The valve present between the left atrium and left ventricle is the Bicuspid valve (also known as Mitral valve). During ventricular contraction, the bicuspid valve prevents backward movement of the blood, i.e. from the left ventricle into the left atrium. 

There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart.

SA node is located in right upper corner of right atrium.
Electrical activity spreads through walls of atria and cause them to contract. This forces blood into ventricles.

The left atrium receives the oxygenated blood from the left and right pulmonary veins, which it pumps to the left ventricle (through the mitral valve) for pumping out through the aorta for systemic circulation.

The duration of the cardiac cycle is reciprocal of heart rate. Assuming a heart rate of 75 beats per minute, each cycle takes 0.8sec.

Atrial diastole is characterized by the relaxation of the atrial muscles. During this stage, the blood enters into the atria, as the volume of the blood in the atria increases the pressure within it decreases.
So, the correct answer is option D.

An adult human has been estimated to have some 60,000 miles (96,560 km) of capillaries with a total surface area of some 8001000 m2. The total volume of this system is roughly 5 liters, the same as the total volume of blood.

P wave in ECG deflection represents atrial depolarization. Atrial repolarization occurs during ventricular depolarization and is obscured. QRS wave: ECG deflection representing ventricular depolarization. T wave: ECG deflection representing ventricular repolarization.

Haemolymph is present in cockroach....

Blood pressure is the measurement of the pressure of the blood in the artery. Blood pressure peaks when the heart muscle contracts and pumps blood, a cycle called systole. It falls when the heart relaxes and refills with blood, a cycle called diastole. Systole is the top number and diastole is the bottom number. An optimal blood pressure level is a reading under 120/80 mmHg. Readings over 120/80mmHg and up to 139/89mmHg are in the normal to high range.

The right atrioventricular valve is also known as the tricuspid valve, since it has three cusps, or flaps, that open and closes. When this valve is open, blood flows freely from the right atrium into the right ventricle. However, when the right ventricle begins to contract, the valve closes, so that blood cannot return to the right atrium; this ensures forward flow into the pulmonary artery.
So, the correct answer is option A.

The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, thereby controlling the sequence of muscle contraction that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemaker of the human body.

Insects, like all other arthropods, have an open circulatory system, whereby blood, (haemolymph), flows freely through the body cavity, (haemocoel). There is a dorsal vessel which is closed at the posterior end of the abdomen, and runs forward along the dorsal midline and opens in the head at the anterior portion. There are several chambers and openings known as ostia along the dorsal vessel where blood enters it through valves. The blood is then pumped forward to the aorta and into the body cavity. 

Therefore, the correct answer is option A.

The deoxygenated blood moves from the right ventricle to the lungs through the pulmonary artery. The oxygenated blood from lungs flows back to the left auricle through pulmonary vein. Then, by auricular contraction, oxygenated blood reaches the left ventricle.

Hemocytometer is a device used to count red blood cells.
Haemoglobinometer is an apparatus for measuring the amount of hemoglobin.
Sphygmomanometer is used to measure blood pressure.
Electrocardiogram is the recording of the electrical activity of the heart.
Thus, the correct answer is option (B), 'Haemocytometer'.