Nucleus

In the syllabus and the exam

The nucleus is central to at least two chapters of the syllabus: cell structure, where it is described as the organelle that controls the cell's activities, and cell division and genetics, where it is described as the store of chromosomes carrying the cell's DNA. Paper 1 commonly tests simple identification of the nucleus in a labelled diagram, while Paper 2 links it to more advanced ideas, such as explaining why a mature red blood cell, which loses its nucleus, cannot divide or make its own proteins, or why the nucleus is described as the 'control centre' of the cell. A frequent point of confusion is between the nucleus of a cell and the nucleus of an atom, a term used in Physics and Chemistry; in Biology answers, 'nucleus' always refers to the membrane-bound structure inside a eukaryotic cell unless the question specifies otherwise. Another common slip is describing the nucleus and the nucleolus as the same structure, when the nucleolus is in fact a smaller, denser region found inside the nucleus, responsible mainly for producing ribosomal components; candidates who blur this distinction in structured answers about organelle function often lose marks for imprecision. Candidates should also be ready to apply the term across kingdoms, correctly stating that plant, animal and fungal cells all have a nucleus, while bacterial cells do not, a comparison often folded into questions on classification and microorganisms. Electron micrographs used in Paper 3 sometimes show the nuclear envelope as a double membrane with visible pores, and candidates should recognise this detail as still referring to the same nucleus described in simpler light-microscope diagrams.

Example

When a cell is stained with a dye such as methylene blue, the nucleus appears as a dark, rounded structure near the centre of the cell, easily distinguished from the surrounding cytoplasm.

Related terms

ChromosomeOrganelleDeoxyribonucleic acid (DNA)

Source:SRC-DSKP-EN