IGCSE Biology Paper-4: Specimen Questions with Answers 247 - 247 of 279

Question 247


Describe in Detail


Mechanically digested food travels from the mouth to the stomach. The gastric juice in the stomach contains hydrochloric acid, giving a low pH environment.

Explain why it is important to have a low pH in the stomach.


  • First Round Defense: The intense acidity of the stomach is inhospitable to most life forms, creating a first round of defense against pathogens and parasites. When the stomach pH gets too high (less acidic) , the bad guys end up surviving and entering the small intestine where they can cause big problems for your gut.
  • Break Down Food: This, of course, is what the stomach is best known for. The acidic environment helps break down all the big macromolecules of food. Things like protein, fiber, and fats into smaller and smaller building blocks that your body can absorb and use.
  • Activate Digestive Enzymes: The stomach lining and pancreas make a whole menu of enzymes that help to break down your food even faster. However, as a safety precaution for your cells, they are made in an inactive state and then sent into the stomach cavity. When the pH is low enough, they “switch on” to their active state and begin the important work of digestion. But only if the pH is low enough. If your stomach is too alkaline, many important enzymes will remain inactive and your digestion will be impaired, causing many other problems later.
  • Prevent Heartburn and Chest Pain: This may surprise you, but the real cause of heartburn and chest pain is not an overabundance of stomach acid. The sensations come from stomach acid getting into the wrong place, namely your esophagus. There is a special valve that separates the stomach and esophagus called the lower esophageal sphincter, or LES. And this valve is pH-activated, much like the digestive enzymes. You see, as you eat food, your stomach begins secreting more stomach acid. The pH gets lower and lower and once it reaches a certain threshold, the LES closes off (but is opened by the swallow reflex) . This keeps the stomach contents in the stomach.
  • Timing of Digestion: Most of your body՚s processes are woven into an intricate and precise network of signals and timing mechanisms to make sure everything happens at just the right time. Your stomach pH is a part of this. It has its own fluctuations in pH that are tied to your daily eating routines, psychological expectations, and even smells. After eating, your stomach will slowly become less acidic as the acid is used to break down food. At a certain pH, the digested food matter (called chyme) is a signal to release the food into the small intestine. But if your stomach pH is too alkaline to begin with, this signaling mechanism is impaired, opening too early and allowing partially digested food into the small intestine.
  • Nutrient Absorption: Many nutrients in food are bound up in hard-to-digest structures like fiber or phytates. This is especially the case for nuts, grains, and fibrous vegetables. Minerals like calcium or essential vitamins like B-12 need a highly acidic environment to pull them out of their complexes so they can be absorbed by our body. Without enough acid, you cannot get the full nutritional value of your food.
  • Manage Gastrointestinal Issues like Gas and Bloating: Earlier we discussed how low acidity can allow the wrong microorganisms into our gut along with partially digested food matter in the chyme. The consequences of this are gas, painful bloating, and an imbalanced microbe. The partially digested food acts as the wrong kind of fuel for your gut bacteria. They ferment it, turning it into gas the same way brewer՚s yeast carbonates beer or baker՚s yeast makes bread rise. The effects are in a different stage of the digestive tract, but the source of the problem lies in a stomach without enough acidity.
  • Mitigates Food Allergies and Leaky Gut: These undigested food particles and bad bacteria then have a second, more subtle effect. The stress they place on your gut can cause micro perforations in the gut lining, commonly referred to as “Leaky Gut.” When this happens, food and bacteria can enter your bloodstream, putting your immune system on high alert.

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