Digestive System Structure and Function Unit Test

Test · Grade 7 · Science

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Part A: Multiple Choice

• Q1. Which of the following correctly lists the three main functions of the digestive system in the order they occur?

  • Absorption, digestion, elimination
  • Elimination, absorption, digestion
  • Digestion, absorption, elimination
  • Digestion, elimination, absorption

  Answer: Digestion, absorption, elimination

  Explanation: The digestive system first breaks food into nutrients (digestion), then moves nutrients into the bloodstream (absorption), and finally removes leftover waste (elimination).

• Q2. What is the term for the muscular contractions that push food through the digestive system?

  • Absorption
  • Emulsification
  • Peristalsis
  • Chemical digestion

  Answer: Peristalsis

  Explanation: Peristalsis refers to the wave-like muscular contractions that move food along the digestive tract.

• Q3. A student is studying how the stomach contributes to digestion. Which of the following BEST describes the stomach's role in mechanical digestion?

  • It produces enzymes that chemically break down proteins into amino acids.
  • It churns food into a thick liquid called chyme, exposing nutrients to enzymes.
  • It absorbs water and compacts waste before elimination.
  • It stores bile and releases it to emulsify fat droplets.

  Answer: It churns food into a thick liquid called chyme, exposing nutrients to enzymes.

  Explanation: The muscular walls of the stomach churn food into chyme through mechanical digestion, increasing the surface area for enzymatic action.

• Q4. The table below shows the digestive enzymes produced by the pancreas and the nutrients each one breaks down. | Enzyme | Nutrient Broken Down | Product | |----------|----------------------------|--------------------| | Amylase | Complex carbohydrates | Simple sugars | | Trypsin | Proteins | Amino acids | | Lipase | Fats | Fatty acids & monoglycerides | A student eats a meal high in protein. Which pancreatic enzyme would be MOST active during digestion of this meal?

  • Amylase, because it breaks down complex carbohydrates into sugars
  • Lipase, because it breaks down fat molecules into fatty acids
  • Trypsin, because it breaks down proteins into amino acids
  • Pepsin, because it is produced by the pancreas to digest proteins

  Answer: Trypsin, because it breaks down proteins into amino acids

  Explanation: Trypsin is the pancreatic enzyme responsible for breaking down proteins into amino acids, so it would be most active during a high-protein meal.

• Q5. Which organ is responsible for storing bile, which is used to emulsify large fat droplets during digestion?

  • Pancreas
  • Gallbladder
  • Liver
  • Duodenum

  Answer: Gallbladder

  Explanation: Bile is stored in the gallbladder and released to emulsify fat droplets, breaking them into smaller pieces so lipase can act more effectively.

• Q6. A scientist ran an experiment tracking how fat Calories are absorbed when different organs are present. The results are shown below. | Setup | Fat Calories Absorbed | |--------------------------------|-----------------------| | Pancreas only | 27 Cal | | Pancreas + Gallbladder | 86 Cal | | Gallbladder only | 3 Cal | | No accessory organs | 0 Cal | What conclusion is BEST supported by the data?

  • The gallbladder alone is sufficient to fully digest and absorb fat Calories.
  • The pancreas and gallbladder work together to maximize fat digestion and absorption.
  • Fat digestion occurs primarily in the stomach without accessory organs.
  • The gallbladder produces lipase, which is the main enzyme for fat breakdown.

  Answer: The pancreas and gallbladder work together to maximize fat digestion and absorption.

  Explanation: The data shows that the combination of the pancreas (which produces lipase) and the gallbladder (which provides bile for emulsification) results in the greatest fat absorption (86 Cal), far more than either organ alone.

• Q7. Which cells in the stomach produce hydrochloric acid (HCl), which creates an acidic environment that helps the enzyme pepsin work effectively?

  • Chief cells, because they secrete digestive enzymes into the stomach
  • Parietal cells, because they produce hydrochloric acid in the stomach
  • Capillary cells, because they transport acid through the bloodstream
  • Villus cells, because they line the small intestine and aid absorption

  Answer: Parietal cells, because they produce hydrochloric acid in the stomach

  Explanation: Parietal cells produce HCl, which acidifies the stomach environment and activates pepsin for protein digestion.

• Q8. [FIGURE: Diagram of the human digestive system showing the mouth, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, and rectum. Arrows indicate the direction of food movement. The small intestine is highlighted in yellow and labeled 'Site of primary nutrient absorption.'] Based on the diagram, which vessels are responsible for absorbing fatty acids from the small intestine into the body?

