What is a photosystem?
units of light that cause electrons to transfer to nadph during photosynthesis
the entire range of visible wavelengths in the electromagnetic spectrum
the name given to the combined light and dark reactions of photosynthesis
the group of proteins and pigments that transfers electrons to reaction centers

The group of proteins and pigments that transfers electrons to reaction centers

Explanation:

Photosystem is responsible for photosynthesis and consists of reaction center pigment and antenna complex.

ANSWER:

The correct option is D - The groups of proteins and pigments that transfer electrons to reaction centres.

EXPLANATION:

Photosystem is a protein complex that plays a major role in photosynthesis. Photosystem absorbs light or photons for the process of photosynthesis and transfers the electrons to reaction centres.

The reaction centres are the functional centres of photosynthesis. The photosystem is present in the chloroplasts and absorb light so that the process of photosynthesis can be triggered.  

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products