Short Notes: Nutrition in Animals | Science Class 7 PDF Download

Ever wondered how animals get their energy and stay healthy? Well, just like us, animals need food to grow, repair their bodies, and stay active. But did you know that different animals eat in different ways?

In this chapter, we're going to learn all about animal nutrition - from the components of food like carbs, proteins, and fats. 

What is Nutrition?

Nutrition is the process of taking in food and turning it into the energy and nutrients needed for an organism to grow and develop.

• Ingestion: This is when you take food into your body.
• Digestion: This is when your body breaks down the food you've eaten into simpler forms that it can use.
• Absorption: This is when your body takes the broken-down food and absorbs it into your bloodstream.
• Assimilation: This is when your body transports the absorbed food to different parts of your body to use for building substances like proteins.
• Egestion: This is when your body eliminates waste products from the body.

What is Nutrition in Animals?

Animal nutrition encompasses understanding the specific nutrients required by different species, how they acquire food, and the processes by which their bodies utilize those nutrients for  growth.

 Do you know!! The process of breaking down complex components of food, such as carbohydrates, into simpler substances that can be utilized by the body for energy and growth is called digestion.

Different ways of taking food

Different types of animals have different ways of eating. For example, bees and hummingbirds drink nectar from flowers, babies and many animals drink their mother's milk, snakes like pythons swallow their prey whole, and some water animals sift tiny bits of food from the water to eat.

Various Modes of Feeding

(i) Chewing: This mode involves the biting and grinding of the food in the mouth by the teeth.
Example - humans, dogs, etc.

(ii) Scraping: In this mode, the food is scraped off the surface by the jaw or an organ.
Examples - snails, ants, etc.

(iii) Siphoning: In this mode, the food is sucked into the mouth.
Example - bees, butterflies, etc.

(iv) Capturing and swallowing: In this mode, they usually capture the food and then swallow it. Example: lizard, etc.

(v) Sucking: This mode involves the piercing of the food and then sucking the liquid out of it.
Example: mosquitoes, etc.

(vi) Sponging: In this mode, the saliva is secreted over the food to dissolve it in order to draw it into the mouth.
Example: houseflies etc. 

Note: Starfish consume animals protected by hard calcium carbonate shells by extending their stomachs through their mouths to access the soft animal inside the shell. Subsequently, the stomach retracts into the body, allowing for the gradual digestion of the consumed food.

Digestion in Humans

When we eat, food goes into our mouth and then travels through a long tube inside our body called the digestive tract.

Human Digestive SystemThis tract is made up of several parts:

(i) Mouth: Where we chew our food.
(ii) Foodpipe or Esophagus: A tube that carries food from the mouth to the stomach.
(iii) Stomach: A pouch-like organ where food is mixed with digestive juices to break it down further.
(iv) Small Intestine: A long tube where most of the digestion and absorption of nutrients from food happens.
(v) Large Intestine: A wider tube where water and minerals are absorbed from the leftover food.
(vi) Rectum and Anus: Where solid waste, called feces, leaves the body.

As food moves through these parts, it gets broken down into smaller pieces by digestive juices produced by glands like the salivary glands, liver, and pancreas. These juices help turn complex food substances into simpler ones that our bodies can absorb.

What happens to food in different parts of the digestive tract? 

1. The mouth and buccal cavity

The buccal cavity is your mouth, where digestion begins with the help of teeth, tongue, and palate.

• Food goes into your mouth and gets chewed up by your different teeth.
• Salivary glands in your mouth make saliva, a clear liquid that helps wet and soften the food.
• Your tongue mixes the saliva with the chewed food. It's also got taste buds that let you taste different flavors.
• After chewing, the food forms a ball called a bolus, which moves down your digestive system for more processing.

2. Oesophagus or the food pipe

The oesophagus, also known as the food pipe, is a tube-like structure.

• Partly digested food travels through the oesophagus.
• The walls of the oesophagus push the food downward toward the stomach.
• If our body rejects any food, it's pushed back up through the mouth, which we call vomiting.

3. Stomach

•  Food from the oesophagus is pushed into the stomach, which is a wide, J-shaped bag.
• Inside the stomach, the inner wall produces mucous that protects it, along with hydrochloric acid that kills bacteria and helps digestive juices work on the food.
• The stomach also releases digestive juices that break down proteins into simpler forms.

4. Small Intestine

• After leaving the stomach, the partially digested food enters the small intestine, which is a long, coiled tube about 7.5 meters in length.
• The small intestine receives bile from the liver, which helps digest fats, and pancreatic juice from the pancreas, which helps digest carbohydrates and proteins.

• Towards the end of the small intestine, intestinal juice finishes breaking down the food. Carbohydrates become glucose, fats turn into fatty acids, and proteins become amino acids.
• The digested food is absorbed through the walls of the small intestine, using tiny finger-like structures called villi. These absorbed nutrients are then carried to various organs in the body through blood vessels.
• Inside cells, glucose is transformed into carbon dioxide and water, releasing energy in the process.

5. Large Intestine

• After leaving the small intestine, undigested food moves into the large intestine, which is shorter and wider, about 1.5 meters long.
• In the large intestine, water and salts are absorbed from the undigested food.
• The leftover solid waste, called faeces, moves into the rectum and is eventually expelled from the body through the anus.

Digestion in grass-eating animals

Animals like cows and buffaloes eat grass quickly and store it in a special part of their stomach called the rumen. In the rumen, the food is partly digested, forming a substance called cud. Later, this cud comes back into the mouth for gradual chewing. This process is called rumination, and animals that do this are called ruminants.

• The bacteria in the rumen of these grass-eating animals, like cattle, help break down the tough cellulose found in grass.
• Animals like horses and rabbits have a large sac-like structure called the caecum, located between the oesophagus and small intestine, which helps them digest cellulose.

Note:  Diarrhoea is when you frequently pass watery stool. It can happen due to infections, food poisoning, or indigestion. It's quite common in India, especially among kids. In severe cases, diarrhoea can be dangerous because it leads to a lot of water and salt loss from the body.

It's important not to ignore diarrhoea. Even before seeing a doctor, the person should drink plenty of boiled and cooled water mixed with a bit of salt and sugar. This mixture is called an Oral Rehydration Solution (ORS).

Feeding and digestion in Amoeba

Amoeba is a tiny, single-celled organism that constantly changes its shape using finger-like projections called pseudopodia.

• It captures food using these pseudopodia, engulfing it to form a food vacuole.
• Inside the food vacuole, digestive juices are released to break down the food into simpler substances. This helps Amoeba grow and sustain itself.