The nucleus consists of a small spherical mass of denser protoplasm, the nucleoplasm, surrounded by a membrane called the nuclear envelope. It is found in the cytoplasm of the cell and controls the normal cell activities. Within the nucleus are the following:

• A network of long thread-like materials known as the chromatin which contains hereditary materials. These materials control the activities of the cell. During cell division the chromatin threads condense and become highly coiled structures called chromosomes. Each chromatin thread is made up of proteins and a compound called deoxyribonucleic acid or DNA. In the DNA, the hereditary information is stored.

• Spherical structures called nucleoli. Each nucleolus plays a part in the building up of proteins.

• The nuclear envelope which separates the nucleus from the cytoplasm.

Cytoplasm

Cytoplasm is the part that surrounds the nucleus. It forms the larger part of the human cell. In the cytoplasm we can find:

• Mitochondria which are responsible for releasing energy during respiration. The energy released is used for vital activities of the body.
• Vacuoles which contain water and food substances.
• Controls which play a part in cell division.

Cell surface membrane (Plasma membrane)