`star` Translocation
`star` Diffusion


● `color{violet}("Plants")` need to move molecules over very `color{brown}("long distances,")` much more than animals do; they also do not have a `color{violet}("circulatory system")` in place.

● Water taken up by the roots has to reach all parts of the plant, up to the very tip of the `color{violet}("growing stem.")`

● The `color{brown}("photosynthates")` or `color{violet}("food synthesised")` by the leaves have also to be moved to all parts including the root tips embedded deep inside the soil.

● Movement across short distances, say within the `color{violet}("cell")`, across the membranes and from `color{violet}("cell to cell")` within the tissue has also to take place.

● In a `color{violet}("flowering plant")` the substances that would need to be transported are `color{violet}("water, mineral nutrients,")` organic nutrients and `color{violet}("plant growth regulators.")`

● Over small distances substances move by `color{brown}("diffusion")` and by `color{brown}("cytoplasmic streaming ")` supplemented by `color{violet}("active transport.")`

● Transport over longer distances proceeds through the `color{violet}("vascular system")` (the xylem and the phloem) and is called `color{brown}("translocation.")`

● An important aspect that needs to be considered is the `color{violet}("direction of transport.")`

● In rooted plants, transport in `color{brown}("xylem")` (of water and minerals) is essentially unidirectional, from roots to the stems.

● `color{brown}("Organic and mineral nutrients")` however, undergo multidirectional transport.

● `color{violet}("Organic compounds synthesised")` in the `color{violet}("photosynthetic leaves")` are exported to all other parts of the `color{violet}("plant including storage organs.")`

● From the `color{violet}("storage organs")` they are later re-exported.

● The `color{violet}("mineral nutrients"0` are taken up by the roots and transported upwards into the stem, leaves and the growing regions.

● When any plant part undergoes `color{brown}("senescence")`, nutrients may be withdrawn from such regions and moved to the `color{violet}("growing parts.")`

● `color{violet}("Hormones or plant growth")` regulators and other chemical stimuli are also transported, though in very small amounts, sometimes in a strictly polarised or unidirectional manner from where they are `color{violet}("synthesised")` to other parts.

● Hence, in a `color{violet}("flowering plant")` there is a complex traffic of compounds (but probably very orderly) moving in different directions, each organ receiving some substances and giving out some others


● Movement by `color{brown}("diffusion")` is passive, and may be from one part of the `color{violet}("cell")` to the other, or from `color{violet}("cell to cell")`, or over short distances, say, from the intercellular spaces of the leaf to the outside.

● No `color{brown}("energy expenditure")` takes place.

● In `color{violet}("diffusion, molecules")` move in a random fashion, the net result being substances moving from regions of higher concentration to regions of `color{violet}("lower concentration.")`

● `color{violet}("Diffusion")` is a slow process and is not dependent on a `color{brown}("‘living system’.")`

● `color{violet}("Diffusion")` is obvious in gases and liquids, but diffusion `color{violet}("𝘪𝘯 𝘴𝘰𝘭𝘪𝘥𝘴")` rather than `color{violet}("𝘰𝘧 𝘴𝘰𝘭𝘪𝘥𝘴")` is more likely.

● `color{violet}("Diffusion")` is very important to plants since it the only means for `color{brown}("gaseous movement")` within the plant body.

● `color{violet}("Diffusion rates")` are affected by the gradient of concentration, the permeability of the membrane separating them, `color{violet}("temperature and pressure.")`