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EdExcel Additional Science
Biology Unit 2 –
The Components of Life
N Smith
St. Aidan’s
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Topic 1 – The Building Blocks of Cells
A Typical Animal Cell
1) Cytoplasm - this is
where the reactions
happen and these are
controlled by enzymes
2) Nucleus –
controls the
cell’s activities
3) Cell Membrane –
controls what
comes in and out
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4) Ribosomes – protein
synthesis happens
here
5) Mitochondria energy is released
here during
respiration
A Typical Plant Cell:
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Cell wall – made
of cellulose which
strengthens the cell
Cell membrane
– controls what
comes in and out
Large vacuole –
contains sap and
helps support the
cell
Chloroplasts (containing
chlorophyll) – this is needed
for photosynthesis
Nucleus – controls
what the cell does and
stores information
Cytoplasm –
Chemical reactions
happen here
Bacteria
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Consider a bacteria cell in more detail:
Bacteria – containing
cytoplasm and a membrane
surrounded by a cell wall.
The genes are NOT in a
distinct nucleus.
The cell contains a number of features,
including:
1) Chromosomal DNA, containing the
genetic info of the cell
2) Plasmid DNA, containing extra
information such as defence
mechanisms
3) Flagella, which helps the cell move
Using a light microscope
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1. Eyepiece
2. Arm
7. Lenses
6. Stage
5. Mirror
3. Focus
adjustor
4. Base
Magnification Calculations
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These microscopes have
different powers of
magnification. Consider this
image of velcro:
A “stereo”
microscope
If the “loop” on this image is measured to be 20cm
tall at a magnification of 100x how big is it really?
An old
microscope!
2mm
Genes, Chromosomes and DNA
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How genes work DNA
Some facts:
- DNA has a “double ______” structure
- This contains instructions on what a cell does, how
the organism should work etc
- The instructions are in the form of a ______
- The code is made up from the four ____ that hold
the strands together with hydrogen bonds
- The bases represent the order in which _____
acids are assembled to make specific ________
Words – helix, amino, code, bases, proteins
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DNA
Task: Find out how the structure of DNA
was discovered, including:
1) An image of Crick and Watson with
their original model
2) A brief desciption of what Crick and
Watson did to discover DNA
3) How Franklin and Wilkins built on their
work
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The Human Genome Project
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In 1990 an international project was launched called the
“Human Genome Project”. The aim was to map the _______
makeup of the human race and includes work from ______ in
18 different countries.
Possible benefits:
• Improved genetic testing
• Improved predictions and screening of ________ diseases
• New gene ________ treatments
• New knowledge of how ______ have changed
Words – scientists, genetic, genes, inherited, therapy
Uses of Genetic Engineering
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With genetic engineering I can
produce milk that contains:
• Extra protein
• Lower levels of cholesterol
• Human antibodies
Basically, genetic engineering is when a gene is removed from
one organism and inserted into another. Consider the example
of making insulin:
Genetic engineering - Insulin
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Step 1: Using RESTRICTION
ENZYMES “cut out” the part of
the human chromosome that is
responsible for producing insulin.
Step 2: Using another restriction
enzyme cut open a ring of bacterial
DNA (a “plasmid”). Other enzymes
are then used to insert the piece of
human DNA into the plasmid.
Step 3: Place the plasmid into a bacterium
which will start to divide rapidly. As it
divides it will replicate the plasmid and
make millions of them, each with the
instruction to produce insulin. Commercial
quantities of insulin can then be produced.
Cell growth 1 - Mitosis
Each daughter cell has
the same number of
chromosomes and genetic
information as the parent.
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Cell growth 2 - Meiosis
Each daughter cell has half
the number of chromosomes
of the parent.
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Mitosis:
1.
Mitosis vs. Meiosis
Used for growth and repair of
cells
2. Used in asexual reproduction
3. Cells with identical number of
chromosomes and genetic
information are produced
(“clones”)
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Meiosis:
1.
Used to produce haploid
gametes for sexual
reproduction
2. Each daughter cell has half the
number of chromosomes of the
parent
During meiosis copies
of the genetic
information are made
and then the cell
divides twice to form
four daughter cells.
Fertilisation
The human egg and
sperm cell
(“GAMETES”) contain
23 chromosomes each
and are created by
meiosis.
