Cell Structure and Microscopes

Every living thing is made of cells, but not all cells are the same! Animal cells contain a nucleus, cytoplasm, ribosomes, cell membrane, and mitochondria that provide energy. Plant cells have all of these plus a tough cell wall, chloroplasts for photosynthesis, and a large vacuole for storage.

Bacterial cells are completely different - they're much simpler with no proper nucleus, just a chromosomal loop of DNA floating freely. They might have a flagellum for movement and small rings of DNA called plasmids.

Light microscopes let you see cells by shining light through them, magnifying up to 1000 times with a resolution of 200nm. Electron microscopes are far more powerful, using electron beams to magnify up to 1,000,000 times with 1nm resolution - that's why you see those incredibly detailed cell photos in textbooks!

Quick tip: Remember the magnification formula: total magnification = eyepiece lens × objective lens magnification.

Enzymes and Biological Processes

Enzymes are your body's molecular machinery - they're biological catalysts that speed up chemical reactions without getting used up. Think of them like incredibly specific tools that only work with one particular job.

The lock and key theory explains how enzymes work: each enzyme has an active site that perfectly fits its substrate, like a key fitting into a lock. This gives enzymes their specificity - they're incredibly picky about what they'll work with!

Temperature and pH massively affect enzyme activity. Human enzymes work best at 37°C (your body temperature) and specific pH levels. Go too hot or change the pH too much, and the enzyme denatures - its shape changes permanently and it stops working.

Carbohydrases like amylase break down starch into simple sugars. Proteases chop proteins into amino acids. Lipases split fats into glycerol and fatty acids. These breakdown processes are essential for digestion and getting energy from food.

Exam focus: You'll likely need to interpret graphs showing how temperature, pH, and substrate concentration affect enzyme activity rates.