Question

The internal cellular energy reserve in autotrophs is

• A. Glycogen
• B. Protein
• C. Starch
• D. Fatty acid

Answer 1

The correct option is C Starch

Hint: Autotrophs can prepare their food through photosynthesis in the form of glucose. Some of it is utilized to support life processes, while some will be stored for future use as a polymer of glucose.

Part 1 - Glucose as a product of photosynthesis

• Organisms with chlorophyll present in their cellular structure can convert $C{O}_2$ and $H_{2}O$ into sugar (glucose) by harvesting the energy from sunlight.
• The reaction proceeds as follows:

$C{O}_2\left(Carbondioxide\right)+H_{2}O\left(Water\right)\to C_6{H}_{12}{O}_6\left(Glucose\right)+O_2\left(Oxygen\right)$

Part 2 - Starch as a storage product

• Food can not be stored in the form of glucose as it is a water-soluble molecule.
• That is why extra glucose in the cytoplasm of a cell can change the osmotic concentration of that cell.
• Starch on the other hand, is water-insoluble.
• Starch is the polymer of glucose in which individual glucose molecules are joined by α-1,4 and α-1,6 glycosidic bonds.

Part 3 - Conclusion

• From the above discussion we can conclude that glucose is the product of photosynthesis in autotrophs but it can't be stored in plant for longer time as it can drastically change the osmolarity of that particular cell.
• Starch on the other hand is an inert and water insoluble molecule and is a perfect choice as a storage molecule.

Final step - The internal cellular energy reserve in autotrophs is starch.