6.1 Digestion
★Explain why digestion of large food molecules is
essential.
★Explain the need for enzymes in digestion.
★State the source, substrate, products and optimum pH
conditions for one amylase, one protease and one lipase.
★Draw and label a diagram of the digestive system.
6.1 Digestion
★Outline the function of the stomach, small intestine and
large intestine.
★Distinguish between absorption and assimilation.
★Explain how the structure of the villus is related to its role
in absorption and transport of the products of digestion.
6.1 Digestion
• Why is digestion necessary?
• 1. If you eat other organisms (plants/animals), we need
to break it down into a form suitable for our human body.
• 2. Most of what we eat is food that is made up of
large/complex organic molecules, which our body cannot
use.
• Large molecules cannot pass into your cell membranes
that line the intestine (absorb nutrients) which pass into
the bloodstream. Have to be small enough to pass into
our cells through diffusion, facilitated transport, or
active transport.
6.1 Digestion
• Digestion is the chemical breakdown of large, insoluble
food molecules into small, soluble molecules (stuff our body
can use and absorb!).
• Food molecules before and after
digestion/breakdown
Molecule type
Molecular form
ingested
Molecular form after
digestion
protein
protein
amino acids
lipids
triglycerides
glycerol and fatty acids
carbohydrates
poly/di/monosaccharid
es
monosaccharides
nucleic acids
DNA/RNA
nucleotides
6.1 Digestion
• The last meal you ate probably had food from plants
and/or animals - once living things.
• These living things have their own DNA which codes
for their specific proteins.
• Digestion allows you to breakdown individual amino
acids so that your own DNA can use them as
building blocks to synthesize proteins your body can
recognize and use.
6.1 Digestion
• Order of digestion:
• Ingestion: you eat the food
• Digestion: series of chemical reactions, whereby you
convert the ingested food to smaller and smaller
molecules.
• Absorption: small molecules are absorbed through cells
of your digestive system and pass into nearby blood
vessels.
• Transport: your circulatory system delivers the small
molecules/nutrients to your body cells.
6.1 Digestion
• Need for enzymes in digestion:
• Digestion of large molecules happens naturally at our
body temperature but only at a very slow rate.
Enzymes are needed to speed up this process!
• Remember, enzymes are proteins that are catalysts -
they speed up chemical reactions.
• As catalysts, the real function of enzymes is they
lower the activation energy needed for the reaction
to occur.
6.1 Digestion
• Digestive enzymes all help to catalyze
hydrolysis reactions.
• You studied hydrolysis - so what is it?
• Hydrolysis is the breakdown of a larger
molecule into smaller molecules, losing water
in the process.
6.1 Digestion
• Examples of Digestive Enzymes
Amylase
Example of this
Salivary amylase
enzyme
Source
Salivary gland
Protease
Lipase
Pepsin
Pancreatic lipase
Wall of stomach
Pancreas
Substrate
Starch
Proteins
Triglycerides
(fats or oils)
Products
maltose and
glucose
Small
polypeptides
Fatty acids and
glycerol
Optimum pH
neutral (pH 7)
Acidic (pH 3)
Neutral (pH 7)
6.1 Digestion
• Draw and label the digestive system
In order:
Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
(colon)
Rectum
6.1 Digestion
• STOMACH
• 1. In the mouth, food is broken down
mechanically (teeth) and chemically (amylase)
• 2. When you swallow, food is passed through
the esophagus through muscle contractions
called peristalsis
• Muscles squeeze around your food, pushing it
down - why it hurts sometimes when you
swallow a ridged chip.
6.1 Digestion
• 3. Digestion of proteins starts in the stomach, with the
help of gastric juice - a mixture of 3 things:
• Pepsin - enzyme most active in high acid, a high acidic
environment is the right condition for it to work.
• Hydrochloric acid - breaks down food, creates the acidic
environment, kills bacteria that could cause food
poisoning. This is what burns your throat when you
throw up.
• Mucus - lines the inside of stomach to prevent
stomach damage from the hydrochloric acid
6.1 Digestion
• 4. The muscular wall of the stomach creates a
churning motion on order to mix the food with the
gastric juice.
• 5. After a period of time, a valve at the lower end
of the stomach opens and the food enters the
small intestine.
6.1 Digestion
• SMALL INTESTINE
• 6. Digestion continues in the small
intestines with more secretions: bile
form the liver/gall bladder and lipase
from the pancreas break down food
further.
