Structure and Function of Animal Cells

A eukaryotic cell is defined as a cell that contains a membrane-bound nucleus and other membrane-bound organelles. This is the key feature that separates eukaryotes from prokaryotes.

The option stating that animal cells have a membrane-bound nucleus containing their DNA directly matches the definition of eukaryotic. This is the single most important distinguishing feature.

Cell walls are found in plant, fungal, and bacterial cells — not animal cells. Chloroplasts are only in plant cells. Animal cells do have many membrane-bound organelles, so the last option is also wrong.

The correct answer is that animal cells have a membrane-bound nucleus — this is the defining feature of all eukaryotic cells, including animal cells.

The question asks why animal cells are eukaryotic. We need to find the feature that defines a eukaryotic cell.

Animal cells do not have a cell wall — this is a feature of plant cells. This option is incorrect.

Animal cells do not have chloroplasts. Chloroplasts are only found in plant cells and some other photosynthetic organisms.

Animal cells actually do have many membrane-bound organelles (mitochondria, Golgi apparatus, lysosomes, etc.), so this option is factually wrong.

The remaining option — a membrane-bound nucleus containing their DNA — is the correct definition of a eukaryotic cell. This is what makes animal cells eukaryotic.

The white blood cell has engulfed a bacterium (a foreign invader). The question asks which organelle is responsible for destroying it inside the cell.

Lysosomes are membrane-bound organelles filled with powerful digestive enzymes. One of their specific roles is to destroy bacteria engulfed by white blood cells, breaking them down into harmless components.

The lysosome is the correct answer. It acts as the cell's recycling and waste disposal system, digesting foreign material such as bacteria.

We need the organelle that breaks down foreign material such as bacteria inside the cell.

Mitochondria carry out aerobic respiration to produce ATP. They do not contain digestive enzymes and play no role in destroying bacteria.

The Golgi apparatus modifies and packages proteins for secretion or internal use. It does not digest foreign material.

The smooth ER synthesises lipids and detoxifies substances like drugs and alcohol. It is not responsible for destroying engulfed bacteria.

Lysosomes contain digestive enzymes specifically used to break down waste materials and foreign invaders like bacteria. This is the correct answer.