Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
Correct answer
Explanation
The correct answer is A, Magnesium. The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
A chlorophyll molecule has a ring-shaped head, called a porphyrin ring, with a magnesium ion held at its centre by four nitrogen atoms, and a long tail that anchors it in the membranes of the chloroplast. This molecule absorbs red and blue light and reflects green, which is why leaves look green, and it captures the light energy used in photosynthesis. When a plant lacks magnesium, the older leaves turn yellow between the veins, a condition called chlorosis.
Option B is wrong because iron is needed to make chlorophyll but is not part of the molecule; iron sits at the centre of haemoglobin in blood. Option C is wrong because calcium is found in plant cell walls, as calcium pectate in the middle lamella. Option D is wrong because copper works in enzymes and in plastocyanin, not in chlorophyll.
Exam tip: Chlorophyll has magnesium, haemoglobin has iron, vitamin B12 has cobalt.
Practice Questions
View allBronze is an alloy of copper and
- A.nickel
- B.iron
- C.tin
- D.aluminium
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Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
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An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
Read the full explanation →Which one of the following cell organelles contains DNA?
- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
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Mitochondria carry their own small, circular DNA and their own ribosomes. Mitochondria are the powerhouses of the cell, where aerobic respiration makes ATP.
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