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B3 Organisation and the Digestive System (Human Digestive System (Large…
B3 Organisation and the Digestive System
Organisation
Tissues
a group of cells with similar structure and function working together
Epithelial tissue
covers some body surfaces
Muscle tissue
contracts and relaxes
Connective tissue
connects and supports other body parts
bone cartilage fat
Nerve tissue
carries messages through the body
Glandular tissue
secretes substances such as enzymes and hormones
Cells
multicellular organisms develop specialised cells to perform particular jobs
the basic building blocks of all organisms
Organs
several tissues working together to perform a specific function
Stomach organ
muscular tissue to churn food
glandular tissue to produce digestive juices
epithelial tissue lines the inner and outer stomach surfaces
Pancreas organ
2 types of glandular tissue
one produces hormones to control blood sugar
the other produces some digestive enzymes
Organ Systems
several organs working together to perform a particular function
Digestive System
digests and absorbs food
Circulatory system
material transport
Respiratory System
gas exchange
systems have adapted to be efficient exchange surfaces
large surface areas
short diffusion paths
rich blood supplies
mechanisms for ventilating surfaces or moving materials
Organism
made up of organ systems that work together
Living Things
MRS GREN
Movement Respiration Sensitivity Growth Reproduction Excretion Nutrition
Human Digestive System
a muscular tube that squeezes food through it
breaks down large insoluble food molecules into smaller soluble molecules
to be absorbed into the blood
Mouth
Salivary Gland
secretes digestive juices with enzymes
amylase
(carbohydrase)
starch digested into smaller sugar molecules
food is chewed (mechanically broken down)
larger surface area for enzymes to work
Teeth
Tongue
alkaline
Oesophagus (gullet)
peristalsis
antagonistic pair of muscles work to
move food
along to stomach
Stomach
Muscle Layers
churns up food into fluid
increases SA for enzymes to digest
mixes food with digestive juices containing enzymes
Epithelial Tissue
secretes
mucus
protects stomach from acid and enzymes
stomach ulcer
protecting mucus lost
acid production increases
lining of stomach attacked
epithelial layer contains
blood vessels
for rich blood supply
Gastric Glands
glandular tissue secretes
stomach acid
HCl acid
kills bacteria
pH1
provides right pH for protease enzymes to work
secrete
enzymes
pepsin
(protease)
protein digested into amino acids
Small Intestine
Duodenum
Liver
releases
bile
into the small intestine when food enters
bile is
alkaline
pH 8-9
gives optimum alkaline pH for pancreatic enzymes
neutralises stomach acid
bile
emulsifies
fat
breaks down large drops of fat into smaller droplets
larger surface area for enzymes to work
Gall Bladder
stores and concentrates
bile
Bile Duct
carries bile from gall bladder and liver to the duodenum
releases bile when food enters small intestine
gall stones
can block the gall bladder and bile duct
stops bile being released onto food
Pancreas
(gland)
releases
enzymes
into the small intestine duodenum
pancreatic amylase
(carbohydrase)
breaks down starch into sugar molecules
trypsin
(protease)
continues to digest protein into amino acids
lipase
breaks down lipids into fatty acids and glycerol
also secretes
hormones
insulin
glucagon
first section of small intestine
Ileum
final section of small intestine
walls of ileum secrete
enzymes
peptidase
(protease)
completes breakdown of proteins (peptides) into amino acids
amylase
(carbohydrase)
completes breakdown of starch into glucose to be absorbed
lipase
completes breakdown of lipids into fatty acids and glycerol
Villi
absorbs digested food molecules from the gut into the bloodstream
either by diffusion or active transport
absorbs glucose, amino acids, fatty acids and glycerol
large surface area
folded membrane
large no. of villi
microvilli
on the surface
small intestine is very long (6-9m)
short diffusion path
thin walls
steep concentration gradient
good blood supply to carry food molecules away
Large Intestine
water is absorbed from undigested food in the gut into the bloodstream
by osmosis
material left forms faeces
Rectum
stores faeces
Anus
faeces excreted out of the body
Appendix
located where small and large intestines meet
Food Chemistry
Carbohydrates
provide
energy
contains carbon, hydrogen, oxygen
made up of sugar units
Simple Sugars
Glucose
one sugar unit
C₆H₁₂O₆
used in respiration
Sucrose
two sugar units joined
everyday 'sugar'
Complex Carbohydrates
Starch
long chain of glucose
Cellulose
long chain of simple sugar units
in cell walls
Glucagon
multibranched glucose
energy store
Proteins
growth and repair
structural components e.g. muscles or tendons
hormones
enzymes
antibodies
made up of long chains of
amino acids
there are 20 different amino acids
various arrangements give you different proteins
long chains are folded into specific 3D shapes
to fit other molecules
bonds holding protein together are very sensitive to temperature and pH
bonds can easily be broken
proteins can
denature
if it changes shape
protein may not function anymore
contains carbon, hydrogen, oxygen, nitrogen
Lipids (fats)
functions
energy store
hormones
cell membrane
nervous system
insulation
contains carbon, hydrogen, oxygen
made up of 3
fatty acid
molecules joined to a
glycerol
molecule
3 fatty acids can vary
different combinations affect where the lipid is solid fat or liquid oil
shorter fatty acid chains give liquids
longer fatty acid chains give solids
glycerol is always the same
all lipids are
insoluble
in water
Required Practical
Food Tests
grind the food sample to a paste using a
mortar and pestle
and
distilled water
transfer paste into beaker and add more distilled water to dissolve chemicals in the food
filter the solution to remove solid food particles, leaving you with a solution which you can see your results clearly in
Testing for Starch
pour 2cm³ of food solution into a test tube
add a few drops of
Iodine solution
(orange)
if starch is present, iodine will turn
blue/black
Safety: iodine solution is
irritant
Testing for (Reducing) Sugars
pour 2cm³ of food solution into a test tube
