Photosynthesis in Higher Plants Test - 1

• Blue Green algae, Green algae, and autotrophic plants are photosynthetic organisms. They carry out photosynthesis using sunlight, water, and carbon dioxide and produce carbohydrates and oxygen.
• Photosynthetic bacteria like purple bacteria or green sulfur bacteria carry out anoxygenic bacterial photosynthesis.
• However, they reduce hydrogen sulfide instead of water and elemental sulfur is evolved instead of oxygen.

Thus, the correct answer is 'Non-Evolution of O₂.'

ATP is synthesized by cells (in mitochondria and chloroplasts) is named phosphorylation.

The Calvin cycle can be described under three stages: carboxylation, reduction and regeneration. Pathway operated in cyclic manner.

Energy produced during light reaction is transferred to the dark reaction in form of ATP to fix the carbon dioxide in form of glucose.

• In the photorespiratory pathway, there is no synthesis of ATP or NADPH. Therefore, photorespiration is a wasteful process.
• In C₄ plants photorespiration does not occur. This is because they have a mechanism that increases the concentration of CO₂ at the enzyme site.

Solarisation is the inhibition of photosynthesis at very high light intensities due to photooxidation of certain compounds and destruction of chlorophyll molecules.

The work of Melvin Calvin is the discovery that the first CO₂ fixation product was a 3-carbon organic acid. He also contributed to working out the complete biosynthetic pathway; hence it was called the Calvin cycle.

• Electrons from excited chlorphyll molecule of photosystem II are accepted first by Quinone.
• Photosystem II is a photosynthetic pigment system along with some electron carriers that is located in the appressed part of the grana thylakoids.
• Photosystem II has chlorophyll a, b and carotenoids. Other components of PS II are phaeophytin, plastoquinone (PQ), cytochrome complex and blue coloured copper-containing plastocyanin.

In C₄ plants, Carbon dioxide is fixed in malic acid with the help of enzyme phosphoenel pyruvate (PEP). Malic acid is a four-carbon compound that later changes into oxaloacetic acid.

Dark reaction of Carbon dioxide fixation in CAM plants is called as ossification because it produces Malic acid. These plants open their stomata during night to prevent transpiration.

Pigments are substances that have an ability to absorb light, at specific wavelengths. The chlorophyll a pigment to absorb lights of different wavelengths.

The light-dependent transfer of electrons by chloroplasts in photosynthesis that results in the cleavage of water molecules and liberation of oxygen is called the Hill reaction. Hill reaction required ferricyanide.

Hill Reaction:

Electrons become excited and jump into an orbit farther from the atomic nucleus. These electrons are picked up by an electron acceptor which passes them to an electrons transport of cytochrome.

In the leaves of C4 plants such as maize, sorghum we can observe the Kranz anatomy.

When several factors affect any [bio] chemical process, Blackman’s (1905) Law of Limiting Factors comes into effect.

• According to this law, If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor that directly affects the process if its quantity is changed.

Splitting of water takes place near PS II, located in the inner side of the thylakoid membrane.

Splitting of water releases oxygen in the atmosphere and generates a proton gradient across the thylakoid membrane.

• Photosystems are the protein complexes involved in photosynthesis. Each photosystem is characterized by the wavelength of light to which its reaction centre is most reactive.
• Photosystem I, reaction centre pigment chlorophyll-a has absorption peak at 700nm.
• Thus Photosystem I is also known as P700​

So, the correct answer is 700 nm.

Light reactions or the ‘Photochemical’ phase include light absorption, water splitting, oxygen release, and the formation of high-energy chemical intermediates, ATP and NADPH. Several complexes are involved in the process.

The presence of the bundle sheath would help you identify the C4 plants. This pathway that has been named the Hatch and Slack Pathway, is again a cyclic process.

Succulents plants have stomata sunken deeply in the leaf epidermis to prevent loss of water by transpiration. These plants open their stomata during the night and follow the CAM pathway for the fixation of carbon dioxide.

• The pathway of photosynthesis was discovered by Melvin Calvin after experiment on single celled algae.
• The first stable product of C3 cycle is a three carbon compound called PGA (phosphoglyceric acid).

• The other pathway, non-cyclic photophosphorylation, is a two-stage process involving two different chlorophyll photosystems. Being a light reaction, non-cyclic photophosphorylation occurs in the thylakoid membrane. First, a water molecule is broken down into 2H⁺ + 1/2 O₂ + 2e⁻ by a process called photolysis (or light-splitting).
• The two electrons from the water molecule are kept in photosystem II, while the 2H⁺and 1/2O₂ are left out for further use. Then a photon is absorbed by chlorophyll pigments surrounding the reaction core centre of the photosystem.
• The light excites the electrons of each pigment, causing a chain reaction that eventually transfers energy to the core of photosystem II, exciting the two electrons that are transferred to the primary electron acceptor, phaeophytin.

Light-harvesting complexes (LHC) within Photosystem I (PS I) and Photosystem II (PS II). These are named in the sequence of their discovery, and not in the sequence in which they function during the light reaction. The LHC is made up of hundreds of pigment molecules.

Photosynthesis occurs in two steps- light reaction and dark reaction. During light reaction ATP and NADPH molecules are formed and in dark reaction carbon dioxide is fixed.

• Chloroplast dimorphism is a characteristic feature of C₄ plants.
• These plants contain two kinds of chloroplast in their leaves, bundles sheath cells contain chloroplast in which grana is absent and mesophyll cells without stroma.