Digestion by R.pdf igcse biology the digestive system

biology

1. DIGESTION

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The body carries out digestionof food to convert large
insoluble food molecules into smaller soluble ones.
carbohydrate
molecule
protein
molecule
fat
molecule
Small food molecules can pass through the walls of the
small intestine and then dissolve into the blood stream.
Large food molecules cannot do this.
What is digestion?

33. The human digestive system
Mouth–mechanical
chewing of the food.
Salivary glands
produce the enzyme
amylase which begins
breaking down
polysaccharides into
simpler sugars.

94. CholeraCholera causes diarrhoea
•Diarrhea is theloss of watery faecesfrom the anus
•If it is severe and continues for a long time, itcan lead to death
•Severe diarrhoeacan cause theloss of significant amounts of
water and ionsfrom the body, causing the tissues and organs to
stop working properly
•It can be effectively treated byoral rehydration therapy
•This is adrink with a small amount of salt and sugardissolved in it
•There are many causes of diarrhoea, one of which is infection
withVibrio cholerae bacteria, which causes the diseasecholera

96. How cholera leads to diarrhoea
•Ingested viainfected water or food, if it enters the small
intestine it can cause illness in the following way:
1.Bacteria attach to the wall of thesmall intestine
2.They produce atoxin
3.The toxin stimulates the cells lining the intestine torelease
chloride ionsfrom inside the cells into the lumen of the
intestine
4.The chloride ions accumulate in the lumen of the small
intestine andlower the water potentialthere
5.Once the water potential is lower than that of the cells lining
the intestine,water starts to move out of the cellsinto the
intestine (byosmosis)
6.Large quantities of water are lost from the body inwatery
faeces
7.The blood containstoo little chloride ions and water