Consider statements about evolution: 1. Variation is necessary for evolution. 2. Natural selection acts on phenotype. 3. Evolution occurs in individuals. Which are correct? MCQ with Answer and Explanation

Explanation:
Louis Pasteur developed the first vaccine against rabies in 1885, using a weakened strain of the virus. He also invented pasteurization and made significant contributions to microbiology, disproving spontaneous generation. Jenner developed smallpox vaccine. Salk developed polio vaccine. BCG for TB was developed later. Pasteur's work laid the groundwork for modern immunology.

Explanation:
Peptide YY (PYY) is a gut hormone secreted by the L cells in the mucosa of the distal small intestine (ileum) and colon, primarily in response to food ingestion, especially fats. Its primary functions are related to the 'ileal brake' mechanism: it inhibits gastric emptying and pancreatic exocrine secretion, slowing down the transit of food through the upper GI tract to allow more time for digestion and absorption in the ileum. It also acts on the hypothalamus to reduce appetite, serving as a satiety signal.

Explanation:
The female gametophyte (embryo sac) in angiosperms is typically monosporic (develops from one functional megaspore). The megaspore undergoes three successive mitotic divisions to form an 8-nucleate, 7-celled structure. This includes 3 antipodal cells, 2 synergids, 1 egg cell, and 1 central cell containing 2 polar nuclei. Exam tip: Remember '8 nuclei, 7 cells' because the central cell has 2 nuclei but is 1 cell.