1) Digestion of large food molecules is essential because molecules must pass through cell membranes to be absorbed and used. During digestion, food molecules are broken down into their smallest components like amino acids and monosaccharides that can then pass through membranes. 2) Enzymes are needed for digestion to break down food molecules. They lower the activation energy of reactions, allowing reactions to occur at normal body temperatures rather than higher temperatures. 3) The small intestine absorbs most digested nutrients through villi in its walls, which increase surface area for absorption into capillaries and lacteals. Nutrients are then transported throughout the body.

1. Eunji Oh

2. 6.1.1 Explain why digestion of large
food molecules is essential
• Many of the food we ingest (eat) have very large
molecules that makes it had to cross any cell
membrane
• Molecules must pass through the cell membranes of
your intestines and through the membrane of a capillary

3. Molecule Type Molecular Form Ingested Molecular Form After Digestion
Protein Protein Amino Acids
Lipids Triglycerides, phospholipids Glycerol and fatty acids (phosphate)
Carbohydrates Polysaccharides,
disaccharides,
monosaccharide
Monosaccharide
Nucleic acids DNA, RNA Nucleotides
• When we digest food molecules, we break them down
(hydrolyze) into their smallest components, which can be
reassembled into larger molecules (macromolecules)
6.1.1 Explain why digestion of
large food molecules is essential

4. 6.1.1 Explain why digestion of
large food molecules is essential

5. Example
• Ate an egg
• In the egg white (protein albumin) is an amino acid called serine
• Egg white albumin chemically digested, leaving serine float feely in
fluid environment of small intestine
• Serine small enough to diffuse through small intestine small capillary
blood vessel pacreas cell
• Build serine into protein (becomes a ‘building block’)
Benefits of digesting protein albumin
• Serine can leave the intestine and diffuse into the bloodstream
• Serine availability dependent on digestion (since protein cannot be
absorbed).
• Cell's DNA dictates final protein polymer [containing serine.]
6.1.1 Explain why digestion of
large food molecules is essential

6. 6.1.2 Explain the need for
enzymes in digestion
• Enzyme: protein molecules that act as catalysts for
reactions
• Each digestive enzyme is specific for a specific food
type
• Enzyme’s function is to lower the activation energy
of the reactions
o Reaction can occur with lower input of energy, which
is typically in the form of heat

7. 6.1.2 Explain the need for
enzymes in digestion
• Enzyme-catalysed reactions proceed at higher
reaction rates at a lower temperature than the same
reaction without an enzyme
o Advantageous for living organisms
o Many reactions of the digestive process would need
far higher temperatures if enzymes were not involved
o Human’s body temperature = 37 degrees Celsius
(stable)
 Warm enough to maintain good molecular movement
 With enzyme, provides enough activation energy for
metabolic reactions (digestion)

8. 6.1.2 Explain the need for
enzymes in digestion
• Digestive enzymes all help to catalyze hydrolysis
reactions
• Amylase holds the starch in its
active site
• Put stress on covalent bonds that
bind the glucose molecule together
• When bonds are stressed,
surrounding thermal energy provide
enough molecular motion to break
bonds
• Enzyme does not cause reaction,
but just makes the reaction more
likely to occur at normal
temperature

9. 6.1.3 State the source, substrate,
products and optimum pH conditions for
one amylase, one protease and one
lipase.
Salivary amylase Pepsin (a protease)Pancreatic lipase
Source Salivary glands Stomach cells Pancreas cells
Substrate Amylose (starch) Proteins
(polypetptides)
Lipids
Products Maltose and glucoseAmino acids Glycerol and fatty
acids
Optimum pH Neutral (pH 7) Acidic (pH 3) Neutral (pH 7)

10. 6.1.4 Draw and label a diagram of
the digestive
system
• Mouth
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Rectum

11. 6.1.5 Outline the function of the
stomach, small intestine and large
intestine
• Stomach
o Food brought by a muscular tube called oesophagus
o Food forced down to stomach by sequential series of
smooth muscle contractions called peristalsis
o Food held for a period of time and muscular walls of
stomach churns in order to mix it with gastric juice
 Pepsin: a protease enzyme most active in acidic pH
 Hydrochloric acid (HCl): helps degrade and break down
foods/ creates acidic pH necessary for pepsin to be active
 Mucus: lines inside of stomach wall to prevent stomach
damage from HCl
o Valve at lower end of stomach opens and food enters
small intestine

12. • http://www.youtube.com/watch?
v=Uzl6M1YlU3w&feature=related

13. 6.1.5 Outline the function of the
stomach, small intestine and large
intestine

14. 6.1.5 Outline the function of the
stomach, small intestine and large
intestine
• Small Intestine
o Duodenum: first portion of small intestine
 Bile from liver and gall bladder
 Trypsin (a protease), lipase, amylase, and bicarbonate from
pancrease
• Inner wall made up of villi
o Function is to greatly increase the surface area for
absorption of molecules, such as glucose, amino
acids, and fatty acids

15. 6.1.5 Outline the function of the
stomach, small intestine and large
intestine
• Each contains a capillary bed and
a lacteal
o Lacteal: small vessel of your
lymphatic system
(transport lymph fluid and immune
cells)
o Capillary bed: absorbs most of
molecules (except fatty acids) that
are taken to a wide variety of body
cells by circulatory systems
o Within body cell, nutrient molecule
used for energy or to help build
larger molecules

16. • http://www.youtube.com/watch?v=yB86O2giBu8

17. 6.1.5 Outline the function of the
stomach, small intestine and large
intestine
• Large Intestine
o Majority of useful nutrients are absorbed inside small
intestine
o Remains of original food that is undigested (much of
water is still present in the remain)
 Leaving water in alimentary canal for a long time is
beneficial because it keeps moving the food
o Primary function of large intestine is water absorption
o Contains a lot of naturally occurring bacteria (E.coli)
 Mutualistic organisms
 Humans provide nutrients, water, and warm environment
 Bacteria synthesize vitamin K and maintain healthy overall
environment

18. 6.1.6 Distinguish between
absorption and assimilation
• Assimilation is the process of bringing the nutrient to
a body cell and using it as a component to help build
larger molecule inside the cell (ex. Amino acids)
o Food becomes part of the body’s tissue
• Absorption is when food molecules pass through a
layer of cells such as passing through the villi

19. 6.1.7 Explain how the structure of the villus is
related to its role in absorption and transport
of the products of digestion
• Undigested nutrients cannot pass
through the villus epithelium
• Digested nutrients in the lumen of
small intestine pass through single-
cell thickness of villus epithelium to
get to capillary bed or lacteal
• Blood from an arteriole enters the
capillary bed
• Blood rich in nutrients leaves via a
venule
• Entire structure creates a
tremendous surface area for
absorption

20. • http://www.youtube.com/watch?
v=UTaPUdWAEnE&feature=related

21. Citations
• http://en.wikivisual.com/images/3/35/Raw_egg.jpg
• http://image.wistatutor.com/content/nutrition/villi-in-
interstine.jpeg
• http://www.pycomall.com/images/P/stomach.jpg
• http://ibhow.files.wordpress.com/2010/06/6-1-41.jpg
• http://2.bp.blogspot.com/_GsPuGchS5Fg/So7giHvB
KCI/AAAAAAAAAIY/7gWtmgiNQ4s/s320/c8.8x13.hy
drolysis.sucrose.jpg