CBSE Class 9 Science Advanced Biology Fundamental Unit of Life MCQs Set 02

Answer: (c) Both have DNA

Explanation:
1. Neither organelle has a nucleus, and both are surrounded by two membranes.
2. Both contain 70S ribosomes (not 80S) and their own circular DNA.
3. So they are similar because both have DNA.

Teacher's Note:
1. Own DNA and 70S ribosomes make them semi-autonomous.
2. Eukaryotic cytoplasmic ribosomes are the 80S type.

Answer: (c) Robert Brown

Explanation:
1. Robert Brown observed the nucleus in the cells of an orchid in 1831.
2. Hooke discovered the cell, Leeuwenhoek the living cell and Virchow added that cells arise from cells.
3. The answer is Robert Brown.

Teacher's Note:
1. Brown - nucleus, Hooke - cell.
2. Do not confuse Robert Brown with Brownian motion; the same scientist noticed that too.

Answer: (a) Vacuole

Explanation:
1. The large central vacuole fills with water and presses the cytoplasm against the cell wall.
2. This pressure keeps the cell firm, that is turgid.
3. The answer is vacuole.

Teacher's Note:
1. The vacuole also helps in maintaining osmotic pressure.
2. A wilting plant has lost the turgidity of its cells.

Answer: (b) Mitochondria

Explanation:
1. Mitochondria release the energy of food and store it as ATP.
2. So they are called the power house of the cell.
3. The answer is mitochondria.

Teacher's Note:
1. Golgi - packaging, ribosome - proteins, lysosome - digestion.
2. Energy is released through respiration in the mitochondria.

Answer: (d) TMV (Tobacco Mosaic Virus)

Explanation:
1. The nucleus, mitochondria and chloroplasts all contain DNA.
2. The tobacco mosaic virus has RNA as its genetic material, not DNA.
3. The answer is TMV.

Teacher's Note:
1. Most plant viruses, including TMV, have RNA as the genetic material.
2. Both DNA and RNA are nucleic acids.

Answer: (a) Red blood corpuscles

Explanation:
1. Mature red blood cells of mammals lose their nucleus, which gives more space for haemoglobin.
2. White blood cells have a nucleus. Platelets are only tiny fragments of other cells, not complete cells.
3. Among the blood cells, the one without a nucleus is the red blood corpuscle.

Teacher's Note:
1. Mammalian RBCs also lack mitochondria and ER.
2. Platelets are cell fragments, so they are not counted as complete cells.

Answer: (b) Nerve cell

Explanation:
1. Liver and kidney cells are only about 20 to 30 µm across.
2. A nerve cell has a fibre up to a metre in length, longer than any muscle cell.
3. Among the options the largest cell is the nerve cell.

Teacher's Note:
1. In size by length the nerve cell is the longest cell of the body.
2. By volume the egg cell is the largest cell of the human body, but it is not among the options.

Answer: (a) Robert Hook

Explanation:
1. Robert Hooke gave the name 'cell' in 1665 after seeing the box-like units of cork.
2. Robert Brown discovered the nucleus, Watson and Crick gave the DNA double helix and Flemming studied mitosis.
3. The answer is Robert Hooke.

Teacher's Note:
1. Hooke's book was Micrographia.
2. Do not mix up Hooke and Brown: cell and nucleus.

Answer: (c) Lysosomes

Explanation:
1. Lysosomes hold strong digestive enzymes.
2. If the cell is damaged, they burst and the enzymes digest the cell itself.
3. That is why they are called suicide bags: the answer is lysosomes.

Teacher's Note:
1. Lysosomes are the waste-disposal system of the cell.
2. Their enzymes are called hydrolases.

Answer: (c) A=3, B=4, C=1, D=2

Explanation:
1. Karyokinesis is the division of the nucleus, so A = 3.
2. Cytokinesis is the division of the cytoplasm, so B = 4.
3. Meiosis takes place in meiocytes, so C = 1, and the cell plate forms in a dividing plant cell, so D = 2.
4. These give A=3, B=4, C=1, D=2, which is option (c).

Teacher's Note:
1. Karyo means nucleus, cyto means cell or cytoplasm.
2. Animal cells divide their cytoplasm by a furrow, but plant cells build a cell plate.