A eukaryote is an organism belonging to the eukaryota taxonomical group, and includes organisms such as animals, plants and fungi; these organisms contain eukaryotic cells with specialised and complex membrane-bound organelles. Eukaryotic cells are also larger and more complex than prokaryotic cells, so have a greater potential and diversity than prokaryotic cells. Some organelles within a eukaryotic cell, such as mitochondria and chloroplasts, are thought to be ancestors of prokaryotes, which once had a symbiotic relationship with the cell, but evolved over time to become integrated within the eukaryotic cell. Eukaryotes are more recent among life than prokaryotes - prokaryotes are thought to have evolved between 3.4 to 2.7 billion years ago, whereas the earliest eukaryote fossils 2.1 billion years ago, from red algae 
Most eukaryotic cells contain:
Nucleus - which contains DNA and controls the synthesis of proteins. The nucleus contains a nucleolus, which is a dense body where ribosomes are made. The nucleus is surrounded by a double membrane, known as the nuclear envelope, with nuclear pores.
Mitochondria - this is the site of aerobic respiration within the cell. They are surrounded by a double membrane (envelope), with the inner membrane folded into finger-like projections called cristae. The central area within the mitochondria contains a jelly-like substance known as the matrix, which contains ribosomes and DNA (as a loop).
rough endoplasmic reticulum - a series of single, flattened sacs enclosed by a membrane, with ribosomes on the surface - this organelle transports proteins to the golgi apparatus/other parts of the cell.
Golgi apparatus - a series of single, curved sacs enclosed by membrane (each sac is smaller than the previous one) and surrounded by vesicles. This organelle modifies and packages proteins in vesicle for transport around the cell or out of the cell.
Lysosomes - vesicle-like structures enclosed by a single membrane, containing digestive enzymes for the breakdown of unwanted structures within the cell.
Ribosomes - the site of protein synthesis (translation)
Eukaryotic cells also contain a cytoskeleton, which holds the cell organelles in place, and cytosol, which is a fluid that surrounds the organelles.