Question

When the stems of cut flowers are held in concentrated \(\mathrm{NaCl}(\mathrm{aq}),\) the flowers wilt. In a similar solution a fresh cucumber shrivels up (becomes pickled). Explain the basis of these phenomena.

Short answer

The flowers wilt and the cucumber shrinks due to the process of osmosis. The water inside both the flower stems and the cucumber, where it is in higher concentration, moves towards the concentrated NaCl solution, which is of lower concentration. This movement of water from a higher to a lower concentration across a semi-permeable membrane is osmosis and results in wilting of flowers and shrinking of cucumbers due to water loss.

Step-by-step solution

Understand Osmosis

Osmosis is a type of diffusion. In osmosis, water molecules move from an area of high concentration (dilute solution) to an area of low concentration (concentrated solution) across a semi-permeable membrane.

Effect of Osmosis on Cut Flowers

When the stem of a cut flower is placed in a concentrated NaCl solution, the water inside the flower's stem (where it is in higher concentration) flows out towards the NaCl solution (where it is in lower concentration). This water loss due to osmosis causes the flower to wilt.

Effect of Osmosis on Cucumbers

Similarly, when a fresh cucumber is placed in a concentrated NaCl solution, the water inside the cucumber (where it is in higher concentration) moves out towards the NaCl solution (where water is in lower concentration). Loss of water due to osmosis causes the cucumber to shrivel up and become 'pickled'.

Key concepts

Diffusion

Diffusion is a fundamental concept in science, focusing on the movement of molecules. This movement occurs naturally, as molecules spread out from areas of high concentration to areas of lower concentration.

Imagine placing a drop of food coloring in water. Over time, the color disperses throughout until evenly distributed. This is diffusion in action! It's all about balancing concentration levels across a space.

In biological systems, diffusion is crucial for nutrient and gas exchange. Cells rely on diffusion to receive oxygen and release carbon dioxide. It's a passive process, needing no energy because molecules move along a concentration gradient, balancing the concentration gradually.

Semi-permeable membrane

A semi-permeable membrane is a special type of barrier. It allows certain substances to pass through while blocking others. Think of it like a sieve or filter. This selectivity is essential for many processes in living organisms.

The cell membrane is a common example of a semi-permeable membrane. It permits the passage of water, oxygen, and small nutrients, but restricts larger molecules and certain ions. This control helps maintain the cell's internal environment, a process known as homeostasis.

This selective permeability is vital for osmosis, where water molecules pass through the membrane to balance concentrations on both sides.

Hypertonic solution

Understanding a hypertonic solution is key to grasping the phenomena of wilting and shriveling discussed in the exercise. A hypertonic solution has a higher concentration of solutes compared to the fluid within the cells that are exposed to it.

When cells (like those in a flower or cucumber) are placed in a hypertonic solution, water molecules inside the cells move out through the semi-permeable membrane. This outward movement is osmosis.

The loss of water leads cells to shrink, causing plants to wilt or food items like cucumbers to become shriveled or even pickled. This concept underpins why flowers wilt in salt water and how pickles are made from cucumbers!