Question

Photosynthesis is divided into two sets of reactions (light-dependent and light-independent). Photosystem I and photosystem II are both light-dependent reactions while the Calvin cycle is light-independent. How are the light-dependent and light-independent reactions similar?
A) Both reactions rely on chemical energy.
B) They take place in the stroma of the chloroplast.
C) Both need light energy at all times in order to occur.
D) They occur in the thylakoid membranes of the chloroplast.

Answer 1

Answer:

D

They occur in the thylakoid membranes of the chloroplast.

Answer 2

Answer:

A) Both reactions rely on chemical energy.

Explanation:

The light-dependent phase of photosynthesis occurs in the chloroplasts' tilacoid membrane, the capture of light energy and the transformation into chemical energy. In this process, the green pigment molecules go into an excited state, emitting part of the absorbed energy. These pigments are organized into two photosystems (I and II), which can be defined as light capture units present in thylacoids.

In this phase, light energy is absorbed by pigments in photosystem II and transferred to chlorophyll molecules in the reaction center. The energized electrons are transferred to an electron receiver. According to the transfer of these electrons, they are replaced by others from water photolysis. Here, too, oxygen is produced.

Some pairs of electrons pass to photosystem I stimulating ATP synthesis. The energy absorbed at that moment stimulates the chlorophyll molecules of the reaction center of this photosystem, and the energized electrons are accepted by a NADP + molecule. The electrons removed from chlorophyll are replaced by others from photosystem II.

The independent light phase occurs in the chloroplast stroma and also depends on the chemical energy. It starts with the process of fixing carbon in an organic compound. In this stage, the molecules of NADPH and ATP produced in the light phase are used for the production of sugars from the reduction of the fixed carbon. The reactions that occur here are called Calvin Cycle and, in the process, most of the fixed carbon is converted into sucrose or starch.