Animal and plant cells: a nucleus

The idea

The nucleus is the membrane-bound organelle found in eukaryotic cells such as animal and plant cells. It contains the cell's genetic material, mainly DNA arranged into chromosomes, and controls the cell's activities by regulating which proteins are made. In an animal cell the nucleus is usually a rounded structure near the centre, while in a plant cell it is often pushed to one side by the large permanent vacuole. A useful method is to picture a cell as a factory: the nucleus is the control room holding the master instructions.

What earns the marks

• States that the nucleus contains the genetic material of the cell, which is DNA arranged into chromosomes.
• Explains that the nucleus controls the cell's activities by controlling the production of proteins.
• Identifies the nucleus as a membrane-bound organelle present in animal and plant cells but absent from prokaryotic cells such as bacteria.
• Recognises the nucleus on a labelled diagram or microscope image of an animal or plant cell.
• Links the nucleus to cell division and the passing of genetic information to daughter cells.

Common mistakes and how to put them right

• Saying the nucleus 'makes' proteins.

  Put it right: The nucleus controls protein production, while ribosomes assemble the proteins.

• Describing the nucleus as present in all cells.

  Put it right: Bacteria have no nucleus and hold their DNA free in the cytoplasm.

• Calling the nucleus the 'brain' of the cell without qualification.

  Put it right: State precisely that it contains DNA and regulates cell activities.

Exam tips

• Use the phrase 'contains genetic material' rather than 'has DNA' alone, because it shows understanding of chromosomes and inheritance.
• When labelling a diagram, draw the label line clearly to the nucleus and write the function as well as the name if the question asks for both.
• In longer answers, link the nucleus to a named process such as protein synthesis or cell division to gain credit for explanation rather than simple recall.