GCSE Biology A (Combined) OCR

Cells

Cell Structure and Function

• All living organisms are composed of basic building blocks known as cells.

• Cells can be categorised into prokaryotic cells (like bacteria) and eukaryotic cells (like plant and animal cells).

• A typical eukaryotic cell comprises a nucleus which controls cell activities and contains the genetic material, DNA.

• Cells also contain cytoplasm - a gel-like substance where most of the cell's metabolism occurs.

• The cell membrane surrounds the cell providing a barrier between the internal cell environment and the outside world.

Specialised Cells

• Some cells become specialised for specific functions. For example, sperm cells in males are specialised for reproduction.

• Specialisation in plant cells could lead to forms such as root hair cells or xylem cells.

• Stem cells have the potential to turn into any type of cell that the body needs.

Microscopy

• Microscopes are essential tools in biology, allowing us to observe cells and their components, which are too small to see with the naked eye.

• Light microscopes are commonly used in schools and can magnify objects up to about 2000 times.

• Electron microscopes can magnify objects up to about 2 million times, providing a high-resolution image of the cell's ultrastructure.

Diffusion

• Diffusion is a process by which molecules move from an area of high concentration to an area of low concentration.

• It's a crucial process in biology, enabling nutrients and waste materials to enter and leave cells.

Osmosis

• Osmosis is a specific type of diffusion involving the movement of water molecules across a partially permeable membrane.

• It's important for the movement of water into and out of cells in plants and animals, impacting cell turgidity and therefore shape and function.

Active Transport

• Active transport is the process by which substances move against a concentration gradient, from a low-concentration area to a high-concentration one.

• It requires energy from the cell and is important for processes like nutrient uptake in plant roots.