Photosynthesis Test - 15

Photosynthesis takes place in the green leaves of plants and other green parts of plants like stem etc. The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialized light-absorbing green pigments, the chlorophylls. When chlorophyll absorbs light, it gets excited and emits electrons. These chlorophylls are found in photosynthetic units called Photosystem I and Photosystem II. Each unit has a specific reaction centre which contains pigment molecules. These molecules absorb light of different wavelengths and emit electrons. Due to the photon of light, electrons of chlorophyll get excited. These electrons are picked up by an electron acceptor which passes them to an electron transport system of cytochromes. The excitement of electrons of chlorophyll b photon of light is the first step of photosynthesis.

The energy of light captured by pigment molecules called chlorophylls, in chloroplasts is used to generate high- energy electrons with great reducing potential. These electrons are used to produce NADPH as well as ATP in a series of reactions called the light reactions because they require light.

The reason of algae float to the surface during the day & sink at night is due to photosynthesis. In Day time, the algae is producing oxygen. When enough Oxygen is produced during the day , it gets trapped in bubbles and it can lift the clumps up to the surface.

Photophosphorylation is the process in which ATP is produced, which is called as energy currency of the cell. During this process, ADP is phosphorylated to give ATP in presence of light energy.
So, the correct answer is option B.

The chlorophyll pigments which are excited give up their electrons and to compensate for the loss of electrons, water is split to release four H⁺ ions and four electrons and O². The electrons that are lost from the PSII enter into an electron transfer chain or ETC.

Photosynthesis occurs in two stages- light reaction and dark reaction. During the light reaction reduced NADPH_2​ and ATP are synthesized. These products are used subsequently to reduce carbon dioxide into sugars. Thus, the purpose of ATP in photosynthesis is to transfer energy from light reaction to dark reaction.

Photosynthesis occurs in two stages- light reaction and dark reaction. During the light, reaction water is oxidized using energy from light and reduced NADPH₂ and ATP are synthesized. The oxidation of water is called photolysis. Oxygen is released as a by-product during the photolysis of water. The NADPH₂ and ATP are used subsequently to reduce carbon dioxide into sugars.

Photolysis of water occurs at grana i.e., lumen side of grana thylakoid membrane with the help of water splitting complex or OEC (oxygen evolving complex). This step is associated with PS- II of Z- scheme.
Three minerals Mn ion, Ca+  +,Cl− are associated with splitting of water.

The evolution of oxygen during the light-dependent steps in photosynthesis (Hill reaction) was proposed and proven by British biochemist Robin Hill. He demonstrated that isolated chloroplasts would make oxygen (O2) but not fix carbon dioxide (CO2).

Hill's reaction or light reaction takes place in thylakoids and the end products of this reaction are ATP and NADPH2. Blackman's reactions or dark reactions take place in the stroma of the chloroplast. In dark reactions, sugars are synthesized from carbon dioxide by using ATP and NADPH2, which are end products of Hill's reaction.

Hence, the correct answer is Option D.

Chlorophyll, any member of the most important class of pigments involved in photosynthesis, the process by which light energy is converted to chemical energy through the synthesis of organic compounds. Chlorophyll is found in virtually all photosynthetic organisms, including green plants, prokaryotic blue-green algae (cyanobacteria), and eukaryotic algae. It absorbs energy from light; this energy is then used to convert carbon dioxide to carbohydrates.

The NADPH2 is synthesized in non-cyclic photophosphorylation in the light phase of photosynthesis. This is used subsequently in the dark phase to reduce carbon dioxide into sugars. NADPH2 is also called as reducing power. The substance provides the hydrogen molecules to perform reduction of the other substance. 

Thus, the correct answer is option D.

Initially chlorophyll captures the electron while ionization of water because trapping of the light energy is the key to photosynthesis. The first event is the absorption of light by a photoreceptor molecule and it is found in chloroplasts of green plants i.e. chlorophyll a.

The Calvin cycle has three stages.
1)carbon fixation
2)reduction
3)regeneration.
At the end of each Calvin cycle net gain is 9ATP and 6 NADPH2.In each Calvin cycle, 3 CO₂ molecules are fixed with RuBP to form 2 molecules of 3PGA in the first step. Later two molecules of 3PGA through a series of reactions regenerate 2RuBP in the third stage. So, for the fixation of one CO₂ carbon dioxide molecule through the Calvin cycle requires 3ATP and 2NADPH2.
So, the correct answer is 'option B'.

