Grade 10

Cell Structure and Function

The smallest thing that counts as alive, taken apart piece by piece and then followed through one working day inside it.

6 lessons

  1. 1What can a microscope show you, and what can it not?A light microscope can magnify almost without limit, but its resolution stops at about two hundred nanometres — roughly the wavelength of light. Past that, magnifying only blurs. Small organelles were therefore only discovered with the electron microscope, and cell theory was built exactly at the edge of what could be seen.30m
  2. 2How is the cell membrane built and what does it decide?The membrane is a double layer of phospholipids: the water-loving heads face outwards and inwards, the water-repelling tails hide in the middle. Proteins float within that layer and let through substances the fat alone would block. The result is a selective boundary — neither a wall nor an opening.35m
  3. 3What is the difference between diffusion, osmosis and active transport?Diffusion is movement from high concentration to low, happening by itself at no cost. Osmosis is the same thing for water across a selective membrane. Active transport pushes a substance against the concentration gradient, and so it costs energy. The distinction explains why a cell in salt water shrinks and in distilled water swells.35m
  4. 4What are the organelles and how do you infer function from structure?Each organelle is a room built for one job: the nucleus keeps the instructions, the ribosome builds proteins, the mitochondrion supplies energy, the endoplasmic reticulum and Golgi process and package. The job can usually be inferred from the structure — internal folding, for instance, always means a large surface area.40m
  5. 5What is the difference between a plant cell, an animal cell and a bacterium?A plant cell has three things an animal cell does not: a rigid cell wall, chloroplasts, and a large central vacuole. A bacterium differs from both far more deeply — it has no nucleus and no membrane-bound organelles, and its genetic material floats within the cell. None of these differences is arbitrary; each serves a way of living.30m
  6. 6How does a protein travel from the gene to outside the cell?The instruction is written in the nucleus and a copy leaves it, a ribosome on the rough endoplasmic reticulum builds the protein from that copy, the reticulum folds it, the Golgi finishes the processing and packages it into a vesicle, and the vesicle travels to the membrane and fuses with it — releasing the contents outside. Every organelle studied earlier appears here in order.40m