When fertilisation happens the
gametes fuse together to make a
single cell called a ZYGOTE
(“diploid”). The zygote has 46
chromosomes (23 pairs) and
continues to grow through mitosis.
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Key words
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Gamete
• Contains half the number of chromosomes
Zygote
•This is formed when an egg is fertilised by a sperm
Diploid
• A section of DNA
Haploid
Gene
• Contains the full number of chromosomes
•An egg or a sperm are called this
Cloning Animals
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Here’s how Dolly the sheep was cloned:
Clone
Host mothers
Pros and cons of cloning
Medicinal Cloning new
organs for use
when humans’
organs fail
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Creating new
food supplies
Cloning
Ethical issues – is it
right to clone
animals or humans?
Risk of creating
deformed animals
or humans
Cell specialisation
During the development of
a multi-celled organism
cells differentiate to
form specialised cells:
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A “stem cell” is a cell that
hasn’t yet become
specialised and can be
found in embryos or bone
marrow. These cells can
be used to treat certain
conditions but the use of
these cells is very
controversial.
Ciliated
epithelial cell
White blood cell
Nerve cell
(neurone)
Egg cell (ovum)
Stem cell research
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Stem cells are cells that have not yet specialised:
Embryo
Egg and
sperm
Cloned
embryos
These stem cells have
the potential to develop
into any kind of cell. In
grown adults they can
be taken from bone
marrow or they can
come from embryos
from unused IVF
treatments. They can be
used to treat conditions
such as paralysis.
The ethical issue:
Should these embryos be treated as humans?
Making proteins
1) DNA “unravels” and a copy of one
strand is made
2) The strand copy is made to
produce mRNA
3) The copy (with its code) then
moves towards the ribosome
4) The ribosome “decodes” the code
which tells the ribosome how to make
the specific amino acid
5) Amino acids are then joined
together to form a polypeptide
(protein)
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Mutating DNA
Each protein has its own
specific number and order
of amino acids. But what
happens when DNA
mutates?
This mutation will cause
different amino acids
(and therefore different
proteins) to be formed.
These mutations can be
beneficial, harmful or
neutral.
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Introduction to Enzymes
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Enzymes are biological catalysts. They help the reactions
that occur in our bodies by controlling the rate of reaction.
An enzyme is basically a protein molecule made
up of long chains of amino acids. These molecules
are then “folded” to create a certain shape.
Proteins are used in DNA replication, protein
synthesis and digestion.
The enzyme’s shape helps another
molecule “fit” into it (“lock and key”):
This shape can be destroyed
(“denatured”) by high
temperatures or the wrong pH:
Enzyme
Substrate
Enzymes
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Enzymes work best in certain conditions:
Enzymes are
denatured
beyond 40OC
Enzyme
activity
400C
Temp
Could be
protease (found
in the stomach)
Could be amylase
(found in the
intestine)
pH
Enzymes are used in industry to bring about reactions at
normal temperatures and pressures that would otherwise be
expensive. However, most enzymes are denatured at high
temperatures and can be costly to produce.
pH
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Topic 2 – Organisms and Energy
Respiration Introduction
I enjoy taking samples using quadrats. In
order to do this, I need energy. Where does
this energy come from?
Our energy comes from a process called
respiration, which basically involves turning
food and oxygen into energy and this
reaction is controlled by enzymes.
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Diffusion
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Diffusion is when something travels from an area of high
concentration to an area of low concentration. For example,
consider the scent from a hamburger…
The “scent particles” from
this hamburger are in high
concentration here:
Eventually they will
“diffuse” out into this area
of low concentration:
Oxygen passes into cells by diffusion
Diffusion Summary
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Diffusion is when particles spread from an area of high
concentration to an area of ___ concentration. The particles
move along a “concentration _____” and this process takes no
_____ (it’s a “passive” process”). Diffusion can be accelerated
by increasing the _______ of the particles, which makes them
move _______.
Words – faster, low, gradient, temperature, energy
Diffusion in the lungs
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Oxygen diffuses in and carbon dioxide diffuses out of blood in
the lungs:
CO2
(Aerobic) Respiration
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All living organisms have to move, _____, reproduce etc. Each
of these life processes needs ENERGY. ___________ is the
process our bodies use to produce this energy:
Glucose + oxygen
water + carbon dioxide + ENERGY
The glucose we need comes from ______ and the oxygen from
_________. Water and carbon dioxide are breathed out.
The MAIN product of this equation is _________.
