Photosynthesis and Light and Dark Reactions

Photosynthesis is a process in which plants and other organisms use sunlight in order to make food from carbon dioxide and water. 

The process for plants would be carbon dioxide plus water plus sunlight turn it into sugar or carbohydrates plus oxygen. 

The formula for Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2

                                                Carbon Dioxide + Water     →  Glucose +Oxygen

                                                                          Light 

For Photosynthesis to work, photosynthesis needs to be broken down. There are two stages for photosynthesis to be broken down.

Breaking Down Photosynthesis: 

Two Stages:

 ➔ Light reactions aka light-dependent meaning that they need light to occur; need photons and water. The light reaction produces oxygen, ATP and NADPH which can be used in dark reactions.

 ➔ Dark reactions aka Calvin Cycle and can also be known as light-independent reactions meaning that it still occurs in the light but that part isn’t dependent on Photons; it doesn't need light. Takes ATP, NADPH and produces PGAL or G3P in the Calvin cycle.

● PGAL = phosphoglyceraldehyde 

● G3P = Glyceraldehyde 3 phosphate

Light reactions need light/sunlight in order to proceed but the dark reaction does not need light, it occurs when the sun is out and they don’t need the photons but needs the byproducts. In both stages of Photosynthesis, the chloroplast is involved in both stages. A Chloroplast is an organelle in the cells of the plant that is where photosynthesis occurs and needs energy in order to grow. Chloroplasts are important because they are needed in order for photosynthesis to occur and without energy then the plant won’t be able to grow. 

Image of Chloroplast below

Light Reaction

Light reactions are light-dependent and need light. Light reactions occur in the thylakoid discs. Thylakoid discs are one disc of a granum. A Granum is a stack of discs and the thylakoid is one of the discs. The discs are important because they trap the energy from the sunlight and that energy trapped is used in the Calvin cycle in order to fix carbon from CO2 and create sugar. In light reactions, water is oxidized and oxygen is released. The electrons are then transferred to ATP and NADPH. The goal of light reactions is to collect energy from sunlight and break down the water molecules in order to produce ATP and NADPH. Once ATP and NADPH are produced then the next stage is the Calvin Cycle.

Dark Reaction

Dark Reactions are also known as the Calvin Cycle. Which is the second stage of photosynthesis and does not require light. The Calvin Cycle occurs in the stroma of the chloroplast. Stroma is the inner liquid portion of the chloroplast. Energy from ATP and NADPH is used to combine carbohydrates molecules such as glucose from carbon dioxide. The product of the Calvin cycle is sugar which is then regenerated and used again in the light-dependent reactions which is the light reaction. 

Photosynthesis is important for plants because plants do photosynthesis in order to create carbohydrates from inorganic substances so that the plant can have energy in order to grow and make their food. While humans eat food in order to get energy, plants need energy through photosynthesis in order to make their food. So, without photosynthesis plants won't be able to grow, have energy or have carbohydrates for respiration.