Digestive System Topic
Must-Know Question

These science revision notes aim to help your child understand the digestive system.

This question can confuse many science students (even the primary 6 students!).

Do focus on the graph (especially the labels).

 

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Question (source: TaoNan Primary School 2022 P4 SA2 Q30)

Maria ate a plate of chicken rice. The graph below shows the amount of undigested food leaving each organ of her digestive system, P, Q, R, large intestine and gullet, after a meal.

(a) Identify organs P and Q. Explain why the amount of undigested food leaving organ P and the large intestine are the same.

STEP 1

Identify the keywords/evidence in the questions:

  • Leaving each organ (not entering each organ!)
  • Amount of undigested food leaving large intestine is the same as P
  • Amount of undigested food leaving gullet is the same as Q

 

STEP 2: What Science topics are tested?

1. Recognise the different parts of the digestive system and their functions.

  • Mouth: produce saliva that contains enzyme which breaks down the food into simpler substances. Saliva also softens the food, making it easier to swallow.
  • Esophagus (gullet): Food travels from the mouth, through the esophagus, to the stomach. No digestive juices are secreted.
  • Stomach: a muscular bag that contracts and relaxes, churning the food and mixing it with gastric juice.
  • Small intestine: Produces intestinal juice that contains enzymes to digest the food into simpler substances. Digestion is completed here and the digested food is absorbed into the bloodstream.
  • Large intestine: Undigested material and water pass along the large intestine. Some of the water is absorbed from the undigested food here.

Refer to this video:

Step 3: Piecing your answer together

Answer: P is small intestine while Q is the mouth. Digestion is completed in the small intestine and no digestion takes place in the large intestine.

 

Common mistakes

Wrong answer: Q is the stomach.

Take note of the keyword. The keyword here is undigested food leaving each organ.

 

(b) Maria cut up her cooked chicken into smaller pieces before eating. Explain how cutting up the chicken meat affects the rate of digestion.

STEP 1: Recall

Identify the keywords/evidence in the questions:

  • Smaller pieces

Whenever keywords such as smaller pieces appear, immediately think about the larger exposed surface area.

 

STEP 2: What Science topics are tested?

  1. Type of digestion that occur.
    • Physical digestion: food is digested into smaller pieces.

E.g.: Chewing food with the teeth

  • Chemical digestion: larger, more complex foods are broken down into smaller, simpler ones.

E.g.: Digestion by digestive juices in the stomach/mouth

Step 3: Piecing your answer together

Answer: Cutting up the chicken meat increases the exposed surface area of the meat to the digestive juices, increasing the rate of digestion.

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