In the symbiotic relationship that forms a lichen, how do the fungal and algal (or cyanobacterial) partners primarily benefit each other?

• A. The alga provides nitrogen fixation for the fungus, while the fungus provides oxygen for the alga through respiration.
• B. The fungus provides protection and absorbs water/minerals, while the alga (or cyanobacterium) provides carbohydrates via photosynthesis.
• C. The fungus performs photosynthesis to feed the alga, while the alga provides structural support and retains moisture.
• D. Both partners benefit mainly by exchanging antibiotics that kill competing microbes.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the nature of the symbiotic relationship in lichens, which is a mutualistic association between a fungal partner (mycobiont) and a photosynthetic partner (photobiont), which can be an alga or cyanobacterium.
2. Step 2: Identify the role of the fungal partner: it primarily provides protection to the photobiont by forming the structure of the lichen, shielding it from environmental stress, and absorbing water and minerals from the environment.
3. Step 3: Identify the role of the algal or cyanobacterial partner: it performs photosynthesis to produce carbohydrates (sugars) that serve as nutrients for both partners.
4. Step 4: Recognize that nitrogen fixation is a function specific to some cyanobacteria but is not a universal benefit provided by the alga to the fungus in all lichens, and that the fungus does not perform photosynthesis or provide oxygen.
5. Step 5: Conclude that the primary mutual benefits are the fungus providing protection and resource absorption, while the alga or cyanobacterium provides carbohydrates through photosynthesis.