Master Chapter 9 Class 7 - Life Processes in Animals (Curiosity) with comprehensive NCERT Solutions, Practice Questions, MCQs, Sample Papers, Case Based Questions, and Video lessons.
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Welcome to Chapter 9. We begin our exploration with a piece of ancient wisdom from the Thirukkural: "If your food is fully digested before you eat again, you won't need medicine for pain"1. This highlights a truth we have always known: our health, our energy, and our very lives are deeply connected to the food we eat and what our bodies do with it.
In Grade 6, we learned that all living things share a set of "life processes" that are essential for survival, including nutrition, respiration, excretion, and reproduction2. This chapter is a deep dive into two of the most critical of these: Nutrition (how we get food) and Respiration (how we get energy from that food)3.
We will embark on a fascinating journey inside the animal body—starting with our own. We will follow a single bite of food from the moment it enters our mouth to the moment its energy is released in our cells.
Animals, including humans, eat to get energy and the raw materials to grow4. The food we eat—like a chapati or a piece of paneer—contains large, complex components like carbohydrates, proteins, and fats5. Our bodies cannot use these large molecules directly. They must first be broken down into simpler, smaller forms that our bodies can absorb6.
This entire process of breaking down complex food is called digestion7. It happens in a long, winding tube that runs through our body called the alimentary canal8. Let's trace the complete journey.
The journey starts the moment food enters your mouth. Digestion begins immediately in two ways:
Mechanical Digestion: Your teeth go to work, crushing, chewing, and grinding the food into small, manageable pieces .
Chemical Digestion: Your mouth produces saliva. This watery liquid does more than just moisten food; it contains a special digestive juice (an enzyme) that immediately starts breaking down complex starch (a carbohydrate) into simpler sugars. This is why, if you chew a piece of plain chapati or rice for a long time, it actually starts to taste sweet! .
After you chew, your tongue helps mix the food with saliva and pushes it to the back of your throat and into a long, flexible tube called the food pipe, or oesophagus13. The food doesn't just fall down this tube. The walls of the food pipe move in a gentle, wave-like motion, contracting and relaxing to carefully push the food downward into the stomach 14.
The food then enters the stomach, a muscular, J-shaped bag 15. Here, the food is churned and mixed with powerful secretions from the stomach wall16. These secretions are:
Digestive Juice: This begins the serious work of breaking down proteins from your food into simpler components17.
Acid: The stomach produces a strong acid (hydrochloric acid) that not only helps digest proteins but also kills many harmful bacteria that may have entered with your food18.
Mucus: This is a thick, protective layer that coats the inside of the stomach, protecting its own walls from being damaged by the strong acid it produces19.
After a few hours of this churning and mixing, the food is transformed into a semi-liquid mass, ready for the next and most important stage of its journey20.
This is where the real magic happens. The food moves from the stomach into the small intestine. Despite its name, this is the longest part of the entire alimentary canal—it's almost 6 metres long (twice the height of a classroom!) 21.
Here, the digestion process is completed with the help of digestive juices from three different sources:
From the Small Intestine itself: Its own walls secrete juices that help break down fats, proteins, and carbohydrates22.
From the Liver: The liver, the body's largest internal organ, produces a juice called bile. Bile is basic in nature, which is crucial because it neutralises the acid coming from the stomach. It also plays a vital role in breaking down large fat globules into tiny droplets, making them easier to digest23232323.
From the Pancreas: The pancreas secretes pancreatic juice (also basic) that acts on all three major food components: carbohydrates, proteins, and fats, breaking them down even further 24.
Once all the food is broken down into its simplest forms (like simple sugars, amino acids, and fatty acids), it is ready to be used. This is where absorption begins25. The inner walls of the small intestine are not smooth; they are covered in thousands of tiny, finger-like projections26. These projections dramatically increase the surface area of the intestine, allowing it to efficiently absorb all the useful nutrients and pass them directly into the blood vessels 27.
After the small intestine has absorbed all the useful nutrients, what is left? A mix of undigested food (like fibre) and water, which now passes into the large intestine. This tube is shorter (about 1.5 metres) but wider than the small intestine 28.
