There are dash biologically important ones and they are joined together by bonds called dash bonds

Organic molecules: are biologically important ones.All macro molecules are made up of simple molecules (monomers) that are bounded by specific bonds .Biologicaly important molecules are proteins ,fats ,carbohydrstes and nuclic acid.All these molecules are formed by condensation of monomers.

proteins: Proteins are made up polymers of amino acids. Aminoacids ae joined together by peptide bond.

A peptide bond is a chemical bond formed between two amino acid molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule and  releasing a molecule of water (H2O).

Carbohydrates: are biological important one are made up of    monosaccharides and the are joined together by glycosidic bond.

Fats: are made up of fatty acids are joined together by covalent bonds called ester bond . Saturated fatty acids are bound by single anu unsaturated are made up of double or triple bonds.

Nucleic acid: are made up of nucleotides .Nucleotides are joined together  by chemical bond called hydrogen bond.It is formed between the phosphate group of one nucleotide and the sugar of a neighboring nucleotide holds the backbone together.

d. changes in climate and historical records

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answer; motor (efferent)neurons;