Download 9.3 Plant Growth

9.3 Plant Growth
3 types of plant tissue
 All plant tissues arise from meristematic tissue
 The plant version of stem cells
 During division one cell stays meristematic and the other differentiates
 Dermal:
 acts like a skin to the plant protecting against infection
 prevents water loss
 Ground tissue
 Photosynthesis
 Storage
 Support
 Secretion
 Vascular tissue
 Phloem and xylem
Apical Meristems
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Aka primary meristem or shoot apex
Occurs at the tips of the stem and roots
Responsible for primary growth of the roots and the stems
Allows the stem to grow longer
Lateral meristems
 Form from cambium cells
in the center of the
vascular bundles
 Vascular cambium:
found in the center of the
xylem and phloem
 Major component of wood
 Cork cambium
 Forms cork
 Occurs in the bark of the
tree

 Causes secondary growth
of the plant
 Results in an increase in
the width of the stem
9.1.6: Comparison of growth
Growth due to apical
meristem
Growth due to lateral
meristem
Occurs at the tips of the
roots and stems
Position of meristem
Occurs laterally between
primary phloem and
xylem
Product of embryonic
cells
Origin
Cambium – meristematic
cells left over from
primary growth
Produces initial tissues
Timing of activity
Functions in older stems
Epidermis, ground
tissues, primary phloem
and xylem
Cell products
Secondary phloem and
xylem
Increases length and
height
Outcome for stem
Increases width and
strengthens stem
Role of Auxin in phototropism
 Plant hormone
 Produced by cells undergoing
repeated cell division
 Highest concentration found in
the stem tips
 Causes positive phototropism
 Accumulates on the shade side
of the plant causing the plant to
grow towards the light
(phototropism – growth
towards the direction of light)
Other uses for Auxin
 Auxin changes the pattern of
gene expression during cell
growth
 Causes cell division in
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
meristematic cells
Causes differentiation of
phloem and xylem
Stimulates flower growth
Causes fruit production
without pollination – creates
seedless fruit
Can develop or suppress
lateral bud growth
9.3 Plant Reproduction
Differences between dicot and
monocot
 Dicot
 Example is a sunflower
 2 embryo seed leaves (cotyledons)
 Broad leaves with veins forming a network.
 Branched roots
 Parts of the flower in 4’s or 5’s
 Vascular bundles in a ring in the stem
 Root system with main taproot
 Monocot
 Example is grass
 1 embryo seed leaves (cotyledon)
 Skinny leaves with parallel veins
 Un-branched roots
 Parts of the flower occur in groups of 3
 Vascular bundles scattered throughout the stem
Flower Structure and Function
Part
Function
Sepal
Protection
Petals
Attract pollinators
Anther
Produces pollen
Filament
Supports anther
Stigma
Sticky part of carpel
where pollen lands
Style
Supports the carpel
Ovary
Base of carpel where
eggs develop
Pistil
The stigma, style and
ovary structure
Stamen
The filament and anther
structure
Pollination
 Transfer of pollen from a mature anther to a receptive stigma
 Self-pollination:
 pollen comes from the same plant or the same flower
 Limits genetic diversity but easier
 Cross-pollination:
 pollen comes from another plant of the same species
 Increases genetic diversity
 Done by insects, animals or wind
 Grasses are wind pollinated and often have small flowers – main cause of
allergies
 Dicots are usually animal pollinated
 Red: birds
 Yellow and orange: bees
 White/scented: nocturnal
 Insect pollinated plants often produce a sugar called nectar
TOK Moment
 Why do bees matter?
 How do we research it?
 How to do we solve the
problem?
Fertilization
 Fusion of male and female
gametes to form a zygote
 Pollen transfers down the style
to the ovule
 Pollen germinates and makes a
pollen tube
 Tube grows down the style and
enters the ovary
 Nucleus in the pollen tube
moves into the egg
 Two male nuclei are needed
 One fertilizes the egg
 The other triggers the
formation of food storage for
the embryo
The Seed
Seed Part
Function
Testa
Protective outer
coat
Cotyledons
Seed leaves
Micropyle
Scar resulting from
the pollen tube
Embryo (root and
shoot)
Becomes the new
plant
 Protective structure that
allows for dispersal of the
embryo
 Seed is dehydrated
 Dormant
Physiology of Seed Germination
 Dormancy
 Many seeds do not germinate as soon as they are dispersed
 Incomplete seed development
 Embryo is immature and becomes mature during the dormancy period
 Presence of a plant growth regulator
 Gibberellic acid (GA)
 Inhibits development
 Disappears from the seed over time
 Impervious seed coat
 Eventually it is made permeable
 Can be by abrasion with the soil, fire or action of microorganisms
 Requirement for pre-chilling
 Need to over-winter
 Has to have a certain temperature for a certain amount of time
Germination
 Germination occurs under the correct conditions
 Water: seed must take up enough water to be fully hydrated
 Oxygen: present for aerobic respiration
 Suitable temperatures: close to optimum for enzymes for
aerobic respiration, for translocation of sugars and synthesis of
intermediates for growth
Metabolic Processes for Germination
 Germination is the resumption of
growth and development from the
seed form
 Water is needed to activate the
enzymes necessary for germination
 Once enough water has been
absorbed the plant produces a
growth hormone called gibberellin
 Amylase breaks down stored starch
into maltose
 Used in cellular respiration
 Also used to make cellulose for the
cell
 Stored proteins and lipids are
hydrolyzed
 Amino acids are used to make new
proteins
 Fatty acids and glycerol are used in
cell membranes and for energy
Control of Flowering
 The main factor affecting flowering is daylight
 The response of the plant to changes in the length of the day
photo morphogenesis
 Phytochrome
 A blue green pigment present in low concentrations
 Highly reactive
 Found in two forms
 PR:
 Inactive form
 absorbs mostly red light in the wavelength of 660nm and changes to the
active form
 Changes quickly
 PFR:
 Active form
 absorbs mostly the far red wavelength of 730nm and changes back to the
inactive form
 Changes slowly
 PFR is responsible for flowering
Short Day Plants
 Flower only if the period of darkness is longer than a critical
point
 Even a brief flash of light will stop the flowering
 PFR acts as an inhibitor and only long periods of darkness will
allow the levels of PFR to drop to low enough levels to allow
flowering
Spinach
Radish
Long Day Plants
 Flower only if the period of darkness is shorter than a critical
point
 PFR promotes flowering in these plants
 A long period of light allows PFR to accumulate