Nutrition: Autotrophic, Heterotrophic, COMMENSALISM, CARNIVOROUS PLANT

Autotrophic Nutrition

This is the type of nutrition in which the organisms are able to manufacture their own food. Organisms that can manufacture or synthesize their own food are called autotrophs. Autotrophic nutrition is carried out by all green plants through the process of photosynthesis and by some certain bacteria through the process of chemosynthesis

Heterotrophic Nutrition

This is the type of nutrition in which organisms cannot manufacture their own food but depends directly on plants for their own food such organisms are called heterotrophs, most heterotrophs are fungi, protozoa and some bacteria

The following are different types of heterotrophic nutrition:

1. Holozoic Nutrition: In this type of nutrition, complex food substances are ingested and transformed into simpler, soluble forms during the process of digestion. The steps involved in holozoic nutrition include ingestion, digestion, absorption, assimilation, and egestion. These processes are applicable to various organisms, ranging from simple protozoans like Amoeba and Paramecium to complex organisms like humans.

2. Parasitic Nutrition or Parasitism: This refers to a symbiotic relationship between organisms of different species, where smaller organisms known as parasites depend on larger partners called hosts for food and nutrients at the expense of the host’s well-being, causing harm and diseases. For example, the association between roundworms and humans. Parasitic nutrition is also observed in certain plants, where plant parasites develop haustoria to absorb nutrients from the host, such as the cassytha and Cuscuta (dodder plant). Another example is the phytophthora, a black pod parasite of cocoa.

3. Symbiotic Nutrition or Mutualistic Nutrition: This type of nutrition involves two organisms of different species living together and deriving mutual benefits from their association. The partners can be plant-to-plant, animal-to-animal, and so on. An example of symbiosis is lichens, which is an association between algae and fungi. The green alga produces food for both organisms, while the fungus protects the alga and absorbs water from the atmosphere for its use. Another example is a hermit crab that carries other organisms on its shell, such as a group of sea anemones. The anemones provide concealment and protection to the crab, while also obtaining transportation, better oxygenation, and potential food particles.

4. Saprophytic Nutrition: This type of feeding involves obtaining nutrients from dead and decaying organic matter, such as plants and animals. The organism engaging in saprophytic nutrition is called a saprophyte, and the process is known as saprophytism. Some bacteria, fungi, and animals exhibit this mode of nutrition. Saprophytes secrete digestive enzymes onto the substrate (the organic matter) from which they feed, and digestion occurs externally. This type of digestion is referred to as extracellular digestion and is responsible for the decay process. The extracellular enzymes released by the organism act in the presence of moisture, and chemical reactions are typically accelerated by higher temperatures.


Commensalism is a type of symbiotic relationship that occurs between organisms of different species, wherein one partner derives benefits from the association while the other remains unaffected, neither benefiting nor being harmed. This interaction is characterized by an asymmetrical exchange, where only one organism benefits while the other remains neutral.

A classic example of commensalism is the relationship between sharks and remora fish. Remoras have a unique adaptation that allows them to attach themselves to the bodies of sharks using a modified dorsal fin called a suction disc. By hitching a ride on the shark, the remora gains several advantages. Firstly, it benefits from the shark’s movement through the water, using it as a means of transportation. Additionally, as the shark hunts and feeds, small scraps of food are often left behind or become dislodged, providing an easily accessible source of nutrition for the remora.

Meanwhile, the shark is neither harmed nor directly benefited by the presence of the remora. While the remora gains advantages from the relationship, such as improved mobility and access to food, the shark’s behavior, physiology, and overall well-being are unaffected. The remora’s presence does not hinder the shark in any significant way, thus exemplifying the concept of commensalism.

This type of association can be observed in various ecosystems and between different organisms, where one species takes advantage of the actions or characteristics of another without causing harm or receiving benefits in return. Commensalism is a fascinating illustration of how certain species can coexist and interact in ways that provide advantages to one party while leaving the other untouched.


Carnivorous plants, also known as insectivorous plants, possess a unique adaptation where, in addition to being autotrophic and photosynthetic, they rely on insects or small animals to supplement their protein needs. These fascinating plants have evolved in nitrogen-poor habitats, and their ability to trap and digest insects serves as a crucial source of nitrogen for their growth and development.

Carnivorous plants employ various strategies to attract and capture insects. They often exhibit vivid colors, emit enticing scents, or produce sweet secretions such as nectar to lure their unsuspecting prey. These enticing features serve as traps, enticing insects to come closer and explore the plant’s structure.

Once an insect lands or comes into contact with a carnivorous plant, specialized mechanisms come into play. The plant secretes enzymes, including proteases, which are capable of breaking down proteins. These enzymes aid in the digestion of the captured insects, breaking them down into simpler compounds that can be absorbed and utilized by the plant.

Different species of carnivorous plants employ various trapping mechanisms. One well-known example is the Venus flytrap (Dionaea). This plant has specialized leaves with trigger hairs. When an insect touches these trigger hairs, the leaves snap shut, trapping the prey inside. The plant then secretes enzymes to digest the insect.

Another notable carnivorous plant is the sundew (Drosera). Sundews have sticky tentacles with glandular structures that produce a sticky substance. When an insect lands on the sundew, it becomes stuck to the adhesive droplets. The plant’s tentacles then bend towards the trapped insect, engulfing it in a sticky embrace. Digestive enzymes are subsequently secreted to break down the insect’s body.

