The correct answer is (a.) less dense than. The water in the Gulf of Mexico is less dense than the water near arctic regions. The Gulf Mexico is an ocean that has been largely surrounded by the continent of North America. The Gulf of Mexico was a result of the plate tectonics 300 year ago.
The presence of the receptor in a cell for a particular hormone decide whether the cell is able to respond to a hormone. Cells which do not have a receptor are not directly influenced by hormone.
Although in many regions of the brain—particularly those that give rise to nuclear cell groups—neurons migrate without the benefit of glial guides, migration along radial glial fibers is always seen in regions where cells are organized into layers, like the cerebral cortex, hippocampus, and cerebellum.
competition, predation, commensalism, mutualism and parasitism.
Answer:
Sponges are a very much important to this biological world. They are very much important in nutrient cycles in the coral reef systems and highly help in supporting the marine food web. Economically they are treated as protective habitats for animals like crustaceans, molluscs, small fishes, etc.