Question

A small aquatic plant was put in each of the petri dishes – x, y & z containing different culture solutions. After six weeks the plant in dish X had the same number of leaves as it had previously & were all small and yellowish. Plant in dish Y had more leaves of normal size and dark green colour. Plant in dish Z had more leaves of normal size but very pale. Which of the following show the elements missing in culture
A. X/ magnesium, Y/ Phosphorus, Z/Nitrogen
B. X/ Phosphorus, Y/ magnesium, Z/Nitrogen
C. X/ Phosphorus, Y/ Nitrogen, Z/magnesium
D. X/ magnesium, Y/ Nitrogen, Z/ Phosphorus

Answer 1

Hint: X, Z dishes are showing some of the similar features of paleness and discoloration which is generally seen when plants produce less chlorophyll in their shoots which in turn makes their stem or leaves become yellowish and discoloured. This can be due to the chlorosis through which these plants went through.

Complete answer:
Yellowish features in the leaves of plants and their discoloration is a sign of chlorosis. Chlorosis is caused by the deficiency of the manganese or zinc. By this we have got the idea that there is deficiency of manganese and zinc which in turn gave us this result. Plants affected by chlorosis have little or almost no ability to synthesize/ manufacture carbohydrates through the process of photosynthesis and can even die due to lack of chlorophyll. In Y dish which has darker green colour of its leaf is a sign of phosphorus deficiency in the aquatic plant though they have normal size of leaves still they tend to appear darker than normal, and phosphorus deficiency has a sign which results in change in colour to darker pigment from green to purplish or red spots. Nitrogen also plays an important role in plant health whether aquatic or non-aquatic.

Hence the correct option is (A) X/ magnesium, Y/ Phosphorus, Z/Nitrogen.

Note: Nitrogen is absorbed by aquatic plants by many forms like urea, nitrate, ammonium etc. Deficiency of nitrogen can be noticed by seeing the size of leaves which is getting smaller and smaller or crippled growth. Magnesium plays an important role in photosynthesis which is an important factor in producing green colour pigment (chlorophyll) of the leaves, its deficiency can cause yellowish or discolouration of the plant.