DAV Class 6 Science Chapter 9 Structure and Function: Animals Solutions (The Living World) & Board PYQs

Ace your examinations with this master guide for DAV Class 6 Science Chapter 9: Structure and Function of the Living Organisms – Animals from the prescribed textbook The Living World. Here you will find 100% textbook exercise solutions (Sections A to E), structured 3-column physiological comparison tables, step-by-step pathway descriptions (Digestive journey, Excretory mechanism, Respiratory mechanics), and authentic DAV Board Exam Common Question Paper PYQs (2022–23 & 2023–24) with official marking rubrics.

Part A: Fill in the Blanks

Carefully study the completed textbook statements with essential anatomical terms highlighted:

• 1. The process, of breaking down of food, into fine and soluble particles, is called digestion. (Concept: Complex insoluble macronutrients are hydrolyzed by digestive enzymes into simple absorbable molecules.)
• 2. Blood vessels, that carry blood from organs to heart, are called veins. (Characteristic: Veins have thin walls and internal pocket valves preventing backflow.)
• 3. The nervous system consists of billions of nerve cells (neurons). (Fact: Neurons are the longest cells in the human body specialized for electrical impulse transmission.)
• 4. The right portion of the brain controls the left part of the body. (Physiology: Contralateral cerebral control where motor nerve fibres cross over in the brainstem.)
• 5. Kidneys are bean shaped organs that help in filtering out waste products. (Function: Paired retroperitoneal organs that continuously cleanse blood of urea and nitrogenous toxins.)
• 6. The skin removes water, and excessive salts, in the form of sweat. (Dual purpose: Excretes mineral wastes and regulates core body temperature by evaporative cooling.)
• 7. The male reproductive organ system has a pair of testes. (Function: Located in the scrotum, they produce male gametes called sperms.)

Part B: Write True or False for the Following Statements

Each statement is evaluated with an authoritative scientific justification:

Part C: Tick the Correct Option

Part D: Answer the Following Questions in Brief

1. How many teeth are present in a four-month-old child’s mouth?
Answer:
Zero (no teeth). At four months of age, teeth have not yet erupted above the gums. The first set of temporary primary teeth (milk teeth) generally begins to emerge between 6 and 8 months of age.

2. Where is saliva produced?
Answer:
Saliva is produced by three pairs of specialized salivary glands situated in the buccal cavity (mouth):
1. Parotid glands (near the ears/cheeks)
2. Submandibular glands (beneath the lower jaw)
3. Sublingual glands (underneath the tongue)

3. Define respiration.
Answer:
Respiration is the vital biochemical process by which oxygen inhaled from atmospheric air is transported to cells to oxidize absorbed digested food (glucose), thereby liberating cellular biological energy (ATP), with carbon dioxide and water vapour expelled as byproducts.

4. Name the flap that shuts off the windpipe when you swallow food.
Answer:
The epiglottis. It is a thin, leaf-shaped flexible cartilaginous flap situated at the root of the tongue that folds backward over the larynx (glottis) during swallowing, preventing food boluses from entering the windpipe (trachea).

5. How many types of vessels are found in the circulatory system of human beings?
Answer:
Three distinct types of blood vessels form the circulatory conduit network:
1. Arteries: Thick-walled, elastic vessels carrying oxygen-rich blood away from the heart under high pressure.
2. Veins: Thinner-walled vessels with valves returning deoxygenated blood toward the heart under low pressure.
3. Capillaries: Microscopic single-celled thin vessels connecting arterioles to venules, permitting nutrient and gas exchange with tissues.

6. List down the main organs of the nervous system.
Answer:
The three primary structural organs composing the human nervous system are:
1. The Brain: The central executive organ housed inside the skull cranium.
2. The Spinal Cord: The elongated neural pathway running down inside the protective vertebral column.
3. The Nerves: Network of cable-like fibres (sensory and motor nerves) spreading throughout the body.

7. Name the structure that protects the spinal cord.
Answer:
The vertebral column (also commonly called the backbone or spine), composed of 33 interlocking ring-shaped vertebrae cushioned by intervertebral discs.

8. Name the process of fusion of an egg with a sperm.
Answer:
Fertilization. The biological fusion of a haploid male gamete (sperm) with a haploid female gamete (ovum/egg) forms a single diploid cell called a zygote.

