Question

1. Describe simple and facilitated diffusion in passive transport?

a. simple diffusion

b. facilitation diffusion

2. Describe osmosis?

Answer 1

1

Answer :-

Cell membranes are selectively permeable, regulating which substances can pass through, Selective permeability is essential to cells’ ability to obtain nutrients, eliminate wastes, and maintain a stable interior environment different than that of the surroundings (maintain homeostasis).

The simplest forms of transport across a membrane are passive. Passive transport does not require the cell to expend any energy and involves a substance diffusing down its concentration gradient across a membrane. A concentration gradient is a just a region of space over which the concentration of a substance changes, and substances will naturally move down their gradients, from an area of higher to an area of lower concentration.

a, Simple Diffusion

Simple diffusion is the process by which solutes are moved along a concentration gradient in a solution or across a semipermeable membrane. Simple diffusion is carried out by the actions of hydrogen bonds forming between water molecules and solutes. Water molecules move in to surround individual solute molecules, which maximizes hydrogen bonding. Hydrogen bonds are extremely temporary, however, and the solution is constantly stirred as a result. This helps distribute the solute evenly throughout the solution. If the molecules are small enough, this simple diffusion can happen across cell membranes, between the individual phospholipids that make up the membrane. Water can move along its concentration gradient through a cell membrane in this manner, a form of simple diffusion known as osmosis.

b Facilitated Diffusion

Cell membranes often incorporate specialized membrane proteins which help transport substances across the membrane. This is known as facilitated diffusion. Facilitated diffusion includes both the active and passive transport of solutes across the membrane. Active transport uses ATP to provide energy to the proteins providing the transport. Unlike in simple diffusion, molecules can be moved against their gradient using active transport systems. Simple diffusion is present in a number of biological systems, including the delivery of oxygen, water, and other small molecules to the cells of the body. While many solutes have the ability to traverse the membrane via simple diffusion, cells will often have protein channels to help speed the process.

2

Answer

Osmosis is the movement of water through a semipermeable membrane according to the concentration gradient of water across the membrane, which is inversely proportional to the concentration of solutes. Semipermeable membranes, also termed selectively permeable membranes or partially permeable membranes, allow certain molecules or ions to pass through by diffusion.

While diffusion transports materials across membranes and within cells, osmosis transports only water across a membrane. The semipermeable membrane limits the diffusion of solutes in the water.

Types of Osmosis

Osmosis is of two types:

• Endosmosis– When a substance is placed in a hypotonic solution, the solvent molecules move inside the cell and the cell becomes turgid or de-plasmolyzes. This is known as endosmosis.

• Exosmosis– When a substance is placed in a hypertonic solution, the solvent molecules move outside the cell and the cell becomes flaccid or plasmolyzes. This is known as exosmosis.

Solvents and Solutes

Osmosis deals with chemical solutions. Solutions have two parts, a solvent and a solute. When solute dissolves in a solvent, the end product is called a solution. Salt water is an example of a solution; salt is the solute, and water is the solvent.

Types of Solutions

In biology, there are three different types of solutions that cells can be in: isotonic, hypotonic, and hypertonic. Different types of solutions have different impacts on cells due to osmosis.

Isotonic

An isotonic solution has the same concentration of solutes both inside and outside the cell. For example, a cell with the same concentration of salt inside it as in the surrounding water/fluid would be said to be in an isotonic solution. Under these conditions, there is no net movement of solvent; in this case, the amount of water entering and exiting the cell’s membrane is equal.

Hypotonic

In a hypotonic solution, there is a higher concentration of solutes inside the cell than outside the cell. When this occurs, more solvent will enter the cell than leave it to balance out the concentration of solute.

Hypertonic

A hypertonic solution is the opposite of a hypotonic solution; there is more solute outside the cell than inside it. In this type of solution, more solvent will exit the cell than enter it in order to lower the concentration of solute outside the cell.

How Osmosis Affects Cells

Osmosis affects plant and animal cells differently because plant and animal cells can tolerate different concentrations of water. In a hypotonic solution, an animal cell will fill with too much water and lyse, or burst open. However, plant cells need more water than animal cells, and will not burst in a hypotonic solution due to their thick cell walls; hypotonic solutions are ideal for plant cells. The optimal condition for an animal cell is to be in an isotonic solution, with an equal amount of water and solutes both inside and outside. When a plant cell is in an isotonic solution, its cells are no longer turgid and full of water, and the leaves of the plant will droop. In a hypertonic solution, water will rush out of both animal and plant cells, and the cells will shrivel (in plants, this is called plasmolyzation). This is why slugs and snails shrivel and die when salt is sprinkled onto them; water leaves their cells in order to balance the higher concentration of salt outside the cells.