Studied by 1 personWhat are meristems?
tissues in a plant consisting of undifferentiated cells capable of indeterminate growth
How do meristems benefit plants?
allow plants to regrow structures or even form new plants (vegetative propagation)
Distinguish between the two types of meristematic tissue
apical meristems: occur at shoot and root tips, responsible for primary growth (plant lengthening), gives rise to new leaves/flowers
lateral meristems: occur at cambium, responsible for secondary growth (plant widening/thickening), responsible for the production of bark
What cellular processes allows for apical growth?
a combination of cell enlargement and repeated cell division aka mitosis and cytokinesis
Describe how apical growth occurs
growth occurs in sections called nodes, the remaining meristem tissue forms an inactive axillary bud which can form new branching shoots with leaves and flowers
What is the main group of plant hormones involved in shoot and root growth? Where is it released?
auxins; released from the shoot apex
Describe how auxins promote apical growth
production of auxins promotes growth in the shoot apex via elongation and division
causes apical dominance meaning that it prevents growth in lateral buds, ensuring that a plant will use its energy to grow up towards the light
as the distance between the terminal bud and axillary bud increases, the inhibition of the axillary bud diminishes
different plant species have different levels of apical dominance
Describe how plant pruning occurs
removing the terminal bud by cutting off the top of the plant allows for dormant lateral buds to develop, allowing for the production of wider plants
Describe how auxin efflux pumps can control the direction of plant growth
they can determine which regions of plant tissue have high auxin levels and hence set up a concentration gradient
Distinguish between the role of auxin in the roots vs the shoots of plants
shoots: auxin stimulates cell elongation so high concentrations of auxin promote growth
roots: auxin inhibits cell elongation so high concentrations of auxin limit growth
Describe how auxin increases the flexibility of the cell wall to promote growth
auxin activates a proton pump in the plasma membrane
H+ ions are secreted into the cell wall
pH decreases which causes cellulose fibers in the cell wall to loosen as bonds are broken
auxin also upregulates the expression of expansins which increases the cell wall elasticity
the influx of water causes the cell to increase in size as the cell wall is now more flexible
What is phototropism
a growth movement in response to a unidirectional light source
What is geotropism
growth movement in response to gravitational forces
aka gravitropism
List 2 other tropisms besides phototropism and geotropism and describe them
hydrotropism: responding to a water gradient
thigmotropism: responding to a tactile stimulus
Describe the change in auxin distribution to enable geotropism
auxin accumulates on the lower side of the plant in response to gravity
high auxin concentrations promote cell elongation in the shoot so the dark side elongates and the shoot grows upwards
high auxin concentrations inhibit cell elongation in the roots so the lower side of the root becomes shorter causing the roots to turn downwards
Describe the change in auxin distribution to enable phototropism
light receptors (phototropins) trigger the redistribution of auxin to the dark side of the plant
the dark side of the shoot elongates and grows towards the light as high auxin concentrations in the shoot promotes growth
the dark side of the root becomes shorter and the roots grow away from the light as high auxin concentrations in the root decreases growth
What is micropropagation
a technique used to produce large numbers of identical plants (clones) from a selected stock plant; plant tissues are cultured in the lab to reproduce asexually
What is vegetative propagation
when a plant cutting is used to reproduce asexually in the native environment
Describe the process of micropropagation
specific plant tissue (usually from the undifferentiated shoot apex) is selected from a stock plant and sterilized
the tissue sample is grown on a sterile nutrient agar gel
the explant is treated with growth hormones like auxin to stimulate shoot and root development
growing shoots can be continuously divided and separated to form new samples
after development, the cloned plant can be moved to soil
Describe how micropropagation can be used for rapid bulking
desirable stock plants are cloned via micropropagation to conserve the fidelity of the selected characteristic
more reliable than selective breeding because new plants are genetically identical to the stock plant
also used to produce large quantities of plants created via genetic modification
Describe how micropropagation is used to produce virus-free strains
plant viruses have the potential to decimate crops
can cripple economies and lead to famine
viruses typically spread through infected plants via vascular tissue
meristems don’t have vascular tissue
propagating plants from non-infected meristems allows for the reproduction of virus-free plant strains
Describe how micropropagation can be used for the propagation of rare species
used to increase rare or endangered plant species
increases the numbers of species that are difficult to breed sexually
can be used to increase numbers of plant species that are in commercial demand
List the methods of plant reproduction
