2e: Nutrition (Humans)

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

1. ingestion

2. mechanical digestion

3. chemical digestion

4. absorption

5. assimilation

6. 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

1. muscles in the wall of the oesophagus create waves of contractions, forcing the bolus along.

2. the bolus has churned into chyme by the time it reaches the stomach.

3. 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

1. carbohydrases

2. proteases

3. 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

1. neutralised hydrochloric acid from the stomach

2. 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