Eukaryotic Cell- Cell Membrane, Characteristics and Functions of Cell Membrane:
The Eukaryotic cell contains four (4) parts:
- Cell Membrane
- Cell Wall (In Plants, Bacteria & Fungi)
It is also called as;
- Plasma membrane; because it covers living material of the Cell called as plasma membrane.
- Unit membrane; it is covering layer of cell and many organelles.
- Selective membrane; it only allows selective things to pass
- Semipermeable membrane; because half of the things can pass through the membrane.
- Differentiated membrane; it differentiates a cell from others.
- Lipid bilayer; made up of layers of phospholipids.
Characteristics of Cell Membrane:
- It is an outer boundary wall of a cell.
- It separates the cell from outer environment.
- It is made up of phospholipids and proteins.
- Phospholipids forms two layers, hydrophilic ends of outer layer faces outside and hydrophilic ends of inner layer faces inside of cell.
- It also contains cholesterol
- Phospholipids are found in lipid states.
Integral Proteins (Intrinsic):
- Located inside the lipid membrane
- Embedded inside the lipid membrane.
- Incorporated inside the lipid membrane.
- Also, called as channel proteins between they provide passage.
Peripheral Proteins (Extrinsic):
- Located out of the cell membrane.
- Loosely connected to membrane, e.g: hemoglobin, receptors, antibodies etc.
Functions of Cell Membrane:
There are several functions performed by the cell membrane, but the most important function is to protect the cytoplasm of the cell and the transport of different substances and to regulate the flow of solution and materials in and out of the cell.
Transport (trans= change + port=place)
There are two types of transport i). Active Transport, ii). Passive Transport
i). Active Transport:
It is simply defined as the movement of molecules form lower concentration to higher concentration by consuming energy. It is further classified into two types, 1. Endocytosis and 2. Exocytosis.
- Endocytosis: It is defined as the transport of molecules or substances into cell (cell membrane helps to take in material by enfolding in the form of vacuole).
- Exocytosis: It is defined as the transport of substance outside of the cell or It is the process of membrane fusion and the movement out of cell.
Endocytosis is further divided into two types, (a). Phagocytosis & (b). Pinocytosis
(a). Phagocytosis (Phago means to eat): It is said as the eating process of the cell. The movement of solid particles in the bulk. e.g- WBC kills the bacterium and harmful foreign bodies.
(b). Pinocytosis (Pino means to drink): It is said as cell drinking process. The movement of liquid particles in the bulk.
ii). Passive Transport:
It is spontaneous and doesn’t requires any energy. The passive transport is classified into two parts, (i). Osmosis & (ii). Diffusion.
Osmosis: Osmosis is the diffusion of water molecules across the plasma membrane form a region of its higher concentration to a region of its lower concentration.
Diffusion: It is the movement of ions or molecules from the region of higher concentration to the region of lower concentration.