Specialized tissue on the wall between the atria. Electrical impulses pass from the pacemaker (SA node) through the _______ and the atrioventricular bundle (bundle of His) toward the ventricles.atrium (pl. atria)One of two upper chambers of the heart.capillary<span>Smallest blood vessel. Materials pass to and from the bloodstream through the thin walls. They have walls that are only one endothelial cell in thickness. This delicate, microscopic vessel carries nutrient-rich, oxygenated blood from the arteries and arterioles to the body cells. There, the nutrients are burned in the presence of oxygen (catabolism) to release energy.
At the same time, waste products such as carbon dioxide and water pass out of the cells and into these blood vessels. Waste-filled blood then flows back to the heart in small venues, which combine to form larger vessels called veins.</span>carbon dioxideGas (waste) released by body cells, transported via veins to the heart, and then to the lungs for exhalation.coronary arteriesBlood vessels that branch from the aorta and carry oxygen-rich blood to the heart muscle.deoxygenated bloodBlood that is oxygen-poor.diastole<span>Relaxation phase of the heartbeat.</span>
The answer for 21 I think is false
Answer: E. Polygenic
Explanation: The color of eyes and hair is due to quantity and accumulation of pigments such melanin. Melanin is synthesize by multiple enzymatic steps and every enzyme is codified by a different gene. That means polygenic inheritance, that several genes are implicated in determined the this trait and its difficult to trace since every gene has a sequence that can vary between families or human groups.
Absence of true roots stems and leaves
