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Which metal ion is a constituent of chlorophyll?
Magnesium is a constituent of chlorophyll. Chlorophylls are the green photosynthetic pigments. Five types of chlorophylls \(a, b, c, d\) and \(e\) occur in plants. Out of these only chlorophylls a and b occur in the chloroplasts of higher plants. Molecular formula of chlorophyll \(a, b, c\) and \(d\) are \(C_{55} H_{72} O_{5} N_{4} M g, C_{55} H_{70} O_{6} N_{4} M g, C_{35} H_{32} O_{5} N_{4} M g\) and \(C_{54} H_{70} O_{6} N_{4} M g\) respectively. Chlorophyll \(e\) is a rare type found in some golden algae.
Which pigment acts directly to convert light energy to chemical energy?
Chlorophyll a is termed a universal photosynthetic pigment as it is found in all photosynthetic plants except bacteria. It is also called primary photosynthetic pigment because it performs the primary reaction of photosynthesis which involves the conversion of light into chemical energy. Other photosynthetic pigments chlorophyll $b$ and carotenoids (carotenes and xanthophylls) are called accessory pigments, as they absorb light energy of different wavelengths, broaden the spectrum of light absorption and hand over the energy to chlorophyll a through electron spin resonance.
Which range of wavelength (in nm) is called photosynthetically active radiation (PAR)?
Sunlight or solar radiations reaching the earth have wavelengths between \(300 n m\) (in the ultraviolet range) to \(2600 n m\) (in the infra-red range). Part of the spectrum used in photosynthesis has a wavelength between \(400-700 n m\), it is called as photosynthetically active radiation \((P A R)\).
Which light range is least effective in photosynthesis?
Photosynthesis is most efficient in the blue and red light spectrums. The energy carried by blue wavelengths of light is greater than that carried by red wavelengths. As a result, the most efficient wavelengths of light for photosynthesis are red light wavelengths. In photosynthesis, green light is the least effective.
Chemosynthetic bacteria obtain energy from
Chemosynthetic autotrophic bacteria (Chemo- autotrophic bacteria) are bacteria which are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions involving oxidation of an inorganic substance present in the external medium. The chemical energy obtained from the oxidation reaction is trapped in \(A T P\) molecules.
Energy required for ATP synthesis in PSII comes from
(a) The synthesis of ATP is directly linked to the development of proton gradient across the thylakoid membranes of a chloroplast. It results when the water molecule splits inside the inner membrane and form \(\mathrm{H}^{+}\)and \(\mathrm{OH}^{-}\)ions.
The energy for ATP synthesis comes from proton gradient which develops along the inner membrane, e.g., in the case of mitochondria in the electron transport chain and in the chloroplast in the PSII.
During light reaction in photosynthesis the following are formed:
(c) Light reactions occur inside thylakoids. It is dependent upon light. It involves photolysis of water (breaking of water into \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\) ) and production of assimilatory power ( \(N A D P H\) and \(A T P\) ). Electron released during photolysis of water are picked up by Peso photocentre of photosystem \(I I\). From here electrons passes over series of carrier which include \(P Q\), cytochrome \(b-f\) complex and \(P C\). While passing over cytochrome complex, the electron losses sufficient energy for creation of proton gradient and \(A T P\) from \(A D P\) and inorganic phosphate. From \(P C\) electron is picked by the trap centre \(P_{700}\) of photosystem \(I\), which pushes out electron after absorbing light energy. Electron passes over carriers \(F e S\), ferredoxin and \(N A D P\)-reductase which gives electron to \(N A D P^{+}\)for combining with \(H^{+}\)to produce \(N A D P H\).
\(
N A D P^{+}+2 e^{-}+H^{+} \underset{\text { NADPreductase }}{\longrightarrow} N A D P H
\)
Dark reaction in photosynthesis is called so because
(b) Biosynthetic phase (dark or Blackman’s reaction) catalyses assimilation of \(C O_{2}\) to carbohydrates. The reactions are called carbon reactions. They occur in the stroma of chloroplasts. The reactions do not require light. Instead, assimilatory power \((A T P\) and \(N A D P H)\) produced during the photochemical phase is used in the fixation and reduction of carbon dioxide. All the enzymes required for the process are present in the matrix or stroma of the chloroplast.
PEP is primary \(\mathrm{CO}_{2}\) acceptor in
(a) PEP is \(3 C\) compound which serves as primary \(C O_{2}\) acceptor in the mesophyll cell cytoplasm of \(C_{4}\) plants like maize, sugarcane,Sorghum etc.
Splitting of water is associated with
(d) Splitting of water is the reaction that occurs inside the thylakoid membrane.
\(2 \mathrm{H}_{2} \mathrm{O} \rightarrow 4 \mathrm{H}^{+} \mathrm{O}_{2}+4 \mathrm{e}-\)
It results in the formation of protons, electrons, and oxygen gas. Replenishing of electrons in the photosystem II is achieved by splitting of water.
The correct sequence of flow of electrons in the light reaction is
(a) \(\text { The correct sequence of flow of electrons in the light reaction is } \\ {\text { PS II, plastoquinone, cytochrome, PS I, ferredoxin. }}\)
The enzyme that is not found in a C3 plant is
(b) PhosphoEnolPyruvate (PEP) carboxylase is present in the mesophyll cells of the \(\mathrm{C}_{4}\) plants and catalyse the conversion PEP to OxaloAecetate. (OAA), the first \(4 \mathrm{C}\) stable compound formed in \(\mathrm{C}_{4}\) plants formed by the acceptance of atmospheric \(\mathrm{CO}_{2}\) by PEP in presence of PEP carboxylase.
The reaction that is responsible for the primary fixation of \(\mathrm{CO}_{2}\) is catalysed by
(c) In \(\mathrm{C}_{3}\) cycle RuBP carboxylase is used to fix atmospheric \(\mathrm{CO}_{2}\) whereas, in \(\mathrm{C}_{4}\) plants \(\mathrm{PEP}\) carboxylase is involved in primary \(\mathrm{CO}_{2}\) fixation. So, both are used in \(\mathrm{CO}_{2}\) fixation but in different cycles.
Other options are incorrect because in (a) and (b) option is giving incomplete information and option (d) \(\mathrm{PGA}\) synthase is not at all involved in \(\mathrm{CO}_{2}\) fixation.
When \(\mathrm{CO}_{2}\) is added to \(\mathrm{PEP}\), the first stable product synthesised is:
(d) Oxaloacetate is a four-carbon compound formed in \(\mathrm{C}_{4}\) cycle and is the first stable product, that is why such plants are called \(\mathrm{C}_{4}\) plants.
Rest of the options are incorrect as because
(a) Pyruvate is formed in glycolysis.
(b) Glyceraldehyde-3-phosphate is also an intermediate compound of glycolysis.
(c) Phosphoglycerate is also an intermediate compound of glycolysis.
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