Practice Test (Survey of Natural Sciences) Flashcards

Which organelle in a eukaryotic cell makes transport vesicles for exocytosis?

Answer: Golgi Body

The Golgi apparatus, or Golgi body, is responsible for modifying, sorting, and packaging proteins and lipids into vesicles for secretion or delivery to other organelles. Specifically, it forms transport vesicles that carry processed materials to the cell membrane for exocytosis, the process of releasing substances outside the cell. The Smooth Endoplasmic Reticulum is involved in lipid synthesis and detoxification, while ribosomes synthesize proteins, and mitochondria produce ATP.

The reaction quotient (Q) for a reaction involving nitrogen monoxide within a sealed flask was determined to be 1.1 × 10² at one point. Which reaction is most likely taking place in the flask if the amount of NO gas in the flask increased after this point?

Answer: N2(g) + O2(g) ↔ 2NO(g) Kc = 4.2 × 102

The reaction quotient (Q) compares the relative amounts of products and reactants present in a reaction at any given time to the equilibrium constant (Kc). If Q < Kc, the reaction will proceed in the forward direction (towards products) to reach equilibrium. The problem states that the amount of NO gas increased, meaning the reaction shifted to the right (towards products). For this to happen, Q must be less than Kc. Option A has Q (1.1 × 10²) < Kc (4.2 × 10²), indicating a shift to the right, which would increase NO.

When reacted with benzene, which of the following will produce an ortho/para configuration?

Answer: 2 of the below

Ortho/para directors are substituents that direct incoming electrophiles to the ortho and para positions on a benzene ring and are typically activating groups or halogens. Activating groups, like alkyl groups (-CH3) or groups with lone pairs (e.g., -NH2, -OH), donate electron density to the ring. Halogens (-Cl) are deactivating but are also ortho/para directors due to resonance effects. Both -Cl and -CH3 are ortho/para directors, making '2 of the below' the correct choice, as -NO2 and -COOH are meta directors.

In humans, cystic fibrosis is a recessive disease. What is the probability that a kid would be born with the condition if one parent is a carrier of the trait and the other parent is homozygous dominant, according to the principles of classical Mendelian genetics?

Answer: 0%

Let 'c' represent the recessive allele for cystic fibrosis and 'C' represent the dominant normal allele. A carrier parent has genotype Cc, and a homozygous dominant parent has genotype CC. When these parents cross (Cc x CC), the possible offspring genotypes are CC and Cc, each with a 50% probability. Since cystic fibrosis is a recessive disease, an individual must have two recessive alleles (cc) to express the condition. Therefore, none of the offspring will be 'cc', meaning the probability of a child being born with cystic fibrosis is 0%.

The cytosol's typical pH is at 7.2. The majority of enzymes in the lysosome, on the other hand, are only active at pH 5. This implies that

Answer: protons are actively pumped into the lysosome

Lysosomes are acidic organelles, with a typical pH of around 5, which is significantly lower than the cytosol's pH of 7.2. This acidic environment is crucial for the optimal activity of lysosomal enzymes, which are hydrolytic enzymes designed to break down waste materials. To maintain this low pH, protons (H+ ions) are actively pumped into the lysosome from the cytosol, requiring energy. This ensures that the enzymes function efficiently within the lysosome and are largely inactive if they accidentally leak into the cytosol, preventing cellular damage.

A compound is fully made up of silicon and oxygen atoms. What is the empirical formula of a compound containing 14.00 g of silicon and 32.0 g of oxygen?

Answer: SiO4

To determine the empirical formula, first convert the mass of each element to moles. For silicon (Si), 14.00 g / 28.09 g/mol ≈ 0.498 mol. For oxygen (O), 32.0 g / 16.00 g/mol = 2.00 mol. Next, divide each mole value by the smallest number of moles (0.498 mol) to find the simplest whole-number ratio. This gives Si: 0.498/0.498 = 1 and O: 2.00/0.498 ≈ 4.01. Thus, the empirical formula is SiO₄.

