Theory:

We have learnt in the previous chapter that plants can prepare their food by photosynthesis with the help of sunlight. But animals cannot produce the food.
 
Since animals cannot make food, they obtain food from different sources. The main two sources through which animals obtain food are plants or other animals.
 
Some animals, like humans, consume both animals and plants. The sources of foods include wheat, rice, pulses, fruits, and vegetables from plants and foods obtained from animals includes milk, curd, cheese, eggs, meat, chicken, and fish.
  
In order to survive, all living organisms require food for obtaining energy, growth, and repair.
The process of taking in food by an animal and its utilisation in the body is called animal nutrition.
The mode of nutrition in animals is called holozoic nutrition.
Holozoic nutrition is the process through which the animal feeds by ingesting complex organic food (either in the solid or liquid form), which is then digested and absorbed into their bodies.
Nutrition in animals takes place through five steps:
 
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Nutrition steps
  
Animal nutrition covers three significant aspects,
  • Nutrient requirement
  • Mode of intake of food
  • Utilisation of food in the body.
Nutrient requirement:
 
There are various types of nutrients available in food, such as carbohydrates, proteins, fats and vitamins. These are the components of food that are necessary to provide energy for the organism to survive. Animals consume the food and obtain the nutrients in different ways.
 
Mode of intake of food:
 
Nutrition in animals is a complex process involving ingestion, digestion, absorption, assimilation and finally unused or unabsorbed food will be excreted out from the body by egestion.
 
Ingestion:
The process of intaking food is called ingestion.
Different animals use different methods of intake of food. Every animal has special organs for taking food.
 
The mode of ingestion in different organisms:
 
Animal
Mode of feeding
AmoebaEngulfs food with the help of pseudopodia (false feet)
SnakesSwallow their food
Honey bees and HummingbirdsCollects nectar from flowers in plants
DogChew and swallow their food using mouth
EagleGrips their prey using beaks (tears flesh with hooked and powerful beaks)
Infants of humanFeeds on mother's milk by using mouth
LiceFeeds by sucking blood from the skin
FrogLong forked tongue to catch insects
 
Ingestion in starfish:
 
Starfish is a sea animal that has a fantastic way of ingestion. Starfish feeds on the other sea organisms such as oysters and shellfish. These are covered by hard shells made of calcium carbonate.
 
After opening its prey's shell, the starfish pops out its own stomach through its mouth to eat the animal present inside the shell. Starfish then brings back the stomach that contains the prey into the body. The food is then digested slowly by it. 
 
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Starfish
 
Ingestion in humans is through the mouth. From these different examples, we can see that various organisms follow many different methods of ingestion in the animals.
Reference:
https://commons.wikimedia.org/wiki/File:Neoferdina_insolita.jpg