Download Enzymes and the Digestive system…

AS Biology
Mr Schofield
UNIT 1
Chapter 1
Causes of Disease
Causes of Disease… 1-Pathogens
• What are pathogens?
• How do they enter the body
• How do they cause disease?
What is a PATHOGEN?
• A pathogen is an entity that causes disease
– Bacteria
– Virus’
– Fungi
• The ability of that particular pathogen to cause a
disease is known as its pathogenicity
• Factors that effect pathogenicity include…
–
–
–
–
Methods of attachment
Toxin release
Infectivity
Invasiveness
How do pathogens enter the body?
• Bacteria and other micro-organisms can be
transmitted usually in one of three ways.
– Air
– Water
– Food
• The BORNE trilogy!!
• However they also enter through body
openings and skin abrasions
Air Borne
• When an infected person breathes,
coughs, or evan talks, the bacteria are
passed into the atmosphere inside tiny
droplets of water or mucus.
• The pathogens are carried by air currents.
• Sick Building Syndrome
Water Borne
• Water Borne bacterial infection results in
Diarrhoea.
• Diarrhoea effects over 1billion people a
year and kills nearly 5 million (in a good
year, i.e. one without a war or famine etc)
• Famous example is Cholera, but the most
common bacterial cause is E. coli…
Food Borne
• Salmonella food poisoning is caused by a
highly motile gram negative bacteria.
• S.typhimurium infects humans, poltry,
pigs, cows and horses. It can also effect
fish, especially those living in polluted
water.
• Many healthy animals are carriers, and the
bacteria is found naturally in their faeces
How do Pathogens cause disease?
• When they get into a body area that is usually
sterile…
• Disease can result because of tissue damage
or through tissue poisoning
– Most bacteria are often found in our own “body
flora”
– Bacteria often reach sterile internal areas through
small wounds and skin abrasions
– E.g. Clostridium Tetani
Tissue Damage
• Bacteria attach to and penetrate cells. They
may also break into blood and lymph vessels.
• Pili and Fimbriaie allow bacteria to attach to
membrane receptors
• E.g. Neisseria Gonorrhoea
– Attaches to manose receptors
– Causes painful blocking and swelling or urethra
and prostate in males, attacks ovaries in females
Production of Toxins
• Bacteria release toxins to break down and
disable cells
• There are two types of toxin
– Exotoxins
– Endotoxins
Causes of disease… 2- Risk Factors:
Lifestyle and Health
• What is a biological risk?
• The factors affecting the risk of cancer
• The factors affecting the risk of Coronary
Heart Disease (CHD)
Risk factors and disease
Chapter 2
Enzymes and the digestive system
Enzymes and the Digestive system… 1Brief Anatomy and Physiology of the
digestive system
• What is the structure and function of the
major parts of the digestive system?
• How does the digestive system break down
food both physically and chemically?
The Oesophagus
• Swallowed food is taken to the stomach via
the oesophagus.
• It is especially adapted for its purpose by
having very thick muscular walls.
– The outer cells are continuously rubbed away by
friction (with the swallowed food), so the mucosa
is folded. This also allows elastic expansion* . The
epithelial layer also contains mucus glands for
lubrication.
*
The Stomach
• The stomach is a muscular bag that can swell out
when full of food
• The major roles of the stomach are
– Temporary food storage
– Mixing the stomach contents with gastric juices
– A little digestion
• Gastric juices (a mixture of HCl and the enzyme
pepsin) are secreted from glands in the mucosa.
Mucus is also secreted to protect the muscle tissue
from the strong acid.
The Small Intestine
• The small intestine actually consists of three parts
– The duodenum
– The jejunum
– The ileum
• The duodenum is the upper part of the SI, the
pancreas and gall bladder empty secretions into it.
• Both the ileum and the duodenum have a folded
mucosa with millions of finger like projections called
Villi. Each villus has a very rich blood supply.
