Digestive system- Sample Qs

Diagram 6 shows the human digestive system. (a) Based on Diagram 6 state the adaptation characteristics of structure B for nutrient and also what happens to the excess amino acids in the body. (4 marks)

(b) Draw and label a cross-section of a villus.
Explain how villus is linked to organ A in the transport of nutrients and also what happens to the excess amino acids in the body. (6 marks)

(c)Describe the digestive actions that take place in the

(i) mouth
(ii) stomach
(iii) small intestine

Explain the roles of the glands secretion, enzyme involved in these digestive process.
(10 marks)

Suggested Answer:

(a)Adaptation of small intestine :
· the great length
· the folded inner surface
· Has a large surface area because it has a lot of finger-like projections on its membrane called microvilli. // Microvilli help increase the absorption of digested food.
· A villus is supplied with a network of blood capillaries which aids in the absorption and transport of digested food. (nutrients)

(b)

· Each villus has blood capillaries that transport nutrients such as glucose and amino acids.

· The blood capillaries converge to form the hepatic portal vein which leads to the liver

· Excess amino acids cannot be stored in the body and are broken down in the liver // deamination

· During deamination, urea and the common nitrogeneous waste product is produced and transported to the kidneys to be excreted.


(c) Mouth
· Food is chewed and broken up into smaller pieces by the teeth.
· The small pieces of food have a larger surface area for the saliva (enzyme) to act upon.
· Salivary gland secretes saliva that is alkaline and contains salivary amylase (ptyalin).
· After the food has been thoroughly chewed and mixed with saliva, the tongue starts the process of swallowing by pushing the bolus (small mass of chewed food).
· Saliva also softens and increases the water content of the food.
· In mouth, only starch is digested. Starch is hydrolysed by amylase into maltose.
Starch + Water -----Amylase ------- Maltose

Stomach
· Secretes gastric juices contains hydrochloric acid and enzyme (rennin and pepsin)
· Hydrochloric acid kills microorganisms and stops the activity of salivary amylase, which functions optimally at the near-neutral pH of saliva and promotes the activity of pepsin.
· Pepsin is a hydrolytic enzymes that acts on protein to produce peptides

Protein + Water--------- pepsin -------- Peptone + polypeptide

Rennin changes caseinogens to casein. Casein is then digested by pepsin

Caseinogens ------- Rennin -------- Casein

Ileum (small intestine)
· There are some digestive glands on small intestine. All these enzymes need an alkaline medium function
· There are 5 types of enzymes produced :
1. Erypsin (peptidase) – hydrolysis of peptide to amino acids
2. Sucrase - hydrolysis of sucrose to fructose and glucose
3. Maltase - hydrolysis of maltose to glucose
4. Lactase - hydrolysis of lactose to glucose and galactose
5. Entrokinase – Activates trypsinogen to trypsin in the
duodenum