The large intestine has one main job: to absorb the water and some salts from the remaining undigested food29. This recycling of water is crucial. As the water is removed, the waste becomes a semi-solid stool, which is stored in the rectum (the last part of the large intestine) until it is finally expelled from the body through the anus303030. This final removal of waste is called egestion31.
This entire journey is a marvel of biological engineering, a perfectly coordinated system of mechanical and chemical processes, with multiple organs working together. It can be a lot to take in—new parts like the pancreas and liver, new chemicals like bile and mucus, and new processes like absorption and egestion.
This is where Teachoo comes in. We are here to be your guide on this "invisible" journey. We break down this complex system into simple, logical steps, just like the ones you've read here. We use clear diagrams and easy-to-understand explanations to help you trace the path of food, understand the job of each organ, and see how it all fits together. We help you build a clear map of this amazing internal world.
Of course, not all animals digest food the same way we do. We will also explore some fascinating variations:
Ruminants (Grass-Eaters): Have you ever, as the chapter asks, seen a cow chewing for hours, even when it is not eating?32. We will learn why. Animals like cows and buffaloes, called ruminants, have a special stomach (including a large part called the rumen) that allows them to partially digest grass, swallow it, and then bring the partially digested food (cud) back up to their mouth to be chewed thoroughly later 33.
Birds: Birds do not have teeth. So how do they break down their food? We will learn about the gizzard, a strong, muscular part of their stomach that, often with the help of tiny stones the bird swallows, grinds the food down 34.
Our journey with food ends once the simple nutrients are absorbed into the blood. But this leads to the next big question: What does the body DO with this food?
The nutrients (like simple sugar, or glucose) are the body's fuel. But fuel is useless without a "spark" to release its energy. That "spark" is oxygen.
The process by which our body uses oxygen to break down nutrients and release usable energy is called respiration35353535.
First, we need to get the oxygen. This is the job of the respiratory system, and the process is called breathing36.
The Pathway: Air enters our nostrils, where tiny hairs and mucus trap dust and dirt37373737. It then travels down the windpipe and into our two lungs38.
The Lungs: Inside the lungs, the windpipe branches into smaller and smaller tubes, finally ending in millions of tiny, balloon-like air sacs called alveoli39.
The Mechanism: We do not "suck" air in. Instead, we use our muscles! To inhale (breathe in), our ribs move up and outwards, and a large, dome-shaped muscle below our lungs called the diaphragm moves downward 40. This increases the space in our chest, and air rushes in to fill it. To exhale (breathe out), the ribs and diaphragm relax, reducing the space and pushing the air out41.
Breathing is just the start. The real work happens in the alveoli.
Gas Exchange: The walls of the alveoli are incredibly thin and are surrounded by tiny blood vessels. Here, oxygen from the air you just inhaled passes through the wall and into the blood 42.
Transport: At the same time, a waste gas called carbon dioxide (which the blood has picked up from the body) passes out of the blood and into the alveoli, ready to be exhaled43. This is why the air we breathe out contains more carbon dioxide than the air we breathe in—a fact we can prove by bubbling our breath through lime water and watching it turn milky 44.
The Chemical Reaction: The blood, now rich with oxygen, is pumped by the heart (part of the circulatory system) to every single cell in your body 45. Inside the cells, this oxygen is finally used to "burn" the glucose from your food. This is the chemical process of respiration46:
Glucose + Oxygen → Carbon~dioxide + Water + Energy
This energy is what lets you walk, run, think, and live. Breathing is the physical process of gas exchange; respiration is the chemical process of creating energy. Both are essential for survival 48.
Just like with digestion, different animals have different ways to get oxygen:
Fish use gills to absorb oxygen that is dissolved in water 49.
Earthworms breathe directly through their moist skin50.
Frogs are special: as tadpoles, they use gills in the water, but as adults, they use lungs on land and their moist skin when they are in the water 51.
This chapter takes us on an incredible journey through two of the most fundamental processes that define animal life.
To get started on this journey, click on any topic link to begin your exploration.