Grade 7 Science - Life Processes in Animals

The Human Digestive System

• Alimentary Canal Overview: A long continuous tube starting at the mouth cavity and terminating at the anus. It includes:

  • Mouth cavity

  • Oesophagus (Food pipe)

  • Stomach

  • Small intestine

  • Large intestine

  • Rectum

  • Anus

• Associated Glands: Liver and pancreas, which secrete specialized digestive juices into the canal.

Digestion in the Mouth Cavity

• Mechanical Digestion: Teeth crush and chew food, breaking it down into smaller, fine particles.

• Role of Saliva: Secreted by salivary glands; moistens and softens food to facilitate swallowing.

• Chemical Action of Salivary Juice: Contains enzymes that convert starch (a complex carbohydrate) into simple sugars.

  • Taste Transition: Chewing plain chapati or boiled rice for $30\text{--}60\,\text{seconds}$ yields a sweet taste as starch breaks down into sugar.

• Tongue Function: Assists in mixing food thoroughly with saliva and pushing the softened mass into the food pipe.

• Oral Hygiene Standards:

  • Clean teeth and tongue twice daily.

  • Rinse the mouth thoroughly with water after every meal to prevent 🦷 decay and halitosis (bad breat)

Food Pipe (Oesophagus) & Peristalsis

• Structure: A long, flexible muscular tube connecting the mouth to the stomach.

• Mechanism of Movement (Peristalsis): Rhythmic, wave-like contractions and relaxations of the oesophageal wall push the swallowed food continuously downward throughout the alimentary canal.

Stomach Structure and Gastric Secretions

• Mechanical Action: Muscular walls contract and relax to churn food into a semi-liquid mass.

• Gastric Lining Secretions:

  • Digestive Juices: Break down complex proteins into simpler components.

  • Hydrochloric Acid: Helps break down proteins and destroys ingested pathogenic bacteria.

  • Mucus: Forms a protective coating over the inner stomach wall to prevent acid erosion and damage.

• Historical Discovery of Stomach Function:

  • In 1822, Alexis St. Martin sustained an accidental shotgun wound to the stomach.

  • Treated by Dr. William Beaumont, the wound healed with a small, permanent open fistula.

  • Dr. Beaumont observed real-time digestion, analyzed the breakdown of different food items, and discovered the influence of emotions on digestive rate.

Small Intestine: Digestion and Absorption

• Dimensions: The longest section of the alimentary canal, measuring approximately $6\,\text{m}$ in length (nearly twice classroom height).

• Secretions Received:

  • Liver: Secretes bile, a mildly basic fluid stored in the gallbladder. Bile neutralizes acidic stomach contents and emulsifies fats into fine droplets.

  • Pancreas: Secretes pancreatic juice (basic in nature), which neutralizes acid and breaks down carbohydrates, proteins, and fats.

  • Intestinal Lining Secretions: Intestinal juices finalize the breakdown of partially digested carbohydrates, proteins, and fats into their simplest units.

• Nutrient Absorption Mechanism:

  • Villi: Thousands of microscopic, finger-like projections (scale approx. $0.5\,\text{mm}$) on the inner wall that dramatically increase surface area for absorption.

  • Blood vessels inside villi transport absorbed nutrients across the body for energy, cell repair, and growth.

• Pathological Note - Celiac Disease:

  • An autoimmune reaction triggered by gluten (a protein found in wheat, barley, and rye).

  • Causes damage to the villi and inner lining of the small intestine, impairing nutrient absorption.

  • Managed strict adherence to a gluten-free diet using natural alternatives such as millets (jowar, bajra, ragi).

Large Intestine and Egestion

• Dimensions: Approximately $1.5\,\text{m}$ long; shorter but noticeably wider than the small intestine.

• Primary Function: Reabsorbs water and residual mineral salts from undigested food matter, transforming waste into a semi-solid stool.

• Storage & Egestion: Stool is stored in the rectum until eliminated through the anus via egestion.

• Dietary Fiber & Gut Microbiome:

  • High-fiber diets (fruits, vegetables, whole grains) enhance stool motility.