Breakdown and digestion: an
important distinction.
• Food is physically and chemically BROKEN DOWN
within the digestive system. This ensures that food
molecules are small enough to be absorbed
(digested) by the small intestine.
• The large intestine does not absorb food molecules.
It reabsorbs much of the water released into the
digestive system during breakdown.
Enzymes and the digestive system… 2Carbohydrates: Monosaccharides
• What is the structure of a monosaccharide?
• How would you carry out the Benedict's test
for reducing and non reducing sugars?
α-glucose
Reducing or non-reducing?
• All monosaccharides are reducing sugars!!
• Some disaccharides are also reducing sugars
• A reducing sugar is one which has a “free
ketone or aldehyde group”. It is able to reduce
the Cu2+ ions in CuSO4 to Cu+
Disaccharides
• Disaccharides are formed when two monosaccharide units are
combined together in a condensation reaction
• Condensation reactions produce water. The two original units
are joined together by a glycosidic bond.
Name
Reducing /
Monosaccharide Monosaccharide
Non-reducing
Maltose
Glucose
Glucose
Reducing
Lactose
Glucose
Galactose
Reducing
Sucrose
Glucose
Fructose
Non-Reducing
Enzymes and the digestive system… 3Carbohydrates: Polysaccharides and
carbohydrate digestion
• How do α-glucose molecules link together to
form starch?
• What is the test for starch?
• How is starch broken down by the digestive
system?
• How are sugars digested?
• Lactose intolerance…
Formation
• Polysaccharides are formed by condensation
reactions. Water is given off.
• The monomers in a polysaccharide are linked
together by a GLYCOSIDIC bond.
Make sure you can draw the structure of a
disaccharide, clearly showing the glycosidic
bond!
Starch
• Starch (amylose) is a polysaccharide found in
plants. It is the most common carbohydrate in
our diet…
• The enzyme amylase catalyses the breakdown
of starch in the mouth (salivary amylase) and
the small intestine (pancreatic amylase).
Make sure you remember the test for
starch… “It turns iodine blue/black”
Carbohydrate enzymes
Enzyme
Substrate
Location
Salivary amylase
Starch
Mouth
Pancreatic amylase
Starch
Small intestine
Sucrase
Sucrose
Small intestine
Maltase
maltose
Small intestine
Lactase
Lactose
Small intestine
Fructase
Fructose
Small intestine
Lactose intolerance
The heart warming tale of the little boy who had 8 teeth out in one sitting
because he didn’t have enough lactase in his small intestine…
Enzymes and the digestive system… 4Amino Acids
• The structure of an amino acid
• How are amino acids linked to form
polypeptides?
H
H
N
H
C
O
C
OH
R
Generic formula for any amino acid
Amino Acids
• The base unit of proteins.
• 20 naturally occurring molecules all have the
same basic structure but a different R group
• Of these 20, 9 are considered to be essential.
We cannot synthesise them in our diet.
• Amino acids form polypeptides as a result of
condensation reactions.
Protein Structure
• All proteins are made from the “pool” of 20
amino acids.
• Different proteins have different shapes
because they are made from different
combinations of amino acid.
• There are four “stages” of protein structure:
Primary, Secondary, Tertiary and Quarternary.
IMPORTANT!
Each protein has a precise and unique structure
that is determined by the amino acid sequence.
All molecules of a particular protein, such as
amylase, have the same amino acid sequence.
So the amino acid chain will always fold in the
same way. Therefore the protein molecule will
always have the same three dimensional shape.
Enzymes and the digestive system…5Secondary and tertiary Structure
• How are polypeptides arranged to form the
secondary structure and then the tertiary
structure of proteins?
A polypeptide chain…
• Despite their individual
chemical differences,
amino acids can be put
into four different
"families" depending on
whether their R-groups
are:
–
–
–
–
acidic
basic
polar - not charged
nonpolar
The alpha helix
Hydrogen Bond
Tertiary Structure
• Similar to 20 structure occurs when
neighbouring residues in the same chain form
bonds with one another.
