Osmosis: Videos & Practice Problems

Osmosis is a vital biological process defined as the passive diffusion of water across a semi-permeable membrane, such as a cell membrane. This process does not require energy, distinguishing it from active transport mechanisms. In osmosis, the solvent, primarily water in biological contexts, moves in response to solute concentrations on either side of the membrane.

The concept of tonicity is crucial in understanding osmosis, as it describes the relative concentration of solutes in a solution. Tonicity can be categorized into three key terms: hypotonic, isotonic, and hypertonic. A hypotonic solution has a lower solute concentration compared to another solution, which can be remembered by the prefix "hypo," meaning low. Conversely, a hypertonic solution has a higher solute concentration, indicated by the prefix "hyper," which signifies excess. An isotonic solution has equal solute concentrations on both sides of the membrane, with "iso" meaning equal.

These terms are comparative; they only make sense when discussing two regions, typically the inside and outside of a cell. For example, if the outside solution has a lower concentration of solutes than the inside, it is labeled hypotonic, while the inside is hypertonic. If the concentrations are equal, both are isotonic. Understanding these relationships is essential for predicting the direction of water flow during osmosis, which will be explored further in subsequent discussions.

In this example, we are examining the concept of tonicity, which refers to the relative concentration of solutes in solutions separated by a semipermeable membrane. Specifically, we are comparing the solute concentration outside a red blood cell to that inside the cell. The outside solution has a solute concentration of 10%, while the inside of the cell has a much lower concentration of 0.1%.

To determine the tonicity of the outside solution, we need to identify the term that describes a solution with a higher solute concentration compared to another. The relevant terms are:

• Hypotonic: A solution with a lower solute concentration compared to another solution.
• Isotonic: A solution with equal solute concentration compared to another solution.
• Hypertonic: A solution with a higher solute concentration compared to another solution.

Given that the outside solution has a higher solute concentration (10%) than the inside of the cell (0.1%), we classify the outside solution as hypertonic. Conversely, the inside of the cell, with its lower solute concentration, is classified as hypotonic.

Thus, the correct answer to the problem is that the outside solution is hypertonic, corresponding to the answer option C. This understanding of tonicity is crucial in biological contexts, particularly in processes such as osmosis, where water moves across cell membranes in response to solute concentration gradients.

Tonicity plays a crucial role in understanding the direction of osmosis, which is the diffusion of water across a semi-permeable membrane. Biological membranes allow certain substances to pass while blocking others, particularly solutes. When solutes cannot diffuse across the membrane, water will move instead. This movement is characterized by the principle that water always flows from hypotonic solutions, which have a lower solute concentration, to hypertonic solutions, which have a higher solute concentration. The goal of this movement is to dilute the hypertonic solution, ultimately striving for isotonicity, where solute concentrations are equal on both sides of the membrane.

It is essential to clarify the terms involved: hypotonic solutions contain a higher concentration of water and a lower concentration of solute, while hypertonic solutions have a lower concentration of water and a higher concentration of solute. This distinction is vital because, although it may seem counterintuitive, water moves from areas of higher water concentration to areas of lower water concentration, which corresponds to the solute concentrations. Thus, when solutes cannot diffuse, water compensates by moving towards the hypertonic solution.

In summary, the key takeaway is that water will always move from hypotonic to hypertonic solutions, effectively balancing solute concentrations across the membrane. This understanding is fundamental for solving problems related to osmosis and tonicity in biological systems.

Understanding the effects of environmental tonicity on cells is crucial in biology, particularly in the context of osmosis. Water movement across a membrane occurs from hypotonic solutions, where solute concentration is lower, to hypertonic solutions, where solute concentration is higher. This principle is essential for grasping how cells respond to different external environments.

When cells are placed in a hypotonic environment, water enters the cells, causing them to swell, much like a balloon inflating with air. This swelling can lead to cell lysis, or bursting, particularly in animal cells, which lack a protective cell wall. For instance, red blood cells in a hypotonic solution may expand until they rupture, which is detrimental to their survival. In contrast, plant cells, equipped with a rigid cell wall, can withstand the influx of water without bursting. Instead, they benefit from increased turgor pressure, which is the pressure exerted by the fluid inside the cell against the cell wall, allowing them to maintain structural integrity and thrive.

In isotonic environments, where the solute concentration is equal inside and outside the cell, water moves in and out at equal rates. This balance means that the size of the cell remains stable, making isotonic conditions ideal for animal cells. However, while plant cells can survive in isotonic conditions, they do not prefer them since the turgor pressure is not maximized, leading to less structural support.

Conversely, in hypertonic environments, where the external solute concentration is higher, water exits the cell, causing it to shrivel and dehydrate. This process is known as crenation in animal cells, while in plant cells, it results in plasmolysis, where the cell membrane pulls away from the cell wall due to loss of turgor pressure. Both conditions are unfavorable, leading to potential cell death if the environment remains hypertonic for an extended period.

In summary, the relationship between tonicity and cellular health is vital. Hypotonic environments can lead to cell swelling and potential lysis in animal cells, while plant cells thrive due to increased turgor pressure. Isotonic conditions are optimal for animal cells, whereas plant cells prefer hypotonic environments for maximum turgor pressure. Hypertonic environments, however, are detrimental to both cell types, leading to dehydration and structural damage.