Cell Ingestion

Endocytosis:

• It is the engulfing of food or foreign particles through the plasma membrane.
• It is of two types – phagocytosis (cell eating), and pinocytosis (cell drinking).
• Phagocytosis refers to the engulfing of solid particles
• Pinocytosis is the engulfing of liquid particles.
• A pinosome or phagosome is a membrane bound vesicle that encloses the liquid or solid material respectively.

Exocytosis (cell vomiting):

• It is the process of exudating the secretory products from the secretory cells to the outside of the cell cytoplasm, in the form of a membranous vesicle.

Cellular movements:

Plasma membrane takes part in cellular movement by pseudopodia (e.g. amoeba) and undulations

1. By pseudopodia formation
   • Pseudopodia are temporary outgrowths of the cell which are used for locomotion
   • Amoeba, macrophages and white blood cells put forth new pseudopodia at the advancing end of the cell.
   • It is partly due to cytoplasmic streaming and partly pseudopodium due to extension of plasma membrane
2. By undulations of plasma membrane
   • Undulations are regular waves of membrane protrusions which occur in the forward region of the cells.
   • Surface protrusions are formed on the cell due to ruffling or undulations of the membrane, which attach the cell temporarily to a solid surface.
   • The protrusions move as waves to propel the cell.
   • This requires no cytoplasmic streaming.

Membrane transport:

• Plasma Membranes are selectively permeable and allow passage of selected molecules.
• These biomembranes are acting as a physical barrier between organelles and cytoplasm and between the cell and extracellular fluids.
• The passage of substances takes place in two ways.

1. Passive Transport
2. Active Transport

Passive Transport

Passive transport occurs in two ways.

1. Diffusion

• • It occurs along the concentration/electrical/electrochemical/pressure gradient of substances.
  • Diffusion is the movement of particles from a region of higher concentration to a region of their lesser concentration.
  • Many water-soluble solutes and ions such as K, Cl and HCO3 diffuse through water filled pores in the membrane, provided the diameter of the pore is larger than that of the diffusing particle.

• E.g. 1. Diffusion of water vapour from inside the leaf into the atmosphere (Transpiration).
• E.g. 2. Diffusion of Carbon dioxide from the blood vessel on the alveolar surface into the alveoli.

2. Osmosis

• • Movement of solvent molecules from a region of higher concentration to a region of lower concentration through a semi permeable membrane

Active Transport

• As the polar molecules cannot pass through the no polar lipid bi-layer, they require a carrier protein of the membrane to facilitate their transport across the membrane.
• A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration.
• Such a transport is an energy dependent process, in which ATP is utilized and is called active transport, e.g., Na+/K+ Pump.