NEET 2018 question paper with solutions

1. Recall the unique nuclear feature found in ciliates, such as Paramoecium, that is not seen in other protozoan groups.

$$\text{Ciliates} \rightarrow \text{Macronucleus + Micronucleus}$$

2. Note that a macronucleus controls the metabolic (vegetative) functions of the cell, while a micronucleus is involved in genetic exchange during conjugation — this dual-nucleus condition is exclusive to ciliates among protozoans.

3. Rule out the other options: contractile vacuoles are common in many protozoans (not unique to ciliates), flagella are used by flagellates (not ciliates), and pseudopodia are used by amoeboid protozoans.

Hence, the correct answer is Option B, having two types of nuclei.

1. Recall the standard components of an operon.

Given that an operon is a prokaryotic gene regulation unit, it typically consists of a promoter, an operator, and structural genes.

2. Identify what is not part of this structure.

Since an enhancer is a regulatory DNA element found in eukaryotes (not part of the prokaryotic operon system), it does not belong among the standard operon components.

Conclusion: Hence, the answer is C, an enhancer.

1. Recall the position of the endodermis: The endodermis is the innermost layer of the cortex, forming a boundary between the cortex and the vascular tissue (stele).

2. Recall the special feature of endodermal cells: The radial and transverse walls of endodermal cells have band-like thickenings made of suberin, a waterproof substance.

3. Name this feature: These suberin deposits are called Casparian strips, and they force water and dissolved minerals to pass through the cell membrane (not between cells), allowing the plant to regulate what enters the vascular tissue.

4. Eliminate the other options: The pericycle, epidermis, and cortex do not have this specific suberin banding.

Hence, Casparian strips occur in the endodermis, so the answer is C.