Free EJU Science Questions and Answers — Questions and Answers
Question 1: The water of 100 g at 10 °C is placed in a container that has a heat capacity of 150 J/K and is at temperature t. After sufficient time elapses, the container's temperature changes to 0.0 °C. Also, a portion of the water in the container turns into ice, with the container now holding ice of 5.0 g at 0.0 °C and water of 95 g at 0.0 °C. The specific heat of water is 4.2 J/(g ‥ K), and the heat of fusion of ice is 330 J/g. Assume that there is no exchange of heat with the environment. <br><br> What is t (in °C)?
- -54
- -43
- -39 (Correct answer)
- -21
- -17
- -4.0
Correct answer: -39
Explanation: <br> Given: <br> *Water: 100 g at 10°C <br> *Container heat capacity: 150 J/K <br> *Ice formed: 5 g <br> *Specific heat of water: 4.2 J/(g·K) <br> *Heat of fusion of ice: 330 J/g <br><br> Steps: <br> 1. Heat lost by water cooling to 0°C: 100 × 4.2 × 10 = 4200J <br> 2. Heat to freeze 5 g of water: 5 × 330 = 1650J <br> 3. Total heat lost: 4200 + 1650 = 5850J <br> 4. Heat gained by container: 150 × (0 − t) = −150t <br> 5. Solve for 𝑡: <br> −150t = 5850 <br> t = −39
Question 2: The following reaction is in an equilibrium state. Among the following statements about this reaction, two are correct. Choose the correct combination. <br><br> (a) If the temperature of this reaction is raised, the equilibrium constant will become smaller. <br> (b) If a catalyst is added, the equilibrium constant will become larger since the rate of reaction increases. <br> (c) Though the path of the reaction will not change by adding a catalyst, the activation energy of the reaction will become smaller. <br> (d) It is impossible to derive an equation explaining the relation between the rate of reaction and the concentration of reactants directly from the chemical equation.
- a, b
- a, c
- a, d (Correct answer)
- b, c
- b, d
- c, d
Correct answer: a, d
Explanation: <br> (a) If the temperature of this reaction is raised, the equilibrium constant will become smaller. <br> - This is correct for exothermic reactions. Increasing temperature shifts the equilibrium to favor the reactants, decreasing the equilibrium constant. <br><br> (d) It is impossible to derive an equation explaining the relation between the rate of reaction and the concentration of reactants directly from the chemical equation. <br> - This is correct. The rate law is determined experimentally and cannot be derived directly from the stoichiometric coefficients of the chemical equation.
Question 3: Among the gases generated by means of the following procedures (a)-(d), two exhibit reducing ability. Choose the correct combination. <br><br> (a) Aqueous sodium hydroxide (NaOH) is added to aluminum (Al). <br> (b) Concentrated sulfuric acid (H≥SO4) is added to sodium chloride (NaCl) and the mixture is heated. <br> (c) Concentrated hydrochloric acid (HCI) is added to manganese(IV) oxide and the mixture is heated. <br> (d) Dilute sulfuric acid (H2SO4) is added to iron(II) sulfide (FeS).
- a, b
- a, c
- a, d (Correct answer)
- b, c
- b, d
- c, d
Correct answer: a, d
Explanation: <br> (a) Aqueous sodium hydroxide (NaOH) is added to aluminum (Al). <br> - This reaction produces hydrogen gas <br><br> (d) Dilute sulfuric acid is added to iron (II) sulfide (FeS). <br> - This reaction produces hydrogen sulfide gas
Question 4: From the choices below, choose the statement that correctly describes ribosomes:
- Ribosomes are the site of protein synthesis. (Correct answer)
- Prokaryotic ribosomes reside in the cytoplasm; eukaryotic ribosomes reside in the nucleus.
- Ribosomes have a double-membrane structure.
- Ribosomes contain an enzyme that breaks down excess proteins.
Correct answer: Ribosomes are the site of protein synthesis.
Explanation: <br> Ribosomes are responsible for translating mRNA into proteins, making them essential for protein synthesis in both prokaryotic and eukaryotic cells.
Question 5: The statements below describe protein structure. Choose the combination indicating the two statements that are correct: <br><br> (a) There are 20 types of amino acids that are used to form proteins. <br> (b) A sequence of amino acids that are linked together is described as the primary structure; the bonds joining these amino acids together are called S-S bonds (disulfide bonds). <br> (c) Some proteins are made up of multiple polypeptide chains aggregated together. <br> (d) The a-helix and B-sheet structures are described as tertiary structures.
- a, b
- a, с (Correct answer)
- a, d
- b, c
- b, d
- c, d
Correct answer: a, с
Explanation: <br> (a) There are 20 types of amino acids that are used to form proteins. - This statement is correct. Proteins are composed of 20 different amino acids, each with unique chemical properties that contribute to protein structure and function. <br><br> (c) Some proteins are made up of multiple polypeptide chains aggregated together. - This statement is also correct. Proteins can have a quaternary structure, which involves multiple polypeptide chains coming together to form a functional protein complex.
Question 6: From the choices below, choose the statement that correctly describes photosynthesis in green sulfur bacteria:
- Photosynthesis in green sulfur bacteria takes place in the chloroplasts.
- Oxygen is released in the process of photosynthesis in green sulfur bacteria.
- A photosynthetic pigment called bacteriochlorophyll is used in photosynthesis in green sulfur bacteria. (Correct answer)
- Electrons from H2O are used to synthesize organic compounds in the process of photosynthesis in green sulfur bacteria.
Correct answer: A photosynthetic pigment called bacteriochlorophyll is used in photosynthesis in green sulfur bacteria.
