6. Plant nutrition

Matter comes from the raw materials; light supplies the energy needed to rearrange that matter into carbohydrate. Oxygen is released as a product.

The arrow means 'are converted into'. The equation conserves the kinds of atoms even though the word equation does not show coefficients.

In a variegated leaf, green regions contain chlorophyll; white regions do not. This difference can be used when testing whether chlorophyll is needed for starch production.

This energy transfer explains why light is required even though light is not a material reactant in the word equation.

Check balance by multiplying every subscript by its coefficient, then total each element on both sides. Light and chlorophyll remain conditions for the reaction.

The form suits the job: insoluble starch remains stored, sucrose is a transport sugar, and cellulose becomes strong wall material.

Both ions are absorbed from the soil through root hairs. Their roles differ: nitrate supplies nitrogen for amino acids, while magnesium is part of chlorophyll production.

Destarch the plant in darkness first, apply the treatment, expose it to light, then test the leaf with iodine. Blue-black shows starch; yellow-brown shows no starch.

Only the region or setup with the requirement should make starch. The control shows that the result is caused by the missing factor rather than another difference.

Use several values, allow equilibration, measure for equal time intervals, repeat and calculate means. Bubble count is less reliable than gas volume because bubbles vary in size.

Rate usually rises as a factor increases, then levels off when another factor limits it. At excessive temperatures the rate can fall because photosynthesis is enzyme-controlled.

In bright light, photosynthesis may remove CO₂ faster than respiration releases it. In darkness, photosynthesis stops but respiration continues, so CO₂ increases.

Compare equal plant amounts in equal indicator volumes for the same time and temperature; include a tube without an organism to show that any colour change is biological.

Identify the factor by asking which change still increases the rate under those exact conditions. A factor can stop being limiting as conditions change, so the limiting factor may shift along one graph.

Glasshouses can increase light, temperature or CO₂ to remove a limitation, but growers must compare the extra crop yield with heating, lighting and CO₂ costs.

Shape works with internal structure: a broad surface intercepts light, while thinness keeps palisade and spongy mesophyll close to the leaf surfaces.

First locate the two epidermal surfaces; then find columnar palisade cells, irregular spongy cells and the vascular bundle. At a surface view, a stoma is the pore, not either surrounding guard cell.

Carbon dioxide moves through a stoma, across interconnected air spaces, dissolves at moist mesophyll surfaces and diffuses into photosynthesising cells. Oxygen moves out along the reverse route when its concentration is higher inside.

No one tissue works alone: transparent surface layers admit light, palisade cells capture it, spongy air spaces deliver CO₂, xylem supplies water and phloem removes products.