Maarg Manthan · Topic 4.5

Animal Nutrition

Science & Technology › Plant Biology and Nutrition · Topic 4.5

Animal nutrition is the way animals obtain and use food for energy, growth and repair. All animals are heterotrophs. Their modes of nutrition include holozoic nutrition, in which solid food is ingested, digested inside the body and the waste is egested, as in humans and amoeba; saprophytic nutrition, in which dead matter is absorbed; and parasitic nutrition, in which food is taken from a living host. By diet, animals are herbivores, which eat plants, carnivores, which eat other animals, omnivores, which eat both, and detritivores, which eat dead matter. Digestion may occur inside cells, as in sponges and amoeba, or outside cells in a gut, as in most animals. Ruminants such as cattle have a four-chambered stomach to digest cellulose with the help of microbes.

5 min read · UPSC Prelims · Science & Technology · Plant Biology and Nutrition

At a Glance

Main mode Holozoic
Diet groups Herbivore, carnivore, omnivore, detritivore
Ruminant stomach Four chambers
Amoeba Intracellular digestion
Filter feeders Sponges, clams, baleen whales
Exam link UPSC Prelims, Science & Technology: Plant Biology and Nutrition

Where Does It Fit?

This is the fifth topic of the macro on plant biology and nutrition. It compares how animals feed, after the human digestive system and plant nutrition topics. Previous topic: Plant Nutrition and Classification by Energy/Carbon Source. Next topic: Cellular Respiration in Plants.

How Do Different Animals Feed and Digest?

Animal	Method of nutrition
Amoeba	Engulfs food with pseudopodia into a food vacuole, digests it with enzymes inside the cell and expels wastes
Hydra	Catches prey with tentacles and stinging cells, digests partly in the gut cavity and partly inside cells
Sponge	A filter feeder. Beating flagella draw water through pores and collar cells trap food particles
Earthworm	Eats soil and organic matter, grinds it in the gizzard and digests it in the intestine, with a typhlosole that increases the absorbing area
Cockroach	Chewing mouthparts, crop for storage, gizzard with teeth and caeca that secrete enzymes
Birds	Beaks instead of teeth, a crop for storage and a muscular gizzard that grinds food with swallowed stones
Mosquito	Piercing and sucking mouthparts. Females take blood and males feed on nectar

What Are the Types of Feeders and How Do Ruminants Work?

Herbivores: eat plants and have broad molars, a long gut and often a caecum. Examples are cow, goat, deer and rabbit.
Carnivores: eat animals and have sharp canines and carnassial teeth with a short gut. Examples are lion, tiger, wolf and eagle.
Omnivores: eat both. Examples are humans, bears, crows and pigs.
Filter feeders: strain small food from water, such as sponges, clams and baleen whales.
Fluid feeders: take blood, sap or nectar, such as mosquitoes, aphids and butterflies.
Ruminants: cattle, buffalo, sheep and goat have a stomach in four chambers: rumen, reticulum, omasum and abomasum. They swallow food quickly and later bring it back as cud to chew again, and microbes in the rumen break down cellulose.
Coprophagy: rabbits eat special soft droppings to take in nutrients that they could not absorb the first time.

What Else Should You Remember and Why Does It Matter?

Digestion types: intracellular digestion occurs inside cells, as in protozoa and sponges, and extracellular digestion occurs in a gut, as in most animals, as in Digestive System and Human Dietary Patterns.
Symbionts: termites have protozoa in their guts that digest wood, and cattle depend on rumen microbes. Gut bacteria in many animals make vitamins.
Parasites: tapeworms absorb digested food through the body wall in the host gut, and ticks and leeches feed on blood.
Energy needs: small and warm-blooded animals such as shrews need more food for their size than large or cold-blooded animals.
Nutrition of the young: mammals feed their young on milk, and the first milk, colostrum, carries antibodies, as in Immune System and Immunity.
Animal feed and husbandry: dairy cattle need green fodder, concentrates and minerals. India is the largest producer of milk in the world, and the White Revolution was led by Verghese Kurien.
Livestock programmes: the National Livestock Mission and the National Gokul Mission aim to improve production and breed quality.
Exam pattern: matching animals with feeding types and the parts of the ruminant stomach.
Animal nutrition and the food chain: animal nutrition links consumers to producers, since herbivores get energy from plants and carnivores get it from other animals, as in food chains.
Holozoic nutrition in humans: holozoic nutrition in humans has five steps: ingestion, digestion, absorption, assimilation and egestion.
Feeding adaptations: a snake swallows prey whole with a loose jaw, a frog catches insects with a sticky tongue, and a butterfly uses a coiled proboscis to suck nectar.
Camel and fat storage: a camel stores fat in its hump, which gives energy when food is scarce, and does not store water there.
Teeth and diet: the four kinds of mammalian teeth are incisors for cutting, canines for tearing, premolars and molars for grinding, and their number and shape differ with diet, as a rodent has chisel-like incisors that grow all its life.