Explanation: <br> Green sulfur bacteria use bacteriochlorophyll as their primary photosynthetic pigment, rather than chlorophyll found in plants. This pigment enables them to perform photosynthesis using light energy to produce organic compounds.
Question 7: What happens in the human body when the body temperature decreases? From the choices below, choose the statement that is NOT correct.
- Heartbeat is accelerated by the action of the sympathetic nervous system.
- Adrenaline secretion is stimulated.
- Arrector pili muscles contract.
- Blood vessels in the skin constrict.
- Metabolism in the liver and skeletal muscles is inhibited. (Correct answer)
Correct answer: Metabolism in the liver and skeletal muscles is inhibited.
Explanation: <br> When body temperature decreases (hypothermia), the body initiates several responses to maintain warmth and normal physiological function: <br> *Heartbeat is accelerated by the action of the sympathetic nervous system: This helps circulate blood faster to distribute heat. <br> *Adrenaline secretion is stimulated: Adrenaline (epinephrine) increases metabolic rate to generate heat. <br> *Arrector pili muscles contract: This causes goosebumps, which can help trap heat. <br> *Blood vessels in the skin constrict (vasoconstriction): This reduces blood flow to the skin, minimizing heat loss.
Question 8: From the choices below, choose the statement that correctly describes a human reflex.
- The center of the patellar tendon reflex is the medulla oblongata.
- The center of the flexor reflex is the midbrain.
- The pathway by which excitation is transmitted during a reflex is called the reflex arc. (Correct answer)
- During a reflex, the excitation is transmitted to the reflex center via the cerebrum.
Correct answer: The pathway by which excitation is transmitted during a reflex is called the reflex arc.
Explanation: <br> A reflex arc is the neural pathway that allows a reflex action to occur in response to a stimulus. It involves sensory neurons detecting the stimulus, transmitting signals to the spinal cord or brainstem (not the cerebrum), and then motor neurons sending signals to produce the reflexive response. This process bypasses conscious control to enable rapid reactions.
Question 9: The substances listed below are believed to have been in existence or formed during the process of chemical evolution that preceded the emergence of life. From the choices below, choose the answer that correctly arranges a - c in the order in which they appeared. <br><br> (a) Proteins, nucleic acids, etc. <br> (b) Amino acids, sugars, phospholipids, etc. <br> (c) Hydrogen sulfide, hydrogen, ammonia, methane, etc.
- a → b → c
- a → c → b
- b → a → c
- b → c → a
- c → a → b
- c → b → a (Correct answer)
Correct answer: c → b → a
Explanation: <br> (c) Hydrogen sulfide, hydrogen, ammonia, methane, etc.: These are simple inorganic molecules that were likely present in the early Earth's atmosphere or hydrothermal vents. <br> (b) Amino acids, sugars, phospholipids, etc.: These are organic molecules that could have formed through prebiotic chemistry, such as the Miller-Urey experiment, which simulated conditions believed to be present on early Earth. <br> (a) Proteins, nucleic acids, etc.: These are complex biomolecules that are essential for life and likely formed later, possibly through the polymerization of simpler organic molecules. <br><br> This sequence reflects a plausible progression from simple inorganic molecules to more complex organic molecules during the early stages of chemical evolution on Earth.
Question 10: Innate behaviors and learned behaviors are two categories of animal behavior. From the choices below, choose the answer that best represents an example of learned behaviors.
- Humans reflexively draw back their hands when their fingers touch something hot.
- During breeding season, male three-spined sticklebacks (a freshwater fish) attack other red-bellied males that enter their territory, but do not attack females whose abdomen is swollen with eggs.
- Male silkmoths are attracted by a pheromone to locate females.
- As exemplified by how earthworms move away from light, some animals move in a certain direction in response to a specific stimulus, such as light or a chemical substance.
- The sea hare retracts its gill when a tactile stimulus is applied to its siphon. However, when the stimulus is applied repeatedly, the sea hare stops retracting its gill. (Correct answer)
Correct answer: The sea hare retracts its gill when a tactile stimulus is applied to its siphon. However, when the stimulus is applied repeatedly, the sea hare stops retracting its gill.
Explanation: <br> Learned behaviors are those that an animal acquires through experience or interaction with the environment. In this case, the sea hare initially responds reflexively to the tactile stimulus by retracting its gill. However, with repeated exposure to the same stimulus, the sea hare learns not to retract its gill, indicating an adaptive change in behavior based on experience.
Question 11: From the choices below, choose the statement that correctly describes carbon dioxide assimilation by cyanobacteria, such as Nostoc:
- They use a photosynthetic pigment called bacteriochlorophyll.
- They have chloroplasts and perform the same type of photosynthesis as land plants.
- They use energy released from the oxidization of inorganic substances such as ammonium ions.
- They take up hydrogen sulfide to perform photosynthesis.
- They produce oxygen by splitting water. (Correct answer)
Correct answer: They produce oxygen by splitting water.
Explanation: <br> Cyanobacteria, including Nostoc, are photosynthetic organisms that utilize water as a source of electrons and protons in the process of photosynthesis. During this process, they split water molecules (H2O) to release oxygen (O2) as a byproduct. This oxygenic photosynthesis is similar to that of plants and algae.
Free EJU Science Questions and Answers
The water of 100 g at 10 °C is placed in a container that has a heat capacity of 150 J/K and is at temperature t.
After sufficient time elapses, the container's temperature changes to 0.0 °C.
Also, a portion of the water in the container turns into ice, with the container now holding ice of 5.0 g at 0.0 °C and water of 95 g at 0.0 °C.
The specific heat of water is 4.2 J/(g ‥ K), and the heat of fusion of ice is 330 J/g.
Assume that there is no exchange of heat with the environment.
What is t (in °C)?