FEEDING MECHANISM

 April 7, 2022 Author: Smartpay

All heterotrophic organisms get their nutritional requirements by taking in or ingesting food in the body, food is broken down into simple, soluble and diffusible substances by mechanical and chemical means. This is known as digestion. The digested food is absorbed as soluble form into the fluids of the organisms and transported to all the body cells where it is used up i.e assimilated. Undigested food is got rid of from the body or egested.

Most heterotrophs ingest, digest absorb and assimilate food. The chemical digestion, absorption and assimilation of food is basically similar in all organisms. The feeding mechanism or way an organism obtains and ingests food varies.Feeding mechanism depend on

• whether an organism is holozoic (this includes carnivorous plants) parasitic or saprophytic;and
• the types of food the organism feeds on.

Types of Feeding and Digestion

Holozoic organisms have special structures for capturing a obtaining the prey or food. These structures depend on whether the food is in a solid form or fluid form. Solid food maybe large or small.
Organisms feeding on large pieces of food or whole organisms use structures such as claws, tentacles, teeth and beaks to seize their food or prey. Those feeding on small pieces of food or tiny prey use filter feeding mechanisms to obtain their food. Fluid feeders have structures for sucking fluid food.
Parasitic and saprophytic organisms take in food in fluid form. Saprophytes have special feeding mechanism for changing solid food to liquid food before absorbing it. Many parasites have structures for boring into the bodies of their host and sucking the tissue fluids on which they feed.
In most holozoic animal, digestion and absorption of food take place in the alimentary canal or gu. A simple unicellular animal does not have an alimentary canal.Digestion takes place inside the cell within a food vacuole. This is known as intracellular digestion. A simple multicellular animal has a mouth for taking in food. The mouth opens into a sac-like gut cavity where food is digested. Digestion in the gut is said to be extra cellular because they got cavity is an extension of the external environment into the animal’s body has such food in the gut cavity is considered as being outside the animal’s body. In most higher animal, the gut cavity of alimentary canal is a long tube with two openings:

1. the mouth at the anterior end for taking in food and
2. the anus at the posterior end for getting rid of undigested food.

FEEDING MECHANISM IN SOME ORGANISMS

• Amoeba : Amoeba is found in muddy water at the bottom of pounds and inches and feet are microscopic organisms smaller than itself older kid food substances found in the water and there’s no matter alimentary canal when it comes across food particles it immediately put out a pseudopodium. This flows around the particles and becomes cup-shaped. Finally, it engulfs the particles. This happens when two ends of the pseudopodium meet and fuse. Some water is also enclosed and the small cavity formed is called a food vacuole. The process is termed ingestion. Enzymes from the cytoplasm of the cell are secreted into the food vacuole to digest the food. The soluble products formed diffuse from the vacuole into the cytoplasm. Undigested material is left behind and egested as waste.

• Paramecium caudatum :This protozoa lives in muddy water and feeds on tiny microscopic organisms like bacteria and decayed particles. The beating of the cilia against the water causes a current of water to enter the gullet through a mouth – like opening. It carries with it particles of food, which are taken to food vacuoles. This vacuole moves around in the cytoplasm. Digestive thus intracellular. The soluble nutrients diffuse into the cytoplasm while the undigested waste product of are passed out through the anal pore. Digestion in paramecium is again said to be intracellular.

• Coelenterate Hydra :This is a carnival that feeds on tiny animals. It waits quietly until prey brushes against one of it’s tentacles. Immediately, the stinging cells on its tentacles are discharged. They inject poison into the prey and stun it. The tentacles coil around the prey and push it into the mouth.The whole prey passes into the guts cavity. Glands cells on the wall (endoderm) of the gut secrete digestive juices containing enzymes. Extracellular digestion of the prey takes place and the food become broken up into small pieces. Amoeboid cells in the endoderm engulf the partially digested solid food particles into food vacuoles. Here, digestion is completed intracellularly. The digestive food then diffuses to all parts of the body. Undigested wastes are got rid of through the mouth.

