Question

100-200 word response. Explain why each of the following misconception about photosynthesis (a) Only plants are autorophs. (b) Plants do not need cellular respiration because they carry out photosynthesis. (c) chorophyll is only plant pigment.

Answer 1

Answer

Photosynthesis is the process of synthesis of glucose from carbon dioxide and water in the presence of energy, manly sunlight. Any organism that can photosynthesize are called phototrophs. Ex. Plants. Other organisms that can't perform photosynthesis and depend on phototrophs for their source of glucose are called heterotrophs.

(a) Although, plants comprise the largest biomass on the earth to perform photosynthesis, there are also certain algae and microbes (cyanobacteria) that are able to perform photosynthesis. Therefore, plants alone are not phototrophs. Even algae and cyanobateria fall under phototrophs.

Phototrophs are again of two types- photo-autotrophs (or autotrophs) and chemo-autotrophs or chemotrophs. The former, synthesize glucose in the presence of light energy (sunight), while the second group produce glucose from carbon dioxide and water in the presence of sources of chemical energy, a process termed 'chemosynthesis'. Ex. Purple-sulphur bacteria synthesize glucose in the presence of chemical energy of sulfur compounds.

Thus both phototrophs and chemotrophs are 'autotrophs' that is, they can prepare their own food.

(b) Cellular respiration is the process of breakdown of complex food, mainly glucose into simple inorganic compounds like water and carbon dioxide with a release of energy. This energy is stored in the form of ATP and used in the various cellular processes. In other words, cellular respiration is the reverse process of photosynthesis. All organisms including plants require cellular respiration to obtain energy from food sources. Plants perform cellular respiration during the day as well as night while photosynthesis is carried out only at daytime in the presence of sunlight.

(c) Photosynthesis requires specialized pigments that can be excited by the sunlight. In higher plants, 'chlorophyll' is the main pigment that is responsible for the capture of light energy. Chlorophyll is present within special cellular organelles called 'chloroplasts'. Although chlorophyll is the main photosynthetic pigment in plants, there are other accessory pigments such as carotenoids and phycobilliproteins that assist chlorophyll in light absorption during photosynthesis.