Organisation: digestion

Main role of the digestive system

To break down large insoluble molecules into small soluble ones so they can be absorbed into the bloodstream.

What is Peristalsis?

The rhythmic contraction and relaxation of muscles in the wall of the gut that pushes food along.

Two roles of Hydrochloric Acid (HCl) in the stomach

1. To kill harmful bacteria/pathogens. 2. To provide the optimum acidic pH (pH 2) for protease enzymes.

Role of stomach mucus

To protect the stomach lining from being digested by its own acid and enzymes.

Small intestine: Villi adaptations

Massive surface area, one-cell thick walls (short diffusion path), and a rich blood supply to maintain a concentration gradient.

Function of the Large Intestine

To absorb water from undigested food, leaving behind solid waste (faeces).

Chemical elements in Carbohydrates and Lipids

Carbon, Hydrogen, and Oxygen.

Chemical elements in Proteins

Carbon, Hydrogen, Oxygen, and Nitrogen.

Monomer vs. Polymer

A monomer is a single small unit (e.g. glucose); a polymer is a long chain of monomers (e.g. starch).

Starch vs. Glucose energy release

Glucose is used for quick energy (respiration); Starch is a polymer that releases glucose slowly.

Enzyme definition

A biological catalyst made of protein that speeds up reactions without being used up.

Lock and Key Theory

The substrate has a shape complementary to the enzyme's active site; they bind to form an enzyme-substrate complex.

What does 'Denature' mean?

High temperature or extreme pH changes the shape of the active site so the substrate no longer fits (the reaction stops).

Amylase (Carbohydrase): Site and Reaction

Produced in Salivary Glands, Pancreas, Small Intestine. Breaks Starch into Glucose.

Protease: Site and Reaction

Produced in Stomach, Pancreas, Small Intestine. Breaks Proteins into Amino Acids.

Lipase: Site and Reaction

Produced in Pancreas and Small Intestine. Breaks Lipids into Glycerol and Fatty Acids.

Bile: Production and Storage

Produced in the Liver; stored in the Gallbladder.

Bile: Role in Neutralisation

It is alkaline to neutralise stomach acid, providing the optimum pH for enzymes in the small intestine.

Bile: Role in Emulsification

It breaks large fat droplets into smaller ones, increasing the surface area for lipase enzymes to work.

Food Test: Starch

Add Iodine solution. Positive result: Orange/Brown turns Blue-Black.

Food Test: Reducing Sugars (Glucose)

Add Benedict’s solution and heat in a water bath. Positive result: Blue turns Brick-Red.

Food Test: Proteins

Add Biuret solution. Positive result: Blue turns Purple/Lilac.

Food Test: Lipids (Ethanol Test)

Add Ethanol to the sample, shake, then add to water. Positive result: A cloudy white emulsion forms.

Vitamin A: Use and Deficiency

Good vision and healthy skin. Deficiency: Night Blindness. Found in liver/carrots.

Vitamin C: Use and Deficiency

Tissue repair and healthy gums. Deficiency: Scurvy. Found in citrus fruits.

Vitamin D: Use and Deficiency

Helps bones absorb calcium. Deficiency: Rickets. Found in eggs/oily fish/sunlight.

Calcium: Use and Deficiency

Strong bones and teeth. Deficiency: Rickets/Osteoporosis. Found in milk/cheese.

Iron: Use and Deficiency

To make haemoglobin for oxygen transport in red blood cells. Deficiency: Anaemia. Found in red meat/spinach.

Metabolism definition

The sum of all the chemical reactions in a cell or the body.

Metabolic reaction examples

Converting glucose to starch/glycogen; forming lipids; breaking down excess proteins into urea.

Energy in Food (J) calculation

Energy (J) = Mass of water (g) x Temperature change (°C) x 4.2.

Role of Dietary Fibre

Provides bulk to help food move through the gut via peristalsis, preventing constipation.