BIOL 101 Homework Learn It Pigments and Photons solutions complete answers
Learn It: Explain how pigments absorb and transfer the energy in photons.
Light energy and chemical energy are two very different forms of energy. Light energy is a type of electromagnetic energy that carries energy in waves. Chemical energy is the energy of electrons in molecular bonds. Sunlight is the main energy source for living things on Earth, but we need chemical energy to stay alive. So how does that work? Green plants are able to convert light energy to chemical energy through the light-dependent reactions of photosynthesis.
Light-dependent reactions take place in the thylakoid membrane of the chloroplast, which contains groups of molecules called photosystems. The photosystems contain molecules of a green pigment called chlorophyll that absorb energy from specific wavelengths of light. Chlorophyll transfers the light energy to low-energy electrons and charges them like a battery. This results in high-energy or "excited" electrons, which escape from the photosystems and move through electron transfer chains (ETCs). The ETCs use the electrons' energy to store chemical energy in two high-energy molecules, ATP and NADPH.
These two molecules, ATP and NADPH, are actually produced by two different photosystems and ETCs (see the figure): First, photosystem II receives low-energy electrons from water, charges them with light energy, and passes them to an ETC that uses their energy to make ATP. Then photosystem I picks up the used electrons, recharges them with light energy, and passes them to another ETC, where they are picked up by NADPH.
Once ATP and NADPH have been produced, the light-dependent reactions have done their job. Light energy has been transformed into chemical energy, and that energy is available for the light-independent reactions of the Calvin cycle.
Photosystems use light energy to energize electrons. ETCs use the high-energy electrons to store chemical energy in ATP and NADPH.
In photosynthesis, what is the function of light-dependent reactions?
To move energy from water into ATP and NADPH
To collect high-energy electrons from sunlight and store them as chemical energy
To transform wave energy into light energy
To transform light energy into chemical energy
A molecule that absorbs the energy in specific wavelengths of light is called which of the following?
NADPH
A photosystem
The ETC
A pigment
Light-dependent reactions store chemical energy in which of the following?
ATP and NADPH
The ETC
Chlorophyll
Pigments
What is the ultimate source of the electrons that are transferred during the light-dependent reactions of photosynthesis?
ATP
NADPH
Water
Oxygen
Excited electrons have energy than non-excited electrons. Electrons in the photosystems of plants are excited by
