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(a) The different types of pathogen that can cause communicable diseases in plants and
animals
To include:



Bacteria – tuberculosis (TB), bacterial meningitis, ring rot (potatoes, tomatoes)
Virus – HIV/AIDS (human), influenza (animals), Tobacco Mosaic Virus (plants)

(b) The means of transmission of animal and plant communicable pathogens
To included direct and indirect transmission, reference to vectors, spores and living conditions –
e
...
climate, social factors (no detail of the symptoms of specific diseases is required)
Pathogens are microorganisms that cause disease
...

Name of disease

Organism that causes disease

Means of transmission

Athlete’s foot (in humans)

Fungus

Direct contact with spores on the
skin surface or on other surfaces

Bacterial meningitis

Bacteria

Direct contact with saliva

Black sigatoka (in bananas)

Fungus

Indirect transmission through
spores spread by the wind

Blight (in potatoes and tomatoes)

Fungus- like organism

Direct contact t between infected
and uninfected seed potatoes: also
indirect by spores in the wind

HIV/AIDS

Virus

Direct transmission from an
infected person by blood to blood
contact; infected needles being
shared or re4usedr; infected and
unsterilized surgical instruments;
accidental needle stick; in semen or
vaginal fluid during unprotected
sexual intercourse; from mother to
baby during birth/ breast-feeding

Influenza

Virus: from family
orthomyxoviridae – flu viruses

Indirect transmission by droplet
infection

Malaria

Protoctistan: plasmodium

Indirect transmission via a vector
(an organism that carries the
pathogen from one host to
another)
...

These organisms usually cause harm by entering host cells and
feeding on the contents as the grow
...


(c) Plant defences against pathogens
To include production of chemicals AND plant responses that limit the spread of the pathogen
(e
...
callose deposition)
Plant defences can be divided into physical and chemical
Physical defences
Cellulose cell walls, lignin thickening of cell walls, waxy cuticles and bark all help to prevent entry of
a pathogen
...

Callose is deposited around the sieve plates in older sieve tubes and blocks flow
...
When pathogens attack, specific chemicals in their cell walls can be detected by
the plant cells
...
The plant responds by
stimulating the defences already present
...
Active defences (to prevent pathogens spreading through the entire
plant) include the following:
1) The stomata close to prevent entry to the leaves
2) Cell walls are thickened with additional cellulose
3) Callose is deposited between the plant cell wall and cell membrane near the invading
pathogen
...

4) Necrosis – cells surrounding the infection are killed to reduced access to water and
nutrients
...
These
enzymes kill damaged cells and produced brown spots on the leaves,
5) Canker – necrosis of woody tissue in the main stem or branch
...
However, other
chemicals can be released when a pathogen is detected
...
g
...
g
...
Tannins
inhibit insect attack by interfering with their digestion
3) Alkaloids (e
...
caffeine, nicotine, cocaine and morphine) – give a bitter taste to inhibit
herbivores feeding
...
These include chitinases, which
break down the chitin in fungal cell walls; glucanases, which hydrolyse the glycosidic bonds
in glucans of bacterial walls; and lysosomes, which degrade bacterial cell walls
...
It provides a barrier to
the entry of microorganisms
Blood clothing and skin repair
Damage to the skin opens the body to infection
...
Blood-clotting involves calcium ions and at
least 12 other clotting factors that are released by platelets or from the damaged tissue
...
The clot dries out to form a
scab
...
Fibrous collagen is
deposited under the scan and stem cells in the epidermis divide to form new cells
...


Inflammation
Inflammation is the swelling and redness seen in infected tissues
...
This is caused by a cell-signalling substance called histamine, Histamine is released from
mast cells and it has a range of effects that act to help combat the infection
...
More plasma
enters the tissue fluid, causing oedema (Swelling)
...

