Class 7 Science Nutrition in Animals Chapter Notes.

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Nutrition in Animals

Animals are heterotrophs. They obtain food from green plants or animals that feed on plants.

Herbivorous Animals: They feed only on plants or plant parts. Examples. Cow, buffalo, goat, deer, rabbit,horse and elephant.

Carnivorous Animals: They feed on the flesh of other animals. Examples: Lion, Tiger and Leopard.

Omnivorous Animals: They feed on both plants and animals. Examples: pig, man, cockroach.

MODES OF NUTRITION IN ANIMALS
The mode of nutrition in herbivorous, carnivorous or omnivorous animals is called holozoic nutrition. However, some animals are parasites, saprophytes or scavengers.

i) Parasitic animals obtain food and shelter form the host. They may be endoparasites or ectoparasites. Endoparasites live inside the host body and derive nutrients from the hosts body fluid blood or tissue.
Examples: Malarial parasites live in RBCs, flat worms and round worms reside in liver or intestine. Ectoparasites such as ticks, mites, body louse and bed bugs cling on the body surface of their hosts and suck their blood.

ii) Saprophytic animals feed on dead and decaying organic matter. Earthworms are saprophytes.

iii) Scavengers feed on decaying animals. Vulture, crow and jackal are scavengers.

PROCESS OF HOLOZOIC NUTRITION
In holozoic nutrition, animals take solid food. Their food contains insoluble complex nutrients. The body can use these nutrients only when these are digested and broken down into simple soluble molecules. The soluble molecules are then absorbed by the intestinal wall.
The process of holozoic nutrition, involves the following steps. Ingestion, digestion, absorbtion, assimilation and egestion.

Ingestion
It is the process of taking in the food items from outside into the body through mouth. Different organisms have different methods of food intake and their food habit also vary. The organ involved in the food intake, i.e., the mouth varies from lowest animals (protozoans) to highest animals (mammals). The mouth part of animals are modified to enable them to catch their prey or procure food. For example: Unicellular Amoeba engulfs tiny particles of food by surrounding it with false feet or pseudopodia. The pseudopodia then join together to form a small cavity, a food vacuole (Fig.1).

Paramoecium, another unicellular organisms has fine hair like structure called cilia all over its body. The cilia sweep the food particles along with the water current into its mouth like structure. (Fig. 2)

In a multicellular organisms like Hydra there are numerous tentacles around its mouth which entangle small aquatic animals and kill them with their stinging cells. Then the food is pushed inside the mouth (Fig.3)

In insects like butterflies houseflies, mosquitoes, bees, etc., the mouth parts are modified to form a feeding tube to suck nector from flowers. The feeding tube is called a proboscis (Fig,.4)

A frog capture its prey with its long sticky tongue. The tongue is thrown out and the insect sticks to the tongue (Fig. 5).

*Spider weave a sticky web in which small insects get stuck.
* An earthworm uses its muscular pharynx to swallow its food.
* Human beings use their hands to put food into their mouths.

Digestion
The food that we take in is normally solid and complex. The cells of the body cannot use their solid food. All living organisms, except parasites must digest their food to get energy. Thus, the process of breakdown of complex food molecules into simpler forms is called digestion. Most animals use both physical and chemical methods for digesting food. Enzymes are the biocatalyst, secreted by glands found in the digestive system.

Enzymes help in the breakdown of complex molecules like carbohydrates, proteins fats etc. into simple molecules.

Digestion in lower animals like Amoeba, Paramoecium is generally intracellular (within the cell) as the food is digested inside the food vacuole and the digestive enzymes are secreted by the cell itself.
The higher animals like frogs humans, etc., the food passes through the alimentary canal and the digestion occurs in its lumen on. In animals with well developed organs and organ systems, digestion is extracellular (outside the cell). Various digestive enzymes are mixed with the food as it passes through the alimentary canal. Examples are saliva in mouth and gastric juices in the stomach.

Hydra is a multicellular organism, where digestion is extracellular (outside the cell) as well as intracellular (in the cells of the inner layer).

Absorption

The digested food mixes in the body fluid the blood of the animal and gets absorbed. In unicellular organisms like Amoeba, the absorption occurs in the cytoplasm. In Hydra, absorption of food occurs by diffusion of digested food through the cells lining the body cavity. In higher organisms (man), absorption of food occurs in the small intestine.

