why do we need food?
to supply us with fuel for energy
to provide materials for growth and repair of tissues
to help fight diseases and keep our body healthy
balanced diet
a diet that contains all the main nutrients in the correct amount to maintain good health
malnutrition
lack of proper nutrition due to various factors
food substances our body needs to stay healthy
carbohydrates, lipids, proteins, minerals, vitamins, dietary fibre, water
carbohydrates
sources: bread, pasta, rice, potatoes function: provides and stores energy
proteins
sources: meat, fish, egg, pulses, nuts function: growth and repair
lipids
sources: butter, oil, nuts function: insulation and energy storage
fibre
sources: vegetables, whole grains function: provides roughage for the intestine to push through
water
sources: water, juice, milk, fruits, vegetables function: needed for cellular chemical reaction
calcium
sources: milk, cheese, eggs function: strong teeth and bones, blood clotting
vitamin a
sources: meat, liver, dairy, leafy green veggies function: pigment in the retina for vision
vitamin d
sources: oily fish, dairy products, sunlight function: absorption of calcium, strong bones
vitamin c
sources: citrus fruits, green vegetables function: collagen protein formation
iron
source: meat, liver, leafy greens function: makes haemoglobin
examples of malnutrition
starvation, coronary heart disease, constipation, obesity
starvation
cause: taking in less energy than needed effect: weight loss, heart damage, immune system damage
coronary heart disease
cause: saturated fat and increased cholestrol effect: heart attack, death
constipation
cause: lack of dietary fibre effect: increased risk of diseases such as bowel cancer
obesity
cause: taking in more energy than used effect: development of many diseases such as heart failure, diabetes
what factors affect dietary requirements?
age, activity levels, pregnancy
digestion
chemical and mechanical breakdown of food where large, insoluble molecules of food are broken down into smaller, soluble molecules to be absorbed and delivered to cells in the body.
what do the small molecules produced in digestion do?
provide cells with energy or with materials to help build, grow and repair other molecules.
alimentary canal
channel through which food flows around the body starting: mouth ending: anus
where does digestion occur
digestion occurs within the alimentary canal
accessory organs
produce substances needed for digestion to occur
5 stages of food breakdown
ingestion
mechanical digestion
chemical digestion
absorption
assimilation
egestion
ingestion
taking in of substances through the mouth
mechanical digestion
breakdown of food without chemical change
chemical digestion
breakdown of large molecules into smaller ones
absorption
movement of small molecules and ions through the wall of the intestine into the build
assimilation
movement of digested food molecules into the cells of the body where they are used
egestion
passing out of food that hasn't been digested, through the anus
peristalsis
mechanism that helps food move along the alimentary canal.
stages of peristalsis
muscles in the wall of the oesophagus create waves of contractions, forcing the bolus along.
the bolus has churned into chyme by the time it reaches the stomach.
it continues onto the small intestine.
peristalsis is controlled by two types of muscles
circular and longitudinal
circular muscles
contract to reduce the diameter of the lumen of the oeosphagus or the small intestine
longitudinal muscles
contract to reduce the length of that section of the oesophagus or the small intestine
mucus in peristalsis
produced to lubricate food mass and reduce friction
dietary fibre in peristalsis
provides roughage required for muscles to push against
digestive enzymes
chemical digestion is controlled by enzymes produced in different areas of the digestive system. enzymes are biological catalysts.
3 main types of sigestive enzymes
carbohydrases
proteases
lipases
carbohydrases
breaks down carbohydrates to simple sugars (amylase, maltase)
amylase
a carbohydrase that breaks down starch into maltose made in: salivary glands, pancreas, small intestine
maltase
breaks down maltose into glucose acts in: mouth, small intestine
proteases
break down proteins into amino acids (pepsin, trypsin, peptidases) acts in: stomach, small intestine
pepsin
a protease that breaks down proteins into small polypeptide chains made in: stomach
trypsin, peptidases
made in: pancreas, small intestine
lipases
break down lipids to glycerol and fatty acids (lipase)
lipase
produced in: pancreas secreted in: small intestine
bile
an alkaline substance produced by cells in the liver
bile storage
stored in the gallbladder before being released into the small intestine
how does bile emulsify fats?
it contains bile salts which emulsify fats
2 roles of bile
neutralised hydrochloric acid from the stomach
emulsification
neutralised hydrochloric acid from the stomach
neutralisation is essential as enzymes in the small intestine have a higher optimum ph (more alkaline) than those in the stomach. the alkaline properties of bile allow this to occur.
emulsification
breaking apart large drops of fat into smaller ones (and so increasing their surface area)
how is the small intestine adapted for absorption?
very long
has a highly folded surface
surface has millions of villi
how does peristalsis aid absorption
it helps by mixing together food and enzymes and keeping things moving along the alimentary canal
villi
tiny finger-like projections on the surface of the small intestine
adaptations of the villi allowing rapid absorption of substances
large surface area
short diffusion distance
steep concentration gradient
large surface area
microvilli further increase the surface available for absorption
short diffusion distance
one cell thick wall of villus
steep concentration gradient
network of blood capillaries for transportation of glucose and amino acids
lacteal running through the center of the villus to transport fatty acid and glycerol
enzymes assist with chemical digestion
movement of villi helps move food along and mix it with enzymes
energy content of a food sample - apparatus
boiling tube
boiling tube holder
bunsen burner
mounted needle
measuring cylinder
balance
thermometer
water
food samples
energy content of a food sample - method
pour 25cm of water into the boiling tube
record starting temperature
weight initial mass of the food sample
set fire to the food sample using the bunsen burner and hold near water until completely burnt
record final temperature of water
recordd the mass of the food sample once cooled
repeat with different samples
energy content of a food sample - results
a larger increase in water temperature indicates a larger amount of energy contained by the sample
equation for energy transfer
(mass of water x temperature increase) / mass of food
energy content of a food sample - limitations
incomplete burning
heat energy loss
energy content of a food sample - CORMMS (CRMMS)
C - type of food R - repeat for different samples M1 - change in temperature of water M2 - mass of food S - volume of water, distance between food sample and boiling tube