11: Transport In Plants : Neet-xi-biology

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Qstn #1
What are the factors affecting the rate of diffusion?

Ans : Diffusion is the passive movement of substances from a region of higher concentration to a region of lower concentration. Diffusion of substances plays an important role in cellular transport in plants. Rate of diffusion is affected by concentration gradient, membrane permeability, temperature, and pressure. Diffusion takes place as long as there is a difference between the concentrations of a substance across a barrier. However, diffusion stops, when the concentrations of the substance on either side of the barrier become equal. The permeability of a membrane affects the rate of diffusion. Diffusion rate increases as membrane permeability increases. Changes in temperature and pressure values also affect the diffusion of substances. Pressure plays an important role in the diffusion of gases as gases diffuse from a region of higher partial pressure to a region of lower partial pressure.

Qstn #2
What are porins? What role do they play in diffusion?

Ans : Porins are types of proteins which form pores of large sizes in the outer membranes of plastids such as chloroplast, mitochondria and the membranes in bacteria. They help in facilitating the passive transport of small-sized protein molecules.

Qstn #3
Describe the role played by protein pumps during active transport in plants.

Ans : In plant cells, active transport occurs against the concentration gradient, i.e., from a region of lower concentration to a region of higher concentration. The process of active transport involves specific protein pumps. The protein pumps are made up of specific proteins called trans-membrane proteins. These pumps first make a complex with the substance to be transported across the membrane, using the energy derived from ATP. The substance finally gets liberated into the cytoplasm as a result of the dissociation of the protein-substance complex.

Qstn #4
Explain why pure water has the maximum water potential.

Ans : Water potential quantifies the tendency of water to move from one part to the other during various cellular processes. It is denoted by the Greek letter Psi or Ψ. The water potential of pure water is always taken as zero at standard temperature and pressure. It can be explained in terms of the kinetic energy possessed by water molecules. When water is in liquid form, the movement of its molecules is rapid and constant. Pure water has the highest concentration of water molecules. Therefore, it has the highest water potential. When some solute is dissolved in water, the water potential of pure water decreases.

#5-a

Diffusion and Osmosis

Ans : Diffusion and osmosis

Diffusion		Osmosis
1.	Diffusion is the passive movement of particles, ions, and molecules along the concentration gradient.	1.	Osmosis is the process in which the diffusion of a solvent (water) occurs across a semi-permeable membrane.
2.	It can occur in solids, liquids, and gases.	2.	It occurs in the liquid medium.
3.	It does not require a semi-permeable membrane.	3.	It requires a semi-permeable membrane.

#5-b

Transpiration and Evaporation

Ans : Transpiration and evaporation

Transpiration		Evaporation
1.	It occurs in plants.	1.	It occurs from any free surface and involves living and non-living surfaces.
2.	It is a physiological process.	2.	It is a physical process.
3.	It occurs mainly through the stomatal pores on plant leaves.	3.	It is occurs through any free surface.
4.	It is controlled by environmental factors as well as physiological factors of plants such as root-shoot ratio and number of stomata.	4.	It is entirely driven by environmental factors.

#5-c

Osmotic Pressure and Osmotic Potential

Ans : Osmotic pressure and osmotic potential

Osmotic pressure		Osmotic potential
1.	It is expressed in bars with a positive sign.	1.	It is expressed in bars with a negative sign.
2.	It is a positive pressure.	2.	It is a negative pressure.
3.	Its value increases with an increase in the concentration of solute particles.	3.	Its value decreases with an increase in the concentration of solute particles.

#5-d

Imbibition and Diffusion

Ans : Imbibition and diffusion

Imbibition		Diffusion
1.	Imbibition is a special type of diffusion. In this process, water is absorbed by solids and colloids, causing an enormous increase in volume.	1.	Diffusion is the passive movement of particles, ions, and molecules along the concentration gradient.
2.	It usually involves water.	2.	It involves solids, liquids, and gases.

#5-e

Apoplast and Symplast pathways of movement of water in plants.

Ans : Apoplast and symplast pathways of movement of water in plants

Apoplast pathway		Symplast pathway
1.	The apoplast pathway involves the movement of water through the adjacent cell walls of the epidermis and cortex. The movement of water is restricted at the casparian strips of the root endodermis.	1.	The symplast pathway involves the movement of water through the interconnected protoplasts of the epidermis, cortex, endodermis, and root pericycle.
2.	It is a faster process of water movement and water moves through mass flow.	2.	It is a slower process of water movement.

#5-f

Guttation and Transpiration.

Ans : Guttation and transpiration

Guttation		Transpiration
1.	It occurs usually at night.	1.	It occurs usually during the day.
2.	Water is lost from the leaves in the form of liquid droplets.	2.	Water is lost from the leaves in the form of water vapour.
3.	It occurs through the vein endings of leaves.	3.	It occurs through the stomata.
4.	It is an uncontrolled process.	4.	It is a controlled process.

Qstn #7
What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?

Ans : The water potential of pure water or a solution increases on the application of pressure values more than atmospheric pressure. For example: when water diffuses into a plant cell, it causes pressure to build up against the cell wall. This makes the cell wall turgid. This pressure is termed as pressure potential and has a positive value.