The number of individuals of a species in a particular ecosystem at a given time remains constant due to

In an association of two animal species,one is a termite which feeds on wood and the other is a protozoan $Trichonympha$ present in the gut of the termite. What type of association do they establish?

In which of the following interactions are both partners adversely affected?

Which one of the following population interactions is widely used in medical science for the production of antibiotics?

Match the pairs of partners showing interspecific interaction from Column-$I$ and Column-$II$:

Column-$I$	Column-$II$
$a$. Sea anemone	$i$. Cyanobacteria
$b$. Plant	$ii$. Man
$c$. Plasmodium	$iii$. Herbivore
$d$. Fungi	$iv$. Clown fish

Match the following columns:

Column-$I$	Column-$II$
$P$. Calotropis	$I$. Special chemical
$Q$. Cactus and Acacia	$II$. Camouflage
$R$. Monarch butterfly	$III$. Thorns
$S$. Some species of insects and frogs	$IV$. Glycosides