotic factors: sunlight (photosynthesis energy), temperature (enzyme activity), water (photosynthesis, transport), soil composition, pH, wind, fire. Both shape ecosystems.
Q80
What is the function of leaves?
Explanation: Leaves: large surface area for light capture, thin (short CO₂ diffusion path), chloroplasts (photosynthesis), stomata (gas exchange, transpiration), vascular tissue (xylem brings water, phloem removes sugar), waxy cuticle (reduce water loss).
Q81
What is the role of ribosomes?
Explanation: Ribosomes: found in cytoplasm (free) or rough ER (bound). Made of rRNA and protein. Small subunit: reads mRNA. Large subunit: catalyses peptide bond formation. Prokaryotic ribosomes (70S) targeted by antibiotics; eukaryotic (80S) not.
Q82
What is the difference between xylem and phloem?
Explanation: Xylem: dead cells (vessels, tracheids), lignified walls, one-directional, water + dissolved minerals. Phloem: living cells (sieve tubes + companion cells), bidirectional, sugars (mainly sucrose). Both form vascular bundles together.
Q83
What is meiosis II?
Explanation: Meiosis II: no DNA replication before it. Phases: Prophase II, Metaphase II, Anaphase II (sister chromatids separate), Telophase II. Each cell produced is haploid with one copy of each chromosome. Tour is where gametes are finalised.
Q84
What is the function of the chloroplast?
Explanation: Chloroplast structure: outer/inner membranes, thylakoid membranes (stacked into grana), stroma. Thylakoids: chlorophyll absorbs light, water split, O₂ released, ATP and NADPH produced. Stroma: Calvin cycle uses ATP+NADPH to fix CO₂ into G3P → glucose.
Q85
What is the difference between DNA and RNA?
Explanation: DNA: ATCG bases, stable, found in nucleus (mainly), carries genetic blueprint. RNA types: mRNA (carries code from DNA to ribosome), tRNA (brings amino acids), rRNA (ribosome structure). RNA is less stable — allows regulation of gene expression.
Q86
What is genetic drift?
Explanation: Genetic drift: Founder effect (small group establishes new population — limited gene pool). Bottleneck effect (population crashes — survivors' genes overrepresented). Not adaptive — driven by chance, not fitness. Reduces genetic diversity. Key factor in speciation of isolated populations.
Q87
What is ecological footprint?
Explanation: Ecological footprint: includes: land for food production, grazing, forest (CO₂ absorption), built-up land, fishing grounds. South Africa's footprint exceeds biocapacity. Biocapacity: what the Earth can regenerate. If footprint > biocapacity = ecological deficit (overshoot).
Q88
What is the role of decomposers in an ecosystem?
Explanation: Decomposers: bacteria and fungi. Detritivores (worms, millipedes): physically break down material before decomposers act on it. Without decomposers: nutrients locked in dead organisms, ecosystem collapse. Essential for: carbon cycle, nitrogen cycle, phosphorus cycle.
Q89
What is osmoregulation?
Explanation: Osmoregulation: kidneys adjust water/salt output. ADH (antidiuretic hormone): increases water reabsorption (concentrated urine). Low ADH: dilute urine. Aldosterone: increases Na⁺ reabsorption (retains water). In fish: freshwater fish (hypertonic to water) actively excrete water; marine fish drink water.
Q90
What is a virus?
Explanation: Virus structure: genetic material (DNA or RNA), capsid (protein coat), some have envelope (lipid membrane). Cannot reproduce alone — hijacks host cell machinery. Not living by cell theory. Examples: HIV (RNA), herpes (DNA), SARS-CoV-2 (RNA). Viruses infect all life forms.
Q91
What is a reflex arc?
Explanation: Reflex arc: knee-jerk: stimulus (hammer) → sensory neuron → synapse in spinal cord → motor neuron → quadriceps contract. Faster than voluntary because it bypasses the brain. Protective function: withdrawal reflex pulls hand from pain source before conscious awareness.
Q92
What is the difference between endocrine and exocrine glands?
Explanation: Types: Air (particulates, CO₂, SO₂, NOₓ), Water (sewage, agricultural runoff, industrial effluent), Soil (heavy metals, pesticides, plastic). Effects: biodiversity loss, human health impacts, food chain contamination. In SA: acid mine drainage, industrial pollution, poorly treated sewage.
Q96
What is the function of insulin?