Respiration happens in _________ in cells.
Words – breathing, energy, grow, respiration, food,
mitochondria
Uses for this energy
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Animals and plants have many uses for the energy they
generate from respiration:
1) To build up sugars in ______
2) To build up body _______
3) To maintain a constant body ___________ (warm-blooded
mammals only)
4) To build up sugars, ________ and other nutrients in plants
5) To build up amino acids and ________
Words – nitrates, tissue, proteins, respiration, plants
Heart
rate/min
225
The Effect of Exercise
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Breathing
rate/min
Rest
Exercise
100
Recovery
175
75
125
50
75
25
5 mins
10 mins
15 mins
20 mins
During exercise the following things happen: heart rate increases,
breathing increases and arteries supplying muscles dilate. These three
things all help muscles to get the oxygen and glucose they need.
Cardiac Output and Heart Rate
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The electrical impulses from
the heart can be monitored
using an electrocardiogram:
Using this information and the
volume of blood pushed by the
heart (the “stroke volume”) you
can calculate the cardiac output
of the heart:
Cardiac output = stroke volume x heart rate
Muscles and exercise
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When we exercise our muscles are supplied with more oxygen
and glucose, increasing the rate of respiration.
Muscles store glucose as glycogen
which can then be converted back
into glucose during exercise.
Anaerobic respiration
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Unlike aerobic respiration, anaerobic respiration is when
energy is provided WITHOUT needing _________:
Glucose
lactic acid + a bit of energy
This happens when the body can’t provide oxygen quick enough
for __________ respiration to take place.
Anaerobic respiration produces energy much _______ than
aerobic respiration but only produces 1/20th as much.
Lactic acid is also produced, and this can build up in muscles
causing ______ and “excess post-exercise oxygen
consumption” (“EPOC”), which explains why breathing and
heart rates remain high after exercise.
Words – debt, oxygen, fatigue, aerobic, quicker
Photosynthesis
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Basically, photosynthesis is the process through which a plant
makes its own food using carbon dioxide and water:
That’s a nice plant. I’m
going to put it in the sun and
give it lots of water and air…
CO2
H2O
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Photosynthesis – the 4 things you need
SUNLIGHT
Gives the plant energy
CHLOROPHYLL
WATER
Travels up
from the roots
CARBON DIOXIDE
Enters the leaf through small
holes on the underneath
The green
stuff
where the
chemical
reactions
happen
Photosynthesis equations
Carbon dioxide + _____
Sunlight
Chlorophyll
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glucose + _____
Sunlight
6CO2
+ 6H20
Chlorophyll
C6H12O6 + 6O2
The GLUCOSE produced by photosynthesis is used by the
plant for _______ (through ____________). It is stored
in the plant as ___________.
Words – respiration, starch, water, oxygen, energy
Structure of the Leaf
Lots of
chlorophyll
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Large
surface area
Transparent
Thin
structure
Packed with
chloroplasts
Network of
veins
Lots of air
spaces
Holes
Limiting Photosynthesis
What factors could limit the rate of photosynthesis?
1. Temperature – the best temperature is
about 300C – anything above 400C will
slow photosynthesis right down
2. CO2 – if there is more carbon dioxide
photosynthesis will happen quicker
3. Light – if there is more light
photosynthesis happens faster
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Drawing graphs of these factors
1. Temperature
Photosynthesis is controlled by
enzymes – these are destroyed
at temperatures above 400C
2. Carbon dioxide
Photosynthesis increases at
first but is then limited by a
lack of increase in temp or light
3. Light
Photosynthesis increases at
first but is then limited by a
lack of increase in temp or CO2
Encouraging Photosynthesis
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Using knowledge of limiting factors, explain how plant growth
is encouraged in a greenhouse:
Water loss
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Water loss through the stomata is biggest on a hot,
dry, windy day. Plants that live in these conditions
often have a thicker waxy layer.