Mucous membranes
Any areas where the skin is incomplete are protected by mucous membranes
...
The mucus traps any pathogens, immobilising them
...
Cilia are tiny, hair-like organelles that can move in a coordinated fashion to
waft the layer of mucus along
...
They respond to the presence of microorganisms or
the toxins they release
...
g
...
In a
cough or sneeze, the sudden expulsion of air carries with it the microorganism causing the irritation
...

Neutrophils are cells that contain a lobed nucleus and dense cytoplasm that contains many
lysosomes and mitochondria
...

Non-self cells are recognised because they have proteins on their cell-surface membranes called
antigens
...

Phagocytosis follows a particular sequence:
1)
2)
3)
4)
5)

The bacteria are engulfed by the neutrophil
They are surrounded by a vacuole called a phagosome
Lysosomes fuse to the phagosome
Lytic enzymes are released into the phagosome
The bacteria are hydrolysed (digested) and the nutrients can be reabsorbed into the cell

Antigen presentation
Some phagocytes (macrophages) can engulf the pathogen and process it so that the antigen is kept
whole
...

This is known as antigen presentation
...


(ii) The examination and drawing g of cells observed in blood smears

(f) The structure, different roles and models of action of B and T lymphocytes in the specific
immune response
To include the significance of cell signalling (reference to in terleukins), clonal selection and clonal
expansion, plasma cells, T helper cells, T killer cells and T regulator cells
...
They have specific receptors on their cell-surface membranes
...

The specific response is more complex than the non-specific response and involved a series of
stages:
1) Antigen presentation
2) Clonal selection
...
Normally, there is a B lymphocyte, a T helper lymphocyte and
a T killer lymphocyte
...
They are selected and
activated by coming into contact with the specific foreign antigen
...
The action of macrophages makes this select
ion more likely
...
There will normally be a clone of B lymphocytes, a clone of T helper
lymphocytes and a clone of T killer lymphocytes
...
The plasma cells are short-lived
...

4) Differentiation – cells from the T helper lymphocyte clone will differentiate into T helper
cells and memory cells
...

cytokines and interleukins that help to stimulate the B lymphocytes and the macrophages
...
If the same pathogen invades again, it will be recognised
and attacked more quickly
...
T regulator cells have a role in closing down the
immune response once the pathogen has been removed
...
This takes a few days as
the specific B and T lymphocytes must be selected, the cells must divide and then differentiate and
the antibodies must be manufactured
...

Secondary responses
On any subsequent invasion by the same pathogen with identical antigens on its surface, the
immune response is a secondary response
...
This is because the blood carries many memory
cells that are specific to this pathogen
...
The response is quick enough to prevent the pathogen taking hold and
causing symptoms of illness
...
Most antibodies are similar in structure and possess the same
basic components
...

On one end of an antibody is known as the constant region
...
It may help bin ding of phagocytes
...
This has binding sites that are specific to a particular antigen
...
The antibody molecule
also has a hinge region that allows some flexibility to enhance binding to more than 1 pathogen
...
This
prevents them from entering cells and reproducing
...
These
can be used to bind to a number of pathogens
...

(j) The differences between active and passive immunity, and between natural and artificial
immunity
To include examples of each type of immunity
Active immunity is acquired through activation of the immune system
...
The memory cells remain
in the blood for a long time, providing long lasting immunity
...
Antibodies may be injected straight into the
blood or acquired from a mother’s milk
...
No memory cells are made, so the immunity
is not permanent
...
Natural active immunity may be the
result of catching a flu virus from someone who sneezes
...
This makes the baby immune to diseases that the
mother is immune to
...

Artificial immunity is acquired by human intervention
...
A person is injected with a weakened pathogen with antigens, and this activates
their immune system (e
...
immunity to TB or influenza)

(k) Autoimmune disease
To include an appreciation of the term autoimmune disease and a named example e
...
arthritis,
lupus
An autoimmune disease is one in which the immune system attacks the body’s own healthy cells and
tissues
...
In an autoimmune disease, the lymphocytes do not distinguish between these ‘foreign’
antigens and your own
...

This attack may be due to the exposure of antigens that are not normally exposed, such as certain
molecules usually found only in the nucleus
...
It
also seems that certain people are more genetically prone to autoimmune disease
...

