STD 12 - 11. organisms and populations — BIOLOGY STD 12 Science — Question

$(a)\; DNA$ is negatively charged molecule and so it is loaded on gel towards the Anode terminal

$(b) \;DNA$ fragments travel along the surface of the gel whose concentration does not affect movement of $DNA.$

$(c)$ Smaller the size of $DNA$ fragment larger is the distance it travels through it.

$(d)$ Pure $DNA$ can be visualized directly by exposing UV radiation.

Choose correct answer from the options given below

$(1)$ Many members of the genus glomusinvolved micorrhiza

$(2)$ It is responsible for all mineralsabsorption from the soil

$(3)$ Such associations show benefitsagainst draught and salinity in plants

$(4)$ Micorrhiza is a symbiotic relation ofalgae and plants

$I$. Removal of $80\; \%$ tigers from an area resulted in greatly increased growth of vegetation.

$II.$ Removal of most of the carnivores resulted in an increased population of deers.

$III.$ The length of food chains is generally limited to $3$ to $4$ trophic levels due to energy loss.

$IV.$ The length of food chains may vary from $2$ to $8$ trophic levels.

Which two of the above statements are correct?