2 or more different atoms are combined in definite proportions in any compound.
Answer: Substances that are protein based cannot cross the lipid cell membrane, but can exert their effect by binding to the proteins based receptors present on the lipid bilayer.
Explanation:
Hormones such as calcitonin , Parathyroid hormone and pituatry horomones are proteins and water soluble.They cannot cross lipid bilayer but can bind to ligand binding protein receptors.
These receptors are protein macromolecules that are specific in nature for specific hormones.
After binding to the receptors, these hormone-recpetor complexes activate second messengers and regulate the downstream effects.
Objects with like charges repel/repulse each other while opposite charges attract each other
The direction of an electric fields is alway the direction electrons would naturally move.
Not sure about the last one, my gut instinct is opposite.
C
A Land mass is large geographical area that is surrounded by oceans. Therefore this can be synonymous to continents.
Explanation:
The crust is divided into tectonic plates that are dynamic because they move on top of the semi-plastic mantle. The movement of the tectonic plates is driven by the convection currents of the mantle that drag along the crust above. The tectonic plates collide at convergent boundaries where tectonic plates are consumed as one is subsided into the mantle. On the other hand, new crust is formed at divergent boundaries where two tectonic plates move away from each other and magma rises from the mantle and cools into new crust.
The convection currents occurs because the lower mantle is hotter and less dense compared to the cooler denser upper mantle. Therefore the upper mantle always tends to sink as the lower mantle rises. These convection currents are the same as in any other fluids that are disproportionately heated.
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