What could arrow 2 possibly represent?

A.Carbon dioxide
B.Oxygen
C.Water
D.Nitrogen

Hint: Photosynthesis is a mechanism by which plants and other species transform light energy into chemical energy, which is then emitted to sustain the organism's metabolic activities by cellular respiration. Carbohydrate molecules including sugars and starches, which are made from carbon dioxide and water, store this chemical energy.

Complete answer: Photosynthesis is the conversion of light energy into chemical energy by phototrophs, which is then used to power cellular activities. Sugars, which are made from water and carbon dioxide, are used to store chemical energy.
Photosynthesis is described as a process that occurs exclusively in chloroplasts and is mediated by photosynthetic pigments such as chlorophyll a, chlorophyll b, carotene, and xanthophyll. Photosynthesis uses carbon dioxide, water, and sunlight to synthesise carbohydrates in green plants and a few other autotrophic species. The mechanism of photosynthesis produces oxygen as a by-product.${{\text{C}}_6}{{\text{H}}_{12}}{{\text{O}}_6} + 6{{\text{O}}_2}{\text{ }} \to {\text{ }}6{\text{C}}{{\text{O}}_2} + 6{{\text{H}}_2}{\text{O}} + {\text{ energy }}$
$6{\text{C}}{{\text{O}}_2} + 6{{\text{H}}_2}{\text{O}} \to {{\text{C}}_6}{{\text{H}}_{12}}{{\text{O}}_6} + 6{{\text{O}}_2}$
Respiration, after all, necessitates the presence of oxygen, which animals obtain by breathing. Blood cells circulating near the lungs absorb oxygen and transport it across the body to the sites of respiration. When the diaphragm bows outward, air is squeezed out of the lungs.
When an animal breathes, oxygen is taken in and carbon dioxide is released into the atmosphere. The carbon dioxide released by the animal's cells during cellular respiration is a waste product.

Animals take oxygen and exhale carbon dioxide, while plants consume carbon dioxide and emit oxygen during respiration.
As a result, arrow 2 reflects carbon dioxide, which is used by plants after being emitted by animals through respiration.
And hence option A is the correct answer.

Note:
The chloroplasts of cells are where photosynthesis takes place. Cellular respiration breaks down food and releases energy, while photosynthesis takes energy and creates food. Plants are able to do both photosynthesis and respiration, while mammals can only do the latter.