Food is needed to…
- Provide us with energy for our daily activities
- Produce heat to maintain our body temperature
- Grow new cells and tissues
- Maintain a healthy body
- Repair worn-out tissues
Carbohydrates
Found in the form of starch, sugar or cellulose
- Big or small molecule size
- Provides immediate source of energy
[Cellulose- found in plants]
Proteins
Made up of several small molecules called AMINO ACIDS
-Large molecule size FUNCTIONS: -To make new cells for body -To repair worn out tissues -To make complex proteins called enzymes
Fats
Made up of glycerol and fatty acids
-Large and insoluble in water
FUNCTIONS:
-Serves as body’s store of energy
-Prevents the body from losing too much heat
Water
-Very small molecule size
- Acts as a solvent, helping to transport soluble nutrients and excretory products around the body via the bloodstream
- Required for important chemical reactions in cells
- To maintain body temperature
Reason for digestion of food
Cell membranes of cells- [partially permeable]
Large molecules e.g. Fats, starch and proteins CANNOT PASS THROUGH a
The large molecules are broken down during digestion,
allowing it to pass through the cell membrane
Mouth
To cut and grind food into smaller pieces.
-Salivary glands secrete saliva which contains the enzyme, salivary amylase
(Tongue)
- Pushes food around the mouth while we chew
- Pushes the food to the back of the mouth and down into the esophagus
Esophagus (gullet)
A muscular tube measuring about 25cm long
-Does not digest food; [transport food]
Stomach
Glands on the stomach walls secrete gastric juice containing:
-Protease
-hydrochloric acid
Small intestine
Food is mixed with intestinal juice, pancreatic juice and bile to help digestion.
- The liver and pancreas are connected to the small intestine
- The final products are absorbed into the bloodstream
- Undigested food passes into the large intestine
Large intestine:
Colon;
Rectum
[Large intestine]
Colon:
- Absorbs water and mineral salts from undigested food
- Bacteria in the colon make vitamins for the body
Rectum:
- Temporarily stores the remaining undigested food (faeces)
- Faeces leave the body through the anus
Small intestine> Bile, intestinal juice, pancreatic juice
Bile: Liver No Enzyme ---------- Intestinal juice: small intestine Maltase, protease, lipase ---------- Pancreatic juice: Pancreas Amylase, Protease, Lipase
Bile
Yellowish-green fluid stored in the gall bladder
When we eat food, the gall bladder contracts and releases bile into the small intestine through the bile duct
- Bile breaks down fat into smaller fat droplets
- Process: emulsification
Absorption in the small intestine
After digestion is completed in the small intestine, the food molecules are absorbed by the body
- Only food molecules that are small enough can pass through the walls of the small intestine and blood vessels
- The small food molecules enter the bloodstream and are transported throughout the body
- Small Food molecules are absorbed by body cells to be used for respiration, cell repair and other processes
Parts of the digestive system working together
[Physical digestion]
-Teeth grind food into smaller pieces
-Stomach muscles contract and relax to digest food
[Chemical digestion]
-Salary amylase digest starch
-Protease digest proteins
-Starch and proteins are further digested and fat digestion begins
The process of digestion might be affected if an organ of the system is not working.
Enzymes
Enzymes are protein molecules produced by our body to help speed up chemical reactions in our bodies
Chemical reactions occur when large food molecules are broken down into smaller and soluble food molecules
Define ‘enzymes’
Enzymes are complex proteins that speed up the rate of chemical reactions. Enzymes remain unchanged at the end of chemical reactions.
Digestive enzymes, act on food molecules
Type of enzyme: acts on: Converted into
Type of enzyme: Acts on: Converted into
Amylase: Starch: Maltose
Maltese: Maltose: Glucose
Protease: Proteins: Amino acids
Lipase: Fats: Fatty acids and glycerol
