Which one of the following classes demonstrates double circulation of blood?
- A.Invertebrates
- B.Fishes
- C.Amphibians
- D.Mammals
Correct answer
Explanation
The correct answer is D, Mammals. Mammals have a four-chambered heart, so blood passes through the heart twice in each round, once for the lungs and once for the body, without oxygenated and deoxygenated blood mixing.
In double circulation the right side of the heart sends blood to the lungs (pulmonary circulation) and the left side sends oxygen-rich blood to the rest of the body (systemic circulation). The complete wall between the left and right ventricles keeps the two streams apart, which gives warm-blooded mammals and birds the steady oxygen supply their high energy needs demand.
A is wrong because invertebrates have no such two-loop system, and many have an open circulation. B is wrong because fishes have a two-chambered heart and single circulation: blood goes from the heart to the gills and then straight to the body. C is wrong because amphibians have a three-chambered heart with one ventricle, where the two kinds of blood mix, so their double circulation is only incomplete.
Exam tip: Fish 2 chambers (single), amphibians 3 (incomplete double), birds and mammals 4 (complete double).
Practice Questions
View allConsider the following statements : 1. The circulation of nitrogen from the inorganic compounds in the soil to form protein in plants and animals and back again is known as the nitrogen cycle. 2. The preparation of ammonia by Haber process is an endothermic reaction. 3. Urea is synthetically made by the action of ammonia and carbon dioxide under high temperature and high pressure. Which of the statements given above is/are not correct?
- A.1 and 3
- B.2 and 3
- C.2 only
- D.1 only
Show answer
The Haber process is exothermic, not endothermic: nitrogen and hydrogen combine to form ammonia and release heat. In the Haber process, N2 + 3H2 ⇌ 2NH3 gives out about 92 kJ for every two moles of ammonia formed.
Read the full explanation →Which one of the following statements about xylem vessels in plants is not correct?
- A.Xylem vessels have lignified cell walls.
- B.Phloem sieve tubes are identical to xylem vessels in structure.
- C.Dead xylem vessels provide structural support to plants.
- D.Water is transported through xylem vessels.
Show answer
Phloem sieve tubes are not like xylem vessels: sieve tubes are living cells with thin walls and sieve plates, while mature xylem vessels are dead, hollow tubes with thick lignified walls.
Read the full explanation →Which one of the following effects best explains the high partial pressure of carbon dioxide causing haemoglobin to release oxygen in actively respiring tissues?
- A.Haldane effect
- B.Allee effect
- C.Bohr effect
- D.Eagle effect
Show answer
The Bohr effect is the fall in haemoglobin's affinity for oxygen when carbon dioxide and acidity rise, so oxygen is unloaded where tissues need it most.
Read the full explanation →Which one of the following statements about arteries is not correct?
- A.The inner lining is made of squamous endothelium.
- B.The middle layer is made of smooth muscle and elastic fibres.
- C.The outer layer is made of fibrous connective tissue with collagen fibres.
- D.Arteries have the thinnest walls amongst any other blood vessels.
Show answer
Arteries have the thickest walls of all blood vessels, not the thinnest, because they carry blood away from the heart under high pressure.
Read the full explanation →Which one of the following is not an exothermic reaction?
- A.Dissolution of calcium oxide in water
- B.Decomposition of vegetable matter into compost
- C.Decomposition of lead nitrate
- D.Dilution of sodium hydroxide with water
Show answer
Lead nitrate breaks down only when it is heated strongly, so the reaction absorbs heat and is endothermic. On heating, lead nitrate gives lead oxide, brown fumes of nitrogen dioxide and oxygen: 2Pb(NO3)2 → 2PbO + 4NO2 + O2.
Read the full explanation →