After reading the paragraphs below, answer the questions that follow.
Over the next several decades, world population growth will necessitate as much as a 60% increase in food production, primarily in developing countries. These countries are often the most seriously affected by drought and salinity. Even if irrigation water is available, flooding fields with irrigation water leads to the gradual accumulation of sodium ions and other salts in the soil.
To respond to this growing problem, scientists at the University of Connecticut have genetically engineered a plant that can survive in salty soil and withstand extended drought conditions. The new transgenic plant contains a gene for an ion pump. Salt ions are transported from the soil and stored in vacuoles in the cytoplasm. The enhanced uptake of ions into their vacuoles in turn improves water retention in the transgenic plants and their resistance to drought. The concentration of solutes inside and outside plant cells affects the direction of water movement through osmosis.
The researchers found that the salt concentration in the cells of the new transgenic plants was significantly higher than in wild plants used as a control. In addition, the transgenic plants survived longer when deprived of water.
The experimental plants were more drought resistant because
◦ salt stored in their vacuoles was equal in amount to the salt in the soil.
◦ salt stored in their vacuoles enabled the cytoplasm to retain water better.
◦ water was stored in their vacuoles until the next rainfall.
◦ their vacuoles pumped water directly into the cytoplasm.
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