Exercises: Types of cells: prokaryotic and eukaryotic

All cells, whatever their type, share three basic components. State them and explain the function of each one.

In the diagram of an animal eukaryotic cell, number 1 points to a large, spherical structure located in the central area, while number 2 points to an oval organelle with internal folds or cristae. State which number points to the nucleus and which number points to a mitochondrion, and explain the function of both structures.

Explain the fundamental difference between a prokaryotic cell and a eukaryotic cell, and give an example of a living thing with each cell type.

In a plant cell, state the function of the cell wall, a chloroplast, and the central vacuole, and explain why these three structures are not found in an animal cell.

Draw up a comparative table of animal and plant cells with these rows: cell wall, chloroplasts, vacuoles, and typical cell shape.

Where is the genetic material (DNA) found in a eukaryotic cell and in a prokaryotic cell? What consequences does this difference have on the internal organisation of each cell type?

In a laboratory, three unlabelled cell samples (A, B, and C) from three different tissues have been mixed up: the wing muscle of a sparrow, the white petal of a daisy, and a green spinach leaf.

When observed under a microscope, these characteristics are recorded:

• Sample A: elongated cells, with very high energy consumption, lacking cell walls and chloroplasts, and packed with mitochondria.

• Sample B: cells with a rigid cell wall, a large central vacuole, and hundreds of chloroplasts.

• Sample C: plant cells with developed walls and vacuoles, but lacking a single chloroplast and with scarce mitochondria.

1. a) Reasonably identify which tissue and living being each sample belongs to, justifying your decision based on the presence, absence, and abundance of each organelle.
2. b) Predict what would happen to the cells of sample B if the plant were kept in a dark room for three weeks: would they be able to continue producing glucose? Would their mitochondria immediately stop functioning? Justify your answer.

A bacterium is about $2\ \mu\text{m}$ long and an animal cell is about $20\ \mu\text{m}$ in diameter. Calculate how many bacteria in a row would fit across the diameter of an animal cell. Assuming that both were spherical, also calculate the surface area of each cell's membrane using the formula $S = 4\pi r^2$ and work out how many times larger the animal cell's membrane surface area is. Use both results to explain why eukaryotic cells can afford to be much larger and what problem size poses when exchanging substances with their surroundings.

Unlike humans (whose mature red blood cells lose their nucleus), amphibians and birds have red blood cells that retain their nucleus throughout their lives.

1. a) When comparing two red blood cells of the same volume, one human and one from a frog, the human red blood cell is able to hold a significantly larger amount of hemoglobin (the oxygen-carrying protein). Justify what causes this functional advantage at the cellular level.
2. b) In a laboratory experiment, both types of red blood cells are exposed to a substance that slowly damages the proteins in their cell membrane. The frog red blood cells manage to synthesize new proteins to repair the membrane and survive, while the human ones cannot repair themselves and die after a few days without being able to divide. Explain the biological cause of this fact by relating the function of the nucleus and DNA to the capacity for cellular self-repair and reproduction.