• This time Disulphide bonds/bridges.
• Disulphide bonds form between Cysteine
residues.
A little diagram…
A
D
E
F
G
A
T
H
Y
V
Z
C
s
s
C
B
T
P
K
A
N
M
Denaturisation
• Each Protein functions between a specific
minimum and maximum temperature
• If the temperature exceeds the maximum limit
the intermolecular forces of attraction which
hold the molecule together break down.
• As a result the amino acid chain unwinds, the
molecule looses shape and therefore cannot
function
Another little diagram…
A protein
A denatured
protein
Quaternary Structure
• Occurs in proteins made up from more than
one polypeptide chain.
• Good examples include Insulin and
Haemoglobin.
• Bonding between the different chains is the
same as in tertiary proteins i.e. disulphide
bonds, H bonds and other intermolecular
forces
Further 40 structure adventures
• Quaternary structures have two basic shapes:
Fibrous or Globular.
• Globular proteins such as haemoglobin curl up
into ball like structures. They are very
important in the physiology of an organism.
• Fibrous proteins such a collagen form long
strands/chains. They are insoluble and are
important in structures such as joints, skin and
blood vessels
Enzymes and the digestive system… 6Enzymes
• How do enzymes speed up a chemical
reaction?
• How does the structure of an enzyme relate to
its function?
• The lock and key mechanism
• The induced fit model
Enzymes
• Enzymes are globular proteins.
• Enzymes are biological catalysts, they alter the
rate of a chemical reaction within an organism
without undergoing a permanent change.
IMPORTANT
Enzymes do not make a reaction happen and
they do not carry out a reaction. Rather, they
provide a surface for the reaction to take place
over, therefore increasing the rate.
Enzyme structure
• Enzymes have a very specific 3d shape.
• Shaping of an enzyme is the direct
consequence of a deliberately arranged amino
acid sequence during primary structure. (fig 2,
pg 31).
• The functional area of an enzyme is called the
active site.
The lock and key mechanism
• Learn the diagram, make sure you can label it
and explain it!
The induced fit model
• A progression of the lock and key theory.
• It currently provides a better explanation for
enzyme activity, such as how competitive
inhibition can occur
Enzymes and the digestive system… 7Factors effecting enzyme action
•
•
•
•
•
Measuring an enzymatic reaction
Temperature
pH
Substrate concentration
Inhibition.
Chapter 3
Cells and the movement in and out of
them
Cells and the movement in and out of them…
1 – Investigating the structure of cells.
• What is magnification and resolution?
• What is cell fractionation?
• How does ultracentrifugation work?
Magnification
• Cells are very small. Very small in fact. So so
small they are probably many times smaller
than the smallest thing you can imagine.
• In order to see and study them we must use a
microscope (obvious!), and YOU must
understand the principles of magnification.
Magnification again
• Cell dimensions are expressed in micrometres
(µm). Most cells range between 10-150µm.
• Micrometres are part of the Système International
(SI) derived units of measure.
• The SI units of length are…
Unit
Symbol
Relative size
Equivalent in
metres (using
maths)
Kilometre
Km
1000 metres
103
Metre
m
1000 millimetres
1
millimetre
mm
1000 micrometres
10-3
micrometre
µm
1000 nanometres
10-6
nanometres
nm
1000 picometres (pm)
10-9
Resolution
• The resolution or resolving power of a
microscope is the minimum distance apart
that two objects can be in order for them to
appear as separate items.
Cell Fractionation
• Cell fractionation is the technique used to
break up a cell so that a scientist may access
the organelles inside it.
• There are two stages to fractionation
– Homogenation
– Ultracentrifugation
Cells and movement in and out of
them… 2- Microscopy: Light v Electron
• Microscopy
• How do electron microscopes (EM) work?
• What are the differences between a
Transmission EM and a Scanning EM?
