Cells & Genetics: The Building Blocks of Life: questions and answers
Study every question with its correct answer and explanation.
1. Who first used the word 'cell' after observing thin slices of cork under a microscope in 1665?
- A. Robert Hooke
- B. Antonie van Leeuwenhoek
- C. Matthias Schleiden
- D. Robert Brown
Answer: Robert Hooke
Robert Hooke described the tiny box-like compartments he saw in cork in his 1665 book 'Micrographia' and called them 'cells'. Robert Brown later discovered the cell nucleus in 1831.
2. Which of these is found in plant cells but not in animal cells?
- A. Mitochondria
- B. Ribosome
- C. Chloroplast
- D. Nucleus
Answer: Chloroplast
Chloroplasts contain the green pigment chlorophyll and are where photosynthesis takes place. Plant cells also have a rigid cell wall, which animal cells lack, while mitochondria, ribosomes and nuclei are found in both.
3. In 1953, which scientists proposed the double-helix structure of DNA?
- A. Gregor Mendel and Charles Darwin
- B. James Watson and Francis Crick
- C. Louis Pasteur and Robert Koch
- D. Robert Hooke and Robert Brown
Answer: James Watson and Francis Crick
Watson and Crick built their double-helix model using X-ray diffraction images of DNA, including the famous work of Rosalind Franklin. Watson, Crick and Maurice Wilkins shared the 1962 Nobel Prize in Physiology or Medicine for this discovery.
4. How many chromosomes are there in a normal human body (somatic) cell?
- A. 23
- B. 44
- C. 46
- D. 48
Answer: 46
A normal human body cell has 46 chromosomes arranged in 23 pairs — 22 pairs of autosomes and one pair of sex chromosomes. Egg and sperm cells carry only 23 each, so fertilisation restores the full set of 46.
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5. Who is known as the 'Father of Genetics' for his experiments on pea plants?
- A. Charles Darwin
- B. Jean-Baptiste Lamarck
- C. Thomas Hunt Morgan
- D. Gregor Mendel
Answer: Gregor Mendel
Gregor Mendel, a friar in what is now the Czech Republic, crossed thousands of pea plants and in 1866 published the basic laws of inheritance — the laws of segregation and independent assortment. His work was largely ignored until it was rediscovered in 1900.
6. Which nitrogen base is found in RNA but not in DNA?
- A. Adenine
- B. Guanine
- C. Cytosine
- D. Uracil
Answer: Uracil
RNA uses uracil (U) in place of the thymine (T) found in DNA. In the DNA double helix, adenine always pairs with thymine and guanine always pairs with cytosine.
7. Which pair of sex chromosomes does a typical human male have?
- A. XX
- B. XY
- C. YY
- D. XO
Answer: XY
Females typically have two X chromosomes (XX), while males have one X and one Y (XY). Because every egg carries an X, whether a baby is a boy or a girl depends on whether the father's sperm carries an X or a Y chromosome.
8. Which type of cell division produces sperm and egg cells with half the usual number of chromosomes?
- A. Meiosis
- B. Mitosis
- C. Binary fission
- D. Budding
Answer: Meiosis
Meiosis halves the chromosome number and produces four genetically different cells from one parent cell. Mitosis, by contrast, produces two identical cells with the full chromosome number and is used for growth and repair.
9. Which cell organelle is nicknamed the 'suicide bag' of the cell?
- A. Golgi apparatus
- B. Endoplasmic reticulum
- C. Lysosome
- D. Vacuole
Answer: Lysosome
Lysosomes are packed with digestive enzymes that break down worn-out organelles, food particles and invading germs. If a lysosome bursts, its enzymes can digest the cell itself, which earned it the nickname 'suicide bag'.
10. The cell wall of plant cells is mainly made of which substance?
- A. Chitin
- B. Cellulose
- C. Starch
- D. Keratin
Answer: Cellulose
Plant cell walls are built mainly from cellulose, a tough carbohydrate made of long chains of glucose, which gives plants their shape and strength. Fungal cell walls, on the other hand, are made mainly of chitin — the same substance found in insect exoskeletons.