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Threat from Diseases and Changing Life
Expectancy
In the 1840s in England and Wales, the median age of death was 83. Several factors
have contributed to changes in life expectancy since then:
Hygiene: Keeping drinking water separate from sewage, which contains
pathogens (microorganisms that cause diseases like cholera and typhoid), is
crucial.
Diet: Improved nutrition strengthens people's ability to fight diseases.
Immunization: Protects against specific diseases, exemplified by the near-
eradication of polio through international immunization programs.
The image below shows individuals with prosthetic legs playing a game, which
demonstrates the impact of diseases like polio and the importance of immunization
programs.
This diagram shows the architecture of an ancient sewage system, which
underscores the importance of hygiene in preventing the spread of pathogens.
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20th-century advances: Introduction of antibiotics has significantly aided
recovery from bacterial diseases.
Today, the main causes of death in developed countries are often diseases caused by
internal bodily changes rather than infections.
Command Words in Answering Questions
Test and exam papers use command words to guide responses. Here's a breakdown:
Command Word What's Needed in the Answer
Name, Give, State Facts, answered in a word or a few words.
Describe Clear and logical sentences to present facts.
Compare,
Similarities and differences between two or more things.
Distinguish
Explain Reasons linked to facts/processes/changes.
Evaluate Evidence for and against, with a conclusion.
Draw, Sketch,
A diagram, chart, or added labels.
Label
Calculate,
Maths-type questions. Show your working.
Estimate
Plot, Find Interpretation of graphs or charts.
Complete, Fill in Missing words or parts of text/diagram.
Use information from a given text or image to answer with one of
Use information...
the above commands.
When answering, pay attention to the command word and the marks allocated to
each question.
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Types of Diseases
Type of Disease Example Cause
Microbe (bacterium, protoctist, virus)
Infectious/Communicable Polio, influenza
enters the body, altering its function.
Anemia, Lack of essential nutrients for healthy
Deficiency
kwashiorkor growth.
Sickle cell
Genetic/Inherited DNA fault changing cell function.
disease
Factors like smoking, unhealthy eating, or
Lifestyle Lung cancer
lack of exercise.
The body's immune system attacks and
Autoimmune Type 1 diabetes
damages its own cells.
The image above shows a man sneezing and expelling droplets. Diseases caused by
pathogens are considered communicable because they can be passed from person to
person. Non-communicable diseases cannot be transmitted between individuals.
Symptoms of infectious diseases can include a raised temperature and/or a rash.
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The image above shows a child with a thermometer in their mouth, possibly
indicating a fever or other symptom of an infectious disease.
Viruses and Disease
Viruses, too small to be seen with a light microscope, cause diseases like chickenpox
and measles. They can infect various organisms.
Viruses consist of a protein coat protecting genetic material but lack other structures
found in living cells, leading some scientists to argue they aren't true organisms.
Viruses infect cells, hijack their genetic material, and produce more viruses, damaging
the cells in the process.
Control Systems: Nervous and Hormonal
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Nervous System
The nervous system detects changes and allows responses, comprising the brain,
spinal cord, and nerves.
Receptor cells in sense organs detect stimuli, producing electrical signals
called impulses.
Impulses travel along nerves to the brain via the spinal cord.
The brain processes information and sends impulses to effectors (muscles and
glands).
Muscles contract, and glands release hormones.
Hormonal System
Hormones are chemical messengers released by glands into the blood. Target cells
or target organs respond to hormones, causing changes.
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Gland Hormone Target Organs Response
Thyroid Controls metabolic rate and normal
Thyroid Many
Hormone bodily functions
Many (including
Adrenal Adrenaline Increases heart rate and breathing rate
heart and lungs)
Controls changes in a girl’s body
Ovary Oestrogen Many
during puberty and menstrual cycle
Growth
Pituitary Many Controls normal growth of children
Hormone
Muscle and Liver
Pancreas Insulin Cells take sugar from blood
Cells
Controls changes in a boy’s body
Testis Testosterone Many
during puberty
Nervous vs. Hormonal Systems
Feature Nervous System Hormonal System
Messengers Electrical impulses along nerves Chemical messengers in the blood
Speed Short, rapid response Longer, slower response
Impulses act only on the effector Messengers can act on many target
Action
connected organs
Shingles is caused by viruses that remain inside nerve cells, potentially causing a
painful rash later in life.