• What are the limitations of electron
microscopy?
The Light Microscope
• Light microscopes use convex lenses and a
beam of light which can be natural or artificial.
• However, because of the long wavelength of
light, a light microscope will only distinguish
between two object 0.2µm apart
Why use electrons?
• A “beam” of electrons has a much shorter
wavelength. It is able to distinguish between
objects only 0.1nm apart.
• There are two types of EM; Transition or
Scanning
Cells and the movement in and out of them… 3 – The
Eukaryotic Cell: Structure and function of the epithelial
cell
• Structure and function of the nucleus
• Structure and function of the mitochondria
• Structure and function of the rough endoplasmic
reticulum
• Structure and function of the Golgi
• Structure and function of the microvilli
• What does the ultrastructure of a cell tell us
about its function?
The Epithelial Cell
• Like all animal (and plant) epithelial cells are
eukaryotic cells.
• A eukaryotic cell is defined as one which has a
distinct membrane bound nucleus
• Epithelial cells secrete and absorb material.
They are found in the mouth, digestive
system, reproductive system and the
respiratory system.
Organelles
• Eukaryotic cells contain membrane bound
structures (in the cytoplasm). These structures
are called organelles
• Organelles carry out different roles within the
cell, e.g. protein synthesis
• Most eukaryotic cells contain the same
organelles yet some cells will contain more of
certain organelles depending on their role
Cells and movement in and out of
them… 4- Lipids and the Fluid Mosaic
Model
•
•
•
•
What is a lipid? Fatty acids and Triglycerides…
What is a phospholipid?
What is the role of lipids in biology?
What is the fluid mosaic model
• How can we identify the presence of a lipid?
Lipids
• In the human body lipids take 3 different
forms: fatty tissue, phospholipids (within the
cell membrane) and as steriods…
• Lipids have many roles within the human
body, mainly within membranes but also…
– An energy source
– Waterproofing
– Insulation
– Protection
Triglycerides
• Triglycerides are formed by a condensation
reaction between fatty acids and an alcohol
molecule called glycerol. Three fatty acids bind
to one molecule of glycerol.
• Fatty acids are linked to glycerol by ester
bonds
Phospholipids
• Phospholipids are very similar in structure to
triglycerides except that one fatty acid has
been replaced by a phosphate group.
The Fluid Mosaic Model
• First proposed in 1972…
• “A dynamic structure in which much of the protein
floats about, although some is anchored to
organelles within the cell. Lipid also moves about”.
• This model has been neither conclusively proven or
disproven, but it is the best model yet to explain the
known physical and chemical properties of the cell
membrane.
Cells and movement in and out of
them… 5- Diffusion
• What is diffusion and how does it occur?
• What affects the rate of diffusion?
• How does facillitated diffusion differ from
diffusion
What is diffusion
• Diffusion is the net movement of molecules or
ions from an area of high concentration to an
area of low concentration.
Make sure you understand this point!!...
Diffusion is a passive process. It does not require
ATP (energy) in order for it to occur. However, the
particles need to have energy in-order for them to
move about (their own Kinetic energy).
The rate of diffusion
• The factors that effect diffusion are…
– Concentration gradient
– The surface area
– Thickness of the exchange surface
• Diffusion can be described as
Surface area x Concentration Gradient
Length of diffusion pathway
Diffusion and the epithelial cell
• The properties of the epithelial cell and
squemous epithelia make them ideal for the
role at exchange surfaces…
– Large SA
– Short diffusion pathway
– Rich blood supply
– Moist environment
Facilitated diffusion
• Facilitated diffusion occurs through protein
channels at specific points along the plasma
membrane.
• Facilitated diffusion is an entirely passive
process. The vast majority of diffusion in
human biology through the plasma membrane
occurs this way…
Cells and movement in and out of
them… 6- Osmosis
• What is osmosis?
• What is water potential and how is it applied
to pure water?
