Given below is a table. Fill in the gaps.
| Property | Simple Diffusion | Facilitated Transport | Active Transport |
|---|---|---|---|
| Highly Selective | No | Yes | - |
| Uphill transport | - | - | Yes |
| Requires ATP | - | - | - |
| Property | Simple Diffusion | Facilitated Transport | Active Transport |
|---|---|---|---|
| Highly Selective | No | Yes | Yes |
| Uphill transport | No | No | Yes |
| Requires ATP | No | No | Yes |
Active Transport It uses energy to pump molecules against a concentration gradient. Hence, different proteins in the membrane play a major role in active transport.
Carrier protein involved in active transport is very specific in what it carries across the membrane.
Facilitated Transport In facilitated transport special proteins help in movement of substances across the membrane without the expenditure of ATP. Facilitated transport is very specific as it allows cell to select substances for uptake.
Simple Diffusion It is a physical phenomenon which involves the movement of water from higher concentration to lower concentration. It is not a selective process and do not require energy.
Water potential is a measure of free energy associated with water per unit volume $\left(\mathrm{JM}^{-3}\right)$. The water potential of pure water $\left(\psi_w\right)$ at atmospheric pressure is zero. The unit of water potential is bars or Pascal ( $1 \mathrm{mPa}=10$ bars).
Solute Potential The addition of solutes reduce water potential (to a negative value). This reduces the concentration of water. Hence, solutions have a lower water potential than pure water, the magnitude of this lowering due to dissolution of a solute is called solute potential or $\psi_{\mathrm{s}}$.
If some solute is dissolved in pure water, solution has fewer free water molecules and the concentration of water decreases, reducing its water potential.
Hence, all the solutions have a lower water potential than pure water. The magnitude of this lowering is due to dissolution of solute is called solute potential or $\psi_s . \psi_s$ is always negative. The more the solute molecules, the lower (more negative) is the solute potential $\psi_s$ water potential of a cell is affected by both solute and pressure potential.
The relationship can be illustrated as
$$\begin{aligned} &\text { Where, }\\ &\begin{aligned} & \psi_w=\psi_s+\psi_p \\ & \psi_w=\text { water potential } \\ & \psi_s=\text { solute potential } \\ & \psi_p=\text { pressure potential } \end{aligned} \end{aligned}$$
An onion peel was taken and
(a) placed in salt solution for five minutes.
(b) after that it was placed in distilled water.
When seen under the microscope what would be observed in (a) and (b)?
(a) Onion peel when placed in salt solution, shrinks as water from cells cytoplasm moves out of the cell i.e., hypertonic solution.
(b) When it is placed again back in distilled water, cell regains it's shape and absorbs water and become turgid (full of water) i.e., hypertonic solution.
Difference between apoplast pathway and symplast pathway is as follows
| Apoplast Pathway | Symplast Pathway |
|---|---|
| It consists of the non-living parts of plant body, i.e., cell walls and inter cellular spaces. There is a little resistance in the movement of water in apoplastic pathway. It is a faster process. |
It consist of living parts of plant body, i.e., protoplast connceted by the plasmodesmata. Some resistance occurs in the movement of water through symplast. It is a slightly slower process. |