The major limiting factors of productivity in the aquatic habitat include the following except?

1. Analyze the question We're asked which option is NOT a major limiting factor of productivity in an aquatic habitat. A limiting factor is something whose shortage restricts how much living matter (biomass) a habitat can produce.

2. Explain the concept Productivity in water is mainly primary productivity, which is photosynthesis by phytoplankton and aquatic plants. What limits it:

• Sunlight: light penetrates only to a limited depth, so photosynthesis happens mostly in the upper (photic) zone.
• Temperature: it affects the rate of enzyme activity, photosynthesis, and the amount of dissolved oxygen.
• Nutrients/food: dissolved minerals such as nitrates and phosphates, and the food available to consumers, restrict how much can grow.
• Dissolved oxygen and carbon dioxide are also important.

3. Work through the options

• A. Food: limits populations and productivity, so it is a limiting factor.
• B. Temperature: affects metabolic rates and oxygen solubility, so it is a limiting factor.
• C. Water: the habitat is water, so it is always present in abundance. It cannot be a limiting factor in an aquatic habitat. (It is a limiting factor in terrestrial/desert habitats, not here.)
• D. Sunlight: limits photosynthesis with depth and turbidity, so it is a limiting factor.

4. Answer The exception is C. Water.

5. Exam tip In "except" questions, ask yourself whether the item is truly scarce in that habitat. Water in an aquatic habitat is like air in a terrestrial one: it's the medium itself, so it never runs short. Remember: aquatic = light, temperature, nutrients, oxygen; terrestrial = water too.