The bell shaped curve indicates polygenic traits. A polygenic trait is controlled by multiple alleles. Hope this makes sense :)
The immune system<span> is made up of a network of cells, tissues, and organs that work together to protect the body. One of the important cells involved are white blood cells, also called leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms or substances.</span>
Answer:
1.It produces silk which is a high quality fibre
2.to destroy the gelatinious substance inside cocoon so as to obtain silk thread
3.To avoid it from hatching
4.they carry pollen grains while roaming plant to plant and help in cross pollination