During non-cyclic electron flow, the electron hole in P-680 (reaction center of pigment system- II) is filled by electrons obtained by photolysis of water. The photolysis is an oxidative process and means splitting of water in the presence of light to form oxygen, protons and electrons. As a result, there is the evolution of oxygen and the electron move through Mn-protein bound to PS- II.

The most important method of ATP synthesis is phosphorylation of ADP using inorganic phosphate and energy difference across membranes. The energy difference is provided by the electrochemical gradient of protons. When the energy of light is used to derive the electrochemical gradient of protons across the thylakoid membranes the process of ATP synthesis is called as photophosphorylation. When the energy obtained by oxidation of reduced coenzymes is used to establish electrochemical gradient of protons across the inner mitochondrial membrane the process of ATP synthesis is called as oxidative phosphorylation. During both photo and oxidative phosphorylation electrons are exchanged between iron containing cytochrome proteins.

During non-cyclic electron flow, the electron ejected on behalf of PS I by the reaction centre P_7​0​0​ moves uphill and reduces an iron-sulphur protein. From here, it moves downhill to ferredoxin (Fd) and then to NADP⁺, which is reduced to NADPH₂​. The enzyme which actually forms reduced NADPH_2​ is ferredoxin NADPH oxidoreductase.

so, the correct answer is option B.

Both respiration and photosynthesis both require Cytochromes.
Both respiration and photosynthesis involve electron transfer across a series of electron carriers embedded in the inner mitochondrial membrane and the thylakoid membranes respectively. Cytochromes are responsible for ATP production through electron transport and are iron-containing proteins. 

Chemically photosynthesis is a redox reaction. During photosynthesis, two substrates (carbon dioxide and water) react in presence of light to produce two products (carbohydrates and oxygen). The water is oxidized in presence of light (photolysis) to release oxygen, whereas the carbon dioxide is reduced in dark to carbohydrates using energy trapped during light reaction.
So, the correct answer is option C.

During noncyclic electron flow the electron hole in P-680 is filled by electrons obtained by photolysis of water. As a result, there is an evolution of oxygen and the electron move through Mn-protein bound to PS II. In this transport Mn⁺⁺ is oxidised to Mn⁺⁺⁺ and then reduced to Mn⁺⁺ in a cyclic manner. The manganese thus transfers electrons from water to photosystem II and thus plays an important role in electron transport in the process of photosynthesis.

Chlorophyll pigments absorb the photons from the light which are destroyed at high intensity.The inhibition of photosynthesis by photo oxidation at higher intensity is called solarization. 

Photosynthesis is the process in which autotrophs such as green plants use carbon dioxide and water in presence of sunlight to synthesize nutrients such carbohydrates in the form of glucose and release oxygen. In this carbon dioxide is reduced to glucose and water is oxidized to release oxygen.

During the light reaction, the path of the electron has been elucidated in the Z-scheme. It is named so because of its shape and was first proposed by Hill and Bendall in 1960. The electron released by reaction center of photosystem II i.e., P680 moves uphill and reduces pheophytin, a nonmagnesium chlorophyll a molecule. From pheophytin, electrons are accepted by plastoquinone which requires two electrons for complete reduction. It also accepts two protons from the stromal side of thylakoid membrane and becomes reduced to PQH2 after accepting 2 electrons and 2 protons. It is the only carrier in the photosynthetic electron transport chain, which can bind both electrons and protons.

The concentration of oxygen in the atmosphere is about 21 percent by volume and it seldom fluctuates. An increase in oxygen concentration decreases photosynthesis and the phenomenon is called Warburg effect. The explanation to Warburg effect lies in the phenomenon of photorespiration. In C₃ plants the rate of light respiration is faster than the dark respiration. This enhanced rate of respiration is called as photorespiration. It operates in high light intensity, high oxygen concentration and high temperature. Here oxygen competes with carbon dioxide for the oxidation of RUBP to phosphoglycolic acid, thus reducing the net fixation of carbon dioxide.

The oxygen-evolving complex (OEC) of PSII is particularly sensitive to heat stress. The OEC comprises four oxygen bridged Mn atoms, Ca+2 and putatively Cl−, which is liganded to the protein matrix formed by the core proteins, viz.