Plant Nutrition-7thB

Plants use the carbohydrates produced during photosynthesis as building blocks to synthesize other organic compounds, including proteins (from amino acids) and fats (lipids) for energy storage and cellular structures.

Proteins are synthesized from amino acids, which contain nitrogen. Plants combine carbohydrates (carbon skeletons) with nitrogen absorbed from the soil to form these amino acids and then proteins.

Nitrogen is a key component of amino acids, the building blocks of proteins. While carbon, oxygen, and hydrogen come from air and water, nitrogen is primarily absorbed from the soil in the form of nitrates or ammonium.

Plants convert excess carbohydrates (glucose) into fats and oils through metabolic pathways. These lipids serve as concentrated energy reserves, especially in seeds.

Seeds store fats and oils as a concentrated energy source to nourish the developing embryo during germination until it can photosynthesize independently. Examples include sunflower seeds, groundnuts, and mustard seeds.

Heterotrophs cannot produce their own food. Non-green plants like Cuscuta, Indian pipe, and some fungi depend on other organisms for nutrition, making them heterotrophic.

A parasite is an organism that lives on or within a host organism, deriving nutrients at the host’s expense. Unlike predators, parasites typically do not kill the host immediately.

The host is the organism that harbors a parasite and provides it with nourishment, often suffering harm in the process.

Cuscuta is a total parasitic plant that lacks chlorophyll and derives all its nutrition by twining around host plants and inserting haustoria into their vascular tissues.

Insectivorous (carnivorous) plants trap and digest insects to obtain nitrogen and other nutrients, typically growing in soils deficient in these elements.

In pitcher plants, the leaf is modified into a pitcher-shaped structure with a lid that contains digestive enzymes to trap and digest insects.

Insectivorous plants grow in nitrogen-deficient soils (like bogs and marshes). They trap insects to obtain nitrogen, which is essential for protein synthesis.

Venus flytrap is a well-known insectivorous plant whose leaves snap shut when trigger hairs are touched, trapping insects for digestion.

Saprotrophs (or saprophytes) feed on dead and decaying organic matter by secreting digestive enzymes externally and absorbing the nutrients.

Bread mold (Rhizopus) grows on decaying organic matter, secreting enzymes to digest it externally, making it a classic example of a saprotroph.

Most fungi are saprotrophs that obtain nutrients by decomposing dead organic matter. Some fungi may be parasitic, but saprotrophic nutrition is their predominant mode.

Saprotrophs release digestive enzymes directly onto dead organic matter to break it down into simpler substances, which they then absorb.

Mushrooms decompose the dead wood of the rotting log, absorbing nutrients from it, which makes them saprotrophs.

Symbiosis refers to a close, long-term interaction between two different species where both derive benefits. It is also called mutualism.

Lichen is a mutualistic association where the fungus provides structure, water, and minerals, while the alga performs photosynthesis to provide food.

The algal component (phycobiont) in lichen performs photosynthesis and supplies carbohydrates to the fungal partner.

The fungal component (mycobiont) absorbs water and minerals from the environment, provides structural support, and protects the alga from harsh conditions.

Rhizobium bacteria form a symbiotic relationship specifically with leguminous plants, forming root nodules where they fix atmospheric nitrogen.

The Rhizobium-legume relationship is mutually beneficial: the bacteria get carbohydrates from the plant, while the plant receives usable nitrogen fixed by the bacteria.

Nitrogen fixation is the process of converting inert atmospheric nitrogen (N₂) into ammonia (NH₃) or other nitrogenous compounds that plants can absorb and utilize.

Atmospheric nitrogen (N₂) has a strong triple bond that plants cannot break; they require nitrogen in combined forms like nitrates or ammonia.

Repeated cultivation of the same crop depletes specific nutrients from the soil, leading to reduced fertility and lower crop yields.

Fertilizers (chemical or organic) and manure add essential nutrients like nitrogen, phosphorus, and potassium back to the soil, restoring fertility.

Rhizobium is the symbiotic bacteria that colonize root nodules of legumes and perform biological nitrogen fixation.

Legumes host Rhizobium bacteria that fix atmospheric nitrogen, enriching the soil naturally and reducing the need for nitrogen fertilizers.

Haustoria are specialized root-like structures that parasitic plants penetrate into host tissues to absorb water and nutrients.

Indian pipe is a non-green plant that derives nutrients from decaying organic matter through mycorrhizal fungi, making it a saprophyte.

Mistletoe contains chlorophyll and can photosynthesize, but it extracts water and minerals from the host tree through haustoria, making it a partial parasite.

Substrate refers to the surface or material on which an organism grows and obtains its nutrition. For saprotrophs, it is the dead organic matter they decompose.

Saprotrophs secrete digestive enzymes externally to break down complex organic compounds (like cellulose and proteins) into simpler soluble forms that can be absorbed.

Animals and non-green plants cannot synthesize their own food and depend directly or indirectly on autotrophs for nutrition, making them heterotrophs.

Mutualism is a type of symbiotic relationship where both participating species gain benefits, such as in lichens (alga + fungus) and Rhizobium-legume associations.

Rhizobium bacteria fix atmospheric nitrogen (N₂) into ammonia (NH₃) through the process of nitrogen fixation.

Continuous monoculture (growing the same crop repeatedly) depletes specific nutrients, whereas fertilizers, manure, and crop rotation replenish soil fertility.

Crop rotation involves growing different types of crops in sequence on the same land to maintain soil fertility, reduce pest buildup, and prevent nutrient depletion.

Leguminous crops host nitrogen-fixing Rhizobium bacteria that enrich the soil with nitrogen, making it available for subsequent crops.

Manure is cost-effective, improves soil texture, enhances water retention, and adds organic matter, whereas chemical fertilizers may degrade soil structure over time.

Rhizobium bacteria colonize root nodules of legumes, forming specialized structures where nitrogen fixation takes place under low-oxygen conditions.

Partial parasites (like mistletoe) contain chlorophyll and perform photosynthesis but rely on host plants for water and mineral nutrients.

Mistletoe is green and photosynthesizes but draws water and minerals from its host tree through haustoria, making it a partial parasite.

Yeast feeds on dead organic matter like sugary substrates, secreting enzymes to break down sugars and absorbing nutrients, making it a saprotroph.

Remora benefits by feeding on shark’s leftovers and gaining transport, while the shark is neither harmed nor benefited, making this commensalism.

Leghemoglobin is a pinkish pigment found in root nodules that binds oxygen, creating a low-oxygen environment essential for nitrogenase enzyme activity in nitrogen fixation.

Nitrogen is a critical component of proteins and nucleic acids. It is often the limiting nutrient in soil because plants absorb it faster than it is naturally replenished.

The atmosphere contains about 78% nitrogen. Through nitrogen fixation (by bacteria, lightning, or industrial processes), atmospheric nitrogen is converted into forms plants can use.