Unit 7: Chemical and Physical
Changes & Balancing
The Digestive System
Amazing Facts 
• We make 1-3 pints of saliva a day.
• The average male will eat about 50 tons
of food to sustain weight of 150 pounds
• A horse’s intestines are about 89 feet
long
How is the digestive
system like a post
office?
ANALOGY
• The digestive system is like a post office it
receives mail which is like the food in the
digestive system, gets processed, and then
is sent out.
Function of the Digestive System
• To Convert large complex molecules
(FOOD) into simpler molecules
(nutrients) that get absorbed into the
body, then move the leftover
food/waste out of the body.
• It takes anywhere from 12-72 hours to
digest food completely, depending on
what the food is.
What is being released when
food is broken down into
smaller molecules?
ENERGY
used for cell activities
Major/Accessory Organs work together
to break down food.
Two types of Digestion
• Mechanical digestion (physical change)
• Chemical digestion (chemical change)
Chemical or Physical change?
• Mouth (teeth): chewing and grinding
physical
• Salivary enzymes (amylase) break down amylose (starch) into
chemical
disaccharides (sugars) ; the Esophagus moves broken down food into
the stomach.
• Stomach: Pepsin with help of HCl break down proteins
chemical
• Small intestine:
 Nutrients are absorbed into Villi in the small intestine;
physical
 Bile (“detergent” from liver) physically breaks down Lipids into smaller
physical
fats
 Other enzymes further break down Lipids into fatty acids , carbs into
chemical
simple sugars, & proteins into amino acids
 Lactase breaks down lactose into glucose and galactose
• Large intestine: absorbs water
• Liver:
 Catalase breaks down H2O2 (toxin) into water and oxygen
chemical
physical
chemical
Catalase in the Liver
• Remember when we were talking
about enzymes? Here’s the video on
how the enzymes in the liver break
down H2O2.
Some people cannot consume
dairy products, such as milk,
without their stomach
becoming upset. Explain.
They lack the enzyme lactase, which
breaks down lactose (sugar) into
simple sugars during digestion.
Where in the body are biomolecules
digested?
Carbohydrates
disaccharides
sugars
Proteins
Lipids
Amino acids
fatty acids
If you ate a meal of spaghetti and
meatballs, where would chemical
digestion of the pasta and meat
begin?
Mechanical digestion:
pasta and meatballs
Chemical digestion:
Pasta (starch) with
amylase
Chemical digestion:
Proteins with
pepsin
Why do systems interact?
To maintain homeostasis
How does digested
food get to cells?
Interactions with
Circulatory system
• The circulatory
system carries
absorbed
nutrients (small
intestine) in the
bloodstream to
all the body
cells.
In cells, nutrients are broken down into even
smaller parts by lysosomes (bags of digestive
enzymes and acids).
Ex. Glucose that can be used by mitochondria to
make ENERGY.
Interactions with
Muscular system
•The muscles help
chew and swallow
food.
• The smooth muscles
of stomach contracts
to push food through.
Interactions with
Endocrine system
• Makes the hormone insulin
to regulate blood sugar.
(When we digest
carbohydrates, they are
converted into sugars, then
the endocrine system yields
the hormone, insulin, to
control how much sugar is in
the blood flow and the
amount at a certain time)
Interactions with
Excretory system
• Digested system breaks
down food into nutrients
that are absorbed in a
small intestine  blood
 transported to all the
cells in the body.
• Cells produce waste 
enter the blood stream
 travel to kidneys 
kidneys filter it out 
turns into urine
Interactions with
Nervous system
• Recieves cellular energy
(ATP) from nutrients
• Sends messages to the
digestive system when body is
hungry and when body is full.
Signals peristalsis (Physical
movement) in the digestive
tract. Signals hydrolytic
enzymes/hormones to be
distributed.
Interactions with
Respiratory system
• Recieves carbs for
cellular respiration
• Provides oxygen
for the process of
cellular respiration
to take place in the
mitochondria to
convert glucose
into ATP.
Enzymes Review
•Enzymes are proteins that
act as biological catalysts.
•Without enzymes, chemical
reactions will not occur fast
enough to sustain life
processes.
Enzymes Review
The ACTIVE SITE is the area of the enzyme
that attaches to the chemical (substrate)
undergoing change.
Enzyme Review
• Enzymes lower or
decrease the
activation energy
needed to start a
chemical reaction;
therefore, enzymes
speed up reactions.
Enzyme Review
• Enzymes are specific to the chemical
reaction they catalyze. They have
unique structures and functions.
• The enzymes remain unchanged
when a reaction is complete and can
assist with the same reaction over
and over again.
Summarize your Cornell Notes