Explanation: Glucose regulation: after eating, blood glucose rises → pancreatic beta cells secrete insulin → cells absorb glucose, liver stores as glycogen → blood glucose falls. If blood glucose too low: alpha cells secrete glucagon → glycogen→glucose. Type 1 diabetes: no insulin produced. Type 2: insulin resistance.
Q97
What is diffusion in living organisms?
Explanation: Examples: O₂ from air into blood in alveoli, CO₂ from blood into alveoli, glucose from gut into blood. Rate of diffusion increases with: steeper gradient, shorter distance, greater surface area, higher temperature, smaller molecules. Facilitated diffusion: uses channel or carrier proteins, still passive.
Q98
What is the water potential concept in plants?
Explanation: Water potential (Ψ) = pressure potential + solute potential. Pure water: Ψ=0. Adding solutes: Ψ decreases (more negative). Increasing pressure: Ψ increases. Water moves from less negative (high) to more negative (low) water potential. Turgor pressure: positive pressure builds in plant cells as water enters.
Q99
What is a food chain vs food web?
Explanation: Food chains show: energy flow direction, trophic levels. Food webs: show multiple feeding relationships, stability (if one species removed, others compensate). Trophic levels: Producer→Primary consumer→Secondary consumer→Tertiary consumer. 10% rule: only ~10% energy transferred between levels.
Q100
What is genetic recombination?
Explanation: Crossing over: homologous chromosomes form bivalents in prophase I, chiasmata form where DNA strands exchange. Result: recombinant chromosomes with new allele combinations. Plus: independent assortment (which chromosome of each pair goes to which pole). Creates enormous diversity — why siblings differ.
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Q101
What is the difference between an innate and acquired immune response?
Explanation: Placenta: selective exchange — O₂, glucose, amino acids, vitamins pass to fetus; CO₂, urea pass to mother. Barrier: prevents most bacteria and some toxins (but some viruses, drugs, alcohol cross). Produces: hCG (maintains corpus luteum), oestrogen, progesterone. Expelled after birth as afterbirth.
Q103
What is protein structure?
Explanation: Protein structure determines function. Denaturation: breaking non-covalent bonds (not primary structure) — unfolding due to heat/pH changes. Some denaturation reversible; most irreversible. Enzymes denature at high temperatures → lose function. Examples: insulin (quaternary), haemoglobin (quaternary — 4 subunits).
Q104
What is community ecology?
Explanation: Community: all species in an area interacting. Niche: organism's role and requirements. Competitive exclusion principle: two species with identical niches cannot coexist (one will outcompete). Keystone species: disproportionate impact on community relative to their abundance. Biodiversity: community-level property.
Explanation: Allopatric speciation: geographic isolation → separate evolution → reproductive isolation (most common). Sympatric: same location, different niches/behaviours. Reproductive isolation: pre-zygotic (different mating seasons, behaviours, habitat) and post-zygotic (hybrid inviability, sterility). Species concept: organisms that can interbreed and produce fertile offspring.
Q107
What is the role of the liver in digestion?
Explanation: Liver digestive roles: bile production (cholesterol-based, emulsifies fats, no digestion per se), deamination of excess amino acids (produces urea), metabolises carbohydrates, fats, vitamins. Kupffer cells: immune function. Also: first pass metabolism of drugs absorbed from intestine.
Q108
What is the effect of temperature on enzyme activity?
Explanation: Enzyme temperature curve: Q₁₀ rule: rate doubles per 10°C increase (up to optimum). Human enzyme optimum: ~37°C. Above optimum: H-bonds and other weak bonds break → enzyme denatures → cannot bind substrate → activity = 0. pH similarly has optimum range. Both affect enzyme shape.
Q109
What is biomagnification?
Explanation: Biomagnification: small amounts in producers → more concentrated in primary consumers (eat large amounts of producers) → even more in secondary consumers. DDT: from banned pesticide → plankton → small fish → large fish → birds of prey (reproduction failure). Mercury: from industrial effluent → fish → humans (Minamata disease).
Q110
What is conservation biology?
Explanation: Conservation biology: in situ conservation (protect in natural habitat — national parks, reserves), ex situ conservation (outside habitat — zoos, seed banks, captive breeding). SA's protected areas: Kruger, Drakensberg, Table Mountain. IUCN Red List: classifies extinction risk. Convention on Biological Diversity (CBD).
Q111
What are adaptations of animals to extreme cold?