• How does water potential affect osmosis?
A definition…
• Osmosis is…
“The passage of water from a region of
high water potential to a region of
lower water potential through a semi
(partially) permeable membrane”
Another definition…
• Water potential…
“The ability of water
molecules to move”
Putting it into practise
The water potential (ψ) of pure water at atmospheric pressure is zero. Water
molecules in solution move around more slowly than those in pure water
“(bonding folks!!)”. Since these molecules cannot move around as freely in
solution the water potential is negative. Solutions always have a water potential
that is less than zero; i.e. a negative water potential.
• Which way will the water move?
• Water molecules move to the region of lowest water
potential
Factors effecting water potential…
Solute potential ψs
• The concentration of solutes inside the cell is
called the solute potential. It is always a negative
value because solutes reduce the ability of water
to move freely
Pressure potential ψp
• The cell membrane (or wall) exerts a force on the
cell contents, in effect squeezing the contents of
the cell and trying to force water out. It is usually
a positive value
Water potential of a cell (ψ) = Solute potential (ψs) + Pressure potential (ψp)
Cells and movement in and out of
them… 7- Active transport / cotransport
• What is active transport?
• What is co-transport?
• How are the products of carbohydrate
breakdown absorbed in the small intestine?
Active Transport
• “the movement of molecules or
ions into or out of a cell from a
region of LOWER concentration
to a region of HIGHER
concentration using energy and
carrier molecules”
Against the gradient
• The cytoplasm of a cell usually holds reserves
of molecules needed for metabolism. The
reserves of useful molecules and ions do not
escape through the plasma membrane.
• However, when more of these useful
substances are available for uptake into the
cell, they will be readily absorbed by active
transport.
The role of ATP
• ATP is energy!
• Think of ATP as being like money. It is often
referred to as the energy currency.
• ATP binds to a receptor found inside the
carrier protein on the cell membrane
• ATP breaks down into ADP and an inorganic
phosphate molecule. This breakdown
“releases” energy and results in the channel
protein opening…
Co-transport
• A combination of active transport and
facilitated diffusion
• TEXTBOOK.
– Pg 64: Make sure you understand this diagram
and the sequential explination.
Symport Protein
• Symport proteins are carrier proteins located
intrinsically within plasma membranes…
• Symport proteins often transport two
different substances in opposite directions; in
and out of the cell. They only work when both
substances are present.
Protein structure folks… The binding of a molecule to a protein will result
in the protein changing its shape slightly, either hindering or helping
another molecule to bind to it
Cells and movement in and out of
them… 8- Cholera
• What causes cholera and what are the
symptoms?
Quick revision
Prokaryotic cells.
• Cholera is a bacterial disease, caused by the
bacteria; Vibrio cholerae.
• Bacteria are prokaryotic cells. How do they
differ from eukaryotic cells?
What is Cholera
• Cholera is a water born bacterial disease
which kills an estimated 120000 people each
year.
• The major symptom of cholera is extreme
diarrhoea.
• The majority of cholera cases occur on the
African continent.
• Why may 120000 be a very low estimate?
How does cholera cause disease?
• The flagellum is used in a corkscrew fashion to
anchor the bacteria to the cell membrane of
the epithelial intestinal wall
• The toxin produced by the bacteria binds to
receptors on the plasma membrane (blue bit)
and causes ion channels within the membrane
to open (red bit).
• Chloride ions flood into the lumen of the small
intestine, lowering its water potential
The diarrhoea part
• The increased Cl- concentration within the GI
lumen reduces its water potential. It is
HYPERTONIC to the inside of the cells.
• Water moves from the cells into the lumen.
• A concentration gradient is setup throughout
the surrounding tissues.
