Question

Define :

(a) Photon (b) Quantum (c)$C_3$ plant (d) $C_4$ plant (e) Light Reaction (f) Photorespiration

(g)Limiting Factor.

Answer 1

(a) Photon - Sun emits energy in the form of electromagnetic radiations. The electromagnetic radiations seem to travel as a stream of tiny packets/unit of energy called photons.

(b) Quantum - The amount of energy contained by an individual 'photon' is called quantum (hv). The energy content of a quantum is related to its wavelength.

(c) C₃ plant - These are the plants that use the Calvin cycle for initial steps that incorporate CO₂ from the air (as the first organic compound produced is three-carbon compound 3-PGA). Almost all the trees and plants fall under this.

(d) C₄ plant - Phosphoenolpyruvate carboxylase (PEP) reacts with CO₂ to form oxaloacetate, a four-carbon compound; this is then converted into malate. Malate is decarboxylated in the bundle-sheath cell (which does not allow CO₂ to be released). Some tropical and sub-tropical grasses and shrubs fall under C₄ plants.

(e) Light Reaction - Photosynthesis is a three-stage process.

Light Reaction occurs in the first two stages. It occurs on thylakoid membranes, stepping where solar energy is absorbed and converted into chemical energy in the form of ATP and NADPH. This reaction powers the Calvin-cycle, and produce ATP, O₂, and NADPH.

(f) Photorespiration - It means that plants take up O₂ in the light and releases CO₂ without ATP or NADPH (meaning oxygen fills up in the plant as the stoma closes up.)

It is quite opposite the usual process of photosynthesis.

(g) Limiting Factor - Limiting factor is defined as a factor present in an environment that controls a process. The control is usually the limitations an environment faces in terms of growth, distribution, and abundance, affecting the ecosystem drastically and subsequently, its organisms.