Cell Structure — Set 3
Biology · कोशिका संरचना · Questions 21–30 of 60
The term 'Protoplasm' was coined by which scientist?
Correct Answer: D. Jan Evangelista Purkyně
Purkyně introduced the term 'protoplasm' in 1839 to describe the living substance within a cell. It includes both the cytoplasm and the nucleus as a unified living entity. This concept helped scientists understand that the cell is not just an empty chamber.
Which organelle is particularly abundant in cells that are very active in protein secretion?
Correct Answer: D. Rough ER
Rough Endoplasmic Reticulum is covered with ribosomes that synthesize proteins for export. Cells in the pancreas, which produce digestive enzymes, have an extensive network of Rough ER. The proteins produced here are typically sent to the Golgi apparatus.
What is the function of 'Pili' in certain bacterial cells?
Correct Answer: B. Attachment and conjugation
Pili are hair-like appendages that allow bacteria to adhere to surfaces or other cells. Specialized 'sex pili' are used to transfer genetic material between bacteria during conjugation. They are distinct from flagella, which are used primarily for locomotion.
Which of the following is responsible for maintaining the shape of a bacterial cell?
Correct Answer: A. Cell Wall
The bacterial cell wall provides structural support and prevents the cell from bursting due to osmotic pressure. It is typically made of a unique substance called peptidoglycan. Scientists use Gram staining to categorize bacteria based on their cell wall structure.
Which organelle is known for producing hydrogen peroxide as a byproduct of metabolism?
Correct Answer: A. Peroxisome
Peroxisomes contain enzymes that break down fatty acids and detoxify harmful substances. They produce hydrogen peroxide during these reactions but quickly convert it to water and oxygen. This specialized metabolism protects the rest of the cell from oxidative damage.
What is the collective term for the DNA and proteins found within the nucleus of a non-dividing cell?
Correct Answer: A. Chromatin
Chromatin appears as a thin, thread-like network of genetic material when the cell is not dividing. During cell division, this chromatin condenses to form distinct, visible chromosomes. It consists of DNA wrapped around proteins called histones.
Which organelle is responsible for the synthesis of ATP through oxidative phosphorylation?
Correct Answer: B. Mitochondria
Mitochondria are the powerhouses of the cell where the majority of ATP is generated. This process occurs across the folded inner membrane known as the cristae. Cells with high energy demands, like muscle cells, contain more mitochondria.
Which type of RNA carries the genetic information from the DNA in the nucleus to the ribosomes?
Correct Answer: D. mRNA
Messenger RNA (mRNA) acts as a transcript of the genetic code that ribosomes can read. It travels through nuclear pores to reach the cytoplasm for translation. This step is essential for the expression of genes into functional proteins.
Which of the following is true regarding the 'Cell Theory'?
Correct Answer: A. Cells arise only from pre-existing cells
The principle that cells come from pre-existing cells was added to the theory by Rudolf Virchow. This debunked the idea of spontaneous generation of life. The theory also states that the cell is the basic structural and functional unit of life.
Which organelle helps in the formation of the cell plate during plant cell division?
Correct Answer: C. Golgi Apparatus
The Golgi apparatus produces vesicles containing cell wall materials that accumulate at the center of the dividing cell. These vesicles fuse to form the cell plate, which eventually becomes the new cell wall. This process is unique to plants because their rigid walls prevent pinching.