What is the focus of the passage?

Scientists have discovered more details about how plants use water. Their findings could help to engineer plants that grow better and more effectively in conditions with higher levels of carbon dioxide. Plants naturally take in carbon dioxide they need for photosynthesis, the process of changing light energy to chemical energy. The carbon dioxide enters the plants through tiny holes or pores on the surface of leaves. However, each time a plant takes in one molecule of carbon dioxide gas, it loses hundreds of water molecules. Scientists say plants lose ninety-five percent of the water they take in through these pores. Some plants’ pores can tighten to save water during conditions of high carbon dioxide. Other plants are not able to do this as well. Now, scientists know how these tiny pores tighten in plants. They identify proteins that control the tightening of a plant’s pores. The proteins are enzymes called carbonic anhydrates. They believe the enzymes could be changed in some plants to increase their ability to store water. Changing plants to save more water will not affect plant growth. This method might be used to help engineer food crops that are resistant to extremely dry conditions. It could help farmers meet a growing demand for food as water supplies decrease.