Assimilation

The process of conversion of absorbed food into living protoplasm is called assimilation. The food absorbed by the body is used as a fuel to produce energy from glucose by respiration for carrying out different life process as like growth, development, etc. Proteins are the building blocks of our body and help in making new tissues as well as repairing worn out tissues.
In case of Amoeba and Paramoecium assimilation of food occurs through streaming movements of protoplasm inside the body cavity. In Hydra, food is assimilated inside the cells.

Egestion
The process of removing undigested solid food parts from the body in the form of faces is called egestion.

In Amoeba, when sufficient amount of undigested food collects inside the body cavity, its cell membrane can rupture at any place to throw out the undigested food.

In Hydra, the waste materials are thrown out through the single body cavity that works both as mouth and anus.

DIGESTION IN HUMANS

Humans have a well developed digestive system. This consists of the gut or alimentary canal, along with the associated digestive glands.

Parts of alimentary canal and accessory glands

The food that we take in can provide energy only if it is digested, absorbed and assimilated to be distributed to all parts of the body.

During digestion large insoluble pieces of food are broken down into soluble substances which are small enough to be absorbed through the walls of the intestine and into the bloodstream. This, process involves certain physical and chemical reactions, as follows:

Physical Action

• Chewing the food with teeth, so as to break the solid food into smaller pieces.

• Churning by the stomach to mix the food with the gastric juices.

Chemical Action

• Carbohydrates to simple sugars.

• Fats to fatty acids and glycero

• Proteins to amino acid.

Enzymes are the digestive juices prepared by cells in various part of the digestive system.

Table 1. Lists the details of the source, their substrates, affects and the resultant products.

The alimentary canal is a long tube of varying diameter which begins from the mouth and ends at the anus.
It consists of mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.

Mouth: Food is ingested by us through the mouth.
The mouth contains tongue, teeth and salivary glands. They work together in chewing (masticating) the food. The chewed food is mixed with saliva, a watery fluid secreted by the salivary glands. This process is called mastication. Saliva contains the enzyme amylase, which converts starch into sugar, so it tastes sweet to us.
Teeth: Our teeth cut, tear and grind the food before we swallow it. We can feel the different shapes of our teeth with our tongue. There are four types of teeth in our mouth.

a) Incisors: These are the front 8 teeth, four on upper and four on lower jaw. These are flat, chisel - shaped teeth, well adapted for cutting and biting of food items.

b) Canines: One incisor each is found on either side of each jaw. These round, sharp and pointed teeth are well adapted to hold and tear the food.

c) Premolars: There are two premolars on each side of each jaw. They have flat surfaces bearing small grooves and ridges, and are well adapted to crush and grind food.

d) Molars: These are the last three teeth on both sides in both the jaws. They have almost flat surfaces with small projections for effective grinding of the food. (Fig. 7)

The white substance that covers our teeth is called enamel. It is the hardest substance in the body. All of us have two sets of teeth in our lifetime. The first set erupts when we are babies and lasts until we are about 8 years old. These are known as the milk teeth or temporary teeth. A child has only 20 such teeth –10 in each jaw. These teeth fall out one by one and are replaced by permanent teeth. A human adult has 32 teeth in all –16 in each jaws.

Structure of a tooth: Each tooth remains buried in the jaw bone by its root and the crown remains outside the gum. Incisors and canines have single root, while premolars and molars have two roots each. The crown is formed of dentine and has a layer of enamel outside.

Enamel forms the shining white part of the crown of each tooth. It is deposited on the surface of crown of the tooth.

Enamel is the hardest substances in our body, even harder than bones. It is also chemically the most stable substance. (Fig. 8).

Tongue: The tongue is a muscular organ and helps to mix saliva in the food. It pushes food towards our teeth. The tongue rolls the food into a bolus which is easy to swallow. It is pushed down the food pipe or oesophagus, by means of a series of rhythmic muscular contractions that go by the name ‘peristalsis’.

The tongue is the main organ of taste. Different sets of taste buds located in specific areas of the tongue, distinguish whether the food is sweet, salty, sour, bitter, etc. Thus, taste buds help us to select the right quality of food. The tongue also helps us to speak

Oesophagus: It is the tube connecting the mouth and the stomach, and is about 30 cm long. It takes about six second for solid food to reach the stomach after it is swallowed. Liquids travel faster down the oesophagus.
The powerful muscles in the oesophagus gently push food down to the stomach in a wave like action, called peristalsis as mentioned earlier.