add 10 drops of Benedict's solution (blue)
place test tube into a hot water bath beaker and leave for 5-10 min
if sugars are present, the benedict's solution will change colour depending on sugar concentration
green
is small amount of sugar
yellow
is more sugar
brick red
shows a lot of sugar is present
Safety: benedict's solution is
irritant
Testing for Proteins
single Biuret solution
add 2cm³ of Biuret solution (blue)
if protein is present the biuret reagent turns
purple
place 2cm³ of food solution into a test tube
Biuret solution A&B
add 2cm³ of food solution into a test tube
add 2cm³ of biuret solution A (clear)
gently trickle into the test tube biuret solution B (blue)
if protein is present, a
purple layer
will form between the two indicators
Safety: solution A = sodium hydroxide -
corrosive
solution B = copper sulphate -
irritant and corrosive
Testing for Lipids
Reagent = Ethanol
place 2cm³ of food solution into a test tube
add 2cm³ of ethanol (clear)
add a bung to the test tube and shake to mix
if lipids are present, the solution turns
cloudy
Safety: ethanol is
highly flammable
, make sure no naked flames present
Reagent = Sudan III
place 2cm³ of food solution into a test tube
add 3 drops of Sudan III (blood red)
if food contains lipids, a
red-stained oil layer
separates on top
shake the test tube gently to mix
do not filter the food and water solution
Safety: contains ethanol, which is
highly flammable
Safety: wear eye protection
Enzymes
biological catalysts
they speed up reactions in living organisms
by bringing reactants together
reducing the
activation energy
needed
they or not used up or changed in the reaction
large proteins
active site
produced from folded amino acid chains
active site has a
specific shape
to bind to specific
substrate
molecules
enzymes control specific reactions
enzymes control the
metabolism
Metabolic reactions
break larger molecules into smaller ones
digestive enzymes
carbohydrates, proteins and lipids into their constituent molecules
cellular respiration breaks down glucose
amino acids into urea
change one molecule into another
isomerase enzymes
converting types of sugar
converting amino acid types
building large molecules from smaller ones
photosynthesis to make glucose
starch, glycogen and cellulose form glucose
glucose and nitrate ions to make amino acids in plants
protein synthesis
protein from amino acids
polymerase enzymes
lipids from fatty acids
metabolism is the sum of all the reactions in a cell or in the body
most enzymes work
inside
the cell
digestive enzymes work
outside
the cells
Lock and Key theory
substrate fits into the active site and binds to enzyme
rapid reaction occurs
products disassociate (released form surface of enzyme)
enzyme ready to use again
Breaking down Hydrogen Peroxide
hydrogen peroxide is a waste product of reactions in cells
poisonous compound
needs to be broken down quickly
irritant
breaks down slowly itself
breaks down into water and oxygen
oxygen is a fire hazard
Testing different catalysts
manganese(IV) dioxide is a inorganic (chemical) catalyst
harmful
liver and potato are organic catalysts
contain the enzyme
catalase
determine the different rates of reaction
measure the amount of oxygen produced in a given time
add washing up liquid and measure height of foam produced
Factors affecting Enzyme action
Temperature
rate of enzyme-controlled reactions increases as temperature increases
same as other chemical reactions
at higher temperatures, molecules move quicker and collide harder and more often
but only until protein structures of enzymes break down
enzymes work fastest at the optimum temperature
at too high temperatures, the rate of enzyme-catalysed reactions drops dramatically
enzyme becomes
denatured
enzymes stop working
denatured enzymes can't be fixed
amino acid chains unfold
substrate no longer fits in active site
active site changes shape
none of the reactions in your body would happen fast enough to keep you alive
it is dangerous if body temperatures are too high when you are ill
optimum temperatures for most human enzymes is 37°C (body temperature)
some bacteria enzymes can work effectively in 80°C or 0°C temperatures
human enzymes start denaturing at 41°C
pH
different enzymes have different optimum pH levels
at the optimum pH, the active site has the best shape for enzymes to work efficiently
body makes chemicals to keep pH ideal for the different enzymes
a change in pH causes the enzymes to
denature
the shape of the active site of an enzyme is held together by
forces
a change in pH affects the forces
shape of active site changes
substrate no longer fits in active site
enzymes stops working
Required Practical
Effect of pH on rate of reaction of Amylase
place one drop of
iodine solution
into each well of a
spotting tile
mix the
starch
solution,
amylase
solution and a
pH buffer
solution into one test tube
place the test tube in a water bath at 30°C (not higher than 37°C) for 10 minutes for them to reach optimum temperature
start a stop watch and transfer a sample of solution to an iodine-filled well on the spotting tile every 30 seconds
to start off, the iodine should turn blue/black, showing starch is present (not yet broken down by amylase)
stop taking samples when the iodine remains orange, showing that starch is no longer present (all broken down into sugars)
repeat the entire experiment using different pH buffers to see the effect pH has on the rate amylase enzymes works
Problems
Timing
approximate time for reaction to complete because samples only taken every 30s
take samples every 10s (at shorter time intervals)
Judgement
the time when iodine does no go blue/black may not be very obvious
colour change tends to be
gradual
have several people judging to see when reaction is complete
put 2cm³ of known concentration of
starch
solution,
amylase
solution and a
pH buffer
solution (to control the pH) into 3 different test tubes
Plotting Graphs
enzyme-controlled reactions can be shown on a
line graph
easy to interpret results and see
trends
a
rate
of reaction always includes
time
calculate the rate of the enzyme-controlled reaction at a given time
calculated by the gradient of the
tangent
drawn at that point on the line/curve
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