Plant Nutrition and Importance of Photosynthesis

The external environment provides the necessary conditions for metabolic activities such as respiration, growth, excretion, and reproduction.

Photosynthetic or holophytic nutrition refers to the process in which green plants manufacture their own organic food from simple inorganic substances such as carbon dioxide, water, sunlight, and chlorophyll while producing oxygen as a by-product. The following equation can summarize this process:

6CO2 + 6H2O + sunlight energy + chlorophyll → C6H12O6 + 6CO2

Photosynthesis occurs in two stages: the light reaction and the dark reaction.

The light reaction, which depends on light, involves the absorption of light energy by chlorophyll. This energy is used to split water into hydroxyl (OH-) and hydrogen (H+) ions through a process called photolysis. The significance of this stage is to convert light energy into chemical energy in the form of ATP (Adenosine Triphosphate) and reduced NADP (Nicotinamide Adenine Dinucleotide Phosphate). In the absence of light, this energy is converted into chemical energy in organic compounds.

Sunlight and chlorophyll play important roles in the light reaction. Water molecules are split into hydroxyl and hydrogen ions, and some electrons, which have lost their energy, combine with hydrogen ions to form hydrogen atoms. These hydrogen atoms are then used to reduce the hydrogen acceptor NADP, converting it into NADPH2. The hydroxyl ion (OH-) donates an electron to stabilize the unstable chlorophyll+ ion, forming water and oxygen. The oxygen is released as a waste product of photosynthesis and diffuses into the atmosphere.

In the dark reaction stage, sugars are synthesized from hydrogen and carbohydrates through a series of complex reactions involving enzymes. Carbon dioxide combines with a five-carbon sugar (ribulose diphosphate) to produce two molecules of phosphoglyceric acid (PGA). The phosphoglyceric acid is then converted into carbohydrates in the presence of ATP and NADPH2. Additionally, proteins and fats are produced as other products of photosynthesis according to the plant’s needs.

The primary product formed during photosynthesis is simple sugar. The plant uses some of the sugar immediately, while the excess is converted into starch for storage. Starch is then transported to other parts of the plant through phloem vessels in a process called translocation.

15 Importance of Photosynthesis

Photosynthesis is of utmost importance for various reasons:

1. Production of Oxygen: Photosynthesis is responsible for the production of oxygen gas (O2) as a by-product. Oxygen is vital for the survival of all aerobic organisms, including humans. It serves as a key component in the process of respiration, enabling organisms to release energy from organic molecules.

2. Carbon Dioxide Reduction: Photosynthesis plays a crucial role in reducing atmospheric carbon dioxide (CO2) levels. Through the process of photosynthesis, plants absorb carbon dioxide from the environment and convert it into organic compounds, such as sugars and carbohydrates. This helps in mitigating the greenhouse effect and regulating the Earth’s climate.

3. Food Production: Photosynthesis is the primary source of energy for the majority of living organisms on Earth. Green plants, algae, and some bacteria are capable of synthesizing their own food using sunlight, water, and carbon dioxide. The organic compounds produced during photosynthesis serve as a fundamental food source for herbivores, which are then consumed by carnivores and omnivores, forming the basis of the food chain.

4. Energy Storage: The process of photosynthesis converts light energy from the sun into chemical energy in the form of glucose and other organic compounds. Plants store this energy in the form of carbohydrates, such as starch. These energy-rich compounds serve as a reservoir for future energy needs, enabling plants to grow, reproduce, and survive during periods of limited sunlight or adverse conditions.

5. Ecological Balance: Photosynthesis plays a vital role in maintaining ecological balance and biodiversity. Plants serve as primary producers, converting inorganic substances into organic matter. This energy flow sustains the entire ecosystem, supporting the growth of other organisms and maintaining the intricate web of life on Earth.

6. Oxygen Production in Aquatic Ecosystems: Photosynthetic organisms, such as algae and phytoplankton, contribute significantly to oxygen production in aquatic ecosystems. These organisms carry out photosynthesis in water bodies, releasing oxygen that supports the survival of aquatic organisms and maintains the health of marine ecosystems.

7. Medicinal and Industrial Applications: Many plant-based compounds produced through photosynthesis have significant medicinal and industrial applications. These include essential oils, pharmaceutical drugs, biofuels, dyes, fibers, and various biomaterials. Photosynthesis provides the foundation for harnessing these valuable resources.

