Chapter 7

Question 1

Describe what is meant by a balanced diet

Answer 1

Diet that contains all the essential nutrients in the correct proportions to maintain good health. The nutrients needed are carbohydrate, fat, protein, vitamins, minerals ions, fibre (roughage) and water

Question 2

State the importance of each nutrient:

Answer 2

Carbs: respiration for energy
Fast & Oils: x2 source energy, hormones, cell membranes, insulation
Protein: growth, tissue repair, enzymes, hormones, cell membranes
Iron: haemoglobin combines with O₂ for transport in RBC (deficiency leads to anaemia)
Calcium: needed for healthy bones and teeth, and normal blood clotting (deficiency leads to rickets)
Vitamin D: needed to absorb calcium from SI (deficiency leads to rickets)
Vitamin C: needed for healthy skin and gums (deficiency leads to scurvy)
Dietary fibre (roughage): adds bulk to undigested food passing through the intestines - maintains peristalsis, prevent constipation
Water: enzymes work in solution, formation of cytoplasm and blood, solvent for transport of nutrients and removal of waste (urine),

Question 3

State all the organs in the alimentary canal and involved

Answer 3

mouth, salivary glands, oesophagus, stomach, small intestine (duodenum, ileum), pancreas, liver, gall bladder, large intestine (colon, rectum, anus)

Question 4

Stages of nutrition

Answer 4

ingestion – the taking of substances into the body
digestion – the breakdown of food
absorption – the movement of nutrients from the intestines into the blood
assimilation – uptake and use of nutrients by cells
egestion – the removal of undigested food from the body as faeces

Question 5

state the function of each organ:

Answer 5

Mouth: food is ingested here, mechanical digestion by teeth
Salivary glands: secrete saliva containing amylase (digest starch to maltose) and water (lubricate food)
Oesophagus: boluses of food pass thru from mouth to Stomach
Stomach: contains gastric juice (HCL: kill bacteria and allow low pH for pepsin) and (Pepsin: digest proteins to peptides) and the muscular stomach walls churn and squeeze the food to mechanically digest them to a paste
Duodenum: food passes thru while the pancreas secretes pancreatic juice (amylase, trypsin, lipase) containing sodium hydrogen-carbonate (alkali) to neutralize the acidity, also receives bile juice (secreted by liver, stored in gall bladder) to emulsify fats to increase SA
Ileum: Food and most water is absorbed here, epithelium lining with enzymes, and villi + microvilli.
Colon: second part of the large intestine, reabsorbs some water (forms faeces) and bile salts
Rectum: Stores faeces until they are egested.
Anus: muscles to control when faeces are egested

Question 6

Difference between physical and chemical digestion

Answer 6

physical digestion – breakdown of food into smaller pieces without chemical change to the food molecules to increase the surface area of food for the action of enzymes in chemical digestion
chemical digestion – break down of large insoluble molecules into small soluble molecules that can be absorbed

Question 7

Describe the different types of physical digestion

Answer 7

Teeth: chewing breaks food into smaller pieces increasing sa
– Incisors: chiseled shaped in front of mouth; biting off
– Canines: pointed, beside incisors; cutting off
– Pre-molar: 2 cusps + 1/2 roots ; tearing and ripping
– Molar: 4/5 cusps + 2/3 roots: chewing and grinding
→ see tooth structure

Stomach walls churn food to make it semi-liquid
→ increases surface area
→ makes food molecules come into contact with enzymes

Bile: made in liver, stored in gall bladder and transferred to duodenum by the bile duct → emulsifies fats, breaking them up into droplets for a larger sa for lipase to act on

Question 8

Describe the different types of chemical digestion:

Answer 8

Enzymes:
– Amylase digests starch into maltose in the mouth and duodenum
– Maltase digests maltose to glucose in the membrane of epithelial lining of the small intestine
– Lipase digests fats/oils to fatty acids and glycerol in the duodenum
– Pepsin digests proteins to amino acids in the stomach
– Trypsin digests proteins to amino acids in the duodenum

Stomach: HCℓ in gastric juice secreted by cells in stomach wall to create an acidic pH of 2 (opt pH for pepsin), denatures enzymes in pathogens killing them

Bile is slightly alkaline, optimum pH for enzymes (sodium hydrogen-carbonate) neutralize acidic mixture of food and gastric juices entering duodenum

Question 9

Describe place of absorption

Answer 9

small intestine is the region where nutrients and water are absorbed, some water is absorbed by the colon; digested food molecules are small enough to pass through the wall of the intestine into the bloodstream.

Question 10

Adaptations of small intestine for absorption

Answer 10

Villi – finger-like projections in the small intestine that increase the surface area for faster (diffusion) absorption; microvilli increase sa further; maltase and peptidase on membrane on the epithelial lining (which is only one cell thick to increase diffusion rate) (also contains mitochondria to provide energy for active uptake of nutrients)

Villus structure:
→ lacteal in centre: absorbs fatty acids and glycerol
→ surrounded by blood capillaries: absorb the rest of nutrients and water; rich blood supply and blood movement to maintain conc. gradient