  • Capillaries, because they absorb all types of nutrients from the small intestine
  • Lymphatic vessels, because they specifically absorb fatty acids from the small intestine
  • Veins, because they carry deoxygenated blood away from the small intestine
  • Bile ducts, because they transport digested fats out of the small intestine

  Answer: Lymphatic vessels, because they specifically absorb fatty acids from the small intestine

  Explanation: Lymphatic vessels in the small intestine absorb fatty acids, while capillaries absorb sugars, amino acids, and water. These are distinct transport systems.

• Q9. A student eats a baked potato, which is mostly starch (a complex carbohydrate). Which sequence correctly describes how the starch is chemically digested?

  • Starch → fatty acids → monoglycerides → absorbed by lymphatic vessels
  • Starch → amino acids → proteins → absorbed by capillaries
  • Starch → simple sugars → absorbed by capillaries in the small intestine
  • Starch → chyme → bile → absorbed by the large intestine

  Answer: Starch → simple sugars → absorbed by capillaries in the small intestine

  Explanation: Amylase breaks complex carbohydrates (starch) into simple sugars, which are then absorbed by capillaries in the small intestine.

• Q10. The table below shows the percentage of protein Calories converted to amino acids under different stomach conditions. | Stomach Condition | Protein Converted to Amino Acids | |-------------------------------------|----------------------------------| | No special cells | ~2% | | Chief cells only (pepsin) | ~40% | | Parietal cells only (HCl) | ~8% | | Chief cells + Parietal cells | ~97% | What does the data suggest about protein digestion in the stomach?

  • Hydrochloric acid alone is sufficient to fully digest proteins into amino acids.
  • Pepsin and hydrochloric acid work independently with no effect on each other.
  • Pepsin and hydrochloric acid together are required for maximum protein digestion.
  • Chief cells produce more acid than parietal cells, making them more important.

  Answer: Pepsin and hydrochloric acid together are required for maximum protein digestion.

  Explanation: The data shows that neither pepsin nor HCl alone achieves high protein conversion, but together they convert ~97% of protein to amino acids, demonstrating their synergistic relationship.

• Q11. Which organ absorbs water and vitamin K from digested food, and also contains bacteria that can break down fiber into absorbable sugars?

  • Small intestine, because it is the primary site of all nutrient absorption
  • Stomach, because it churns food and absorbs vitamins during digestion
  • Large intestine, because it absorbs water, vitamin K, and fiber-derived sugars
  • Rectum, because it stores and compacts waste before elimination

  Answer: Large intestine, because it absorbs water, vitamin K, and fiber-derived sugars

  Explanation: The large intestine absorbs water and vitamin K, and its bacteria break down fiber into sugars that are also absorbed there.

• Q12. [FIGURE: Flow diagram showing the path of a fat molecule through the digestive system. Boxes labeled in order: 'Mouth (mechanical chewing)' → 'Stomach (churning → chyme)' → 'Small Intestine (bile emulsifies fat droplets)' → 'Small Intestine (lipase breaks fat into fatty acids)' → 'Lymphatic vessels (fatty acids absorbed)' → 'Bloodstream.' Arrows connect each step.] According to the diagram, what role does bile play in fat digestion?

  • Bile chemically breaks fat molecules into fatty acids and monoglycerides.
  • Bile emulsifies large fat droplets into smaller droplets for lipase to act on.
  • Bile transports fatty acids from the small intestine into the lymphatic vessels.
  • Bile activates the enzyme lipase by creating an acidic environment.

  Answer: Bile emulsifies large fat droplets into smaller droplets for lipase to act on.

  Explanation: Bile does not chemically digest fat; instead, it emulsifies fat by breaking large droplets into smaller ones, increasing the surface area for lipase to work.

• Q13. A student designs two digestive systems and tests how many Calories each absorbs from the same food. | System | Organs Included | Calories Absorbed | |--------|------------------------------------------------------|-------------------| | A | Mouth, Esophagus, Small Intestine, Rectum | 41% | | B | Mouth, Stomach, Small Intestine, Pancreas, Rectum | 79% | Which explanation BEST accounts for why System B absorbed more Calories than System A?

  • System B has a rectum, which absorbs the remaining Calories before elimination.
  • System B includes the stomach and pancreas, which improve mechanical and chemical digestion so more nutrients are exposed and broken down for absorption.
  • System A lacks a mouth, so food was never chewed into small enough pieces to be digested.
  • System B absorbed more Calories because the esophagus in System A blocked nutrient flow.

  Answer: System B includes the stomach and pancreas, which improve mechanical and chemical digestion so more nutrients are exposed and broken down for absorption.

  Explanation: The stomach churns food into chyme (mechanical digestion) and the pancreas provides enzymes for chemical digestion, both of which increase the amount of nutrients available for absorption in the small intestine.

• Q14. Mechanical digestion and chemical digestion both play important roles in breaking down food. Which of the following BEST explains how they work together?

