When you eat a cheeseburger from Macdonald, the burger isn’t simply absorbed straight into your body. Your body must break this food down into smaller molecules that can pass into the plasma membrane of the cells in the gut. This process of breaking down complex organic matter into simple organic matter is down by most organisms.

Chemical

Chemical digestion is more complex than physical digestion. Chemical digestion relies on chemicals and specialised digestive enzymes.   

Physical

Like the name suggests Physical digestion, is when food is Mechanically broken down.

Your mouth and stomach both assist in mechanical digestion of your food.

Mechanical digestions is similar to putting food in a blender. It breaks up food into smaller pieces.

Observe the video to the right. The video shows a Didinium digesting a paramecium.

The Didinium engulfs the paramecium through phagocytosis and will releases enzymes to digest it.

In more complex organisms, there are two types of digestion that work together; Physical and Chemical.

During digestion polymers are broken down into their basic monomers through a process known as hydrolysis.

The animation to the left is a hydrolysis reaction of a di-peptide.

Adding water molecule, splits the amino acids. This process is sped up with the help of enzymes.

Chemical digestion occurs through out the whole body. From the mouth to the stomach, the food is constantly being broken down via powerful digestive enzymes.

Within the digestive system there are three main kinds of digestive enzymes

•  Amylases - acts on carbohydrates
•  Proteases - acts on proteins
•  Lipases - acts on lipids

We can break up chemical digestion into two areas, Extra-cellular digestion and Intracellular digestion.

Extra-cellular digestion

This occurs out side of the cell.

In some cases, digestive enzymes are located outside the cell. Breaking down molecules and allowing them to pass immediately into the cell.

The video to the left shows a starfish eating. Starfish will often turn their stomach inside out and release enzymes directly onto the food. This is a form of extra-cellular digestion.

Intra-cellular digestion

This occurs inside.

Most single celled organisms and invertebrates use intracellular digestion to breakdown food.

Food is taken into the cell via phagocytosis and digestive enzymes are released into the vacuole. The enzymes breakdown the food into smaller molecules, capable of passing through the vacuole membrane

This is seen in the animation to the right.

Click here to learn more about the different digestive systems

The reason we chew our food before swallowing it is to increase its surface are to volume ratio. This allows enzyme more space to work on.

Questions

1. What is the purpose of digestion?

2. Which enzyme is used to digest proteins?

3. Which enzyme is used to digest carbohydrates?

4. Define the term hydrolysis?

5. What do enzymes do?

6. What is the difference between physical and chemical digestion and list 2 forms of physical and chemical digestion?

7. Define intra-cellular digestion and give and example

8. Define extra-cellular digestion and give and example

9. Through what process is food ingested into the cell?

10. What is the small membrane sack which holds the food called?