MODE OF NUTRITION
- 1. Autotrophic Nutrition is the type of nutrition in which the organisms can manufacture their food. Organisms that can manufacture or synthesize their food are called autotrophs. Autotrophic nutrition is carried out by all green plants through the process of photosynthesis and by certain bacteria through the process of chemosynthesis
2. Heterotrophic Nutrition is the type of nutrition in which organisms cannot manufacture their food but depend directly on plants for their own food such organisms are called heterotrophs. Most heterotrophs are fungi, protozoa and some bacteria
There are various types of heterotrophic nutrition as follows
a. Holozoic Nutrition: This is the type of nutrition in which solid complex food substances are ingested and changed into a simple, soluble form during digestion. The processes involved in holozoic nutrition include ingestion, digestion, absorption, assimilation, and egestion. These processes apply to simple animals from protozoans such as Amoeba and Paramecium to complex organisms, including humans.
b. Parasitic Nutrition or Parasitism: This is an association between the organisms of different species in which the smaller organisms, called parasites, depend on the larger partner, called the host, for food and nutrients at the expense of the host, i.e., causing harm and diseases to the host. For example association between roundworms and humans. Parasitic nutrition is also seen in plants where the plant parasite develops haustorium with which it absorbs nutrients from the host, cassytha and cuscuta (dodder plant). Others are phytophtora black pod parasite of cocoa.
c. Symbiotic Nutrition or Mutualistic Nutrition: This is a type of nutrition in which two organisms of different species live together to derive mutual benefit from their association. The partners may be a plant to plant, animal to animal, e.t.c. Examples of organisms that engage in symbiosis are lichens (an association of algae and fungus partnership). The green alga manufactures food for both organisms while the fungus protects the alga and absorbs water from the atmosphere for the use of the alga. Another example is a hermit crab inhabiting on molluscian shell carrying other organisms on its shell. The organism may be a group of sea anemones that afford concealment protection for the crab and themselves, obtain transport, better oxygenation, and possibly particles floating up while the crab is feeding.
d. Saprophytic Nutrition: This is a form of feeding in which the organism derives its food from the remains of dead and decaying organic matter, such as plants and animals. The organism is called a saprophyte, while the process is called saprophytism. This mode of nutrition is exhibited by some bacteria, fungi, and some animals. Saprophytes secrete digestive enzymes onto the substrate (the organic matter) on which they feed digestion takes place outside the organism. This type of digestion is called extracellular digestion, and it is the process that causes the decay. The extracellular enzymes the organism releases to the food surface act only in the presence of moisture, and the chemical reactions are usually sped up by a rise in temperature.
COMMENSALISM
Is an association between the organisms of different species in which only one partner benefits from the relationship, while the other neither gains nor suffers any harm. For example, the association between the shark and the remora fish.
CARNIVOROUS PLANT
These are plants that, apart from being autotrophic and photosynthetic, feed on insects or small animals to supplement their protein needs. These insectivorous plants are found in nitrogen-poor habitats, and they do trap insects as a source of nitrogen. The insects are attracted by their colour, scent, or sweet secretion (nectar) of the plants. They also have enzymes with which they digest the insects before being absorbed into their body. These plants include Venus fly trap (Dionaea), sundew plant(Drosera), the pitcher plant(Nepenthes) and bladderwort (Utricularia).
FILTER FEEDING
Filter feeding is a feeding mechanism used by some aquatic animals to feed on tiny microorganisms in the water, called phytoplankton (plants) and zooplankton (tiny animals). These aquatic animals have to wallow in water through a sieve-like structure on their body to collect a large quantity in the water current. Examples of filter feeders are mosquito larvae, mussels, ducks, prawns, lobsters etc.
FLUID FEEDING
Fluid feeding is a method of feeding adopted by some animals that involves feeding on fluid material from plant (nectar) or the blood of animals or humans. They have special mouth parts for piercing the skin of their prey, e.g. mosquito. Other insects, such as aphids, feed on the sap of plants whose mouthparts are is for piercing and sucking. Some larger animals, such as bees, butterflies, and hummingbirds, suck the nectar of flowers.
Evaluation
- Explain the following mode of nutrition
.I. Commensalism II. Parasitism III. Symbiotic IV. Holozoic
2. Explain I. Fluid feeding ii. Filter feeding