The correct option for the route a piece of bread takes through the digestive system of a mammal is
A. oral cavity - oesophagus - stomach - ileum - rectum.
Step-by-Step Explanation:
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Oral Cavity: The journey begins in the oral cavity (mouth), where the bread is mechanically broken down by chewing (mastication) and mixed with saliva. Saliva contains enzymes like amylase that start the process of carbohydrate digestion.
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Oesophagus: After chewing, the bread forms a soft mass called a bolus. This bolus is pushed to the back of the throat and enters the oesophagus, a muscular tube that connects the mouth to the stomach. The movement through the oesophagus is facilitated by peristalsis, which are wave-like muscle contractions that push the bolus down.
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Stomach: Once the bolus reaches the stomach, it is mixed with gastric juices, which contain hydrochloric acid and digestive enzymes. This acidic environment helps further break down the food and kill any harmful bacteria. The bread is transformed into a semi-liquid substance called chyme.
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Ileum: The chyme then moves into the small intestine, specifically the ileum, which is the final part of the small intestine. Here, nutrients from the bread are absorbed into the bloodstream. The ileum is lined with villi and microvilli, which increase the surface area for absorption.
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Rectum: After the nutrients have been absorbed, any remaining undigested material moves into the large intestine and eventually reaches the rectum, where it is stored until it is expelled from the body as feces.
Why Option A is Correct:
- Option A correctly outlines the entire digestive process from the oral cavity to the rectum, including all necessary organs in the correct order. It accurately reflects the pathway food takes through the digestive system of a mammal.
Why the Other Options are Incorrect:
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Option B (oral - cavity - stomach - oesophagus - duodenum - ileum - rectum): This option incorrectly places the stomach before the oesophagus. The oesophagus must come after the oral cavity and before the stomach in the digestive pathway. Additionally, the duodenum is part of the small intestine but is not mentioned in the correct sequence for this question.
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Option C (oral cavity - oesophagus - duodenum - rectum): This option omits the stomach entirely. After the oesophagus, the food must pass through the stomach before reaching the duodenum. The rectum is also incorrectly placed as it should come after the ileum, not directly after the duodenum.
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Option D (oral cavity - oesophagus - ileum - stomach - duodenum - rectum): This option incorrectly places the ileum before the stomach. The correct sequence must have the stomach before the ileum, as digestion and nutrient absorption occur in that order.
Common Pitfalls:
- Confusing the order of the digestive organs can lead to incorrect answers. Remember that the oesophagus always comes after the oral cavity and before the stomach.
- Not recognizing the role of each organ in the digestive process can lead to misunderstandings about nutrient absorption and digestion.
Revision Summary:
- The correct digestive pathway for a piece of bread is: oral cavity → oesophagus → stomach → ileum → rectum.
- The oral cavity initiates digestion with mechanical and enzymatic breakdown.
- The oesophagus transports the bolus to the stomach via peristalsis.
- The stomach further digests food before it enters the ileum for nutrient absorption.