  • The large intestine hosts beneficial gut bacteria that digest complex fibers, synthesize essential nutrients, and maintain bowel health.

  • Fermented foods supporting gut flora include curd, buttermilk, shrikhand, kanji, pickles, gundruk, and poita bhat.

• Ayurvedic & Mindful Health Insights:

  • Charaka Samhita stresses easily digestible foods and therapeutic spices (ginger, black pepper, cumin).

  • Optimal digestion requires set meal schedules, mindful chewing, and avoidance of overeating.

Comparative Digestion in her Animals

• Ruminants (Grass-Eating Mammals - Cows, Buffaloes, Goats):

  • Rapidly swallow partially chewed grass into a specialized stomach chamber called the rumen.

  • Partial digestion occurs in the rumen to form cud.

  • Cud is periodically brought back up to the mouth for detailed chewing (rumination).

  • A single cow spends roughly $8\,\text{hours}$ per day ruminating.

• Avian Digestive Adaptations (Birds):

  • Lack teeth entirely.

  • Possess a muscular chamber called the gizzard.

  • Walls of the gizzard contract vigorously, using swallowed small stones (grit) to mechanically grind coarse food.

Respiration in Humans

• Definition: The biochemical process by which body cells utilize oxygen to break down glucose and release energy.

• Word Equation for Cellular Respiration:   $\text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon dioxide} + \text{Water} + \text{Energy}$

Structure of the Human Respiratory System

• Nostrils: Twin exterior openings through which air is drawn.

• Nasal Passages: Lined with fine hair and mucus to capture airborne dust, particulates, and pathogens.

• Windpipe (Trachea): Rigid air passage extending from the nasal tract, dividing into two primary bronchi entering each lung.

• Lungs: Protected within the thoracic cavity by the rib cage and diaphragm.

• Alveoli: Microscopic, balloon-like terminal air sacs enveloped by dense capillary networks, where systemic gas exchange occurs.

• Pathological Note - COVID-19: Caused by the SARS-CoV-2 virus, attacking respiratory pathways, causing pulmonary impairment and acute breathing distress.

Mechanism of Breathing

• Inhalation (Inspiration):

  • Rib cage moves up and outwards.

  • Diaphragm contracts and moves downwards.

  • Thoracic volume increases, decreasing internal air pressure and drawing fresh air into the lungs.

• Exhalation (Expiration):

  • Rib cage moves down and inwards.

  • Diaphragm relaxes and ascends back upwards into a dome shape.

  • Thoracic volume decreases, forcing air enriched with carbon dioxide out of the lungs.

• Model Demonstration (Activity 9.2):

  • Plastic bottle without a base = Thoracic cavity.

  • Y-tube = Trachea and primary bronchi.

  • Internal balloons = Lungs.

  • Lower rubber sheet = Diaphragm.

  • Pulling the rubber sheet down inflates the balloons; releasing it upward deflates them.

Composition of Inhaled vs. Exhaled Air (Activity 9.3)

• Lime Water Demonstration:

  • Test tube A receives ambient atmospheric air via a syringe.

  • Test tube B receives exhaled air blown through a drinking straw.

  • Lime water in test tube B turns milky cloudy rapidly due to higher concentration of $\text{CO}_2$.

• Gas Concentrations:

  • Inhaled Air: Approximately $21\%$ Oxygen ($\text{O}_2$) and $0.04\%$ Carbon Dioxide ($\text{CO}_2$).

  • Exhaled Air: Approximately $16\text{--}17\%$ Oxygen ($\text{O}_2$) and $4\text{--}5\%$ Carbon Dioxide ($\text{CO}_2$).

Distinction Between Breathing and Respiration

• Breathing: Physical mechanism involving external gas intake (inhalation) and exhaust (exhalation).

• Respiration: Chemical metabolic process inside cells that releases chemical energy from nutrient breakdown.

Cultural Breathing Techniques

• Pranayama: Ancient Indian breath control practice enhancing pulmonary efficiency and focus.

