Comprehensive Biology AQA Mock Exam Notes

Communicable vs Non-Communicable Diseases

Ever wondered why you can catch a cold but not cancer? Communicable diseases are the nasty ones that spread from person to person or between animals and humans. These troublemakers are caused by bacteria, viruses, parasites, and fungi - think measles or malaria.

Non-communicable diseases work differently. They can't spread between people, but they typically stick around for ages and often get progressively worse. Cancer, asthma, and coronary heart disease fall into this category.

Quick Tip: Remember "communicable" = "contagious" - if it can spread, it's communicable!

Using a Light Microscope

Getting up close with cells requires proper technique, and the onion cell practical is your chance to master microscope skills. Start by adding a water drop to your slide, then carefully peel off onion epidermal tissue with tweezers.

Iodine solution acts as your highlighting stain, making cell structures pop out clearly. Place your cover slip down slowly to avoid air bubbles - they'll ruin your view completely.

Use the lowest powered objective lens first, then adjust the coarse focus knob whilst looking down the eyepiece. You should spot the cell wall, cytoplasm, and nucleus clearly in onion cells.

Exam Focus: Always draw observations in pencil and label structures clearly - this technique appears frequently in practicals!

Heart Structure and Function

Your heart is basically a muscular pump that never gets a break, keeping blood flowing around your body 24/7. The walls are packed with muscle tissue, and clever valves ensure blood only flows in the right direction.

The right side handles blood going to your lungs (via the pulmonary artery), whilst the left side pumps oxygenated blood around your body through the aorta. The vena cava brings deoxygenated blood back to start the cycle again.

Arteries have incredibly strong, elastic walls with thick muscle layers. Their walls are thick compared to the lumen (the hole in the middle), which helps them cope with high-pressure blood flow.

Memory Trick: Arteries carry blood Away from the heart - both start with 'A'!

Blood Vessels: Capillaries and Veins

Capillaries are the tiny heroes of your circulatory system, branching off from arteries to reach every single cell in your body. They're incredibly thin - just one cell thick - which makes diffusion super efficient for exchanging oxygen, food, and waste like CO₂.

These microscopic vessels have permeable walls, allowing substances to move in and out easily. Their small lumen and thin walls are perfectly designed for this crucial exchange job.

Veins form when capillaries join back together, carrying blood back to your heart. They've got larger lumens than arteries to help blood flow smoothly, plus valves to prevent any sneaky backflow.

Key Point: Wall thickness tells you the job - thick walls (arteries) handle pressure, thin walls (capillaries) enable exchange!

Plant Structure and Osmosis

Plant leaves are engineering marvels with specialised tissues doing specific jobs. The waxy cuticle stops water loss, whilst the transparent upper epidermis lets light through to the palisade mesophyll below where photosynthesis happens.

Xylem and phloem act like the plant's transport system, delivering water and nutrients whilst taking away glucose. The spongy mesophyll and air spaces help with efficient gas exchange.

Osmosis is water's movement across a partially permeable membrane from high to low concentration. Think of it as water trying to "even things up" - it'll always move to dilute concentrated solutions.

Exam Essential: Osmosis is just a special type of diffusion, but only for water molecules!

How Osmosis Works

Picture a partially permeable membrane as a selective bouncer - it lets small water molecules through but blocks larger sucrose molecules. Water molecules bounce around randomly, moving both ways across the membrane.

However, if there's more water on one side, you'll get a net movement towards the area with less water. This steady flow continues until concentrations balance out, with the sucrose solution becoming more diluted.

This process happens because water molecules are constantly moving due to their kinetic energy. The membrane's selectivity creates the concentration gradient that drives osmosis.

Real-Life Example: This is exactly how plant roots absorb water from soil!

Digestive Enzymes

Your digestive system faces a massive challenge: starch, proteins, and fats are simply too big to pass through digestive system walls. That's where digestive enzymes become absolute lifesavers, breaking down these giants into absorbable pieces.

Carbohydrases (like amylase) convert carbohydrates into simple sugars. You'll find amylase working hard in your salivary glands, pancreas, and small intestines, turning starch into maltose.

Proteases tackle proteins, chopping them into amino acids. These powerful enzymes operate in three key locations: your stomach, pancreas, and small intestine.

Memory Aid: Each enzyme name hints at its job - protease breaks down protein, lipase tackles lipids!

Enzyme Testing and Lipases

Lipases complete the enzyme trio by converting lipids into glycerol and fatty acids. You'll find these fat-busting enzymes working in your pancreas and small intestine.

The Benedict's test reveals reducing sugars through a brilliant colour change. Heat your food sample with Benedict's solution at 75°C, and watch it transform from blue to green, yellow, or brick-red if sugars are present.

Testing for starch is even simpler with iodine solution. Just add iodine to your food sample and give it a gentle shake - it'll change from browny-orange to blue-black if starch is detected.

Practical Tip: Always use a water bath for Benedict's test - direct heating can give unreliable results!

The Complete Digestive System

Your digestive system is like a well-organised factory with each organ having a specific role. Salivary glands kick things off by producing amylase, whilst your stomach creates protease and hydrochloric acid to kill bacteria.

The liver produces bile (stored in the gall bladder) which neutralises stomach acid and breaks down fats. Your pancreas is the enzyme powerhouse, producing protease, amylase, and lipase for the small intestine.

The small intestine completes digestion with its own enzyme production, whilst the large intestine handles the final job of absorbing excess water from food.

System Summary: Each organ specialises in different enzymes - teamwork makes digestion work!

Antibiotics and Resistance

Painkillers might make you feel better, but they're just masking symptoms - they don't actually kill the pathogens causing your illness. Antibiotics are the real fighters, killing or preventing bacterial growth, though different types target different bacterial strains.

The scary bit? Bacteria can become resistant to antibiotics through mutation. When you take antibiotics, only non-resistant bacteria die, leaving resistant ones to survive and reproduce like crazy.

This creates a population of resistant bacteria that's much harder to treat. That's why doctors are careful about over-prescribing antibiotics - we need to slow down resistance development to keep these life-saving medicines working.

Global Issue: Antibiotic resistance is becoming a serious worldwide health threat - responsible use is crucial!