Cells, Disease & Microscope Investigation

Light Microscope (الميكروسكوب الضوئي)

Uses visible light and glass/plastic lenses to magnify specimens.

• Magnification: Up to 2,000×
• Advantages: Can observe living cells and dynamic processes in real-time; relatively inexpensive and easy to use
• Limitations: Lower resolution compared to electron microscopes; cannot see very small organelles in detail
• Use in school: All microscopes you use in the lab are light microscopes

A compound light microscope – the type you'll use in your lab

Transmission Electron Microscope (TEM)

Focuses a beam of electrons through a thin specimen to create an image.

• Magnification: Up to 50,000,000× (50 million times!) with very high clarity
• Advantages: Reveals the internal structure of cells in extraordinary detail
• Limitations: Specimen must be dead and ultra-thin; expensive; requires extensive preparation
• Best for: Studying what's inside cells – organelles, membranes, and internal architecture

A Transmission Electron Microscope (TEM) – reveals internal cell structure at up to 50 million × magnification

Scanning Electron Microscope (SEM)

Focuses a beam of electrons across the surface of a specimen, producing detailed 3D surface images.

• Magnification: Up to 2,000,000× (2 million times)
• Advantages: Produces stunning 3D images of surfaces; great surface detail
• Limitations: Cannot see inside cells; specimen must be dead and coated with a thin metal layer
• Best for: Studying the topography (surface shape) of specimens – like the surface of a virus, a pollen grain, or an insect eye

SEM image of a flea (false colour) – notice the stunning 3D detail of the exoskeleton surface

Scanning Acoustic Microscope (SAM)

Uses sound waves to scan and create images of internal specimen features.

• Magnification: Variable – depends on sound wave frequency
• Advantages: Can examine specimens without destroying them; useful for examining internal features non-invasively
• Limitations: Lower resolution than electron microscopes
• Best for: Biology and medical applications – inspecting tissue samples and biological structures without cutting them

Diagram of a Scanning Acoustic Microscope – uses sound waves instead of light or electrons

Environmental Factors

Exposure to pollution, toxic chemicals, or radiation can cause non-infectious diseases.

Examples:

• Air pollution from factories → can cause cancer and chronic respiratory diseases
• Water pollution with heavy metals → can damage kidneys and liver
• Radiation exposure → increases cancer risk

Genetic Factors

Some diseases result from inherited gene mutations passed from parents to children.

Examples:

• Type 1 Diabetes – a genetic mutation affecting insulin production
• Sickle Cell Disease – a mutation in the haemoglobin gene
• Some cancers – linked to inherited genetic predispositions (e.g., BRCA genes)

Age-Related Factors

As people grow older, the risk of many non-infectious diseases increases simply due to the ageing process.

Examples:

• Cancer risk increases with age
• Cardiovascular disease becomes more common in older adults
• Neurodegenerative diseases like Alzheimer's primarily affect the elderly

Lifestyle and Habits

Daily choices about diet, exercise, smoking, and other behaviours significantly affect disease risk.

Examples:

• Type 2 Diabetes – linked to high sugar intake, obesity, and lack of exercise
• Heart disease – linked to high fat diet, smoking, and sedentary lifestyle
• Lung cancer – strongly linked to smoking

Viruses (الفيروسات)

The smallest pathogens – they're not even technically "alive" because they can't reproduce on their own.

Examples of viral diseases:

• COVID-19 (SARS-CoV-2)
• Influenza (the flu)
• HIV/AIDS
• Measles

Bacteria (البكتيريا)

Single-celled organisms that can reproduce rapidly. Some are beneficial; many cause serious disease.

Examples of bacterial diseases:

• Tuberculosis (TB) – caused by Mycobacterium tuberculosis
• Cholera – caused by Vibrio cholerae
• Salmonella food poisoning

Fungi (الفطريات)

Organisms including moulds, yeasts, and mushrooms. Some cause skin and internal infections.

Examples of fungal diseases:

• Athlete's foot
• Ringworm
• Candidiasis (yeast infection)

Parasites (الطفيليات)

Organisms that live on or inside a host and benefit at the host's expense.

Examples of parasitic diseases:

• Malaria – caused by Plasmodium parasites (the most important example in this LO!)
• Worm infections (helminths)
• Toxoplasmosis

Definitive Host (العائل النهائي)

The host inside which the parasite undergoes sexual reproduction.

Key characteristic: The parasite mates (sexual reproduction) inside this host.

Malaria example: The female Anopheles mosquito is the definitive host – Plasmodium parasites undergo sexual reproduction inside the mosquito's stomach.

Intermediate Host (العائل الوسيط)

The host inside which the parasite undergoes asexual reproduction only.

