C.

Ventral nerve cord

Ventral nerve chord is the characteristic of lower chordates like leech, cockroach and scorpion

D.

neurotransmitters are released by the axon endings and not by dendrites.

Neurotransmitters are molecules that fit like a lock and key into a specific receptor. The receptor is located on the next cell in the line. Therefore, nerve impulses cannot travel in the opposite direction, because nerve cells only have neurotransmitter storage vesicles going one way, and receptors in one place.

D.

3.1 billion.

Genome size is usually stated as the total number of base pairs; the human genome contains roughly 3 billion base pairs.

B.

SA node - pacemaker

The sinoatrial node (SA node), also known as sinus node, is a group of cells located in the wall of the right atrium of the heart. These cells have the ability to spontaneously produce an electrical impulse, that travels through the heart via the electrical conduction system causing it to contract. In a healthy heart, the SA node continuously produces action potential, setting the rhythm of the heart and so is known as the heart's natural pacemaker.

B.

Photosynthetic bacteria

Anoxygenic photosynthetic bacteria consume carbon dioxide but do not release oxygen. These include Green and Purple bacteria as well as Filamentous Anoxygenic Phototrophs (FAPs), Phototrophic Acidobacteria, and Phototrophic Heliobacteria.

Instead of using water to photosynthesize, like plants and cyanobacteria, purple sulfur bacteria use hydrogen sulfide as their reducing agent, which is why they give off sulfur rather than oxygen.