Cell Biology AQA Study Guide

Cell Types and Structures

Your body is made up of eukaryotic cells - cells where the genetic material is safely tucked away inside a nucleus. These are much more complex than prokaryotic cells (like bacteria) where the DNA just floats around freely.

Plant and animal cells have some brilliant organelles that keep them running smoothly. Mitochondria are like tiny power stations where respiration happens to give cells energy. Ribosomes act as protein factories, churning out all the proteins your body needs.

Plant cells have extra features that make them special. Chloroplasts contain chlorophyll and handle photosynthesis - basically turning sunlight into food. The cell wall made of cellulose gives plants their strength, whilst the vacuole filled with cell sap helps maintain the plant's shape.

Key Point: Remember that animal cells and plant cells are both eukaryotic, but plant cells have additional structures like chloroplasts and cell walls that animal cells don't have.

Specialised Cells and Microscopy

Different jobs require different tools, and cells are no exception. Sperm cells are perfectly designed for their mission to fertilise an ovum - they're streamlined and packed with mitochondria for energy.

Nerve cells are the body's electrical cables, sending impulses around your body at lightning speed. The myelin coating acts like insulation on a wire, speeding up transmission. Muscle cells contain protein fibres that contract to create movement.

Plant cells have their own specialists too. Root hair cells have tiny hairs that massively increase surface area for absorbing water and nutrients. Xylem cells transport water upwards using thick walls reinforced with lignin, whilst phloem carries sugars both up and down the plant.

When studying cells, electron microscopes give much better magnification and resolution than light microscopes. This means you can see much finer details - essential for understanding how cells actually work.

Key Point: Each specialised cell has specific features that perfectly match its function - form always follows function in biology!

Cell Division and Transport

Bacteria reproduce through binary fission - basically splitting in two. The number of bacteria grows exponentially following the pattern 2ⁿ, which is why bacterial infections can spread so quickly.

Mitosis is how your body grows and repairs itself. The DNA replicates, chromosomes get pulled apart, and one cell becomes two identical cells. This process is crucial for growth, repair, and asexual reproduction.

Stem cells are like biological Swiss Army knives - they're undifferentiated and can become any type of cell. Embryonic stem cells are the most versatile, whilst adult stem cells from bone marrow are more limited but still incredibly useful for medical treatments.

Understanding how substances move in and out of cells is essential. Diffusion moves particles from high to low concentration - think of how oxygen gets into your blood. Osmosis is specifically water moving through membranes, whilst active transport uses energy to move substances against the concentration gradient.

Key Point: The surface area to volume ratio is crucial for diffusion efficiency - smaller cells are generally better at exchanging materials with their environment.