Topic 6.1 Digestion

Question 1

6.1.1 Explain why digestion of large food molecules is essential.

Answer 1

most food = solid, in form of large complex molecules, insoluble & chemically inert (not readily usable)

• since food is synthesized from other organisms, contains materials not suitable for human tissue that need to be separated and removed
• large molecules need to be broken down into smaller molecules so it’s readily absorbed across membranes into cells
• ∴ small molecules can be reassembled into new products (e.g. amino acids → new proteins)

Question 2

6.1.2 Explain the need for enzymes in digestion.

Answer 2

Enzymes:

• break down large food molecules
• are biological catalysts → speed up rate of chemical reaction (e.g. digestion) by lowering activation energy
• allow digestive processes to occur efficiently at body temp
• are specific for a given substrate and so can allow digestion of certain molecules to occur independently of others

Question 3

6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase.

Answer 3

Question 4

6.1.4 Draw and label a diagram of the digestive system.

Answer 4

• mouth
• pharynx
• esophagus
• stomach
• liver
• gall bladder
• bile duct (little extension off gall bladder)
• pancreas (behind stomach)
• small intestine
• large intestine
• rectum
• anus

Question 5

6.1.5 Outline the function of the stomach, small intestine and large intestine.

Answer 5

Stomach

• temporary storage tank where protein digestion begins
• secretes HCL (highly corrosive) from gastric glands which kills bacteria in food and helps break it down
• releases hormone gastrin that regulates stomach secretions
• secretes pepsin for protein digestion
• 3 layers of muscle contract to churn and mix food contents, promoting digestion

Small Intestine

• enzyme secretions sent from pancreas and gall bladder (via bile duct) break down fat and peptides in sm. intestine
• first 25 cm of sm. intestinal walls (duodenum) secretes enzymes to break down other nutrients
• has villi to ↑ surface area & optimize absorption rate of nutrients into bloodstream
• lined with smooth muscle to allow for mixing and moving of digested food products
• contains small pits that secrete intestinal juices

Large Intestine

• moves undigested material along
• absorbs water and dissolved minerals from indigestible food residues
• produces semi-solid feces from fluid state

Question 6

6.1.6 Distinguish between absorption and assimilation.

Answer 6

Absorption: the movement of food molecules across a layer of cells (a membrane) and into body tissue

Assimilation: conversion of food molecules to become part of the body tissue

Question 7

6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

Answer 7

• many villi increase surface area for absorption
• microvilli on villi increase surface area for further absorption
• epithelium is only 1 cell layer thick so food is quickly absorbed
• protein channels and pumps on microvilli for rapid absorption
• mitochondria in epithelium provide ATP for active transport
• blood capillaries close to epithelium so diffusion distance is small
• lacteal takes away fats after absorption
• intestinal crypts located between villi release juices that act as carrier fluid for nutrients