A bioreactor (10; 110; 210; 300; 310; 320; 330; 340; 350; 360; 370; 380; 410; 510; 550; 610; 710; 810; 910; 1010; 1110; 1590) for growing cells or microorganisms therein, the bioreactor comprising: - a closed vessel enclosing a space therein; - a first barrier (12; 112; 212; 512; 522; 612; 712; 812; 912; 1012; 1112; 1505; 1512) having a plurality of pores therein, the first barrier is sealingly disposed within the space configured to divide the space into a first lower chamber (14A; 114A; 214A; 314A; 324A; 334A; 344A; 354A; 364A; 374A; 384A; 514A; 520A; 614A; 714A; 814A; 914A; 1014A; 1014A; 1550) and a second upper chamber (14B; 114B; 214B; 314B; 324B; 334B; 344B; 354B; 364B; 374B; 384B; 514B; 520B; 614B; 714B; 814B; 914B; 1014B; 1014B; 1540), wherein the second chamber is configured to accommodate the growing cells or microorganisms therein, and wherein a diameter of the pores is configured to allow a fluid flow solely between the first chamber and the second chamber and vice versa, and wherein the first barrier does not allow cells or microorganisms grown in the vessel to pass between the first chamber and the second chamber; - one or more fluid inlet ports (16; 116; 448) for introducing the fluid into the first chamber; - one or more fluid outlet ports (26, 27; 227; 126A-126D; 527) for allowing the fluid to exit from the second chamber; wherein the fluid flow comprises an upstream flow in a first direction from the first lower chamber towards the second upper chamber; and - an aligning barrier (12D; 1600) having a plurality of pores (1601, 1602) therein, the aligning barrier sealingly disposed within the space of the first chamber under the first barrier, the aligning barrier configured to align the fluid flow when the fluid flows in the first direction, to control the velocity of the fluid when the fluid flows in the first direction, and to prevent bubbles passage, wherein the first barrier and the aligning barrier are disposed such that the fluid flows in the first direction from the aligning barrier to the first barrier, wherein at least the second chamber comprises an increasing transversal cross sectional area from the bottom to the top of the second chamber, configured to provide a fluid velocity gradient in the fluid disposed within the second chamber when the fluid flows in the first direction, such that the velocity of the fluid decreases in a when the fluid flows in the first direction from the first barrier towards a top surface of the fluid. - a closed vessel enclosing a space therein; - a first barrier (12; 112; 212; 512; 522; 612; 712; 812; 912; 1012; 1112; 1505; 1512) having a plurality of pores therein, the first barrier is sealingly disposed within the space configured to divide the space into a first lower chamber (14A; 114A; 214A; 314A; 324A; 334A; 344A; 354A; 364A; 374A; 384A; 514A; 520A; 614A; 714A; 814A; 914A; 1014A; 1014A; 1550) and a second upper chamber (14B; 114B; 214B; 314B; 324B; 334B; 344B; 354B; 364B; 374B; 384B; 514B; 520B; 614B; 714B; 814B; 914B; 1014B; 1014B; 1540), wherein the second chamber is configured to accommodate the growing cells or microorganisms therein, and wherein a diameter of the pores is configured to allow a fluid flow solely between the first chamber and the second chamber and vice versa, and wherein the first barrier does not allow cells or microorganisms grown in the vessel to pass between the first chamber and the second chamber; - one or more fluid inlet ports (16; 116; 448) for introducing the fluid into the first chamber; - one or more fluid outlet ports (26, 27; 227; 126A-126D; 527) for allowing the fluid to exit from the second chamber; wherein the fluid flow comprises an upstream flow in a first direction from the first lower chamber towards the second upper chamber; and - an aligning barrier (12D; 1600) having a plurality of pores (1601, 1602) therein, the aligning barrier sealingly disposed within the space of the first chamber under the first barrier, the aligning barrier configured to align the fluid flow when the fluid flows in the first direction, to control the velocity of the fluid when the fluid flows in the first direction, and to prevent bubbles passage,