Show Menu

9.3 Growth in Plants Cheat Sheet by

Ib 2016 syllabus plant biology HL


Undiff­ere­ntiated cells in the meristems of plants allow indete­rminate growth
Meristems are tissues in a plant consisting od undiff­ere­ntiated cells capable of indete­rminate growth.
Meristems tissue can be divided into apical meristems and lateral meristems.
Apical meristems
Occur at the shoot and root tips.
Responsible for primary plant growth
Give rise to new leaves and flowers.
Lateral meristems
Occur at the cambium.
Responsible for secondary growth.
Produce bark.

Apical Growth in Roots and Shoots

The Role of Auxin in Apical Dominance


Auxin efflux pumps can set up concen­tration gradients of auxin in plant tissue.
Auxin efflux pumps can set up concen­tration gradients within tissues - changing the distri­bution of auxin within the plant.
These pumps can control the direction of plant growth by determ­ining which regions of plant tissue have high auxin levels.
Auxin efflux pumps can change position within the membrane and be activated by various factors.
Auxin has different mechanism of action in the roots of plants versus the shoot of plants.
Auxin stimulates cell elonga­tion, so high concen­tra­tions of auxin promote growth as cells become larger.
Auxin inhibits cell elonga­tion, so high concen­tra­tions of auxin limits growth as cells become relatively smaller.
Auxin influences cell growth rates by changing the pattern of gene expres­sion.
Auxin is a plant hormone that influences cell growth rates by changing the pattern of gene expression with a plant's cells. Its mechanism of action is different in roots and shoots as different gene pathways are activated in each tissue.
In shoots, auxin increases the flexib­ility of the cell wall to promote plant growth via cell elonga­tion.
Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall.
The resultant decrease in pH causes cellulose fibres within the cell wall to loosen (by breaking the bonds between them).
Additi­onally, auxin upregu­lates expression of expansins, which similarly increases the elasticity of the cell wall.
With the cell wall now more flexible, an influx of water (to be stored in the vacuole) causes the cell to increase in size.

Apical vs Lateral Meristems

Apical growth

Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and develo­pment of leaves.
Growth at the tips of roots and shoots is due to a combin­ation of cell enlarg­ement and repeated cell division.
Differ­ent­iation of the dividing meristems produces a variety of stem tissues and struct­ures.
In the stem, growth occurs in sections called nodes, while the remaining meristem tissue forms an inactive axillary bud.
These axillary buds have the potential to form new branching shoots.
Plant hormones control growth in the shoot apex.
The growth of the stem and the formation of new nodes is controlled by plant hormones released from the shoot tip, with one of the main groups of plant hormones involves in shoot and root growth being auxins.
When auxins are produced n the shoot apical meristem, it promotes growth in the shoot apex via cell elongation and devision.
Prevents growth in lateral buds, a condiment known as apical dominance.
Apical dominance ensures that a plant will use its energy to grow towards the light in order to outcompete other plants.
As the distance between the terminal and axillary bud increases, the inhibition of the axillary bud by auxin decreases.

Mechanism of Auxin Action in Plant Shoots


Plant shoots respond to the enviro­nment by tropisms.
Tropisms describe the growth or turning movement of an plant in response to a direct­ional external stimulus.
Photot­ropism is the growth movement in response to a unidir­ect­ional light source.
Geotropism is a growth movement in reposing to gravit­ational forces.
Hydrot­ropism is growth in response to a water gradient.
Thigmo­tropism is growth in response to tactile stimulus.
Both photot­ropism and geotropism are controlled by the distri­bution of auxin within the plant cells.
- in geotro­pism, auxin will accumulate on the lower side of the plant in response to the force of gravity.
- in photot­ropism, light receptors trigger the redist­rib­ution of auxin to the dark side of the plant.


Microp­rop­agation of plants using tissues from the shoot apex, nutrient agar gels and growth hormones.
Microp­rop­agation is a technique used to produce large numbers of identical plants from a selected stock plant.
Plants can reproduce asexually from meristems because they are undiff­ere­ntiated cells capable of indete­rminate growth.
- when a plant cutting is sued to reproduce asexually in the native enviro­nment it is called vegetative propag­ation.
- when plant tissues are cultured in vitro to reproduce asexually, it is called microp­rop­agation.
Steps of microp­rop­aga­tion:
1. Specific plant tissue (typically undiff­ere­ntiated shoot apex) is selected from the stock plant and steril­ised.
2. The tissue sample (explant) is grown on a sterile nutrient agar gel.
3. The explant is treated with growth hormones to stimulate shoot and root develo­pment.
4. The growing shoots can be contin­uously divided and separated to form new samples in the multip­lic­ation phase.
5. Once the root and shoot are developed, the cloned plant cane transf­erred to soil.
Use of microp­rop­agation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propag­ation of orchids and other rare species.
Rapid bulking
Desirable stock plants can be cloned via microp­rop­agation to conserve the fidelity of the selected characteristic.
This process is more reliable than selective breeding because new plants are geneti­cally identical to the stock plant.
This technique is also used to rapidly produce large quantities of plants created via genetic modifi­cation.
Virus-Free Strains
Plant viruses have the potential to decimate crops, and viruses typically spread through infected plants via the vascular tissue - which meristems do not contain.
Propagating plants from the non-in­fected meristems allows fro the rapid reprod­uction of virus-free plant strains.
Propag­ation of rare species
Microp­rog­agation is commonly used to increase numbers of rare or endangered plant species.
It is also used to increase numbers of species that are difficult to breed sexually.
It may also be used to increase numbers of plant species that are commer­cially in demand.


No comments yet. Add yours below!

Add a Comment

Your Comment

Please enter your name.

    Please enter your email address

      Please enter your Comment.

          Related Cheat Sheets

          SCENE SIX - A Streetcar Named Desire Cheat Sheet
          German grammar Cheat Sheet
          IB psychology revision sheet Cheat Sheet

          More Cheat Sheets by Arsh.b

          5.1 Evidence for evolution Cheat Sheet
          9.1 Oxidation and reduction Cheat Sheet
          19.1 Electrochemical Cells Cheat Sheet