Tag: metabolism, cell respiration, and photosynthesis

The process of photosynthesis in plants involves a series of steps and reactions that use solar energy, water, and carbon dioxide to produce organic compound. One of the first steps in this complex process depends on chlorophyll and other pigment molecules. Chlorophyll is the green pigment molecule that make plants appear green. In photosynthetic plant cells, chlorophyll molecules are embedded in stacked membranes (thylakoids) contained in special membrane-bound organelles called chloroplast. The chlorophyll molecules are arranged in discrete units called photosystems. Each one of it contains hundreds of pigment molecules arranged into an "antenna complex" surrounding a reaction center.

• When Ttrr x Rrtt is performed, 4 types of phenotypes are obtained in equal numbers. (1:1:1:1)
  
• The gametes for Ttrr are Tr and tr and for Rrtt are Rt and rt.
• The possible genotypes are TtRr, Ttrr, ttRr, ttrr which are all different phenotypically.
• So. the correct answer is '1:1:1:1'.

Since carotene (alpha and beta), chl A, chl B are all found in both photosystem, the one which is only present in PS II is xanthophyll.

P ${ _7}$${ _0}$${ _0}$ is the reaction center of the PS-I. So, when PS- I receives light energy electron is released by P ${ _7}$${ _0}$${ _0}$.

Photosystem II has P680 reaction center wherein oxygen atoms of two water molecules bind to a cluster of manganese atoms. These Mn atoms are bound to the reaction center and associated with an enzyme that splits water, removes electrons one at a time. These electrons fill the holes which are left in the reaction center due to released to light-energized electrons. Immediately after removal of four electrons from the two water molecules, O2 is released. The absence of PS II results in cyclic photophosphorylation by PSI that does not have water splitting complex and no oxygen is released. Phytochromes are blue-green, proteinaceous pigments that are involved in physiological responses to light. Phycocyanin is the photosynthetic pigment of cyanobacteria. Thus, the correct answer is option B.

Like most other photosynthetic bacteria, purple and green sulphar bacteria do not produce oxygen (anoxygenic), because the reducing agent (electron donor) involved in photosynthesis is not water. They use H$ _{2}$S or Elementary Sulphur as electron donor. In any photosynthetic organism, CO$ _{2}$ is not used as electron donor. Rhodopseudomonas uses isopropanol as electron donor.
So, the correct answer is option B.

There are only two photosystems PS I and PS II. Photosynthetic bacteria have only PS I and absence of PSII makes them carry out cyclic photophosphorylation wherein $H _2S$ serves as an electron donor, rather than water, and there is no release of oxygen. The low light intensity and anaerobic conditions favor cyclic photophosphorylation. The correct answer is B.

Chloroplasts are eukaryotic cell organelles. They are covered by the double membrane and also have an internal membrane system comprised of thylakoid membranes. The thylakoid membranes are of two types. The membranes which make grana are called granal lamellae. The other thylakoid membranes are called stromal membranes . The non-appressed membranes (stromal membranes and edges of granal membranes) are in direct contact with the stroma. The PS- I is abundant in non-appressed membrane whereas PS- II is abundant in granal membranes.

There are two photosystems PS I and PS II. Photosynthetic bacteria have only PS I and absence of PSII makes them carry out cyclic photophosphorylation wherein $H _2S$ serves as an electron donor, rather than water, and there is no release of oxygen. The low light intensity and anaerobic conditions favor cyclic photophosphorylation. The correct answer is A.