Nutrition in Animals - Class 7 Notes & Olympiad Questions

Nutrition in Animals

a) Nutrition in animals refers to how animals obtain and utilise the necessary nutrients for their growth, development, and overall well-being. It involves the process of acquiring food, breaking it down, absorbing nutrients, and eliminating waste.
b) Animals have different dietary preferences based on their feeding habits. Herbivores primarily consume plants as their main source of nutrition. They have specialised digestive systems that allow them to efficiently extract nutrients from plant material, which often contains complex carbohydrates and fibre.
c) Carnivores, on the other hand, are animals that rely on a diet primarily composed of other animals. They have sharp teeth and strong jaws to capture and consume prey. Their digestive systems are adapted to digest and absorb nutrients from animal tissues, which are rich in proteins and fats.
d) Omnivores have a more flexible diet and can consume both plant and animal matter. They have a wider range of food options available to them and possess digestive systems that can process and extract nutrients from both plant and animal sources.
e) Regardless of their dietary preference, animals require essential nutrients such as carbohydrates, proteins, fats, vitamins, minerals, and water to maintain their health. These nutrients serve various functions in the body, including providing energy, building and repairing tissues, supporting growth, and regulating bodily functions.

Holozoic Nutrition in Animals

Holozoic nutrition is a type of nutrition observed in animals, including humans. It involves several sequential processes that enable animals to obtain nutrients from their food and utilise them for energy production, growth, and overall bodily functions. The main steps of holozoic nutrition are as follows:

1. Ingestion: This is the process of taking in solid or liquid food through the mouth. Animals have specific adaptations for acquiring and consuming their food, such as teeth, beaks, or tongues.

2. Digestion: After ingestion, the food undergoes digestion, which is the process of breaking it down into simpler, soluble forms. Digestion involves the use of digestive juices, which are produced in the body and contain enzymes that help break down complex nutrients into smaller molecules.

3. Absorption: Once the food is broken down into simpler forms, it is absorbed into the body fluids, typically the bloodstream. Absorption occurs primarily in the small intestine, where nutrients pass through the walls of the intestine and enter the bloodstream.

4. Assimilation: After absorption, the absorbed nutrients are utilised by the body cells. This process is called assimilation. Nutrients are transported by the bloodstream to various cells and tissues, where they are used for energy production, growth, and repair.

5. Egestion: The final step in holozoic nutrition is egestion, which is the removal of undigested food or waste matter from the body. The waste materials are eliminated through processes such as defecation, urination, or excretion, depending on the animal species.

Different Modes of Feeding

1. Scraping

Animal: Snail
Kind of food: Leaves and insects
Mode of feeding: Snails use a scraping feeding mode. By scraping off small particles of food, the snail can ingest and digest them.

2. Chewing

Animal: Ant
Kind of food: Food particles
Mode of feeding: Ants have jaws that are adapted for chewing. Ants commonly scavenge for food, and their chewing ability allows them to consume a wide range of food sources.

3. Capturing and swallowing

Animal: Eagle
Kind of food: Small animals
Mode of feeding: Eagles are carnivorous birds of prey. They have sharp beaks and strong talons, which they use to capture and immobilize their prey. Their feeding strategy ing other animals for their nutrition.

4. Sucking

Animal: Hummingbird
Kind of food: Nectar of flowers
Mode of feeding: Hummingbirds have long, slender beaks and specialised tongues. They insert their beaks into flowers to access the nectar, and their tongues extend deep into the floral structures to suck up the liquid.

5. Blood-sucking

Animals: Lice and Mosquito
Kind of food: Blood
Mode of feeding: Lice and mosquitoes feed on the blood of other animals. These mouthparts allow them to extract blood and obtain the necessary nutrients for their survival and reproduction.

6. Syphoning

Animals: Butterfly and Housefly
Kind of food: Butterfly: Nectar of flowers, Housefly: Almost everything
Mode of feeding: Both butterflies and houseflies use a syphoning feeding mode. They have a tubular mouthpart. This adaptation enables them to feed on various food sources by sucking up the available fluids.

Human Digestive System

The human digestive system involves two main processes: mechanical digestion and chemical digestion.

Mechanical Digestion

a) This includes the physical breakdown of food through chewing and the churning action in the stomach.
b) Chewing breaks down food into smaller pieces, increasing its surface area for better digestion.
c) In the stomach, muscular contractions mix and churn the food, further breaking it down.

Chemical Digestion

a) This involves the use of enzymes to break down complex food molecules. Enzymes are substances that help speed up chemical reactions in the body. Different organs and glands secrete digestive enzymes.
b) For example, salivary glands produce amylase to break down carbohydrates, the stomach produces pepsin to break down proteins, and the pancreas produces enzymes for breaking down carbohydrates, fats, and proteins. The small intestine also produces enzymes for further digestion.

Parts of the Human Digestive System

1. Mouth

a) The mouth, also known as the buccal cavity, is an important part of the digestive system. It consists of several components, including the teeth, tongue, and salivary glands.
b) In the mouth, the process of digestion begins. Food enters the mouth, where it is broken down through chewing and grinding with the help of teeth. The teeth play a crucial role in breaking the food into smaller, more manageable pieces.
c) During chewing, the tongue assists in mixing the food with saliva. Saliva is produced by the salivary glands and contains a digestive enzyme called amylase. This enzyme starts the digestion of carbohydrates by breaking down complex carbohydrates into simpler sugars, such as glucose.
d) Additionally, the tongue is responsible for our sense of taste. It contains taste buds that allow us to perceive different flavours, enhancing our eating experience.

