Solutions-NCERT-Class-7-Science-Curiosity-Chapter-9-Life Processes in Animals-CBSE

(a) Complex food components like carbohydrates, proteins, and fats are broken down into simpler forms through a process called digestion, which involves both mechanical actions (like chewing) and chemical actions (using digestive juices).

These simpler forms are absorbed by the alimentary canal and transported via the blood to various body parts to support growth, repair, and energy needs.

(b) The process is not the same in all animals; for example, ruminants like cows bring food back to their mouths to chew it again, and birds use a specialized chamber called a gizzard to crush food.

Yes, the mouth feels watery because saliva is released when you think about or recall your favourite food.

Saliva moistens food to make it soft and easy to swallow, and it contains digestive juices that specifically help break down starch into sugars.

When you chew food like chapati or rice for 30–60 seconds, it begins to taste sweet. This happens because the saliva in your mouth is breaking down the starch (a complex carbohydrate) into simpler sugars.

Food moves down the food pipe (oesophagus) through a wave-like motion where the walls of the pipe gently contract and relax to push the food forward into the stomach.

The inner lining of the small intestine has thousands of finger-like projections (villi) that increase the surface area. These projections allow digested nutrients to pass into the blood vessels found in the intestinal walls.

After nutrients are absorbed in the small intestine, the undigested food moves into the large intestine.

Even though it is shorter (1.5 metres) than the small intestine (6 metres), it is called the large intestine because it is wider.

Yes, the process as fascinating because it efficiently absorbs necessary nutrients while eliminating waste to keep the body healthy.

No, the process of respiration is not the same in all animals; different animals have different breathing mechanisms to suit their unique habitats.

Oxygen is used during respiration to break down glucose (sugar) into carbon dioxide and water, a process that releases energy for the body.

Yes, they are different. Breathing is a physical process of inhaling and exhaling air, while respiration is a chemical process that occurs inside the body to convert nutrients into usable energy.

We cannot survive more than a few minutes without breathing because our bodies require a continuous supply of oxygen to produce the energy needed for life through respiration.

We inhale air through our nostrils. During inhalation, the ribs move up and out while the diaphragm moves down, increasing space in the chest so air enters the lungs. During exhalation, the ribs move down and in while the diaphragm moves up, pushing air out.

Yes, these tiny hairs, along with mucus, trap dust and dirt from the air we breathe in to protect our respiratory system.

The food we eat is broken down into simple substances like glucose. Oxygen then helps break down this glucose to release energy through the process of respiration.

• Birds breathe through their lungs, similar to humans.
• Fish have specialized structures called gills that allow them to exchange gases (oxygen and carbon dioxide) dissolved in water.

Food → Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Anus

Sahil: Test Tube A (Pieces of Chapati) :

• Observation: The chapati pieces will turn blue-black upon adding iodine solution.
• Reason: Chapati contains starch. Iodine solution is a chemical indicator that produces a blue-black color when it reacts with starch.

Neha: Test Tube B (Chewed Chapati) :

• Observation: The chewed chapati will either not change colour or turn only a very light blue-black.
• Reason: During chewing, saliva is mixed with the food. Saliva contains digestive juices that break down starch into simpler sugars. Because the starch has been converted into sugar, the iodine solution has little to no starch left to react with.

Santushti: Test Tube C (Boiled and Mashed Potato) :

• Observation: The mashed potato will turn blue-black.
• Reason: Similar to rice and chapati, potatoes are rich in starch. When iodine solution is added, it reacts with the starch present in the potato to produce the characteristic blue-black color. (Note: While the source specifically mentions starch in chapati and rice, the same principle of the iodine test applies to other starchy foods like potatoes).

(iii) To help in inhalation and exhalation

(i) Nostrils - (a) fresh air from outside enters

(ii) Nasal passages - (d) tiny hair and mucus help to trap dust and dirt from the air we breathe

(iii) Windpipe - (e) air reaches our lungs through this part

(iv) Alveoli - (b) exchange of gases occurs

(v) Ribcage - (c) protects lungs

To help Anil understand that respiration and breathing are two different processes, Sanvi can ask him the following questions :

• Is breathing a physical process or a chemical process? : (Breathing is a physical process, while respiration is a chemical process.)
• Does breathing release energy from food? : (No. Respiration releases energy from food.)
• Does breathing happen in the lungs only or in all body cells? : (Breathing happens in the lungs, but respiration takes place in every cell of the body.)
• Can breathing be shown by a chemical equation? : (No. Only respiration has a chemical equation that shows how food is broken down to release energy.)

These questions will help Anil understand that breathing and respiration are related but different processes.

Tanu's statement "We inhale air rich in oxygen" is the most accurate description of the breathing process compared to exhalation.

Reason :

• Inhaled air contains approximately 21% oxygen and a very small amount (0.04%) of carbon dioxide.
• Exhaled air, by contrast, contains about 16–17% oxygen and a much higher amount (4–5%) of carbon dioxide.
• Because inhaled air has a higher concentration of oxygen than the air we breathe out, it is correctly described as being "rich in oxygen".

• Sneezing is a natural defense mechanism triggered when the sensitive lining of the nasal cavity is irritated.

• When we breathe in dusty air, the dust particles irritate the inner lining of the nose.
• The tiny hairs and mucus inside the nose usually trap dust and dirt, preventing them from entering the lungs. However, when too much dust enters the nose, it causes irritation.
• As a result, the body reacts by producing a sneeze, which forcefully pushes air out through the nose to remove the dust and clean the nasal passages.

This process ensures that the air reaching our lungs is as clean as possible.

Anusha could have been breathing faster than Paridhi for several reasons:

1. She ran faster or covered a longer distance than Paridhi, so her body needed more oxygen and produced more carbon dioxide.
2. She may have a lower fitness level than Paridhi, causing her to breathe faster after the same amount of exercise.

Other possible reasons include:

• She may have been more tired or exerted more effort while running.

Therefore, Anusha's faster breathing rate could be due to greater physical effort or differences in fitness and health conditions.

Yadu wants to test the action of saliva on starch. Specifically, he is investigating whether saliva can break down the starch present in rice flour into simpler sugars.

Explanation of Results :

• Test Tube A (Rice Flour + Water): This test tube turns blue-black upon adding iodine solution. This happens because rice flour contains starch, and iodine is a chemical indicator that produces a blue-black color when it reacts with starch.
• Test Tube B (Rice Flour + Water + Saliva): This test tube does not change to a blue-black color (it remains the light orange/yellow color of the iodine). This is because the saliva added to the mixture contains digestive juices that broke down the starch into simpler sugars during the 35–45 minute waiting period. Since the starch was no longer present, the iodine had nothing to react with.

Conclusion :

The experiment confirms that digestion begins in the mouth, where saliva starts the chemical process of breaking down complex carbohydrates like starch into simpler forms.

Rakshita is trying to investigate whether exhaled air contains more carbon dioxide than the air we inhale.

How She Can Confirm Her Findings :

She can confirm her findings by observing the change in the appearance of the lime water in each test tube:

• Test Tube A (Inhaled Air): When surrounding air is passed through the lime water, it will not change colour (it will remain clear). This is because inhaled air contains only a very small amount of carbon dioxide (approximately 0.04%).
• Test Tube B (Exhaled Air): When exhaled air is blown into the lime water, it will turn milky or cloudy.

The Reason for the Confirmation: Lime water is a chemical indicator that turns milky when it reacts with carbon dioxide. The fact that only the lime water in Test Tube B changes colour confirms that exhaled air contains a much higher concentration of carbon dioxide (nearly 4–5%) than the air we normally breathe in.