Before we move towards the complex and difficult terms of the chapter, let's try and understand what this chapter 11 transportation in animals and plants is really about. 

 

Any flowering plant will have a set of movements and processes to transport various materials like food, water, minerals, and nutrients throughout the plant body. The transport can be small as well as long. For instance, it can be the transfer between two cells via cell membrane or water or minerals from the root to the leaves and stem. Depending upon the length of the transportation, the time taken to complete the transportation varies as well. 

 

If we're talking about the transport of water and minerals through the different cells, then the process takes place by diffusion or cytoplasmic streaming. On the other hand, if the transportation is complicated, it may take a longer route. This takes place with the help of the xylem and phloem. It is known as translocation.

 

As discussed earlier, the transfer of various materials occurs throughout the plant due to various ways and means. It can either be one way, i.e. unidirectional or in two ways, i.e. bidirectional. Let's discuss them in detail: 

 

1. Diffusion 

In this process, the ions or molecules move from higher concentration to lower concentration. It does not involve the spending of energy. However, the rate of diffusion is extremely slow, and this process can take a long time. Any form of matter, be it solid, liquid, or gas, can be transferred through this process. It is the only method through which gases are transferred in plants. 

 

Diffusion is affected by: 

• • • • Temperature 
      • Pressure
      • Density 
      • Membrane permeability 
      • Concentration gradient

     2. Facilitated Diffusion 

In this type of diffusion, the rate is dependent solely on the size of the molecules; the smaller the size, the faster it will travel. The solubility of the molecules in the lipids also determine the rate of diffusion. Transport proteins are extremely important in diffusion.

 

This process is called facilitated diffusion. There is no movement from low to high concentration. The rate is maximised when all the protein is utilised.

Facilitated Diffusion is extremely selected and allows only a few substances to transfer. 

 

There are two transport proteins present. One is known as carrier proteins and the other as channel proteins. Carrier proteins bind to the solute that will be transported and then delivered to its destination. Channel proteins form channels for easy diffusion. 

 

About facilitated diffusion, there's also the concept of:

• • • • • Symport: Both the molecules that cross the membrane move in the same direction.
        • Antiport: In this, the molecules tend to move in the opposite direction.
        • Uniport: When a molecule moves independently, it is called uniport..

      3. Active Transport 

This type of transport uses energy in the form of ATP to facilitate the transfer of molecules against the concentration gradient. It has movable carrier proteins that are called pumps. They can help in transporting materials from low concentration to high concentration. They are specific in determining the materials that are being transferred.

Comparison of all means of transportation 

Water is essential for all the processes that take place in a plant. Some of its importance are: 

• • • • It is important for all the physiological processes that take place in plants as well as animals.

      • The protoplasm of cells is made up of water. All the minerals are dissolved in it. 

      • Plants absorb a lot of water and release it back in the form of transpiration.

      • It helps in plant growth.

Water potential is an important concept that we need to understand. It is defined by pressure potential and solute potential. 

Some of the important points to note about water potential are:

• • • • The more the concentration of water, the more will be its kinetic energy. Kinetic energy is also the water's potential. 

      • Water potential is measured in Pascal (Pa). 

      • At standard temperature and pressure, the water pressure of pure water is counted as zero.

      • The lowering of water potential due to the dissolution of the solute is called solute potential. It is always negative.

      • Suppose pressure is applied to pure water, its potential decreases. Remember, the pressure should be greater than atmospheric pressure. It is positive. 

      • The relationship of water potential with solute and pressure potential is:

Osmosis 

The diffusion of water or other materials across a semipermeable membrane is called osmosis. In this, water moves from higher to lower concentrations until an equilibrium is established. 

 

Osmotic pressure is defined as the pressure needed to prevent water from diffusion. The more the concentration of solute, the greater the osmotic pressure. Osmotic pressure is equal to osmotic potential. However, the sign used for both is different. One is positive, while the other is negative.

• • If the surrounding solution has a pressure that can balance the cytoplasmic osmotic pressure, the solution is isotonic. 

  • If the surrounding solution is dilute, it is a hypotonic solution. The cells swell up in this case. 

  • If the surrounding solution is concentrated, it is a hypertonic solution that can cause the cells to shrink.

Check out a few more important terms that you should know about-

 

• • Plasmolysis: In this, the cytoplasm shrinks away from its wall due to the presence of hypertonic solution. The pressure may be reversible if the solution is hypotonic.

• • Imbibition: In this, water gets absorbed by colloids and causes an increase in volume.

  • Turgor Pressure: The pressure that builds up against the cell wall due to the movement of water inside is known as turgor pressure.

When the transfer of water, minerals, or nutrients has to take place for long distances, it employs a mass or bulk flow system.

Mass Flow is the movement of substances in masses or bulks from one point to another due to the pressure difference. They move at the same speed. 

 

Bulk Flow is developed by a positive or negative hydrostatic pressure gradient. 

 

Translocation is the movement of various substances through conducting or vascular tissues present in plants. The tissues associated with translocation are the xylem and phloem.

 

Xylem transports water, salts, minerals, and hormones from the roots to the other parts.

Phloem transports inorganic solutes from leaves to the other parts of plants.

It is the process of loss of water by the stomata of plants. It occurs by evaporation. Stomata is responsible for the exchange of gases through the leaf pores. The opening or closing of the stomata is governed by the guard cells. 

 

When there is an increase of turgidity in the guard cells, the outer walls bulge out and form a crescent shape. This marks the opening of the guard cells. 

 

When they lose turgidity due to the loss of water, the thin walls regain their shape, and this marks the closing of the guard cells.

Transpiration is affected by: 

• • Temperature 

  • Sunlight

  • Wind Speed 

  • Humidity

 

The minerals enter the roots by active absorption. The reasons include:

• • The concentration of ions in roots > The concentration of ions in the soil.

  • Ions in the soil can not move across cell membranes.

  • Minerals are moved from older parts of the plant to new and budding parts.

  • The sink of mineral elements are leaves, apical meristem, growing fruits and flowers, and so on. 

  • ATP is needed for active absorption. 

  • The elements that can move swiftly are nitrogen, sulphur, and phosphorus.

As we know, the transport of food or minerals takes place through the phloem. Sucrose (food) is transported in that way. The part where the food is synthesised is called the source. The destination of the food is called a sink. 

The direction in which phloem transports sucrose is always bi-directional. Phloem sap consists of water and sucrose mainly, but other hormones are also transmitted sometimes.

 

Pressure or Mass Flow Hypothesis

The sucrose moves into the companion cells and further into sieve tube cells by the process of active transport. A pressure gradient is created that stimulates the movement.

The sieve tube cells of phloem possess a column with holes in them. The cytoplasmic strands pass through this hole and create a filament. That's how the sap moves in the phloem.

At the sink (destination), it is moved or secreted as complex carbohydrates.

      1. What are the topics that are included in Chapter 11, Biology Class 11? 

 The topics are means of transport, plant-water relations, transpiration, long-distance transport of water, uptake and transport of minerals, and phloem transport.

      2. What causes the opening and closing of guard cells? 

 The increase or decrease in turgidity.

      3. Why would you prefer class 11 Biology Chapter 11 NCERT Solutions prepared by experts? 

 It will give a detailed and clear view of all the important topics in ‘Transport in plants’ and prepare you for all the major examinations.