Asexual reproduction involves one parent creating offspring that are identical or very similar to the parent, without mating. Sexual reproduction requires two parents, each contributing specialized sex cells (sperm and eggs), which combine during fertilization to form genetically diverse offspring. Asexual reproduction produces clones with no genetic variation, while sexual reproduction generates offspring with unique combinations of traits from both parents. This difference in offspring diversity distinguishes these two modes of reproduction.

In the described setup:
– Test-tube A contains a snail, which produces carbon dioxide (CO₂) through respiration.
– Test-tube B has a water plant that utilizes CO₂ during photosynthesis to produce oxygen.
– Test-tube C contains both a snail and a water plant.

The test-tube with the highest concentration of CO₂ would likely be Test-tube A, where the snail is present.

Here’s the rationale:
– Test-tube A (Snail): The snail undergoes respiration, releasing carbon dioxide as a byproduct. In the absence of a photosynthesizing organism (like the water plant), the CO₂ released from the snail’s respiration accumulates in the water, leading to a higher concentration of carbon dioxide.

– Test-tube B (Water Plant): The water plant consumes CO₂ during photosynthesis and produces oxygen. While it may initially release some CO₂ during the absence of light (dark respiration), overall, the net production of oxygen might exceed the small amount of CO₂ produced.

– Test-tube C (Snail and Plant): Here, the water plant absorbs some of the carbon dioxide produced by the snail during respiration and uses it for photosynthesis. The net concentration of CO₂ might be lower compared to the test-tube with only the snail.

Therefore, the test-tube with the highest concentration of CO₂ is likely Test-tube A, where only the snail is present, as it continually releases CO₂ through its respiration process without any counterbalancing effect of photosynthesis.