NCERT Book Class 12 Biology Chapter 12 Ecosystem

CHAPTER 12

12.1 Ecosystem–Structure
and Function
An ecosystem can be visualised as a functional unit of
12.2. Productivity nature, where living organisms interact among themselves
and also with the surrounding physical environment.
12.3 Decomposition Ecosystem varies greatly in size from a small pond to a
large forest or a sea. Many ecologists regard the entire
12.4 Energy Flow biosphere as a global ecosystem, as a composite of all
local ecosystems on Earth. Since this system is too much
12.5 Ecological Pyramids
big and complex to be studied at one time, it is convenient
to divide it into two basic categories, namely terrestrial
and aquatic. Forest, grassland and desert are some
examples of terrestrial ecosystems; pond, lake, wetland,
river and estuary are some examples of aquatic
ecosystems. Crop fields and an aquarium may also be
considered as man-made ecosystems.
We will first look at the structure of the ecosystem, in
order to appreciate the input (productivity), transfer of
energy (food chain/web, nutrient cycling) and the output
(degradation and energy loss). We will also look at the
relationships – cycles, chains, webs – that are created as
a result of these energy flows within the system and their
inter- relationship.