There are four distinct phases in the bacterial growth curves that is lag, log, stationary and death phase. The lag phase of the bacterial growth curve is characterized by very little increase in the cell number.
The growth rate of bacteria in the lag phase is slow because the medium is new to the bacterial culture and it requires time for bacteria have to adapt to the new cultural environment and to synthesize enzymes required for substrate utilization.
After getting adapt in their new environment bacteria starts to grow at an exponential rate. So little increase in cell number characterizes the lag phase.
In humans, the yolk sac is the
site of origin for blood cells and primordial germ cells. The human yolk sac is
a membrane located outside the embryo and it is connected by a tube through the
umbilical opening to the embryo's midgut. The yolk sac serves as an early site
for the formation of blood and in time, is incorporated into the primitive gut
of the embryo.
