I'm writing a lab report, and if anyone could explain to me the dark cycle and the light cycle in photosynthesis and the differences between the two, that would be great. I read the chapter in my book and it doesn't really help me all that much.

Hope you have your answer to this one. Photosynthesis is no more than combining carbon dioxide, water, and sunlight and giving off the byproducts of glucose, oxygen, and energy in the form of ATP. The circles you may be referring to are no more than graphics to help understand the cycle.

Hope this helped and not too late

Might be a difference in what is happening at night verse daylight activity which would be when the chlorophyll is being activated by the light to produce glucose if I recall correctly. At night, I think that glucose (c2 h12 o6) may then be converted to other products for the plants use, storage, and removal of waste. Also seem to recall something about a resting period to allow the plant to be ready to perform photosynthesis again when stimulated with the light.

Forgive me if not totally accurate, it's been nearly 25 years since I had that class.

(DARK CYCLE)During photosynthesis, light energy is used to generate chemical free energy, stored in glucose. The light-independent Calvin cycle, also (misleadingly) known as the "dark reaction" or "dark stage", uses the energy from short-lived electronically-excited carriers to convert carbon dioxide and water into organic compounds that can be used by the organism (and by animals which feed on it). This set of reactions is also called carbon fixation. The key enzyme of the cycle is called RuBisCO. The enzymes in the Calvin cycle are functionally equivalent to many enzymes used in other metabolic pathways such as gluconeogenesis and the pentose phosphate pathway, but they are to be found in the chloroplast stroma instead of the cell cytoplasm, separating the reactions. They are activated in the light (which is why the name "dark reaction" is misleading), and also by products of the light-dependent reaction. These regulatory functions prevent the Calvin cycle from operating in reverse to respiration, which would create a continuous cycle of carbon dioxide being reduced to carbohydrates, and carbohydrates being respired to carbon dioxide. Energy (in the form of ATP) would be wasted in carrying out these reactions that have no net productivity.

(LIGHT CYCLE)The light reaction happens in the thylakoid membrane and converts light energy to chemical energy. This chemical reaction must, therefore, take place in the light. Chlorophyll and several other pigments such as beta-carotene are organized in clusters in the thylakoid membrane and are involved in the light reaction. Each of these differently-colored pigments can absorb a slightly different color of light and pass its energy to the central chlorphyll molecule to do photosynthesis. The central part of the chemical structure of a chlorophyll molecule is a porphyrin ring, which consists of several fused rings of carbon and nitrogen with a magnesium ion in the center. The energy harvested via the light reaction is stored by forming a chemical called ATP (adenosine triphosphate), a compound used by cells for energy storage. This chemical is made of the nucleotide adenine bonded to a ribose sugar, and that is bonded to three phosphate groups. This molecule is very similar to the building blocks for our DNA.

Your welcome glad to help!