`star` Uptake of Mineral Ions
`star` Translocation of Mineral Ions


● `color{violet}("Plants")` obtain their carbon and most of their `color{brown}("oxygen from" CO_2)` in the atmosphere.

● However, their remaining `color{violet}("nutritional")` requirements are obtained from `color{brown}("minerals and water")` for hydrogen in the soil.

● Unlike water, all `color{violet}("minerals")` cannot be passively absorbed by `color{violet}("the roots.")`

● Two factors account for this:

(i) `color{violet}("Minerals")` are present in the soil as `color{brown}("charged particles (ions)")` which cannot move across cell membranes and

(ii) The concentration of `color{violet}("minerals")` in the soil `color{brown}("is usually lower")` than the concentration of `color{violet}("minerals in the root.")`

● Therefore, most `color{violet}("minerals")` must enter the root by `color{brown}("active absorption")` into the `color{violet}("cytoplasm")` of `color{violet}("epidermal cells. ")`

● This needs energy in the form of `color{brown}("ATP. ")`

● The active uptake of ions is partly responsible for the `color{brown}("water potential gradient ")` in roots, and therefore for the uptake of `color{violet}("water by osmosis.")`

● Some ions also move into the `color{brown}("epidermal cells passively.")`

● Ions are absorbed from the soil by both `color{brown}("passive and active")` transport.

● Specific proteins in the membranes of `color{brown}("root hair cells actively")` pump ions from the soil into the `color{violet}("cytoplasms")` of the `color{violet}("epidermal cells.")`

● Like all cells, the `color{brown}("endodermal cells")` have many `color{brown}("transport proteins")` embedded in their plasma membrane; they let some solutes cross the membrane, but not others.

● 𝘛𝘳𝘢𝘯𝘴𝘱𝘰𝘳𝘵 𝘱𝘳𝘰𝘵𝘦𝘪𝘯𝘴 𝘰𝘧 𝘦𝘯𝘥𝘰𝘥𝘦𝘳𝘮𝘢𝘭 𝘤𝘦𝘭𝘭𝘴 𝘢𝘳𝘦 `color{brown}("𝘤𝘰𝘯𝘵𝘳𝘰𝘭 𝘱𝘰𝘪𝘯𝘵𝘴")`, 𝘸𝘩𝘦𝘳𝘦 𝘢 𝘱𝘭𝘢𝘯𝘵 𝘢𝘥𝘫𝘶𝘴𝘵𝘴 𝘵𝘩𝘦 `color{brown}("𝘲𝘶𝘢𝘯𝘵𝘪𝘵𝘺 𝘢𝘯𝘥 𝘵𝘺𝘱𝘦𝘴")` 𝘰𝘧 𝘴𝘰𝘭𝘶𝘵𝘦𝘴 𝘵𝘩𝘢𝘵 𝘳𝘦𝘢𝘤𝘩 𝘵𝘩𝘦 𝘹𝘺𝘭𝘦𝘮.

● Note that the `color{violet}("root endodermis")` because of the layer of suberin has the ability to `color{violet}("actively transport ions")` in one


● After the `color{violet}("ions")` have reached xylem through `color{brown}("active or passive uptake,")` or a combination of the two, their further transport up the stem to all parts of the plant is through the `color{brown}("transpiration stream.")`

● The `color{brown}("chief sinks")` for the mineral elements are the growing regions of the `color{violet}("plant")`, such as the apical and lateral meristems, young leaves, developing flowers, fruits and seeds, and the `color{violet}("storage organs.")`

● `color{violet}("Unloading of mineral ions")` occurs at the `color{brown}("fine vein endings")` through `color{brown}("diffusion and active uptake")` by these cells.

● Mineral ions are frequently `color{brown}("remobilised,")` particularly from older, senescing parts.

● Older dying leaves export much of their `color{violet}("mineral")` content to `color{violet}("younger leaves.")`

● Similarly, before leaf fall in `color{brown}("decidous plants,")` minerals are removed to other parts.

● Elements most readily mobilised are `color{brown}("phosphorus, sulphur, nitrogen")` and `color{brown}("potassium.")`

● Some elements that are `color{violet}("structural components")` like `color{brown}("calcium")` are not remobilised.

● An analysis of the `color{violet}("xylem exudates")` shows that though some of the `color{violet}("nitrogen travels as inorganic ions,")` much of it is carried in the `color{brown}("organic form")` as amino acids and related compounds.

● Similarly, small amounts of `P` and `S` are carried as `color{brown}("organic compounds. ")`

● In addition, small amount of exchange of materials does take place between `color{brown}("xylem and phloem.")`

● Hence, it is not that we can clearly make a `color{brown}("distinction")` and say categorically that `color{violet}("xylem transports")` only `color{violet}("inorganic nutrients")` while phloem transports only `color{violet}("organic materials,")` as was traditionally believed.