Test medicina Pleven: simulazione gratuita con soluzioni

Risposta: B

The small intestine is lined by a single layer of tall columnar cells (with microvilli and goblet cells), suited to absorption and secretion. Stratified squamous epithelium protects surfaces that are rubbed (skin, mouth, oesophagus); transitional epithelium lines the bladder, which stretches; simple squamous epithelium is for diffusion (alveoli, capillaries).

Risposta: C

Blood is a connective tissue: cells in a fluid extracellular matrix, the plasma. The epidermis is epithelial tissue, cardiac muscle is muscle tissue, and neuroglia (the supporting cells of the nervous system) belong to nervous tissue.

Risposta: A

There are 12 pairs: 7 pairs of true ribs joined directly to the sternum by their own cartilage, 3 pairs of false ribs joined indirectly, and 2 pairs of floating ribs with no anterior attachment. Each pair articulates with one of the 12 thoracic vertebrae.

Risposta: A

In the sliding-filament model the actin filaments slide over the myosin filaments; neither filament shortens. The A band is the length of the myosin filaments, so it stays the same, while the I band (actin only) and the H zone (myosin only) narrow and the sarcomere as a whole shortens.

Risposta: D

Mature red blood cells (erythrocytes) lose their nucleus and most organelles during development, which leaves more room for haemoglobin and gives them their biconcave shape. All white blood cells, including neutrophils, lymphocytes and monocytes, keep their nucleus.

Risposta: B

Group A means the red cells carry antigen A, so the plasma cannot contain anti-A (it would destroy the person's own cells); it contains anti-B. Group B has anti-A, group O has both, and group AB has neither.

Risposta: D

The left atrioventricular valve has two cusps: the bicuspid or mitral valve. The tricuspid valve is the right atrioventricular valve; the pulmonary and aortic valves are the semilunar valves at the exits of the right and left ventricles.

Risposta: B

The thoracic duct, the largest lymphatic vessel, drains most of the body and empties into the venous system at the junction of the left subclavian and left internal jugular veins. The right lymphatic duct drains the upper right quarter of the body into the right subclavian vein. Lymph never enters an artery or the portal system.

Risposta: C

About 70% of CO₂ travels as HCO₃⁻: in red blood cells carbonic anhydrase converts CO₂ and water to carbonic acid, which dissociates, and the hydrogen carbonate passes into the plasma. About 20% is carried bound to haemoglobin's amino groups and less than 10% is dissolved. CO₂ does not bind to the iron, which is where oxygen binds.

Risposta: A

Inspiration is active: the diaphragm contracts and flattens and the external intercostals lift the ribs, so the thoracic volume increases, the pressure in the lungs falls below atmospheric pressure and air flows in. The diaphragm relaxing and the internal intercostals lowering the ribs belong to expiration.

Risposta: C

Pepsin, secreted as inactive pepsinogen by the chief cells and activated by hydrochloric acid, splits proteins into polypeptides in the stomach. Trypsin continues protein digestion in the small intestine; amylase digests starch and lipase digests fats.

Risposta: D

Vitamin D is needed to absorb calcium and phosphate from the gut; without it growing bones are poorly mineralised, soft and deformed (rickets). Vitamin A deficiency causes night blindness, vitamin B12 deficiency anaemia, and vitamin C deficiency scurvy.

Risposta: B

The nephron filters the blood (in the renal corpuscle: glomerulus and Bowman's capsule), then reabsorbs and secretes along its tubules to make urine; each kidney has about a million. The glomerulus is only one part of it; the renal pelvis collects urine and the ureter carries it to the bladder.

Risposta: A

To lose heat, skin arterioles dilate (vasodilation), so more warm blood flows near the surface and heat is radiated, and the sweat glands secrete more sweat, which cools the skin as it evaporates. Vasoconstriction, raised hairs and shivering are responses to cold.

Risposta: C

The secondary oocyte released at ovulation is caught by the uterine tube, and fertilisation usually happens in its outer, wider part (the ampulla). The zygote then divides as it moves down the tube and implants in the uterus as a blastocyst about a week later.

Risposta: B

The interstitial cells of Leydig, between the seminiferous tubules, secrete testosterone under the control of LH. Sertoli cells inside the tubules support and nourish developing sperm; spermatogonia are the stem cells that give rise to sperm; the epididymis stores and matures sperm.