Transpiration
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1) Water evaporates
through the stomata
2) Water passes back into the
leaf through xylem vessels by
osmosis
3) Water is then pulled upwards
through the xylem tissue
4) This is replaced by water
entering from the root tissue
5) Water enters root hair cells by
osmosis to eventually replace the
water lost through respiration
Xylem and Phloem
Xylem are used by the plant
to transport water and
soluble mineral salts from
the roots to the stem and
the leaves.
Phloem are tubes used by
the plant to transport
dissolved food to the whole
plant for respiration and
storage.
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Root hair cells
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Plant roots are made of “root hair cells” which have two
features that help them to take in water and nutrients
(“active uptake”):
Root
hair
cells
Large surface area
Thin cell membrane
More on Active Transport
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In diffusion substances moved along a concentration gradient.
In active transport, substances move against this gradient:
Outside cell
Inside cell
Cell membrane
This process takes ______ and
this comes from ___________.
It enables cells to take in
substances even though there
are in very small __________.
Root hair cells take in ______
using active transport.
Words – concentration, energy,
respiration, nutrients
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Diffusion and Active Transport in plants
Mineral
More
concentrated
Carbon dioxide diffuses
into the leaf through
holes in the bottom
surface.
Less
concentrated
…while plant nutrients are taken
in by root hair cells using active
transport.
Osmosis
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Osmosis is a “special kind of ___________”. It’s when water
diffuses from a __________ area to a less concentrated area
through a partially permeable _________ (i.e. one that allows
water to move through but not anything else):
Water
Sugar solution
In this example the water
molecules will move from
left to right (along the
concentration ______) and
gradually _____ the sugar
solution.
Words – membrane, concentrated, dilute, diffusion, gradient
Potato cells
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Strong
sugar
solution
Medium
sugar
solution
Weak
sugar
solution
Osmosis of water from leaves
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Low conc.
of water
Water leaves
the plant by
diffusing
through osmosis
into the air
spaces and then
evaporating.
Low conc.
of water
High conc.
of water
Taking samples of an ecosystem
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Using different “sampling techniques” we can measure changes
in an ecosystem. The two main measurements are:
1) The physical conditions of a habitat (temperature etc)
2) The populations of different species in that habitat
Some common ways of measuring…
Help!
Measuring
temp, pH etc
Taking animal
samples
Taking samples
using quadrats
Topic 3 – Common Systems
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Fossils
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Fossils provide evidence of early life and could have been formed in many
ways. Four examples:
This fossil of a bat
was formed due to
hard parts of the
animal not decaying
This fossil was formed by
parts of its body being
replaced by minerals
Why could there be
gaps in the fossil
record?
This bee and orchid
pollen were preserved
in amber – the amber
lacked some of the
conditions needed for
decay to happen
Fossilised footprints
Fossil records
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Fossil records can provide a useful way of observing a species’
development:
The “Stenheim
skull”, found in
Germany in 1933
Oh
no…
The problem is, many early forms of life only had soft bodies
and the few remaining traces of them have been destroyed by
geological activity. This makes it difficult for scientists to
know what happened in the distant past.
The Pentadactyl Limb
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The “pentadactyl limb” refers to features like our hands that
have five “digits”. It’s a common feature for mammals. How
does that provide evidence for evolution?
Plant Growth
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Plants grow due to their cells dividing through mitosis and
each cell growing through elongation. The cells then specialise
into root hair cells, palisade cells etc. Unlike animals, plants
continue to grow for the rest of their lives.
Human Growth
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In humans, we grow by cell division through mitosis and cell cells becoming
specialised. There are five main areas of human growth:
1) Infancy (up to two years)
2) Childhood (2-11)
3) Puberty (11-13/15)
4) Adulthood (15 upwards)
5) Old age (60+ years)
Growth rate
(cm/year)
Age
The four parts of blood
1. RED BLOOD CELLS – contain haemoglobin
and carry ______ around the body. They
have no _______ and a large surface area.
2. PLATELETS – small bits of cells that lie
around waiting for a cut to happen so that
they can ____ (for a scab).
3. WHITE BLOOD CELLS – kill invading
_______ by producing _________ or
engulfing (“eating”) the microbe.
These three are all carried around by the
PLASMA (a straw-coloured liquid). Plasma
transports CO2 and ______ as well as
taking away waste products to the ______.
Words – antibodies, clot, kidneys,
oxygen, nucleus, glucose, microbes.
