Biology - The digestive system

Question 1

What is the function of the mouth?

Answer 1

Where food enters the alimentary canal and digestion begins by amylase enzyme in the saliva starting the digestion of starch.

Question 2

What is the function of the oesophagus?

Answer 2

Muscular tube which moves ingested food to the stomach.

Question 3

What is the function of the stomach?

Answer 3

Muscular organ where digestion continues. Protease is secreted to begin the digestion of proteins.

Question 4

What is the function of the pancreas?

Answer 4

Produces the digestive enzymes carbohydrase, protease and lipase. These enzymes are secreted from here into the small intestine.

Question 5

What is the function of the liver?

Answer 5

Produces bile and secretes it to the gall bladder for storage.

Question 6

What is the function of the Gall bladder?

Answer 6

Stores bile before releasing it into the first section of the small intestine.

Question 7

What is the function of the bile duct?

Answer 7

Takes bile from the gall bladder to the first section of the small intestine.

Question 8

What is the function of the small intestine?

Answer 8

Where food is mixed with digestive enzymes and bile and digested food is absorbed into the blood.

Question 9

What is the function of the large intestine?

Answer 9

Where water is reabsorbed.

Question 10

What is the function of the anus?

Answer 10

Where feces leave the alimentary canal.

Question 11

What is the function of bile?

Answer 11

it neutralises the acid - providing the alkaline conditions needed in the small intestine
it emulsifies fat - turning large droplets of fat into lots of smaller droplets, thus providing a larger surface area over which the lipase enzymes can work

Question 12

How is starch digested?

Answer 12

Starch is a long chain carbohydrate. It is insoluble. During digestion the enzyme carbohydrase breaks it down into single molecules of glucose which are small and soluble enough to be carried in the blood to the cells for respiration, or to be stored as glycogen in the liver.

Question 13

How are proteins digested?

Answer 13

Proteins are long chains of amino acids. During digestion the enzyme protease breaks them down into single amino acids which are small and soluble and can be used by cells to build new proteins.

Question 14

How are lipids digested?

Answer 14

Lipids are large molecules. During digestion the enzyme lipase breaks them down into fatty acids and glycerol. These can be used by the body to provide energy.

Question 15

How do you test food for starch?

Answer 15

Starch – the test for starch is a chemical called iodine. Iodine solution is a brown coloured liquid. If it comes into contact with starch it turns blue/black.

Question 16

How do you test food for Glucose?

Answer 16

Glucose – The test for glucose requires a chemical called Benedict’s reagent. It is blue in colour and needs to be heated vigorously with the sample to show a colour change. If glucose is present, a range of colours may be seen which determines the relative concentration of glucose in the sample.
Green - very low
Yellow - low
Orange - medium
Red - high

Question 17

How do you test food for protein?

Answer 17

Protein – The test for protein requires a chemical called biuret solution. It is blue in colour but turns violet in the presence of protein.

Question 18

What is the process of peristalsis?

Answer 18

The muscles in the oesophagus contract above the bolus to push food down the oesophagus.
The muscles work together to produce wave-like contractions. These have a squeezing action that pushes the bolus through the gut.
(Bolus - ball of food)

Question 19

What is hydrochloric acid?

Answer 19

The stomach produces hydrochloric acid. It kills many harmful micro-organisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions – at a low pH. Protein digestion starts here.

Question 20

What is absorption?

Answer 20

Absorption is the movement of digested food molecules through the wall of the intestine into the blood.

Question 21

How has the small intestine adapted for absorption?

Answer 21

The small intestine has a large internal surface area for absorption to happen quickly and efficiently. This large surface area is due to the presence of many finger-like projections called villi.

Question 22

How has the villi adapted for absorption?

Answer 22

The good blood supply around the villi quickly takes away absorbed nutrients, this maintains a steep concentration gradient so that more diffusion of digested nutrients from the small intestine into the blood can occur.

Question 23

What is an experiment to model absorption?

Answer 23

We can model the process occurring in the small intestine using a piece of apparatus called Visking tubing. Visking tubing is a selectively permeable membrane, this means it has pores in it which allow small molecules through but not larger molecules.
At regular intervals the liquid inside and outside of the Visking tubing is sampled and tested for starch (using iodine) and glucose (using Benedict’s solution). The results show the larger molecules like starch are still present in the Visking but glucose is present outside the visking tubing.

Question 24

What is the function and some typical sources of Carbohydrates?

Answer 24

Typical sources - Rice, potatoes, pasta, sugar and vegetables.
Function - Source of energy

Question 25

What is the function and some typical sources of Proteins?

Answer 25

Typical sources - Meat, fish, eggs, peas, beans, lentils and soya.
Function - Growth and repair of cells.

Question 26

What is the function and some typical sources of Lipids?

Answer 26

Typical sources - Cheese, butter, margarine, oils and nuts
Function - Source of energy, In the body lipids provide storage and insulation.

Question 27

What is an experiment to find the energy content of food?

Answer 27

Calorimetry
-pour 10 cm3 cold water into a boiling tube
-record the starting temperature of the water
-record the mass of the food sample
-heat the food in a Bunsen flame until it catches fire
-heat the water using the flame from the burning food
-record the final temperature of the water

Question 28

What are a few sources of error in calorimetry (experiment for energy in food)?

Answer 28

-It is difficult to maintain a constant distance between the burning food and the tube, varying the heat loss to the environment
-It is difficult to minimise heat loss when transferring the burning food from the flame to the tube
-In this method it is possible that incomplete burning of the crisp gives an inaccurate measurement of the mass burned

Question 29

How is a bomb calorimeter an improvement?

Answer 29

-Sample is burned in a sealed chamber to reduce heat loss to the environment
-Sample chamber is surrounded by another chamber of water in which the temperature change is measured
-Sample is burned in pure oxygen to ensure complete combustion