Which of the following is a primary lymphoid organ?
A. Bone marrow
B. Spleen
C. Tonsils
D. Lymph node
Answer: Option A
Solution (By JKExamLibrary)
Primary lymphoid organs are where lymphocytes are produced and mature. Bone marrow (where B cells mature) and thymus (where T cells mature) are primary. Secondary lymphoid organs, like spleen, lymph nodes, and tonsils, are where mature lymphocytes encounter antigens and initiate immune responses. The bone marrow also is the site of hematopoiesis.
Explanation:
Charles Darwin's 1859 book 'On the Origin of Species by Means of Natural Selection' laid out the theory of evolution by natural selection. Mendel's work on heredity was published later, Wallace independently conceived natural selection but Darwin's book detailed the evidence comprehensively. Lamarck proposed earlier theories.
Explanation:
Phototropism (positive in shoots) is caused by the migration of auxin to the shaded side of the shoot, promoting cell elongation more on that side, causing the shoot to bend towards light. This asymmetric auxin distribution was demonstrated by Went's experiments. Auxin is sensitive to light and moves laterally. This is a growth response to directional light.
Explanation:
A test cross is used to determine the genotype of an individual expressing a dominant phenotype by crossing it with a homozygous recessive individual. The resulting phenotypic ratios reveal whether the dominant individual is homozygous (all offspring dominant) or heterozygous (1:1 ratio). It is a valuable tool in genetic analysis.
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