Skip to content
2.73K viewsGeneral

What is photosynthesis?

Print Friendly, PDF & Email
Changed status to publish

 The short answer to this question is: Photosynthesis is the process used by plants, algae, and certain bacteria to harness energy from sunlight and carbon dioxide into chemical energy in the form of sugar (glucose) and oxygen as a byproduct. 

Although there are several steps involved in the process, the following is the main formula.

6 CO2 + 6 H2O + light → C6H12O6 + 6 O2

Carbon Dioxide + Water + Light  ⇒Glucose + Oxygen

Carbon Dioxide + Water + Light ⇒Glucose + Oxygen

The process

In a plant, the carbon dioxide enters via leaf stomates by diffusion. Water is absorbed through the roots and is transported to leaves through the xylem. Solar energy is absorbed by chlorophyll in the leaves. Photosynthesis occurs in the chloroplasts of plants. In photosynthetic bacteria, the process takes place where chlorophyll or other pigment is embedded in the plasma membrane. The oxygen and water produced in photosynthesis exit through the stomata.

Plants reserve use only a small portion of the glucose immediately. Glucose molecules are combined by dehydration synthesis to form cellulose, which is used as a structural material. Dehydration synthesis is also used to convert glucose to starch, which plants use to store energy.

The stages

6 CO2 + 6 H2O + light → C6H12O6 + 6 O2   does not happen all at once. 

Tere are two distinct phases:

Dark and Light phases

The light reactions use light, while the dark reactions use enzymes.  It is important to clarify that dark reactions don’t necessarily require dar. However, they do not depend on light to occur.

The light reactions absorb light and harness the energy to powder electron transfers. Most photosynthetic organisms capture visible light, although there are some that use infrared light.

Products of these reactions are adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). In plant cells, the light-dependent reactions occur in the chloroplast thylakoid membrane. The overall reaction for the light-dependent reactions is:

2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2

In the dark stage, ATP and NADPH ultimately reduce carbon dioxide and other molecules. Carbon dioxide from the air is “fixed” into a biologically usable form, glucose. In plants, algae, and cyanobacteria, the dark reactions are termed the Calvin cycle. Bacteria may use different reactions, including a reverse Krebs cycle. The overall reaction for the light-independent reaction of a plant (Calvin cycle) is:

3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O

During carbon fixation, the three-carbon product of the Calvin cycle is converted into the final carbohydrate product.

Factors That Affect the Rate of Photosynthesis

1. availability of the reactants

It is understandable that the rate of photosynthesis depends on the amount of (ingredients so to speak)reactants. determines the number of products that can be made. Reducing the amount of carbon dioxide or water slows the production of glucose and oxygen.

2. temperature

The rate of any chemical reaction is affected by temperature and photosynthesis is no different.

3. Health of the plant or another organism

The plant or bacteria in which the photosynthesis is happening is analogous to the factory that produces a certain product.  Following that same factory analogy, If there are plenty of ingredients or raw materials but the building and machinery are at capacity or not in good condition, the production rate would be affected. The same thing happens with plants or other organisms and photosynthesis. The more optimal the health of the organism, the higher the rate of photosynthesis.

There are technically three types of photosynthesis but basically two pathways of photosynthetic processes:  light or oxygenic photosynthesis and dark anoxygenic photosynthesis.  Light/Oxygenic photosynthesis is the most common We find it in plants, algae, and cyanobacteria.

During light oxygenic photosynthesis, light energy transfers electrons from water (H2O) to carbon dioxide (CO2), which produces carbohydrates. During this reaction, the CO2 is “reduced,” or receives electrons, and the water becomes “oxidized,” or loses electrons. Ultimately, oxygen is produced along with carbohydrates.

Light photosynthesis can be seen as the other side of the respiration coin so to speak; it takes carbon dioxide produced by all breathing organisms and produces oxygen to be used by all living organisms.

Dark photosynthesis uses electron donors other than water and typically occurs in bacteria such as purple bacteria and green sulfur bacteria.

Dark or Anoxygenic photosynthesis bears the name it does because it does not produce oxygen. Instead, it produces other substances depending on the particular electron donor. Sometimes the product is bad smelling gas.

O+ 2H2A + Light Energy → [CH2O] + 2A + H2O   is the generic formula for Anoxygenic photosynthesis.

6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O is the generic formula for Oxygenic photosynthesis





Print Friendly, PDF & Email
Changed status to publish
Scroll To Top