CD4 and CD 8 are molecules present on the surface of T cells where they interact with major histocompatibility (MHC) Molecules.
CD4 and CD8 improve T cell signalling by attaching to MHC class II (CD4) or MHC class I (CD8) molecules on APCs.
- The association of CD4 with MHC class II significantly decreases the number of antigenic peptides necessary for T cell activation (5) and significantly boosts cytokine output by helper T cells.
The MHC molecules' wide polymorphism is their distinguishing trait.
- This polymorphism is crucial for T cell antigen recognition.
- A T cell detects antigen as a peptide bound by a specific allelic variation of an MHC molecule and will not identify the identical peptide bound by other MHC molecules.
- This type of T cell activity is known as MHC limitation.
Hence, the correct answer is option C
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The correct option is C.
The pyramid of numbers and the pyramid of biomass can be inverted but the pyramid of energy can not be treated in the same way. The pyramid of energy is a graphical representation of the flow of energy in the ecosystem. The ultimate source of energy in the ecosystem is the sun. The plants, which are called the producers use the energy of the sun to produce their own foods. It is the energy that the primary consumers obtained from the producers that will be pass on to others in the ecosystem. Thus, the value of the energy reduce gradually as it is passed from one level to another.
<h3><u>Answer;</u></h3>
d. a neuron recharges before it can fire again.
<h3><u>Explanation;</u></h3>
- <em><u>Refractory periods are a short phase in time following an action potential where another action potential cannot be generated. </u></em>
- <em><u>It is the period immediately following the transmission of an impulse in nerve or muscle, in which a neuron or muscle cell regains its ability to transmit another impulse. </u></em>
- There are two types of refractory period, that is the absolute refractory period and the relative refractory period. Absolute refractory period is the first part of a refractory period during which, the neuron will not fire again no matter how great the stimulation and this only lasts for a short time.
- Relative refractory period occurs when a stronger than usual stimulus is required to trigger the action potential before the neuron returns to resting state.
One grow/develop 2 reproduce 3 obtain/ use energy 4
It maintains homeostasis by controlling the body's temperature and releasing excess heat through sweat.
