Question

Write notes on
(a) Compensation point

(b) The blackman's principle of limiting factors

(c) Rubisco

(d) Photorespiration and aerobic respiration

(e) Light reaction and dark reaction

(f) $C_3$ and $C_4$ plants

Answer 1

(a) The compensation point is the light intensity on the light curve where the rate of photosynthesis exactly matches the rate of cellular respiration. This means that the carbon dioxide released from respiration is equivalent to that which is taken up during photosynthesis. The compensation point is reached as light intensity increases.

(b) Blackman proposed the law of limiting factors in 1905. According to this law, when a process depends on a number of factors, its rate is limited by the pace of the slowest factor. Blackman's law of limiting factors determines the rate of the photosynthesis.

(c) The key enzyme that accomplishes the fixing of carbon is Rubisco, and at low concentrations of CO2, it begins to fix oxygen instead.

(d) Photorespiration does not involve glycolysis, Krebs cycle and ETS. Aerobic respiration is completed in glycolysis, Krebs cycle and ETS. Photorespiration is completed in three organelles – Chloroplasts, Peroxisomes and Mitochondria. Do not produce energy-rich molecules such as ATP.

(e) Light reactions need light to produce organic energy molecules (ATP and NADPH). They are initiated by coloured pigments, mainly green coloured chlorophylls. Dark reactions make use of these organic energy molecules (ATP and NADPH). This reaction cycle is also called Calvin Benison Cycle, and it occurs in the stroma.

(f) In C3 plants the first carbon compound produced during photosynthesis contains three carbon atoms and a C4 plant is a plant that cycles carbon dioxide into four-carbon sugar compounds to enter into the Calvin cycle. These plants are very efficient in hot, dry climates and make a lot of energy.