NCERT Textbook_Science_Curiosity_GRADE 7_CH-9_ Life Processes in Animals

Ajouté : 2026-05-25

[00:00:06]Namaste. Dear students, have you ever wondered why your elders say, "Eat only when you are hungry?"

[00:00:14]Or why we are told to chew our food 32 times?

[00:00:19]In your previous class, in class sixth, we learned that food gives us energy.

[00:00:26]But how does a piece of roti or an apple turn into energy?

[00:00:31]Read the quote given on the screen, which is taken from Tirukkural 942.

[00:00:38]If your food is fully digested before you eat again, you won't need medicine for pain.

[00:00:46]Today, we explore the curiosity within our bodies.

[00:00:51]The mode of taking food into the body varies across different organisms.

[00:00:58]Each species has adapted a specific method based on its physical structure and habitat.

[00:01:07]We have few examples.

[00:01:10]Like swallowing. Snakes such as python swallow the animals they prey upon in their entirety.

[00:01:19]Sucking. Insects like bees and birds like sunbirds suck nectar from flowers.

[00:01:27]Feeding on mother's milk. Infants of humans and many other mammals stay nourished by nursing.

[00:01:35]Filtering. Many aquatic animals filter tiny food particles floating nearby and feed upon them.

[00:01:44]Animals require food for growth, repair, and the functioning of the body.

[00:01:50]However, the components of food are complex and must undergo a chemical change to be utilized.

[00:01:59]Our food contains complex components such as carbohydrates.

[00:02:05]These are large molecules that cannot be used by the body directly.

[00:02:12]To make these nutrients useful, they must be broken down into simpler substances.

[00:02:19]Now, we can define digestion.

[00:02:22]The breakdown of complex components of food into simpler substances is called digestion.

[00:02:30]And this breaking down of complex food components into simpler forms occurs in a long tube.

[00:02:39]We can say the process of digestion starts in the mouth and ends at the anus.

[00:02:47]Look at the diagram on the screen. It looks like one long tube.

[00:02:54]If we were to stretch this tube inside a human adult, how long do you think it would be?

[00:03:01]It's nearly 9 m.

[00:03:03]Let's begin with the starting point, the mouth cavity.

[00:03:08]Digestion doesn't start in the stomach.

[00:03:11]It starts right here.

[00:03:14]Have you noticed your mouth watering when you smell or see your favorite food?

[00:03:20]This happens because of more saliva that gets released when you see or recall your favorite food.

[00:03:29]Saliva helps to break down components of food into simpler ones.

[00:03:35]As we discussed, the process of breaking complex food components into simpler forms in the body is called digestion.

[00:03:44]Food is partially digested in the mouth.

[00:03:48]Saliva present in our mouth helps in digesting the starch by converting it into sugars.

[00:03:55]And it also helps in making the food soft and easy to swallow.

[00:04:01]Before we swallow, our teeth do the heavy work. We have different types of teeth. Incisors for biting, canines for tearing, and premolars and molars for grinding food into a fine paste.

[00:04:17]Tongue helps in mixing the food with saliva and pushing it into a long flexible tube called the food pipe or esophagus. Now the food enters the food pipe.

[00:04:31]But here is a puzzle.

[00:04:32]How does the food know it has to go down?

[00:04:36]Why doesn't it just get stuck?

[00:04:40]It's not just falling down because of gravity. Even if you were hanging upside down, the food would still move toward your stomach.

[00:04:51]This is because the walls of the food pipe are like a smart tube. They gently contract and relax in a rhythmic wave-like motion to push the food along.

[00:05:04]And this moment takes place throughout the alimentary canal, which pushes the food forward. Now, the food has moved down the esophagus and reached its next destination, the stomach.

[00:05:21]Look at the diagram on your screen.

[00:05:23]Does it look like a simple bag to you?

[00:05:26]It is actually a thick-walled alphabet J-shaped organ, and it is the widest part of our entire alimentary canal.

[00:05:36]But what happens inside this bag? The inner lining of the stomach secretes three very important things: mucus, hydrochloric acid, and digestive juices.

[00:05:50]Wait, if there is acid, why doesn't the stomach burn itself?

[00:05:55]That's the magic of mucus.

[00:05:58]It acts as a protective shield, coating the lining so the acid touch it.

[00:06:06]The acid has a very important job. It kills many bacteria that might enter along with our food.

[00:06:15]It also makes the environment inside the stomach acidic, which helps the digestive juices do their work of breaking down proteins into simpler substances.

[00:06:28]Now the food is partially digested and transformed into a semi-liquid mass, preparing it for the next stage of digestion.

[00:06:38]After that, the food enters the small intestine.

[00:06:43]It is a coiled tube about 7.5 m long. It receives digestive juices from three major sources.

[00:06:54]First is the liver, which secretes bile juice to break down fats.

[00:07:00]Bile juice is basic in nature.

[00:07:03]It neutralizes acids present in the food.

[00:07:08]The second gland is pancreas.

[00:07:11]It secretes pancreatic juice, which is also basic in nature, like the bile juice, and breaks down fats, proteins, and carbohydrates.

[00:07:25]The third source of secretion of digestive juices is the wall of the small intestine itself, which further break down fats, proteins, and partially digested carbohydrates into simpler ones.

[00:07:42]Can you imagine how does the liquid food enter our blood?

[00:07:47]Look closely at the inner walls of the intestine.

[00:07:51]They have millions of tiny finger-like projections called villi.

[00:07:57]Villi increase the surface area for nutrient absorption and these allow the digested nutrients to pass into the blood which carries them to different parts of the body.

[00:08:10]This process is called absorption of nutrients.

[00:08:15]Let us come to the next step of the food journey.

[00:08:19]What about the food that cannot be digested?

[00:08:22]It moves into the large intestine.

[00:08:26]This is the next destination of food journey in elementary canal.

[00:08:32]It is wider, but much shorter.

[00:08:36]Only 1.5 m.

[00:08:39]It absorbs water and some salts from the undigested waste. The remaining waste then becomes semi-solid and is stored in the rectum until it is removed through the anus.

[00:08:55]This is the final step, which is called egestion.

[00:08:59]Now, let's discuss digestion system in animals.

[00:09:04]Do all animals digest food the same way as humans do?

[00:09:09]Okay, let's explore. Have you noticed cows or buffaloes constantly chewing even when they are not eating grass?

[00:09:20]Why do they do this?

[00:09:22]They are called ruminants.

[00:09:25]Grass is rich in cellulose, a complex carbohydrate that is very hard to digest. Humans can't digest it at all.

[00:09:36]Cows swallow the grass quickly into a big storage bag, which is called the rumen.

[00:09:43]Here, the food is partially digested into something called cud.

[00:09:49]Later, when the cow is resting, the cud returns to the mouth in small lumps for the cow to chew it again.

[00:10:00]It's their way of breaking down cellulose, so they can get energy from it.

[00:10:06]Let us talk about birds. Birds do not have teeth. Instead, they have a muscular chamber called a gizzard. They even swallow tiny stones or grit to help the gizzard crush food.

[00:10:22]This shows that animals exhibit variations in the structure and function of the alimentary canal to adapt to different ways of digesting different kinds of food and take nutrients from it. In this session, we discussed the incredible 9-m journey of food through the alimentary canal.

[00:10:44]But, remember, nutrition is only half the story of survival. In our next session, we will discuss the process by which nutrients are converted into usable energy, called respiration.

[00:11:01]We are hoping that all of you have found this journey of food very interesting.

[00:11:07]Thank you.

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