HIM
John Snow
Not him
Cholera outbreak in London 1854
• John Snow investigated Cholera in Soho, London in 1854
• He collected evidence to show where cholera victims
lived and where they got their water
• 73 of 83 victims lived closer to Broad Street pump than
any other pump
• 8 of remaining 10 had drunk water from Broad Street
pump
• Snow removed handle of Broad Street pump (to disable
it)
• The epidemic then ended
• John Snow collected data and presented his findings
• His investigations confirmed his hypothesis that cholera was
spread by contaminated water
• He persuaded people to accept his findings in order to
improve the health of many people
• 30 years later Robert Koch finally isolated cholera bacteria
Cells and movement in and out of
them… 9- ORT/S
• Oral Rehydration Therapy…
• Oral Rehydration solutions…
ORT
• Oral Rehydration Therapy is needed to replace
the fluids and solutes lost from the body
during diarrhoea.
• ORT using specialised solutions is a more
effective method of rehydration than water
alone.
• ORT makes use of Symport proteins and active
transport mechanisms within the SI
ORS uses
co-transport
Oral rehydration solution (ORS)
• ORS is simple and cheap
• It is a solution of sugars and salts taken
orally
• It is used as a treatment for diarrhoeal
diseases e.g. cholera
• It’s saved 50 million lives in 25 years
• Preferable to intravenous rehydration
which is difficult to administer and could
cause fluid overload and death
• New ORS formulations are being trialled
which are more effective
• Added zinc reduces severity and duration
of diarrhoea and has a protective
function
Making a better oral rehydration solution
• A better ORS may provide nutrients that developing child
needs
• ORS based on rice-flour help children overcome malnutrition
(high in starch)
• At high concentrations rice-flour ORS too thick
• Scientists can measure viscosity using a viscometer
• Viscosity is measured in centipose (cp)
• Below 1000 cp a solution flows like water
• Between 10 000 and 30 000 cp soup-like flow
• Above 35 000 cp will not flow out of a cup
Viscosity
• In everyday terms (and for fluids only),
viscosity is "thickness."
• Thus, water is "thin," having a lower viscosity,
while honey is "thick" having a higher
viscosity.
• Viscosity describes a fluid's internal resistance
to flow and may be thought of as a measure of
fluid friction.
An experiment to investigate the effect of different concentrations of
amylase in reducing the viscosity of flour solutions
• Make up amylase solutions
– 0%. 20%. 40%. 50%. 60%. 70%. 80%. 100%
• Place range of amylase solutions into water bath at 20oc
• Add 5ml of amylase solution to 10ml flour solution: water
bath 5 min
• Add suitable amount of this solution into viscometer (2/3 ml)
• Measure the viscosity of the rice-flour using viscometer
• Calculate the mean viscosity for each amylase concentration
• Repeat for each concentration of amylase.
Questions on the experiment
• What was the independent variable?
• What was the dependent variable?
• List the other variables that might influence the results.
Describe how these confounding variables should be kept
constant.
• Suggest a suitable control
• How can you make the results more reliable?
• What affects the precision of the results?
• What should be done with any anomalous results?
Chapter 4
Lungs and Lung Disease
Chapter 5
The heart and heart disease
The Cardiac Cycle.
Systole:
• Systole is the term given to the contraction of
cardiac muscle.
• Atrial systole occurs when the atria contract
and force blood into the ventricles.
• Ventricular systole occurs when the ventricles
contract and force blood out of the heart
through the arteries
Cardiac Cycle
• Diastole
• Diastole is the term given to cardiac muscle
which is relaxed
• During ventricular diastole the ventricles are
in a relaxed state and fill with blood.
Chapter 6
Immunity
Immunity… 1- A Brief look at bacterial
disease
• The ability of a bacteria to cause disease is
known as it’s pathogenicity
• Factors that effect pathogenicity include…
– Methods of attatchment
– Toxin release
– Infectivity
– Invasiveness
When does a colony of bacteria cause
disease?
