Organisation

• • Cells make up the basis of all living entities.
  • A tissue is a collection of specialized cells with a similar structure and function.
  • Organs are a collection of tissues that work together to carry out a specific function.
  • Organ systems are collections of organs, collaborating to carry out a specific function.
• The purpose of the digestive system is to break down large molecules into smaller, soluble molecules, which are then absorbed into the bloodstream. The rate of these reactions is increased by enzymes.
• Label the following organs/glands in the digestive system:

  A) Mouth

  B) Salivary glands

  C) Oesophagus

  D) Liver

  E) Stomach

  F) Pancreas

  G) Large intestine

  H) Rectum

  I) Small intestine

  J) Gallbladder

  K) Anus

  
• Glands (including the salivary glands and the pancreas) that secrete digestive juices containing enzymes to breakdown food.

  • The stomach, responsible for producing hydrochloric acid, which not only destroys bacteria but also establishes the optimum pH for the activity of the protease enzyme.
  • The small intestine, the site where soluble molecules get absorbed into the bloodstream.
  • The large intestine plays a role in absorbing water from undigested food material to form faeces, which are eventually expelled from the body through the rectum and anus.
• • The liver which produces bile, stored in the gallbladder, assisting in the digestion of lipids. Biles has two main roles:
  • It is alkaline to neutralise hydrochloric acid from the stomach. The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
  • It breaks down large drops of fat into smaller ones, increasing surface area. This is known as emulsification.
• • Enzymes are biological catalysts - substances that increase the rate of reaction without being used up themselves
  • Enzymes play a crucial role in many body reactions.
  • They have the ability to either break down large molecules or combine smaller ones.
  • Enzymes are proteins and their shapes are fundamental to their function.
  • The unique shape of an enzyme’s active site is important as it is the place where the substrate binds to.
• The Lock and Key Hypothesis

  • The substrate has a shape that is complementary to the active site of the enzyme
  • This results in the formation of an enzyme-substrate complex when they bind.
  • The reaction occurs and the products are released from the enzyme.

  
• Enzymes have an optimum temperature.

  • The optimum temperature for most is approximately 37 degrees Celsius (body temperature).
  • The rate of reaction increases with increasing temperature up to this point as molecules have more kinetic energy,
  • Beyond the optimum temperature, the rate decreases sharply, eventually stopping the reaction.
  • Elevated temperatures can break the bonds in the structure, changing the active site shape and preventing substrate binding.
  • In such cases, the enzyme becomes denatured, making it non-functional.

  
• Enzymes have an optimum pH:

  • The optimum pH for the majority of enzymes is 7, although some enzymes have lower optimum pH, such as enzymes in the stomach, which is acidic.
  • Changes in pH (too high or too low) break the bonds holding the amino acid chains, changing the shape of the active site and preventing substrates from binding.
  • This also leads to the enzyme becoming denatured.

  
• As all molecules need to be broken down to be absorbed into the bloodstream, enzymes are important.

  • They are released by cells in many different organs, and are specific to a specific molecule.
• 1. Carbohydrases: Transform carbohydrates to simple sugars.

  • E.g., Amylase breaks down starch into maltose, and is produced in the salivary glands, pancreas, and small intestine (primary site for starch digestion).
• 1. Proteases: Breaks down proteins into amino acids.

  • E.g., Pepsin is produced in the stomach, with other forms present in the pancreas and small intestine.
• 1. Lipases: Breaks down lipids to fatty acids and glycerol, produced in the pancreas and small intestine.
• • Soluble substances like glucose, amino acids, fatty acids, and glycerol are transported in the bloodstream to cells throughout the body, serving as building blocks for new carbohydrates, lipids, and proteins, with some glucose used in respiration.
• • Various tests can test the presence of carbohydrates, proteins, or lipids in a solution:
  • Benedict's test: Identifies sugars, turning brick red.
  • Iodine test: Identifies starch, turning blue-black.
  • Biuret test: Identifies proteins, results in a purple color.
  • Emulsion test: Identifies lipids, using ethanol. Results in a cloudy layer if lipids are present.
  • Alternatively, Sudan III test for lipids forms a red layer on top.
• • Bile, produced in the liver and stored in the gallbladder, is released into the small intestine.
  • It has two functions:

  1. It has an alkaline nature to neutralize the stomach's hydrochloric acid, accommodating the higher (more alkaline) optimal pH of the small intestine enzymes.
  2. Causes large fat droplets to be broken down into smaller droplets (emulsifies), providing a larger surface area for lipase to quickly breakdown lipids into glycerol and fatty acids.
• Effect of pH on the Rate of Reaction of Amylase (Required Practical):

  • Iodine is used to test for the presence of starch. If starch is present, the colour will change to blue-black.
  • The independent variable in the investigation is the pH of the buffer solution.
  • The dependent variable in the investigation is the time taken for the reaction to complete (how long it takes for all the starch to be digested by the amylase).
• Effect of pH on the Rate of Reaction of Amylase (Required Practical):

  • Method:
  • Place iodine drops in each well of a spotting tile.
  • Warm a mixture of amylase, starch, and a buffer solution using a water bath or electric heater (alter the independent variable - buffer solution in each trial).
  • Periodically, extract solution samples and place them in the wells.
  • The end of starch breakdown is indicated by the iodine solution remaining brown instead of turning blue-black. Time this.
  • Replicate the experiment at various pH levels, maintaining consistency in influential factors like temperature.
• • In experiments assessing product formation or reactant consumption over time, use the equation: rate = change/time to determine the rate.
• • The respiratory system, found in the upper part of the body (the thorax), is protected by the ribcage.
  • This system is crucial for supplying oxygen to the blood and eliminating carbon dioxide.
  • The process of gas exchange takes place in the lungs through various structures and mechanisms.
• Components of the Gas Exchange System

  • Trachea: The airways (windpipe) for the movement of air.
  • Intercostal muscles: Contract and relax to ventilate the lungs.
  • Bronchi: air from the trachea moves into bronchi, leading to each lung.
  • Bronchioles: Bronchi split into bronchioles.
  • Alveoli: Small air sacs where gas exchange occurs.
  • Diaphragm: Separates the lungs from digestive organs and aids in inhalation by moving downward.
• Ventilation Process

  1. The ribcage moves up and out and the diaphragm moves down, increasing the chest volume.
  2. This volume increase causes a decrease in pressure, drawing air into the chest.
  3. Air moves from areas of higher pressure (outside the body) to lower pressure (inside the lungs).
  4. The opposite process occurs during exhalation.
• 1. The alveoli fill with oxygen upon inhalation.
  2. Deoxygenated blood in the surrounding capillaries (coming from the pulmonary vein) carries a high concentration of carbon dioxide, a byproduct of respiration.
  3. Oxygen moves down its concentration gradient into the capillary bloodstream, which has a lower oxygen concentration.
  4. Carbon dioxide travels down its concentration gradient from the blood to the alveoli.

  
• Alveoli Adaptations

  • Alveoli are small and arranged in clusters, offering a large surface area for diffusion.
  • A rich blood supply from the capillaries maintains the concentration gradient.
  • Alveoli walls are extremely thin, providing a short diffusion distance.

  Breathing rate can be computed by dividing the number of breaths by the number of minutes.
• • The circulatory system is responsible for transporting oxygen and nutrients to every cell in the body, and it also carries away waste products.
  • At the center of this system is the heart, an organ with a critical role in moving blood through two separate circuits in a double circulatory system.
• The Heart

  • The heart has a double circulatory system, which involves two different circuits:
  • Deoxygenated blood enters the right atrium, moves to the right ventricle, and is then pumped to the lungs for gas exchange.
  • Oxygenated blood enters the left atrium, flows into the left ventricle, and is then circulated throughout the body.

