OCR A-Level Biology A sample questions and answers (H420)
Guide overview All 26 sections Sample questions Papers and weighting Look inside Questions and answers
78 sample questions and answers
Taken from every section of OCR A-Level Biology A, specification H420. The full guide has 1,833.
Component 01, Component 02, Component 03
Cell Structure
68 questions in the guide, across 5 subtopics. More from this section
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Microscopy, slide preparation and staining
When preparing a microscope slide, what is the first step involving the specimen?
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Place a thin specimen on a glass slide. -
Microscopy, slide preparation and staining
After focusing on the stage micrometer, what must be done with the eyepiece graticule?
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Align the eyepiece graticule with the stage micrometer. -
Biological drawings, magnification and resolution
State the formula used to calculate magnification.
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Magnification = image size ÷ actual size (M = I/A).
Component 01, Component 02, Component 03
Biological Molecules
113 questions in the guide, across 10 subtopics. More from this section
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The properties of water
Explain how water acts as a solvent for ionic compounds.
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Water's polarity allows it to surround ions with hydration shells, separating and dissolving ionic compounds and other polar molecules. -
Monomers, polymers and the elements of life
What happens during a condensation reaction?
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A molecule of water is removed and a covalent bond is formed between two monomers, joining them together. -
Monosaccharides and disaccharides
What is the structural difference between α-glucose and β-glucose?
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The position of the hydroxyl group on carbon 1: in α-glucose it is below the plane of the ring, in β-glucose it is above the plane.
Component 01, Component 02, Component 03
Nucleotides and Nucleic Acids
58 questions in the guide, across 5 subtopics. More from this section
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Nucleotide structure and the bases
Which pentose sugar is found in DNA nucleotides?
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Deoxyribose. -
Nucleotide structure and the bases
Is guanine a purine or a pyrimidine?
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Guanine is a purine. -
Polynucleotides, ADP and ATP
What type of reaction breaks down polynucleotides into individual nucleotides?
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A hydrolysis reaction.
Component 01, Component 02, Component 03
Enzymes
43 questions in the guide, across 3 subtopics. More from this section
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Enzyme action: lock and key and induced fit
Name an enzyme that catalyses intracellular reactions.
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Catalase. -
Enzyme action: lock and key and induced fit
How does the induced-fit hypothesis differ from the lock and key model?
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The induced-fit hypothesis proposes that the active site changes shape slightly as the substrate binds, forming a more precise fit. -
Factors affecting enzyme activity
In the Q₁₀ formula, what do R₁ and R₂ represent?
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R₁ is the rate of reaction at the lower temperature; R₂ is the rate of reaction at a temperature 10°C higher.
Component 01, Component 02, Component 03
Biological Membranes
60 questions in the guide, across 4 subtopics. More from this section
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Membrane structure and the fluid mosaic model
Explain how phospholipids are arranged in a membrane bilayer.
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Phospholipids arrange with their hydrophilic (phosphate) heads facing outward towards the aqueous environments and their hydrophobic (fatty acid) tails facing inward, away from water. -
Membrane structure and the fluid mosaic model
What is the function of carrier proteins in membranes?
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They bind to specific molecules and change shape to transport them across the membrane, in facilitated diffusion or active transport. -
Factors affecting membrane permeability
Why does ethanol increase the leakage of pigment from beetroot cells?
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Ethanol dissolves the phospholipids in the tonoplast and plasma membrane, allowing the red pigment (betalain) to leak out.
Component 01, Component 02, Component 03
Cell Division, Cell Diversity and Cellular Organisation
80 questions in the guide, across 6 subtopics. More from this section
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The cell cycle
What is the main event of the S phase?
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DNA replication occurs, producing two identical copies of each chromosome. -
The cell cycle
Define cytokinesis.
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The division of the cytoplasm following mitosis to form two separate cells. -
Mitosis and observing it in root tips
What happens to spindle fibres during anaphase?
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They shorten, pulling chromatids to opposite poles.
Component 01, Component 03
Exchange Surfaces
64 questions in the guide, across 5 subtopics. More from this section
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Surface area to volume and the features of an exchange surface
Why do multicellular organisms require specialised exchange surfaces?