Explanation: Cold adaptations: Emperor penguins (huddling, thick blubber), polar bears (hollow fur traps heat, thick fat layer), Arctic hares (white camouflage, compact body). Countercurrent: blood in arteries warms venous blood returning from extremities. Bergmann's rule: larger body → smaller surface:volume ratio → less heat loss.
Question 112 of 150
What is the cell theory?
Explanation: Cell theory (Schleiden, Schwann, Virchow): 1) All living organisms are composed of cells, 2) The cell is the basic unit of structure and function, 3) All cells arise from pre-existing cells (biogenesis).
Question 113 of 150
What is the difference between prokaryotic and eukaryotic cells?
Explanation: Prokaryotes: DNA in nucleoid region, no membrane-bound organelles, smaller (~1-10μm). Eukaryotes: nucleus, membrane-bound organelles (mitochondria, ER, Golgi), larger (~10-100μm). Eukaryotes evolved from prokaryotes.
Question 114 of 150
What is osmosis?
Explanation: Osmosis: passive (no energy needed), water moves down its concentration gradient. Hypotonic (lower solute) → hypertonic (higher solute). Turgor pressure: water entering plant cells inflates them. Plasmolysis: water leaving causes wilting.
Question 115 of 150
What is the difference between diffusion and active transport?
Explanation: Diffusion: passive, high → low concentration, no ATP needed. Examples: O₂ into cells, CO₂ out. Active transport: requires ATP, moves substances against gradient. Examples: Na⁺/K⁺ pump, mineral uptake by plant roots.
Question 116 of 150
What are the phases of mitosis?
Explanation: PMAT: Prophase (chromosomes condense, spindle forms), Metaphase (chromosomes align at equator), Anaphase (chromatids pulled to poles), Telophase (nuclear envelopes reform). Then Cytokinesis (cytoplasm divides).
Question 117 of 150
What is the role of enzymes?
Explanation: Enzymes: specific (lock-and-key or induced-fit model), reusable, affected by temperature and pH. Active site binds substrate. Denaturation: enzyme loses shape (not function reversibly — wait, high temp causes irreversible denaturation above optimal).
Question 118 of 150
What is genetic variation and why is it important?
Explanation: Genetic variation sources: mutation (random DNA changes), sexual reproduction (meiosis + fertilisation), crossing over (recombination). Variation provides raw material for natural selection. Without variation, species cannot adapt to environmental change.
Question 119 of 150
What is the difference between genotype and phenotype?
Explanation: Genotype: Tt, AA, RrBb (allele combinations). Phenotype: tall, round seeds, blue eyes (expressed traits). Phenotype = genotype × environment. Example: genotype for height interacts with nutrition to produce final height.
Question 120 of 150
What is a food web?
Explanation: Food web: more realistic than single food chain. Producers (plants) → Primary consumers (herbivores) → Secondary consumers → Tertiary consumers → Decomposers. Energy lost at each level (~90% as heat) — explains why food chains are short.
Question 121 of 150
What is biodiversity?
Explanation: Biodiversity: genetic (variation within species), species (number of species in an area), ecosystem (variety of habitats). South Africa is megadiverse — 3rd most biodiverse country. Threats: habitat destruction, pollution, invasive species, climate change.
Question 122 of 150
What is the carbon cycle?
Explanation: Carbon cycle: plants fix CO₂ via photosynthesis → animals eat plants (carbon moves up food chain) → respiration releases CO₂ → decomposition releases CO₂ → fossil fuels (long-term storage) → combustion releases stored carbon. Human activity is disrupting balance.
Explanation: Homeostasis examples: thermoregulation (37°C body temperature), blood glucose (insulin/glucagon), blood pH, osmoregulation (water balance). Negative feedback: deviation from set point triggers response that reverses the change.
Question 125 of 150
What is the difference between aerobic and anaerobic respiration?
Explanation: Aerobic: glucose + O₂ → CO₂ + H₂O + ~38 ATP. Occurs in mitochondria. Anaerobic (lactic acid fermentation): glucose → lactic acid + 2 ATP. Anaerobic (alcoholic fermentation): glucose → ethanol + CO₂ + 2 ATP. Anaerobic used when O₂ is limited.
Question 126 of 150
What is the structure of a neuron?
Explanation: Neuron: Dendrites receive signals → cell body processes → axon conducts electrical impulse → synaptic terminals release neurotransmitters across synapse to next neuron. Myelin speeds conduction. Nodes of Ranvier: gaps in myelin.
Question 127 of 150
What is transpiration?
