SSC CGL Biology · Cell Biology
Cell Structure and Organelles
The cell wall and membrane with the people who studied them, each organelle and its job, and how prokaryotic cells such as bacteria differ from eukaryotic ones.
Why this matters
Twenty-five questions in the bank: 12 from the 2023 shifts, nine from the 2024 shifts and four from the 2025 shifts. Most name an organelle and ask its job, or the reverse, so the organelle table answers the bulk of them.
Concept 1 of 3: Cell wall, membrane and early discoveries
Definition
The covers:
- The cell wall is found in plant cells only (among plants and animals) and is their outermost cover. It is made mainly of cellulose; pectin cements cells together in the middle lamella.
- The plasma membrane is a phospholipid bilayer with proteins in it. It is selectively permeable; water diffuses from higher to lower concentration.
Discoveries:
- Robert Hooke described cells in 1665.
- Anton van Leeuwenhoek saw living single-celled organisms in 1674.
- Gorter and Grendel (1925) spread red-cell lipids into a layer twice the cell's area and concluded the membrane is a bilayer.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 1 · Cell Biology · Cell Structure and Organelles
The nucleolus is not plant-only
Concept 2 of 3: Organelles and their jobs
Definition
The organelles:
- Ribosome: the protein factory; made of rRNA and protein, with no membrane.
- Mitochondrion: the powerhouse; makes ATP; folded inner membrane (cristae).
- Golgi apparatus: modifies and packages proteins; first seen by Camillo Golgi (1898).
- Lysosome: intracellular digestion; the suicidal bag.
- Peroxisome: oxidation reactions that make hydrogen peroxide.
- Smooth ER: lipid synthesis. The nucleus holds the DNA and controls the cell.
- Cytoskeleton: the protein network that supports every eukaryotic cell.
- Plastids: chloroplasts (green, with grana); leucoplasts are colourless: amyloplasts store starch, proteinoplasts protein, elaioplasts oils (found in the tapetum of pollen sacs).
Animal cells have ribosomes, mitochondria and lysosomes; fungi have no chloroplasts.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 2 · Cell Biology · Cell Structure and Organelles
Fungi have no chloroplasts
Concept 3 of 3: Prokaryotic cells
Definition
Prokaryotes:
- Bacteria and blue-green algae; kingdom Monera in Whittaker's five kingdoms.
- No nuclear membrane and no mitochondria. Yeast, algae, fungi, Plasmodium and Leishmania are all eukaryotes.
- The bacterial glycocalyx is a loose slime layer or a thick, tough capsule.
- PPLO (mycoplasma) are the smallest living cells, about 0.1 micrometre. A bacterium is 3 to 5 micrometres, a typical eukaryotic cell 10 to 20.
Practise this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 3 · Cell Biology · Cell Structure and Organelles
Slime layer loose, capsule thick
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (3)
Watch out for (3)
- The nucleolus is not plant-only→ Cell wall, membrane and early discoveries
- Fungi have no chloroplasts→ Organelles and their jobs
- Slime layer loose, capsule thick→ Prokaryotic cells
Test yourself on Cell Biology
15 past SSC CGL questions from this chapter, timed at 9 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.