Cell Structures and Types

Every living thing is made of cells, which are like tiny factories with different parts doing specific jobs. Plant cells and animal cells share some organelles but have key differences that you need to know for exams.

Both cell types contain a nucleus (the control centre with genetic material), cytoplasm (where most chemical reactions happen), mitochondria (powerhouses for respiration), and ribosomes (protein factories). The cell membrane acts like a bouncer, controlling what enters and leaves.

Plant cells have three extra features: a tough cell wall made of cellulose for support, chloroplasts for photosynthesis, and a large vacuole filled with cell sap. Bacterial cells are different altogether - they're prokaryotic (no proper nucleus) whilst plant and animal cells are eukaryotic (with a nucleus).

Quick Tip: Remember that substances move around cells through diffusion (high to low concentration), osmosis (water through membranes), and active transport (low to high concentration, needs energy).

Diseases and Leaf Structure

Understanding cardiovascular disease and cancer helps explain major health risks you'll encounter in exams. Cardiovascular disease happens when fatty deposits clog coronary arteries, potentially causing heart attacks - risk factors include smoking, high blood pressure, and poor diet.

Cancer occurs when cells divide uncontrollably, forming benign tumours (harmless lumps) or dangerous malignant tumours (aggressive and spreading). Key risk factors include smoking, poor diet, sun exposure, and unprotected sex.

Leaf structure is perfectly designed for photosynthesis and gas exchange. The upper epidermis protects the leaf, whilst palisade mesophyll contains loads of chloroplasts for photosynthesis. Spongy mesophyll has air spaces for gas exchange, and guard cells control the stomata (tiny pores).

Transpiration (water loss from leaves) increases with bright light, high temperature, and wind, but decreases with high humidity. The xylem transports water whilst phloem carries food around the plant.

Disease Alert: Know your pathogens - viruses (measles, HIV), bacteria (salmonella, gonorrhoea), fungi (rose black spot), and parasites (malaria) all spread differently and cause different symptoms.

Immune System and Drug Development

Your immune system is like your body's personal army, with white blood cells leading the charge against pathogens. These clever cells produce antibodies to recognise invaders, antitoxins to neutralise poisons, and can directly consume harmful microorganisms.

Vaccination works by introducing small amounts of dead or inactive pathogens, allowing your immune system to develop antibodies safely. This means future infections can be dealt with quickly - it's why diseases like smallpox have been completely wiped out.

New drug development involves testing for toxicity (how much is safe), efficacy (how well it works), and finding the right dose. Many medicines come from natural sources - penicillin from mould, digitalis from foxgloves for heart problems, and aspirin from willow bark.

There are pros and cons to vaccination programmes - they save lives and create herd immunity, but can cause side effects and don't always work for everyone.

Historical Fact: Alexander Fleming discovered penicillin in 1928, revolutionising medicine and saving millions of lives from bacterial infections.

Key Biological Processes

Stem cells are incredibly versatile cells that could treat diseases like diabetes and cancer, but their use raises ethical questions about destroying embryos. The debate continues between potential medical breakthroughs and moral concerns.

Photosynthesis is the process plants use to make food: water + carbon dioxide + light → glucose + oxygen. This endothermic reaction (takes in energy) happens in chloroplasts and needs sunlight. Meanwhile, respiration releases energy from glucose - it's the opposite process and happens in all living cells.

Digestive enzymes break down your food using the 'lock and key' model. Amylase tackles starch, protease breaks down proteins, and lipase handles fats. These enzymes are produced in your salivary glands, stomach, pancreas, and small intestine.

Anaerobic respiration happens without oxygen - in yeast, it produces alcohol (useful for drinks and bread), whilst in your muscles during exercise, it creates lactic acid that makes you feel the burn.

Energy Tip: Aerobic respiration produces much more energy than anaerobic respiration, which is why you can't sprint forever without oxygen!