Why is plant growth "open"? And in arithmetic vs geometric growth, which daughter cell keeps dividing?

7 answers & replies

• [+][–]Meera Patel11thSample· 2mo ago

  On open growth: in animals, growth is largely confined to a period (it stops once the adult body plan and size is reached), and cell division happens in many tissues but not in a way that keeps adding new organs forever. Plants retain meristems, which are regions of self-perpetuating cells, so they keep forming new organs (leaves, flowers, roots) throughout life. That is what open means.

  Meristems: apical (root and shoot tips, give primary growth, increasing length), intercalary (in grasses, between mature tissues, at the base of the internodes; helps regeneration after grazing, e.g. in grasses), lateral (vascular cambium and cork cambium, secondary growth, increasing girth). Within one growing region there are three phases: meristematic, elongation and maturation.

  Report
• [+][–]Lakshmi TripathiDropperSample· 2mo ago

  In both arithmetic and geometric growth, both daughter cells go on to divide, the only difference is how fast the cells are dividing. Arithmetic is slow, steady division, geometric is fast division.

  Report

  • [+][–]Rahul DubeyDropperSample· 2mo ago

    Lakshmi, that's the exact point, and it's different. In arithmetic growth only one daughter cell keeps dividing, while the other differentiates and matures. So the number of dividing cells stays constant, and the length goes up by the same amount each time, linear. In geometric growth both daughter cells divide, so cell number doubles in each round and the growth is exponential. It is about how many cells go on dividing, not how quickly each divides.

    Report

    • [+][–]Sara Fernandes11thSample· 2mo agoAuthor

      ahhh that makes sense! it's about how many cells keep dividing. Now my curve notes are fixed, thank you Rahul bhaiya and everyone 🙏

      Report
• [+][–]Ishita GoyalDropperSample· 2mo ago

  Formulas: $L_t = L_0 + rt$: $L_t$ is length at time $t$, $L_0$ length at time zero, $r$ is the growth rate, elongation per unit time, and it's constant. Example: a root elongating at a constant rate.

  $W_1 = W_0 e^{rt}$: $W_1$ final size (weight, height, number etc.), $W_0$ initial size at the beginning of the period, $r$ is the relative growth rate (the ability of the plant to produce new plant material, an efficiency index), $t$ is time, $e$ is the base of natural logarithms.

  The geometric curve is sigmoid because there are three phases: lag (slow start), log/exponential (rapid growth), and stationary (slows down because nutrients become limiting).

  Report
• [+][–]Farhan ShaikhDropperSample· 2mo ago

  Measuring: no, you don't pick randomly, you pick what fits the object. NCERT's examples: growth of a pollen tube in terms of length, a dorsiventral leaf in terms of surface area, a mass of cells in a culture in terms of cell number, and fresh/dry weight for the whole plant or an organ. Fresh weight changes with the water level (a plant wilts and weight drops) so dry weight is the steadier measure of real growth. Hack: if the test question says "which parameter is used to measure growth in X" look at the shape of X: long and thin = length, flat = area, a cell mass = number.

  Report

  • [+][–]Aarav Kulkarni11thSample· 2mo ago

    dry weight tip is going into my checklist. fresh weight is basically water, lol.

    Report