The nucleus is the control centre of the cell. It consists of three main parts.
Nuclear Envelope: The nuclear envelope surrounds the entire nucleus. Its purpose is to control the entry and exit of molecules into the cell and help the nucleus to maintain its shape. It is made of a double membrane that is perforated with tiny holes called nuclear pores. On the nucleus side of the envelope is a layer of protein that allows the nuclear envelope to help the nucleus retain its shape.
Chromatin (Chromosomes): The chromatin is a structure inside the nucleus that is made of DNA and proteins.
Together they make up the chromosomes of a cell. The chromosomes are coiled up tightly so that they can fit inside the nucleus. The chromosomes carry all of a cells genetic information.
Nucleolus: The nucleolus is a round structure found in the nucleus of a cell that isn’t dividing. They are involved in the production of ribosomes. When a cell is about to divide the nucleolus becomes disordered and reappears after cell division. The nucleolus is made of proteins and rDNA (ribosomal DNA).

Golgi bodies are found within the cytoplasm of a cell. They are a succession of flattened, diskshaped sacks. The sacks membrane-bound and are called cisternae. Their main function is to process and package the products of the Endoplasmic Reticulum such as proteins and lipids. It often prepares proteins for secretion.

Ribosomes are small structures that are made of proteins and rRNA (ribosomal RNA). They are manufactured inside the nucleolus to be distributed through the nuclear pores. Some ribosomes are free within the cytoplasm and others attach themselves to the Endoplasmic Reticulum (rough
ER). Their main purpose is to produce proteins.

Lysosomes are tough membranous sacks that are pinched off from the Golgi Body. They contain the digestive enzymes that are used to break down food inside the cell. Lysosomes are generally absent from plant cells.

The endoplasmic reticulum is a network of membranes that run through the cytoplasm. It acts as a transport system for the cell; various chemicals can be shipped to different parts of the cell. Also, many chemical reactions can take place on its surface and is involved in the synthesis of various compounds. There are two types of endoplasmic reticulum:
Smooth ER: Smooth ER is involved in the metabolism of lipids and carbohydrates. It also synthesizes hormones such as steroids. Smooth ER can also help store calcium in muscles and in some cells is involved in secretion. Liver cells’ smooth ER helps to detoxify poisons and drugs.
Rough ER: Rough ER gets its name from its rough appearance due to it being covered in ribosomes.
Rough ER is the site of protein and membrane synthesis. In white blood cells, rough ER creates antibodies.

Mitochondria are oval-shaped organelles that are bound by a double membrane. They convert energy into a form that the cell can use; ATP (adenosine triphosphate). Mitochondria are also the site of aerobic respiration and contain their own DNA or RNA, ribosomes and protein-making-machinery.

Microtubules are one of the three types of cytoskeleton fibers. They are the thickest of the three and run throughout the cell. They are hollow tubes made of globular proteins (tubulins) that form a spiral. Microtubules as well as the other types of cytoskeleton fibers (microfilaments and intermediate fibers) give support to the cell’s shape and are useful for movement.

The cytoplasm is a watery solution that fills a cell. The solution contains many enzymes such as, fatty acids, amino acids and sugars that keep the cell working. The cell’s organelles are suspended within the fluid.

The plasma membrane is a a semi-permeable covering that keeps the cell separate from the outside medium. Its main purpose is to control which substances enter and exit the cell. In plant cells, the plasma membrane is encased by the cell wall but in animal cells the plasma membrane is the only separation the cell has from the outside world.

Plastids are loosely defined as membrane-bound structures found only in plant cells. Plastids can change their function to suit the needs of the cell. There are many different types, three of them are listed below:
Leucoplasts: Leucoplasts are mainly used for starch, lipid and protein storage. However, leucoplasts are not always used for storage and are sometimes involved in the synthesis of fatty and amino acids. They are not pigmented like the chloroplasts so do not have the characteristic green colouring. They are generally found in parts of a plant that do not carry out photosynthesis such as the roots.
Chromoplasts: These plastids are involved in the synthesis and storage of the coloured pigments that give various parts of the plant colour, for example, the petals on a flower. Their colour is masked by the green of chloroplasts but in autumn, the chlorophyll in some plants break down and the orange/yellow colour of the leaves’ chromoplasts shows through.
Chloroplasts: Chloroplasts are oval organelles found in cells that perform photosynthesis. They are green in colour and give plant leaves their characteristic colour. Chloroplasts absorb light energy and with the use of water and carbon dioxide create glucose to feed the cell with.

Chromoplasts
Chloroplasts
Leucoplasts

Vacuoles are a sort of bag that is enclosed with membranes. They have no internal structure.
Animal Vacuoles:
• Used to engulf food and keep it until it is digested by the lysosomes
Plant Vacuoles:
• They are much larger than animal vacuoles
• Store various compounds
• They contain the digestive enzymes that are usually found in the lysosomes
• Store waste that could be potentially poisonous to the cell
• Contain pigments to colour flower petals and fruit
• Some store poisons as a protection against herbivores