vegetative propagation (asexual reproduction from a plant cutting)
spore formations
pollen transfer (occurs in flowering plants)
List the three phases in plant sexual reproduction
pollination, fertilization, and seed dispersal
Describe how pollination occurs
pollen grains from an anther (male plant structure) to a stigma (female plant structure)
many plants possess both male and female structures (monoecious); thus can potentially self-pollinate
cross-pollination is preferable as it improves genetic diversity
Describe how fertilization occurs
fusion of a male gamete nuclei with a female gamete nuclei to form a zygote
male gamete is stored in the pollen grain and the female gamete is found in the ovule
Describe how seed dispersal aids in plant reproduction
fertilization of gametes results in the formation of a seed which moves away from the parental plant
seed dispersal reduces competition for resources between germinating plant and parental plant
seed dispersal mechanisms: wind, water, fruits, animals
Describe the relationship between the pollinator and the flowering plant
mutualistic relationship
flowering plant gains a means of reproduction via the transference of pollen between plants
animal gains a source of nutrition through nectar
List examples of pollinators
birds, bats, insects (bees, butterflies)
some flowers are structured to optimize access for certain pollinators like tube shaped flowers for birds with long beaks
Describe the production of flowers
develop from the shoot apex
changes in gene expression trigger the enlargement of the shoot apical meristem
tissue differentiates to form the different flower structures (sepals, petals, stamen, pistil)
What causes the activation of the gene responsible for flowering
typically linked to the seasons
typically come into bloom when a suitable pollinator is most abundant
the most common trigger is day/night length (photoperiodism)
Distinguish between the terms monoecious and dioecious
monoecious: possesses both male and female structures
dioecious: may only possess one structure
Label the parts of a flower
List the parts of a stamen
anther and filament
Describe the function of the anther
pollen producing organ of the flower, pollen is the male gamete of a flowering plant
Describe the function of the filament
slender stalk supporting the anther, makes the anther accessible to pollinators
List the parts of the pistil
stigma, style, ovule
Describe the structure & function of the stigma
sticky, receptive tip of the pistil that is responsible for catching the pollen
Describe the structure and function of the style
tube-shaped connection between the stigma and ovule (elevates the stigma to catch pollen)
Describe the function of the ovule
contains the female reproductive cells (after fertilization it develops into a seed)
List other flower reproductive structures excluded from the pistil and stamen and describe their function
petals: brightly colored modified leaves that attract pollinators
sepal: outer covering which protects the flower when in bud
peduncle: stalk of the flower
Describe the function of phytocromes
leaf pigments that are used by the plant to detect periods of light and darkness
Describe what occurs when phytocromes detect light
inactive form of phytochrome is converted into the active form when it absorbs red light
active form of phytochrome is broken down into the inactive form when it absorbs far red light
active form gradually reverts to the inactive form in the absence of light
Distinguish between the flowering of short and long day plants
Short-day plants
flower when the days are short meaning that they require the night period to exceed a critical length
flowering occurs at at low levels of Pfr (the active form of phytochrome)
Long-day plants
flower when the days are long meaning that the night period must be less than a critical length
flowering occurs at high levels of Pfr
Describe how horticulturalists can trigger long-day plants and provide an example
typically don’t flower during winter and autumn months
can trigger flowering by exposing the plant to a light source during the night
ex) carnations
Describe how horticulturalists can trigger long-night plants and provide an example
typically don’t flower during the summer months
can trigger by covering the plant with an opaque black cloth for around 12 hours each day
ex) crysanthemums
List the features of a seed
testa, micropyle, cotyledon, plumule, radicle
State the function of the testa of a seed
an outer seed coat that protects the embryonic plant
State the function of the micropyle of a seed
a small pore in the outer covering of the seed that allows for the passage of water
State the function of the cotyledon of a seed
contains the food stores for the seed and forms the embryonic leaves
State the function of the plumule of a seed
the embryonic shoot aka the epicotyl
State the function of the radicle of a seed
embryonic root
List the factors needed for germination of all seeds and the reasons for requirement
oxygen: for aerobic respiration as the seed needs lots of ATP
water: for metabolic activation as it triggers the synthesis of gibberellin
temperature: for optimal function of enzymes
pH: for optimal function of enzymes
List the specialized conditions for germination and the reasons for them
fire, freezing, digestion to erode the seed coat, washing to remove inhibitors, scarification to weaken the seed coat
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