Dissolved oxygen in streams is

The correct answer is Option A: Maximum at noon

Let's break down why:

* Dissolved Oxygen (DO): This refers to the amount of oxygen gas that is present in the water.

* Photosynthesis: Aquatic plants (like algae) and phytoplankton in streams perform photosynthesis. This process uses sunlight to convert carbon dioxide and water into glucose (food) and, importantly, oxygen. This oxygen is released into the water, increasing the DO.

* Sunlight and Photosynthesis: Photosynthesis is dependent on sunlight.

* Noon: Around noon, sunlight is typically at its strongest intensity.

* Therefore, maximum photosynthesis occurs around noon, leading to a maximum level of dissolved oxygen in the stream.

* Midnight: At midnight, there is no sunlight, so photosynthesis stops. Respiration by aquatic organisms (which *consumes* oxygen) continues. Therefore, DO is typically *lowest* at night.

* So, the dissolved oxygen is not the same throughout the day.