Risposta: D

A stimulus is detected by the receptor, carried to the spinal cord by the sensory (afferent) neuron, passed on by an interneuron, and carried out by the motor (efferent) neuron to the effector, a muscle or gland. The first option is the arc reversed; the second swaps the sensory and motor neurons.

Risposta: C

The parasympathetic system governs 'rest and digest': it slows the heart (through the vagus nerve), constricts the pupils, and increases salivation, gut movement and digestive secretions. Speeding the heart, dilating the pupils and inhibiting digestion are sympathetic effects.

Risposta: B

ADH, made in the hypothalamus and released from the posterior pituitary, makes the collecting ducts more permeable to water, so more water is reabsorbed and less, more concentrated urine is made. Oxytocin is also released there but acts on the uterus and breast; TSH and prolactin come from the anterior pituitary.

Risposta: C

Thyroxine (T4) and triiodothyronine (T3) contain iodine atoms (four and three). Lack of iodine causes goitre, an enlarged thyroid. Iron is needed for haemoglobin and calcium for bones, muscle and clotting.

Risposta: A

Cones, concentrated in the fovea, contain three kinds of photopsin sensitive to different wavelengths and give colour vision and sharp detail in good light. Rods are more sensitive and work in dim light but do not distinguish colours. Bipolar and ganglion cells are neurons that carry signals on, not photoreceptors.

Risposta: D

The three semicircular canals, set at right angles to each other, contain endolymph that moves when the head rotates and bends the hair cells in their ampullae. The cochlea is the organ of hearing; the tympanic membrane and the ossicles belong to the outer and middle ear and carry sound.

Risposta: D

Glycogen is the animal storage polysaccharide of glucose, highly branched so that it can be broken down quickly. Starch is the plant store, cellulose forms plant cell walls, and chitin forms the exoskeleton of arthropods and the cell walls of fungi.

Risposta: A

An enzyme binds the substrate at its active site and provides a pathway with a lower activation energy, so more molecules can react at body temperature. It does not change the temperature or the position of equilibrium, and it is not consumed: it is released unchanged after each reaction.

Risposta: C

A phospholipid has a hydrophilic head (phosphate group) and two hydrophobic fatty-acid tails, so in water phospholipids arrange themselves in a bilayer with the tails inside. Triglycerides are storage fats with no polar head; glycogen and nucleotides are not lipids.

Risposta: D

RNA contains uracil in place of thymine, so its bases are A, U, G and C; DNA's are A, T, G and C. Adenine, guanine and cytosine are found in both.

Risposta: A

The code is read in triplets: each codon of three nucleotides codes for one amino acid, so 300 ÷ 3 = 100 amino acids. The stop codon, which was excluded, codes for none.

Risposta: B

Translation, the synthesis of a polypeptide from mRNA, happens on ribosomes, free in the cytoplasm or attached to the rough ER. Transcription happens in the nucleus; the Golgi apparatus modifies and packages finished proteins, and lysosomes digest.

Risposta: C

Viruses are obligate intracellular parasites: they have no metabolism or ribosomes of their own and use the host cell's machinery to make new virus particles. They do not divide, and each virus has either DNA or RNA as its genome, not both. Binary fission is how bacteria reproduce.

Risposta: A

Bacteria have no nucleus: their main DNA is one circular chromosome in a region of the cytoplasm called the nucleoid, and many carry plasmids, small circular DNA molecules that can carry genes such as antibiotic resistance. Linear chromosomes in a nucleus, packed with histones, are eukaryotic.

Risposta: D

Lysosomes are vesicles with a single membrane full of hydrolytic enzymes that work at acid pH; they digest material taken in by endocytosis and worn-out organelles. They are formed from the Golgi apparatus, which packages them, but the Golgi itself does not digest.

Risposta: B

Movement down a gradient is passive, and when a channel or carrier protein is needed it is facilitated diffusion. Active transport moves substances against their gradient and uses ATP; osmosis is the movement of water; exocytosis releases materials in vesicles.

Risposta: C

Pinocytosis ('cell drinking') takes in fluid and dissolved substances in small vesicles. Phagocytosis ('cell eating') engulfs large particles such as bacteria; both are forms of endocytosis. Exocytosis is the opposite process, releasing material from the cell.

