Plants take up more carbon dioxide through photosynthesis than they release through respiration throughout the day or in the spring and summer, and therefore carbon dioxide concentrations in the air drop. The amount of carbon dioxide taken up by plants is dependent on several factors such as sunlight, temperature, water, and nitrogen fertilizer if applied. Carbon dioxide is also released into the atmosphere through natural processes such as decomposition of organic matter (e.g., dead organisms), emissions from volcanoes, and fire. Human activities such as deforestation for farmland and fuel wood, land clearance for livestock farming, and fossil fuel combustion contribute to the increase in atmospheric CO2 concentration. In conclusion, plants take up more carbon dioxide through photosynthesis than they release through respiration throughout the day, and therefore carbon dioxide concentrations in the air drop. Some other factors such as sunlight, temperature, water, and nitrogen fertilizer affect the rate at which plants take up carbon dioxide too.