A Level Biology B OCR

Cells

Cell Structure and Function

• Every cell is a self-sustaining unit that functions independently but works alongside others to fulfil an organism’s needs.
• Cells possess a variety of organelles, each with a specific function and structure.
• Nucleus: The control centre of the cell. It contains the cell's DNA and controls gene expression.
• Mitochondria: Responsible for the production of ATP via cellular respiration. They have a distinctive double membrane.
• Ribosomes: Small organelles that synthesise proteins from amino acids, according to the instructions given by the DNA.
• Endoplasmic Reticulum (ER): A network of membranes for the production, processing, and transport of proteins and lipids.
• Golgi Apparatus: Responsible for modifying, sorting, and packaging proteins and lipids for transport to targeted destinations.
• Lysosomes: Contain digestive enzymes for breaking down waste materials and cellular debris.
• Membrane-bound organelles are a distinguishing character of eukaryotic cells.

Cell Division

• Cells reproduce through a process called cell division.
• Cell division allows for growth, repair and reproduction, resulting in two daughter cells.
• There are two types of cell division: Mitosis and Meiosis.
• Mitosis results in two genetically identical daughter cells and is key to growth and repair.
• Meiosis results in four genetically diverse cells. It is integral to sexual reproduction and ensures genetic diversity.

Transport in Cells

• Cell transport is essential for homeostasis and cell function.
• Diffusion is a passive process where molecules move from an area of high concentration to a lower concentration.
• Osmosis is the diffusion of water across a semi-permeable membrane.
• Active transport requires energy (ATP) to move substances against their concentration gradient.
• Endocytosis and exocytosis are complex movements where cells take in or eject large particles.

Cell Specialisation

• A specialised cell is a cell that has adapted to perform a specific function.
• These adaptations could be structural, such as large amounts of certain organelles, or functional.
• Examples of specialised cells include neurons, muscle cells, and red blood cells.

Remember, an understanding of cells and cell processes are fundamental concepts in biology. Keep revisiting these key principles to ensure a solid foundation.