Explanation: Transpiration: water vapour exits through stomata. Transpiration pull: creates tension that pulls water up xylem. Factors increasing transpiration: high temperature, low humidity, wind, high light intensity. Guard cells regulate stomatal opening.
Question 128 of 150
What is the immune response?
Explanation: Immune response: First line (skin, mucus). Second line (inflammation, phagocytosis, NK cells). Third line (specific): B-lymphocytes produce antibodies (humoral), T-lymphocytes destroy infected cells (cellular). Memory cells: faster response on re-exposure (basis of vaccination).
Question 129 of 150
What is the role of the kidneys in excretion?
Explanation: Kidney filtration: 180L filtered daily, 1.5L urine produced. Glomerular filtration → tubular reabsorption (glucose, amino acids, water) → tubular secretion → urine. ADH controls water reabsorption. Urea: formed in liver from ammonia.
Question 130 of 150
What are the parts of the digestive system in order?
Explanation: Genetic engineering: recombinant DNA technology — cut desired gene (restriction enzymes), insert into vector (plasmid), introduce to host. Applications: insulin production (bacteria), GM crops (pest resistance), gene therapy. Concerns: safety, ethics, biodiversity.
Question 134 of 150
What is ecological succession?
Explanation: Primary succession: bare rock → pioneer species (lichens) → soil formation → grassland → shrubland → forest. Secondary succession: after disturbance where soil remains. Climax community: stable, self-sustaining. SA example: fynbos post-fire succession.
Question 135 of 150
What is the nitrogen cycle?
Explanation: Nitrogen cycle: N₂ fixation (Rhizobium bacteria in legume roots → NH₃), Nitrification (NH₃ → NO₂ → NO₃ by bacteria), Plant uptake, Animal consumption, Decomposition (organic N → NH₃), Denitrification (NO₃ → N₂). Disrupted by fertiliser runoff.
Question 136 of 150
What is HIV/AIDS?
Explanation: HIV transmission: unprotected sexual contact, blood (sharing needles, transfusion), mother-to-child (birth, breastfeeding). CD4 count: healthy >500. AIDS diagnosis: <200 CD4 cells/μL. ARVs (antiretrovirals) allow near-normal lifespan.
Question 137 of 150
What is the water cycle?
Explanation: Water cycle: Solar energy → Evaporation (water→vapour) + Transpiration → Condensation (clouds form) → Precipitation (rain, snow) → Surface runoff → Infiltration (groundwater) → Taken up by plants → Repeat. Also: sublimation, freezing, melting.
Question 138 of 150
What are the adaptations of desert plants?
Explanation: Desert plant adaptations: succulents (store water in tissues), reduced/absent leaves (spines in cacti), waxy cuticle, deep taproots OR shallow spreading roots, CAM photosynthesis (stomata open at night), dormancy during drought.
Question 139 of 150
What is the difference between a parasite and a mutualist?
Explanation: Ecological relationships: Mutualism (+/+): both benefit (clownfish/anemone, bees/flowers). Commensalism (+/0): one benefits, other unaffected. Parasitism (+/-): parasite benefits, host harmed (tapeworm, mosquito). Predation: predator kills prey.
Question 140 of 150
What is biotic vs abiotic?
Explanation: Biotic factors: plants, animals, fungi, bacteria, dead organic matter. Abiotic factors: sunlight (photosynthesis energy), temperature (enzyme activity), water (photosynthesis, transport), soil composition, pH, wind, fire. Both shape ecosystems.
Question 141 of 150
What is the function of leaves?
Explanation: Leaves: large surface area for light capture, thin (short CO₂ diffusion path), chloroplasts (photosynthesis), stomata (gas exchange, transpiration), vascular tissue (xylem brings water, phloem removes sugar), waxy cuticle (reduce water loss).
Question 142 of 150
What is the role of ribosomes?
Explanation: Ribosomes: found in cytoplasm (free) or rough ER (bound). Made of rRNA and protein. Small subunit: reads mRNA. Large subunit: catalyses peptide bond formation. Prokaryotic ribosomes (70S) targeted by antibiotics; eukaryotic (80S) not.
Question 143 of 150
What is the difference between xylem and phloem?
Explanation: Xylem: dead cells (vessels, tracheids), lignified walls, one-directional, water + dissolved minerals. Phloem: living cells (sieve tubes + companion cells), bidirectional, sugars (mainly sucrose). Both form vascular bundles together.
Question 144 of 150
What is meiosis II?
