Nokea
How do animal cells divide during cytokinesis?
- A. Contractile ring
- B. Cell plate
- C. Both
- D. None of the above
Correct Answer: A
Rationale: Animal cells divide using a contractile ring during cytokinesis. The contractile ring is composed of actin and myosin filaments and contracts to pinch the cell into two daughter cells. In contrast, cell plate formation is a mechanism observed in plant cells, not animal cells. Therefore, the correct answer is the contractile ring.
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Human cells need oxygen for respiration. What system of the body is responsible for transporting an oxygen molecule to different locations throughout the body?
- A. Skeletal.
- B. Lymphatic.
- C. Respiratory.
- D. Circulatory.
Correct Answer: D
Rationale:
What is the characteristic of the cell membrane consisting of a bilayer of phospholipids with proteins, cholesterol, and glycoproteins that creates a hydrophobic region between two layers of lipids?
- A. Impermeable
- B. Permeable
- C. Selectively permeable
- D. Selectively impermeable
Correct Answer: C
Rationale: The correct answer is 'C: Selectively permeable.' The cell membrane is selectively permeable because it allows certain molecules to pass through while restricting the passage of others. The hydrophobic region formed by the lipid bilayer makes it selectively permeable by controlling the movement of substances in and out of the cell. This selective permeability is vital for cellular functions, as it regulates the transport of essential molecules and maintains the internal environment required for proper cell operation and overall cellular homeostasis.
Why do cells require a large surface-to-volume ratio?
- A. For complexity.
- B. Compartmentalization.
- C. Size of organelles.
- D. Nutrient and gas exchange.
Correct Answer: D
Rationale: The correct answer is D: Nutrient and gas exchange. Cells require a large surface-to-volume ratio to efficiently exchange nutrients and gases with their environment. With a larger surface area, cells can absorb more nutrients and oxygen while expelling waste and carbon dioxide more effectively.
Rationale:
1. Nutrient exchange: A larger surface area allows for more nutrient absorption, essential for cell metabolism and function.
2. Gas exchange: A high surface-to-volume ratio facilitates the exchange of gases like oxygen and carbon dioxide necessary for cellular respiration.
3. Efficiency: Cells need to maintain a balance between surface area and volume to ensure optimal nutrient and gas exchange.
4. Other choices:
- A: Complexity is not directly related to the surface-to-volume ratio.
- B: Compartmentalization refers to the organization of organelles within a cell, not the surface-to-volume ratio.
- C: While size of organelles can affect cell function, it is not the primary reason for requiring a
A mother is homozygous recessive for freckles (ff) and a father is heterozygous for freckles (FF). Which genotypic ratio for freckles do their children have?
- A. 50% ff, 50% FF.
- B. 25% ff, 75% Ff.
- C. 25% FF, 75% ff.
- D. 50% ff, 50% Ff.
Correct Answer: A
Rationale: Correct Answer: A (50% ff, 50% FF)
Rationale:
1. The mother is homozygous recessive (ff) and the father is heterozygous (FF).
2. The father can only pass on the dominant allele (F) to all offspring.
3. All offspring will inherit one F allele from the father and one f allele from the mother.
4. The genotypic ratio will be 50% FF (f from father) and 50% ff (f from mother).
Summary:
- Choice B is incorrect because the father cannot pass on the recessive allele.
- Choice C is incorrect as the mother is homozygous recessive.
- Choice D is incorrect because it does not consider the father's genotype.
The cell membrane consists of a bilayer of phospholipids with proteins, cholesterol, and glycoproteins. This bilayer creates a hydrophobic region between two layers of lipids, making it which of the following?
- A. Impermeable
- B. Permeable
- C. Selectively permeable
- D. Selectively impermeable
Correct Answer: C
Rationale: The cell membrane is composed of a phospholipid bilayer with proteins, cholesterol, and glycoproteins. This structure results in the creation of a hydrophobic region between the lipid layers. The cell membrane is termed 'selectively permeable' because it allows certain substances to pass through while restricting the passage of others, based on factors like size and charge. This property is essential for regulating the transport of ions and molecules in and out of the cell to maintain cellular function and homeostasis.