--- title: "Leaving Cert Biology — Example Quiz" tags: [biology, leaving-cert, science, second-level] time_limit: 30 allow_overrun: true random_order: false --- ##### Question q001 type: single_choice correct: [c] Which structure is present in a plant cell but **absent** from an animal cell? A. Mitochondrion B. Ribosome C. Cellulose cell wall D. Nucleus ###### Explanation All four structures occur in plant cells, but only the cellulose cell wall is absent from animal cells. Mitochondria, ribosomes and a nucleus are found in both. Note that a *cell membrane* is present in both — it is the rigid cellulose **wall** outside the membrane that is unique to plants. --- ##### Question q002 type: single_choice correct: [b] An enzyme is described as having an **optimum pH**. What does this mean? A. The enzyme can only function at that exact pH and is destroyed at any other B. The enzyme works at its fastest rate at that pH C. The enzyme changes shape permanently at that pH D. The enzyme stops being a catalyst above that pH ###### Explanation The optimum is the pH at which the rate of reaction is highest. The enzyme still works either side of it, just more slowly, because the active site shape is progressively distorted. Only at extremes does denaturation become permanent — so B, not A. --- ##### Question q003 type: multi_choice correct: [a, c] Which TWO of the following are products of the **light stage** of photosynthesis? (Select two.) A. ATP B. Glucose C. Oxygen D. Carbon dioxide ###### Explanation The light stage produces ATP, NADPH and oxygen. Oxygen comes from the photolysis (splitting) of water. Glucose is made in the dark stage, using the ATP and NADPH from the light stage. Carbon dioxide is a raw material for the dark stage, not a product. --- ##### Question q004 type: true_false correct: [b] Anaerobic respiration in human muscle produces more ATP per glucose molecule than aerobic respiration. ###### Explanation False, and by a wide margin. Aerobic respiration yields far more ATP per glucose because the pyruvate is fully oxidised through Krebs cycle and the electron transport chain. Anaerobic respiration in muscle stops at lactic acid and yields only the small amount of ATP from glycolysis. --- ##### Question q005 type: single_choice correct: [c] In DNA, adenine always pairs with which base? A. Cytosine B. Guanine C. Thymine D. Uracil ###### Explanation Adenine pairs with thymine (two hydrogen bonds); cytosine pairs with guanine (three hydrogen bonds). Uracil replaces thymine in **RNA**, not DNA — a common trap in this question. --- ##### Question q006 type: sequence correct: [c, a, d, b] Place the following stages of **protein synthesis** in the correct order. A. mRNA travels from the nucleus to a ribosome B. Amino acids are joined by peptide bonds to form a polypeptide C. DNA is transcribed into mRNA in the nucleus D. tRNA molecules bring amino acids to the ribosome ###### Explanation Transcription happens first, in the nucleus. The mRNA then leaves through a nuclear pore and attaches to a ribosome. Translation follows: tRNA delivers amino acids matching each codon, and peptide bonds join them into a polypeptide. --- ##### Question q007 type: single_choice correct: [b] Which blood vessel carries **deoxygenated** blood? A. Pulmonary vein B. Pulmonary artery C. Aorta D. Renal artery ###### Explanation The pulmonary artery is the exception to the usual rule: it carries deoxygenated blood from the right ventricle to the lungs. The pulmonary vein is the matching exception, carrying oxygenated blood back to the heart. --- ##### Question q008 type: single_choice correct: [c] What is the role of **bile** in digestion? A. It digests protein into amino acids B. It digests starch into maltose C. It emulsifies fats into smaller droplets D. It neutralises saliva in the mouth ###### Explanation Bile contains no digestive enzymes. It emulsifies fat — breaking large globules into small droplets, which increases the surface area available to lipase. It is produced by the liver, stored in the gall bladder, and released into the small intestine. --- ##### Question q009 type: multi_choice correct: [b, d] Which TWO of the following occur during **meiosis** but not during mitosis? (Select two.) A. Chromosomes replicate before division begins B. Crossing over occurs between homologous chromosomes C. The nuclear membrane breaks down D. The chromosome number is halved ###### Explanation Meiosis is distinguished by crossing over during prophase I and by the halving of chromosome number, producing haploid gametes. Replication before division and breakdown of the nuclear membrane happen in both processes. --- ##### Question q010 type: single_choice correct: [a] In a food chain, organisms that make their own food are called: