One of the major categories of receptors in the plasma membrane reacts by forming dimers. name this major category

Receptor Tyrosine Kinase

Explanation:

Tyrosine kinase receptor has a transmembrane spanning domain, an extracellular N terminal domain and an intracellular C terminal domain. It is a kinase receptor which means it phosphorylates the substrate molecule. When a ligand binds to the extracellular domain of the receptor, the receptor dimerizes.

Due to dimerization, the cytoplasmic kinase domains of the receptor are activated. Tyrosine residues of one receptor molecule are phosphorylated by the kinase activity of the partner receptor molecule hence it is called as trans phosphorylation. Due to phosphorylation, binding sites are created on receptor for various types of protein which leads to a signalling cascade.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.

i think its both a and b