Risposta: A

Glycolysis uses 2 ATP in its first steps and makes 4 later, a net gain of 2 ATP (plus 2 NADH) per glucose. 4 is the gross number; about 30-38 ATP is the total for complete aerobic respiration, most of it from oxidative phosphorylation.

Risposta: D

The electron transport chain and ATP synthase are embedded in the inner mitochondrial membrane, folded into cristae; protons pumped into the intermembrane space flow back through ATP synthase. Glycolysis is in the cytoplasm and the Krebs cycle in the matrix.

Risposta: B

DNA is copied in the S (synthesis) phase of interphase, so each chromosome enters mitosis as two sister chromatids. G1 is growth before replication; metaphase and telophase are stages of mitosis, when no DNA is made.

Risposta: C

Crossing over happens in prophase I, when homologous chromosomes pair up (synapsis) and non-sister chromatids exchange segments at the chiasmata. It is one of the two sources of new allele combinations in meiosis, with the independent assortment of homologues in metaphase and anaphase I.

Risposta: D

This is a test cross. The AaBb parent makes four kinds of gametes (AB, Ab, aB, ab) in equal numbers, and the aabb parent only ab, so the offspring are AaBb, Aabb, aaBb and aabb in equal proportions: 1 : 1 : 1 : 1. 9 : 3 : 3 : 1 is the ratio from AaBb × AaBb.

Risposta: A

The father is XᴺY and gives his X, carrying the normal allele, to every daughter, so no daughter can be colour-blind: half are carriers (XᴺXᶜ) and half are not. Half of the sons, who get their X from the mother, are colour-blind. 1/4 is the chance for any child, son or daughter.

Risposta: B

Pink is RW. RW × RW gives RR, RW, WR and WW in a 1 : 2 : 1 ratio, and with incomplete dominance each genotype has its own phenotype: 1 red : 2 pink : 1 white. 3 : 1 would be complete dominance; 9 : 3 : 3 : 1 needs two genes.

Risposta: C

A neutral sulfur atom has 16 electrons; the 2− charge means it has gained two more, so S²⁻ has 18, the same as argon. 14 would be S²⁺, and 32 is sulfur's mass number, not an electron count.

Risposta: A

Isotopes have the same number of protons (the same atomic number, so the same element) and different numbers of neutrons: carbon-12 and carbon-14 both have 6 protons, with 6 and 8 neutrons. ¹⁴C and ¹⁴N have the same mass number but are different elements; O₂ and O₃ are allotropes; H₂O and H₂O₂ are different compounds.

Risposta: D

A d sublevel has five orbitals, and each orbital holds at most two electrons of opposite spin (the Pauli principle): 5 × 2 = 10. An s sublevel holds 2 (one orbital) and a p sublevel 6 (three orbitals); 8 is the number in a full outer s + p shell.

Risposta: B

A hydrogen bond needs H attached to a small, very electronegative atom with a lone pair: N, O or F. Water (O-H) and ammonia (N-H) qualify. In CH₄ the C-H bond is barely polar, and in HCl chlorine is too large for strong hydrogen bonding, so HCl molecules are held by dipole-dipole forces.

Risposta: C

Nitrogen has four electron pairs, three bonding and one lone pair, arranged roughly tetrahedrally; the shape of the molecule is described by the atoms only, which form a trigonal pyramid with H-N-H angles of about 107°. Tetrahedral is the shape of CH₄, which has no lone pair; trigonal planar is BF₃.

Risposta: B

The oxidation numbers add up to zero: 2(+1) + 2Cr + 7(−2) = 0, so 2Cr = +12 and each Cr is +6. +12 is the total for both chromium atoms; +3 is chromium in Cr³⁺ salts, the usual product when dichromate acts as an oxidising agent.

Risposta: D

Hydrogen goes from +1 in HCl to 0 in H₂: H⁺ gains electrons, is reduced, and so is the oxidising agent. Zinc goes from 0 to +2: it is oxidised and is the reducing agent. Chloride does not change (−1 on both sides).

Risposta: C

Carbon forms two double bonds, O=C=O, so four bonds in all: valence IV. Carbon is tetravalent in almost all its compounds. II would be the valence of oxygen, which forms two bonds.