(l) The principles of vaccination and the role of vaccination programmes in the prevention of
epidemics
To include routine vaccinations AND reasons for changes to vaccines and vaccination programmes
(including global issues)
...
Antigenic material can be:






Whole live microorganisms (this is more effective than using dead ones as the live organisms
can reproduced and mimic an infection better)
Dead microorganisms
Attenuated (weakened) organisms
A surface preparation of antigens
A toxoid (a harmless form of a toxin)

Herd and ring vaccination
In order to be effective, vaccinations need to be used appropriately
...
This prevents the pathogen being
transmitted from person to person
...
All the people in
the area surrounding the outbreak are vaccinated in order to prevent transmission and to isolate the
outbreak in one area
...
Microorganisms and plants
produce a wide range of molecules that may be of benefit in fighting disease
...
We just need to find them
...
It is therefore important that we try to maintain biodiversity and conserve as many
species as possible, just in case the molecules they are capable of producing may prove to be useful
...
As sequencing technology and molecular modelling techniques
improve, it may be possible to sequence the DNA of an individual to asses a specific genetic disorder
and develop a treatment personalised to the individual, such as an individualised combination of
drugs
...
In the future, it may even become possible to design a
drug that is specific to the needs of one individual
...
Synthetic biology is the development
of new molecules or systems
...
For example, bacteria are being genetically modified for
use as biosensors
...

(n) The benefits and risks of using antibiotics to manage bacterial infection
To include the wide use of antibiotics following the discovery of penicillin in the mid-20th century
AND the increase in bacterial resistance to antibiotics (Examples to include Clostridium difficile
and MRSA) and its implications
...
Since then, may
different antibiotics have been discovered and used widely to treat bacterial infections
...
However, their misuse has enabled microorganisms to develop resistance
...

(a) How biodiversity may be considered at different levels
To include habitat biodiversity (e
...
sand dunes, woodland, meadows, streams), species
biodiversity (species richness and species evenness) and genetic biodiversity (e
...
different breeds
within a species)
...
It includes all the different plant, animal, fungus and microorganism
species in the world, the genes they contain and the ecosystems of which they form a part
...
e
...
g
...
It is assumed that the sample plots are representative of the
entire habitat
...

Techniques
There are 2 main techniques for sampling: random and non-random
...
It can be achieved by using a computer to generate random numbers,
which are then used as coordinated to locate sample areas on a imaginary grid placed over the
habitat
...
It is important to measure both the number of species (species
richness) and the number of individuals in each species (species evenness)
...
Smaller plants can be sampled using quadrats
...
A quantitative sample can be achieved by measuring the
percentage cover of each species within the quadrat
...


Animals
Large animals can be sampled by careful observation and counting
...

Small mammals can be trapped using a humane trap such as a Longworth trap
...
This involves 2 separate trapping
sessions
...
If the
number of animals trapped in the first session is T1, the number caught in the second session is T2
and the number caught in the second session that are already marked is T3, the total population can
be given by the formula:
Number in population = T1 x T2/T3
Ground-living invertebrates can be collected using a pitfall trap, whereas invertebrates in leaf litter
can be collected using a Tullgren funnel
...
Invertebrates in grass
and shrubs can be collected by sweep netting, and pond life can be sampled by netting
...
However, a habitat that
is dominated by just one species with only one or two individuals of each of the other species would
not be considered to be biologically diverse
...
This is known as species evenness
...
A diverse habitat would contain a large number of species, all of them
represented by a sizeable population rather than by just one or two individuals
...

Where n = the total number of
individuals in a particular species
and N = the total number of
individuals in all species

Simpsons Index of Diversity measures the biodiversity of a habitat
...
The resultant value always rages between
0 and 1
...

