FEEDING MECHANISMS IN HOLOZOIC ORGANISMS

There are five modifications and mechanisms of feeding associated with someorganisms. These feeding mechanisms include:

1) Absorbing mechanisms, e.g. tapeworm The tapeworm is an endoparasite which carries out parasitic feeding on its host i.e ., the man. It has no mouth but absorbs digested food from the intestine of its host.

The body of the tapeworm is modified and adapted for parasitic feeding as follows:

• The alimentary canal is absent, hence food is absorbed through its entire body surface.
• The tapeworm has hooks and suckers which are used for attachment to the intestine of the host to avoid dislodgement.
• The body has thick cuticle which resists digestive enzymes of the host. The flat body surface of the tapeworm provides a large surface area for the absorption of already digested food.
• The entire body surface is used also for the absorption of food.

 

2) Biting and chewing mechanism, e.g. grasshopper or cockroach: The grasshopper or cockroach has mouth parts adapted for biting and chewing.

These insects have four different mouth parts which are modified and adapted for biting or chewing food. These mouth parts are:

• Labrum or upper lip: The grasshopper has labrum or upper lip which prevents the food from falling off the mouth.
• Mandibles: It possesses a pair of mandibles which are heavy, toothed and jaw-like structure used for cutting and chewing food materials.
• Maxillae: The grasshopper also has a pair of maxillae which is also a biting blade. This breaks down the food which the mandibles have chewed into smaller particles.
• Labium: The labium (lower lip) prevents the wastage of food from the mouth.

 

(3) Sucking mechanisms: There are three popular organisms which exhibit sucking mechanism. These are mosquito, butterfly and housefly.

These insects have different modifications of mouth parts adapted for feeding on food through the mechanism of sucking.

 

a) Mosquito

• The mosquito possesses a piercing mouth parts called the proboscis used for sucking the blood of man and animals.
• The mouth parts altogether form a strong stylet capable of penetrating the skin to suck blood.
• The stylet except the labium is sharp and pointed to ease penetration into the skin.
• The mouth can produce saliva to prevent clotting of blood while it is being sucked in.
• It 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.

 

b) Butterfly

The butterfly feeds on liquid food like nectars of flowers.

It has its mouth parts modified for sucking in the following ways:

• It possesses a long, coiled proboscis used for sucking nectars of flowers.
• The insect is capable of recoiling the long proboscis under its head when not in use.
• There is the non-functioning of the other mouth parts due to the type of food taken by the insect.

 

c) Housefly

The housefly feeds on liquid food materials.

It has mouth parts modified for sucking in the following ways:

• The housefly possesses enlarged labella which are sucking structures for liquid food.
• The housefly has the ability to feed on solid food, e.g. sugar by pouring out its saliva to change the food to a liquid state.
• It 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.
• The labella have fine channels which aid rapid absorption of liquid food into the mouth.

 

4) Grinding mechanism: Grinding mechanism is common among mammals, e.g. man, cattle, sheep, goat etc. These animals are capable of grinding the food before swallowing. This grinding is aided by the presence of hard and strong teeth made of enamel and dentine.

 

The animals are adapted to the grinding mechanism by the following features:

• They possess different sets of teeth to grind food.
• The teeth are hard and strong to withstand biting, chewing or grinding and cracking of food.
• They possess incisors which are sharp with flat edges used for cutting off bits of food.
• Animals have pointed canine teeth which are used for tearing food.
• There is presence of premolars and molars with undulating and wide surfaces used for grinding of food.
• The absence of front teeth (incisors) in sheep (a herbivore) is a special adaptation as it helps to grip the grasses during feeding by the animal.

 

5) Trapping and absorbing mechanism: The trapping and absorbing mechanism are common among the insectivorous or carnivorous plants such as bladderwort and sundew.

Bladderwort and sundew have structures which enable them to adapt to this mode of feeding.

• Sundew, for example, traps insects by undergoing nastic movements in response to touch from the body of the insects.
• The sundew leaf has long hairs which carry digestive glands.
• Insect on landing on these hairs causes other hairs to curl over the insect and cover it.
• The sundew is capable of secreting a fluid rich in enzyme to digest the Insect externally.
• The protein so synthesised is easily absorbed by the carnivorous plant into its body.