Studied by 0 peoplewhen can a plant grow?
plant have indeterminate growth meaning that they can grow throughout their lives when conditions permit them
where in the plant is growth concentrated?
in meristem at the tip of the root and shoots which are made up of undifferentiated cells that go through mitosis
explain the concentred in the root and tips and shoots
as new cells form the cells at the very tip, or apex remain meristematic
the other cells first grow longer in the zone of elongation and then begin to specialise in the zone of differentiation
allowing plants to grow and produce the type of cells needed for functions of life
apical meristem refers to
growth areas, apical referring to the apex or tip of root or shoot
root apical meristem
the root apical meristem elongates the root and allows it to grow deeper into the ground and around obstacles as needed
root cap
root cap protects the meristem and sheds cells as the root grows through the soil
how many cells differentiate?
half of cells remain undifferentiated while the other half specialises and contributes to growth and development
mitosis and cell division in plants in the tip of the stem in apical meristem cause?
produces cells to increase the length of the stem and develop leaves, buds and any other above ground structures
apical meristem give rise to differentiated tissues that can be further differential and will develop into functioning leaves
the rpo cambium gives rise to the xylem and pholem
protoderm will become epidermis 3)ground meristem will become cortex and mesophyll
creates also dormant meristem in the axillary buds where the leaf joins the stem
these have the potential to grow into new shoots or branches
when plants sense a change in environmental conditions they respond in
-changing the number of cells produced by the meristem
altering the spatter of growth and specialisation to produce
ex: flowers in correct reasons
ex: chemicals to ward off insect attacks
Hormones
chemical messengers that carry information from one cell to another
hormones in plant are size and amount of concentration needed to start a reaction
small molecules and little concentration is needed to trigger a change in the organism
auxin
a plant hormone that synthesised in spical meristem and travels down the stem
what does auxin cause
causes cell elongation and inhibits the growth of axillary (side) buds in nods
the inhabitation of axillary buds cause (meaning of apical dominance)
the plant to grow vertically
what happens when the apex has grown enough
when the shoot apex has grown for enough above an axillary bud the auxin concentration becomes too low and inhibits the growth and the buds start to develop
what provides cell division and mitosis in the shoot apex meristem
provides cells needed for extension of the stem and development of leaves
plant tropism
the response to light and gravitropism/geotropism the response to gravity
what direction can plant grow with stimulus
can grow towards the stimulus (positive) or towards (negative)
shoots usually show positive phototropism and negative gravitropism thus the shoot receives maximum light energy for photosynthesis
meaning that they grow towards the direction of the light
and away from gravity which generally brings them towards the light
what do plants root generally show in terms of stimuli direction?
plant roots generally show positive gravitropism and negative phototropism meaning that they move away from light and towards gravity —> roots grow in soil
other tropism includes
other tropism include hydrotropism (water), chemotropism (chemicals), thigmotropism (growing in respond to touch)
many grow in negative thigmotropism allowing them to grow around obstacles
unique distractions of auxin allow roots and stems to grow unevenly turning in a specific direction
what happens whn light is present
auxin is produced at the shoot apex and diffuses evenly down the stem
when do plants use auxin transporters
is plant sense that light source is to the side of a stem it uses auxin transporters to redistribute auxin so that it accumulates on the side with the least light
cell of shaded side reacts to the increase concentration of auxin by growing faster than side of the stem in the light causing a bend towards the light source
auxin and gravitropism
the concentration of auxin that elongates shoot cells in the phototrophic response above inhibits the growth of cell in the root -in a root placed horizontally light from above and gravity in both cause redistribution of auxin so it accumulates on the lower shaded side -this causes inhibition of cell elongation in the shaded root cells while cells on the upper side elongates normally
effect of auxin and gravitropism
effect; bending towards gravity (away from light) showing positive gravities and negative phototropism
in shoot auxin control
Stem elongation , by increasing elongation of new cells formed by the apical meristem
Apical dominance , allowing the shoot to elongate before the axillary buds begin growing
Tropisms , allowing directional growth by causing different rates of cell elongation on different sides of the stem.
