Life Processes in Animals
Class 07 ScienceLife processes such as nutrition, circulation, respiration, excretion, and reproduction are essential for the survival of living beings. These processes are collectively called life processes.
Animals, including humans, obtain energy from food, which enables them to carry out various life processes. Animals consume food that contains complex components, such as carbohydrate, protein, and fat. These complex food components have to be broken down into simpler forms before the body can use them.
Breaking down of complex food components into simpler forms occurs in a long tube called the alimentary canal. This process starts in the mouth and ends at the anus. As food moves through this canal, digestive juices secreted at different parts break it down into simpler forms. This simpler form of food is absorbed by different parts of our alimentary canal and transported to various parts of our body to carry out various functions.
Digestion in Human Beings
1. Beginning with the mouth cavity
The journey of the food begins when it enters the mouth. The teeth break down food into smaller pieces by the processes of crushing and chewing. This process of initial breakdown of food into fine pieces is called mechanical digestion.
Saliva secretion in the mouth helps break down starch into sugars. This process of breaking complex food components into simpler forms in the body is called digestion. Food is partially digested in the mouth.
2. Food pipe (Oesophagus): A passage from the mouth to the stomach
When you chew your food, your saliva not only helps in digesting the starch but also moistens it, making it soft and easy to swallow. The tongue helps in mixing chewed food with saliva and pushing this softened food into a long, flexible tube called the food pipe or oesophagus.
The walls of the food pipe gently contract and relax in a wave-like motion to push the food down into the stomach. This movement takes place throughout the alimentary canal and pushes the food forward.
3. Stomach
In the stomach, the walls contract and relax to churn the food. The churned food is then mixed with a secretion from the inner lining of the stomach. The secretion from stomach contains digestive juice, acid, and mucus.
The digestive juice of the stomach breaks down proteins present in the food into simpler components.
The acid not only helps break down proteins but also kills many harmful bacteria. The mucus protects the stomach lining from the acid, preventing damage. In the stomach, the food is partially digested and transformed into a semi-liquid mass, preparing it for the next stage of digestion.
4. Small intestine
After its journey through the stomach, the partially digested food moves into the small intestine. The small intestine receives digestive secretions from three sources - the inner lining of the small intestine itself, and two more structures associated with the alimentary canal - the liver and the pancreas.
The liver secretes bile, which is mildly basic in nature. Bile neutralises acids present in the food moving down from the stomach and breaks down fats into tiny droplets, making its digestion easier.
The pancreas secretes pancreatic juice, which is also basic in nature and helps neutralise acids present in the food. Additionally, pancreatic juice also 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.
The digested nutrients pass on from the small intestine into the blood present in blood vessels found in the walls of the small intestine. This process is called absorption of nutrients. The inner lining of the small intestine is thin and 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. These nutrients provide energy, support growth and repair, and help the body function properly.
5. Large intestine
After most of the nutrients are digested and absorbed in the small intestine, the undigested food moves into the large intestine. It is wider than the small intestine.
The large intestine absorbs water and some salts from the undigested food, thus making the waste semi-solid. This semi-solid waste is called stool. The stool is then stored in the lower part of the large intestine, called the rectum, until the body is ready to get rid of it.
Eating fibre-rich foods like fruits, vegetables, and whole grains helps the large intestine function properly by making the stool easier to pass. Finally, it is expelled through the anus - a process known as egestion.
Nutrition 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.
Grass-eating Animals
Grass-eating animals, such as cows and buffaloes, partially chew the grass and swallow it into their stomachs. In the stomach, partial digestion of the food takes place. The partially digested food is brought back to the mouth for gradual chewing. This process is called rumination, and these animals are called ruminants.
Birds
Birds do not have teeth, but they have a chamber called a gizzard. Food is broken down by the contraction and relaxation of the walls of the gizzard, often with the help of grit (small stones) that the birds swallow.
Respiration in Humans
The nutrients from digested food are carried to different parts of the body. Some of the nutrients help build and repair the body, while others, like sugar, are broken down inside the body to release energy. The process by which nutrients are converted into usable energy is called respiration.
We 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 also has a specific system for breathing and respiration. This system is called respiratory system. In this system, the exchange of gases follows a specific pathway. The pathway through which the air is inhaled and exhaled involves various parts of the respiratory system assisting in the process of breathing and respiration.
The respiratory system begins with a pair of nasal openings called nostrils through which we inhale and exhale air. The inhaled air passes into a pair of small passages called the nasal passages. Tiny hair inside the nostrils, along with mucus, help trap dust and dirt from the air we breathe in. This is why we should breathe through the nose and not through the mouth.
From the nasal passages, the air reaches lungs through the windpipe. The windpipe forms two branches, which 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.
When we breathe in (inhale), the 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 we breathe out (exhale), the ribs move down and inwards, and the diaphragm moves upwards, reducing space and pushing air out of the lungs.
How does the exchange of gases happen?
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 called respiration. The word equation of the process of respiration is as follows:
Glucose + Oxygen → Carbon dioxide + Water + Energy
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.
Breathing in other Animals
Animals, such as birds, elephants, lions, cows, goats, lizards, and snakes, breathe through their lungs. Although all these animals have lungs, the structure of their lungs are quite different. Most aquatic animals like fish, have specialised structures known as gills. These 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. For example, tadpoles breathe through gills, while adult frogs use lungs for breathing on land and skin for gas exchange when they stay in water. This adaptation helps them survive both in water and on land, showing how animals have adapted over time to different environments. Earthworms use their moist skin for the exchange of oxygen and carbon dioxide.