• Filter feeders :Some animals feed on plankton floating in the aquatic environment.To trap this rich source of food, water is drawn towards the animal either by

– the movement of its appendages; or
– the action of cilia.
The water usually passes through a kind of sieve at the front end of the gut which filters out the food before the water passes out of the body. Large amount of water are continuously drawn in through filtering device in this way. Some examples of filter feeders are whales, flamingos, oysters, mosquito larva and copepods
Certain whales have baleen instead of teeth on upper jaws.The baleen consists of closely – packed plate or whalebone which acts as a strainer. It separates out the plankton from the water which enters the whale’s mouth. The flamingo has a straining device in its bill to separate out food particles in muddy waters.
In oysters gills are used to strain food. The action of the cilia on the gills draws in water. The food in water is trapped by the muscus – covered surface of the gills. This food is then pushed towards the mouth by the action of the cilia. The mosquito larva has a pair of mouthparts, each bearing a dense fringe of bristles. These are called feeding brushes. The continuous revolving movement of this brushes sweep water containing microscopic organisms into its mouth. Straining devices separate out the food particles in the foregut.
In a planktonic copepods, water currents are caused by special brush-like appendages which vibrate between 600 and 2640 times the minute. The water is directed into a filter chamber where the tiny food particles are filtered out.

• Fluid Feeders :Some animals are adapted to feed on fluid. Nectar, a sugary fluid found in flowers, is an important source of food for many animals such as hummingbirds,bees, butterflies and moths.Because nectar is found at the base of the flower, adaptations of mouth parts are necessary for these animals to reach the nectar. Thus,hummingbirds have long pointed beaks and tongues, while butterflies have long feeding tubes called proboscis. Many external parasites are also fluid feeders. Insects like aphids leaf hoppers and white flies feed on the sap of plants. They have feeding organs that can pierce the surface of plants and suck the sap in the phloem. Insects such as mosquitoes, assassin bugs and ticks suck the body fluid of other animals. Ticks pierce the skill of the host by means hooked mouth parts and feed on the blood.

FEEDING ADAPTATION IN INSECTS

Insects feed on a variety of foods. Grasshoppers and cockroaches feed on solid food. Moths and butterflies are fluid feeders, sucking nectar from flowers. Mosquitoes Pierce the skin of animals in order to suck blood. Houseflies cannot take in solid food. They externally digest solid food into a liquid form and then suck it up.
All insect have basic mouth parts which are modified according to the food they eat. The mouth part of the Grasshopper consist of several parts, each of which has a particular function as shown in the table. In the butterfly the maxilla are modified into a long proboscis for sucking up liquid. The mandible and labrum are reduced because they are no longer needed. When the proboscis is not in use, it is coiled up. It is uncoiled by pumping blood into it from the body cavity.

MOUTH PARTS AND FUNCTIONS

MANDIBLE: Heavy, toothed, jaw-like structure to cut and crush plant material.
MAXILLA: Inner part of maxilla, directs food to mandibles, and also cuts and grinds the food
MAXILLARY AND LABIAL PALP: Sensory function.
LABRUM:Helps to hold food material.
HYPOPHARYNX: Tongue – like structure being opening of salivary glands.
LABIUM:Assist in manoeuvering food.

Like the butterfly, the mosquito takes in liquid food only and has mouthparts modified into a proboscis. The male mosquito feeds on nectar and plant juices. Its proboscis is used for sucking only. The female feeds on the blood of animals. Its proboscis is modified for piercing and sucking. The proboscis consists of four long sharp stylet, modified from the mandible and maxilla for piercing through skin. The labrum is deeply grooved. When the hypopharynx is fitted closely against it, it forms a channel along which fluid food is pumped. The hypopharynx also contains a salivary duct which injects saliva into the wound. The saliva prevents the blood from clotting and also causes itching and swelling of the skin. The labium is shealth-like and holds the different parts of the proboscis together.
In the butterfly, the proboscis, formed from a modified labium is a sponge-like organ composed of two halves, called labella (singular:labellum) each labellum has numerous fine food channels which join to form a central proboscis canal. When feeding, the proboscis is extended by blood pressure and pressed on the food. If the food is solid, saliva is secreted on i. The saliva contains enzymes which digest the food extracellularly and change it to a liquid. The liquid food moves up the fine channels in the labella by capillary action and is then sucked into the alimentary canal.