• 7. Now some molecules are small
enough to be absorbed.
• The inner wall of the intestine is made
up of thousands of finger-like
extensions called villi.
6.1 Digestion
• 8. Each villus contains a capillary bed so absorbed
molecules can be taken from the small intestine, and
pass through a layer of cells into other body cells
through the bloodstream.
• Once a nutrient molecule enters a body cell, it leaves
the circulatory system and the cell may use it for
energy (ex: glucose) or maybe it's used as a building
block to build a larger molecule (ex: amino acids)
• If the nutrient molecule is used for building larger
molecules, the process of bringing the nutrient to a
body cell then using it is called assimilation.
6.1 Digestion
• LARGE INTESTINE (COLON)
• 9. Most of the useful nutrients in food has already been
absorbed by the small intestine. What remains of the
original food by the time it gets to the beginning of the
large intestine is undigested (unabsorbed).
• 10. Primary function of the large intestine is to absorb
water.
• The LI is also home to many bacteria (ex: E.coli) that we
provide nutrients/water to while they make vitamin K and
maintain a overall healthy environment in our LI.
6.1 Digestion
• 11. Any food undigested by us or the bacteria in your
LI exits the body as solid waste through the rectum
then out the anus.
6.1 Digestion
• 1. What does the digestion of starch by amylase
produce?
• A. Lactose
• B. Sucrose
• C. Cellulose
• D. Maltose
• Answer: D
6.1 Digestion
• 2. Which of the following is correct for lipase?
Substrate
Source
pH optimum
A
triglycerides
pancreas
pH = 7
B
fatty acids
small intestine
pH = 7
C
triglycerides
small intestine
pH = 9
D
fatty acids
pancreas
pH = 9
• Answer: A
6.1 Digestion
• 3. Which of the following parts of the digestive system
secrete proteases?
Stomach
Small Intestine
Large
Intestine
A
Yes
Yes
Yes
B
Yes
No
Yes
C
Yes
No
No
D
No
No
No
• Answer: C
6.1 Digestion
• 4. The diagram below shows parts of the human
digestive. Which points are linked by the small intestine?
• A. I and III
• B. II and III
• C. II and IV
• D. III and IV
• Answer: B
6.1 Digestion
• 5. What are the names of the organs labelled I and II in
the diagram below?
I
II
A
pancreas
liver
B
small
intestine
large
intestine
C gall bladder
pancreas
D
stomach
esophagus
• Answer: C
6.1 Digestion
• 6. Celiac disease causes the destruction of the villi cells.
Which of the following is most likely to happen to people
with celiac disease?
• A. Incomplete digestion of fats
• B. Poor absorption of calcium
• C. Increased levels of glucose in blood
• D. Damage in the esophagus caused by increase
in acid content of the stomach
• Answer: B
6.1 Digestion
• 7. What processes occur during assimilation and
absorption of lipids?
Assimilation
Absorption
A
lipids are broken down by
enzymes
lipids are ingested
B
lipids are incorporated into
new membranes
lipids pass into the vili
lipids pass into the villi
lipids are incorporated into
new membranes
lipids are ingested
lipids are broken down by
enzymes
C
D
• Answer: B
6.1 Digestion
• 8. What is the main function of the large intestine?
• A. Absorption of water
• B. Digestion of fats and proteins
• C. Absorption of nutrients
• D. Recycling of digestive enzymes
• Answer: A
6.3 Defense against infectious disease
★Define pathogen.
★Explain why antibiotics are effective against bacteria but
not against viruses.
★Outline the role of skin and mucus membranes in defense
against pathogens.
★Outline how phagocytic leucocytes ingest pathogens in
the blood and in body tissues.
6.3 Defense against infectious disease
★Distinguish between antigens and antibodies.
★Explain antibody production.
★Outline the effects of HIV on the immune system.
★Discuss the cause, transmission and social implication of
AIDS.
6.3 Defense Against Infectious Diseases
• Pathogen and Antibiotics
• Pathogen: any living organism or virus that is capable of
causing a disease.
• EX of Pathogens: viruses, bacteria, fungi, and various
worms.
• BUT exposure to most pathogens do not result in a
disease.
• Our body has amazing defenses for most pathogens
that enter out body and in the case when they do
enter, we usually have already developed an immunity
to that pathogen.
6.3 Defense Against Infectious Diseases
• For some, like bacteria, there are chemicals called antibiotics that
can work against living bacterial cells that do not affect our own
body cells.