where is auxin produced
Auxin is produced in the shoot apical meristem but acts on other target cells in the plant
how is auxin transported mainly
most transported in the bulk flow of the phloem but that also move from other methods:
what is another way auxin is transported
a group of proteins called phototropic are produced to detect light intensity
when light is equally bright on all sides of the shoot tip—> auxin moves symmetrically downwards being pumped into and out of successive layers of cell through specialised protein pumps
plant cells have auxin influx carrier in there apical (top) membrane and auxin efflux carrier in their bottom (basal) cell membranes
allowing cells to move auxin continually downwards this even distribution of auxin leads to even cell growth and vertical extension of stem
what happens when there is different brightness of different sides of the plant
when there is different brightness on different side of the shoot, phototropism
cause some type of auxin carrier to increase on the internal lateral side membrane causes transport of auxin to the shaded part of plant and establishes a concentration grader
shaded side of shoot experiences greater cell elongation bending the stem towards the light
what happens when auxin accumulates in the shaded side
allow multiple responses including cell elongation that lead to phototropic or other tropic responses
effects of what happens when auxin accumulates in the shaded side
1)Auxin alters gene expression in several gene families. The expression of these genes is also linked to other factors in the cell, allowing auxin to trigger a wide variety of responses depending on the type of cell and environmental conditions.
Auxin stimulates the transcription of genes that produce proton pumps. 2)Auxin stimulates cell elongation in the stem.
Auxin stimulates proton pumps that use ATP to move protons (hydrogen ions, H ) out of the cytoplasm and into the cell wall.
A higher H+ concentration in the cell wall means the cell wall becomes more acidic (a decreased pH).
The acidic pH breaks bonds between cellulose fibres in the cell wall directly by disrupting hydrogen bonding and indirectly by activating pH-dependent expansin proteins that sever cellulose connections.
The reduced number of bonds between cellulose microfibrils makes the cell wall more flexible.
Cellulose fibres can slide apart as they are pushed by turgor pressure inside the cell, thus the cell elongates as the cell wall becomes softer and more flexible.
what is micropropagation
micropropagation is a technology that uses plant flexible growth patter to produce large numbers of clones from original parent plants
undifferentiateion and differentiation
meristemic plant cells are totipotent meaning that they can differentiate into any plant tissue plants have a larger ability to undo specialisation in their cells process called dedifferentiation
benefits of micropropagation
1)When a new variety of plant is created, micropropagation allows rapid increase in numbers of plants, known as 'bulking up' a new variety. Other methods of plant cultivation would take much longer. 2) Production of virus-free individuals of existing varieties. Even when a parent plant is infected with a virus, the virus is usually not found in the newly produced cells of the apical meristem. The sterile micropropagation technique allows uninfected individuals to be grown from an infected parent. 3) Production of orchids and other rare species. Orchids are delicate and difficult to breed, as well as difficult to grow from their tiny seeds. Micropropagation allows many individuals to be created from a callus, bypassing issues with breeding and germination.
outline steps of micropropagation
small tissue sample is taken usually from shoot apical meristem and sterilised
it is grown in a sterile medium with concentration of auxin that promote cell growth but not differentiation
produces a large mass of undifferentiated cells called callus
callus can then break up to create tiny cell sample that grow in a different medium this one with concentrations of hormones that trigger cell differentiation and plant development
outline role of gene exression in stem growth
undeffirentiated cells in meristems allow continued growth
meristems are regions of plants where cell division or mitosis occurs
plant growth is affected by changes in gene expression
changes in gene expression lead to cell elongation or flowering or differenitation
plant growth is affected by hormone auxin
auxin stimulates cell elongation in stem plain grow affected by tropism
light changes the distribution of efflux plump protein in the stem or light causes the auxin concentration to increase on the shade s
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