Common Diseases and Their Causes

Understanding different types of pathogens helps you recognise how diseases spread and how to prevent them. Each type of pathogen has its own characteristics and treatment methods.

Viral infections like measles spread through coughs and sneezes but can be prevented with vaccines. HIV damages your immune system and spreads through bodily fluids, whilst TMV creates mosaic patterns on plant leaves through direct contact.

Bacterial diseases include salmonella (causing fever and stomach cramps from contaminated food) and gonorrhoea (a sexually transmitted infection treated with antibiotics). Good hygiene and safe practices prevent most bacterial infections.

Key Tip: Viruses need vaccines for prevention, bacteria can be treated with antibiotics, but good hygiene prevents both!

Fungal and Protist Diseases

Fungal diseases like rose black spot create distinctive black spots on leaves, reducing photosynthesis when leaves drop off. The spores spread through wind, but fungicides can control the infection effectively.

Malaria is caused by a protist that creates recurring fever symptoms. Mosquitoes spread this disease through their bites, making mosquito nets and antimalarial drugs essential in affected areas.

Remember: Each pathogen type (virus, bacteria, fungus, protist) requires different prevention and treatment strategies.

Cell Structure Basics

All living things are made of cells, but not all cells are the same. The main difference lies in whether they have a nucleus or not.

Prokaryotic cells (like bacteria) have no nucleus - their DNA floats freely in the cytoplasm. They're simpler but still contain ribosomes, cell membranes, and often cell walls, plasmids, and flagella for movement.

Eukaryotic cells (like plant and animal cells) have a proper nucleus containing their DNA. They're more complex, with mitochondria for energy and various other organelles for different functions.

Quick Check: Remember - PRO-karyotic = NO nucleus, EU-karyotic = nucleus present!

Digestive System Organisation

Your digestive system is perfectly organised to break down food efficiently. It's built from cells that form tissues, tissues that form organs, and organs that work together as organ systems.

Digestion is essential because food molecules like carbohydrates, proteins, and lipids are too large to enter your bloodstream directly. Digestive enzymes break these big molecules into smaller ones that can be absorbed.

The stomach contains both muscle tissue (for churning) and glandular tissue (for producing enzymes), showing how different tissues work together in one organ.

Key Point: Bigger molecules need breaking down before absorption - that's what digestion is all about!

The Digestive Process

Your digestive journey starts in your mouth where enzymes in saliva begin breaking down starch. The food travels down the oesophagus to your stomach, where hydrochloric acid helps enzymes digest proteins.

The stomach's churning action increases surface area, giving enzymes more space to work effectively. After several hours, the liquid mixture moves into the small intestine.

The pancreas releases enzymes for starch, protein, and lipid digestion, whilst the liver produces bile to speed up lipid breakdown and neutralise stomach acid. This teamwork ensures complete digestion.

Memory Trick: Think of your digestive system as a factory production line - each station has a specific job!

Antibodies and Immune Defence

White blood cells protect you by producing highly specific protein molecules called antibodies. These antibodies stick to particular pathogens, marking them for destruction like a targeting system.

The amazing thing about antibodies is their specificity - each type only works against one particular disease. However, they can remain in your body long-term, providing protection if you encounter the same pathogen again.

Antitoxins are another weapon in your immune arsenal. Some bacteria release harmful toxins, but white blood cells produce antitoxins that bind to these toxins and prevent cellular damage.

Cool Fact: Your immune system has a memory - that's why you rarely get the same disease twice!

How Your Immune System Works

Your immune system is like a sophisticated defence force that destroys pathogens and protects against future attacks. It has multiple strategies to keep you healthy.

Phagocytosis is when white blood cells literally eat pathogens! They detect chemicals released by invaders, move towards them, engulf them completely, then use enzymes to destroy them from the inside.

This process is your body's first line of active defence, working alongside antibody production to eliminate threats efficiently.

Visual Tip: Think of white blood cells as cellular Pac-Men, hunting down and consuming the bad guys!

Understanding Diffusion

Diffusion happens everywhere around you - it's how perfume spreads across a room or how cells get the nutrients they need. Molecules naturally move from crowded areas to less crowded ones.

The cell membrane is partially permeable, meaning it's picky about what gets through. Water, glucose, and amino acids can pass through easily, but larger molecules cannot.

This selective barrier is crucial for cell survival, allowing necessary substances in whilst keeping harmful ones out.

Real-World Example: Diffusion is like people spreading out in a crowded room - they naturally move to less crowded spaces!

Factors Affecting Diffusion Rate

Three main factors control how fast diffusion happens, and understanding these helps explain many biological processes.

Concentration gradient matters most - the bigger the difference between concentrations, the faster molecules move. Higher temperatures give molecules more energy to move quickly, speeding up diffusion.

Surface area also affects rate - larger surface areas provide more space for molecules to pass through, increasing diffusion speed significantly.

Exam Tip: Remember the three factors - concentration difference, temperature, and surface area all increase diffusion rate!

Osmosis in Action

Osmosis is a special type of diffusion involving only water movement through partially permeable membranes. Water moves from areas of high water concentration to low water concentration.

The classic potato experiment demonstrates osmosis perfectly. By placing potato chips in different sugar concentrations, you can observe how water moves in or out of the cells.

This practical works with various vegetables (carrots work too) and different solutions (salt solutions work as well as sugar). It's cheap, reliable, and clearly shows osmosis in action.

Practical Tip: Potatoes are used because they're cheap, store well, and give clear results every time!