Transport across Cell Membrane• Diffusion is the process of cells moving from areas of high concentration to areas of low concentration. – This random movement causes the molecules to become evenly spread out.
Diffusion• Cells use diffusion to get substances into and out of the cell. – Example: During photosynthesis, oxygen is produced inside the cell. When this happens the concentration of oxygen becomes higher inside the cell than outside and oxygen diffuses out of the cell.
• Osmosis is the diffusion of water through a membrane. – Water moves into an area with low concentrations and out of areas with high concentrations.• Both diffusion and osmosis are forms of passive transport (they require no energy)
Transport across Cell Membrane: Active Transport• materials move from low concentration to high concentration. requires energy!
Endocytosis– moving a particle into the cell • Phagocytosis • Pinocytosis– Exocytosis: moving a particle from inside the cell to outside.
• PINOCYTOSISIngestion of minute particles e.g proteinmolecules• PHAGOCYTOSISIngestion of large particles, such as bacteria, whole cells or portions of degenerated tissue.
Movement thru the Cell Membrane: Active Transport Endocytosis Exocytosis
Cell Locomotion• Amoeboid movement• Ciliary movement
Ameboid movement• Movement of an entire cell in relation to its surroundings• Involves pseudopodium and ATP• Mechanism – formation of new cell membrane & exocytosis at one end – Attachment of pseudopodium to tissues • Receptor proteins – Absorption of the membrane & endocytosis in mid & rear portions – Detachment of receptor proteins
Ameboid movement• Cells that exhibit ameboid motion – WBC – Fibroblasts – Embryonic cells• Control of ameboid motion – Chemotaxis • Positive • Negative
Cilia and Ciliary movements• Whiplike movement of cilia on the surfaces of cells• A sharp pointed hair projecting 2- 4micrometers from the surface of the cell.
Structure of a cilium• Covered by an outcropping of cell membrane• Supported by 11 microtubules, 9 double tubules at the periphery and 2 single tubules down the center.• Each cilium is an outgrowth of a structure that lies immediately beneath the cell membrane, called basal body of the cilium
• All the tubules are linked to one another by a complex of protein cross linkages, together called the axoneme.• Multiple protein arms composed of the protein dynein (having ATPase activity) project outward from each double tubule• ATP and appropriate magnesium and calcium concentration required.
Mechanism of ciliary movement• Sudden fast forward whip like stroke• Slow backward stroke• An effective way of pushing the fluid in the direction of forward stroke.
• CELLS EXHIBITING CILIARY MOVEMENT• 1- Respiratory airways• 2- Uterine tubes of the female reproductive tract.