AS Biology

Enzymes & Digestion

Major parts of the digestive system:

• Oesophagus- carries food from mouth to the stomach. Adapted for transport rather than digestion so is made up of thick muscular wall.
• Stomach- muscular sac with an inner layer that produces enzymes. Role is to store and digest food, especially proteins. Other glands in stomach produce mucus which prevents stomach being digested by its own emnzyes.
• Small intestine- long muscular tube. Food is further digested by enzymes produced in its walls/glands. Inner walls are folded into villi/microvilli to give large surface area. This adaptation is so it can absorb products of digestion into bloodstream.
• Large intestine-absorbs water, food becomes drier and forms faeces.
• Rectum- Faeces are stored here, before being removed via anus in process called eggestion.
• Salivary glands-situated near mouth, pass secretions via duct into mouth, secretions contain amylase which breaks down starch into glucose.
• Pancreas- large gland situated below stomach, produces pancreatic juice, contains protease to digest protein, lipase to digest lipids and amylase to digest starch

What is Digestion?

In humans, as with many organisms, digestion takes place in two stages:

• physical breakdown

Physical breakdown is when the food is large and is broken down into smaller pieces by structures such as teeth. This makes it possible to ingest food and also provides it with a larger surface area for chemical digestion. Food is churned up by the muscles in the walls of the stomach aswell, this is another form of physical digestion.

• chemical breakdown

Chemical digestion breaks down large, insoluble molecules into smaller soluble ones. It is carried out by enzymes. All digestive enzymes function by hydrolysis.There are different types of digestive enzymes, three of which are of importance;Carbohydrases breaks down carbohydrates to monosaccharides, Lipases break down lipids into glycerol and fatty acids, Protease breaks down proteins into amino acids.

Pathogens

'Microorganism' is a genera lterm for a single-celled organism that is too small to be seen without a microscope. Microorganisms include bacteria and viruses. Some microorganisms cause disease and these are called pathogens.

Disease is a description of certain symptoms, either physical or mental. It also suggests a malfunction of the body or mind which adversley affects effects health.

For microorganisms ro be considered as pathogens they must;

• gain entry to host,
• colonise the tissues of the host,
• resist the defences of the host,
• cause damage to the host tissues

Examples include bacteria, viruses and fungi. If a pathogen gets into the host and colonises its tissues an infection results. Disease occurs when an infection leads to recognisable symptoms in the host. When a pathogen is transferred from one individual to another it is known as Transmission.