Explanation: Meiosis II: no DNA replication before it. Phases: Prophase II, Metaphase II, Anaphase II (sister chromatids separate), Telophase II. Each cell produced is haploid with one copy of each chromosome. Tour is where gametes are finalised.
Question 145 of 150
What is the function of the chloroplast?
Explanation: Chloroplast structure: outer/inner membranes, thylakoid membranes (stacked into grana), stroma. Thylakoids: chlorophyll absorbs light, water split, O₂ released, ATP and NADPH produced. Stroma: Calvin cycle uses ATP+NADPH to fix CO₂ into G3P → glucose.
Question 146 of 150
What is the difference between DNA and RNA?
Explanation: DNA: ATCG bases, stable, found in nucleus (mainly), carries genetic blueprint. RNA types: mRNA (carries code from DNA to ribosome), tRNA (brings amino acids), rRNA (ribosome structure). RNA is less stable — allows regulation of gene expression.
Question 147 of 150
What is genetic drift?
Explanation: Genetic drift: Founder effect (small group establishes new population — limited gene pool). Bottleneck effect (population crashes — survivors' genes overrepresented). Not adaptive — driven by chance, not fitness. Reduces genetic diversity. Key factor in speciation of isolated populations.
Question 148 of 150
What is ecological footprint?
Explanation: Ecological footprint: includes: land for food production, grazing, forest (CO₂ absorption), built-up land, fishing grounds. South Africa's footprint exceeds biocapacity. Biocapacity: what the Earth can regenerate. If footprint > biocapacity = ecological deficit (overshoot).
Question 149 of 150
What is the role of decomposers in an ecosystem?
Explanation: Decomposers: bacteria and fungi. Detritivores (worms, millipedes): physically break down material before decomposers act on it. Without decomposers: nutrients locked in dead organisms, ecosystem collapse. Essential for: carbon cycle, nitrogen cycle, phosphorus cycle.
Question 150 of 150
What is osmoregulation?
Explanation: Osmoregulation: kidneys adjust water/salt output. ADH (antidiuretic hormone): increases water reabsorption (concentrated urine). Low ADH: dilute urine. Aldosterone: increases Na⁺ reabsorption (retains water). In fish: freshwater fish (hypertonic to water) actively excrete water; marine fish drink water.
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DNA (deoxyribonucleic acid) is the molecule that carries genetic information in living organisms. It is a double helix consisting of two complementary strands of nucleotides. Each nucleotide contains a sugar (deoxyribose), a phosphate group, and one of four bases: adenine (A), thymine (T), guanine (G), or cytosine (C). A pairs with T; G pairs with C.
Mitosis produces two genetically identical daughter cells with the same chromosome number as the parent (diploid). It is used for growth, repair, and asexual reproduction. Meiosis produces four genetically different daughter cells with half the chromosome number (haploid). It is used to produce gametes (sperm and eggs) for sexual reproduction.
Natural selection is the mechanism of evolution proposed by Charles Darwin. It occurs when individuals with heritable traits better suited to their environment survive and reproduce more successfully than others. Over generations, favourable traits become more common in the population. Requirements: variation exists, variation is heritable, variation affects survival/reproduction.
Photosynthesis converts light energy into chemical energy (glucose): 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. It occurs in chloroplasts. Cellular respiration releases energy from glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. It occurs in mitochondria. They are essentially opposite processes.
Homeostasis is the maintenance of a stable internal environment in the body despite external changes. It relies on negative feedback systems. Examples: thermoregulation (body temperature around 37°C), blood glucose regulation (insulin and glucagon), osmoregulation (water balance), and blood pH regulation.
An ecosystem consists of all living organisms (the community) and their physical environment in a defined area, and all the interactions between them. Components: producers (plants — convert sunlight to energy), consumers (animals that eat producers or other consumers), decomposers (bacteria and fungi — break down dead matter). Energy flows in one direction; nutrients cycle.
Genotype is the genetic makeup of an organism — the alleles it carries (e.g., Tt, AA, bb). Phenotype is the observable physical expression of those genes (e.g., tall, round seeds, blue eyes). Phenotype is determined by genotype plus environmental influences. Dominant alleles are expressed even in heterozygous (Tt) organisms.
HIV (Human Immunodeficiency Virus) attacks CD4+ T-helper cells, which coordinate the immune response. As HIV replicates inside T-cells and destroys them, the CD4 count drops. When CD4 count falls below 200 cells/μL, the immune system can no longer fight infections — tour stage is called AIDS. ARV (antiretroviral) treatment suppresses viral replication but does not cure HIV.