9.3 Growth in Plants

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First found May 22, 2018

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Respond to changes in the environment
Regulate growth
Regulate reproduction and flowering
Regulate water loss
Regulate growth by controlling mitosis and
cell division
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Undifferentiated tissues that become many
different types of tissues
Located where plants exhibit major growth
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Apical Meristems
◦ Located at the top and the root
of plants
◦ Allows for growth of new leaves
and flowers
◦ Allows roots to grow down into
the soil
◦ Elongation of plant
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Lateral Meristems
◦ Responsible for secondary
growth in woody plants
◦ Allows them to increase stem
and root thickness
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Animal embryos have a fixed number of parts
that will develop and are considered
determinate growth
◦ 2 legs, 2 arms, 10 fingers/toes etc.
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The growth in plants is much different and is
considered to be INDETERMINATE.
◦ Meaning apical meristems can continue to increase
the lengths of stem and root throughout the life of
a plant and can produce any number of extra
branches of the stem or root. They can also
produce any number of extra leaves or flowers.
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Occur in the shoot apex
Provide cells needed for extension of the
stem at that location
Also important for development of leaves.
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A directional movement in plants in response
to a stimulus
Type of Tropism
Response
Phototropism
Response to light
Gravitropism
Response to gravity
Thigmotropism
Response to touch
Thermotropism
Response to temperature
Chemotropism
Response to substance
Hydrotropism
Response to water
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Responsible for phototropism
Affects cells on the dark side of the plant
◦ causes the cells away from light to elongate
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When light shines directly down on a plant
shoot auxin is equally distributed this causes
the plant to grow straight
This hormone is released in abundance of
blue light in the shoot tip.
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Auxin efflux pumps can set up concentration
gradients of auxin in plant tissue.
◦ Moves Auxin from cytoplasm to cell wall
◦ Lower concentration on light side and higher
concentration on dark side.
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Auxin influences cell growth by changing the
pattern of gene expression.
◦ These genes cause secretion of H+ ions into cell
walls that loosen connections in the cellulose fibers
that allow cells to expand.
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The practice of rapidly multiplying stock plant
material to produce a large number of plants,
using modern plant tissue culture methods.
◦ Can create virus-free strains of existing plants
◦ Can propagate rare species - Orchids
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Uses tissue from shoot apex, nutrient agar
gels and growth hormones
Used in plants to increase population faster
than seeding time would allow
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