Cell Structure and Function Questions and Answers

Answer: C

The organelles with their own DNA are A, B and C: plastids, mitochondria and the nucleus.

The nucleus holds most of the cell's DNA in its chromosomes. Mitochondria and plastids (such as chloroplasts) also have their own small, circular DNA and ribosomes and can make some of their own proteins, which is evidence that they descend from free-living bacteria.

The vacuole is a membrane-bound sac storing water, food and wastes; it has no DNA. So options naming D are wrong, and 'B and C' leaves out the plastids.

Answer: A

The only correct statement is D: all cells have a cell membrane.

The cell (plasma) membrane surrounds every cell, plant, animal or bacterial, and controls what enters and leaves it.

The others have exceptions. Not all cells are microscopic: a hen's or ostrich's egg is a single cell visible to the naked eye, and some nerve cells are very long. Animal cells have no cell wall. Bacteria and blue-green algae are prokaryotes and have no nuclear membrane. So 'A and D', 'B and C' and 'Only A' are wrong.

Answer: C

The answer is Protein.

The analogy pairs each cell organelle with what it makes. Mitochondria, the powerhouses of the cell, produce ATP by cellular respiration. Ribosomes are the site of protein synthesis, where amino acids are joined according to the instructions in messenger RNA.

Carbohydrates are made in chloroplasts by photosynthesis, fats (lipids) are made mainly in the smooth endoplasmic reticulum, and vitamins are not synthesised in ribosomes.

Answer: A

Both (A) and (R) are true but (R) is not the correct explanation of (A).

The assertion is true: the nucleus is a distinct, usually spherical structure, typically near the centre of the cell. The reason is also true: the nucleus lies in the cytoplasm, the jelly-like substance between it and the cell membrane.

But being surrounded by cytoplasm is not why the structure is called the nucleus or why it is spherical and central. The two statements are separate facts, so (R) does not explain (A).

Answer: C

The statements that are not true are (iii) and (iv).

Blue-green algae (cyanobacteria) are prokaryotes: their cells have no membrane-bound nucleus, so (iii) is false. Eukaryotic cells are defined by a nucleus enclosed in a nuclear membrane, so (iv), which says they lack one, is also false.

Statements (i) and (ii) are true: eukaryotes include unicellular organisms such as Amoeba and yeast as well as multicellular plants and animals, and they have a well-organised nucleus. So options containing (i) or (ii), and 'Only (iv)', are wrong.

Answer: A

(A) and (R) are both correct and (R) is the correct explanation for (A).

Dried raisins have a high concentration of sugars inside their cells. In plain water, water moves into the cells by osmosis, from the region of higher water concentration to lower, so the raisins swell (A).

Osmosis needs a selectively permeable membrane that lets water through but holds back the dissolved sugars; plant cell membranes are such membranes (R). So R explains why water enters and A happens.

Answer: B

The true statement is that cells of a tissue have similar structure.

A tissue is a group of cells that are similar in structure and work together to perform a particular function, such as muscle tissue or nervous tissue.

The other statements are false. Cells come in many shapes: nerve cells are long and branched, muscle cells spindle-shaped, red blood cells disc-shaped. Cells vary in size even within one organism, from small red blood cells to very long nerve cells. And not all cells have a nucleus: bacteria have no true nucleus, and mature human red blood cells lose theirs.