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I/GCSE Biology - Digestive System

Digestive System

July 5, 2021

The purpose of digestion is to break food into molecules that are small enough to be absorbed into the bloodstream. There are two types of digestion in I/GCSE Biology;  👇ðŸŧ 👇ðŸŧ 👇ðŸŧ

Mechanical Digestion: digestion by physically breaking food into smaller pieces (i.e. not using enzymes). Carried out by;

  • mouth and teeth chewing food👄ðŸĶ·
  • stomach churning food

Chemical Digestion: digestion using enzymes

You need to know the following enzymes in I/GCSE Biology;  👇ðŸŧ 👇ðŸŧ 👇ðŸŧ

Bile salts are not technically enzymes. They are made in the liver and stored in the gall bladder. They help by emulsifying lipid (i.e. turning large fat droplets into lots of tiny droplets). This increases the surface area, which helps lipase actually break the lipid down.

 

Bile also has a second job. Bile is alkali, which is important for neutralizing stomach acid as soon as it leaves the stomach. Stomach acid is important because it kills any bacteria that enter the stomach. Stomach acid does not play a significant role in digestion in I/GCSE Biology.

 

 

Ingestion: taking food into the digestive system

Digestion: breaking food down into molecules small enough to be absorbed into the bloodstream.

Absorption: taking molecules into the bloodstream. This happens almost entirely in the small intestine (ileum)

Assimilation: using food molecules to build new molecules in our bodies. I.e. the food molecule physically becomes part of our body.

Egestion: Removing unwanted food from the digestive system (having a poo!). This is not excretion, because the unwanted food has never, technically, been inside the body.

Peristalsis: the contraction of muscle in the intestine wall behind a bolus of food (ball of food). This pushes the bolus through the intestine.

Small intestine adaptations:

Adaptation

 

Explanation

 

Thin wall

 

The intestine wall in thin, which speeds the rate of diffusion of molecules into the blood

 

Rich blood supply

 

This helps carry absorbed molecules away from the intestine quickly. This means there is always a low concentration of food molecules in the blood, which maintains a high concentration gradient

 

Intestine length

 

Roughly 7m long, which increases the surface area

 

Surface Area

Villi and microvilli increase the surface area of the small intestine by 1000x

That's the end of the topic!

Drafted by Joey (Biology)

Reference:

https://getrevising.co.uk/resources/biology_revision_notes8