Pitcher plants (Nepenthes) possess modified leaves that form a pitcher-like structure filled with digestive fluids. Insects are attracted to the nectar and aromatic compounds within the pitcher. Once inside, the insects often slip on the slippery walls, falling into the fluid-filled cavity. Within the pitcher, enzymes break down the captured prey, and the plant absorbs the resulting nutrients.

Bladderworts (Utricularia) are aquatic carnivorous plants. They possess tiny bladder-like structures with a suction mechanism. These bladders are equipped with trigger hairs and a trapdoor. When a small aquatic organism, such as a water flea, triggers the hairs, the trapdoor opens, and the prey is sucked into the bladder within a fraction of a second. Digestive enzymes are then released to break down the captured organism.

Carnivorous plants exhibit remarkable adaptations to survive in nutrient-poor environments by supplementing their nutrient requirements with captured prey. Through their unique trapping mechanisms, these plants have evolved fascinating strategies to secure essential nitrogen and other nutrients vital for their growth, enabling them to thrive in habitats where traditional autotrophic plants may struggle.


Filter feeding is a remarkable feeding mechanism employed by numerous aquatic animals to extract nourishment from the vast abundance of tiny microorganisms suspended in the water, including phytoplankton (microscopic plants) and zooplankton (tiny animals). These filter-feeding organisms have developed specialized adaptations that allow them to efficiently collect and consume large quantities of these minute food particles.

The process of filter feeding typically involves the animal positioning itself in a water current and utilizing various structures or mechanisms to filter out the desired food particles. One common adaptation is the presence of sieve-like structures, such as gill rakers or comb-like appendages, which act as filters to trap the food particles while allowing water to pass through. These filters may be located in the oral cavity, gill arches, or other specialized feeding apparatus.

Mosquito larvae are an example of filter-feeding organisms found in aquatic environments. They possess a specialized mouthpart known as a “brush” that they extend into the water to filter out small organic particles, including algae and other microscopic organisms. By continuously sweeping the brush through the water, mosquito larvae are able to gather a substantial amount of food to support their growth and development.

Mussels, another prominent example of filter feeders, are bivalve mollusks that live in both freshwater and marine habitats. They utilize their unique anatomical structure, consisting of two hinged shells, to create a water current that carries suspended particles toward their gills. The gills possess numerous cilia and mucus-covered filaments that capture and sort the phytoplankton, detritus, and other organic matter, which the mussels then consume.

Ducks, particularly species known as dabbling ducks, also exhibit filter-feeding behavior. These ducks typically inhabit shallow water bodies and employ a feeding strategy known as “dabbling.” By upending themselves in the water, they submerge their heads and use specialized lamellae on their bills to filter out small invertebrates, aquatic plants, and seeds from the water. The water is expelled from their bills, while the retained food particles are consumed.

Crustaceans such as prawns and lobsters are notable examples of filter-feeding animals. They possess appendages called maxillipeds that function as filters, allowing them to sift through the water for microscopic organisms. These crustaceans generate a water current by beating their appendages or through specialized appendages like the “feathery” exopods found in some species, which efficiently capture and direct food particles toward their mouthparts.

Filter feeding is a highly efficient method of feeding, allowing aquatic organisms to capitalize on the abundant resources present in the water column. Through their specialized adaptations and filter-feeding strategies, these animals can extract vital nutrients and energy from the microscopic organisms that make up the foundation of aquatic food webs.

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Fluid feeding is a fascinating feeding strategy utilized by certain animals, enabling them to extract nourishment by consuming fluids such as plant nectar or the blood of animals, including humans. These animals possess specialized mouthparts that allow them to pierce the targeted source and access the desired fluid for sustenance.

One example of fluid feeders is mosquitoes. Female mosquitoes require blood meals to obtain the necessary nutrients for egg development. With their elongated proboscis, they skillfully pierce the skin of their hosts and feed on their blood. Mosquitoes have evolved intricate mouthparts that include fine, needle-like structures to penetrate the skin painlessly, while other parts of their mouthpart facilitate the extraction of blood.

Insects like aphids have developed mouthparts specifically adapted for fluid feeding on plant sap. Aphids possess a stylet-like structure known as a rostrum, which they use to pierce the tissues of plants, accessing the phloem sap that flows within. By inserting their rostrum into plant tissues, aphids can tap into the nutrient-rich sap, extracting sugars and other essential compounds necessary for their survival.

Larger animals, such as bees, butterflies, and hummingbirds, are also known for their fluid-feeding habits. These creatures rely on the consumption of nectar, a sweet, sugary fluid produced by flowering plants. Bees and butterflies possess elongated mouthparts called proboscises that allow them to probe deep into the floral structures to access the nectar. They lap up the nectar with their tongues, extracting energy-rich sugars and other nutrients in the process. Hummingbirds, on the other hand, have long, specialized beaks that enable them to reach into the nectar-filled flowers and sip the sweet liquid.

The consumption of fluids as a primary source of sustenance has led to remarkable adaptations in these animals. Their specialized mouthparts and feeding behaviors have evolved to exploit specific fluid resources. This ability to fluid feed has allowed them to tap into diverse food sources, whether it be the blood of animals, the sap of plants, or the nectar produced by flowers. By adapting to these unique feeding strategies, fluid-feeding animals have found ways to extract vital nutrients and energy from their environment.

Read also:

Growth | Mitosis, Aspect of Growth, Hormones, Animal

Ecology | Definition, Concept, Components, US Ecology

Cargill animal nutrition: Food substance

Nutrient Cycling

Plant Nutrition

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