A. Producers B. Primary consumers C. Decomposers D. Secondary consumers ###### Explanation Producers — typically green plants — convert light energy into chemical energy by photosynthesis and form the first trophic level. Consumers obtain energy by eating other organisms; decomposers break down dead material. --- ##### Question q011 type: single_choice correct: [c] Which vessel in a plant transports **water** from the roots to the leaves? A. Phloem B. Stomata C. Xylem D. Cambium ###### Explanation Xylem carries water and dissolved minerals upwards, driven largely by transpiration pull. Phloem transports the products of photosynthesis in both directions. Stomata are pores in the leaf; cambium is a layer of dividing cells. --- ##### Question q012 type: true_false correct: [a] Genes carried on the X chromosome are described as sex-linked. ###### Explanation True. Sex linkage refers to genes located on a sex chromosome, in practice usually the X chromosome. Because males have only one X, a single recessive allele is expressed — which is why conditions such as haemophilia and red-green colour blindness are far more common in males. --- ##### Question q013 type: single_choice correct: [b] A student tests a food sample with Benedict's reagent and heats it. The solution turns brick red. This indicates the presence of: A. Starch B. Reducing sugar C. Protein D. Lipid ###### Explanation Benedict's reagent turns from blue through green and orange to brick red in the presence of a reducing sugar, the colour reflecting concentration. Starch is tested with iodine (blue-black), protein with the biuret test (purple), and lipid with the brown paper or emulsion test. --- ##### Question q014 type: single_choice correct: [d] Which organ is chiefly responsible for **osmoregulation** in humans? A. Liver B. Pancreas C. Lung D. Kidney ###### Explanation The kidney regulates the water and salt content of the blood, adjusting urine concentration under hormonal control. The liver handles deamination and detoxification, the pancreas secretes enzymes and hormones, and the lungs exchange gases. --- ##### Question q015 type: multi_choice correct: [a, b, d] Which THREE of the following are conditions required for **seed germination**? (Select three.) A. Water B. Oxygen C. Light D. A suitable temperature ###### Explanation Water, oxygen and a suitable temperature are required. Light is **not** a general requirement — many seeds germinate perfectly well in darkness, and some are inhibited by light. Light becomes essential only afterwards, once the seedling must photosynthesise. --- ##### Question q016 type: single_choice correct: [b] Two heterozygous tall pea plants (Tt) are crossed. What proportion of the offspring would be expected to be short? A. 0% B. 25% C. 50% D. 75% ###### Explanation A Tt x Tt cross gives TT, Tt, Tt and tt — a 3:1 ratio of tall to short. Only tt is short, so 25%. The other three carry at least one dominant T allele and are tall. --- ##### Question q017 type: single_choice correct: [c] What is the function of the **ribosome**? A. Photosynthesis B. Storage of genetic material C. Protein synthesis D. Removal of waste ###### Explanation Ribosomes are the site of translation, where mRNA is read and amino acids are assembled into polypeptides. They may be free in the cytoplasm or bound to the rough endoplasmic reticulum. --- ##### Question q018 type: sequence correct: [b, d, a, c] Arrange the following levels of ecological organisation from **smallest to largest**. A. Community B. Organism C. Ecosystem D. Population ###### Explanation An organism is a single individual; a population is all the individuals of one species in an area; a community is all the populations of different species in that area; an ecosystem is the community together with its non-living environment. --- ##### Question q019 type: single_choice correct: [a] Which of the following best describes a **catalyst**? A. It speeds up a reaction without being used up B. It provides the energy needed for a reaction C. It is consumed in equal proportion to the reactants D. It raises the activation energy of a reaction ###### Explanation A catalyst increases the rate of reaction by providing an alternative pathway with **lower** activation energy, and is unchanged at the end. It does not supply energy, and it is not consumed — which is why enzymes work in very small quantities. --- ##### Question q020 type: true_false correct: [b] Arteries carry blood towards the heart and veins carry blood away from it. ###### Explanation False — it is the other way round. Arteries carry blood **away** from the heart, which is why they have thick muscular walls to withstand high pressure. Veins return blood **to** the heart at lower pressure and contain valves to prevent backflow. ---