Key characteristic: The parasite multiplies but does NOT mate (only asexual reproduction) inside this host.

Malaria example: The human is the intermediate host – Plasmodium undergoes asexual reproduction in the human liver and red blood cells.

Reservoir Host (العائل الخازن)

An animal that serves as a long-term storage source for a pathogen. These animals carry enormous amounts of pathogens and cannot be fully treated – they are a constant, potential source of infection.

Key characteristics:

• Always an animal (never a human)
• Acts as a potential source of infection that can't be eliminated
• May also be classified as a definitive or intermediate host depending on what the parasite does inside it

Examples:

• Cats – carry Toxoplasma and other parasites; this is why they need regular vaccinations
• Pigs – reservoir for influenza viruses and other pathogens

Transport Host (العائل الناقل)

A host that carries the pathogen from one place to another but:

1. Is NOT affected by the pathogen (non-infected)
2. The pathogen undergoes NO development inside it (no reproduction, no changes)
3. Acts purely as a transporter

Example: A fish carries a parasite without being affected → a human eats the fish → the human gets infected. The fish was just a transport vehicle.

Key difference from a vector: In a vector, the pathogen develops/reproduces inside it. In a transport host, the pathogen enters exactly as it exits – no changes.

Mutualism (التبادل المنفعي)

Both organisms benefit from the relationship.

The "T" in mutualism can help you remember: Together – both benefit together!

Example: E. coli bacteria in the human small intestine:

• Bacteria benefits: Gets food (nourishment) and shelter from the human body
• Human benefits: The bacteria produces Vitamin K that the human needs

Both sides win = Mutualism ✅

Commensalism (التعايش التكافلي)

One organism benefits, the other is neither helped nor harmed.

Remember: Think of a benchwarmer on a football team – they're there, but they don't help or hurt the team.

Example: Staphylococcus bacteria living on human skin:

• Bacteria benefits: Gets food from skin secretions (oils, dead cells)
• Human: Neither benefits nor is harmed – the bacteria is just "there"

One benefits, one is neutral = Commensalism ✅

Parasitism (التطفل)

The parasite benefits, the host is harmed.

This is the relationship behind infectious disease – the pathogen takes from the host at the host's expense.

Example: Plasmodium (malaria parasite) in human blood:

• Parasite benefits: Feeds on the host's red blood cells (RBCs)
• Human is harmed: Destruction of RBCs causes anaemia, fever, and potentially death

One benefits, one is harmed = Parasitism ✅

Acute Infection (عدوى حادة)

• Short duration – comes fast, hits hard, resolves quickly
• Severe symptoms with rapid onset
• Example: Influenza (the flu), common cold

Think: Like a storm – intense but brief.

Chronic Infection (عدوى مزمنة)

• Long duration – persists for months or years (possibly a lifetime)
• Slow onset, symptoms may come and go
• Example: Hepatitis B, HIV, diabetes, hypertension

Think: Like a persistent drizzle – lasts forever.

Latent Infection (عدوى كامنة)

• The pathogen remains dormant (inactive/sleeping) inside the host
• No symptoms during the dormant period – the person doesn't know they're infected
• May reactivate later if immunity drops
• Example: Latent TB – a person can carry TB bacteria for decades without symptoms. If their immune system weakens (due to HIV, old age, or stress), the TB can reactivate into active TB disease

Think: Like a sleeping volcano – quiet now, but could erupt.

Local Infection (عدوى موضعية)

The infection stays restricted to one area – it doesn't spread beyond the initial site.

Example: An eye infection that stays in the eye only.

Systemic (Generalised) Infection (عدوى جهازية)

The infection spreads through the bloodstream to affect the entire body – all organ systems.

Example: Sepsis – a blood infection that reaches every organ through blood vessels.

Focal Infection (عدوى بؤرية)

The infection starts locally in one area, then spreads to a distant organ (not through blood, but through tissue). Different from systemic because it moves to specific locations, not everywhere.

Example: A dental infection that spreads to the heart valves, causing secondary infection there.

Plasmodium falciparum

• Most dangerous and most deadly species
• Highest risk of death (especially in children and pregnant women)
• Most common in Africa
• Causes cerebral malaria (brain infection → seizures, coma, death)
• Frequently drug-resistant (especially to chloroquine)

Plasmodium vivax

• Common in Asia and Latin America
• Can stay dormant in the liver → symptoms can return months or years later (relapses)
• Has the longest incubation period among all species
• Less deadly but more persistent

Plasmodium ovale

• Similar to P. vivax – can also cause relapses from dormant liver stages
• Less common than other species

Plasmodium malariae

• Causes milder disease than other species
• Can persist in the blood for many years if untreated
• Slower reproductive cycle