Every eukaryotic cell has two major parts – nucleus and the cytoplasm with its organelles. The nucleus contains the genetic material of an organism. While the cytoplasm is the part of a cell outside of nucleus which contains:
1. organelles included in making proteins – ribosomes, Golgi apparatus, and endoplasmic reticulum
2. organelles included in storage, cleaning, and support – lysosomes, the cytoskeleton, vacuoles, and vesicles
3. organelles that receive and unload the energy – chloroplast, and mitochondria.

Proteins are synthesized in a translation process that occurs in the ribosomes. Ribosomes that are attached on the endoplasmic reticulum makes that part of this organelle granulated. Protein enters this organelle, where its structure may be altered. Ribosomes of the endoplasmic reticulum make proteins for the cell membrane or the ones that develop functions outside of the cell. Ribosomes that are free in the cytoplasm make proteins that remain inside the cell. Protein molecules come out of endoplasmic reticulum in a vesicle and go to the Golgi apparatus. They are altered, stored or prepared to be released from the cell in this very organelle.

Organelles included in storage, cleaning, and support are lysosomes, the cytoskeleton, vacuoles, and vesicles.
Vacuoles are larger membrane-enclosed organelles than vesicles. In vacuoles are stored water molecules, proteins, carbohydrates and salts. Vesicles are much smaller and contain molecules that are meant to be stored in a cell or transport them between different organelles, or to and from the cell membrane.
Lysosomes are organelles which contain enzymes and are included in the processes of decomposing lipids, carbohydrates, and proteins so their particles could be used by the cell. They also remove the waste from the cell.
The cytoskeleton contains protein fibers that make the form of the eukaryotic cells and they help in their motion.

Plant cells contain chloroplasts which receive solar energy and changes it into food. These molecules next enter the mitochondria in which they are transformed into chemical energy, that can be easily used in all the cellular processes. Therefore, plant cells must contain both of these organelles in order to transform solar into chemical energy.

The cell membrane separates the cell from the outer environment. It has a function in protection and passing molecules in and out of the cell. The cell membrane is semipermeable, which means that some molecules can move through it, while others can’t. Molecules that can’t cross the cell membrane are usually large or strongly charged.
The structure of a cell membrane allows it to be semipermeable. It is composed of the lipid bilayer with protein molecules in it, while carbohydrates are attached to its surface.

Chloroplasts and mitochondria are the only cell organelles that contain their own DNA molecules, which are found to be inherited from a mother. Based on the presence of DNA, a scientist Lynn Margulis suggests that these organelles were once independent prokaryotic organisms.
The endosymbiotic theory states that ancient bacteria and photosynthetic cyanobacteria merged with the early eukaryotic cells and formed a symbiosis.