What is a threshold in terms of biology? ?
what does it mean by absolute threshold and difference threshold?

The threshold in biology is explained in terms of neuroscience or action potential that affects nervous system.

The threshold value is the value that identifies incoming signals that should be sufficient enough to generate an action potential. The potentials generated by the signals are additive, and reaches threshold depends on their amplitude and frequency.

An absolute threshold is defined as the minimum level of signals like light, touch or sound , detected by any organism and allows them to react.

While Difference threshold allow to detect difference between two different signals.

4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."    

the endomembrane system i think