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Cells, tissues, organs and systems
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Basically, all living things are
made up of cells…
A group of CELLS makes up a
TISSUE
A group of TISSUES makes up
an ORGAN
A group of ORGANS makes up a
SYSTEM
A group of SYSTEMS make up an
ORGANISM
Another example
Here’s another example in humans:
Muscle cells
Muscle tissue
Organ
System
Organism
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The Circulatory system
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The circulatory system is responsible
for pumping ______ around the body.
We need blood to be taken around the
body because blood contains ________
and _______. These are needed so
that all the ____ in our bodies can
produce _____ through _________.
The main organs in the circulatory
system are the _____, the lungs and
the kidneys.
Words – energy, heart, blood, glucose,
respiration, oxygen, cells
The Heart
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1. Deoxygenated
blood (i.e. blood
without oxygen)
enters through the
vena cava into the
right atrium
4. Oxygenated
blood from the
lungs enters
through the
pulmonary vein into
the left atrium
2. It’s then
pumped through
the tricuspid valve
into the right
ventricle
5. It’s then pumped
through the
bicuspid valve into
the left ventricle
3. It’s then pumped
through the semi-lunar
valve up to the lungs
through the pulmonary
artery
6. It’s then pumped
out of the aorta to
the rest of the
body
“Double Circulation”
1) Blood gets pumped
from the heart to the
lungs and picks up oxygen.
The haemoglobin in the
cells becomes
oxyhaemoglobin
5) After the oxygen and
glucose have been removed
for respiration the blood is
sent back to the heart and
starts again
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2) The blood is then
taken back to the
heart…
3) The heart pumps
the blood to the
intestine (where
oxygen and glucose
are removed). The
oxyhaemoglobin is
split up into oxygen
and haemoglobin…
4) … and to the rest of
the body (where oxygen
is also removed)
Arteries, veins and capillaries
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Arteries carry high pressure
blood away from the heart.
They have smaller lumen and
no valves.
Capillaries have thin walls
(one cell thick) to allow
glucose and oxygen to pass
through. Also used to
connect arteries to veins.
Veins carry low pressure blood back to the
heart. They have thinner, less elastic walls and
have valves to prevent backflow of blood.
The Digestive System
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Match these functions with the parts of the digestive
system that do them…
In here the food is chewed to
This tube uses muscle contractions
to push the food down
start breaking it down. An
enzyme (amylase) is also added.
Bile is produced here
Bile is stored
here
Excess water is
absorbed here
Food is absorbed into the
bloodstream here
This organ mixes the
food with
hydrochloric acid to
kill bacteria
Enzymes are
made here
Peristalsis
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“Peristalsis” is the
movement of muscles to
push food down the gullet.
The digestive system
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The whole point of digestion is to break down our food so
that we can get the bits we need from it…
The main foods
affected are
CARBOHYDRATES –
these are broken down
into GLUCOSE.
Hydrochloric acid is
produced in the
stomach to kill bacteria.
Digestion also depends
on “enzymes”...
Enzymes in digestion
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Carbohydrase (produced in the mouth,
pancreas and small intestine) breaks
_______ (a carbohydrate) down into
glucose:
Protease (produced in the stomach,
pancreas and small intestine) breaks
_______ down into amino acids:
Lipase (produced in the pancreas and
small intestine) breaks fats (_____)
down into fatty acids and glycerol:
Words – blood, lipids, proteins, digestion, starch, smaller
Bloodstream
Enzymes can be produced by the body to help _______. When they come
into contact and react with food they break it down into ______ pieces
which can then pass into the ______:
Bile and The Liver
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Bile is a chemical produced in the
liver and stored in the gall
bladder. It has 2 functions:
1) It neutralises stomach acid
and produces alkaline
conditions for enzymes to
work in
2) It emulsifies (“breaks down”
fats:
Fat
globules
Fat
droplets
Diffusion in Villi
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In the intestine, large food molecules are broken down into
smaller ones that then diffuse into the blood through villi in
the intestine.
Villi also have a very good blood supply and a large surface
area. They have tiny folds in their cell membrane called
microvilli, which increase the surface area.
Functional Foods
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“Functional foods” is a term that describes foods like:
Task: find out the claimed benefits of functional foods,
including:
1) Probiotics
2) Prebiotics
3) Plant esters