PinkMonkey Online Study Guide-Biology
iv) Responsiveness to Stimuli
All living things are able to respond to stimuli
in the external environment. Stimuli originate from different sources.
a) physical: light, heat, temperature, sound.
b) chemical: acids and alkali.
c) mechanical: friction, pressure.
The body has specialized tissue or higher centers
to detect stimuli, such as eyes for light, ears for auditory stimuli,
the nose for olfactory stimuli, the tongue for taste, the skin for
An organism must co-ordinate well to give an appropriate
response to the stimuli from the environment. All systems of the
body help in this co-ordination, like nerves from the nervous system,
and certain chemical regulators called hormones from the endocrine
system. This simultaneously produces an effect of co-ordination
and acts as a sensing system. To respond to the stimuli, the organism
has certain efferent units like muscles, glands, hair, etc. The
process of response involves the use of energy.
The responses are of two types:
a) generalized, and
Protective responses help to promote survival and
thus sustain life. A generalized response contribute to the behavior
patterns of an organism. For certain classes, the response occurs
with a definite pattern which is innate to the organism.
Nonliving things donít respond to stimuli as living
Living organisms normally interact with the environment
for their daily requirements. There are always changes going on
in the environment. To adapt to these changes, there are genetic
changes in the animal. The process of adaptation in a new generation
animal in the population is called evolution. Evolution allows for
changes in interactions between the organism and its environment.
The evolved organism is more capable of adapting to changes in the
environment. This adaptation in the organism leads to the formation
of a new species and also newer organisms within the species. So
with evolution, a new species is formed but certain characteristics
from the previous generation remain intact.
Ecology is the study of the relationships between
the environment and the organism, and between various organisms
. Due to interaction with the environment, the organism and its
environment continuously influence each other. Animate organisms
can migrate to another place if the environment is not suited to
their survival in a given region. For instance, frogs cannot live
in water if there are too many crocodiles on their side of the pond.
Nonliving things cannot change their environment