As an analytical point, mouthparts, teeth and the gut are shaped by diet. Comparing them shows how natural selection fits structure to function.

Why Is This Topic Important?

Facts Feeding types asked
Concept Ruminant digestion
Link Dairy and livestock

What Came Next?

The next topic covers cellular respiration in plants. Next topic: Cellular Respiration in Plants.

Key People and Terms

Holozoic Ingesting and digesting solid food
Herbivore Plant eater
Ruminant Animal that chews cud
Filter feeder Strains food from water
Detritivore Feeds on dead matter
Cud Regurgitated food

Exam Corner

Points to Remember

Ruminant stomach: rumen, reticulum, omasum, abomasum.
Amoeba: intracellular digestion.
Sponge: filter feeder.
Bird gizzard grinds food.
India: largest milk producer.

Do Not Confuse With

Holozoic and saprophytic Ingests food versus absorbs dead matter
Herbivore and ruminant Plant eater versus cud chewer
Intracellular and extracellular digestion Inside cells versus in a gut

Memory Hook

Holozoic ingests, saprophyte absorbs, parasite sucks; ruminant four chambers, rumen, reticulum, omasum, abomasum.

Mains Angle

Questions compare feeding structures in animals. These points add depth.

Modes Holozoic and others
Structure Teeth and gut
Use Dairy and livestock

A Question You May Face

An original practice question, not a past paper question.

“Describe the different modes of nutrition in animals and explain how ruminants digest cellulose.”

How to Answer

Modes Three.
Feeders Diet groups.
Ruminants Four chambers.
Use Livestock.

GS Relevance

Prelims: modes of nutrition, ruminant stomach, feeding types, digestion in simple animals. GS Paper 3: science and technology, animal husbandry.

Frequently Asked Questions

What is holozoic nutrition?

Holozoic nutrition is the mode of nutrition in which an animal ingests solid or liquid food, digests it inside its body, absorbs the nutrients and egests the undigested waste. It is the main mode in animals from amoeba to humans, and it is different from saprophytic nutrition, in which dead matter is absorbed, and parasitic nutrition.

How do ruminants digest food?

Ruminants such as cattle have a stomach in four chambers: rumen, reticulum, omasum and abomasum. They swallow plant food that is fermented by microbes in the rumen, bring it back as cud to chew again, and then pass it on, so the microbes break down cellulose that the animal's own enzymes cannot digest.

What are filter feeders?

Filter feeders are animals that strain small food particles from water. Sponges draw water through pores and trap food with collar cells, clams and mussels use their gills, and baleen whales use plates in their mouths to strain krill, so they can feed on very small organisms in large amounts.

How does an amoeba digest food?

An amoeba surrounds a food particle with pseudopodia and takes it into a food vacuole. Digestive enzymes enter the vacuole and break down the food, the nutrients are absorbed into the cytoplasm, and the undigested remains are expelled when the vacuole fuses with the cell membrane, which is called intracellular digestion.

What is the difference between herbivores, carnivores and omnivores?

Herbivores eat only plants, and have broad grinding teeth and a long gut, as in cattle. Carnivores eat other animals, and have sharp teeth and a short gut, as in lions. Omnivores eat both plants and animals, and have a mixture of tooth types, as humans, bears and crows do.

PYQ Practice — Statement Analysis

1 Ruminants have a four-chambered stomach.

True

Rumen, reticulum, omasum and abomasum.

2 Amoeba shows extracellular digestion.

False

It shows intracellular digestion.

3 Sponges are filter feeders.