How the body breaks food down and absorbs it: the organs of the digestive system, the role of bile, and what carbohydrates, proteins and lipids become.
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1.What is a tissue?
A group of cells with a similar structure and function, working together.
2.What is an organ?
A group of different tissues working together to perform a specific function.
3.What is an organ system?
A group of organs working together to perform a particular job in the organism.
4.State the levels of organisation from smallest to largest.
Cells, then tissues, then organs, then organ systems, then the whole organism.
5.What is the job of the digestive system?
To break large insoluble food molecules down into small soluble ones that can be absorbed into the bloodstream.
6.Why must large food molecules be broken down?
They are too large and insoluble to pass through the wall of the small intestine into the blood.
7.Name the organs food passes through, in order.
Mouth, oesophagus, stomach, small intestine, large intestine.
8.What happens to food in the mouth?
Teeth chew it to increase the surface area, and salivary glands release amylase which starts breaking down starch.
9.What is the function of the oesophagus?
It carries food from the mouth down to the stomach.
10.What is peristalsis?
Waves of muscular contraction in the gut wall that squeeze food along.
11.What happens in the stomach?
Muscular walls churn the food, hydrochloric acid is added, and protease begins digesting protein.
12.Give two reasons the stomach produces hydrochloric acid.
It kills most bacteria in the food, and it provides the acidic pH that stomach protease works best at.
13.What happens in the small intestine?
Digestion is completed by enzymes from the pancreas and intestine, and the soluble products are absorbed into the blood.
14.What is the function of the large intestine?
It absorbs water from the undigested food, leaving faeces.
15.What does the liver produce?
Bile.
16.Where is bile stored before it is used?
In the gall bladder.
17.State the two functions of bile.
It neutralises the acid from the stomach, and it emulsifies fats.
18.What does it mean to emulsify fat, and why does it help?
Large fat droplets are broken into many small ones. This increases the surface area for lipase to work on, so fat is digested faster.
19.Is bile an enzyme?
No. It is an alkaline liquid. It speeds fat digestion up without being a catalyst itself.
20.Why does bile need to be alkaline?
Enzymes in the small intestine work best in alkaline conditions, so the acid carried over from the stomach has to be neutralised.
21.Which three enzymes does the pancreas produce?
Amylase, protease and lipase. They are released into the small intestine.
22.What is starch broken down into?
Sugars, ending as glucose.
23.What is protein broken down into?
Amino acids.
24.What are lipids broken down into?
Fatty acids and glycerol.
25.What are the products of digestion used for?
Building new carbohydrates, lipids and proteins for the body. Some glucose is used in respiration to release energy.
26.How is the small intestine adapted for absorption?
It is long and lined with villi, giving a very large surface area, with thin walls and a good blood supply.
27.Which gland releases the amylase that acts in the mouth?
The salivary glands.
28.Roughly what pH does stomach protease work best at?
About pH 2, which is strongly acidic.
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