Proportion of polymorphic gene loci = number of polymorphic gene loci / total number of loci
Suitable populations include zoos (captive breeding), rare breeds and pedigree animals
The genetic diversity of a population may be important to conservationist wishing to maintain the
health of a captive population in a zoo or rare-breed centre
...
Genetic diversity is increased when there is more than one gene variant (allele) for a
particular locus
...
A measure of genetic
diversity is given by the formula above
...
The main factors
that affect biodiversity include:
1) The rapid human population growth, which means that more space and resources are taken
up to supply living space and food
2) The increasing use of agriculture (monoculture) as an efficient way to produce food and
other products
...
This is particularly true where keystone species are involved
...
All those species would be lost if beavers were not present
...
The ecological reasons for
maintaining the correct functioning of ecosystems include:








Fixing of energy from sunlight
Regulation of the oxygen and carbon dioxide levels in the atmosphere
Fresh water purification and retention
Soil information
Maintenance of soil fertility
Mineral recycling
Waste detoxification and recycling
Economic reasons

Economic reasons for conserving species include:






Growth of food and timber relies on the correct functioning of ecosystems
...
If an ecosystem is disrupted, the effects may
be far-reaching
...

This is particularly obvious where monoculture is used constantly
...

Natural predators to pests reduce the need for pesticides
...

Aesthetic reasons

Aesthetic reasons for maintaining biodiversity are important:




Everyone enjoys nature or its benefits in one way ro another
...

The loss of habitat and a number of endangered species is a worldwide problem; therefore
international cooperation is needed to conserve the species under threat
...

This includes looking after wildlife habitats, retaining the traditional character of the land
and protecting historic features and natural resources
It applies to land that is not considered to be an environmentally sensitive area
...


Biologists use biological classification of species to place living things into groups to make them
easier to study
...
The taxonomic hierarchy is shown below
...
The first
name is the name of the genus to which the species belongs and the second name is the specific or
species name
...
Both of the Latin names should always be written with an upper case first letter,
whereas the species should be in lower case
...

The binomial system is recognised worldwide
...
He used
the organisms’ observable features and grouped them according to the number of similarities
present
...
They then decide if any differences are simple a variation within the species or significant
enough to classify the organism as a different species
...
This evidence from biological molecules provides a genetic and biochemical comparison,
which is thought to be more accurate than comparing observable features
...
As changes in the DNA sequence are caused by
mutation and mutations are random, it is assumed that more mutations means a longer time has
been elapsed since the species became separate
...

As the DNA sequencing is used to produce proteins, it is equally valid for studying amino acid
sequences in proteins
...

The best proteins are those that occur in all living things, such as proteins associated with respiration
and protein synthesis
...

Once the taxonomic groups are constructed on the basis of genetic similarities, they will
automatically reveal the evolutionary relationships between organisms (phylogeny)
...
However,
recent research has revealed that this hierarchy may not be accurate
...

One kingdom, the Prokaryotae, consists of a wide diversity of prokaryotic organisms
...
This led to the idea that the
kingdom should be divided into 2 major groups or domains: bacteria and archaea
...
The archaea are still prokaryotic, but they are
more similar to eukaryotes
...

(d) The relationship between classification and phylogeny
Natural classification systems group living things according to their similarities
...
Phylogeny is the
evolutionary history or the evolutionary relationships between organisms and groups of organisms
...
Phylogeny can be represented in an
evolutionary tree such as Darwin’s tree of life
...

At the same time that Darwin was piecing his theory of evolution together; another scientist was
doing the same thing
...

Evidence for evolution
There are many lines of evidence for the theory of evolution
...

Fossil evidence
Darwin used a lot of evidence from fossils to back up his theory of natural selection
...
They are formed when an organism leaves an imprint in soft
mud or dies and comes to rest in the mud
...
Fossils formed relatively recently are near the surface of modern rocks, whereas
those formed many millions of years ago are found further below the surface
...

Similarities between fossils can be used to reveal evolutionary relationships (phylogeny)
...
Variation is
caused by changes (mutations) in the DNA, which produced changes in proteins
...
Therefore, closely related species have similar DNA and proteins, but more
distantly related species have DNA and proteins that are more different
...
This reveals their evolutionary relationships in the same way that similarities in
anatomy and morphology reveal evolutionary relationships
...

