The termite provides shelter and space for the protozoan Trichonympha to live. The protozoan present in gut digests the wood, which termite feeds upon.
In the absence of Trichonympha, the termite is unable to digest wood and hence dies. Thus, the association of two given animal species represents mutualism.

The type of association the lianas have with the trees is commensalism because the plant gets the support of tree without affecting, harming or providing any benefit to the tree.

A population has the following characteristics that are employed in human population census:
(i) Natality and mortality
(ii) Sex ratio
(iii) Population density
(iv) Age distribution

The ecological principle behind the biological control of pest insects is based on the ability of predator to reduce prey population in that habitat

Streptococcus faecalis, Escherichia coli.

Heliophytes are those plants which grow in strong light so are commonly called Sun plants e.g. sunflower, while sciophytes are those plants which prefer to grow in lower light intensities or shade loving plants e.g. money plant, fir etc. 

Contractile vacuole helps in maintaining salt and water level called osmoregulation. Because of the cellular environment of a freshwater organism such as Amoeba, Paramecium being hypertonic, the water diffuses inside the cell constantly and gets collected in the contractile vacuole, which squeezes the extra water out of the periodically.
Thus, keeping the internal environment constant. While in case of marine protozoans organisms, this does not occur due to high salt concentration. These organism live in isotonic conditions in sea water. Thus there is no need for contractile vacuole.

No, a freshwater fish placed in the aquarium containing sea water, will not be able to survive. Because its body system is adapted to function normally in a narrow range of salinity and it cannot survive in the high salinity of sea water.

Zero population growth rate refers to the situation when the number of deaths and emigration is equal to the number of births and immigration in a give period of time.