In the human body, blood flows through a process of double circulation. Which one of the following statements is true in this regard?
- A.Oxygenated blood reaches the left side of the heart from the lungs.
- B.Blood in the left side of the heart is poor in oxygen and is brought to the right side of the heart.
- C.Deoxygenated blood from the left side of the heart is brought to the lungs for oxygenation.
- D.Oxygenated blood from the right side of the heart is sent around the body.
Correct answer
Explanation
The correct answer is A, oxygenated blood reaches the left side of the heart from the lungs. The pulmonary veins carry oxygen-rich blood from the lungs into the left atrium.
In double circulation, blood passes through the heart twice in each full round. In the pulmonary circuit, the right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs, where it picks up oxygen; the pulmonary veins then return it to the left atrium. In the systemic circuit, the left ventricle pumps this oxygenated blood through the aorta to the whole body, and deoxygenated blood comes back through the venae cavae to the right atrium. The right side of the heart therefore always holds deoxygenated blood and the left side oxygenated blood, and the septum keeps them apart.
B is wrong: blood in the left side is rich in oxygen, and it goes to the body, not to the right side.
C is wrong: deoxygenated blood goes to the lungs from the right side.
D is wrong: oxygenated blood is sent to the body from the left side.
Exam tip: right side = deoxygenated, to lungs; left side = oxygenated, to body; pulmonary vein carries oxygenated blood.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →