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Questions and Answers
What determines the specificity of an enzyme for its substrate?
What determines the specificity of an enzyme for its substrate?
What effect does increasing temperature have on enzyme activity, up to the optimum temperature?
What effect does increasing temperature have on enzyme activity, up to the optimum temperature?
If an enzyme becomes denatured, what is the most likely consequence?
If an enzyme becomes denatured, what is the most likely consequence?
Which pH condition would most likely lead to a decrease in enzyme activity?
Which pH condition would most likely lead to a decrease in enzyme activity?
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How does an increase in substrate concentration affect enzyme reactions?
How does an increase in substrate concentration affect enzyme reactions?
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What is the role of salivary amylase in the digestive system?
What is the role of salivary amylase in the digestive system?
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What does a bomb calorimeter measure regarding food energy?
What does a bomb calorimeter measure regarding food energy?
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In the Visking tubing experiment, why can glucose diffuse through the tubing but starch cannot?
In the Visking tubing experiment, why can glucose diffuse through the tubing but starch cannot?
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Which enzyme is responsible for breaking down proteins into peptides in the stomach?
Which enzyme is responsible for breaking down proteins into peptides in the stomach?
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What is the main advantage of using a bomb calorimeter over simple calorimeters?
What is the main advantage of using a bomb calorimeter over simple calorimeters?
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What happens to the frequency of successful enzyme-substrate collisions when the enzyme is denatured?
What happens to the frequency of successful enzyme-substrate collisions when the enzyme is denatured?
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What product is formed when maltose is further broken down by maltase?
What product is formed when maltose is further broken down by maltase?
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Which factor does NOT affect enzyme activity?
Which factor does NOT affect enzyme activity?
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What is produced when lipase acts on lipids?
What is produced when lipase acts on lipids?
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What is a balanced diet primarily composed of?
What is a balanced diet primarily composed of?
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Which nutrient is primarily stored in plant cells as starch?
Which nutrient is primarily stored in plant cells as starch?
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What can result from a deficiency of calcium in the human body?
What can result from a deficiency of calcium in the human body?
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Which vitamin is essential for preventing scurvy?
Which vitamin is essential for preventing scurvy?
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What is the main function of lipids in the body?
What is the main function of lipids in the body?
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Which process is primarily involved in the breakdown of food in the esophagus?
Which process is primarily involved in the breakdown of food in the esophagus?
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What indicates the presence of starch in a food test?
What indicates the presence of starch in a food test?
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Which nutrient is necessary for muscle growth and repair?
Which nutrient is necessary for muscle growth and repair?
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What is indicated by the blue color in the Benedict’s test for normal amylase at the start of the experiment?
What is indicated by the blue color in the Benedict’s test for normal amylase at the start of the experiment?
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Why does the iodine test remain orange for boiled amylase at both the start and end of the experiment?
Why does the iodine test remain orange for boiled amylase at both the start and end of the experiment?
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How does a lack of iron affect the body?
How does a lack of iron affect the body?
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What is the primary role of dietary fiber?
What is the primary role of dietary fiber?
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What is the purpose of the Visking tubing used in the experiment?
What is the purpose of the Visking tubing used in the experiment?
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Which type of fat is considered healthier?
Which type of fat is considered healthier?
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What does a green to orange color change in the Benedict’s test signify?
What does a green to orange color change in the Benedict’s test signify?
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What role do villi play in lipid digestion which is not simulated in this experiment?
What role do villi play in lipid digestion which is not simulated in this experiment?
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Which of the following statements about proteins is correct?
Which of the following statements about proteins is correct?
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What is the reason for the statement that starch is unable to diffuse through the Visking tubing?
What is the reason for the statement that starch is unable to diffuse through the Visking tubing?
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What substance is primarily produced by the liver to aid lipid digestion?
What substance is primarily produced by the liver to aid lipid digestion?
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Which condition is linked with the lack of phosphorus in the body?
Which condition is linked with the lack of phosphorus in the body?
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What happens to the amylase after it is boiled?
What happens to the amylase after it is boiled?
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What condition is observed regarding glucose at the end of the experiment using normal amylase?
What condition is observed regarding glucose at the end of the experiment using normal amylase?
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Why does the iodine test remain unchanged for normal amylase at the end of the experiment?
Why does the iodine test remain unchanged for normal amylase at the end of the experiment?
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Which factor primarily impacts amylase's ability to interact with starch?
Which factor primarily impacts amylase's ability to interact with starch?
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Study Notes
Balanced Diet
- A balanced diet contains carbohydrates, lipids, proteins, vitamins, minerals, fiber, and water in the right proportions.
- This ensures the optimal intake of all necessary nutrients for the body to function correctly.
Energy Requirements
- Peak energy requirements are typically around 25 years old.
- Energy requirements decrease after peak age.
- Pregnant women need more energy.
- Active lifestyles require more energy.
Food Groups and Function
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Carbohydrates
- Composed of carbon, hydrogen, and oxygen.
- Found in starch, fructose, lactose, and sucrose.