Stomach: It is a J-shaped muscular bag. It can hold upto two litres of food at a time. Food stays in the stomach from a few minutes to a few hours depending on the type of food. Gentle movements of the stomach wall churn the food up with digestive juices like hydrochloric acid and gastric juices and change it into a semi-liquid state called chyme. The enzymes present in the gastric juices break down proteins. The hydrochloric acid kills the harmful bacteria and also helps the enzymes to work. In the stomach, the milk is changed to curd. Thus, food gets partly digested in the stomach.
Sometimes, we experience vomiting. It is nothing but antiperistaltic movements of the stomach wall and oesophagus.

Small intestine: The food leaves the stomach at intervals and enters the small intestine, which is the longest part of the digestive system. It is about twenty feet or seven meters long and is a highly coiled tube, consisting of three parts - duodenum, jejunum and ileum.
In the duodenum the liver and pancreas pour their secretions, bile and pancreatic juices respectively. These juices contain salts and enzymes. The bile break up fat into tiny droplets which are then acted upon the enzymes and split up into fatty acids and glycerol by the action of enzymes. The pancreatic juice breaks down starch into simple sugars and proteins into amino acids.

Minerals and vitamins do not need to be changed. Cells are able to absorb them as they are. As the food moves further into the jejunum and ileum - the lower part of the
small intestine it is in simple soluble form and is readily absorbed into the bloodstream. Absorption occurs through numerous finger - like projections on the inner walls of the
small intestine called the villi, which have fine blood capillaries. After absorption, the food mixes in the bloodstream and is carried to all the cells of the body by the blood. The cells utilise this food and release energy.

Large intestine: Not all the food that we eat is digested and absorbed. The undigested food enters the large intestine where water is absorbed from it. The semi solid residue is
stored in the last part of the large intestine called the rectum and is finally thrown out of the body through the anus. The large intestine is about 1.5 metre long and has a larger
diameter than the small intestine. (Fig.10).

Liver and Pancreas

Liver is the largest gland of the body weighing about 1.2 to 1.5 kg in an adult human. It is situated in the abdominal cavity, just below the diaphragm and has two lobes. The
hepatic lobules are the structural and functional units of liver containing hepatic cells arranged in the form of cords.

Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule. The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and
concentrated in a thin muscular sac called the gall bladder.
The duct of gall bladder (cystic duct) along with the hepatic duct from the liver forms the common bile duct. (Fig. 11)The bile duct and the pancreatic duct open together
into the duodenum as the common hepato - pancreatic duct. The pancreas is a compound (both exocrine and endocrine) elongated organ situated between the limbs of
the ‘U’ shaped duodenum. The exocrine portion secretes an alkaline pancreatic juice containing enzymes and the endocrine portion secretes hormones, insulin and glucagon.

Digestion in grass eating animals

Humans cannot digest the cellulose present in the food as the human system lacks the cellulase enzyme required to digest it. Ruminants are hooved, plant eating animals that digest their food in two steps. Their stomachs are divided into four compartments the rumen, reticulum, omasum and abomasum.
The half-chewed food is swallowed and it first goes from mouth to the rumen, the first chamber of the stomach. Here it is acted upon by bacteria and micro-organisms. This half digested food then goes to the second muscular chamber, the reticulum, from where it is sent back to the mouth as cud to be chewed again: the action known as ruminating. Grass eaters which chew the half-digested food, i.e., ruminate are called ruminants. Examples are cows, buffaloes, goats, sheep, bison, etc.

The rechewed food is swallowed for the second time. Bypasssing the first two chambers, it enters the third chamber, the omasum. Here the food is further broken down into still smaller pieces and finally enters the fourth chamber, the abomasum. Here, the enzymes act upon the food and digestion is completed as in the human stomach.

After this, the digested food is sent to the small intestine, where the nutrients are absorbed.

Answer the following in very briefly:

1. Defne holozoic nutrition

2. Name the organ which produces bile juices.

3. Name the glands associated with digestion.

4. Name the stomach secretion which kills germs.

5. What is the role of large intestine?

6. What is the type of nutrition in Amoeba and Hydra?

Anser the following in brief:

1. What are the differences between milk teeth and permanent teeth.

2. What are the function of gastric juice?

3. Name differnet types of teeth found in man.

Nutrition in Animals Class VII-Biology

4. How does amoeba ingest its food?

5. What are enzymes? Give two examples.

Answer the following in details:

1. Explain all the steps involved in a holozoic nutrition.

2. With the help of diagram, describe nutrition in Amoeba.

3. Describe an adult human dentition. Explain the role of the different teeth in digestion.

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