Final answer:
The cell membrane consists of a phospholipid bilayer with proteins and carbohydrates that facilitate its functions, including selective permeability for passive and active transport processes.
Step-by-step explanation:
The cell membrane is a crucial component of all cells, encasing and protecting the cell's interior. It is structured as a bilayer of phospholipids with embedded proteins and carbohydrates that contribute to its function. The membrane is dynamic and fluid, facilitated by the configuration of fatty acid tails and the presence of cholesterol, especially in animal cells. Understanding the composition and behavior of the cell membrane helps us grasp how substances can pass through it via different modes of transport, such as diffusion, facilitated transport, and active transport.
Passive transport includes diffusion and osmosis, which enable substances to move from areas of high concentration to low concentration without the input of energy. Conversely, active transport requires energy to move substances against their concentration gradient. The structure of the cell membrane allows for the selective permeability required for these processes to maintain homeostasis within the cell.