- Starch is stored in plant cells and is a large, insoluble molecule.
- Glycogen is stored in animal cells and is a large, insoluble molecule.
- Provide the main source of short-term energy.
- Broken down into smaller soluble molecules like glucose to allow for diffusion.
- Used in respiration to release energy.
- Starvation can occur from lack of carbohydrates.
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Lipids
- Made of oxygen, hydrogen, and carbon.
- Contained in fats, oils, and waxes.
- Act as insulation under the skin reducing heat loss.
- Protect organs from mechanical damage.
- Provide a long-term store of energy.
- Saturated fats have no double bonds and are more common in animal sources.
- Unsaturated fats have double bonds and are linked to a healthier diet than saturated fats.
- Contribute to 10% of the body's mass.
- Flaky skin and a thin body may be signs of lipid deficiency.
- Overconsumption can lead to obesity, high cholesterol, heart disease, high blood pressure and Type 2 Diabetes.
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Proteins
- Contain carbon, oxygen, hydrogen, nitrogen, and sulfur.
- Made of amino acids linked together.
- Humans require 20 amino acids, 10 of which can be synthesized by the body.
- Involved in muscle growth and tissue repair.
- Critical components of enzymes, DNA, and RNA.
- The shape of a protein is vital in its function.
- Contribute to 18% of the body's mass.
- Protein-deficiency disease, known as Kwashiorkor, is common in poorer countries.
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Iron
- Approximately 3g found in the human body.
- Deficiency can lead to anemia.
- Iron deficiency compromises the blood's ability to carry oxygen, causing a pale complexion, dizziness, and tiredness.
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Calcium
- Approximately 1000g found in the human body.
- Helps build and strengthen teeth and bones.
- Deficiency can cause rickets, characterized by soft bones.
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Phosphorus
- Approximately 650g found in the human body.
- Involved in the formation of teeth and bones.
- Phosphorous is a component of DNA, RNA, and ATP.
- Deficiency can cause hypophosphatemia.
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Sodium
- Approximately 100g found in the human body.
- Crucial for regulating body fluids, particularly blood.
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Chlorine
- Approximately 100g found in the human body.
- Vital for regulating body fluids, particularly blood.
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Magnesium
- Approximately 30g found in the human body.
- Contributes to bone formation and is key to cell function.
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Vitamin A
- Deficiency can lead to night blindness and damage to the cornea (xerothalmia).
- Improves night vision.
- Aids in maintaining a healthy immune system.
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Vitamin B1
- Deficiency leads to Beri-beri.
- Vital for cellular respiration.
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Vitamin B2
- Deficiency causes poor growth and dry skin.
- Crucial for cellular respiration.
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Vitamin B3
- Deficiency leads to Pellagra, causing a dry, red rash, poor growth, and digestive issues.
- Important for cellular respiration.
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Vitamin C
- Deficiency causes scurvy.
- Scurvy results in wounds failing to heal, bleeding gums, and weakness.
- Involved in connective tissue, skin, blood vessels, and cartilage.
- Helps heal wounds.
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Vitamin D
- Deficiency can cause rickets.
- Helps bones absorb calcium and phosphate.
- Aids in maintaining strong bones.
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Dietary Fiber
- Type of carbohydrate known as cellulose (used in plant cell walls).
- Cellulose is not digestible by humans.
- Helps prevent constipation by providing bulk for bowel movements.
- Reduces the risk of bowel cancer.
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Water
- Necessary for essential chemical reactions within the body, including those within the plasma and cytoplasm.
- Acts as a solvent and transportation medium for reactions and temperature regulation.
Digestive System
-
Mouth/Tongue
- Mechanically breaks down food into smaller pieces (bolus).
- Mixes food with salivary amylase to begin starch digestion.
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Salivary Gland
- Secretes salivary amylase, an enzyme that breaks down starch.
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Esophagus
- Transports food from the mouth to the stomach.
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Liver
- Produces bile, which emulsifies lipids (reduces size) to increase surface area for digestion by lipase enzymes.
- Helps neutralize hydrochloric acid from the stomach.
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Stomach
- Stomach walls secrete hydrochloric acid (pH 2).
- Kills bacteria ingested with food.
- Secretes pepsin, which breaks down proteins into peptides.
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Gall Bladder
- Stores bile produced by the liver.
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Pancreas
- Produces pancreatic enzymes.
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Small Intestine (Duodenum & Ileum
- Absorbs soluble products from digested food, including water.
- Small villi increase surface area for efficient diffusion.
- Capillaries in the villi transport absorbed nutrients to the circulatory system.
- Lacteals in the villi transport dietary lipids.
- Amino acids are transported directly into the blood.
- Epithelium is one cell thick to enhance diffusion rate.
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Large Intestine (Colon & Rectum
- Stores indigestible waste (mainly cellulose, water, and indigestible remains).
- Absorbs water.
- The rectum stores semi-solid waste (feces).
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Anus
- Ejects feces from the body.
Peristalsis
- Two pairs of muscles in the gut work together to push food along.
