Digestion and Absorption

Peptic cells – Secrete the proenzyme pepsinogen. Goblet cells – Secrete mucus. Oxyntic cells – Secrete HCl and intrinsic factor needed for the absorption of Vitamin $B_{12}$. Hepatic cells – Secrete bile which is stored and concentrated in the gall bladder.

Fructose and some amino acids are absorbed with the help of carrier proteins, without using energy. This is facilitated transport.

Glucose and amino acids such as glycine are absorbed in the small intestine by active transport.
Fatty acids and glycerol are absorbed as micelles and move into lymph as chylomicrons.

Absorption in the intestine takes place by passive, facilitated and active transport.
The NCERT text on which this question is based states that substances like fructose and some amino acids are absorbed with the help of carrier ions like $Na^+$, a mechanism called facilitated transport.
Fatty acids and glycerol are insoluble in water; they are incorporated into micelles, re-formed into chylomicrons in the mucosal cells and passed into the lacteals, without the help of $Na^+$.
Hence carrier ions like $Na^+$ facilitate the absorption of fructose and some amino acids.

Oxyntic (parietal) cells of the gastric glands secrete intrinsic factor, which is essential for the absorption of vitamin $B_{12}$ in the intestine, in addition to secreting HCl.

Rennin (a proteolytic enzyme that curdles milk proteins) is found in gastric juice, particularly important in infants for digesting milk.

Correct sequence: Fatty acids and glycerol are incorporated into small droplets called micelles (C) → Micelles move into the intestinal mucosa (B) → Within the mucosal cells, micelles are reformed into small protein-coated fat globules called chylomicrons (A) → Chylomicrons are transported into the lacteals (E) → Lacteals release the absorbed substances into the bloodstream (D). Order: C, B, A, E, D.

The parietal or oxyntic cell is a source of HCl and intrinsic factor. HCl converts iron present in the diet from ferric to ferrous form so that it can be absorbed easily and used during erythropoiesis. Intrinsic factor is essential for the absorption of vitamin $B_{12}$ and its deficiency causes pernicious anaemia.

Kupffer cells are phagocytic cells of the liver. Zymogen cells are enzyme-producing cells. Paneth cells secrete lysozyme, which acts as an antibacterial agent. Argentaffin cells are hormone-producing cells.

The pancreatic juice contains inactive enzymes (zymogens): trypsinogen, chymotrypsinogen and procarboxypeptidases, along with amylases, lipases and nucleases.
So what is actually poured into the duodenum is trypsinogen, not trypsin.
Trypsinogen is activated to trypsin in the intestine by enterokinase, an enzyme secreted by the intestinal mucosa (it is a constituent of intestinal juice, not pancreatic juice).
Trypsin in turn activates chymotrypsinogen to chymotrypsin, so chymotrypsin is also formed only inside the intestine.
Hence the constituent of pancreatic juice poured into the duodenum is trypsinogen.

Milk proteins are first acted upon in the stomach, by the enzymes of gastric juice.
Rennin is the milk-coagulating proteolytic enzyme found in the gastric juice of infants; in calves it is the main milk-digesting enzyme.
In adult humans rennin is absent, and the initial step in the digestion of milk protein (casein) is carried out by pepsin in the acidic medium of the stomach.
Trypsin acts later, in the small intestine, and lipase acts on fats, not on milk protein.
The answer accepted in the key is pepsin.
Note: some books give rennin for this question on the basis of its presence in infants; the key of the source PDF (pepsin) is retained here.

Boiled potato contains starch, a little cellulose, and the DNA (and RNA) of the potato cells.
Starch is digested by salivary and pancreatic amylases. Humans do not produce cellulase, so cellulose is not digested.
Potato has no lactose (milk sugar).
The nucleic acids are digested in the small intestine by pancreatic nucleases (DNase and RNase) into nucleotides.
So the food contains DNA, which can be digested by pancreatic DNase.

The gastric glands have three types of cells: mucus neck cells (mucus), peptic or chief cells (pepsinogen) and parietal or oxyntic cells (HCl and intrinsic factor).
HCl provides the acidic pH (about 1.8) that is optimal for pepsin, and it converts the proenzyme pepsinogen into active pepsin.
Pepsin converts proteins into proteoses and peptones.
If the parietal cells are partly non-functional, less HCl is secreted; the pH of the stomach rises (it does not fall), less pepsin is formed and it works poorly.
Trypsin, lipase and steapsin are pancreatic enzymes that act in the alkaline medium of the intestine and are not directly affected.
Hence proteins will not be adequately hydrolysed by pepsin into proteoses and peptones.

About 30 per cent (not 60 per cent) of starch is hydrolysed in the mouth by salivary amylase.
Pepsinogen is secreted by the peptic (chief) cells; the oxyntic (parietal) cells secrete HCl and intrinsic factor.
Chylomicrons are small protein-coated fat globules that are transported into the lymph vessels (lacteals) of the villi, not into the blood capillaries.
The NCERT text on which this question is based states that fructose and some amino acids are absorbed with the help of carrier ions like $Na^+$ (facilitated transport).
Hence the true statement is that fructose and amino acids are absorbed through the intestinal mucosa with the help of carrier ions like $Na^+$.