AIPMT 2007 question paper with solutions

1. Recall what a prothallus is.

A prothallus is the free-living gametophyte of vascular cryptogams (pteridophytes), which bears both antheridia (producing antherozoids) and archegonia (producing eggs).

2. Understand the significance of different maturation times.

When the antherozoids and eggs on the same prothallus mature at different times, it means the male and female gametes are not ready to fuse simultaneously within the same individual.

3. Determine the consequence of this timing difference.

Since the gametes are not available together, self-fertilisation (fusion of gametes from the same prothallus) is prevented, promoting cross-fertilisation with gametes from a different prothallus instead.

4. Eliminate the other options.

This timing difference does not cause sterility (option A), does not indicate apomixis (asexual seed formation without fertilisation, option B), and it does actually affect the fertilization dynamics rather than leaving it unchanged (option D).

Hence, the answer is Option C.

1. Evaluate Options A, C, and D: mycoplasma are indeed pleomorphic (variable in shape), cause diseases in both plants and animals, and are also known as Pleuro Pneumonia Like Organisms (PPLO) — all three statements are correct.

2. Evaluate Option B: recall that since mycoplasma completely lack a cell wall, and penicillin works specifically by inhibiting bacterial cell wall synthesis, penicillin has no target to act on in mycoplasma.

$$\text{Mycoplasma (no cell wall)} \rightarrow \text{Insensitive to penicillin (sensitive to tetracyclines instead)}$$

Hence, since this statement wrongly claims mycoplasma are sensitive to penicillin, the wrong statement is Option B.

1. Recall what hybrid vigour (heterosis) means.

Given that hybrid vigour refers to the phenomenon where a hybrid offspring shows superior characteristics compared to both of its parents, this effect is exploited commercially in crops like maize, sorghum, and bajra.

2. Recall how hybrid vigour is achieved.

Since this superiority becomes most apparent when two genetically distinct, inbred parental lines are crossed with each other, breeders first develop pure inbred lines and then cross them to produce vigorous hybrids.

3. Recall the typical breeding steps.

Given that this process involves selecting parents, self-pollinating them to create inbred lines, followed by controlled emasculation, bagging, and crossing between the desired inbred lines, and finally harvesting the hybrid seeds.

4. Rule out the other options.

Since bombarding seeds with DNA (gene gun technique) is used for genetic transformation, not for producing hybrid vigour, this does not match. Given that harvesting seeds from the most productive plants describes simple selection, not hybridisation between inbred lines, this is also incorrect. Since inducing mutations is a separate breeding technique (mutation breeding) unrelated to crossing inbred lines, this does not fit either.

5. Conclusion.

Since hybrid vigour in maize is specifically exploited by crossing two inbred parental lines, this matches option A.

Hence, the answer is option A.