why do we need energy to survive

All lifeforms need energy to survive. Energy is the resource that allows organisms to do things. What kinds of things might an organism do with energy? The answer to this question is as varied as the lifeforms that use energy.

Some, like the African Lion, use energy to chase after prey. Other lifeforms, like many creatures we find in the depths of the Earth's oceans, use energy to create their own light. Living things use energy to grow, to defend themselves, and to move around.
External functions supported by energy include exercise, work and play.

If you are active and have a high lean body mass to fat ratio, your energy needs are greater than someone who leads a sedentary lifestyle or has a high body fat composition, according to Sheri Barke, MPH, RD, College of Canyons Student Health and Wellness Center.

Fighting invading organisms that cause infection and disease uses massive amounts of physical energy.

Fever drains energy stores to restore and maintain normal temperature balance. Resting metabolic rates increased by 8 percent in 25 study participants infected with respiratory tract infections, according to a report published in the July/August 2010 issue of the БAmerican Journal of Human Biology.

Б Study results indicate even modest physiological responses to infection might cause substantial increases in energy usage.