Structure and functions of organelles

The nucleus is bound by two membranes known as the nuclear envelope, which has perforations called nuclear pores. Chromatin within the nucleus condenses to form chromosomes during cell division. The nucleus controls all cellular activity. During mitosis, it also undergoes division so that cell replication may occur. It contains the DNA and produces RNA. Within the nucleus is the nucleolus, a body rich with ribosomal RNA. Its function is to produce ribosomes
Mitochondrion is an elongated structure with two membranes. The outer membrane is separated from the inner membrane by the intermembranal space. The inner membrane is also highly folded to form extensions known as cristae, which increase the surface area for respiratory processes to take place. On the cristae are stalked particles, which protrude into the matrix. The stalked particles allow the flow of protons back to the matrix of the mitochondrion, acting as the driving force to combine ADP with inorganic phosphate to form ATP.
The lysosome is a small spherical structure containing digestive enzymes. These enzymes enable it to undergo autophagy (digest cytoplasmic organelles and other membranes), exocytosis (release its enzymes out of the cell), and autolysis (self-destruction of the entire cell itself). They are only found in animal cells.
Ribosomes are composed of two subunits, and they assist in protein synthesis by forming polyribosomes along the mRNA.
Chloroplasts contain the enzymes necessary for the Calvin cycle in the stroma. They also contain chlorophyll and other pigments that are required for the light reactions on the thylakoid membrane (PS 1 and PS2). They also store photosynthetic products in the stroma(glyceraldehyde-3-phosphate is subsequently converted to starch grains).
Centrioles are the apparent organizers of the mitotic spindle, and they are only found in animal cells. They consist of a pair of cylindrical structure that are found in teh centrosome. Each centriole is composed of 9 groups of microtubules. Microtubules radiating from the centrioles form the spindle fibers during mitosis.