Transport materials across a cell membrane may occur in either active or passive movement. There are two types of cell to cell transport systems (short distance transport) that are namely:

1. Passive transport: A cell transport system that does not require any energy and proceeds through diffusion is called the passive transport of materials across cell membranes. Processes that involve passive transport are diffusion, facilitated diffusion, filtration, osmosis etc. 
2. Active transport: A cell transport system that requires energy to transport through cell membranes is the active transport system. 

Active Transport

In an active transport system, materials are moved against a concentration gradient, i.e. movement of materials from a low concentration gradient to a region of a high concentration gradient. Since there is a movement against the gradient in an active transport system, it requires energy, and thus, active transport is an energy-dependent process. 

• If two distinct molecules are coupled and transported, such active transport is called co-transport. 
• If the movement of transport of two molecules is in the same direction, it is called symport, and if the movement of transport of two molecules is in the opposite direction, it is called antiport. The uptake of glucose molecules in kidneys coupled to the parallel transport of sodium is an example of a symporter.
• An example of an antiporter is a sodium-potassium ion pump where both sodium ions and potassium are pumped in two opposite directions. 
• If there is the movement of a single molecule, then it is called uniport.

Passive Transport

Active transport examples in plants can be seen in the following cases:

• Ions move from the soil to the roots of plants.
• Chloride and nitrate are transported from the cytosol to the vacuole.
• Photosynthesis sugars move from leaves to the fruit.
• Calcium moves between cells with the help of ATP energy.
• Minerals move through a stem to different parts of the plant.
• Water moves from plant roots to other plant cells due to root pressure.

Factors that affect the diffusion rate in plants

Several factors, including the influence on the rate of diffusion;

1. Concentration gradient: The greater the concentration difference, the faster the diffusion. The slower the rate of diffusion becomes as the material distribution approaches equilibrium.
2. Mass of diffusing molecules: Because heavier molecules move more slowly, they diffuse more slowly. For lighter molecules, the opposite is true.
3. Temperature: As the temperature rises, so does the energy and thus the movement of the molecules, which increases the rate of diffusion. Lower temperatures reduce the energy of the molecules, resulting in a slower rate of diffusion.
4. Solvent density: As the density of a solvent increases, so does the diffusion rate. Because it is more difficult for the molecules to move through the denser medium, they slow down. Diffusion increases as the medium become less dense. Because cells primarily use diffusion to move materials within the cytoplasm, increasing cytoplasm density will impede material movement.
5. Solubility: As previously stated, nonpolar or lipid-soluble materials pass more easily through plasma membranes than polar materials, allowing for a faster diffusion rate.

Plasma membrane surface area and thickness: A larger surface area accelerates diffusion, whereas a thicker membrane slows it down.

Distance travelled: The slower the rate of diffusion, the greater the distance that a substance must travel. This imposes a size restriction on cells. Because nutrients and waste cannot reach or leave the cell’s centre, a large, spherical cell will die. As a result, cells must either be small, as in many prokaryotes or flattened, as in many single-celled eukaryotes.

Some of the examples of active transport in plants

• Chlorophyll is the significant colour utilised in photosynthesis. 
• However, there are a few kinds of chlorophyll and various shades that react to light, including red, brown, and blue colours. 
• These different colours might assist the channel with lighting energy to chlorophyll and shield the cell from photograph harm. 
• For instance, the photosynthetic protists called dinoflagellates, liable for the “red tides” that frequently expeditious alerts against eating shellfish, contain an assortment of light-touchy shades, including both chlorophyll and the red colours liable for their sensational tinge.

Conclusion :

Transport of materials across a cell membrane may occur in either active or passive movement. There are two types of cell to cell transport systems (short distance transport). We know that some biological/cellular membranes are semi-permeable, and some are selective. Semi-permeable membranes allow transport of only certain materials, i.e. large and charged molecules can not be transported. However, particular types of cellular membranes allow the movement of materials that can not freely cross.