Risposta: A

Diluting lowers the concentration of H⁺, so collisions are less frequent and the reaction slows down. Powder has a larger surface area, warming gives more particles at least the activation energy, and a higher concentration gives more collisions: all three speed it up.

Risposta: B

A catalyst offers an alternative mechanism with a lower activation energy, so both the forward and the reverse reactions go faster. The energies of reactants and products are unchanged, so ΔH is the same, and so are the equilibrium constant and the equilibrium composition: equilibrium is only reached sooner.

Risposta: C

By Le Chatelier's principle, a rise in temperature favours the endothermic direction, which absorbs heat: here the forward reaction, so more brown NO₂ forms. Cooling would favour the colourless N₂O₄. Equilibrium is dynamic and never 'stops'.

Risposta: A

Kc is the product of the products' concentrations over the product of the reactants', each raised to the power of its coefficient: [HI]² / ([H₂][I₂]). The second option is the inverse (the constant for the reverse reaction); coefficients become powers, never multipliers or sums.

Risposta: D

In osmosis only the solvent (water, in living things) crosses a semipermeable membrane, moving from the solution with less solute to the one with more, until the concentrations would equalise. The movement of solute particles down a gradient is diffusion; movement against a gradient needs energy (active transport).

Risposta: B

Mass percent is the mass of solute per 100 g of solution: 5% of 200 g = 0.05 × 200 = 10 g of NaCl (and 190 g of water). 5 g would be in 100 g of the solution.

Risposta: C

Ethanoic acid dissociates only partly (CH₃COOH ⇌ CH₃COO⁻ + H⁺), so its solution conducts weakly. Salts such as NaCl, strong acids such as HCl and strong bases such as KOH dissociate completely: strong electrolytes.

Risposta: A

A salt dissociates into its ions: two sodium ions, each Na⁺, and one sulfate ion, SO₄²⁻, which stays together as a polyatomic ion. The charges balance (2 × +1 = +2 against −2). There is no Na₂²⁺ ion, and the sulfate group does not break apart.

Risposta: D

NaOH is a strong base: [OH⁻] = 10⁻³ mol/dm³, so pOH = 3 and pH = 14 − 3 = 11. pH 3 is what 0.001 mol/dm³ of a strong acid gives; a base must have a pH above 7.

Risposta: B

Brønsted-Lowry acids donate protons and bases accept them. An electron-pair donor is a Lewis base; a source of OH⁻ in water is the Arrhenius definition of a base.

Risposta: C

Sodium carbonate is the salt of a strong base (NaOH) and a weak acid (carbonic acid). The carbonate ion hydrolyses, CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻, producing hydroxide ions, so the solution is basic. Salts of a strong acid and a strong base, such as NaCl, give neutral solutions.

Risposta: A

Colloidal particles (about 1 to 1000 nm) are large enough to scatter light, so the beam becomes visible: the Tyndall effect distinguishes a colloid from a true solution, whose ions or small molecules are too small to scatter it. Pure water and salt solutions are true solutions.

Risposta: D

Each carbon in ethyne forms two σ bonds (one to H, one to the other C) and two π bonds, so it uses two sp hybrid orbitals and two unhybridised p orbitals; the molecule is linear (180°). sp³ is the carbon of alkanes, sp² that of alkenes and benzene.

Risposta: B

Cis-trans isomerism needs a C=C double bond with two different groups on each carbon. In but-2-ene (CH₃-CH=CH-CH₃) each double-bonded carbon has H and CH₃. In but-1-ene and propene one carbon of the double bond carries two H atoms, and in 2-methylpropene one carries two CH₃ groups, so none can.

Risposta: C

Alkanes have the general formula CₙH₂ₙ₊₂; for n = 6 that is C₆H₁₄. C₆H₁₂ fits a hexene or cyclohexane, C₆H₆ is benzene and C₆H₁₀ a hexyne or cyclohexene.

Risposta: A

Light splits Cl₂ into chlorine radicals, which replace hydrogen atoms one at a time in a chain reaction (CH₄ + Cl₂ → CH₃Cl + HCl, then CH₂Cl₂ and so on). Alkanes are saturated, so they cannot undergo addition; electrophilic addition is the typical reaction of alkenes.

