After immersion in a 0.1 mol/dm³ KNO₃ solution, the potato tissue will appear relatively unchanged. The texture might be slightly firmer than the control (distilled water), but significant changes will not be immediately apparent. This is because the water potential outside the potato is very close to that inside, leading to minimal net movement of water.

In a 0.5 mol/dm³ KNO₃ solution, the potato tissue will show a noticeable change. The tissue will likely appear firmer and more turgid than in the 0.1 mol/dm³ solution. The cells will have taken up water, increasing the internal pressure and pushing against the cell walls. This is due to the higher concentration of solutes outside the potato cells, creating a lower water potential outside and causing water to move into the cells by osmosis.

Finally, after immersion in a 1.0 mol/dm³ KNO₃ solution, the potato tissue will appear significantly different. The tissue will be noticeably firmer and more rigid. The cells will be highly turgid, and the potato may feel quite hard. The high concentration of solutes outside the potato cells creates a much lower water potential outside, resulting in a large influx of water into the cells. This increased water uptake significantly increases the internal pressure, leading to the tissue becoming very firm. However, if the immersion time is extended, the potato tissue may eventually become waterlogged and potentially burst.

Explanation in terms of osmosis: Osmosis is the net movement of water across a semi-permeable membrane from a region of high water potential to a region of low water potential. In this experiment, the potato cells act as the semi-permeable membrane. The water potential inside the potato cells is higher than the water potential in the solutions of different concentrations. Therefore, water moves into the potato cells by osmosis, causing them to become turgid. The higher the concentration of solutes in the external solution, the lower the water potential outside the potato cells, and the greater the rate of water movement into the cells.

Water is an excellent solvent due to its polarity, which allows it to dissolve a wide range of substances, particularly ionic and polar molecules. This property is crucial for various life processes.

Digestion: Water is essential for the digestion of food. Saliva, which contains enzymes like amylase, is largely water. Water helps to dissolve the food particles, facilitating enzyme action and the breakdown of complex carbohydrates into simpler sugars. It also aids in the transport of digested food (chyme) through the digestive system. The watery environment within the digestive system allows for the diffusion of nutrients across the epithelial cells lining the gut.

Excretion: Water is the primary solvent for waste products in excretion. The kidneys filter blood, removing metabolic waste such as urea and excess salts. These waste products are dissolved in water to form urine. The water in urine helps to flush out these toxins from the body. Without water, these waste products would not be able to be effectively removed.

Transport: Water is the main component of blood, lymph, and sap, all of which are vital for transport. Blood is a complex solution where various substances like oxygen, carbon dioxide, nutrients, and hormones are dissolved in plasma, which is mostly water. This allows these substances to be transported throughout the body. In plants, water acts as a solvent for sugars produced during photosynthesis, which are transported via the xylem. The movement of sap through the vascular tissues relies on the solvent properties of water.

Key properties of water that contribute to its solvent ability:

• Polarity: The uneven distribution of electrons creates a positive and negative charge within the water molecule, allowing it to interact with and dissolve other polar molecules.
• Hydrogen Bonding: Water molecules form hydrogen bonds with each other and with other polar molecules, which helps to break apart ionic compounds and dissolve them.
• High cohesive properties: Water molecules are strongly attracted to each other, which helps to transport substances through the circulatory system.

Turgor pressure is crucial for plant rigidity. It acts like internal scaffolding, pushing the cell contents against the cell wall. This outward pressure makes the plant cells firm and prevents them from collapsing. The rigidity of the plant is directly related to the turgor pressure within its cells.

When turgor pressure decreases, the plant cells become flaccid. This happens when the plant loses water through transpiration or when the water potential in the cells is reduced. The loss of turgor pressure causes the cell contents to move to a lower concentration, reducing the pressure against the cell wall. As a result:

• The plant loses its rigidity and wilts.
• Leaves droop and become limp.
• The overall shape of the plant is altered.
• Photosynthesis can be reduced as the leaves are not in an optimal position for light absorption.