Carnivorous plants
Carnivorous plants are special devices for attracting and trapping insects. These devices usually have bright colours scents and sugary liquids. Once an insect is trapped, the plants secrete enzymes-rich digestive juices to kill and digest it. The soluble nitrogenous compounds are then absorbed and assimilated by the plants.
Carnivorous plants have several devices for trapping insects. In the pitcher plant, a leaf is modified into a picher containing digestive fluid. The rim of the pitcher is colourful and smooth., and nectar is secreted near it. Insects are attracted to the nectar and while trying to get at it, they slip and fall into the digestive fluid in the pitcher.
In the Venus flytrap, the leaf is like an animal trap and the two halves fold inwards. There are long sensitive hairs along the edge of the leaf. If an inside brushes on one of these hairs as it lands on the leaf, the two halves quickly shut to trap it.
In the sundew, the Upper surface of the leaf has colourful minute sticky hairs. This trap an insects that lands on The leaf.
The bladderwort is a floating aquatic plant that is insectivorou. It has finely divided leaves that bear many small bladders used for trapping insects.Each bladder has a narrow opening, blocked by a valve with a hair-like trigger. When an insert touches the trigger, the valve open;water rushed into the bladder, sucking in the insect with it.

• Saprophytes

Rhizopus nigricans
This fungus is one of the “bread moulds”. It is commonly known as the bread mould because it grows on moist, stale bread. It appears as a delicate black mass.
The mycelium grows on the surface and also inside the bread. The bread is known as the substrate. There are three types of hyphae:

• The stolons growing horizontally on the substrate.
• The rhizoids or root – like hyphae arising at points where the stolons come into contact with the substrate ;and
• The sporangiophores bearing the sporangia which contains spores.

The rhizoids branch and penetrate into the substrate. The tips of the rhizoids secret enzymes such as amylases and proteases. These diffuse out of the hyphal walls into the bread and bring about the extracellular digestion of carbohydrates and protein to glucose and amino acids respectively. This soluble end – products diffuse into hyphal walls where they are assimilated into the cytoplasm.
The thin – walled highly branched mycelium of the Rhizopus is well suited for this mode of feeding as it can it can penetrate into the substrate, as well as, provide a suitable large surface area for the absorption of digested food.

• Parasite : Parasitic plants The doodler plants cannot make its own food as it has little chlorophyll. It is totally dependent on its host for food so is a total parasite. It grows on plants such as alfalfa, clover and cashew. It consist of thin, golden-yellow, twinning stem which bears small scale leaves. The stem attaches itself to the host by means of suckers. Food is obtained by means of special absorbing organs called haustoria. The haustoria penetrate the stem of the host up to the region of the vascular bundles. They absorb water, mineral salts and food substances from the host.

The mistletoe can manufacture food by photosynthesis but us dependent on the host for water and mineral salts. It is, therefore, a partial parasite. It grows on cultivated trees like cacao. It has small green leaves. A sucker at the base fixes the plant to the stem of its host. Haustor develop from the sucker and penetrate to the xylem tissue where they absorb water and mineral salts. These are then used in the manufacture of food.

• Parasitic animals :Fleas, ticks, bugs, and leeches are ectoparasites. Most ectoparasites have mouth parts that are modified for

1. piercing or boring into the skin (animal) or epidermal layer (plant) ;and
2. sucking the blood fluid (animals) or sap (plants) of the host. (The females mosquitoes and aphids exhibit adaptations for this mode of feeding)

An endoparasites is more highly specialised than an ectoparasite and shows more adaptations, many of which are related to it’s host’s mode of life. The Liver fluke, hookworm, and tapeworm are good examples of endoparasites. Some important adaptations exhibited by endoparasites are discussed.
Many highly specialized endoparasites that live in the gut absorb the digested food of the host through their body surfaces. Such parasites, like the tapeworms, have no feeding mouthparts or alimentary canals. Other endoparasites, like the roundworms, that feeds on the body fluids of the host usually have simple alimentary canals.