8. Atmospheric Oxygen Balance: Photosynthesis helps maintain the balance of atmospheric oxygen levels. It counteracts the oxygen consumption that occurs through processes such as respiration, combustion, and decay. Without photosynthesis continuously replenishing atmospheric oxygen, oxygen levels would gradually decrease, making it difficult for many organisms to survive.

9. Climate Regulation: Photosynthesis plays a critical role in regulating global climate patterns. Through the absorption of carbon dioxide, plants help stabilize and reduce the concentration of this greenhouse gas in the atmosphere. This helps mitigate the greenhouse effect, which contributes to climate change. By sequestering carbon, photosynthesis assists in regulating Earth’s temperature and maintaining climatic stability.

10. Soil Conservation: Photosynthetic plants, particularly those with extensive root systems, help prevent soil erosion. The roots of plants hold the soil together, preventing it from being washed away by water or blown away by wind. This helps maintain soil fertility, prevents nutrient loss, and protects against desertification.

11. Oxygen for Aquatic Life: Photosynthesis in aquatic ecosystems, including marine plants and algae, contributes significantly to oxygen production. Underwater photosynthetic organisms release oxygen through the same process as terrestrial plants, sustaining the oxygen levels necessary for the survival of aquatic life forms such as fish and other organisms.

12. Biodiversity Support: Photosynthesis provides the foundation for biodiversity by supporting the growth of various plant species. Plants serve as habitats, food sources, and shelter for a wide range of organisms. The diverse array of plant life made possible by photosynthesis contributes to the overall biodiversity and ecological balance of ecosystems.

13. Fossil Fuel Formation: The organic matter produced through photosynthesis millions of years ago has transformed into fossil fuels such as coal, oil, and natural gas. These fossil fuels are essential energy resources that power modern society. Without the initial process of photosynthesis, these energy-dense fuels would not exist.

14. Oxygen Therapy: Photosynthesis indirectly contributes to medical treatments through the production of oxygen. Oxygen therapy is widely used to treat various respiratory conditions and to support patients with low blood oxygen levels. The oxygen used in these treatments originates from photosynthetic processes, either directly from plants or indirectly through oxygen released by photosynthetic organisms in the ocean.

15. Environmental Stewardship: Understanding the importance of photosynthesis encourages responsible environmental stewardship. Recognizing the role of plants in capturing carbon dioxide and producing oxygen emphasizes the need for sustainable practices, conservation efforts, and the preservation of natural habitats to ensure the continuity of photosynthesis and the health of ecosystems.

Overall, photosynthesis is a fundamental process with wide-ranging significance. Its impact extends from the balance of atmospheric gases and climate regulation to supporting biodiversity, energy production, and human well-being. Without photosynthesis, life as we know it would not be possible on Earth.

In summary, photosynthesis is crucial for the production of oxygen, reduction of carbon dioxide, food production, energy storage, ecological balance, oxygen production in aquatic ecosystems, and various practical applications. It is a fundamental process that sustains life on Earth and shapes the functioning of ecosystems.

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Chemosynthetic nutrition is a fascinating process employed by certain bacteria, known as autotrophs, to produce their own food using simple inorganic substances. Unlike photosynthetic organisms that rely on sunlight as their primary source of energy, chemosynthetic bacteria harness the chemical energy released during specific chemical reactions.

One notable example of chemosynthesis is demonstrated by sulfur bacteria found in soil environments. These bacteria possess specialized enzyme systems that enable them to utilize hydrogen sulfide (H2S) as a source of energy. Through a series of reactions, they oxidize hydrogen sulfide in the presence of oxygen (O2), resulting in the release of chemical energy.

The chemical equation representing this process is:

2H2S + O2 → S + 2H2O + Chemical energy

During this reaction, two molecules of hydrogen sulfide combine with one molecule of oxygen, producing sulfur (S) and two molecules of water (H2O) as by-products. The most significant outcome of this reaction is the release of chemical energy, which is harnessed by the bacteria for various metabolic activities.

The enzyme systems within the bacteria play a crucial role in trapping and utilizing the chemical energy derived from these reactions. They have evolved to efficiently capture and store this energy, enabling the bacteria to synthesize organic compounds necessary for their growth and survival.

Chemosynthetic bacteria are typically found in unique environments such as deep-sea hydrothermal vents, volcanic areas, or sulfur-rich soils, where sunlight is scarce or absent. In these extreme environments, chemosynthesis serves as a vital energy source, supporting the existence of diverse microbial communities and contributing to the overall ecosystem dynamics.

