All Free Biology MCQs with Answers
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19844 questions · page 677 of 1985
6761. Cell theory was formulated by Schleiden (1838) and Schwann (1839) which was later modified by:
- A. Robert Whittaker
- B. Madam Curie
- C. Rudolf Virchow
- D. Antonie van Leeuwenhoek
Explanation: The cell theory, initially formulated by Matthias Schleiden in 1838 and Theodor Schwann in 1839, was later modified by Rudolf Virchow.
Correct answer: Rudolf Virchow6762. Keeping in view the fluid mosaic model for the structure of cell membrane, which one of the following statements is correct concerning the movement of lipids and proteins from one lipid monolayer to the other described as a flip-flop movement?
- A. Both lipids and proteins can flip-flop
- B. Lipid can rarely flip-flop, proteins cannot
- C. Proteins can flip-flop, lipids can not
- D. Neither lipids nor proteins can flip-flop
Explanation: Lipids can flip-flop, which means that they can move from one leaflet of the membrane to the other. However, this process is very rare because it requires the lipid to pass through the hydrophobic core of the membrane, which is a high-energy barrier. Proteins, on the other hand, cannot flip-flop. This is because they are anchored to the membrane by either their amino acid side chains or by covalent bonds to the phospholipids.
Correct answer: Lipid can rarely flip-flop, proteins cannot6763. The diagram shows a model of the structure of a biological membrane. Identify the hydrophobic part of the phospholipid bilayer.
- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: Option A shows the hydrophobic tails of the phospholipid molecules which are facing inwards.
Correct answer: Option A6764. Cells without nucleoli die because they do not possess:
- A. Centrioles, and are unable to undergo cell division
- B. Lysosomes, and are unable to destroy worn-out organelles
- C. Mitochondria, and are unable to obtain energy
- D. Ribosomes, and are unable to manufacture proteins
Explanation: Cells without nucleoli die because they do not possess ribosomes, and are unable to manufacture proteins. Ribosomes are the protein factories of the cell. They are made up of RNA and protein, and they are responsible for translating the genetic information in DNA into proteins. Without ribosomes, cells are unable to synthesize proteins, which are essential for all cellular functions.
Correct answer: Ribosomes, and are unable to manufacture proteins6765. How many units occur in each stockpile of Golgi apparatus?
- A. 4 to 8
- B. 4 to 6
- C. 2 to 6
- D. 2 to 8
Explanation: The number of compartments in any one Golgi apparatus is usually between 4 and 8.
Correct answer: 4 to 86766. It is synthesized by free-floating ribosomes of cytoplasm in humans:
- A. Pancreatic lipase
- B. Salivary amylase
- C. Insulin
- D. DNA helicase
Explanation: DNA helicase, since it is the only one whose final destination is inside the cell. These Helicases come under the class of enzymes that are essential to all organisms. These are motor proteins that move directionally along with the nucleic acid, separating two hybridized nucleic acid strands, using the energy from ATP hydrolysis. Their role or function is to unpack an organism's genetic material.
Correct answer: DNA helicase6767. These play a vital role in the defense activity of macrophages:
- A. Mitochondria
- B. Lysosomes
- C. Lysozymes
- D. Ribosomes
Explanation: "Lysosomes" play a vital role in the defense activity of macrophages. Macrophages are immune cells that play a critical role in the body's defense against pathogens. Lysosomes are membrane-bound organelles found within macrophages and other cells. They contain various enzymes that are involved in the breakdown and digestion of cellular waste, pathogens, and other foreign substances.
Correct answer: Lysosomes6768. Damage to one of the following immediately kills the cell whether it's prokaryotic or eukaryotic:
- A. Mitochondria
- B. Cell membrane
- C. Cell wall
- D. Golgi apparatus
Explanation: The cell membrane, also known as the plasma membrane, is a crucial component of all cells. It forms a protective barrier that separates the interior of the cell from the external environment. If the cell membrane is severely damaged or disrupted, it can result in the loss of cell integrity and the inability to regulate essential cellular processes. This can lead to immediate cell death.
Correct answer: Cell membrane6769. Movement of Na+ across axon membrane via Na+-K+ pump is an example of:
- A. Active transport
- B. Diffusion
- C. Passive transport
- D. Osmosis
Explanation: The Na+-K+ pump is an integral membrane protein that actively transports Na+ out of the cell and K+ into the cell, against their concentration gradients. In the case of the Na+-K+ pump, it uses the energy from ATP hydrolysis to pump three Na+ ions out of the cell for every two K+ ions it pumps into the cell.so this is an example of active transport in which forthe movement of ions or molecules across a cell membrane against their concentration gradient
Correct answer: Active transport6770. Which one always passes through the nuclear membrane from nucleoplasm to the cytoplasm?
- A. Proteins
- B. DNA nucleotides
- C. Enzymes
- D. RNA
Explanation: RNA always passes through the nuclear membrane from the nucleoplasm to the cytoplasm. RNA molecules are synthesized within the nucleus through the process of transcription. After synthesis, RNA molecules need to be transported from the nucleus to the cytoplasm, where they can perform their functions in protein synthesis and other cellular processes.
Correct answer: RNA