Answer:
The source of carbon atoms in a plant's cells is carbon dioxide (CO2) that they absorb from the atmosphere during photosynthesis.
Step-by-step explanation:
Plants obtain carbon atoms, which they use to build their cellular structures, through a process called photosynthesis. During photosynthesis, plants take in carbon dioxide (CO2) from the atmosphere through tiny openings called stomata in their leaves. They also absorb water through their roots. With the help of chlorophyll, a pigment in their cells, they use energy from sunlight to convert carbon dioxide and water into glucose (a type of sugar) and oxygen. The carbon from the carbon dioxide is incorporated into the plant's tissues, such as leaves, stems, and roots, making up the bulk of the plant's biomass. This process is crucial for the growth and survival of plants, and it also plays a fundamental role in the carbon cycle, as the carbon stored in plants can be transferred through the food chain when animals eat plants.