Importance of Water & Inorganic Ions to Plants

Photosynthesis: Water is a direct reactant in the light-dependent stage of photosynthesis, providing electrons and hydrogen ions necessary to produce glucose.

Turgidity and Support: Water fills the central vacuole, exerting turgor pressure against the cell wall. This pressure keeps the plant upright and prevents wilting by providing mechanical support to non-woody tissues.

Transport Medium: Water serves as the solvent for the translocation of minerals in the xylem and organic solutes (like sucrose) in the phloem, facilitating the distribution of resources throughout the plant.

Thermoregulation: Through the process of transpiration, the evaporation of water from leaf surfaces absorbs heat energy, helping to maintain an optimal temperature for enzyme activity.

Nitrate Ions ($NO_3^-$): These are fundamental for the synthesis of amino acids, which build proteins (including enzymes), and are also required for the production of DNA and chlorophyll.

Magnesium Ions ($Mg^{2+}$): Magnesium is the central atom in the chlorophyll molecule; without it, plants cannot capture light energy for photosynthesis.

Calcium Ions ($Ca^{2+}$): These ions are vital components of the middle lamella in cell walls, where they form calcium pectate to 'glue' adjacent cells together and provide structural strength.

Chlorosis: A condition where leaves turn yellow due to a lack of chlorophyll, typically caused by a deficiency in either magnesium or nitrate ions.

Stunted Growth: A general reduction in plant size and development, often resulting from nitrate deficiency (lack of proteins for new cells) or calcium deficiency (poor cell wall formation).

Necrosis: The death of plant tissue, which can appear as brown spots or withered leaf edges when essential minerals are severely lacking.

Link Function to Symptom: Always explain why a deficiency causes a symptom. For example, 'Lack of $Mg^{2+}$ means less chlorophyll, leading to yellow leaves and reduced photosynthesis.'

Experimental Controls: In questions about mineral deficiency experiments, identify the control broth (containing all minerals) and the independent variable (the specific ion being omitted).

Precision in Terminology: Use terms like 'turgid' rather than 'stiff' and 'chlorosis' rather than 'yellowing' to secure higher marks in technical descriptions.

Variable Management: Ensure you mention keeping light intensity, temperature, and the age/species of the seedlings constant to ensure the validity of the results.