Nokea
Which vitamin requires intrinsic factor for proper absorption?
- A. Vitamin A
- B. Vitamin C
- C. Vitamin D
- D. Vitamin B12
Correct Answer: D
Rationale: Vitamin B12 requires intrinsic factor, a glycoprotein secreted by the parietal cells of the stomach, for proper absorption in the small intestine. Intrinsic factor binds to vitamin B12 and facilitates its absorption in the ileum. Deficiency in intrinsic factor can lead to pernicious anemia, a condition characterized by a lack of vitamin B12 absorption. Options A, B, and C are incorrect. Vitamin A is absorbed in the small intestine with the help of bile salts; Vitamin C is absorbed in the small intestine via active transport; Vitamin D is absorbed in the small intestine through a process involving bile salts and micelles. It is essential for students to understand this relationship as it highlights the importance of intrinsic factor in the absorption of specific vitamins and the consequences of its deficiency.
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What happens to the potential energy of an object as it falls freely near the Earth's surface?
- A. Potential energy decreases
- B. Potential energy increases
- C. Potential energy remains constant
- D. Potential energy becomes zero
Correct Answer: A
Rationale: As an object falls freely near the Earth's surface, its potential energy decreases. This decrease occurs because the gravitational potential energy is being converted into kinetic energy as the object accelerates due to gravity. According to the law of conservation of energy, the total mechanical energy (the sum of potential and kinetic energy) remains constant in the absence of non-conservative forces like air resistance. Choice B ('Potential energy increases') is incorrect because the object's potential energy is being converted into kinetic energy, leading to a decrease. Choice C ('Potential energy remains constant') is incorrect as the conversion of potential energy to kinetic energy results in a decrease in potential energy. Choice D ('Potential energy becomes zero') is incorrect because potential energy is not reduced to zero but is transformed into kinetic energy as the object falls.
Which of the following best describes a chemical change?
- A. Melting ice to form water
- B. Dissolving sugar in water
- C. Burning wood to produce ash
- D. Crushing a can to reduce its size
Correct Answer: C
Rationale: A chemical change involves a chemical reaction where new substances are formed. Burning wood to produce ash is an example of a chemical change because the wood undergoes a chemical reaction to form a new substance (ash). In this process, the chemical composition of wood changes to produce ash, which is a new substance. On the other hand, melting ice to form water, dissolving sugar in water, and crushing a can to reduce its size are examples of physical changes. In these instances, the substances may change their physical state or appearance but do not undergo a chemical reaction to form new substances. Therefore, choice C is the correct answer as it represents a chemical change, while choices A, B, and D represent physical changes.
Which type of mutation involves a change in the number of chromosomes?
- A. Point mutation
- B. Frameshift mutation
- C. Missense mutation
- D. Aneuploidy
Correct Answer: D
Rationale: A) Point mutation involves a change in a single nucleotide base pair within the DNA sequence.
B) Frameshift mutation involves the insertion or deletion of nucleotides, causing a shift in the reading frame of the genetic code.
C) Missense mutation involves a single nucleotide change that results in a codon that codes for a different amino acid.
D) Aneuploidy involves a change in the number of chromosomes, where an individual may have an extra chromosome (trisomy) or a missing chromosome (monosomy). Aneuploidy can lead to genetic disorders such as Down syndrome (trisomy 21) or Turner syndrome (monosomy X). Changing the number of chromosomes is a characteristic feature of aneuploidy, making it the correct answer. Point mutation, frameshift mutation, and missense mutation do not involve a change in the number of chromosomes and are focused on alterations at the nucleotide level within the DNA sequence.
Which type of immune cell does the human immunodeficiency virus (HIV) target and destroy?
- A. Neutrophils
- B. Macrophages
- C. Helper T cells
- D. Memory B cells
Correct Answer: C
Rationale: HIV targets and destroys Helper T cells, which are vital for coordinating the immune response against infections. The destruction of Helper T cells weakens the immune system, leading to acquired immunodeficiency syndrome (AIDS). Neutrophils (Choice A) are primarily involved in acute inflammatory responses and fighting bacterial infections. Macrophages (Choice B) play a role in phagocytosis and antigen presentation but are not the primary target of HIV. Memory B cells (Choice D) are responsible for mounting a quicker and more robust antibody response upon re-exposure to a pathogen, but they are not the main target of HIV infection.
The largest level of ecological organization is a:
- A. Population
- B. Community
- C. Ecosystem
- D. Biome
Correct Answer: D
Rationale: A) Population: A population consists of individuals of the same species living in the same area. It is a smaller level of ecological organization compared to a biome.
B) Community: A community consists of populations of different species living and interacting in the same area. It is a larger level of organization than a population but smaller than an ecosystem or biome.
C) Ecosystem: An ecosystem includes all living organisms (biotic factors) and their physical environment (abiotic factors) interacting in a particular area. It is a larger level of organization than a community but smaller than a biome.
D) Biome: The correct answer is D - Biome. A biome is the largest level of ecological organization and encompasses a large geographic area characterized by a specific climate, vegetation, and animal life. Biomes can be found on multiple continents and are defined by similar abiotic and biotic factors. Therefore, it is the largest level of ecological organization among the options provided, making it the correct answer.