Immunity

1. Phagocyte recognises the antigens on a pathogen

2. The cytoplasm of the phagocyte moves around the pathogen- engulfing it in a phagocytic vacuole.

3. A lysosome, that contains lysosomal enzymes, fuses with the vacuole and the enzymes break down the pathogen.

4. The phagocyte then presents the antigens from the pathogen to activate other immune system cells.

Nucleus

• The nuclear envelope - double membrane surrounding the nucleus, controlling the entry and exit of materials in the nucleus, often with ribosomes on the surface
• Nuclear pores - allow the passage of large molecules, such as messenger RNA, out of the nucleus. 
• Nucleoplasm - granular, jelly-like material that makes up most of the nucleus
• Chromatin - DNA found within the nucleoplasm
• Nucleolus - Small spherical body within the nucleoplasm

Functions:

• act as the control centre of the cell through the production of mRNA and protein synthesis
• retain the genetic material of the cell in the form of DNA or chromosomes
• manufacture ribosomal RNA and ribosomes

• Double membrane - surrounds the organelle, the outer one controlling entry and exit of material, the inner one folding to from extensions called cristae
• Cristae - shelf-like extensions of the inner memebrane, providing a large surface area for the attachment of enzymes involved in respiration
• Matrix - makes up the remainder of the mitochondrion. It is a semi-rigid material containing protein, lipids and traces of DNA that allow the mitochondria to control the production of its own proteins.

Functions;

Mitochondria are the sites of certain stages of respiration. They are responsible for the production of ATP (energy carrier molecule) from carbohydrates.

The number and size of the mitochondria and the number of cristae in them increases in cells that have a high level of metabolic activity, and need a plentiful supply of ATP.

RER;

• Provide a large surface area for the synthesis of proteins and glycoproteins
• Provide a pathway for the transport of materials, expecially proteins, throughout a cell

SER;

• Synthesise, store and transport lipids
• Synthesise, store and transport carbohydrates

Similar to the SER but more compact. It is made of a small stack of membranes that make up flattened sacs, or cisternae, with small rounded hollow structures called vesicles. The proteins and lipids produced by the ER are passed through the Golgi apparatus. The Golgi modifies these proteins, often adding non-protein components, such as carbohydrate, to them. It also 'labels' them, allowing them to be accurately sorted and sent to their correct destinations.

Functions;

• add carbohydrate to form glycoproteins
• produce secretory enzymes, such as those secreted by the pancreas
• secrete carbohydrates, such as those used to make cell walls in plants
• transport, modify and store lipids
• form lysosomes

The Golgi body is especially well developed in secretory cells, such as the epithelial cells that line the intestines.

Formed when vesicles from the Golgi body contain enzymes like proteases and lipases. Lysosomes isolate potentially harmful enzymes from the rest of the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell.  

Functions;

• break down material ingested by phagocytic cells, such as white blood cells
• release enzymes to the outside of the cell in order to destroy material around the cell
• digest worn out organelles so that the useful chemicals they are made of can be re-used
• completely break down cells after they have died

They are especially abundant in secretory cells, such as epithelial cells, and in phagocytic cells.

Small cytoplasmic granules found in all cells. May occur in cytoplasm or be associated with the RER. There are two types;

• 80S - found in eukaryotic cells, around 25nm in diameter
• 70S - found in prokaryotic cells, slightly smaller

Two subunits - one large, one small

Both contain ribosomal RNA and protein.

Occur in vast numbers and account for 25 per cent of the dry mass of a cell.

Ribosomes are important in protein synthesis. 

Finger-like projections of the epithelial cell that increase its surface area to allow more efficient absorption.