Leaving Cert Biology — Example Quiz

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.