Nokea
Which of the following is the primary physical barrier the body uses to prevent infection?
- A. mucus membranes
- B. stomach acid
- C. skin
- D. urine
Correct Answer: C
Rationale: The correct answer is 'C: skin.' The skin is the primary physical barrier the body uses to prevent infection. It acts as a protective shield that prevents harmful microorganisms from entering the body. The outer layer of the skin, known as the epidermis, acts as a tough physical barrier that blocks the entry of pathogens. Additionally, the skin has special immune cells that can help fight off invaders that manage to breach the physical barrier. Choices A, B, and D are incorrect. While mucous membranes, stomach acid, and urine play important roles in the body's defense against pathogens, the primary physical barrier is the skin, which covers the entire body and provides a robust protective barrier.
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Which of the following distinguishes the isotopes of an element?
- A. Isotopes are atoms of the same element that have different ionic charges.
- B. Isotopes are atoms of elements within the same group on the periodic table.
- C. Isotopes are atoms of the same element that have different numbers of neutrons.
- D. Isotopes are atoms of the same element with different electron configurations.
Correct Answer: C
Rationale: Isotopes are defined as atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. This leads to variations in atomic mass for isotopes of an element. The different number of neutrons in isotopes results in differences in their atomic mass and properties while still belonging to the same element. Choice A is incorrect because isotopes do not have different ionic charges, they have the same chemical properties. Choice B is incorrect because isotopes are not atoms of elements within the same group on the periodic table; they are variants of the same element. Choice D is incorrect because isotopes of an element have the same electron configuration, differing only in the number of neutrons in the nucleus.
What describes a cell's reaction to being placed in a hypertonic solution?
- A. The cell will shrink as water is pulled out of the cell to equalize the concentrations inside and outside of the cell.
- B. The cell will swell as water is pulled into the cell to equalize the concentrations inside and outside of the cell.
- C. The cell will remain the same size since the concentrations inside and outside the cell are equal to begin with.
- D. The pH inside the cell will drop in order to equalize the pH inside and outside the cell.
Correct Answer: A
Rationale: A cell placed in a hypertonic solution has a higher solute concentration outside the cell compared to inside. This creates a concentration gradient that causes water to move out of the cell through osmosis to equalize the concentrations on both sides. As a result, the cell will shrink or undergo plasmolysis, as water is pulled out of the cell. Choice B is incorrect because a hypertonic solution causes water to move out of the cell, leading to shrinkage rather than swelling. Choice C is incorrect as a hypertonic solution results in a concentration gradient that leads to water leaving the cell, causing it to shrink. Choice D is incorrect because pH is not directly affected by being placed in a hypertonic solution; the change in solute concentration primarily impacts water movement.
What is the initial step of the scientific method?
- A. construct a hypothesis
- B. make observations
- C. analyze data
- D. form a question
Correct Answer: B
Rationale: The first step of the scientific method is to make observations. This involves collecting data and information about a specific phenomenon or problem. Observations serve as the basis for developing a question to be explored further. Forming a hypothesis (Choice A) comes after making observations, as the hypothesis is an educated guess to explain the observations. Analyzing data (Choice C) occurs later in the scientific method after data has been collected and experiments conducted. Forming a question (Choice D) is a crucial step but typically follows observations in the scientific process.
What type of reaction is represented by the following equation: 2C₆Hâ‚â‚„ + 19Oâ‚‚ → 12CO + 14Hâ‚‚O?
- A. Substitution reaction
- B. Acid-base reaction
- C. Enzyme reaction
- D. Combustion reaction
Correct Answer: D
Rationale: The given chemical equation represents a combustion reaction. Combustion reactions involve the burning of a hydrocarbon (C₆Hâ‚â‚„) in the presence of oxygen (Oâ‚‚) to produce carbon monoxide (CO) and water (Hâ‚‚O). Combustion reactions typically release heat and light energy. In this case, the reactants are a hydrocarbon and oxygen, resulting in the formation of carbon monoxide and water. Choices A, B, and C are incorrect because the reaction does not involve substitution, acid-base reactions, or enzyme catalysis. Combustion reactions are characterized by the rapid combination of a substance with oxygen, leading to the production of heat and light energy.
The above experimental design description is an example of which of the following types of experiments?
- A. field experiment
- B. natural experiment
- C. controlled experiment
- D. observational study
Correct Answer: C
Rationale: The above experimental design description involves the manipulation of an independent variable (light exposure) to observe its effects on the dependent variable (plant growth) under controlled conditions. In a controlled experiment, researchers actively manipulate one or more variables while keeping all other variables constant to establish cause-and-effect relationships.
Choice A, a field experiment, typically takes place in a real-world setting but still involves manipulation and control of variables. Choice B, a natural experiment, involves observing naturally occurring differences in variables without researcher intervention. Choice D, an observational study, does not involve manipulation of variables, making it different from the described experimental design.