IB DP Biology Topic 6: Human physiology : 6.1 Digestion and absorption Question Bank HL Paper 1

IB Biology HL (HIGHER level)- 2024 – Practice Questions- All Topics

Topic 6.1 Digestion and absorption

Topic 6 Weightage : 20% 

All Questions for Topic 6.1 – Digestive System, Mechanical Digestion, Chemical Digestion, Small Intestine, Absorption, Starch Digestion, Modelling Digestion, Stages of Digestion, Lipid Digestion, Lipid Absorption, Sections of the Gut

Question

A fluid sample is taken from the digestive tract of a mammal. The sample is basic (alkaline) and able to digest starch and proteins. From which part of the digestive tract was the fluid taken?

A Mouth

B Stomach

C Small intestine

D Gall bladder

▶️Answer/Explanation

Ans: C

The small intestine is the primary site of nutrient absorption in the digestive tract. Its fluid is alkaline and contains enzymes that digest carbohydrates, proteins, and lipids. Therefore, the fluid sample you described was likely taken from the small intestine, its made up of three parts: the duodenum, jejunum, and ileum. The duodenum is the first section of the small intestine, where digestive enzymes from the pancreas and bile from the liver are added to the fluid to aid in the digestion of fats. The jejunum and ileum are the remaining sections of the small intestine, where most of the nutrient absorption occurs.

Question

Where is absorption of digested food carried out?

I. Villi

II. Pancreas

III. Small intestine

A. I only

B. I and II only

C. I and III only

D. I, II and III

▶️Answer/Explanation

Markscheme

C

The absorption of digested food occurs in the small intestine, specifically in the villi and microvilli. The villi are finger-like projections that line the inner surface of the small intestine and increase the surface area available for absorption. The microvilli are tiny hair-like structures that are located on the surface of the villi and further increase the surface area.

As food passes through the small intestine, it is broken down into nutrients by enzymes. These nutrients are then absorbed into the villi and microvilli, where they enter the bloodstream and are transported to the rest of the body. The villi and microvilli are lined with specialized cells that transport the nutrients across the intestinal wall and into the bloodstream.

Once the nutrients are absorbed, they are transported to the liver, where they are processed and distributed to the rest of the body.

Therefore, the correct answer is C) I & III only.

Question

Where does the digestion of polypeptides start in humans?

A. Mouth

B. Esophagus

C. Stomach

D. Small intestine

▶️Answer/Explanation

Markscheme

C

The digestion of polypeptides starts in the stomach. The stomach contains gastric glands that secrete hydrochloric acid and the enzyme pepsinogen. Hydrochloric acid creates an acidic environment in the stomach, which denatures the proteins and activates pepsinogen, converting it into its active form, pepsin.

Pepsin is a protease enzyme that breaks down polypeptides into smaller peptides. The acidic environment of the stomach also helps to break down the polypeptides into smaller peptides by exposing the peptide bonds to hydrolysis.

Once the polypeptides have been broken down into smaller peptides, they are transported to the small intestine, where they are further broken down by enzymes secreted by the pancreas. The pancreas secretes enzymes such as trypsin, chymotrypsin, and carboxypeptidase, which break down the peptides into amino acids. The amino acids are then absorbed into the bloodstream and transported to the liver, where they are processed and distributed to the rest of the body.

 

Question

Which organ in the human body secretes lipase, amylase and protease?

A. Pancreas

B. Liver

C. Gall bladder

D. Small intestine

▶️Answer/Explanation

Markscheme

A

The pancreas secretes lipase, amylase, and protease.

Lipase is an enzyme that breaks down lipids (fats) into fatty acids and glycerol. Amylase is an enzyme that breaks down carbohydrates (starches) into simple sugars. Protease is an enzyme that breaks down proteins into peptides and amino acids.

The pancreas is a gland located behind the stomach in the upper abdomen. It secretes digestive enzymes into the small intestine through a duct called the pancreatic duct. When food enters the small intestine, hormones signal the pancreas to release its enzymes into the small intestine. The enzymes then mix with the food and break down the lipids, carbohydrates, and proteins into their respective components.

The breakdown of these nutrients allows them to be absorbed into the bloodstream and transported to the rest of the body.

Question

Glucose is absorbed through protein channels in the plasma membrane of epithelium cells in the small intestine. Which characteristics of glucose prevent its diffusion through the phospholipid bilayer?

A. It is non-polar and therefore hydrophobic.

B. Its hydrogen bonds link with amino acids in the protein channel.

C. It is polar and therefore hydrophilic.

D. Its covalent bonds interact with the phospholipids

▶️Answer/Explanation

Markscheme

C

C. It is polar and therefore hydrophilic.

Glucose is a polar molecule and therefore hydrophilic, meaning it can form hydrogen bonds with water molecules. The phospholipid bilayer of the cell membrane is made up of nonpolar fatty acid tails, which repel polar molecules like glucose. Therefore, glucose cannot diffuse through the lipid bilayer. Instead, it is transported across the membrane through protein channels called glucose transporters, which allow glucose to pass through the membrane via facilitated diffusion.

Question

In which process is “surface area” of key importance for humans?

A. Reabsorption of glucose in the proximal convoluted tubule
B. Release of surfactants by type I pneumocytes
C. Display of antibodies by red blood cells
D. Secretion of enzymes by villi of the small intestine

▶️Answer/Explanation

Markscheme

Ans:A

The reabsorption of glucose in the proximal convoluted tubule is not a process where surface area is of key importance for humans.

The reabsorption of glucose in the proximal convoluted tubule is a process that occurs in the kidneys, where glucose that has been filtered out of the blood is reabsorbed back into the bloodstream. This process occurs through the use of glucose transporters, which are proteins that are embedded in the membranes of the cells in the proximal convoluted tubule.

While the surface area of the proximal convoluted tubule is important for the overall function of the kidneys, it is not a key factor in the reabsorption of glucose. Instead, the reabsorption of glucose is dependent on the presence of glucose transporters, which are located on the membranes of the cells in the proximal convoluted tubule.

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