• How antibiotics work against bacteria:
• 1. Bacteria are prokaryotes and our body cells are eukaryotes.
Antibiotics take advantage of the differences between our cells and
bacteria. Can you some of those differences?
• Prokaryotes: Cell wall, nucleoid (free floating DNA), no nucleus
• Antibiotics are chemicals produced by microorganisms,
Example: Pencillium fungus produces penicillin to kill bacteria
6.3 Defense Against Infectious Diseases
• 2. There are different categories of antibiotics - some
block protein synthesis in bacteria (but have no effect on
ours because our DNA is in a nucleus), others may stop
the production of a new cell wall by bacteria (thus blocking
their ability to grow and divide.
• 3. This also explains why antibiotics do not work on
viruses. Viruses use your own body cells as a host to
create new viruses. Any chemical that would stop viruses
would also damage your own cells
• When you get a cold - doctor's can't do anything for you
because antibiotics don't work on the influenza virus,
you just have to let it run its course!
• Preventing Pathogens From Entering Our Bodies
• It isn't possible to isolate yourself and stay away from
every possible source of infection, so your body has some
awesome ways to make it difficult for pathogens to enter
your body and start an infection.
• Skin: it is a barrier to infection with 2 layers
• Underneath layer (dermis) is very alive with sweat
glands/capillaries/sensory receptors.
• Top layer (epidermis) is constantly being replaced as the
dead cells from the dermis keep moving up. So this
layer of dead cells is a great barrier against pathogens
because it isn't truly alive.
• As long as our skin remains intact, it defends against
pathogens.
• This is why it is so important to clean and take care of cuts
to the skin to quickly heal the top layer of skin or else
pathogens enter our blood stream through that cut.
6.3 Defense Against Infectious Diseases
• Stomach Acid: some pathogens enter the body in food and
water.
• The very acidic environment of the stomach helps to kill
most of these ingested pathogens.
• Mucus: other pathogens enter in the air we breathe (either
through nose or mouth)
• This route is lined with a type of tissue known as mucous
membrane.
• Why it's better to breathe through your nose than mouth:
the hairs in your nose serve as the first filter to separate
pathogens from the air going into your lungs.
• Cells of mucus membranes produce and secrete a lining of
sticky mucus which can trap incoming pathogens and
prevent them from reaching cells they could infect.
• Some mucus membranes are lined with cilia - hair like
extensions with a wave-like movement that traps
pathogens too.
• Also, the cells that secrete mucus also secrete an
enzyme called lysozyme - which chemically damages
many pathogens.
Area w/ Mucus Membrane
What it is/does
Trachea
Tube carried air to and from lungs
Nasal Passages
Tubes allow air to entier the nose and then the trachea
Urethra
Tube carried urine from bladder to outside
Vagina
Reproductive tract leading from uterus to the outside
6.3 Defense Against Infectious Diseases
6.3 Defense Against Infectious Diseases
• What Happens When Pathogens Do Get In?
• Besides your skin/mucus/stomach acid, our body has
another defense against pathogens!
• Leucocytes (white blood cells) are in out blood to help us
fight off pathogens that make it that far, and also
remember them when they enter again helping us keep an
immunity against repeat pathogens.
• Some of the leucocytes in blood are phagocytes.
• Phagocytes can identify pathogens, determining if they
are a natural part of the body, and if not, ingest them by
endocytosis.
6.3 Defense Against Infectious Diseases
• The pathogens are then killed and
digested inside the phagocytes by
enzymes.
• Phagocytic leucocytes can ingest
pathogens in the blood
• Using their flexible cell membrane,
they easily change shape and can
squeeze out through the walls of
capillaries and move through tissues
to get to the site of the infection.
• Large numbers of phagocytes at
the infection site is PUS!
6.3 Defense Against Infectious Diseases
• Antigens and Antibodies
• Antigens are proteins found in the cell membranes or
cell walls of bacteria/viruses .
• These antigens allow your body to recognize a
pathogen as being an invader in your body or "not
self," which give a clear signal to switch on your
immune response with a rapid production of
antibodies.
• Antibodies are protein molecules that are produced by
your body in response to any pathogen antigen's that
enters your body.
6.3 Defense Against Infectious Diseases
• There are millions of different antibodies and each one is
specific to an antigen.
• EX: the antibodies produced in response to infection by the
chicken pox pathogen is very different from the influenza
virus antibodies.