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Their lower surface area to volume ratio combined with higher metabolic activity means simple diffusion across the body surface is inadequate to supply sufficient oxygen and remove waste products. -
Surface area to volume and the features of an exchange surface
Why is a thin barrier important for an efficient exchange surface?
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A thin barrier reduces the diffusion distance, allowing molecules to cross more rapidly according to Fick's law. -
The mammalian gas exchange system
What is the function of cartilage in the trachea and bronchi?
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Cartilage provides structural support to keep the airways open and prevent them from collapsing during pressure changes.
Component 01, Component 03
Transport in Animals
103 questions in the guide, across 8 subtopics. More from this section
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Why animals need transport systems
What defines a single circulatory system?
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Blood passes through the heart once per complete circuit of the body. -
Arteries, veins and capillaries
How do arterioles differ from arteries in terms of smooth muscle, and what does this allow?
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Arterioles have relatively more smooth muscle than arteries, allowing vasoconstriction and vasodilation to control blood flow to tissues. -
Tissue fluid and lymph
What is the net direction of fluid movement at the arterial end of a capillary, and why?
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Net outward movement occurs because hydrostatic pressure exceeds oncotic pressure, forming tissue fluid.
Component 01, Component 03
Transport in Plants
56 questions in the guide, across 5 subtopics. More from this section
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Xylem, phloem and vascular tissue
Why can water flow uninterrupted through xylem vessels?
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Xylem vessels have no end walls between adjacent cells, forming continuous tubes. -
Xylem, phloem and vascular tissue
In a herbaceous dicotyledonous leaf, where is the xylem positioned relative to the phloem within the veins?
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Xylem is on the upper side and phloem is on the lower side. -
Transpiration and the potometer
Explain how higher temperature increases transpiration rate.
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Higher temperature increases the kinetic energy of water molecules and decreases relative humidity of surrounding air.
Component 02, Component 03
Communicable Diseases, Disease Prevention and the Immune System
88 questions in the guide, across 8 subtopics. More from this section
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Pathogens and how disease is transmitted
Which viral disease affects animals such as birds and pigs?
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Influenza. -
Plant defences and non-specific animal defences
Why is blood clotting considered a primary non-specific defence?
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Blood clotting is a primary non-specific defence because it seals wounds to prevent pathogen entry, regardless of the type of pathogen. -
Phagocytes and phagocytosis
What are antigen-presenting cells and what do they do after engulfing pathogens?
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Antigen-presenting cells are phagocytes that display pathogen antigens on their surface after engulfing pathogens, allowing recognition by other immune cells.
Component 02, Component 03
Biodiversity
70 questions in the guide, across 6 subtopics. More from this section
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The three levels of biodiversity
Name the three levels at which biodiversity can be considered.
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Habitat biodiversity, species biodiversity, and genetic biodiversity. -
The three levels of biodiversity
What is species biodiversity?
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The diversity of species in an area, encompassing both species richness and species evenness -
Sampling methods and equipment
Describe stratified sampling as a non-random method.
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The habitat is divided into distinct sub-groups (strata) based on a particular characteristic, and samples are taken from each stratum in proportion to its size or importance.
Component 02, Component 03
Classification and Evolution
52 questions in the guide, across 5 subtopics. More from this section
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The taxonomic hierarchy and binomial naming
What taxonomic rank falls between phylum and order?
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Class -
The taxonomic hierarchy and binomial naming
What is the lowest (most specific) level in the taxonomic hierarchy?
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Species -
The five kingdoms and the three domains
State three features that define Kingdom Animalia.
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Multicellular eukaryotes with no cell walls, heterotrophic nutrition, and nervous coordination.
Component 01, Component 03
Communication and Homeostasis
32 questions in the guide, across 3 subtopics. More from this section
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Cell signalling and communication systems
How do communication systems help multicellular organisms interact with their surroundings?
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They allow organisms to respond to changes in the external environment. -
Cell signalling and communication systems
Define cell signalling.
