Which plant hormone is primarily responsible for apical dominance?
A. Gibberellin
B. Ethylene
C. Cytokinin
D. Auxin
Answer: Option D
Solution (By JKExamLibrary)
Auxin (indole-3-acetic acid) produced at the shoot apex suppresses the growth of lateral buds, a phenomenon called apical dominance. Removing the apex allows lateral buds to grow. Cytokinin promotes cell division and counteracts apical dominance. Gibberellin stimulates stem elongation, and ethylene is involved in fruit ripening and senescence. The auxin-cytokinin ratio determines root and shoot differentiation in tissue culture.
Explanation:
Acetobacter aceti and related species oxidize ethanol to acetic acid (vinegar) in the presence of oxygen. This is an aerobic fermentation process. Lactobacillus produces lactic acid, Pseudomonas can spoil food, Bacillus includes various industrial strains. Vinegar is used as a condiment and preservative.
Consider statements about the cell wall: 1. Plant cell walls are made of cellulose. 2. Fungal cell walls contain chitin. 3. Bacterial cell walls contain peptidoglycan. Which are correct?
Explanation:
The cell wall composition varies across kingdoms. Plant cell walls are primarily composed of cellulose, a complex polysaccharide. Fungal cell walls are characterized by the presence of chitin, providing structural rigidity. Bacterial cell walls consist of peptidoglycan (murein). Therefore, all three statements accurately describe the cell wall composition of these respective groups.
Explanation:
The Haversian system (osteon) is the characteristic structural unit of compact (cortical) bone in mammals. It consists of a central Haversian canal (containing blood vessels and nerves) surrounded by concentric layers of calcified matrix called lamellae. Between the lamellae are small spaces called lacunae, which house osteocytes (bone cells). Canaliculi connect the lacunae. Bird bones are pneumatic (hollow), and cartilage lacks Haversian systems.
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