FEEDING MECHANISMS IN HOLOZOIC ORGANISMS What are holozoic organisms?
Holozoic organisms are organisms that feeds on other organisms or solid organic food substances synthesized by green plants.
There are five modifications and mechanisms of feeding associated with some holozoic organisms
these feeding mechanisms include
Holozoic nutrition (Greek: holo-whole ; zoikos-of animals) is a type of heterotrophic nutrition that is characterized by the internalization (ingestion) and internal processing of gaseous, liquid or solid food particles. Protozoa, such as amoebas, and most of the free living animals,such as animals, exhibit this type of nutrition.
what are Holozoic nutrition
the energy and organic building blocks are obtained by ingesting and then digesting other organisms or pieces of other organisms, including blood and decaying organic matter.
This contrasts with holophytic nutrition, in which energy and organic building blocks are obtained through photosynthesis or chemosynthesis, and with saprozoic nutrition, in which digestive enzymes are released externally and the resulting monomers (small organic molecules) are absorbed directly from the environment.
several stages of holozoic nutrition,
which often occur in separate compartments with in holozoic organismsn an organism (such as the stomach and intestines):
Ingestion in holozoic organisms:
In animals, this is merely takes place by engulfing the food totally in the mouth. In protozoa, this most commonly occurs through phagocytosis.
ABSORBING MECHANISMS IN HOLOZOIC ORGANISMS:
TAPEWORM is a holozoic organism. A typical example of an organism possessing the sucking or absorbing mechanism is the tapeworm.
The body of the tapeworm is modified and adapted for parasitic feeding as follows
i. The tapeworm has no elementary canal hence food is absorbed through its entire body surface.
ii. The tapeworm has hooks and suckers which are used to attach itself to the wall of the intestine of the host to avoid dislodgement.
iii. The body of a tapeworm has thick cuticle which resists digestive enzymes of the host
iv. The tapeworm’s flat body surface provides a large surface area for the absorption of already digested food.
v. The entire body surface of a tapeworm is used for the absorption of food
BITING AND CHEWING MECHANISM OF FEEDING IN HOLOZOIC ANIMALS:
biting and chewing adaptations in HOLOZOIC ANIMALS
E.g. grasshoppers and cockroach
The grasshopper and cockroach has mouth parts that are adapted for biting and chewing.
These insect types have four different mouth parts which are modified or adapted for biting and chewing food.
These mouth parts are
i. LABRUM OR UPPER LIP: THE GRASSHOPPER HAS UPPER LIP OR LABRUM WHICH PREVENTS FOOD FROM FALLING OUT
ii. MANDIBLES: the grasshopper or the cockroach has or possesses a pair of mandibles which are heavy, toothed and jaw-like structure used for cutting and chewing food materials
iii. MAXILAE: the grasshopper or cockroach has a pair of Maxillae which serves as biting blade. This breaks down the food which the mandibles have chewed into smaller particles
iv. LABIUM: the labium also known as the lower lip prevents the wastage of food from the mouth
There are three popular organisms which exhibits sucking mechanism. These organisms are mosquito, butterfly and housefly. They insects have different modifications of mouth marts adapted for feeding on food through the mechanism of sucking.
So let’s treat them one after the other
i. Mosquito as an example of sucking insect: the mosquito possesses a piercing mouth part called the proboscis. The proboscis is used for sucking the blood of man and other animals
ii. The mouth parts altogether form a strong stylet capable of penetrating into the skin to suck
iii. The stylet except the labium is sharp and pointed to ease penetration into the skin
iv. The mouth of a typical mosquito can produce saliva to prevent clotting of blood while it is being sucked in
v. The mosquito has the ability to fold back the labium easily so as to allow the stylet to perform its work of penetration of the skin to suck blood
The butterfly feeds on liquid food like nectars of flowers. The butterfly has its mouth parts modified for sucking in the following ways
i. The butterfly possesses a long coiled proboscis used for sucking nectars of flowers
ii. The butterfly as an insect is capable of recoiling the long proboscis under its head when not in use.
iii. There is a nonfunctioning of the other mouth parts due to the type of food taken by the insect
SUCKING MECHANISM OF THE HOUSEFLY
The housefly mainly feds on liquid food materials. It has mouth parts modified for sucking in food in the following ways
i. The housefly possesses enlarged labella which are sucking structures for sucking liquid food
ii. The housefly has the ability to feed on solid food like SUGAR by pouring out its saliva to change the food to a liquid state.
iii. The housefly has a sucking mechanism called SPONGING in which the mouth is placed on the liquid food and it will start to rush into the mouth
iv. The labella of the housefly have fine channels which aid rapid absorption of liquid food into the mouth
THE GRINDING MECHANISMS
Grinding mechanism is common among mammals e.g. man, goat, sheep, lion etc. these animals are capable of grinding the food before swallowing. The grinding of food is aided by the presence of hard and strong teeth made of enamel and dentine.
The animals are adapted to the grinding mechanisms by the following
i. They possess different types or sets of teeth
ii. The teeth are strong and hard to withstand biting, chewing or grinding and cracking of solid food like bones
iii. The possess incisors which have sharp and flat edged used for biting off bits of food
iv. Animals have pointed canine teeth used for tearing solid food
v. There is the presence of pre-molars and molars with undulating and wide surface to enable grinding of food
vi. The absence of front teeth or incisors in herbivores like sheep is a special adaptation as it helps to grip the grasses during feeding by the animal.
TRAPPING AND ABSORBING MECHANISM
The trapping and absorbing mechanism are common among insectivorous or carnivorous plants such as bladderwort and sundew.
The bladderwort and sundew have structures which enable them to adapt to this mode of feeding or nutrition
i. Sundew for example is capable of trapping insect by undergoing nastic movement in response to touch from the body of the insect
ii. The sundew leaf has long hairs which carry digestive glands
iii. Insect landing on these hairs causes other hairs to coil over it
iv. The sundew is capable of secreting a fluid rich in enzymes to digest the insect externally
v. The protein so synthesized is easily absorbed by the carnivorous plant into its body
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