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The image above shows someone wearing a brain-scanning cap, which is used to
determine which parts of the brain are active during a task.
Testing Medicines
Medicines are drugs used to treat or prevent disease.
Antibiotics: Treat bacterial diseases by killing bacteria.
Antivirals: Treat diseases caused by viruses.
Vaccines: Prevent illness caused by specific pathogens.
Medicines can have additional effects called side effects.
The image below shows a skier in action, but the discussion is about medicines, not
sports. This makes the image irrelevant.
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Many drugs originate from traditional remedies, such as artemisinin from wormwood
for malaria. New medicines undergo a rigorous testing process:
Stage What Is Done Why It Is Done
Tests on diseased See medicine's effect on pathogens and
1
cells/tissues/organs in lab whether it harms cells.
See how all systems in a body react to the
2 Tests on animals
medicine without risk to humans.
Make sure the drug is safe for humans and
3 Tests on a few healthy people
check for general side effects.
Make sure the drug works well, find the right
Tests on many people with
4 dose, and check for side effects in different
the disease
people.
Placebo Effect: The effect of believing you will get better. This is more effective
when treating pain.
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Median and Quartiles
In clinical trials, data is analyzed by dividing participants into groups.
Median: The middle value when values are written in order.
Quartiles: Values that are one-quarter and three-quarters into the set of
values.
Interquartile range: Difference between upper (UQ) and lower quartile (LQ)
values. Formula: U Q − LQ.
Quartiles are the values that are one-quarter and three-quarters
into the set of values. The interquartile range is the difference
between upper and lower quartiles in a data set.
Continuous variation can be plotted as a bell-shaped curve (normal distribution).
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Interquartile Range (IQR)
The interquartile range is a useful measure for comparing the variation in two
different groups because extreme values can bias a comparison if the ranges of all
the data are compared.
Small IQR: Little variation
Large IQR: A lot of variation
Bell-shaped graph illustrating the distribution of leaf lengths on Tree A
Graph illustrating the distribution of leaf lengths on tree B
Bell curve graph illustrating the distribution of people's ability to absorb
cholesterol
Bar graph illustrating the changes in the risk of heart attack for different quartiles
of cholesterol absorption
Ecology: Estimating Abundance
Abundance measures how common something is in an area. Methods to measure
organism abundance include:
Quadrat: Used to sample static or slow-moving organisms.
Beating a tree: Causes organisms to fall onto a cloth.
Sweep nets: Trap small organisms in tall plants.
Pitfall traps: Capture small animals on the ground.
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Population size can be estimated using samples:
totalsizeof area
populationsize = numberof organismsinsample×
samplearea
Accuracy depends on sample size, ease of recording, and distribution.
Image depicting individuals in protective gear transporting a body bag
Distribution Types
Random
Regular
Clumped
Image depicting two men in a forest with one ziplining and the other crawling on a
sheet
When distribution isn't easy to see, scientists sample along a line or transect.
Image depicting a rugged coastal landscape with a colony of gannets
Image depicting two individuals conducting a transect survey in a grassy field
Surface Area:Volume Ratio
Unicellular organisms rely on diffusion to supply their volume. Larger organisms
require specialized organs with large surface areas and transport systems.
Surface area:volume (SA:V) ratio affects substances and energy transfer.
Smaller animals cool faster due to a larger SA:V ratio.
The SA:V ratio of a cuboid is calculated as:
surf acearea
SA : V ratio =
volume
where:
surf acearea = 2(l×h) + 2(l×w) + 2(w×h)
volume = l×w×h
Image depicting a small creature clinging to a tree trunk
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Image depicting two giant anteaters walking side by side
Osmosis
Partially permeable membranes allow some molecules to pass through.
Osmosis is the movement of solvent molecules through a partially permeable
membrane from an area of higher concentration to lower concentration.
Image depicting a partially permeable membrane separating two solutions
Microscopic view of the small intestine's villi
Microscopic view of a tissue sample with flattened villi, indicative of tropical sprue
Combating Pandemics
Pandemic: An infectious disease that spreads rapidly across multiple
countries.
Diseases like Ebola, SARS, bird flu and swine flu cannot be treated with antibiotics
because they are caused by viruses. Isolation is key to controlling outbreaks.
Image depicting a scene in an airport or travel hub
Image depicting a large room filled with hospital beds and patients
Image depicting a man in protective gear standing in front of a group of people
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