Digestion

1. Digestion – Grade 10 HSB
Based on CSEC Concise Human &
Social Biology

2. What is Digestion?
•
•
•
•
•
•
Digestion is the process by which large,
insoluble food molecules are broken down into
small, soluble molecules that can be absorbed
and used by the body.
Ingestion – Taking in food.
Digestion – Mechanical and chemical
breakdown of food.
Absorption – Movement of digested food into
blood and lymph.
Assimilation – Use of absorbed food in cells.
Egestion – Removal of undigested food as
faeces.

3. Types of Digestion
•
•
1. Mechanical Digestion – Physical
breakdown (chewing, churning). Increases
surface area.
2. Chemical Digestion – Enzymes, acids
and bile break down food into simpler,
soluble molecules.

4. The Alimentary Canal
• A long muscular tube starting at the
mouth and ending at the anus. Includes
mouth, oesophagus, stomach, small
intestine, large intestine, rectum and anus.

5. Organs and Functions
Organ Function Digestion Type
Mouth Chewing, saliva with amylase
acts on starch
Mechanical & Chemical
Stomach Stores food, churns, pepsin
digests proteins, HCl kills
bacteria
Mechanical & Chemical
Small Intestine Duodenum receives bile and
pancreatic juice, Ileum
absorbs nutrients
Chemical & Absorption
Large Intestine Absorbs water, salts, vitamins Absorption

6. Digestive Juices and Enzymes
•
•
•
•
•
Mouth – Salivary Amylase: Starch →
Maltose
Stomach – Pepsin: Proteins → Peptides,
HCl activates enzymes
Pancreas – Amylase, Lipase, Trypsin
Liver & Gall Bladder – Bile emulsifies fats
Small Intestine – Maltase, Lactase,
Sucrase, Peptidase, Lipase

7. Absorption
•
•
•
•
Occurs in the ileum. Adaptations: villi &
microvilli, thin walls, rich blood supply,
lacteals.
Carbohydrates → Glucose → Blood
Proteins → Amino acids → Blood
Fats → Fatty acids + Glycerol → Lacteals

8. Assimilation & Egestion
•
•
Assimilation: Use of absorbed food.
Glucose for energy, amino acids for
proteins, fats for membranes and storage.
Egestion: Removal of undigested waste
through anus (not excretion).

9. Key Terms
•
•
•
•
Peristalsis – Rhythmic contraction
pushing food
Bolus – Chewed food + saliva
Chyme – Semi-liquid food in stomach
Emulsification – Breakdown of fats into
droplets by bile

10. Exam Tips
•
•
•
•
•
Always state enzyme + substrate + product.
Compare mechanical vs chemical digestion.
Differentiate absorption, assimilation,
egestion.
Know ileum adaptations.
Excretion vs Egestion difference.