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The process by which cells communicate with each other. -
Homeostasis, negative and positive feedback
What is the functional difference between receptors and effectors?
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Receptors detect changes in conditions, whereas effectors carry out responses to restore conditions.
Component 01, Component 03
Excretion as an Example of Homeostatic Control
110 questions in the guide, across 9 subtopics. More from this section
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Excretion and nitrogenous waste
Why must carbon dioxide be excreted from the body?
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Carbon dioxide combines with water to form carbonic acid, which lowers blood pH. -
The liver: structure and function
What are hepatocytes and how are they arranged within a lobule?
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Hepatocytes are the main liver cells, arranged in rows radiating out from the central vein. -
The structure of the kidney
What is the function of the ureter?
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The ureter carries urine from the kidney to the bladder.
Component 01, Component 03
Neuronal Communication
56 questions in the guide, across 5 subtopics. More from this section
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Sensory receptors and the Pacinian corpuscle
Describe the structure of a Pacinian corpuscle.
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It consists of a sensory nerve ending surrounded by layers of connective tissue called lamellae, which are separated by gel. -
Sensory receptors and the Pacinian corpuscle
What type of ion channels open when the lamellae press on the nerve ending in a Pacinian corpuscle?
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Stretch-mediated sodium channels open. -
Types of neurone and myelination
Describe the structural features of relay neurones.
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Relay neurones have short axons and many dendrites.
Component 01, Component 03
Hormonal Communication
47 questions in the guide, across 4 subtopics. More from this section
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Hormones and the adrenal glands
What are the two distinct regions of the adrenal gland?
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The outer cortex and the inner medulla. -
Hormones and the adrenal glands
What are the functions of glucocorticoids such as cortisol?
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They regulate metabolism and the immune response, and help the body respond to stress. -
The pancreas and the islets of Langerhans
Which cells in the islets of Langerhans secrete glucagon?
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Alpha cells.
Component 01, Component 03
Plant and Animal Responses
80 questions in the guide, across 7 subtopics. More from this section
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Tropisms and plant responses to stress and herbivory
Distinguish between positive and negative tropism.
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Positive tropism is growth towards a stimulus; negative tropism is growth away from a stimulus. -
Tropisms and plant responses to stress and herbivory
How can pheromones released by plants in response to herbivory benefit the plant?
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They can attract predators of the herbivores or warn neighbouring plants of the threat. -
Plant hormones and their commercial uses
Define apical dominance.
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The phenomenon where the main central stem grows more strongly than lateral branches, inhibiting their growth.
Component 01, Component 03
Photosynthesis
58 questions in the guide, across 5 subtopics. More from this section
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Photosynthesis and chloroplast structure
What structure surrounds the chloroplast?
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The chloroplast is surrounded by a double membrane (an outer and an inner membrane) called the envelope. -
Photosynthesis and chloroplast structure
Where in the chloroplast does the light-dependent stage of photosynthesis occur?
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The light-dependent stage occurs on the thylakoid membranes. -
Photosynthetic pigments and chromatography
What are photosystems?
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Photosystems are protein complexes containing pigments that absorb light and initiate electron transfer.
Component 01, Component 03
Respiration
74 questions in the guide, across 6 subtopics. More from this section
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Respiration, ATP and the mitochondrion
State two processes in animals that require ATP from respiration.
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Muscle contraction and active transport. -
Respiration, ATP and the mitochondrion
What are cristae and what is their function?
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Cristae are folds of the inner mitochondrial membrane that increase surface area for electron carriers and ATP synthase. -
Glycolysis
What happens in the second phosphorylation step during glycolysis?
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A second phosphate group is added from another ATP molecule.
Component 02, Component 03
Cellular Control
62 questions in the guide, across 6 subtopics. More from this section
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Gene mutations and their effects
Why might a single nucleotide substitution have no effect on the protein produced?
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It may result in a silent mutation if the new codon still codes for the same amino acid due to the degeneracy of the genetic code. -
Gene mutations and their effects
Under what circumstances could a gene mutation be considered beneficial?
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When the altered protein confers a selective advantage to the organism. -
The lac operon
What does the lacA gene encode in the lac operon?
