# Life Processes in Animals

## Overview

This chapter explores two key life processes in animals—**nutrition** and **respiration**—and highlights how these processes differ among species. It explains the journey of food through the human digestive system and how animals like cows, birds, and fish digest food differently. It also examines how breathing and respiration occur in humans and other animals, emphasizing the exchange of gases and the role of the circulatory system.

## Key Topics Covered

### 1. Nutrition in Animals

Animals obtain energy by consuming food. The food contains complex components—carbohydrates, proteins, and fats—which must be broken down into simpler forms through **digestion**.

#### A. Digestive System in Humans

* **Alimentary Canal**: Begins at the mouth and ends at the anus. Digestive juices from various parts help break down food.

##### i. Mouth

* Teeth crush and chew food (mechanical digestion).
* Saliva contains enzymes that convert starch to sugar (chemical digestion).

##### ii. Oesophagus (Food Pipe)

* Softens and pushes chewed food to the stomach using wave-like motions (peristalsis).

##### iii. Stomach

* Secretes digestive juice, acid, and mucus.
* Digestive juice breaks down proteins.
* Acid helps digestion and kills bacteria.
* Mucus protects the stomach lining.

##### iv. Small Intestine

* Longest part (around 6 metres).
* Receives digestive secretions from:

* Liver (bile breaks down fats and neutralises acid)
* Pancreas (pancreatic juice breaks down carbs, proteins, fats)
* Small intestine lining (further digestion)
* Inner walls have finger-like projections (villi) for **absorption** of nutrients into the blood.

##### v. Large Intestine

* About 1.5 metres long.
* Absorbs water and salts.
* Forms semi-solid stool, stored in rectum and released through anus (egestion).

#### B. Digestion in Other Animals

##### i. Ruminants (e.g., cows, buffaloes)

* Swallow partially chewed food.
* Later, bring it back to the mouth for re-chewing (rumination).

##### ii. Birds

* No teeth; have a **gizzard** where food is ground using small stones they swallow.

> Different animals have adapted their digestive systems to suit their diets.



### 2. Respiration in Animals

Respiration is the process where oxygen is used to break down glucose (from food) to release energy.

#### A. Respiration in Humans

##### i. Breathing vs. Respiration

* **Breathing**: Physical process of inhaling and exhaling air.
* **Respiration**: Chemical process where glucose and oxygen convert into carbon dioxide, water, and **energy**.

**Equation**:
Glucose + Oxygen → Carbon dioxide + Water + Energy

##### ii. Human Respiratory System

* Begins at **nostrils**, leads to **nasal passages** with hair and mucus to trap dust.
* Air moves to **lungs** through the **windpipe**.
* Inside lungs, air reaches **alveoli**—tiny balloon-like sacs where gas exchange occurs.
* Oxygen from alveoli enters blood; carbon dioxide from blood is released out.

##### iii. Mechanism of Breathing

* **Inhalation**:

* Ribs move outward and diaphragm moves downward.
* Chest cavity increases, air enters lungs.
* **Exhalation**:

* Ribs move inward and diaphragm moves upward.
* Chest cavity decreases, air pushed out.

##### iv. Composition of Inhaled and Exhaled Air

* Inhaled: \~21% oxygen, \~0.04% CO₂
* Exhaled: \~16-17% oxygen, \~4-5% CO₂

#### B. Circulatory System

* Includes **heart**, **blood**, and **blood vessels**.
* Distributes oxygen and nutrients throughout the body.
* Removes waste products.

---

### 3. Respiration in Other Animals

Animals breathe in different ways, depending on their **habitat** and **body structure**.

#### i. Lungs

* Animals like birds, mammals, reptiles (snakes, lizards), and amphibians (frogs on land) use lungs.

#### ii. Gills

* Aquatic animals like fish use **gills**, which are richly supplied with blood vessels.
* Gills help exchange gases from water.

#### iii. Skin

* Animals like **earthworms** and **frogs (in water)** use moist skin for gas exchange.

> Thus, animals have evolved different respiratory systems to adapt to their surroundings.

---

## New Terms and Definitions

| Term | Simple Definition |
| ---------------- | -------------------------------------------------------------------------- |
| Digestion | Breaking food into simpler substances that the body can use |
| Alimentary canal | Tube through which food travels in the body from mouth to anus |
| Saliva | Watery liquid in the mouth that begins breaking down food |
| Peristalsis | Wave-like movements that push food through the food pipe |
| Villi | Small finger-like structures in the small intestine that absorb nutrients |
| Egestion | Removal of undigested food from the body |
| Respiration | Process of breaking down food using oxygen to release energy |
| Alveoli | Small air sacs in the lungs where gas exchange happens |
| Diaphragm | Dome-shaped muscle below lungs that helps in breathing |
| Ruminant | Animal that brings partially digested food back to the mouth to chew again |
| Gizzard | A thick muscular part of a bird’s stomach used to grind food |
| Gills | Organs in aquatic animals for breathing under water |

---

## Practice Questions

### 🟢 Easy (3 Questions)

**1. What is the role of saliva in digestion?**
**Answer:** Saliva breaks down starch (a carbohydrate) into sugar.
**Explanation:** Saliva contains an enzyme that begins chemical digestion in the mouth.

---

**2. Which organ helps in the absorption of nutrients?**
**Answer:** Small intestine.
**Explanation:** It has villi that increase the surface area for nutrient absorption into the blood.

---

**3. What is the name of the tube that carries food from mouth to stomach?**
**Answer:** Oesophagus (or food pipe).
**Explanation:** The food pipe uses peristalsis to push food into the stomach.

---

### 🟡 Medium (2 Questions)

**4. What are the main differences between breathing and respiration?**
**Answer:**

* Breathing is the physical act of inhaling and exhaling air.
* Respiration is the chemical process where oxygen breaks down glucose to release energy.
**Explanation:** Breathing brings in oxygen; respiration uses that oxygen to produce energy inside cells.

---

**5. Why does lime water turn milky when we exhale into it?**
**Answer:** Because exhaled air contains carbon dioxide.
**Explanation:** Lime water reacts with carbon dioxide to form a milky precipitate of calcium carbonate.

---

### 🔵 Difficult (3 Questions)

**6. Why are the small intestine and large intestine named the way they are?**
**Answer:** The small intestine is longer (\~6m) but narrower; the large intestine is shorter (\~1.5m) but wider.
**Explanation:** The names refer to their diameter, not their length.

---

**7. Explain the process of rumination in ruminants.**
**Answer:** Ruminants swallow partially chewed food, store it in their rumen, then bring it back to the mouth to chew again.
**Explanation:** This allows better digestion of fibrous plant material.

---

**8. Describe the journey of food through the human digestive system.**
**Answer:** Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus
**Explanation:** Each organ has a specific role in breaking down food and absorbing nutrients or eliminating waste.

---

### 🔴 Very Difficult (2 Questions)

**9. How does the respiratory system ensure efficient gas exchange?**
**Answer:** The alveoli have thin walls and are surrounded by blood vessels. Oxygen passes into the blood, and carbon dioxide leaves the blood into the alveoli.
**Explanation:** The structure of alveoli maximizes surface area and enables quick diffusion of gases.

---

**10. Birds and mammals both use lungs to breathe. How are birds able to fly at high altitudes with low oxygen levels?**
**Answer:** Birds have more efficient lungs and air sacs that allow continuous oxygen flow during both inhalation and exhalation.
**Explanation:** Their respiratory system is specially adapted for high-efficiency oxygen exchange.

---