Risposta: B

By Markovnikov's rule the hydrogen adds to the carbon of the double bond that already has more hydrogens (the CH₂ end), and bromine to the middle carbon: CH₃-CHBr-CH₃. 1,2-dibromopropane is the product with Br₂, and propane the product with H₂.

Risposta: D

Water adds across the triple bond to give an unstable enol, CH₂=CH-OH (vinyl alcohol), which rearranges at once to the aldehyde ethanal, CH₃CHO. Ethanol would need the addition of water to ethene, not ethyne.

Risposta: C

With a Lewis-acid catalyst (FeCl₃ or AlCl₃) benzene undergoes electrophilic substitution: C₆H₆ + Cl₂ → C₆H₅Cl + HCl, keeping the aromatic ring. Hexachlorocyclohexane is the addition product, which forms only with UV light and no catalyst.

Risposta: A

Toluene is methylbenzene, C₆H₅-CH₃. Hydroxybenzene is phenol and aminobenzene is aniline.

Risposta: B

In a secondary alcohol the carbon carrying the OH is bonded to two other carbons: in propan-2-ol, CH₃-CHOH-CH₃, it is the middle carbon. Propan-1-ol is primary, methanol is a special case usually grouped with the primary alcohols, and 2-methylpropan-2-ol is tertiary (three carbons on the C-OH).

Risposta: D

The nitrogen of an amine has a lone pair, which can bind H⁺ (R-NH₂ + H⁺ → R-NH₃⁺), so amines are Brønsted bases and form salts with acids, as ammonia does. Releasing H⁺ is acidic behaviour; amines have no OH group.

Risposta: C

Aldehydes are oxidised to carboxylic acids and reduce the blue Cu²⁺ complex in Fehling's solution to brick-red Cu₂O. A silver mirror is the result with Tollens' reagent. Ketones give no change with either, which is how the tests tell them apart.

Risposta: A

Reducing a ketone gives a secondary alcohol: the C=O of CH₃-CO-CH₃ becomes CH-OH, giving CH₃-CHOH-CH₃. Reducing an aldehyde (propanal) gives the primary alcohol propan-1-ol. Propanoic acid would come from oxidising propanal, not from reducing anything.

Risposta: B

A carboxylic acid is neutralised by a base to a salt and water: CH₃COOH + NaOH → CH₃COONa + H₂O. Hydrogen gas forms with a reactive metal such as sodium, not with NaOH; ethyl ethanoate is an ester, formed from the acid and ethanol.

Risposta: D

A fat is a triester of glycerol. Boiled with NaOH or KOH it is hydrolysed to glycerol and the sodium or potassium salts of the fatty acids, which are soaps. Free fatty acids form in acid hydrolysis; in alkali they are at once turned into their salts.

Risposta: A

Glucose, C₆H₁₂O₆, has six carbons (a hexose) and an aldehyde group at carbon 1 in its open-chain form (an aldose): an aldohexose. Fructose is the ketohexose; ribose is an aldopentose.

Risposta: C

Ribose is a pentose, C₅H₁₀O₅. Deoxyribose, the sugar in DNA, has one oxygen fewer (C₅H₁₀O₄: no OH at carbon 2). C₆H₁₂O₆ is a hexose such as glucose and C₁₂H₂₂O₁₁ a disaccharide such as sucrose.

Risposta: B

Maltose is two α-glucose units joined by an α-1,4 glycosidic bond, so hydrolysis gives two glucose. Glucose and fructose come from sucrose, glucose and galactose from lactose.

Risposta: D

Cellulose is a straight chain of β-glucose joined by β-1,4 glycosidic bonds, which lets chains lie side by side and hydrogen-bond into strong fibres. Starch and glycogen are made of α-glucose, which is why humans can digest them and not cellulose.

Risposta: D

Amino acids are amphoteric. At the isoelectric point the molecule carries one positive and one negative charge, +H₃N-CHR-COO⁻, so its net charge is zero and it does not move in an electric field. Below that pH it is mostly a cation, above it an anion.

Risposta: A

A peptide bond joins two amino acids, so a chain of n amino acids has n − 1 peptide bonds: a tripeptide has 2. Each bond forms by a condensation reaction that releases one molecule of water.