Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant. Chloroplasts capture light energy from the sun to produce the free energy stored in ATP and NADPH through a process called photosynthesis.

Mitochondria are the “powerhouses” of the cell, breaking down fuel molecules and capturing energy in cellular respiration. Chloroplasts are found in plants and algae. They’re responsible for capturing light energy to make sugars in photosynthesis.

Endoplasmic reticulum (ER), in biology, a continuous membrane system that forms a series of flattened sacs within the cytoplasm of eukaryotic cells and serves multiple functions, being important particularly in the synthesis, folding, modification, and transport of proteins .

It is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is not found in red blood cells, or spermatozoa.

Proteins are synthesized on the rough ER. Those that are processed are inserted cotranslationally into the ER. Such insertion requires the presence of a signal peptide at the N terminus, which is recognized by a specific receptor (docking protein) on the ER membrane.

sER is a membrane-bound network of tubules (see Figs. sER is not involved in protein synthesis. Its main function is the synthesis of lipids, steroids, and carbohydrates, as well as the metabolism of exogenous substances, such as drugs or toxins.

The surface of the rough endoplasmic reticulum contains ribosomes on the surface which gives them a rough appearance while the smooth endoplasmic reticulum does not contain the ribosomes. The most important function of the endoplasmic reticulum is the process of synthesis of proteins.