Cell Structure and Microscopy

Ever wondered what makes plant and animal cells different? Both types share some key organelles - the cytoplasm where chemical reactions happen, the nucleus containing genetic material, ribosomes that make proteins, and mitochondria for aerobic respiration. The cell membrane controls what enters and exits the cell.

Plant cells have three extra features that animals don't: chloroplasts for photosynthesis, a large vacuole containing cell sap, and a tough cell wall for support. These adaptations help plants survive as stationary organisms that make their own food.

Light microscopes let you see these structures up close. The key is starting with low magnification, clipping your slide onto the stage, and carefully adjusting the focus. Remember the magnification formula: magnification = image size ÷ real size - you'll definitely need this for exams!

Quick Tip: Always start microscope work with the lowest magnification objective lens to avoid damaging slides.

Specialised Cells and Mitosis

Your body contains billions of cells, but they weren't always specialised. Through differentiation, cells develop specific structures for particular jobs - it's like career training for cells!

Nerve cells are incredibly long to carry electrical signals across your body quickly. Muscle cells are also lengthy so they can contract effectively. Root hair cells have massive surface areas to absorb water and minerals from soil, while xylem and phloem cells have hollow centres for transporting water and food through plants.

Mitosis is how your body makes new identical cells for growth and repair. The DNA replicates first, then chromosomes get pulled to opposite ends of the cell before it splits in two. This produces two diploid cells with exactly the same genetic information.

Stem cells are the ultimate flexible cells - they can become any type of specialised cell. This makes them incredibly valuable for treating diseases, though there are ethical concerns about using embryonic stem cells.

Remember: Mitosis produces identical diploid cells, whilst meiosis (covered later) produces genetically different gametes.

Transport and Exchange Systems

Moving substances around your body isn't just about simple diffusion. Active transport lets cells absorb materials against concentration gradients - like root hairs taking in minerals from soil even when there's more inside the plant than outside. This process needs energy from respiration to work.

Your lungs are perfectly designed for gas exchange with millions of tiny alveoli providing massive surface area. Similarly, your small intestine is covered in villi that dramatically increase absorption area for digested food molecules.

The digestive system is a coordinated team effort. Your salivary glands and pancreas produce digestive juices, the liver makes bile, your stomach breaks down food, and the large intestine absorbs water from waste.

Enzymes are biological catalysts that speed up reactions by providing an active site where substrates can bind. Amylase breaks down starch into sugars, proteases split proteins into amino acids, and lipases convert lipids into glycerol and fatty acids.

Key Point: Enzymes are specific - each one only works with particular substrates that fit perfectly into its active site.

Heart and Circulation

Your heart is essentially two pumps working together. The right side pumps deoxygenated blood to your lungs via the pulmonary artery, whilst the left side pumps oxygenated blood around your body through the aorta. Valves prevent backflow, keeping blood moving in the right direction.

Blood vessels have different jobs and structures. Arteries carry blood away from your heart and have thick muscular walls to handle high pressure. Capillaries have thin walls with tiny gaps for substance exchange with body cells. Veins return blood to your heart and contain valves to prevent backflow.

Your blood contains four main components: red blood cells carry oxygen, white blood cells fight infection by producing antibodies and antitoxins, platelets help blood clot at wounds, and plasma transports everything else including hormones and waste products.

Too much cholesterol can cause fatty deposits in arteries. Statins are drugs that reduce cholesterol levels, lowering risks of heart attacks and strokes, though they need to be taken regularly and can have side effects.

Exam Tip: Remember that arteries carry blood away from the heart - use the 'A' for away to help you remember!

Disease and Defence

Cancer occurs when cell division goes wrong, creating tumours. Benign tumours stay in one place and aren't dangerous, but malignant tumours can spread through your bloodstream to other body parts, making them life-threatening.

Your body has multiple defence systems. Your skin blocks pathogens, nose hairs trap particles, mucus catches invaders, and stomach acid kills harmful microorganisms. White blood cells fight back through phagocytosis (engulfing pathogens), producing antibodies to mark invaders, and releasing antitoxins to neutralise bacterial toxins.

Common diseases include salmonella (food poisoning causing fever and vomiting), gonorrhoea (sexually transmitted with painful urination), measles (viral infection causing rashes and fever), and HIV (virus spread through sexual contact). Malaria comes from protist parasites spread by mosquitoes.

Vaccinations work by injecting small amounts of dead or inactive pathogens, training your immune system to recognise real threats. They've controlled many communicable diseases, though they don't always work for everyone and can occasionally cause reactions.

Important: Many diseases that were once deadly are now preventable through vaccination programmes.

Drug Development and Plant Biology

Modern medicines often come from natural sources. Aspirin originated from willow bark, digitalis from foxgloves treats heart conditions, and penicillin from mould kills bacteria. However, all drugs must undergo rigorous testing.

Preclinical testing starts with human cells and tissues in labs, then moves to animal testing for efficacy, toxicity and dosage. Clinical trials on human volunteers come next - first healthy people check for side effects, then patients test effectiveness. Double-blind trials using placebos ensure results aren't influenced by expectations.

Photosynthesis is how plants make food: carbon dioxide + water → glucose + oxygen (using light energy). Plants use glucose in multiple ways - for respiration, making cellulose cell walls, creating amino acids for proteins, producing oils and fats for seed storage, and converting to starch for energy storage.

Guard cells around stomata control gas exchange and water loss. When plants have plenty of water, guard cells swell and open stomata for photosynthesis. During water shortage, they become flaccid and close stomata to prevent water loss.

Fun Fact: Almost all energy on Earth ultimately comes from photosynthesis - even fossil fuels are ancient stored sunlight!