Answer:
Having considered how an appropriate primary immune response is mounted to pathogens in both the peripheral lymphoid system and the mucosa-associated lymphoid tissues, we now turn to immunological memory, which is a feature of both compartments. Perhaps the most important consequence of an adaptive immune response is the establishment of a state of immunological memory. Immunological memory is the ability of the immune system to respond more rapidly and effectively to pathogens that have been encountered previously, and reflects the preexistence of a clonally expanded population of antigen-specific lymphocytes. Memory responses, which are called secondary, tertiary, and so on, depending on the number of exposures to antigen, also differ qualitatively from primary responses. This is particularly clear in the case of the antibody response, where the characteristics of antibodies produced in secondary and subsequent responses are distinct from those produced in the primary response to the same antigen. Memory T-cell responses have been harder to study, but can also be distinguished from the responses of naive or effector T cells. The principal focus of this section will be the altered character of memory responses, although we will also discuss emerging explanations of how immunological memory persists after exposure to antigen. A long-standing debate about whether specific memory is maintained by distinct populations of long-lived memory cells that can persist without residual antigen, or by lymphocytes that are under perpetual stimulation by residual antigen, appears to have been settled in favor of the former hypothesis.
there is no clear evidence about plants evolving in the desert, or fossils of any kind of cactus despite their distribution over a large area. But, scientists are of the opinion that they acquired specific attributes millions of years ago, as a response to the vastly changing climate and conditions.
-Desert plant root system
A typical desert plant has a deep root system, which is a specific physical mechanism. As the roots grow deep down the soil, they absorb soil water, which is then transported to the upper portions of the plant.
-Desert plant leaves
Bear small foliage with waxy surface to minimize transpiration (loss of water through stomatal pores), which in turn, helps to conserve water.
They were able to show how to produce the best plant with the right amount of light that the plant is exposed to.
They were also able to show how to draw blood plasma from the blood by studying its response to various stimuli.