  • Mechanical digestion produces enzymes that chemically break down nutrients into simpler molecules.
  • Chemical digestion physically grinds food into smaller pieces to prepare it for absorption.
  • Mechanical digestion breaks food into smaller pieces, increasing surface area so chemical enzymes can break down nutrients more effectively.
  • Mechanical and chemical digestion occur in separate organs and have no effect on each other.

  Answer: Mechanical digestion breaks food into smaller pieces, increasing surface area so chemical enzymes can break down nutrients more effectively.

  Explanation: Mechanical digestion (teeth, stomach churning) breaks food into smaller pieces, exposing more surface area for digestive enzymes to act on during chemical digestion.

• Q15. [FIGURE: Bar graph titled 'Nutrient Absorption by Vessel Type and Location' with four grouped bars. The x-axis shows four scenarios: 'Capillaries – Small Intestine,' 'Capillaries – Large Intestine,' 'Lymphatic – Small Intestine,' 'Lymphatic – Large Intestine.' The y-axis shows Calories absorbed (0–300). Bars show: Sugars absorbed (blue) highest in 'Capillaries – Small Intestine' (~272 Cal); Fatty acids absorbed (orange) only present in 'Lymphatic – Small Intestine' (~175 Cal); Amino acids absorbed (green) only in 'Capillaries – Small Intestine' (~21 Cal); Water absorbed shown as a separate small bar.] A nutritionist wants to maximize absorption of ALL macronutrients (sugars, amino acids, and fatty acids) from food. Based on the graph, which combination of vessels and locations would achieve this goal?

  • Capillaries on the small intestine only, because they absorb the greatest total Calories
  • Lymphatic vessels on both the small and large intestines, because they absorb fatty acids most efficiently
  • Capillaries on the small intestine AND lymphatic vessels on the small intestine, because together they absorb sugars, amino acids, and fatty acids
  • Capillaries on the large intestine AND lymphatic vessels on the large intestine, because the large intestine absorbs all remaining nutrients

  Answer: Capillaries on the small intestine AND lymphatic vessels on the small intestine, because together they absorb sugars, amino acids, and fatty acids

  Explanation: Capillaries in the small intestine absorb sugars and amino acids, while lymphatic vessels in the small intestine absorb fatty acids. Together, they cover all three macronutrients. Neither the large intestine nor lymphatic vessels alone can achieve this.

Part B: True / False

• Q1. Mechanical digestion in the stomach churns food into a thick liquid called chyme, which increases the surface area of nutrients exposed to digestive enzymes.

  Answer: true

  Explanation: The muscular walls of the stomach churn food, transforming food chunks into chyme. This exposes more nutrients to the action of digestive enzymes, making chemical digestion more effective.

• Q2. Fatty acids from digested fats are absorbed directly into the capillaries of the small intestine, following the same pathway as sugars and amino acids.

  Answer: false

  Explanation: Fatty acids are absorbed through the lymphatic vessels of the small intestine, NOT through capillaries. Sugars and amino acids are absorbed through capillaries, but fatty acids require lymphatic vessels because fat does not mix well with the water-based environment of capillaries.

• Q3. The large intestine plays no role in nutrient absorption — its only function is to store and compact waste before elimination.

  Answer: false

  Explanation: The large intestine does absorb nutrients. Bacteria in the large intestine break down some types of fiber into sugars, and the large intestine absorbs those sugars as well as water and vitamin K. It is not limited only to waste storage.

• Q4. The enzyme pepsin works most effectively when the stomach also contains hydrochloric acid produced by parietal cells, because pepsin functions best in an acidic environment.

  Answer: true

  Explanation: Pepsin, produced by chief cells, breaks down proteins into amino acids. Parietal cells produce hydrochloric acid (HCl), which creates the acidic environment that allows pepsin to work at peak efficiency. Together, they significantly increase the amount of protein converted to amino acids.

• Q5. [FIGURE: Diagram of the human digestive system showing the path of food from the mouth through the esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, and rectum, with the pancreas and gallbladder labeled as accessory organs attached near the duodenum.] Based on the diagram, the pancreas and gallbladder are organs through which food passes directly as part of the main digestive pathway from mouth to rectum.

  Answer: false

  Explanation: The pancreas and gallbladder are accessory organs — they do not form part of the main tube through which food travels. Instead, they secrete substances (enzymes and bile, respectively) into the small intestine to aid digestion, but food does not pass through them directly.

Part C: Short Answer

• Q1. The digestive system carries out three major processes in order. Name and briefly define each of the three processes, and identify at least one organ involved in each process.

