Biology

• What is the purpose of the cortical reaction in fertilization?

  It prevents polyspermy by modifying the zona pellucida
• Which structure in the sperm cell allows it to digest the zona pellucida?

  The acrosome, which contains hydrolytic enzymes
• Why do sperm cells have a high density of mitochondria in the midpiece?

  Mitochondria generate ATP needed for movement
• What are the stages of mitosis?

  • Prophase: Chromosomes condense
  • Metaphase: Chromosomes align at the equator
  • Anaphase: Sister chromatids separate
  • Telophase: Nuclear membranes reform
• How do transcription factors regulate gene expression?

  They bind to DNA near target genes to increase or decrease expression
• What is the role of epigenetics in gene expression?

  Epigenetic mechanisms like DNA methylation and histone modification alter expression
• What are totipotent, pluripotent, and multipotent stem cells?

  • Totipotent: Can become any cell type, including placenta
  • Pluripotent: Can become any cell type except placenta
  • Multipotent: Can become a limited range of cell types
• How does meiosis increase genetic variation?

  Through crossing over and independent assortment during gamete formation
• What is the function of xylem and how is it adapted?

  Xylem transports water and minerals; it has dead, lignified cells
• How does phloem differ from xylem?

  Phloem transports sugars using living sieve tube elements
• What role does cellulose play in the plant cell wall?

  Cellulose forms microfibrils with high tensile strength
• How do auxins influence phototropism?

  Auxins redistribute to the shaded side, promoting cell elongation
• What are seed banks and why are they important?


  Seed banks store seeds to preserve genetic diversity
• How is DNA used in classification?

  DNA barcoding compares genetic markers to classify organisms
• What are the advantages of sustainable agriculture?

  It conserves biodiversity and reduces environmental impact