• When bacteria get into a body area that is
usually sterile
• Most bacteria are often found in our own
“body flora”
• Bacteria often reach sterile internal areas
through small wounds and skin abrasions
– E.g. Clostridium Tetani
Invasion and Colonisation
• Bacteria attach to and penetrate cells. They may also
break into blood and lymph vessils.
• Pili and Fimbriaie allow bacteria to attatch to
membrane receptors
– E.g. Neisseria Gonorrhoea
– Attaches to manose receptors
– Causes painthful blocking and swelling or urethra and
prostate in males, attacks overies in females
Release of Toxins
• Bacteria release toxins to break down and
disable cells
• There are two types of toxin
– Exotoxins
– Endotoxins
Unit 2
The variety of Living Organisms
Chapter 7
Variation
Chapter 8
DNA and Meiosis
DNA and Meiosis… 1- DNA
• The structure of DNA…
• The function of DNA and the triplet code…
The Double Helix
• DNA is a polynucleotide molecule comprised of
repeating units of Phosphate, Deoxyribose sugar and
an organic base.
• The polynucleotide is arranged into a double helix
structure…
• The Double Helix was elucidated by James Watson
and Francis Crick at Cambridge University in 1953.
They based their hypothesis on x ray evidence
produced by the pioneering female scientist Rosalind
Franklin. Watson and Crick won Nobel prizes for their
work.
The Nucleotide…
• The individual nucleotide is made up…
Phosphate
Base
Sugar
• A Phosphate group.
• A pentose sugar: Deoxyribose.
• An organic base (Adenine, Cytosine, Guanine and
Thymine).
Base Pairing
•
Textbook: Chapter 8, pg 131.
The Triplet Code
• DNA base sequences code for amino acids,
which can be assembled to manufacture a
protein.
• A sequence of three bases codes for one
specific amino acid.
• Pg 136-137
DNA and Meiosis… 2- Genes
• What is a gene?
• How are genes arranged on DNA?
• Alleles…
A Gene
• A sequence of DNA which codes (usually) for a
specific protein or polypeptide.
• An individual gene may have more than one
form, these will differ very slightly from the
others in their nucleotide sequence.
• The different forms of a gene are called
alleles.
DNA and Meiosis… 3- Chromosomes
• What is a chromosome?
• Homologous chromosomes…
Chapter 9
Genetic Diversity
Genetic Diversity… 1- Diversity
• Why are organisms different from one
another?
• What factors influence genetic diversity?
• Selective breeding?
Key principles…
• The greater the number of different alleles of a gene
within a species the greater the genetic diversity of
the species…
• The greater the diversity the wider the total range of
characteristics across a species…
• A species has a greater probability of adapting to a
change in it’s environment if it has a wide spread of
characteristics…
Environmental Change
•
5 events that may result in an environmental
change…
1.
2.
3.
4.
5.
Volcanic Eruption
Flooding
Drought
Disease
Hunting
Genetic Bottlenecks
• The Cheetah population shows very little
genetic diversity. It is thought to have
undergone several genetic bottlenecks.
Describe a genetic bottleneck and explain how
it may result in a population with very similar
physical characteristics?
• 6 Marks
Answer…
1.
2.
3.
4.
5.
6.
Chance event significantly reduces number within a population
Surviving individuals have fewer alleles
Less diversity
Recovering population can only contain these alleles
Less variety in genotypes of “new” population
Less variety in phenotypes / physical characteristics
A model answer…
“A genetic bottleneck occurs when a chance event, such as major
flooding, significantly reduces the number of organisms within the
population of a particular species. Surviving members of the population
have a reduced number of alleles amongst them and are therefore less
genetically diverse than before. Subsequent generations of organisms
from within this population can only contain the surviving alleles;
consequently there will be less variety in the genotypes of these
organisms and therefore less variety in the overall phenotype exhibited
by members of this population”
Artificial Selection: Cultivating Characteristics for our benefit…
Wheat
•
•
•
Wheat grows in dry sunny conditions, producing
grains on the end of a flowering stem called a rachis.
