Biology: Y8

Enzymes and Their Roles in Digestion

Enzymes are biological catalysts that speed up chemical reactions in the body, particularly in digestion, where they break down complex food molecules into simpler, absorbable substances.

  1. Carbohydrase (e.g., Amylase):

    • Breaks down carbohydrates into simple sugars, such as glucose.

    • Found in saliva (produced by salivary glands) and pancreatic juice.

    • Begins carbohydrate digestion in the mouth, allowing for quick energy release.

  2. Protease (e.g., Pepsin and Trypsin):

    • Breaks down proteins into amino acids, which are essential for growth and tissue repair.

    • Active in the stomach (where pepsin works in acidic conditions) and the small intestine.

    • Stomach acid provides an optimum pH for protease enzymes in the stomach, activating them to break down protein chains into smaller peptides.

  3. Lipase:

    • Breaks down lipids (fats) into fatty acids and glycerol.

    • Mainly produced by the pancreas and acts in the small intestine.

    • Requires bile for optimal function, as bile emulsifies fats, breaking them down into smaller droplets that make it easier for lipase to act.

Bile:

  • Produced: In the liver.

  • Stored: In the gallbladder, released into the small intestine.

  • Function: Emulsifies fats, increasing the surface area for lipase to work on. Bile neutralizes stomach acid to create an alkaline environment in the small intestine, optimal for enzyme activity.

Digestive System and the Pathway of Food

The digestive system consists of a series of organs that process food, absorb nutrients, and eliminate waste.

  1. Mouth:

    • Chewing (mastication) breaks down food mechanically.

    • Saliva contains amylase, starting carbohydrate digestion.

    • Food becomes a soft mass called a bolus, making it easier to swallow.

  2. Oesophagus (Gullet):

    • A muscular tube connecting the mouth to the stomach.

    • Moves food via peristalsis—a series of muscle contractions that push food downward.

  3. Stomach:

    • Food is mixed with gastric juices, containing hydrochloric acid and pepsin, beginning protein digestion.

    • The acidic environment kills bacteria and activates protease enzymes.

    • Food becomes a semi-liquid substance called chyme.

  4. Small Intestine:

    • Divided into three parts: the duodenum, jejunum, and ileum.

    • Duodenum: Receives bile and pancreatic juices; site of most enzyme action.

    • Jejunum and Ileum: Primary sites for nutrient absorption into the bloodstream through villi (small finger-like projections that increase surface area).

  5. Large Intestine (Colon):

    • Absorbs water and salts from undigested food, forming solid waste.

    • Home to gut bacteria, which help break down any remaining nutrients and produce vitamins like Vitamin K.

  6. Rectum:

    • Stores faeces until it’s ready to be expelled.

  7. Anus:

    • The final exit point for waste removal from the body.

Digestive Juices:

  • Contain enzymes like amylase, protease, and lipase to break down food into absorbable units.

  • Prevent nutrient wastage and aid in the efficient uptake of essential nutrients.

Nutrients and Their Importance

Nutrients provide the building blocks for growth, energy, and maintenance of body functions.

  1. Carbohydrates:

    • Primary source of energy.

    • Simple sugars like glucose are absorbed quickly, while complex carbohydrates (like starch) provide sustained energy.

    • Excess carbohydrates are stored as glycogen in muscles and liver or converted to fat.

  2. Lipids (Fats and Oils):

    • Store energy, provide insulation, and protect organs.

    • Essential fatty acids (like omega-3 and omega-6) support brain health and cell structure.

    • Cholesterol, a lipid, is crucial for cell membranes and hormone production but can lead to health problems in excess.

  3. Proteins:

    • Composed of amino acids that are the building blocks of body tissues.

    • Essential for muscle growth, repair, and the production of enzymes and hormones.

    • Complete proteins (like those from animal sources) contain all essential amino acids, while plant-based proteins may need to be combined to ensure all amino acids are consumed.

  4. Vitamins:

    • Support various functions such as immune health (Vitamin C), bone health (Vitamin D), and eye health (Vitamin A).

    • Two types: water-soluble (e.g., B-vitamins and Vitamin C) and fat-soluble (Vitamins A, D, E, K).

    • Fat-soluble vitamins are stored in the body, while water-soluble ones need to be replenished regularly.

  5. Minerals:

    • Important for strong bones (calcium), oxygen transport (iron), and fluid balance (sodium and potassium).

    • Trace minerals (like zinc and selenium) are needed in small amounts but are vital for various biochemical processes.

  6. Water:

    • Essential for hydration, digestion, temperature regulation, and waste elimination.

    • Acts as a solvent for nutrients and helps transport them around the body.

  7. Fiber:

    • Mostly indigestible plant matter that adds bulk to the diet.

    • Helps maintain bowel health, supports digestion, and regulates blood sugar levels.

    • Found in fruits, vegetables, and whole grains.

Breathing and Gas Exchange

Breathing, or respiration, is the process of taking in oxygen and expelling carbon dioxide.

  1. Path of Air:

    • Inhalation: Air enters through the nose/mouth, passes through the trachea, bronchi, and bronchioles, and finally reaches the alveoli.

    • Exhalation: The process reverses, removing carbon dioxide.

  2. Gas Composition and Exchange:

    • Inhaled Air:

      • Nitrogen (N₂): 78%

      • Oxygen (O₂): 20.96%

      • Carbon Dioxide (CO₂): 0.04%

      • Other gases: 1%

    • Exhaled Air:

      • Nitrogen (N₂): 78%

      • Oxygen (O₂): 16%

      • Carbon Dioxide (CO₂): 4%

      • Other gases: 2%

  3. Alveoli and Gas Exchange:

    • Small air sacs in the lungs where gas exchange occurs.

    • Oxygen diffuses from alveoli into blood capillaries, while carbon dioxide diffuses from blood into alveoli to be exhaled.

    • Surrounded by a network of capillaries to facilitate efficient gas exchange.

  4. Mechanics of Breathing:

    • Inhalation:

      • Intercostal muscles contract, lifting the ribcage.

      • Diaphragm contracts and flattens, expanding the chest cavity.

      • Increased chest volume decreases internal pressure, drawing air in.

    • Exhalation:

      • Intercostal muscles relax, lowering the ribcage.

      • Diaphragm relaxes, moving upward, reducing chest volume.

      • Decreased chest volume increases internal pressure, pushing air out.

  5. Control of Breathing:

    • Managed by the brainstem, which detects CO₂ levels in the blood.

    • Higher CO₂ triggers faster breathing to expel it and maintain the oxygen-carbon dioxide balance.