  
• • Characteristics of the heart's structure:
  • Has muscular walls to facilitate a strong heartbeat.
  • The left ventricle has a thicker muscular wall as it pumps blood throughout the entire body, unlike the right ventricle which only pumps it to the lungs.
  • Contains four chambers that segregate oxygen-rich blood from oxygen-poor blood.
  • Equipped with valves to prevent the backflow of blood.
  • Covered in coronary arteries that supply it with oxygenated blood.
• The Process of Blood Circulation

  1. Blood enters the right atrium through the vena cava, and the left atrium through the pulmonary vein.
  2. The atria contract, moving the blood into the ventricles.
  3. Ventricles contract and send blood from the right ventricle to the lungs via the pulmonary artery and from the left ventricle to the rest of the body through the aorta.
  4. Valves close to prevent blood from flowing backwards.

  
• Heart Rate Regulation

  • The natural resting heart rate is around 70 beats per minute, regulated by a group of cells in the right atrium functioning as a pacemaker. These cells emit small electrical impulses that prompt the heart muscles to contract, ensuring sufficient oxygen is distributed to the rest of the body.
  • An artificial pacemaker might be needed to normalize the heartbeat in individuals experiencing irregular rhythms.

  
• 1. Arteries - transport blood away from the heart.

  • Strong muscle layers in the walls.
  • Elastic fibres allow them to expand.
  • Designed to withstand the high pressure from the heart's pumping.

  
• 1. Veins - direct blood towards the heart.

  • Feature a wide lumen to facilitate the flow of low-pressure blood.
  • Contain valves to direct the blood flow correctly.
• 1. Capillaries - facilitate the close passage of blood to cells for substance exchange.

  • Have one-cell-thick walls for a short diffusion distance.
  • Permeable walls enable substance transfer.

  
• Coronary Heart Disease (Non-Communicable)

  • Occurs when the coronary arteries, which supply blood to the heart, are obstructed by a buildup of fatty substances.
  • This blockage reduces the blood and oxygen supply to the heart, potentially leading to a heart attack.
• Solutions for Coronary Heart Disease

  1. Stents (Metal mesh tubes placed in arteries)

  • Ensures arteries remain open for blood flow.
  • Pros:
  • Significantly reduces the heart attack risk.
  • Quick recovery time post-surgery.
  • Cons:
  • Possible heart attack during the procedure or post-operative infection.
  • Potential for blood clot formation near the stent (Thrombosis).
• 1. Statins (Drugs that lower levels of LDL or bad cholesterol)

  • Pros:
  • Decreases the risk of strokes, coronary heart disease, and heart attacks.
  • Elevates levels of HDL or good cholesterol.
  • Cons:
  • Continuous intake may be inconvenient.
  • Potential for side effects.
  • May not offer immediate results as it only decelerates the deposition rate.
• Faulty Valves

  • Occur when a heart valve stiffens or gets damaged, causing inefficient heart function due to blood flowing the wrong direction.
• Solutions for Faulty Valves

  1. Biological Valve Replacement (using pig or cattle valves)

  • Pros:
  • Highly effective.
  • Cons:
  • Limited lifespan (12-15 years).
• Solution for faulty valves:

  1. Mechanical Valve Replacement (man-made)

  • Pros:
  • Durable.
  • Cons:
  • Requires ongoing medication to prevent blood clotting around the valve.
• Heart Failure

  • Can be addressed with a heart transplant.
  • Pros:
  • Artificial hearts are less likely to be rejected as foreign by the immune system.
  • Cons:
  • Limited availability of donors who have recently passed away.
  • Increased vulnerability to infections during surgery.
  • Possible wear and tear of mechanical components and motor failure.
  • Blood clot formation risk, potentially leading to strokes.
  • Blood-thinning medications are necessary but may influence the person's bleeding response to injuries.
• Extreme Blood Loss

  • Can be managed with artificial blood transfusions.
  • Pros:
  • Can sustain individuals even with a loss of 2/3 of their red blood cells, providing more time for new blood cell generation.
  • Cons:
  • Can only be used temporarily before a blood transfusion becomes necessary.