Organelle

In the syllabus and the exam

Organelles are examined mainly through structure-function matching: candidates need to link each named organelle to what it does and, for a growing number of higher-order questions, explain why an organelle's internal structure suits that function, such as the folded inner membrane (cristae) of the mitochondrion increasing surface area for aerobic respiration, or the stacked thylakoid membranes of the chloroplast increasing surface area for light absorption. Paper 1 often tests direct recall of an organelle's function from a diagram or an electron-microscope image, while Paper 2 may ask candidates to explain why a particular cell type (a liver cell, a muscle cell, a root hair cell) contains an unusually large number of a specific organelle, connecting organelle number to the cell's energy or protein demands. A common mistake is confusing similarly named organelles with different roles, especially the rough and smooth endoplasmic reticulum, or mixing up the nucleus (which stores genetic information) with the nucleolus (a structure inside the nucleus involved in producing ribosomes). Some candidates also incorrectly treat the cell membrane or cell wall as organelles; strictly, an organelle is a distinct internal structure with its own membrane or defined shape, so the cell membrane, which forms the cell's outer boundary, is not usually classified this way in SPM answers. Candidates preparing for Paper 3 should also be able to identify organelles from real electron-micrograph images, not only textbook line diagrams, since practical questions increasingly present photographic or magnified views that look less tidy than a labelled cartoon of a cell. Candidates should also remember that the number of a given organelle within a single cell can vary according to that cell's energy or functional demands, rather than staying fixed across every cell type in an organism's body.

Example

The mitochondrion, the chloroplast and the ribosome are all organelles, each carrying out one specific job that keeps the cell functioning.

Related terms

CellNucleus

Source:SRC-DSKP-EN