Cell Structure and Types

Ever wonder what makes bacteria so different from the cells in your body? It all comes down to whether they have a nucleus or not. Prokaryotes (like bacteria) don't have a nucleus - their genetic material just floats around in a single DNA loop plus small rings called plasmids. They're also much smaller and simpler.

Eukaryotes are the fancy cells with a proper nucleus that controls everything. Only eukaryotic cells have mitochondria - the powerhouses that make energy through aerobic respiration. Think of prokaryotes as studio flats and eukaryotes as proper houses with separate rooms.

Plant cells are basically animal cells with three extra features: a cell wall made of cellulose for support, chloroplasts containing chlorophyll for photosynthesis, and a permanent vacuole for storage. Animal cells have the core components: nucleus (control centre), cytoplasm (where chemical reactions happen), cell membrane (security guard), and ribosomes (protein factories).

Key tip: Remember that 1 order of magnitude = 10 times larger. This helps when comparing cell sizes under microscopes!

Microscopy and Cell Specialisation

Light microscopes are your everyday lab equipment - cheaper, easier to use, and you can observe living samples in colour. Electron microscopes are the high-tech option with much better resolution, but samples must be dead and they're expensive. The key formula you need is: Image Size = Actual Size × Magnification.

When preparing microscope slides, you'll peel off a thin layer of tissue, add iodine solution as a stain, and carefully place it on the slide without air bubbles. Always start with the lowest objective lens and gradually increase magnification.

Stem cells are the ultimate shape-shifters - unspecialised cells that can become anything. Differentiation is when these cells specialise for specific jobs. Embryonic stem cells can become any type of cell, whilst adult stem cells (found in bone marrow) are more limited.

Specialised cells are perfectly designed for their jobs. Sperm cells are streamlined with lots of mitochondria for energy and enzymes to digest egg membranes. Nerve cells have a myelin sheath for insulation and dendrites to connect with other nerves. Muscle cells contain protein fibres that can change length and are packed with mitochondria for energy.

Remember: Plant stem cells are found in meristems and can differentiate throughout the plant's life, unlike animal stem cells which are mainly active during the embryo stage.

Specialised Cells and Binary Fission

Root hair cells are like tiny straws designed to suck up water and minerals from soil. They have increased surface area through their hair-like projections and lack chloroplasts since they're underground. Xylem and phloem are the plant's transport system - xylem moves water and minerals upward in one direction, whilst phloem transports sugars both ways.

Binary fission is how bacteria multiply - it's much simpler than human cell division. The circular DNA replicates, plasmids multiply, and the cell simply splits into two identical daughter cells. Bacteria love growing in nutrient broth or on agar gel plates in warm conditions.

When studying bacteria in the lab, everything must be sterile. Clean benches with disinfectant, wash hands with antibacterial soap, and sterilise equipment with flames. This prevents contamination that could ruin your experiment.

Testing antibiotics and disinfectants involves placing treated paper discs on bacterial cultures and measuring the zone of inhibition - the clear area where bacteria couldn't grow. The larger the zone, the more effective the treatment.

Lab safety: Always tape agar plates and incubate them upside down at 25°C to prevent contamination and avoid growing dangerous bacteria.

Mitosis and Stem Cells

Mitosis is how your body grows and repairs itself - one cell becomes two identical cells. The process involves DNA replication, chromosomes lining up in the centre, then being pulled apart before the cell splits. Unlike binary fission, this is much more complex because eukaryotic cells have way more genetic material to organise.

Embryonic stem cells can become absolutely any type of cell, making them incredibly valuable for treating diseases like diabetes (by creating insulin-producing cells) or paralysis (by creating new nerve cells). Adult stem cells from bone marrow are more limited but can replace faulty blood cells.

Therapeutic cloning creates embryos with the same genes as patients, so the cells won't be rejected. However, this raises ethical concerns for some people based on religious beliefs about embryo use.

Diffusion is particles moving from high to low concentration - like oxygen entering your blood and carbon dioxide leaving. Temperature and surface area affect diffusion rates. Osmosis is specifically water moving through membranes from dilute to concentrated solutions.

Practical tip: When measuring percentage change in osmosis experiments, use the formula: % change = (change in value ÷ original value) × 100

Active Transport

Sometimes cells need to move substances against the concentration gradient - from low to high concentration. This is like swimming upstream and requires energy from respiration. This process is called active transport.

Root hair cells use active transport to absorb minerals from soil even when mineral concentration is higher inside the cell than outside. Your small intestine does the same thing to absorb glucose from food into your bloodstream, even when glucose levels are already high in your blood.

The key difference between diffusion, osmosis, and active transport is energy. Diffusion and osmosis happen naturally without energy, whilst active transport needs energy because it's working against the natural flow. Think of it like riding a bike downhill (diffusion) versus cycling uphill (active transport).

Memory trick: Active transport is "active" because it requires energy - just like being active in sports requires energy from you!