Photosynthetic reactions occur in the grana and stroma of chloroplasts.
Thylakoids of grana are the sites for light reactions of photosynthesis.
The granum (plural grana) is a stack of which contains the photosynthetic pigments; this is where the light dependent stage takes place:
The invention of the microscope enabled Robert Hooke, (1665) and Anton van Leuwenhoek (1675) to see and draw the first 'cells', a word coined by Hooke to describe the cells in a thin slice of cork, which reminded him of the rooms where monks lived.
Photosynthesis can be divided into two parts: the light reactions and the light-independent reactions (also referred to as the "dark" reactions). This tutorial will cover the light reactions. This is when light energy is transformed into energy that can be used by cells. The next tutorial will cover the light-independent reactions, which is when sugar is actually made.
By the end of this tutorial you should have an understanding of:
This brings us back to the third question posed about light. What happens when light reaches another object? We have all seen light reflect off of a mirror, hence we can see ourselves. We have also avoided wearing a black shirt (compared to a white shirt) in the summer because of the heat it absorbs. These two properties of reflection and absorption can help us to understand how plants use light.
Because light consists of photons of energy, reflection can be thought of as photons bouncing off of a leaf. However sometimes the photons of light are absorbed by the leaf to do work. Pigments are compounds that absorb light. Different pigments absorb different wavelengths of light. If a structure (e.g., a leaf) lacks pigments that absorb light in a given wavelength range, then that wavelength of light will be reflected. In other words, the color perceived is that which is not absorbed.
Along with these components, starch and lipid globules as well as ribosomes, enzymes and ions are present in the stroma.
Grana and stroma play an important role in photosynthesis and photorespiration.
In eukaryotes the light reactions of photosynthesis occur in the thylakoids of chloroplasts. Chloroplasts appear as stacked structures. These stacks are called grana, which consist of thylakoids that are actually flattened membranes. Thylakoids house the essential components of the light reactions of photosynthesis. The thylakoid is covered with several types of pigments arranged in photosystems. (This figure depicts chlorophyll molecules embedded in a photosystem.) There are two types of photosystems, and each consists of a few hundred pigment molecules.