Which of the following functional groups has the highest priority in IUPAC nomenclature when numbering a parent chain?

Answer: Esters

In IUPAC nomenclature, functional groups are assigned priorities for naming and numbering the parent chain. Carboxylic acids have the highest priority, followed by esters, amides, nitriles, aldehydes, ketones, alcohols, amines, alkenes, alkynes, and then alkanes. Among the given options, esters have a higher priority than amines, alkenes, alkynes, and alkanes, meaning the carbon atom of the ester group would be numbered C1 in the parent chain.

Multiple binding sites exist on __________ enzymes.

Answer: Allosteric

Allosteric enzymes possess multiple binding sites: an active site where the substrate binds, and one or more allosteric sites where regulatory molecules (allosteric effectors) bind. The binding of an effector to an allosteric site induces a conformational change in the enzyme, which can either activate or inhibit the enzyme's activity at the active site. This mechanism allows for sophisticated regulation of metabolic pathways.

Caffeine can attach to the adenosine receptor but cannot activate it since its structure is very similar to that of adenosine. When caffeine binds to the adenosine receptor, which of the following best characterizes the effect?

Answer: Caffeine blocks the effect of adenosine by preventing the binding of adenosine to the adenosine receptor

Caffeine acts as an antagonist to adenosine receptors because it binds to the receptor but does not activate it, preventing adenosine from binding and exerting its normal effects. Adenosine typically promotes relaxation and drowsiness, so by blocking its binding, caffeine prevents these effects, leading to increased alertness. This is a classic example of competitive inhibition at a receptor site.

N₂(g) + O₂(g) + Cl₂(g) ↔ 2NOCl(g) ΔG° = 132.6 kJ/mol What would happen to the value of ΔG° in the equilibrium below if the concentration of N2 were to increase, and why?

Answer: It would stay the same because the value of Keq would not change

The standard Gibbs free energy change (ΔG°) is a thermodynamic constant that describes the spontaneity of a reaction under standard conditions (1 M concentration, 1 atm pressure, 298 K). It is directly related to the equilibrium constant (Keq) by the equation ΔG° = -RTlnKeq. Therefore, ΔG° is independent of the actual concentrations of reactants or products. While increasing N₂ concentration would shift the equilibrium to the right according to Le Chatelier's principle, it would not change the value of ΔG° or Keq.

The melting point of which of the following is the highest?

Answer: 2,2-Dimethylpropane

The melting point of alkanes is influenced by molecular size and the efficiency of molecular packing in the solid state. While larger molecules generally have higher melting points due to increased van der Waals forces, molecular symmetry also plays a crucial role. 2,2-Dimethylpropane is a highly symmetrical, spherical molecule that can pack very efficiently into a crystal lattice, leading to stronger intermolecular forces and a significantly higher melting point compared to its linear isomer, pentane, or smaller alkanes like ethane, propane, and butane.

Involuntary muscles that do not contain striations are referred to as

Answer: smooth muscle

Smooth muscle is a type of muscle tissue found in the walls of internal organs like the stomach, intestines, bladder, and blood vessels. It is characterized by its involuntary control, meaning its contractions are not consciously directed, and the absence of striations (bands) when viewed under a microscope. Cardiac muscle is also involuntary but is striated, while skeletal muscle is voluntary and striated.

Which of the following properties holds the water molecules in a vertical column of water in a plant's xylem vessels together?

Answer: the strong cohesion of property of water

The strong cohesion property of water is essential for its transport in a plant's xylem vessels. Cohesion refers to the attraction between water molecules themselves, primarily due to hydrogen bonding. This strong intermolecular attraction allows water molecules to stick together, forming a continuous, unbroken column that can be pulled upwards from the roots to the leaves through transpiration, resisting the force of gravity.

Three gases are contained in a sealed, rigid container: 28.0 g nitrogen, 40.0 g argon, and 36.0 g water vapour. What is the partial pressure of nitrogen if the total pressure exerted by the gases is 2.0 atm?

