Unmyelinated nervous system components make up grey matter, while myelinated axons make up white matter. The cerebral cortex on the surface of the brain contains unmyelinated neural tissue, namely the cell bodies of neurons in the central nervous system. This region is rich in connections. Below its surface lie many myelinated axon tracts to inner nuclei, the cerebellum, other areas of the cortex, and the spinal cord.    

Folds are present in the human brain due to the rapid evolution of brain-related tasks while the skull shape and size remained relatively constant; therefore, folds are present as modifications to limited surface-area-to-volume ratios in the skull cavity.

In the blind spot, there is a lack of photoreceptors as the optic nerve exits the optic disk. We normally overcome this automatically when our brains use the information of the surrounding visual field and "fills in" the blind spot. 

Bacteria, a prokaryote, has circular DNA, as do mitochondria and chloroplasts. This provides support for the Endosymbiotic Theory, which states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote).

Chloroplasts and mitochondria reproduce through fission, the same process through which bacteria reproduce. Eukaryotes reproduce through mitosis or meiosis, depending upon the type of cell.

The Endosymbiotic Theory states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). Mitochondria and chloroplasts have a double membrane (the inner membrane would have initially been the ingested prokaryote’s single membrane).

Prokaryotic cells, mitochondria, and chloroplasts have 70S ribosomes, whereas eukaryotic cells have 80S ribosomes. This provides support for the Endosymbiotic Theory, which states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote).

The Endosymbiotic Theory states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). The aerobic bacteria were initially free-living prokaryotes, before being ingested by anaerobic bacteria.

The Endosymbiotic Theory states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). This theory explains the origin of eukaryotic cells. Numerous lines of evidence exist, including that mitochondria and chloroplasts have their own circular DNA (prokaryotes also have circular DNA), mitochondria and chloroplasts have a double membrane (the inner membrane would have initially been the ingested prokaryote’s single membrane, and the outer membrane initially would have come from the cell that engulfed it), mitochondria and chloroplasts have 70S ribosomes (prokaryotes 70S have ribosomes, whereas eukaryotes have 80S ribosomes).

Endocrine signals are signals from distance cells that move using the bloodstream, paracrine signals are signals used to communicate between cells in close proximity, and autocrine signals are signals that are received by the same cell in which the signal originated. Paracrine signals are signal are short-lasting, whereas endocrine signals are long-lasting.