• Tummo Breathing: Practiced in Ladakh to optimize lung capacity and produce body heat in extreme cold conditions.

• Rhythmic Chanting: Merges structured respiration with sound resonance to cultivate mental composure.

Transport and Respiratory Systems in Other Animals

• Circulatory System: Consists of the heart, blood vessels, and blood; pumps oxygen and absorbed nutrients to cells while collecting biological waste products.

• Health Warning on Smoking: Directly damages pulmonary alveoli, causes chronic coughing, triggers serious respiratory illnesses, and induces lung cancer. Secondhand/passive smoking poses high health risks to children, pregnant women, and the elderly.

• Breathing Mechanisms Across Species:

  • Terrestrial Vertebrates (Birds, Elephants, Lions, Cows, Lizards, Snakes): Breathe via structural lungs.

  • Fish: Use highly vascularized gills to absorb dissolved oxygen directly from water.

  • Amphibians (e.g., Frogs): Tadpoles utilize external gills; adult frogs utilize lungs on land and gas exchange through moist skin in water.

  • Earthworms: Perform gas exchange entirely across their moist outer skin surface.

Summary Matrix of Digestive and Respiratory Features

Review Questions & Exercises

• Question 1 (Alimentary Canal Pathway):

  • Complete sequence: Mouth $\rightarrow$ Oesophagus $\rightarrow$ Stomach $\rightarrow$ Small Intestine $\rightarrow$ Large Intestine $\rightarrow$ Rectum $\rightarrow$ Anus.

• Question 2 (Iodine Testing Experiment):

  • Sahil (Test Tube A - Unchewed Chapati): Turns blue-black because intact starch is present.

  • Neha (Test Tube B - Chewed Chapati): Remains clear/light brown because saliva converted starch into simple sugar.

  • Santushti (Test Tube C - Boiled & Mashed Potato): Turns deep blue-black because mashed potato contains high levels of starch without salivary enzymes.

• Question 3 (Diaphragm Role):

  • Correct answer: (iii) To help in inhalation and exhalation.

• Question 4 (Matching Parts and Functions):

  • (i) Nostrils $\rightarrow$ (a) fresh air from outside enters.

  • (ii) Nasal passages $\rightarrow$ (d) tiny hair and mucus help to trap dust and dirt from the air we breathe.

  • (iii) Windpipe $\rightarrow$ (e) air reaches our lungs through this part.

  • (iv) Alveoli $\rightarrow$ (b) exchange of gases occurs.

  • (v) Ribcage $\rightarrow$ (c) protects lungs.

• Question 5 (Breathing vs. Respiration Conceptual Questions):

  • Probe 1: Does breathing take place inside cells or through respiratory tracts?

  • Probe 2: Does breathing release energy from food, or is energy released through cellular chemical reactions?

• Question 6 (Inhalation Accuracy Analysis):

  • Tanu's statement ("We inhale air rich in oxygen") is correct. We do not inhale pure oxygen (Shanu) or raw unfiltered gas without specific utilization (Anu); atmospheric air composed of $21\%$ oxygen enters the lungs.

• Question 7 (Sneezing Reflex):

  • Sneezing is an involuntary reflex triggered by irritation of the nasal mucosa when dust particles bypass nasal hairs, expelling trapped foreign matter.

• Question 8 (Post-Exercise Respiration Variations):

  • Explanation 1: Anusha may have exerted higher muscular effort or run at a faster speed, demanding higher ATP/energy output requiring elevated oxygen uptake.

  • Explanation 2: Variable underlying lung capacity, basal metabolic rate, or cardiovascular conditioning.

• Question 9 (Yadu's Rice Flour & Saliva Experiment Analysis):

  • Objective: To test if saliva breaks down starch present in rice flour into sugars over an incubation period of $35\text{--}45\,\text{minutes}$.

• Question 10 (Rakshita's Lime Water Experiment):

  • Objective: To compare $\text{CO}_2$ concentration in inhaled atmospheric air versus exhaled alveolar air.

  • Confirmation: Test tube B turns milky much faster than test tube A due to high $\text{CO}_2$ in exhaled breath.