Page 108 - Biology Form Two

Biology for Secondary Schools

contraction. When muscles of the right Pressure builds up in the left ventricle
ventricle relax, the ventricle is filled up as blood flows in. The muscles of the
with blood. The tricuspid valve closes left ventricle contract, pumping blood
to prevent blood from flowing back through the semilunar valve into the
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into the right auricle. aorta. The aorta branches into smaller
arteries that transport blood to all parts
The right ventricle pumps deoxygenated of the body.

blood to the lungs through the
pulmonary artery. When the right The heart beats in such a way that when
ventricle is full, the increased pressure the auricles contract, the ventricles
causes the muscles to contract, and relax and vice versa. Usually an adult

the semilunar valve in the pulmonary heart beats about 60 to 80 times per
artery to open. Blood flows into the minute. A baby’s heart beats faster than
pulmonary artery, and the semilunar the adult heart, about 70 to 190 beats
valve closes to prevent back flow of per minute because babies have higher

blood. The pulmonary artery transports metabolic rates than adults.
deoxygenated blood to the lungs. Blood Exercise 5.1
picks up oxygen in the lungs, and thus
becomes oxygenated. 1. There would be no life for a
mammal without the heart.
The oxygenated blood flows from the Explain.
lungs to the heart through the pulmonary 2. What distinguishes the bicuspid

vein. This vein is connected to the left valve from other heart valves?
auricle. When the left auricle relaxes, 3. Differentiate between the
blood from the pulmonary vein flows pulmonary artery and pulmonary

into it. Pressure increases in the left vein.
auricle as it fills up with blood which 4. What would happen if the aorta
causes the muscles of the auricle to were blocked?
contract and pump blood through the
bicuspid valve into the left ventricle. Adaptation of the heart to its

The muscles of the left ventricle functions
The heart has several features that
relax, allowing blood to flow in. The enable it to function well. Table 5.1
bicuspid valve closes to prevent blood shows how the heart is adapted to its

from flowing back into the left auricle. functions.

102 Student’s Book - Form Two

05/10/2024 15:36:37
BIOLOGY FORM 2 NEW.indd 102
BIOLOGY FORM 2 NEW.indd 102 05/10/2024 15:36:37