• Each antibody molecule has a basic Y shape, and the tops of
the Y are specific binding sites that give every antibody its
unique properties.
• These specific binding sites attach to the corresponding
antigen site, and once it is bound to the pathogen's
antigens, it can destroy it (deactivate its DNA or cause their
cell wall to explode.
6.3 Defense Against Infectious Diseases
6.3 Defense Against Infectious Diseases
• HIV and AIDS
• AIDS shows just how crucial the
body's defenses are against
diseases. Destruction of the
immune system eventually leads to
death, which ultimately is what
AIDS does.
• A syndrome, like AIDS (acquired
immunodeficiency syndrome), is
a group of symptoms that are
found together.
6.3 Defense Against Infectious Diseases
• Cause of Aids - HIV: HIV (human immunodeficiency virus)
causes AIDS.
• The virus infects a type of lymphocyte that plays a vital role in
antibody production.
• Over a period of years, these lymphocytes are destroyed and
antibodies cannot then be produced.
• Without a functioning immune system, the body is vulnerable
to pathogens that normally would be controlled easily.
• Individuals with AIDS have low numbers of lymphocytes, weight
loss, and other diseases caused by viruses/bacteria is what
leads to their death.
6.3 Defense Against Infectious Diseases
• Transmission of AIDS:
• HIV does not survive long outside the body and cannot easily
pass through the skin, so it requires body fluids to be
transferred from one person to another.
• Through small cuts, tears in the vagina/penis/mouth during
vaginal/anal/oral sex.
• In traces of blood from sharing needles through drug use.
• Across the placenta from mother to baby, through cuts
during childbirth, or in milk during breast-feeding.
• In transfused blood - rarely happens today as donated
blood goes through several tests until it is give to a patient
6.3 Defense Against Infectious Diseases
• Social Implication of HIV/AIDS:
• Families and friends suffer grief from prolonged sickness than
can last decades, then eventually death.
• Families become poorer if the individual with AIDS was the
wage earner and is refused life insurance, or if that person
has no medical insurance to pay for the medicine to prolong
their life.
• Individuals infected with HIV may become stigmatized and not
find partners, housing or employment.
• Sexual activity in a population may be reduced of the fear of
AIDS.
6.3 Defense Against Infectious Diseases
• 1. Which factors related to mucus membranes protect the
body against microbes?
• I. Production of lysozyme
• II. Secretion of alkaline solutions
• III. Trapping of microbes
• A. I and II
C. I and III
• B. II and III
D. I, II and III
• Answer: C
6.3 Defense Against Infectious Diseases
• 2. What prevents antibiotics from being effective against
viruses?
• A. Viruses have a high rate of mutation.
• B. Viruses have no RNA.
• C. Viruses have no metabolism.
• D. Viruses have a protein shell that protects them.
• Answer: C
6.3 Defense Against Infectious Diseases
• 3. Which term describes a molecule capable of triggering
an immune response?
• A. Antibody
• B. Antigen
• C. Pathogen
• D. Antibiotic
• Answer: B
6.3 Defense Against Infectious Diseases
• 4. What does the nucleus of a human lymphocyte
contain?
• A. Only the genes to produce a specific antigen
• B. Only the genes to produce a range of antibodies
• C. Only the genes that control the growth and
development of a lymphocyte
• D. The whole genetic information for a human.
• Answer: D
6.3 Defense Against Infectious Diseases
• 5. Which of the following statements about antibodies is
correct?
• A. Antibodies are polypeptides
• B. Antibodies are produced by the bone marrow.
• C. Antibodies are pathogenic foreign substances.
• D. Antibodies kill bacteria but not viruses.
• Answer: A
6.3 Defense Against Infectious Diseases
• 6. What stimulates the production of antibodies?
• A. AIDS
• B. Antibiotics
• C. Anticodons
• D. Antigens
• Answer: D
6.3 Defense Against Infectious Diseases
• 7. What are 2 effects of HIV on the immune system?
• A. Reduction in antibody production and increase in
active lymphocytes.
• B. Increase in antibody production and decrease in
red blood cells.
• C. Reduction in antibody production and decrease
in active lymphocytes.
• D. Increase in antibody production and increase in
red blood cells.
• Answer: C
6.3 Defense Against Infectious Diseases
• 8. Where in a cell are antigens found?
• A. In the nucleus
• B. In the cytoplasm
• C. In the plasma membrane
• D. On the surface of the golgi apparatus
• Answer: C