(f) The different types of variation
To include intraspecific and interspecific variation AND the differences between continuous and
discontinuous variation, using examples of a range of characteristics found in plants, animals and
microorganisms AND both genetic and environmental causes of variation
...

Variation is the differences that arise between living organisms
...
These differences could be:




Simple observable features such as colour
Biochemical differences such as the precise sequence of amino acids in a protein
Behavioural differences such as the type of food eaten

These differences are usually relatively minor, but they can be more obvious such as the differences
between sexes
...
This
depends on how closely related one species is to the other:



If the species are closely related, such as the lion and the tiger, the differences may not be
great
If the species are not closely related, the differences will be greater

Remember that variation is the key to evolution – variation must occur before any characteristic can
become beneficial and selected for
...
There is a full range
between two extremes
...
The continuously variable feature
can be quantified and data are usually presented in the form of a histogram
...
This type of variation is usually caused by one gene (or possibly a small number of
genes)
...
Examples of discontinuous variation include gender and
possession of resistance or immunity
...
Many variable features may be affected
by both causes
...
However, exposure to
the sun results in the production of extra pigmentation, causing skin to tan
...
They are
caused by mutation that arise spontaneously and randomly, and are passed n from one generation
to the next
...
Examples include:




Number of limbs
Eye colour
Ability to roll the tongue

Environmental causes
Environmental causes of variation are caused by variations in exposure to vertain environmental
conditions
...
Examples include:



Skin colour resulting from exposure to sunlight
Body mass

(g) The difference types of adaptations of organisms to their environment
Anatomical, physiological and behavioural adaptations AND why organisms from different
taxonomic groups may show similar anatomical features, including the marsupial mole and
placental mole

All members of a species possess similar adaptations, which enable the species to survive and thrive
in their environments
...

Anatomical adaptations
Anatomical adaptations are those that are associated with structure:





Predators have sharp teeth to help kill and chew their prey
...
This allows them to digest plant
tissues, which are much more difficult to digest than animal tissues
Plants have long, deep roots with many root hairs
...
This allows the roots to gain oxygen from the air above the anaerobic soil

Physiological adaptations
Physiological adaptations are those that are associated with how the body systems function:







Fish pass water over their gills in one direction, as opposed to mammals which have a tidal
flow of air into their lungs
...

The kidneys of mammals extract water from the urine before excreting nitrogenous waste
...

Some plants, called C4 plants, use an unusual way of collecting carbon dioxide at night
...

Yeast respires anaerobically when there is no oxygen in their habitat
...


Behavioural adaptations
Behavioural adaptations are those that are associated with feeding, nesting and mating:



Robins usually choose a nest site in a hole in a tree stump or wall a few inches above the
ground
...

In dry conditions, some plants open their stomata to make the leaves wilt
...


Convergent evolution
In some cases, organisms from different taxonomic groups become adapted to the same habitat by
adopting similar anatomical features
...
They have independently evolved similar
traits as a result of having to adapt to similar environments or ecological niches
...
Some variations are better adapted to survive than others, passing on their alleles to the
next generation in greater numbers
...

(i) How evolution in some species has implications for human populations
To include the evolution of pesticide resistance in insects and drug resistance in microorganisms
The implications of evolution for humans
Modern examples of evolution include pesticide resistance in insects and drug resistance in
microorganisms
Pesticide resistance in insects
When pesticides are used, they kill all susceptible insects
...
These few individuals may survive and breed to pass on their
resistance to following generations
...
As successive
generations show some variation, it is possible for the insects to become increasingly resistant to
higher and higher concentrations of the pesticide
...

Drug resistance in microorganisms
Most bacteria are susceptible to antibiotics, but some microorganisms may show drug resistance
...
The
implications are that there are only a certain number of antibiotics and, once bacteria have evolved
resistance to them all, we will have no further defences to help us combat disease

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