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Edexcel Biology
SB5 + SB6
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Cards (165)
Viruses are not
cells
; they are a
protein
coat around a strand of genetic material.
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Viruses need to
infect
a living cell (host) to
reproduce.
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Specific viruses will only affect specific
cells.
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Virus Lifecycle
1.
Infects
new host cell
2. Reproduces by
lytic
pathway
3. Reproduces by
lysogenic
pathway
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Lytic pathway
1.
Virus
attaches to specific
cell
2. Injects
genetic
material
3. Uses
host proteins
and
enzymes
4. Assembles
viral
components
5. Host cell
splits
and
releases
new viruses
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Lysogenic pathway
1. Injected genetic material incorporated into host genome
2. Viral genetic material
replicated
with host DNA
3. Virus remains
dormant
4. Trigger causes viral material to enter
lytic
pathway
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STI’s are spread through
sexual contact.
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STI examples
Chlamydia
HIV
/
AIDS
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Chlamydia
A kind of
bacterium
but behaves like a
virus
because it can only reproduce inside host cells
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Chlamydia
doesn’t cause symptoms but can result in
infertility.
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The spread of Chlamydia can be reduced by wearing a
condom
or being treated for the
infection.
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HIV
Human
immunodeficiency
virus
kills white blood cells
important in immune response
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HIV eventually leads to
AIDS
(
Acquired immune deficiency syndrome
).
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The infected person’s
immune system deteriorates
and eventually fails, making them vulnerable to infections by other
pathogens.
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HIV
is spread by
infected bodily fluids.
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One of the main ways to prevent the spread of HIV is to use a
condom.
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Drug users should avoid sharing
needles
to reduce the spread of
HIV.
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Plants have
physical
defences against
pathogens
and pests.
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Waxy cuticle
Provides a barrier stopping pathogens entering or
damaging
leaves and stems
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Waxy
cuticle may also stop
water
collecting on the leaf, reducing the risk of infection from pathogens transferred between plants and water.
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Plant cells are surrounded by cell walls made from
cellulose
, forming a physical barrier against
pathogens.
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Chemical defences in plants
Produce chemicals called
“antiseptics”
which kill bacteria and fungal pathogens<|>Produce chemicals to stop pests feeding on their
leaves
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Some
plant
chemicals are used as
drugs
by humans.
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Plant-derived
drugs
Quinine
Aspirin
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Quinine
Comes from
bark
and is used to treat
malaria
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Aspirin
Found in bark and leaves of
willow
trees and is used to treat pain and
fever
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Plant
pathologists
recognise symptoms of
diseases
in the field, such as abnormal growth or yellow leaves.
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Pathogens
spread in different ways, allowing
pathologists
to analyse the distribution of diseased plants to identify the kind of pathogen involved.
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Lab testing will give accurate identification of the
pathogens.
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Antigens
Unique
molecules
on the surface of
pathogens
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Antigens from a particular
pathogen
will be present in an
infected
plant and can be detected using a sample of tissue.
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The detection of an
antigen
allows that
pathogen
to be identified and the disease diagnosed.
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If a plant is infected with a pathogen, the pathogen’s
DNA
will be in the plant's
tissues.
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Scientists detect
pathogen DNA
using techniques on the smallest amount of
pathogen DNA
from the tissue.
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Physical and chemical barriers stop
pathogens
entering the human body.
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Physical barriers
The skin acts as a barrier to pathogens<|>Hairs and
mucus
in the nose trap particles<|>Cells in trachea and bronchi produce
mucus
and have cilia
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If the skin gets damaged, the
blood clots
quickly sealing any cuts to keep
micro-organisms
out.
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Stomach
acid kills most
pathogens
that are swallowed.
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The eyes produce
lysozyme
(in tears) which kills
bacteria
on the surface of the eye.
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If a
pathogen
makes it into your body, your immune system kicks in to
destroy
them.
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