  Answer: The three processes are: (1) Digestion — the breaking down of food into simple nutrients; organs include the mouth, stomach, and small intestine. (2) Absorption — the movement of nutrients into the bloodstream; organs include the small intestine (via capillaries) and lymphatic vessels. (3) Elimination — the removal of leftover waste from the body; organs include the large intestine and rectum.

• Q2. A student ran an experiment testing how well a digestive system broke down a baked potato (mostly complex carbohydrates) with and without a stomach. The results are shown in the table below. | Digestive System Setup | Complex Carbs Remaining (Cal) | Sugars Produced (Cal) | |------------------------|-------------------------------|------------------------| | Without stomach | 196.68 | 31.32 | | With stomach | 22.26 | 205.74 | Using the data table, explain why the system WITH a stomach converted significantly more complex carbohydrates into sugars. Include the terms 'mechanical digestion,' 'chyme,' and 'enzyme' in your answer.

  Answer: The system with a stomach converted far more complex carbohydrates into sugars (205.74 Cal vs. 31.32 Cal) because the stomach performs mechanical digestion by churning food into a thick liquid called chyme. This process breaks large food chunks into smaller pieces, exposing more surface area to digestive enzymes such as amylase. When food is in smaller pieces, enzymes can act on more of the nutrients, resulting in greater breakdown of complex carbohydrates into simple sugars.

• Q3. [FIGURE: Diagram of the human digestive system showing the mouth, esophagus, stomach, small intestine (labeled with duodenum, jejunum, and ileum), large intestine, and rectum. Arrows indicate the direction of food movement. The small intestine is shown as a long, coiled tube, and the inner wall of the small intestine is shown in an inset with finger-like projections labeled 'villi.' Capillaries and lymphatic vessels are shown threading through the villi.] Using the diagram, explain how the structure of the small intestine is specialized for absorption. In your answer, describe the roles of BOTH capillaries and lymphatic vessels in absorbing different types of nutrients.

  Answer: The small intestine is specialized for absorption because its inner walls are lined with villi — finger-like projections that increase surface area. Capillaries inside the villi absorb sugars and amino acids into the bloodstream. Lymphatic vessels absorb fatty acids from fat digestion. Together, these two vessel types ensure that carbohydrates, proteins, and fats are all absorbed efficiently from the digested food (chyme) passing through the small intestine.

• Q4. A student notices that when the gallbladder is added to a digestive system model, fat digestion improves dramatically. The data below shows the results. | Setup | Fat Calories Converted to Fatty Acids | |-------|---------------------------------------| | Pancreas only (no gallbladder) | 27 Cal | | Pancreas + Gallbladder | 86.36 Cal | Using the data and your knowledge of digestion, explain WHY adding the gallbladder caused such a large improvement in fat digestion. What substance does the gallbladder store, and how does that substance help the enzyme lipase do its job?

  Answer: Adding the gallbladder caused fat digestion to improve from 27 Cal to 86.36 Cal — more than three times as much. The gallbladder stores bile, a chemical that emulsifies fat. Emulsification breaks large fat droplets into many tiny droplets, which greatly increases the surface area of fat exposed to the enzyme lipase. Because lipase is water-based and fat does not normally mix with water, the large fat droplets are difficult for lipase to act on. Once bile breaks the fat into tiny droplets, lipase can efficiently break down the fat into fatty acids and monoglycerides, resulting in much greater fat digestion.

• Q5. A biomedical engineer is designing an artificial digestive system for a research study. She wants the system to absorb as many Calories as possible from a meal that contains carbohydrates, proteins, and fats. Using your knowledge of mechanical digestion, chemical digestion, and absorption, recommend which organs and accessory structures she should include and explain the specific role each plays. Your response should address all three nutrient types.

  Answer: To maximize Calorie absorption from all three nutrient types, the engineer should include the following: (1) Mouth — performs mechanical digestion by chewing food into smaller pieces, increasing surface area for enzymes. (2) Stomach — performs further mechanical digestion by churning food into chyme, exposing more nutrients to enzymes; chief cells produce pepsin to begin protein digestion, and parietal cells produce HCl to create an acidic environment that activates pepsin. (3) Pancreas — produces amylase (breaks complex carbohydrates into sugars), trypsin (breaks proteins into amino acids), and lipase (breaks fats into fatty acids and monoglycerides). (4) Gallbladder — stores bile to emulsify fats, allowing lipase to work more effectively on fat digestion. (5) Small intestine — the primary site of absorption; capillaries absorb sugars and amino acids into the bloodstream, and lymphatic vessels absorb fatty acids. Including all of these organs ensures that carbohydrates, proteins, and fats are all broken down and absorbed efficiently.

Grade

• 7

Subject

• Science

Difficulty

• Medium

Total Points

• 65

Total Questions

• 25

Estimated Time Minutes

• 80

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