Select the related word that completes the analogy: AIDS is related to VIRUS in the same way as MALARIA is related to which of the following?

Introduction / Context:
This analogy is based on diseases and their causative agents. The pair AIDS : VIRUS indicates that AIDS is a disease caused by a virus, specifically the human immunodeficiency virus. The second part of the analogy asks for the type of organism responsible for causing malaria. Recognising which organisms cause which diseases is part of basic general science and biology knowledge frequently tested in aptitude and entrance examinations.

Given Data / Assumptions:
- AIDS is a disease caused by a virus.
- The word VIRUS in the pair describes the causative agent type, not the specific virus name.
- Malaria is another infectious disease transmitted by the bite of certain mosquitoes.
- The options list different groups of microscopic organisms: Protozoa, Bacteria, Fungi, and Algae.

Concept / Approach:
The relation is disease to causative agent. Therefore we must identify the organism group that causes malaria. Biology tells us that malaria is caused by parasites belonging to the genus Plasmodium. Plasmodium species are protozoan organisms, not bacteria, fungi, or algae. Thus the correct completion of the analogy is MALARIA : PROTOZOA. The other organism groups are associated with other types of infections or roles in ecosystems but not with malaria specifically.

Step-by-Step Solution:
Step 1: Interpret the given pair. AIDS is caused by a virus, so AIDS : VIRUS follows the pattern disease to causative agent type. Step 2: Recall that malaria is caused by Plasmodium parasites. Step 3: Classify Plasmodium. It belongs to the kingdom of protozoa, a group of single celled eukaryotic organisms. Step 4: Option A, Protozoa, matches this classification directly. Step 5: Option B, Bacteria, refers to prokaryotic organisms which cause other diseases like tuberculosis but not malaria. Step 6: Option C, Fungi, includes yeasts and moulds, responsible for fungal infections, and option D, Algae, mainly describe photosynthetic aquatic organisms. Step 7: Therefore MALARIA : PROTOZOA mirrors the pattern of AIDS : VIRUS.

Verification / Alternative check:
As a verification step, we can rewrite both pairs explicitly. AIDS is caused by a virus is accurate, and malaria is caused by protozoa is also accurate. Malaria is not caused by bacteria, fungi, or algae, so any attempt to substitute those groups produces a false statement. This confirms that the only correct choice is Protozoa. Many biology textbooks and exam syllabi highlight this specific cause, which supports the analogy.

Why Other Options Are Wrong:
Bacteria are important disease causing agents but are not responsible for malaria. Fungi cause conditions like ringworm and candidiasis. Algae can cause blooms in water bodies but are not considered parasites in the same sense. Hence, choosing any of these would misrepresent the well established medical fact about malaria. Since the analogy depends on correct scientific relationships, only Protozoa satisfies the requirement.

Common Pitfalls:
Some learners may confuse bacteria and protozoa because both are microscopic and associated with infectious diseases. Others might simply pick any organism that sounds familiar without recalling the specific disease agent. To avoid such mistakes, it helps to remember standard examples: AIDS virus for viral disease, Plasmodium protozoa for malaria, and tubercle bacillus for a bacterial disease. Mnemonics and repeated practice with such analogies can make these associations easier to recall in exams.

Final Answer:
Since malaria is caused by protozoan parasites, the correct completion of the analogy is MALARIA : PROTOZOA, and option A is correct.