Within each grain is an embryonic plant with a “food
source”. Wheat grains are rich in carbohydrate and
protein
Modern wheat differs from ancestral wild wheat in
three ways:
1. Strength of rachis
2. Size of grain
3. Chromosome number
Selective Cultivation of wheat
•
Wheat growers use very intensive methods
to produce high yields of wheat grain. They
selectively cultivate wheat using four
characteristics…
1.
2.
3.
4.
Short stems
Standing Power
Resistance to shedding
Resistance to fungi
Suggest how each these four characteristics increase the yield
of wheat…
Why select for…
Short stems…
•
•
Less energy is used by the plant for stalk growth,
making more available to the grain.
A larger grain contains a greater amount of
carbohydrate and protein
Why select for…
Standing Power…
• Weak stalks are prone to collapse under the
weight of the grain, especially during bad
weather.
• More grain will be collected from stalks that
remain upright, allowing more to be sold and a
greater profit to be made.
Why select for…
Resistance to shedding…
• Grain is very lightweight and easily shed by strong
winds and animal activity.
• Less grain is lost before and during the harvest.
Why select for…
Resistance to fungi…
• Wheat leaves are prone to fungal conditions such as
mildew.
• Maintaining healthy leaves promotes more efficient
photosynthesis and healthy plant growth.
Exam Questions…
b) EXPLAIN why the DIVERSITY of animals is HIGHER natural
woodland THAN in conifer plantations.
• More light reaches the ground therefore more plants
have the opportunity for photosynthesis.
• There are a greater number of producers, increasing
the size of the food web.
• More plants provide more habitats, such as nesting
sites for animals
in
c) …EXPLAIN how a programme of selection MIGHT affect the
VARIETY OF ALLELES in a population.
• Selection reduces the variety of alleles
because only certain characteristics are
allowed to continue.
• Non selected alleles will reduce in frequency,
selected alleles will increase.
Think bottleneck !
Cattle
• What products do we get from cattle?
Chapter 10
The variety of life
The Variety of Life… 1- Haemoglobin
• Haemoglobin structure…
• Loading and unloading oxygen…
• Oxygen dissociation curves…
Haemoglobin
Human blood cell haemoglobin consists of:
• 4 polypeptide chains or globins (2 alpha and 2 beta).
• 4 iron-containing molecules (haem), one for each chain.
• Each haem group contains one iron (Fe) atom in the middle of
the molecule
• Each iron atom is joined to 1 end of their respective globin –
• Each iron atom bonds with one oxygen molecule
• Hence, one haemoglobin is able to carry a maximum of 4
oxygen molecules
Haemoglobin that combines with an oxygen
molecule is called oxyhaemoglobin.
Normal haemoglobin (with no oxygen
molecule attached) is actually purplish red
in colour. It only turns bright red (the colour
that we see when we bleed) when it
combines with an oxygen molecule.
The variety of life… 2Oxyhaemoglobin Dissociation Curves
• What are oxyhaemoglobin dissociation curves
• What is the Bohr effect
• Using an oxyhaemoglobin dissociation curve
Approx concentration of
O2 in alveoli
Approx concentration of O2
in normally respiring tissue
1kNm-2 = 1kPa
A Definition
• A graph showing the amount of oxygen
carried by haemoglobin in the blood plotted
against the concentration of oxygen present.
Important points to remember…
• The partial pressure of oxygen in a healthy
lung is approximately 13kPa.
• At this concentration Hb is approximately 95%
saturated.
• The partial pressure of oxygen in a normally
respiring tissue is approximately 5kPa
The Bohr shift
• The effect of increasing CO2 concentration on
an Oxyhaemoglobin dissociation curve.
• The greater the amount of CO2 the further the
curve shifts to the right
• In the presence of CO2, Hb gives up a greater
amount of the oxygen it is carrying.
Percentage saturation of Hb
has decreased. It has given
up more oxygen