Which statement best describes an immune response that occurs in invertebrates? a)cytotoxic t cells recognize infected cells and then bind to and destroy them. b)enzymes such as lysozyme break down the cell walls of harmful bacteria. c) t cells produce antibodies when a foreign antigen is recognized. d)natural killer cells engulf infected cells, destroying them via phagocytosis.

Ans.

Lysozymes are hydrolytic enzymes, synthesized and secreted by various organisms as a defense mechanism against bacterial infections. Invertebrates show type-i lysozymes (invertebrate lysozyme).

Lysozyme kills gram-positive bacteria by breaking bacterial cell walls as it prevents polymerization of components, required for cell wall synthesis. Invertebrates do not have immune cells, such as T cell, B cells, and natural killer cells.

Thus, the correct answer is 'option b). enzymes such as lysozyme break down the cell walls of harmful bacteria.'

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]

this age may represent the age of the earth's accretion, of core formation, or of the material from which the earth formed. this dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.