Signal transduction: .
a. relies on the uptake of an external signal molecule from the cell.
b. relies on the release of an internal signal molecule from the cell.
c. relies on cell surface proteins changing shape.

a) relies on the uptake of an external signal molecule from the cell

Explanation: Signal transduction is known as the transmitting of any signal of a molecule from exterior of cell to interior of cell.This technique is termed as critical is taken care of successful transmission of signal effectively and positive result and reception is done by the cell surface receptors.It is also known as cell signalling. Thus,option(a) is the correct option of all.

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the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.