The discovery and study of chemosynthetic bacteria have expanded our understanding of the remarkable adaptability of life forms and their ability to thrive in seemingly inhospitable environments. These organisms provide insights into alternative mechanisms for energy acquisition and nutrient cycling, highlighting the diverse strategies employed by living organisms to sustain themselves in different ecological niches.

Experiments to test for photosynthesis

Experiment 1

Aim: To test for the presence of starch in the leaf

Material Required: Fresh leaves from the outdoor plant, beaker, boiling tubes, dropping tube, white tile and iodine solution.

Method: First boil the leaf in water for 4-6 minutes so as to

(i)         Kill the cell

(ii)        To inactivate the enzyme

(iii)       To burst starch grain present

Then dip the leaf into a test tube containing 90% alcohol to decolorise the leaf. After that, the leaf is dipped into water to soften it later pour a few drops of iodine solution on the leaf in the control experiment a leaf from a plant kept in the dark cupboard is plucked and tested for starch.

Observation: The leaf that was plucked from the potted plant outside turned blue-black with an iodine solution while the other leaf control experiment remained colorless.

Conclusion: Since the leaf in the real experiment has turned blue-black with the iodine solution, it shows that photosynthesis has taken place or starch is present in the leaf.

Experiment II

Aim: To show that sunlight is necessary for photosynthesis

Material Required: A potted plant, strip of black, paper, clips, cupboard

Method: The potted plant is first de-starched by putting it in a dark cupboard for 1-2 days. This is to remove all the traces of starch formed in the leaves. After this, the middle of one of the leaves is covered by a strip of black paper, both at the front and back with the acid of a clip. The whole plant is then placed in sunlight.

After about 3-5 hours, the paper is removed, and the leaf is then tested for starch.

Observation: Only the exposed parts turned blue-black with the iodine solution which shows the presence of starch while the area that was covered with black paper will remain colorless showing that starch is absent

Conclusion: The experiment shows that sunlight is necessary for photosynthesis

Experiment III

Aim: To show that carbon (iv) oxide is necessary for photosynthesis

Material Required: A potted plant, Vaseline, conical flask, split cork, retort stand, and caustic soda (sodium hydroxide solution)

Method: Use a leaf attached to a potted plant. The leaf is enclosed in the conical flask and contains a caustic soda solution. The solution will absorb any traces of carbon (iv) oxide inside the flask. The flask’s mouth is corked and smeared with Vaseline at the neck to make it airtight. The whole experiment is now exposed to sunlight for several hours. Two leaves (one from the flask) and the other outside the flask (control experiment) are plucked and tested for starch.

Observation: After testing the leaf inside the flask did not show a blue-black color indicating the absence of starch formation because of lack of carbon (iv) oxide inside the flask while the leaf outside has a positive test

Conclusion: The experiment emphasizes the importance of carbon (iv) oxide in photosynthesis to take place

Experiment IV

Aim: To show that chlorophyll is necessary for photosynthesis

Material Required: A variegated plant like croton, coleus, or acalpha plant. A variegated plant has green and white patches on the leaf.

Method: The potted variegated plant is exposed to sunlight for about 3-5 hours after which a variegated leaf is plucked fresh from the plant during the daytime when there is sunlight. The variegated leaf is tested for starch

Observation: It will be noticed that the green plants of the variegated leaf are stained blue-black with iodine solution while the parts remain colorless

Conclusion: The experiment shows that chlorophyll is necessary for photosynthesis to take place

Experiment V

Aim: To show that oxygen is given out as a by-product during photosynthesis

Material Required: A water plant e.g. Elodea, glass funnel, beaker, water, test tube, glowing splinter

Method: An elodea plant is kept in a beaker filled with water. This is followed by filling the test tube with water and then inverting it over the stem of the funnel. The whole set-up is then placed in the sunlight for several hours. Tiny bubbles of gas will start to appear on the surface of the leaves and accumulate at the top of the test tube. The gas is tested with a glowing splinter

Observation: It will be seen that the gas formed at the top of the tube rekindles a glowing splinter showing the presence of oxygen.

Conclusion: The experiment shows that oxygen is given off a by-product during photosynthesis

Read also:

Growth | Mitosis, Aspect of Growth, Hormones, Animal

Ecology | Definition, Concept, Components, US Ecology

Nutrition: Autotrophic, Heterotrophic, COMMENSALISM, CARNIVOROUS PLANT

Food Substance: Carbohydrates, Proteins, Fats and Oils, Mineral Salts, Vitamins & Water

Nutrient Cycle, Carbon Cycle & Water Cycle

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