Temperature is considered as the most ecologically relevant environmental factor because it affects ______________ of organisms.
A. Physiology
B. Morphology
C. Geographical distribution
D. All of these

Hint: The living organisms are influenced by a number of different factors of the environment which are known as environmental factors. The different factors are physical or abiotic factors or biotic factors. The abiotic factors affect the different features of the living organism and influence their biological activities.

Complete answer:
The different types of abiotic factors reflect the different types of environmental conditions. The environmental factors affect the various aspects of the organism and it causes to define the different activities of the organism that lives in those conditions. The factors such as temperature, water, humidity, pH are considered as the primary factors that affect the organisms.
Temperature is one of the most important and vital environment factors. The different types of organism are exposed to several types of changes in the temperatures. The changes in temperature are caused due to the position of the sun rays, air currents and other factors.
It influences the distribution of species as the species are able to grow within a narrow range of temperature which is known as the optimum temperature. The optimum temperature is needed for various types of physiological activities such as enzymatic activities and other types of biological activities. The functioning of the enzymes can occur only at proper temperatures and due to this reason, the living organism is required to maintain specific internal temperatures.
The distribution of the organism is also limited by the temperature conditions. Animals when faced with changes in the temperature either respond by several adaptations such as migration or changes in the activities in the form of hibernation or aestivation to avoid extreme conditions of temperature.
The temperature also brings changes related to the morphological features of the organism. The organism residing in a colder environment bears various types of adaptations such as presence of fur or hairs, thick layer of subcutaneous layer of fat. In the higher temperatures, the organism possesses adaptations such as skin that is resistant to increased temperature and other adaptations.

Hence, the correct answer is option (D).

Note: Temperature is an important ecologically relevant environmental factor and affects the different aspects of the living organism. The distribution, morphology and geographical distributions of the living organism are all affected by the temperature conditions. In order to survive, the organism maintains all biological processes within an optimum temperature.