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It is a structural gene that codes for transacetylase, involved in lactose metabolism.
Component 02, Component 03
Patterns of Inheritance
89 questions in the guide, across 7 subtopics. More from this section
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Genetic and environmental variation
How can diet affect phenotypic variation in animals?
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Nutrient availability influences growth, body mass, coat condition, and other physical characteristics. -
Genetic and environmental variation
Why does polygenic inheritance produce continuous variation?
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Each gene adds a small effect to the phenotype, so the many possible combinations of alleles give a wide range of intermediate values, which environmental effects blur further into a continuous range. -
Monogenic and dihybrid inheritance, sex linkage and epistasis
Define codominance.
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Codominance occurs when both alleles are expressed equally in the phenotype of a heterozygote.
Component 02, Component 03
Manipulating Genomes
42 questions in the guide, across 4 subtopics. More from this section
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DNA sequencing and bioinformatics
What advantages does high throughput sequencing offer compared to Sanger sequencing?
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It allows much faster and cheaper sequencing of entire genomes. -
DNA sequencing and bioinformatics
What is synthetic biology?
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The designing and constructing of new biological parts, devices and systems using gene sequencing data. -
DNA profiling, PCR and gel electrophoresis
What happens during the denaturation step of PCR and at what temperature does it occur?
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At approximately 95°C, the double-stranded DNA separates into two single strands.
Component 02, Component 03
Cloning and Biotechnology
120 questions in the guide, across 10 subtopics. More from this section
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Natural plant cloning and taking cuttings
How do tubers enable vegetative propagation?
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Tubers are swollen underground stems or roots that store nutrients and have buds (eyes) that can sprout to produce new genetically identical plants. -
Micropropagation
What is an explant in micropropagation?
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A small piece of tissue taken from the parent plant to initiate the culture. -
Advantages and disadvantages of plant cloning
Why is artificial plant cloning independent of season?
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Plants can be propagated year-round in controlled laboratory conditions regardless of external climate or season.
Component 02, Component 03
Ecosystems
52 questions in the guide, across 4 subtopics. More from this section
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Ecosystems, biotic and abiotic factors
Give an example of a large ecosystem.
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A playing field. -
Ecosystems, biotic and abiotic factors
Name four examples of biotic factors.
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Competition, predation, disease, and availability of food. -
Biomass transfer between trophic levels
State the formula for calculating the efficiency of biomass transfer.
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Efficiency = (biomass transferred ÷ biomass intake) × 100.
Component 02, Component 03
Populations and Sustainability
52 questions in the guide, across 5 subtopics. More from this section
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Population size and limiting factors
What is meant by carrying capacity?
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Carrying capacity is the maximum population size that an environment can sustain indefinitely given the available resources. -
Population size and limiting factors
How can mineral ion availability limit a population?
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Mineral ions are needed for synthesising essential molecules (e.g. proteins, nucleic acids); deficiency restricts growth and reproduction. -
Predator-prey cycles and competition
Describe the characteristic pattern seen in predator-prey population graphs.
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Both populations show oscillations over time, with predator population peaks lagging behind prey population peaks.
Component 01, Component 02, Component 03
Practical Skills and Mathematical Requirements
104 questions in the guide, across 6 subtopics. More from this section
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Planning investigations and choosing apparatus
Why are repeat readings taken at each value of the independent variable?
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Repeats allow a mean to be calculated, anomalous readings to be spotted, and the spread of the results to show how precise the data are. -
Planning investigations and choosing apparatus
What ethical requirements apply when people are the subjects of a physiological investigation such as measuring pulse rate?
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Participants must give informed consent, be free to withdraw at any time and have their data kept anonymous, and anyone at risk, such as a person with a heart condition, must be excluded from exercise. -
Recording and presenting data
Round 0.004872 mm to 2 significant figures.
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0.0049 mm: the leading zeros are not significant, so the first two significant figures are 4 and 8, and the following 7 rounds the 8 up to 9.
OCR A-Level Biology A Active Recall Guide
The other 1,755 questions, with the answers printed after each section.