Chapter Notes

Life Processes in Animals

Life processes such as nutrition, respiration, excretion, and reproduction are essential for the survival of living beings.

Nutrition in Animals

Animals obtain energy from food containing complex components like carbohydrates, proteins, and fats. These complex components must be broken down into simpler forms before the body can use them. This breakdown occurs in the alimentary canal, a long tube starting at the mouth and ending at the anus. Digestive juices secreted in different parts of the alimentary canal break down the complex food into simpler forms. These simpler forms are then absorbed and transported to various parts of the body.

Digestion in Human Beings

The journey of food begins in the mouth cavity. Teeth break down food into smaller pieces through mechanical digestion, which involves crushing and chewing. Saliva, released in the mouth, contains a digestive juice that breaks down starch into sugar. This is why starchy foods like chapati taste sweet after chewing for a while.

This activity demonstrates that iodine reacts with starch to produce a blue-black color. In test tube A, the blue-black color indicates the presence of starch. In test tube B, the absence or slight change in color indicates that the starch has been broken down into simple sugars by saliva.

The process of breaking down complex food components into simpler forms is called digestion.

Food Pipe (Oesophagus): A Passage from the Mouth to the Stomach

When food is chewed, saliva moistens it, making it easier to swallow. The tongue mixes the chewed food with saliva and pushes it into the food pipe or oesophagus, a long, flexible tube. The walls of the food pipe contract and relax in a wave-like motion to push the food down into the stomach. This movement occurs throughout the alimentary canal and pushes the food forward.

Stomach

In the stomach, the walls contract and relax to churn the food. The churned food mixes with secretions from the inner lining of the stomach, including digestive juice, acid, and mucus. The digestive juice breaks down proteins into simpler components. The acid kills harmful bacteria and helps break down proteins. The mucus protects the stomach lining from the acid. In the stomach, food is partially digested and transformed into a semi-liquid mass.

Small Intestine

Partially digested food moves from the stomach into the small intestine, which is about 6 meters long. The small intestine receives digestive secretions from its inner lining, the liver, and the pancreas.

The liver secretes bile, which is mildly basic and neutralizes acids from the stomach. Bile also breaks down fats into tiny droplets, making their digestion easier.

The pancreas secretes pancreatic juice, which is also basic and neutralizes acids. Pancreatic juice breaks down carbohydrates, proteins, and fats. The digestive juice secreted by the wall of the small intestine further breaks down fats, proteins, and partially digested carbohydrates into simpler forms.

Digested nutrients pass from the small intestine into the blood vessels in its walls through a process called absorption of nutrients. The inner lining of the small intestine has thousands of finger-like projections that increase the surface area for efficient nutrient absorption. These finger-like projections allow the digested nutrients to pass into the blood, which carries them to different parts of the body for energy, growth, and repair.

Large Intestine

After most nutrients are digested and absorbed in the small intestine, undigested food moves into the large intestine, which is about 1.5 meters long. The large intestine absorbs water and some salts from the undigested food, making the waste semi-solid. This semi-solid waste is called stool. The stool is stored in the rectum, the lower part of the large intestine, until it is expelled through the anus in a process called egestion.

Digestion in Other Animals

Animals exhibit variations in the structure and function of the alimentary canal to adapt to different ways of digesting different kinds of food.

Birds have a gizzard, a chamber where food is broken down by the contraction and relaxation of its walls, often with the help of grit (small stones) that the birds swallow.

Grass-eating animals, such as cows and buffaloes, partially chew the grass and swallow it into their stomachs. Partial digestion of the food takes place in the stomach. The partially digested food is brought back to the mouth for gradual chewing. This process is called rumination, and these animals are called ruminants.

Respiration in Animals

Respiration is the process by which nutrients are converted into usable energy.

Respiration in Humans

Humans breathe in (inhale) and breathe out (exhale) air continuously to obtain oxygen and release carbon dioxide. The process of inhaling and exhaling air is called breathing.

The body has a respiratory system for breathing and respiration. This system consists of various parts, including the nostrils, nasal passages, windpipe, and lungs.

The respiratory system begins with a pair of nostrils through which we inhale and exhale air. The inhaled air passes into a pair of small passages called the nasal passages. Tiny hairs and mucus in the nasal passages trap dust and dirt from the air. From the nasal passages, the air reaches the lungs through the windpipe. The windpipe forms two branches that enter the two lungs. In the lungs, these branches further divide into smaller and finer branches that end in small balloon-like sacs called alveoli. The lungs are protected by the rib cage.

In this model, the balloons represent the lungs, and the rubber sheet represents the diaphragm.

When you breathe in (inhale), your chest expands as the ribs move up and outwards. The diaphragm (a dome-shaped muscle below the lungs) moves downwards during inhalation. This increases the space inside the chest, and air enters the lungs. When you breathe out (exhale), the ribs move down and inwards, and the diaphragm moves upwards, reducing space and pushing air out of the lungs.

This indicates that the exhaled air contains more carbon dioxide than the air we inhale. Lime water turns milky when it reacts with carbon dioxide.

Through the process of breathing, fresh air from outside enters the lungs and fills the alveoli. The alveoli have thin walls surrounded by fine tubes containing blood. Blood carries carbon dioxide from the body to the alveoli, where it is released into the air. At the same time, oxygen from the alveoli passes into the blood and is transported to all parts of the body.

When we eat food, our body breaks it down into simple substances like sugar (glucose). Oxygen helps break down glucose to release energy. This process is respiration. The word equation of the process of respiration is as follows:

$\text{Glucose} + \text{Oxygen} \longrightarrow \text{Carbon dioxide} + \text{Water} + \text{Energy}$

During breathing, we inhale air from our surroundings and exhale air having more carbon dioxide than the inhaled air. This exchange of gases ensures that each segment of our body gets oxygen to produce energy and remove waste products. Breathing brings in oxygen and removes carbon dioxide, while respiration uses oxygen to break down food and release energy.

Breathing is a physical process, while respiration is a chemical process that occurs inside the body.

The circulatory system transports nutrients, oxygen, and other substances to all parts of the body. It includes the heart, blood, and blood vessels. The heart pumps blood through blood vessels, delivering oxygen and nutrients while also removing waste from the body.

Respiration in Other Animals

Different animals have different breathing mechanisms adapted to suit their habitats.

Animals, such as birds, elephants, lions, cows, goats, lizards, and snakes, breathe through their lungs. Most aquatic animals like fish, have specialised structures known as gills. Gills are richly supplied with blood vessels. The exchange of oxygen and carbon dioxide between the blood and the gases dissolved in water takes place across the gills.

Amphibians, like frogs, live both on land and in water. They use different body parts for breathing at various stages of their life. Tadpoles breathe through gills, while adult frogs use lungs for breathing on land and skin for gas exchange when they stay in water. Earthworms use their moist skin for the exchange of oxygen and carbon dioxide.