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Chapter 11: Human Digestive System - Coggle Diagram
Chapter 11: Human Digestive System
why do we need food?
it provides us with energy for daily activities (e.g. walking)
it produces heat to maintain our body temperature
it helps us maintain a healthy body
it helps with the growth of new cells and tissues
it repairs worn-out tissues
what is in the food we eat?
carbohydrates
size of molecule can either be big or small
examples
starch - rice, bread, noodles and potatoes
sugar - found in the form of sucrose, glucose and maltose - found in fruits (e.g. bananas and apples
cellulose - found in plants
functions
an immediate source of energy
some carbohydrates make up part of the fibre that the body cannot digest. fibre passes out undigested and forms the bulk in our faeces
simplest form: glucose
proteins
size of molecule is very large
functions
to make new cells for body growth and to repair worn-out tissues
to make complex proteins called enzymes. enzymes speed up the breaking down of food substances in out body
examples: meat, fish, milk, yoghurt and eggs
simplest form: amino acids
fats
size of molecule is large and insoluble in water
function: reserves energy and prevents the body from losing too much heat
examples: butter and cheese
simplest form: fatty acids and glycerol
why must food be digested?
each cell membrane in our body is partially permeable. it allows small molecules to pass through. nutrients (e.g. starch, proteins and fats) are large, complex molecules. these nutrients cannot pass through the cell membrane
large molecules must be broken down into smaller molecules that are small enough to pass through the cell membranes. this occurs during digestion
human digestive system
the mouth
teeth
chew to cut and grind food into smaller pieces. this increases the surface area which enzymes can act on
tongue
rolls food into small balls
salivary glands
produce saliva which wets food to aid swallowing and it contains the salivary amylase, that digests starch into maltose
the oesophagus
food is pushed down the oesophagus to the stomach
no digestion here
the stomach
a muscular bag
contracts and relaxes to churn food, resulting in the breakdown of food into smaller pieces
has glands in the walls
secretes gastric juice that contains the enzyme, protease, that digests proteins into simpler protein molecules. hydrochloric acid, which helps protease to work. the acid also kills bacteria present in the food
the small intestine
long muscular tube
contracts and relaxes, which mixes bile, intestinal juice and pancreatic juice with food to help digestion
absorbs digested food molecules into the bloodstream
digestion ends here
the large intestine
colon
absorbs water and mineral salts from undigested food. what remains is a near-solid waste substance called faeces
rectum
temporarily store faeces
anus
expels faeces in egestion
liver
bile
bile is a fluid produced by liver. it doesn't contain digestive enzymes, but it is able to break up fats into smaller fat droplets (emulsification)
emulsification
it increases the surface area of fats. it allows the lipases in pancreatic juice and intestinal juices to digest fats quickly
intestinal juice
it contains the enzymes maltase, protease and lipase
pancreatic juice
digestive enzymes
what are enzymes?
enzymes are complex proteins that speed up the rate of chemical reactions. enzymes remain unchanged at the end of chemical reactions
types of digestive enzymes
carbohydrases (amylase, maltase)
acts on starch and maltose
protease
acts on protein
lipase
acts on fats