Answer:
The answer is A.
Explanation:
The permeability of the pacemaker cell's membrane is the factor that controls the density of the materials inside the cell which also includes sodium and that controls the neurons and muscles. So if we were able to artificially alter the pacemaker cell's membrane parmeability, for the heart it would result in a quicker satisfaction of the threshold value and therefore would increase the heart rate.
I hope this answer helps.
Well , the humans have a closed double circulatory system as the blood passes by the heart twice per one cycle and doesn't leave the blood vessels like in insects.
》Pulmonary circulation : Blood is circulated to the lungs where it is oxygenated.
》Systemic circulation : Blood is circulated through all the other parts of the body where it unloads oxygen.
Oxygenated blood coming from the lungs enters the heart through the pulmonary vein which takes blood to the first chamber it meets ; the Left atrium. Left atrium pumps blood to the second chamber , which is left ventricle and during this time , the semi lunar valves are closed to prevent back flow of blood and the bicuspid valve will be open . Now , the left ventricle is filled with oxygenated blood so it will pump this blood to the whole body via the largest artery which is Aorta.
Oxygenated blood will unload oxygen to cells in need of it and will return back now to the heart as deoxygenated . This deoxygenated blood will enter the heart through superior and inferior vena cava which will take the blood to the third chamber , right atrium . Right atrium will pump blood to right ventricle so the semi lunar valves will be closed during this time and the tricuspid will remain open. Now that the fourth chamber is filled with deoxygenated blood , it will pump this blood through pulmonary artery when the semi lunar valves opens , to the lungs again to be oxygenated once more.
Notice that you have to know exactly the position of the valves that I have mentioned in the heart so that you could understand the blood flow better. You can refer to any heart labelled diagrams in your textbook or the internet.
Photosynthieis sry if spelled wrong
Cyanobacteria are primitive organisms where chloroplasts are believed to be originated. These phototrophic organisms benefit the environmental and the clinical aspects because of their unique physiology. For instance, they contribute to energy attainment from sunlight which helps other organisms gain energy when this is consumed. Another is the contribution to biogeochemical cycles. And lastly, how these can aid in many medical discoveries and treatments.
