Give reasons:
Sieve tubes does not contain nucleus but they are regarded as living cells.
Lysosomes are known as suicidal bags.
Raw tomatoes are green in color while ripened tomatoes are red in color.
Answers
1. Sieve tube cells are closely related to the companion cells via the plasmodesmata. At the start, they possess a nucleus, however, at the prime stage they lose the ribosomes, nucleus, and vacuoles and get segregated for the conduction of food. The nuclei of the companion cells monitor the activities of the sieve tube cells via plasmodesmata. Hence, even the mature sieve tubes are enucleated, they remain living.
2. With the destruction of the cell, one of the lysosomes bursts, discharging those digestive enzymes. The discharged enzymes then digest their own cell and eventually, the cell dies. Hence, lysosomes are known as the suicide bags of the cell.
3. The tomatoes comprise two pigments for photosynthesis, that is, chlorophyll, which is green, and lycopene, which is red. As the tomatoes grow, they comprise much less lycopene in comparison to chlorophyll that imparts them the green color.
As the tomato ripens, its color begins to modify from green to yellow and then finally to red. This is because of the dissociation of chlorophyll that in turn produces a red carotenoid, lycopene.