Part E: Answer the Following Questions (Long Answers)

1. What is digestion? Starting from the mouth, state the various steps involved in digestion.
Answer:
Definition: Digestion is the biochemical and mechanical breakdown of complex, insoluble dietary nutrients into simple, soluble molecules that can be absorbed through intestinal walls into the bloodstream.
Sequential Digestive Pathway:

1. Mouth Cavity (Ingestion & Mastication): Teeth chew and grind food mechanically; tongue mixes it with saliva. The enzyme salivary amylase breaks down insoluble starch into sweet maltose sugar.
2. Oesophagus (Food Pipe): Rhythmic muscular contractions and relaxations called peristalsis propel the lubricated food bolus down into the stomach without chemical digestion.
3. Stomach (Gastric Digestion): Food is churned for 2 to 3 hours with gastric juice. Hydrochloric acid (HCl) creates an acidic medium and kills swallowed germs, while the enzyme pepsin begins the chemical digestion of complex proteins into peptones.
4. Small Intestine (Complete Digestion & Absorption): Chyme enters the duodenum where bile (from liver) emulsifies fats, and pancreatic and intestinal juices break down proteins into amino acids, carbohydrates into glucose, and fats into fatty acids/glycerol. Microscopic finger-like projections called villi absorb these digested nutrients directly into blood capillaries.
5. Large Intestine (Water Reabsorption): The indigestible residue passes into the large intestine, which reabsorbs excess water and mineral salts, condensing semi-solid waste into faeces.
6. Rectum and Anus (Egestion): Faecal waste is stored in the rectum and periodically expelled through the anal sphincter.

2. Draw / describe the tongue and show the location of the taste buds on it.
Answer:
The human tongue is a muscular sensory organ bearing microscopic sensory structures called taste buds distributed across distinct zones:
• Tip of the Tongue: Primarily sensitive to Sweet taste.
• Anterior Sides (Front Edges): Sensitive to Salty taste.
• Posterior Sides (Back Edges): Sensitive to Sour taste.
• Back Base of the Tongue: Highly sensitive to Bitter taste.
(Central upper surface has relatively fewer taste buds and functions mainly for manipulating food and speech.)

3. Explain the role of the diaphragm in the process of breathing.
Answer:
The diaphragm is a large, dome-shaped sheet of skeletal muscle that separates the thoracic (chest) cavity from the abdominal cavity. It actively powers mechanical ventilation through two coordinated actions:

4. Give the function of the heart, and the blood vessels, in the circulatory system.
Answer:
• The Heart: Acts as a tireless muscular double-pump that maintains continuous systemic blood circulation. The right chambers receive deoxygenated blood from the body and pump it to the lungs for oxygenation, while the left chambers receive oxygen-rich blood from the lungs and pump it out forcefully through the aorta to all body tissues.
• The Blood Vessels: Form a closed vascular transit circuit:
– Arteries: Distribute oxygenated blood under high pressure away from the heart to all tissues.
– Capillaries: Ultra-thin conduits allowing glucose, oxygen, and metabolic wastes to diffuse between bloodstream and living cells.
– Veins: Collect deoxygenated blood and metabolic waste fluids from tissues and safely return them back to the heart.

5. State the function of the nervous system. Briefly explain the role of nerves in it.
Answer:
• Function of the Nervous System: It acts as the central command, control, and coordination network of the human body. It detects external and internal environmental stimuli, processes sensory data, makes decisions, and coordinates both voluntary actions (running, writing) and involuntary functions (heartbeat, breathing, peristalsis).
• Role of Nerves: Nerves function as high-speed biological communication cables:
1. Sensory Nerves: Transmit incoming sensory nerve impulses from receptors (eyes, ears, skin) to the brain and spinal cord.
2. Motor Nerves: Transmit outgoing motor command impulses from the brain and spinal cord to effector organs (muscles and endocrine glands), instructing them to contract or secrete.

6. Give a brief outline of the process of excretion, by the kidneys, in human beings.
Answer:
Excretion is the biological removal of toxic metabolic waste substances from the body. In the human urinary system, this occurs via the following stages:
1. Blood Influx: Waste-laden blood enters the kidneys through the renal arteries.
2. Nephronic Filtration: Inside the kidneys, millions of microscopic filtering units (nephrons) filter water, urea, uric acid, and excess mineral salts from the blood capillaries, while retaining red blood cells and vital proteins.
3. Urine Formation: The filtered toxic liquid waste forms urine.
4. Transit & Storage: Two muscular tubes called ureters carry urine continuously from the kidneys down into the expandable urinary bladder, where it is temporarily held.
5. Micturition: When the bladder expands, urine is expelled out of the body through the urethra under conscious control.

Value-Based Questions (VBQ) & HOTS

🎯 DAV Board Exam Corner: Authentic PYQs (2022–23 & 2023–24)

The following questions are extracted directly from official DAV Public Schools Half-Yearly and Annual Board Papers for Chapter 9: