Key Steps of Photosynthesis and Why They Matter
Photosynthesis is the process of capturing light energy and transforming it into chemical energy. Green plants and several other organisms use light energy and convert carbon dioxide and water into glucose. In this process, oxygen is produced as a by-product. This process can be seen in green plants and photosynthetic bacteria. They use electromagnetic radiation and convert it into chemical energy. With the help of water and sunlight, they absorb carbon dioxide from the atmosphere and turn it into oxygen and carbohydrates.
The process provides not only energy needed but also helps in forming biomolecules. This reaction is an oxidation-reduction reaction that uses sunlight and nitrogen available in the atmosphere. It is the basic element in the food cycle. All the other organisms derive their energy from green plants and other photosynthetic bacteria. Hence, these plants are called autotrophs as they prepare their own food with the help of naturally available elements. One of the essential requirements for this process is a pigment called “chlorophyll”. This pigment is present in green plants and some bacteria. It helps in tapping sunlight and starting the entire process.
This process of converting light energy to other forms differs in plants and other bacteria. In the case of plants, water is used to form energy in the form of glucose and oxygen. On the other hand, in the case of bacteria, hydrogen sulphide replaces the water along with carbon dioxide to release carbohydrates, sulfur, and water molecules. Some of the photosynthetic pigments are chlorophyll, phycobilins, bacteriorhodopsin, carotenoids. Chlorophyll is present in most green plants and helps in receiving sunlight and converting it into energy and glucose. They have single and double bonds alternatively, this makes them effective photoreceptors. Bacteriorhodopsin is another photosynthetic pigment that is generally present in Halobacteria. Phycobilins are present in cyanobacteria and red algae.
The photosynthesis process step by step conducts these reactions and maintains the balance of oxygen and carbon dioxide in the atmosphere. However, photosynthesis in plant leaves usually occurs in two ways. These are light-dependent reactions and light-independent reactions or dark reactions.
Light-Dependant Reaction
This process happens in the thylakoid membrane and needs a constant supply of photons or light energy. Chlorophylls use this energy and produce ATP and NADPH. Water molecules are transformed into oxygen through this process.
Light-Independent Reaction
This reaction happens in the stroma and can take place in the absence of light. It takes up ATP and NADPH produced from the light reaction to break down carbon dioxide. This process helps in forming three types of carbon sugars that create glucose.
Let’s understand the photosynthesis process step by step!
Step by Step Procedure of Photosynthesis
Fig: Process of photosynthesis
Plant leaves absorb the photons from sunlight that excite chlorophyll and activate electrons. In the first step, the water absorbed by plant roots is split into oxygen and hydrogen ions.
Then the excited electrons from ATP and NADPH. This process happens through the electron chain. Likewise, in this process, oxygen is released into the atmosphere through leaves.
In the next step, the energy from the light reaction transforms carbon dioxide into glucose. This whole process takes place in several stages. The series of reactions start with 3-Ribulose biphosphate (RuBP) and ends with the same molecule forming glucose.
The Rubisco enzyme is an essential component of this Calvin Cycle that initiates all the reactions.
All the significant reactions of the photosynthesis process generally take place during the daytime in the chloroplasts of leaves.
Following is the fundamental equation of photosynthesis
6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2
This is the overall overview of how the photosynthesis process step by step takes place.
Factors that Affect Photosynthesis
Following is the list of factors that influence the rate of photosynthesis.
Temperature and Light Intensity
Generally, with higher light and temperature intensity, the rate of photosynthesis increases. However, after a specific intensity of light, this rate saturates. It solely depends on the growing condition and species of the plants.
Water
The rate of photosynthesis depends on a steady water supply. A minimal amount of water is required to conduct the reactions. The maximum amount of water transpires through the stomata of leaves.
In arid areas, therefore, the opening and closing of stomata are limited. This allows reserving the water supply and overall temperature of leaves.
Carbon Dioxide
The concentration of carbon dioxide influences mainly the dark reactions of photosynthesis. Hence, this rate increases with the increased supply of carbon dioxide.
Minerals
A few minerals like potassium, iron, magnesium, phosphate, etc. are essential for plant growth. They also hasten the rate of photosynthesis of plants.
Apart from that, a few other factors like environment, species, etc. affect the rate of photosynthesis.
Importance of Photosynthesis
Introduce energy and fixed carbon into the ecosystem.
Reduce a large quantity of carbon dioxide from the atmosphere.
Produces oxygen that sustains all life.
Photosynthesis happens in the autotrophs, so they indirectly introduce energy into the ecosystem and that energy travels to other trophic levels
It is very important also for the heterotrophs which are dependent on autotrophs for energy.
It helps to maintain a healthy relationship between animals, plants, and humans making them mutually dependent.
Sunlight becomes the primary source of energy in the world and facilitates photosynthesis.
Pop Quiz
Photosynthesis is a/an _______________ process.
_______________ colour of light is responsible for photosynthesis in bacteria.
Which metal is present in both chlorophyll “a” and “b”?
Magnesium
Iron
Manganese
Copper
Chlorophyll is the structural unit of photosynthesis. True/False.
Answers: 1- Anabolic, 2-Red, 3-a), 4- False.
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FAQs on Photosynthesis Process: Complete Guide for Students
1. What is the process of photosynthesis?
Photosynthesis is a vital physicochemical process used by green plants, algae, and some bacteria to convert light energy into chemical energy. In this process, organisms use sunlight, water, and carbon dioxide to create their own food in the form of glucose (a sugar) and release oxygen as a by-product. It is the primary source of all food on Earth and is responsible for the oxygen in our atmosphere.
2. What is the overall chemical equation for photosynthesis?
The overall balanced chemical equation that summarises the entire process of photosynthesis is:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
This equation shows that six molecules of carbon dioxide (CO₂) and six molecules of water (H₂O), in the presence of sunlight and chlorophyll, react to produce one molecule of glucose (C₆H₁₂O₆) and six molecules of oxygen (O₂).
3. Where exactly in a plant cell does photosynthesis take place?
Photosynthesis occurs within specialised cell organelles called chloroplasts. These are mainly found in the mesophyll cells of plant leaves. Inside the chloroplast, the process is further divided:
- The light-dependent reactions happen in the thylakoid membranes (grana).
- The light-independent reactions (Calvin Cycle) happen in the stroma, which is the fluid-filled space surrounding the grana.
4. What are the key raw materials required for photosynthesis and what are its main products?
The photosynthesis process requires four essential raw materials and produces two main products.
- Raw Materials:
- Carbon Dioxide (CO₂): Obtained from the atmosphere through small pores in the leaves called stomata.
- Water (H₂O): Absorbed from the soil by the roots.
- Sunlight: The energy source, captured by chlorophyll.
- Chlorophyll: The green pigment that absorbs light energy.
- Products:
- Glucose (C₆H₁₂O₆): A sugar used by the plant for energy and growth, or stored as starch.
- Oxygen (O₂): Released into the atmosphere as a by-product.
5. What is the specific function of chlorophyll during the photosynthesis process?
Chlorophyll is the green pigment in chloroplasts that plays the crucial role of a photoreceptor. Its primary function is to absorb light energy from the sun, specifically in the blue and red regions of the light spectrum. This absorbed energy excites electrons, initiating the light-dependent reactions and converting light energy into the chemical energy needed to power the synthesis of glucose.
6. How do the light-dependent and light-independent reactions of photosynthesis differ?
The two stages of photosynthesis are distinct in their requirements, location, and products.
- Light-Dependent Reactions:
- Requirement: Directly dependent on sunlight.
- Location: Occurs in the thylakoid membranes (grana) of the chloroplasts.
- Process: Uses light energy to split water molecules (photolysis), releasing oxygen, and producing energy-carrying molecules ATP and NADPH.
- Light-Independent Reactions (Calvin Cycle):
- Requirement: Does not directly need light but depends on the products of the light reaction (ATP and NADPH).
- Location: Occurs in the stroma of the chloroplasts.
- Process: Uses the energy from ATP and NADPH to convert carbon dioxide into glucose.
7. What are the major factors that can limit the rate of photosynthesis in a plant?
The rate of photosynthesis is affected by several external factors. According to the Law of Limiting Factors, the rate is limited by the factor that is in the shortest supply. Key limiting factors include:
- Light Intensity: At low intensities, the rate is slow. It increases with intensity up to a saturation point, beyond which it can cause photo-oxidation.
- Carbon Dioxide Concentration: An increase in CO₂ concentration increases the rate, but it becomes limiting if light or temperature is low.
- Temperature: Photosynthesis has an optimal temperature range. Temperatures that are too low or too high can inactivate the enzymes involved, slowing down the process.
- Water: Water stress can cause stomata to close to conserve water, which in turn reduces the intake of CO₂ and limits photosynthesis.
8. Why is photosynthesis considered the most important process for sustaining life on Earth?
Photosynthesis is fundamentally important for two main reasons. First, it is the primary source of all food energy on the planet. Plants, as autotrophs, produce their own food, forming the base of every food chain. All heterotrophs, including humans, depend directly or indirectly on this process for energy. Second, it is the only major natural process that replenishes the Earth’s atmosphere with oxygen, which is essential for the aerobic respiration of most living organisms.
9. Can photosynthesis happen in non-green parts of a plant or in plants that aren't green?
This is a common point of confusion. Photosynthesis is tied to the pigment chlorophyll, not necessarily the colour green.
- Non-green parts: Stems, if they are green (containing chlorenchyma), can perform photosynthesis, but non-green parts like roots or woody stems cannot.
- Non-green plants: Some plants, like the red-leafed coleus, have leaves that don't appear green. However, they still contain chlorophyll. The green colour is simply masked by other pigments like anthocyanins. Photosynthesis still occurs in these leaves. True non-photosynthetic plants, called parasitic plants, lack chlorophyll entirely and steal nutrients from other host plants.
