Photosynthesis in Plants

Green algae have chloroplasts that contain chlorophyll a and b, giving them a bright green color, as well as the accessory pigments beta carotene and xanthophylls, in stacked thylakoids. The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch. The end products of photosynthesis in these green algae are starch and proteins.

CO$ _{2}$ is needed for photosynthesis is shown by Moll's half leaf experiment. In this experiment, only that part of the leaf will show blue color which was present outside the bottle because they are able to take carbon dioxide from the stomata of the leaf.

Calvin cycle is used for the fixation of carbon dioxide to produce glucose. Radioactive isotopes of carbon (C-14) and phosphorus (P-32) was used to trace the path for the carbon assimilation. A photosynthesizing plant does not strongly discriminate between the most abundant natural carbon isotope C-12 and C-14. During photosynthesis in the presence of 14$CO _2$, the compounds formed become labeled with the radioisotope.

During the day, CAM plants decarboxylate malic acid that was stored in vacuoles overnight, releasing CO2 internally for the Calvin cycle. This allows them to fix carbon while keeping their stomata closed to conserve water. Thus, the procured CO2 comes directly from malic acid.

In Moll's half leaf experiment a destarched plant is used.Half part of one of the leaves from the plant is inserted into a corked bottle containing either KOH solution or KOH palletes. The plant is then placed in sunlight for a few hours. The leaf is then tested for starch with iodine solution. Part of the leaf that was inserted in the bottle does not turn blue or test positive for starch. This is because $CO _2$ present in the bottle was aborbed by KOH and the bottle was corked to prevent any entry of air.Proving that $CO _2$ is essential for photosynthesis.

Molls experiment evidently shows that plants do not form starch when carbon dioxide is not at their disposal, all the carbon dioxide contained in the bottle having been absorbed by the caustic potash solution.

The complete process of photosynthesis is studied under two phases - photochemical phase and biosynthetic phase. Photochemical phase involves absorption of light energy, photolysis of water with the release of $O _{2}$ and production of assimilatory power (i.e. ATP + NADPH).$CO _{2} $ fixation occurs during biosynthetic phase of photosynthesis. 

The respiratory quotient (or RQ or respiratory coefficient), is a dimensionless number used in calculations of basal metabolic rate (BMR), when estimated from carbon dioxide production.
RQ = CO$ _{2}$ eliminated / O$ _{2}$ consumed. Thus, option A is incorrect. Photosynthetic coefficient is the specific light spectrum at which chlorophyll absorbs light. Thus, option B is wrong. Photosynthetic yield is the quantity of the end product of the photosynthesis. Thus, option C is wrong. The temperature coefficient (Q$ _{10}$) represents the factor by which the rate (R) of a reaction increases for every 10-degree rise in the temperature (T). The rate (R) may represent any measure of the progress of a process. Thus option D is correct.

During aerobic respiration, O$ _2$ is consumed and CO$ _2$ is released. The ratio of the volume of CO$ _2$ evolved to the volume of O$ _2$ consumed in respiration is called as the respiratory quotient (RQ) or respiratory ratio. Thus, the following expression is used to calculate the value of RQ.
RQ = volume of CO$ _2$ evolved/ volume of O$ _2$ consumed.
In an actively photosynthesizing tissue, the net volume of carbon dioxide evolved (i.e., volume of carbon dioxide produced in respiration minus that utilised in photosynthesis) is equal to net volume of oxygen (i.e., volume of oxygen consumed in respiration minus that evolved in photosynthesis). 

Compensation point is the value of a factor where the rate of photosynthesis is equal to the rate of respiration.  At this point, carbon dioxide released from respiration is equivalent to that which is taken up during photosynthesis. When the light intensity increases, the compensation point is reached. When light intensity is increased beyond the compensation point, the rate of photosynthesis increases proportionally until the point of light saturation is reached. Beyond light saturation point, the rate of photosynthesis is no longer affected by light intensity. Compensation point varies in different species of plants. It even varies in response to changes in temperature and other environmental factors.

The compensation point is the light intensity on the light curve for which the rate of photosynthesis is equal to the rate of respiration in the plant cell i.e., the rate of cellular fixation of Carbon dioxide through photosynthetic pathway is equal to the respiratory release of Carbon-dioxide and the release of Oxygen by photosynthesis is equals to the rate of consumption by respiration in a plant cell. At the compensation point, the organism is not building any biomass nor consuming any biomass.

About $1-5\%$ of incident solar energy or $2-10\%$ of PAR is captured by the photosynthetic organisms for the synthesis of organic matter(Gross primary productivity). Roughly $20\%$ of it is consumed in respiration so that net capture of energy(net primary productivity) is $0.8-4\%$ of incident radiation or $1.6-8\%$ of PAR.

The nutrient synthesized by plants through photosynthesis is carbohydrates. Plants are autotrophs and they synthesize their own food by the process of photosynthesis. During photosynthesis, they convert carbon dioxide and water in presence of sunlight and chlorophyll to produce carbohydrates (glucose) and oxygen. 

The major pigments present in algae is chlorophyll. It is a photosynthetic pigment. Apart from it, algae contain carotenoids and phycobilins pigments. Haemoglobin pigment is present in the red blood cells. It carries oxygen from the lungs to different parts of the body. Plasma is the colourless liquid part of the blood which contains all the components of blood except red blood cells, white blood cells and platelets.