SBI 4U1 Cohen
The Effects of Light Intensity on the Rate of Photosynthesis in Green Cambomba
Bill Crothers Secondary School
Prepared for Mr. Pearce
By: Gabby Cohen
Factors Affecting the Rate of Photosynthesis in Green Cambomba
Light is a form of electromagnetic radiation, and is a type of energy that travels in waves. Photosynthetic organisms like plants, contain light-absorbing molecules called pigments that absorb only specific wavelengths of visible light (Khan Academy, 2017). Photon light comes from the sun, which enters the plant through its leaves, starting from the top of the leaf through the cuticle and the upper epidermis (which is thin and transparent to allow more light to reach the palisade cells), then through the palisade mesophyll. In the cell, the light travels through the cell membrane and into the chloroplasts, and then the thylakoid membranes, where it finally gets absorbed by the electrons in the pigment molecules (BBC, 2014).
The structure of a photosystem consists of a large antenna complex which contains proteins and pigment molecules surrounding a reaction centre, and its function is to assist in the light reaction process of photosynthesis by absorbing photon light, which gets transferred through electrons from pigment molecule to pigment molecule, to end up at the reaction centre where the electron is stolen from the primary electron acceptor. In photosynthesis, the light reactions begin at photosystem II, where electrons in the pigment molecules absorb light energy from the photons (sunlight) and become excited, jumping up an orbital and then returning to ground state, releasing this energy in the form of light to a different electron in a nearby pigment molecule and that electron then becomes excited. This process continues until the energized electron from the last pigment molecule reaches the reaction center. At the reaction center, electrons get excited and stolen by the primary electron accepter and move through the proteins due to increasing electronegativity onto photosystem I. Photosystem II is now down two electrons which get replenished from the splitting of water into ½ O2 and 2H+ (H+ that get released increase [H+] in the thylakoid space). Electrons travelling through the proteins, power the proton pumps to actively transport H+ form the stroma into the thylakoid space, forming the electrochemical gradient as H+ and in [high] in the thylakoid space and [low] in the stroma, and the electrons end up at photosystem I. The same process occurs at photosystem I, except that electrons entering the reaction center come from photosystem II, and not water. After electrons get accepted by the primary electron acceptor, NADP+ gets reduced (gaining e- from the last protein) with a H+ from the stroma into NADPH (which lowers [H+] in stroma). Due to the electrochemical gradient, H+ are forced through ATP synthase, which want to reach equilibrium with H+ in the stroma, and this powers ATP synthase to...