2.3 THE BALANCE OF THE MATTER AND ENERGY EXCHANGE (pages 53 – 61)

THE EARTH IS AN OPEN AND A CLOSED SYSTEM

! The Earth is a closed system in relation to matter and an open system in relation to energy. There is a constant input of energy into the biosphere and a constant output of radiant energy (heat) to space.

! The amount of sunlight that is received by an ecosystem affects the amount and the type of productivity of an ecosystem.

! Productivity: the rate at which an ecosystem’s producers capture and store energy within organic compounds over a certain length of time.

! Commonly measured in terms of energy per area, per year; (J/m2/a)

! Productivity is the rate at which organisms produce new biomass. Productivity can also be expressed in terms of biomass of vegetation added to an ecosystem per year; (g/m2/a).

!  Comparing productivity of ecosystems in terms of (A) the percentage of Earth’s surface and (B) average net productivity. Net productivity here is the total amount of radiant energy that is transformed to chemical energy by producers, minus the amount used by the producers during cellular respiration.

What factors affect the productivity of an ecosystem?

PRODUCTIVITY VARIES AMONG ECOSYSTEMS; THE RATE OF PRODUCTIVITY DEPENDS ON MANY VARIABLES:

! number of producers present in the ecosystem

PRODUCTIVITY VARIES AMONG ECOSYSTEMS; THE RATE OF PRODUCTIVITY DEPENDS ON MANY VARIABLES:

!  the amount of light and heat available (solar radiation)

PRODUCTIVITY VARIES AMONG ECOSYSTEMS; THE RATE OF PRODUCTIVITY DEPENDS ON MANY VARIABLES: !  the amount of rainfall the system receives

PRODUCTIVITY VARIES AMONG ECOSYSTEMS; THE RATE OF PRODUCTIVITY DEPENDS ON MANY VARIABLES: !  the amount of available

nutrients

ANSWER THE QUESTIONS…

! Question 1. Explain how increased amounts of sunlight can have both positive and negative effects on productivity.

! Question 2. What are two major factors (other than available nutrients) that can limit productivity?

GAIA HYPOTHESIS ! Organisms must maintain an internal balance to

remain healthy (homeostasis). The Gaia hypothesis considers homeostasis on a global level. The Gaia hypothesis states:

“the entire range of living matter on Earth from whales to viruses and from oaks to algae could be regarded as constituting a single living entity capable of maintaining Earth’s atmosphere to suit its overall needs and endowed with faculties and powers far beyond those of its constitute parts”.

ANSWER THE QUESTION…

! Question 3. State the Gaia hypothesis in your own words.