Answer: 0.50 atm

According to Dalton's Law of Partial Pressures, the partial pressure of a gas is its mole fraction multiplied by the total pressure. First, calculate the moles of each gas: N₂ (28.0 g / 28.0 g/mol = 1.0 mol), Ar (40.0 g / 40.0 g/mol = 1.0 mol), H₂O (36.0 g / 18.0 g/mol = 2.0 mol). The total moles are 1.0 + 1.0 + 2.0 = 4.0 mol. The mole fraction of nitrogen is 1.0 mol / 4.0 mol = 0.25. Therefore, the partial pressure of nitrogen is 0.25 * 2.0 atm = 0.50 atm.

For this molecule, how many stereoisomers are there?

Answer: 4

The number of stereoisomers for a molecule can be determined by the formula 2^n, where 'n' represents the number of chiral centers (carbon atoms bonded to four different groups). For the given molecule, there are two chiral centers. Therefore, the total number of possible stereoisomers is 2^2 = 4. These include two pairs of enantiomers or diastereomers, depending on the specific configurations.

In nucleic acids, which of the following is not a pyrimidine base?

Answer: Adenine

Nucleic acids (DNA and RNA) contain five main nitrogenous bases, which are classified into two groups: purines and pyrimidines. Purines have a double-ring structure and include Adenine and Guanine. Pyrimidines have a single-ring structure and include Cytosine, Thymine (in DNA), and Uracil (in RNA). Therefore, Adenine is not a pyrimidine base; it is a purine.

Bacteria that cannot survive in the presence of oxygen are known as:

Answer: Obligate Anaerobes

Obligate anaerobes are microorganisms that cannot survive in the presence of oxygen. Oxygen is toxic to these organisms, often because they lack the enzymes (like superoxide dismutase and catalase) necessary to detoxify reactive oxygen species formed during aerobic respiration. They rely on anaerobic respiration or fermentation for energy production.

High-energy photons hit neutral chlorine atoms, forcing electrons to expel from the various filled subshells. After being ejected, which subshell's electrons would have the maximum velocity?

Answer: 3p

When high-energy photons eject electrons from an atom, the kinetic energy of the ejected electron is equal to the photon's energy minus the electron's binding energy. Electrons in higher energy subshells (further from the nucleus) have lower binding energies. Therefore, for a given photon energy, electrons ejected from the outermost subshell (3p in chlorine) will have the lowest binding energy and thus the highest kinetic energy and maximum velocity.

What is this atom's hybridization?

Answer: sp2

Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds. To determine hybridization, count the number of electron domains (lone pairs and bonding groups) around the central atom. An atom with three electron domains (e.g., one double bond and two single bonds, or two double bonds, or three single bonds and one lone pair) will have sp2 hybridization, forming a trigonal planar geometry.

What is the empirical formula of an unknown compound with a carbon content of 48.02 percent, a hydrogen content of 18.74 percent, and a nitrogen content of 33.24 percent? (Nitrogen has an atomic weight of 14.0 g.)

Answer: C₅H₂₄N₃

To find the empirical formula, first assume a 100 g sample, so you have 48.02 g C, 18.74 g H, and 33.24 g N. Convert these masses to moles using their atomic weights (C=12.01, H=1.01, N=14.01): C: 48.02/12.01 ≈ 4.00 mol; H: 18.74/1.01 ≈ 18.55 mol; N: 33.24/14.01 ≈ 2.37 mol. Next, divide each mole value by the smallest number of moles (2.37 mol): C: 4.00/2.37 ≈ 1.69; H: 18.55/2.37 ≈ 7.83; N: 2.37/2.37 = 1. To get whole numbers, multiply by a factor (e.g., 3 for C and H to be close to integers): C ≈ 5, H ≈ 23.5, N = 3. Rounding H to 24, the empirical formula is C₅H₂₄N₃.