Q1.
Source: CSIR NET NOV 20; Session II
Following are certain statements regarding nitrogen uptake and assimilation by plants:
A. Plant roots can take up nitrogen in the form of NO3- or NH4+
B. NH4+ taken up by plants can be directly assimilated into amino acids
C. Amino acids are synthesised exclusively in plastids and chloroplast of roots and leaves respectively
D. NO3- can be stored in vacuoles of both, roots and leaves
Which one of the following combination is correct?
a. A,B, and C
b. B,C, and D
c. A,B, and D
d. A,C, and D
Statement Analysis
Plants absorb nitrogen primarily as nitrate (NO3-) and ammonium (NH4+), making statement A correct.
Ammonium can be rapidly incorporated into amino acids through the GS-GOGAT pathway, making statement B correct.
Plants can also store excess nitrate in the vacuoles of both roots and leaves, making statement D correct.
Statement C is incorrect because amino acid synthesis is not restricted exclusively to plastids and chloroplasts. Several steps occur in other cellular compartments as well.
Correct answer: c. A,B, and D
Q2.
Source: GATE, 2020
In a typical green plant, the first stable product of calvin cycle is:
a. Oxaloacetic acid
b. Succinic acid
c. Maleic acid
d. 3-phosphoglyceric acid
Statement Analysis
The first stable product of the Calvin cycle is 3-phosphoglyceric acid (3-PGA).
When carbon dioxide combines with RuBP (ribulose-1,5-bisphosphate), a 5-carbon molecule, an unstable 6-carbon intermediate is formed. This intermediate immediately splits into two molecules of 3-PGA.
Since the first stable product contains three carbon atoms, plants that use this pathway are known as C3 plants.
Correct Answer: d. 3-phosphoglyceric acid
Exam insights
Carbon count matters!
- RuBP = 5 carbon
- COâ‚‚ = 1 carbon
- Unstable intermediate = 6 carbons
- First stable product (3-PGA) = 3 carbons
Your Score?
How many did you get right this week?
2/2 – Plant Physiology Pro!
1/2 – Good attempt!
0/2 – Time for a quick revision!