Class 9 – Science Extra Questions – Ch. 5 – The Fundamental Unit of Life

Ans: B

Explanation: ATP (adenosine triphosphate) is often referred to as the “energy currency” of the cell. It stores and releases energy in a form that cells can readily use for various metabolic processes, such as muscle contraction, nerve impulse transmission, and chemical synthesis. Mitochondria are organelles responsible for ATP production through cellular respiration, but they are not the molecule itself. FAD is an electron carrier involved in energy production, but not the primary energy currency. Glucose is a fuel source that is broken down to produce ATP, but it is not the immediate energy-carrying unit.
Correct Option: B

Ans: C

Explanation: Euglena, Paramecium, and Amoeba are all unicellular organisms. Euglena has a pellicle which allows for some flexibility in shape but it is not as dramatic as an amoeba. Paramecium has a slipper-like shape due to its rigid cilia and pellicle. Acetabularia is a single-celled green alga with a very specific and fixed shape resembling a mushroom or umbrella. Amoeba, on the other hand, moves and feeds by extending pseudopods, which are temporary extensions of its cytoplasm, causing its shape to constantly change and not be fixed.
Correct Option: C

Ans: C

Explanation: Lysosomes are membrane-bound organelles that contain digestive enzymes. These enzymes are responsible for breaking down waste materials, cellular debris, and engulfed foreign substances, thus playing a crucial role in cellular waste disposal and recycling. Mitochondria are responsible for cellular respiration and energy production. Ribosomes are responsible for protein synthesis. The endoplasmic reticulum is involved in protein and lipid synthesis and transport.
Correct Option: C

Ans: B

Explanation: The question asks for a nanoscale biological entity that exhibits characteristics of life *only* when inside a host cell. Bacteria, amoebas, and sperm are all microscopic but are considered living organisms capable of independent reproduction and metabolic processes outside of a host. Viruses, on the other hand, are acellular and obligate intracellular parasites; they are inert outside of a host cell and only replicate and exhibit life-like properties once they infect a host cell. Viruses are also generally considered to be nanoscale entities, with most ranging from 20 to 300 nanometers in diameter.
Correct Option: B

Ans: A

Explanation: A compound light microscope uses two main sets of lenses to magnify an object. The objective lens, located near the specimen, provides initial magnification, and the eyepiece lens (or ocular lens), where the observer looks, further magnifies the image.
Correct Option: A

Ans: C

Explanation: Chromosomes are complex structures found in the nucleus of eukaryotic cells. They are primarily composed of DNA, which carries the genetic information, and proteins, mainly histones. These proteins help to package and condense the long DNA molecule into a compact form that can fit inside the nucleus. Therefore, the composition of chromosomes is DNA and protein.
Correct Option: C

Ans: B

Explanation: Mitochondria are enclosed by a double membrane (inner and outer). The nucleus is also enclosed by a double membrane (nuclear envelope). Plastids, like chloroplasts, are also enclosed by a double membrane. Vacuoles, however, are typically enclosed by a single membrane called the tonoplast.
Correct Option: B

Ans: A

Explanation: The history of the cell’s documentation begins with Robert Hooke’s microscopic observations of cork in 1665. He coined the term “cell” to describe the small, box-like structures he observed. His influential work, “Micrographia,” was published in London and is considered the foundational text in cell biology. Robert Brown later discovered the nucleus in 1831. Starburger (likely a misspelling of Strasburger) and Dujardin were also important figures in cell theory but came much later.
Correct Option: A

Ans: A

Explanation: Ribosomes are the only cellular components among the options provided that do not have a surrounding membrane. The nucleus is enclosed by a double membrane (nuclear envelope), mitochondria are enclosed by a double membrane, and chloroplasts are also enclosed by a double membrane. Ribosomes, on the other hand, are complex structures made of ribosomal RNA and proteins, and they exist freely in the cytoplasm or are attached to the endoplasmic reticulum.
Correct Option: A

Ans: C

Explanation: Mature red blood cells in mammals lack several organelles, including the nucleus, mitochondria, and Golgi complex. Mitochondria are essential for cellular respiration, the process by which glucose is broken down to produce ATP (energy). Without mitochondria, red blood cells cannot perform aerobic respiration and therefore cannot use glucose in this way. Instead, they rely on anaerobic glycolysis to generate energy.
Correct Option: C