compare the structure of a prokaryotic cell as found in a typical bacterium with the structures of typical eukaryotic cells in plants and animals

Objective

Compare the structure of a prokaryotic cell (typical bacterium) with the structures of typical eukaryotic cells in plants and animals.

Key Structural Features

Prokaryotic Cell (Bacterium)

• Size: 0.5–5 µm in diameter.
• No true nucleus – DNA forms a nucleoid region.
• Cell wall composed mainly of peptidoglycan.
• Plasma membrane underlying the cell wall.
• Ribosomes are 70 S (30 nm) and free in the cytoplasm.
• May possess external structures such as:

  • Flagella (for motility)
  • Pili or fimbriae (for attachment)

• No membrane‑bound organelles (e.g., mitochondria, chloroplasts, endoplasmic reticulum).

Eukaryotic Plant Cell

• Size: 10–100 µm in diameter.
• True nucleus enclosed by a double membrane (nuclear envelope) containing nucleolus.
• Cell wall composed of cellulose, hemicellulose and pectin.
• Plasma membrane just inside the cell wall.
• Membrane‑bound organelles:

  • Mitochondria (site of cellular respiration)
  • Chloroplasts (site of photosynthesis, contain thylakoid stacks)
  • Endoplasmic reticulum (rough and smooth)
  • Golgi apparatus
  • Vacuole (large central vacuole for storage and turgor)

• Ribosomes are 80 S (20–30 nm) and may be free or bound to rough ER.

Eukaryotic Animal Cell

• Size: 10–30 µm in diameter.
• True nucleus with nucleolus.
• No rigid cell wall; only a flexible plasma membrane.
• Membrane‑bound organelles similar to plant cells except:

  • Absence of chloroplasts.
  • Presence of centrosomes (microtubule‑organising centres) and often multiple small vacuoles.

• Ribosomes are 80 S, free or attached to rough ER.
• Often possess surface specialisations such as:

  • Cilia or flagella (e.g., sperm cells)
  • Microvilli (in intestinal epithelium)

Comparative Table

Functional Implications of Structural Differences

1. Compartmentalisation: Eukaryotic cells separate metabolic pathways into organelles, allowing greater regulation and efficiency.
2. Genetic control: The nucleus protects DNA and provides a site for transcription regulation, whereas prokaryotes rely on simultaneous transcription‑translation.
3. Energy acquisition: Chloroplasts give plant cells the unique ability to convert light energy into chemical energy, a feature absent in both animal cells and most bacteria.
4. Structural support: The rigid cell wall in plants and bacteria protects against osmotic stress; animal cells rely on the cytoskeleton and extracellular matrix.
5. Size limitation: Lack of internal membranes restricts prokaryotes to a smaller size, influencing surface‑area‑to‑volume ratios and diffusion rates.

Summary

Prokaryotic cells are simpler, lacking a nucleus and membrane‑bound organelles, and are typically smaller with a peptidoglycan cell wall. Eukaryotic plant and animal cells share many organelles and a true nucleus, but differ in the presence of a cellulose cell wall and chloroplasts in plants, and in specialised structures such as centrosomes and lysosomes in animals. These structural distinctions underpin the diverse metabolic capabilities and ecological roles of each cell type.