4. Nutrition In Humans

Question 1

function of mouth (3 parts and its functions)

Answer 1

1. Mouth and buccal cavity
   (a) Teeth: chewing, breakdown large pieces of food to smaller size.
   • Increase surface area to volume ratio of the food that enzyme can act
   on more eficiently.
   (b) Salivary glands: Secrete saliva into mouth via salivary ducts.
   • saliva contains salivary amylase that
   digest starch to maltose
   (c) Tongue: mix food with saliva into bolus

Question 2

function of salivary glands (2)

Answer 2

Salivary glands: Secrete saliva into mouth via salivary ducts.
• saliva contains salivary amylase that
digest starch to maltose

Question 3

function of oesophagus (2)

Answer 3

• A narrow muscular tube that connects the buccal cavity and stomach
• It is made up of two layers of muscle. The external layer is the
  longitudinal muscle and the inner layer is the circular muscle.

Question 4

function of stomach (3)

Answer 4

Stomach wall has pits that lead to gastric gland, which secretes
(1) mucus which protects the stomach walls
(2) gastric acid/dilute hydrochloric acid
• Gastric acid is pH 2, denatures salivary amylase thus stop its activity
• changes the inactive pepsinogen into the active form, pepsin
• provides an acidic environment as pepsin optimum pH is 2
• kills germs and bacteria.
(3) pepsinogen (inactive form)
• dilute HCl activates pepsinogen to pepsin
• pepsin digest proteins to polypeptides
- Food normally remains in the stomach for about three to four hours. The partly
digested food becomes liquefied, forming chyme.
- The pyloric sphincter is located at the place where the stomach joins the small
intestine. When the muscle contracts, the entrance to the small intestine
closes. When the ring relaxes, chyme passes in small amounts into the
duodenum

Question 5

function of duodenum (3,1)

Answer 5

In the duodenum, chyme from the stomach mixes with
1. Pancreatic juice secreted from pancreas
2. Intestinal juice secreted by epithelial cells of small intestine
3. Bile from gall bladder
• all three juices are alkaline, thus they neutralise the acidic chyme from
stomach and provide an optimum alkaline environment for pancreatic and
intestinal enzymes

Question 6

function of pancreas

Answer 6

makes pancreatic juices

Question 7

function of liver (3)

Answer 7

(i) the metabolism of glucose
(ii) the metabolism of amino acids and the formation of urea
(iii) the breakdown of alcohol

Question 8

function of colon

Answer 8

absorb the remaining water and mineral

salts that have not been absorbed by the small intestine

Question 9

function of ileum

Answer 9

absorption nutrients such as vitamin b12

Question 10

function of hepatic portal vein (2)

Answer 10

• Digested food molecules such as amino acid and glucose
are absorbed by villi on the small intestine
• They converge into a large blood vessel called the hepatic
portal vein, which transport blood rich in absorbed
nutrients from the small intestine to the liver

Question 11

Role of liver (3)

(i) the metabolism of glucose (2)
(ii) the metabolism of amino acids and the formation of urea (3)
(iii) the breakdown of alcohol (3)

Answer 11

1. Regulation of blood glucose concentration (carbohydrate
   metabolism)
   • When blood glucose is higher than normal, the islets of Langerhans
   in the pancreas will secrete insulin. Insulin will stimulate liver cells to
   convert excess glucose to glycogen and stored in liver. This decrease
   blood glucose level back to normal.
   • When blood glucose level is lower than normal, the islets of
   Langerhans in the pancreas will secrete glucagon. Glucagon
   stimulates the liver cells to convert stored glycogen in the liver back
   into glucose. The glucose is released into the blood, which increase
   blood glucose level back to normal.
2. metabolism of amino acids
   • The liver synthesis essential proteins from amino acids in the diet, including
   blood clotting proteins like prothrombin and fibrinogen.
3. Deamination
   • Excess amino acid is deaminated by the liver, which is the removal of the
   amino group (–NH2) from an amino acid.
   • The amino group is first converted into ammonia, which is toxic to cells,
   then converted to urea by enzymes in the liver, and eventually removed in urine
4. Detoxification
   - The liver breaks down toxic substances for excretion in urine or bile.
   - E.g. alcohol is broken down acetaldehyde, catalysed by alcohol dehydrogenase.
   - Acetaldehyde is then converted to harmless acetic acid by acetaldehyde dehydrogenase

Question 12

function of anus

Answer 12

external opening of the rectum to dispose waste products out of the body

Question 13

describe the function of amylase, listing the

substrate and end-products

Answer 13

digest starch to maltose

Question 14

describe the function of maltase, listing the

substrate and end-products

Answer 14

digest maltose to glucose

Question 15

describe the function of protease, listing the

substrate and end-products (2)

Answer 15

1. Protein to polypeptides (trypsin)

2. polypeptides to amino acids (erepsin)

Question 16

describe the function of lipase, listing the

substrate and end-products

Answer 16

digest fats to fatty acids and glycerol

Question 17

function of bile

Answer 17

Bile emulsifies large fat droplets into smaller fat droplets,
increasing the surface area to volume ratio of the fats for lipase
to work on and speeds up fat digestion