Background Information

Question:

How much acidity can an elodea plant tolerate before it dies, and how will the cellular structure of the plant change based on different underwater circumstances?

Background Information:

Elodea plants are herbaceous perennials that feature dark green leaves arranged in whorls of two to seven along the stem. Aquatic plants such as Elodea make adaptations when living submerged in water, or at the water's surface. The most common adaptation is the presence of lightweight internal packing cells and aerenchyma ("a soft plant tissue containing air spaces, found especially in many aquatic plants (Oxford Dictionary))".

 One of the ways the Elodea plant adapts to different underwater pressures is by having leaves that lie flat on the water for maximum sunlight collection. The Elodea plant floats above the water because air spaces in the stem and other parts of the plant keep them afloat by reducing the mass of the plant. The reason why plants such as the Elodea can survive underwater is because the waxy coating on the leaves’ surfaces prevents the leaves from decaying in the water. 

Submerged plants are able to adapt to underwater pressures and environments because, when the plants are submerged they become highly dissected or divided. This creates a very large surface area for photosynthesis and absorption; it also minimizes water resistance and potential damage to the leaves. 

Elodea plants are able to get carbon dioxide underwater because they have thin and edgy leaves that increase the flow of carbon dioxide. The leaves are surrounded by thin porous cuticles, through which carbon dioxide enters into the plant. When a plant cell is submerged in water, fluid will enter the cell via osmosis (" the movement of water across a semipermeable membrane("a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion (environment data)) (Future Learn).") until the osmotic potential ("The potential of water molecules to move from a hypotonic solution (more water, fewer solutes) to a hypertonic solution (less water, more solutes) across a semipermeable membrane (Biology Online).") is balanced by the cell wall's resistance to expansion. 

The plant will become rigid and submerged because of the water gained by osmosis. Turgor pressure ("Pressure exerted by fluid in a cell that presses the cell membrane against the cell wall (Britannica)") develops against the cell wall ( a rigid external layer made to provide structural support to the plant) after water enters the cells vacuole ( cell vacuoles are storage bubbles found within cells). If an Elodea plant is placed into basic water (no acidity) then the cells will swell up and the plant will become more rigid. Elodea plants take out the acidity from the water and produce oxygen.