BIOLOGY 2 Marks Questions

(1) Climactic Respiration : Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called respiratory climactic.
(2) Bakanae (Foolish Seedling): Some farmers of Japan saw plants with thin and yellow leaves, taller and less productive in the paddy fields. This disease of paddy was called Bakanae disease or foolish seedling disease. This disease is caused by a fungus called Gibberella fujikuroi. Yabuta, Yumiki and Hayashi isolated gibberellin from this fungus and named it gibberellic acid. They found that spraying the juice extracted from this fungus on healthy paddy plants also causes disease in them.

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There are mainly three stages of growth:
(i) Cell formation stage: In this stage, meristem cells divide and form new cells.
(ii) Cell elongation stage: Made up of meristems cells change their shape by increasing in length, width and volume.
(iii) Cell maturation stage: Elongated cells form permanent tissue as a result of various types of thickening on their cell wall.

Water, oxygen and nutrients are necessary for growth. The plant cells grow in size by cell enlargement which in turn requires water. Turgidity of cells helps in extension growth. Thus, plant growth and further development is intimately linked to the water status of the plant. Water also provides the medium for enzymatic activities needed for growth. Oxygen helps in releasing metabolic energy essential for growth activities. Nutrients (macro and micro essential elements) are required by plants for the synthesis of protoplasm and act as source of energy. In addition, every plant organism has an optimum temperature range best suited for its growth. Any deviation from this range could be detrimental to its survival. Environmental signals such as light and gravity also affect certain phases/stages of growth.

When the bud at the top of the main stem continues to grow, the lateral axillary buds below the main stem do not grow. This is called apical dominance. As soon as the top buds are cut, the side buds grow and make the bushes dense.