Photosynthesis in Higher Plants

Question 1

Photorespiration reaction catalyzed by RuBisCo is shown below: RuBP + O₂ → 3-Phosphoglycerate + X. Identify 'X' from the given options:

Accepted Answer

2-Phosphoglycolate. RuBisCO can bind O₂ as well as CO₂. When it binds oxygen the six-carbon intermediate is not formed; instead RuBP is cleaved into one three-carbon 3-phosphoglycerate and one two-carbon 2-phosphoglycolate. That is the wasteful first step of photorespiration.

Answer

Phosphoenolpyruvate

Answer

Oxaloacetate

Answer

Malate

Question 2

Which pigment has absorption peak at 700 nm in the photosynthetic reaction centre PS I (P700)?

Accepted Answer

Chlorophyll a. Only chlorophyll a occupies the reaction centre; every other pigment is accessory and merely passes energy to it. In photosystem I that reaction-centre chlorophyll a absorbs maximally at 700 nm, which is exactly what the label P700 records.

Answer

Chlorophyll b

Answer

Xanthophylls

Answer

Carotenoids

Question 3

Select the correct sequence of experiments that led to a gradual understanding of photosynthesis in green plants.

Accepted Answer

Role of air → release of oxygen → production of glucose → absorption spectra of chlorophyll a and b. The history runs from the crudest observation to the most refined. Priestley showed air was involved in 1770; Ingenhousz then showed the gas released was oxygen and only in light; Sachs demonstrated glucose production in 1854; and Engelmann later mapped the absorption spectrum of the pigments themselves.

Answer

Absorption spectra of chlorophyll a and b → production of glucose → release of oxygen → role of air

Answer

Release of oxygen → production of glucose → absorption spectra of chlorophyll a and b → role of air

Answer

Production of glucose → role of air → release of oxygen → absorption spectra of chlorophyll a and b

Q1.Photorespiration reaction catalyzed by RuBisCo is shown below: RuBP + O₂ → 3-Phosphoglycerate + X. Identify 'X' from the given options:

Q2.Which pigment has absorption peak at 700 nm in the photosynthetic reaction centre PS I (P700)?

Q3.Select the correct sequence of experiments that led to a gradual understanding of photosynthesis in green plants.