Explanation:
Photosystems are the practical components for photosynthesis, well-defined by a specific stain association and connotation patterns, whose work is the absorption and allocation of light energy, which suggests transfer of electrons. Physically, photosystems are initiate in the thylakoid membranes. A photosystem consists of a light-harvesting complex and a reaction center. Pigments in the light-harvesting complex pass light energy to two special chlorophyll a molecules in the reaction center. Photosystem I or PS I and Photosystem II or PS II are the protein-mediated complex, and the main aim is to produce energy (ATP and 
), which is used in Calvin cycle, the PSI uses light energy to convert NADP+ to .
There are many grains of starch in the cortex because it represents the reserve food material of plants.
This source of food material is consumed during plant metabolism, as food when plants are under stress, or as an energy source in seed germination and early seedling stages.
The cortex, in plants, is a vascular tissue responsible for the transport of food (processed sap) from the leaves to the rest of the plant .
Starch grains are the most common solid particles that plant cells develop within plastids.
Assimilation starch is a temporary product of photosynthesis and is formed in chloroplasts, while reserve starch is formed in amyloplasts, which are contained in parenchymal cells of the cortex, in vascular tissues of stems and roots, in the pith of stems, in fruits, leaves, fleshy cotyledons and in modified stems, such as tubers and rhizomes.
Starch is the main energy and carbon reserve in plants, supplying the energy and carbon skeletons necessary for the plant's metabolism during periods of darkness, when photosynthesis is inactive.
Therefore, we can conclude that starch grains (ergasstic substances) are found in abundance in the cortex because it represents a reserve of essential molecules for the functioning and maintenance of the cellular structure.
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