Human nutrition

• what does a balanced diet involve?

  carbohydrates, proteins, lipids, vitamins, minerals, water and dietary fibre in appropriate proportions
• source and function of carbohydrates

  bread, rice; source of energy
• source and function of protein

  meat, eggs; growth and repair of tissues
• source and function of lipids

  butter, oil; insulation and energy storage
• source and function of dietary fibre

  vegetables, whole grains; provides roughage for intestine to push food through it
• source and function of water

  water, fruits; needed for chemical reactions (e.g. water)
• source and function of calcium

  milk, eggs; strong teeth + bones, and clotting of blood
• source and function of vitamin D

  oily fish, dairy; helps body absorb calcium - strong bones and teeth
• source and function of vitamin C

  citrus fruits, green vegetables; in collagen protein, which makes up skin, hair and bones
• source and function of vitamin A

  meat, dairy; to make pigment in retina for vision
• source and function of iron

  red meat, liver; to make haemoglobin in red blood cells
• energy/nutritional requirements change based on...

  activity levels, age, pregnancy
• how age changes your energy requirements

  children need more protein and energy for growth; energy needs decrease as you age
• how activity levels change your energy requirements

  the more active you are, the more energy is needed as muscles are respiring faster
• how pregnancy changes your energy requirements

  energy needs increase to support growth of fetus
• function of digestive system

  break down and absorbs nutrients from food
• structure of digestive system

  see diagram

  
• function of mouth and salivary glands

  mechanical digestion by chewing; amylase enzymes in saliva (made in salivary glands) digest starch into maltose
• function of oesophagus

  connects mouth to stomach
• function of stomach

  mechanical digestion by churning; protease enzymes digest proteins; hydrochloric acid kills bacteria
• function of small intestine

  made of duodenum and ileum; duodenum - digestion through enzymes; ileum - absorption of food molecules
• function of large intestine

  water is absorbed from remaining material
• function of rectum and anus

  rectum stores and anus releases faeces
• function of pancreas

  produces and secretes enzymes (amylase, protease, lipase)
• function of liver

  produces bile
• emulsification

  breaks up large fats into smaller ones to increase surface area that enzymes can use to digest it
• function of gall bladder

  stores bile
• how is food moved through oesophagus

  peristalsis; wave of contractions of muscles
• role of digestive enzymes

  break down food to small soluble molecules that can be absorbed into the bloodstream
• enzymes that digest starch into glucose

  amylase and maltase
• enzymes that digest proteins into amino acids

  proteases
• enzymes that digest lipids into fatty acid and glycerol

  lipase
• role of bile

  neutralises hydrochloric acid from stomach; emulsification
• how is the small intestine adapted for absorption

  very long, highly folded, millions of villi; increases surface area so absorption rate increases
• adaptations of villi

  have microvilli, increasing surface area; one cell thick diffusion distance; maintains a steep concen. gradient bc it has lots of blood capillaries that quickly move glucose/amino acids away from small intestine

  
• practical - investigating energy content of a food sample

  1) Measure out 25cm3 water in a boiling tube

  2) Record starting temp of water and mass of food sample

  3) Set fire to sample with bunsen burner and hold near boiling tube till completely burnt

  4) Record final temp of water

  5) Energy transferred per gram of food = (mass of water x energy increase x 4.2) / mass of food sample