Types of Teeth

a) Incisors: There are four incisors in each jaw, located at the front of the mouth. Incisors are flat and straight with sharp edges. They are primarily used for biting and cutting food.

b) Canines: There are two canines in each jaw, situated on either side of the incisors. Canines are sharp and pointed teeth. They are designed for tearing and ripping food.

c) Premolars: There are four premolars in each jaw, located next to the canines. Premolars have a flat surface with cusps (points) that are specialised for crushing and grinding food.

d) Molars: There are six molars in each jaw, positioned at the back of the mouth behind the premolars. Molars have a larger surface area with multiple cusps. They are primarily used for crushing and grinding food.

2. Oesophagus

a) The oesophagus is a long, muscular tube that connects the mouth to the stomach. It plays a crucial role in the process of digestion by transporting food from the mouth to the stomach.
b) When we swallow food, the muscles of the oesophagus contract and relax in a coordinated manner. This contraction and relaxation process is known as peristalsis. Peristalsis helps push the food down the oesophagus towards the stomach. It is like a wave-like motion that propels the food forward.
c) It is important to note that no digestion occurs in the oesophagus itself. The main function of the oesophagus is to provide a pathway for food to travel from the mouth to the stomach.

3. Stomach

a) The stomach contains gastric glands that secrete digestive juices and hydrochloric acid. These substances help in the process of digestion.
b) The hydrochloric acid in the stomach creates an acidic environment. This acid activates the enzyme called pepsin. Pepsin plays a significant role in breaking down proteins into simpler substances called peptones.
c) So, the stomach is where the digestion of proteins begins. However, it's important to remember that digestion continues in the small intestine, where proteins are further broken down and absorbed by our body.

4. Small Intestine

a) The small intestine is a long tube-like organ in our body that comes after the stomach. It is about 7.5 meters long and has three main parts called the duodenum, jejunum, and ileum.
b) The duodenum is the first part of the small intestine. It receives special juices called bile and pancreatic juice. Bile helps break down fats, while pancreatic juice helps break down carbohydrates, proteins, and fats.
c) The jejunum is the middle part of the small intestine. It has tiny finger-like parts called villi. These villi help absorb nutrients and energy from the digested food. Nutrients like glucose, amino acids (from proteins), and fatty acids (from fats) are absorbed into the bloodstream through the walls of the small intestine.
d) The ileum is the last part of the small intestine. It continues absorbing nutrients and water from the digested food. Any waste that is left moves into the large intestine.

5. Large Intestine

a) The large intestine is the last part of our digestive system. Any food that couldn't be digested in the small intestine moves into the large intestine. This includes things like fibre and other substances that our body can't break down.
b) The large intestine is made up of three parts: the caecum, colon, and rectum. These parts work together to process the undigested materials.
c) Unlike the small intestine, the large intestine doesn't produce enzymes for digestion. One important task of the large intestine is to absorb water from undigested food. This helps make the waste material more solid.
d) The large intestine stores the waste material in the rectum, which is the last part of the large intestine. When the rectum is full, our body signals that it's time to eliminate the waste. This process is called defecation or passing stool, and it happens through the anus.

Digestion in Ruminants

Ruminants are grass-eating mammals such as cows, buffalos, goats, sheep, and deer. They have a unique digestive system that allows them to efficiently extract nutrients from plant material. Digestion in ruminants includes the following steps:

1. Swallowing without chewing: Ruminants swallow plenty of grass without chewing it much.

2. Partial digestion in the rumen: The swallowed grass goes into a large chamber called the rumen, where it mixes with bacteria. These bacteria help break down the tough parts of the grass, like cellulose, with the help of enzymes they produce.

3. Cud formation and rumination: The partially digested food forms a clump called cud. The ruminant brings the cud back to its mouth and chews it again. This is called rumination. Chewing the cud helps break down the grass even more and improves digestion.

4. Other stomach chambers: After complete chewing, the food goes to other stomach chambers, including the reticulum, omasum, and abomasum. These chambers have different roles in breaking down the food further.

5. Intestine for complete digestion: Finally, the digested food moves into the small intestine, where it undergoes complete digestion and absorption of nutrients. The small intestine takes out all the useful nutrients from the food.

Nutrition in Amoeba

Amoeba is a microscopic organism that obtains nutrition in a unique way. The steps involved are:

1. Ingestion: Amoeba ingests food by extending temporary finger-like projections called pseudopodia around it. It eats by wrapping its body around food and forming a temporary "stomach" called a food vacuole.

2. Digestion: Inside the food vacuole, the amoeba secretes digestive juices. These juices break down the food into simpler substances.

3. Absorption: Once the food is broken down, the amoeba absorbs the simpler substances into its body. It uses these substances for growth, energy, and maintaining its functions.

4. Waste removal: Any parts of the food that couldn't be digested or waste materials are expelled from the food vacuole. This ensures that only useful nutrients are kept.