- Circular muscles form rings around the gut.
- Longitudinal muscles run along the length of the gut.
- Waves of muscle contractions move food through the digestive system.
Enzymes
- Biological catalysts that speed up the rate of reaction by lowering the activation energy in living organisms.
Food Tests
-
Starch
- Place a sample on a spotting tile.
- Add 2-3 drops of iodine solution.
- A blue-black color indicates the presence of starch.
- An orange-brown color indicates the absence of starch.
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Glucose
- Place sample of food into a test tube.
- Add 5cm3 of water.
- Add 5cm3 of Benedict's solution.
- Mix thoroughly.
- Heat the test tube in a water bath at 80-100°C for 5 minutes.
- Blue color indicates no glucose present.
- Green or yellow color indicates a small amount of glucose present.
- Brick red color indicates a significant amount of glucose present.
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Protein
- Mix the sample with Biuret solution.
- Shake thoroughly.
- A purple color indicates the presence of protein.
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Lipids
- Add water to a test tube.
- Add sample to test tube.
- Add a few drops of ethanol to the test tube.
- Shake the mixture.
- A milky white color (emulsion) indicates the presence of lipids.
Enzymes
- Enzymes are proteins that catalyse specific reactions.
- Enzymes are specific to their substrates, meaning they only work on one type of molecule.
- The shape of the active site on an enzyme is complementary to the shape of the substrate.
- An enzyme and substrate join at the active site to form an enzyme-substrate complex, which lowers the activation energy needed for the reaction to occur.
- After the products are formed, they leave the active site.
Factors Affecting Enzymes
Temperature
- Increasing temperature up to the optimum temperature increases the rate of reaction.
- This is because increased temperature provides more kinetic energy to the enzyme and substrate molecules, leading to more collisions and enzyme-substrate complex formation.
- However, increasing the temperature past the optimum temperature causes enzymes to denature.
- Denaturation changes the shape of the active site, preventing substrates from binding and decreasing the rate of reaction.
pH
- pH affects the structure of the enzyme molecule.
- Changes in pH can alter the shape of the active site, preventing substrates from binding.
- As a result, the number of successful collisions between enzyme and substrate decreases, lowering the rate of reaction.
Concentration of Substrate
- As the concentration of substrate increases, the rate of reaction increases.
- This is because there are more substrates available to collide with the enzyme, leading to more enzyme-substrate complexes forming.
Digestive Enzymes
| Enzyme | Function | Source of Enzyme | Where it is Secreted |
|---|---|---|---|
| Salivary Amylase | Starch → maltose | Salivary glands | Mouth |
| Pancreatic Amylase | Starch → maltose | Pancreas | Small intestine |
| Maltase | Maltose → glucose | Wall of small intestine | Small intestine |
| Pepsin | Proteins → peptides | Stomach wall | Stomach |
| Trypsin | Proteins → peptides | Pancreas | Small intestine |
| Peptidases | Peptides → amino acids | Wall of small intestine | Small intestine |
| Lipase | Lipids → glycerol and three fatty acids | Pancreas | Small intestine |
Calorimeters
- Calorimeters measure the energy released from food samples by burning them.
- The energy released by the food heats up the water in the calorimeter.
- The energy released is calculated using the volume of water, mass of food, and change in temperature.
Bomb Calorimeter Features
- Improved accuracy because energy from food isn't lost while transferring.
- Minimal heat loss to the surroundings.
- Complete combustion of food due to oxygen supply, ensuring all energy is released.
- Insulation to minimize heat loss from the water.
Visking Tubing Experiment
- Visking tubing is a partially permeable membrane that allows small, soluble molecules to pass through but not large, insoluble molecules.
- Starch is large and insoluble, while glucose is small and soluble.
- This experiment models the ileum in the small intestine, where only small, soluble molecules can pass through the wall and into the capillaries.
Visking Tubing Experiment Components
-
Boiling Tube 1: Normal Amylase and Starch
- Start: Iodine test is orange, indicating no starch outside the tubing (amylase hasn't broken it down yet). Benedict's test is blue, indicating no glucose outside the tubing (amylase hasn't broken down starch into maltose and glucose).
- End: Iodine test is orange, indicating no starch outside the tubing (starch can't pass through the membrane). Benedict's test is green to orange, indicating a positive result for glucose. This shows that amylase broke down the starch into small, soluble glucose molecules that diffused through the Visking tubing.
-
Boiling Tube 2: Boiled Amylase (denatured) and Starch
- Start: Iodine test is orange, indicating no starch outside the tubing (starch is too large to pass through the membrane). Benedict's test is blue, indicating no glucose outside the tubing.
- End: Iodine test is orange, indicating no starch outside the tubing (starch is too large to pass through the membrane). Benedict's test is blue, indicating no glucose outside the tubing. This is because boiling the amylase denatures it, changing the active site shape and preventing it from breaking down starch into glucose.
-
The Visking tubing experiment is a good model of the ileum in the small intestine; however, it doesn't simulate the villi that help break down lipids.
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IGCSE Biology Edexcel DS
