Plant stuff Flashcards
5 key traits that appear in all plants but are absent from charophytes?
- Alternation of generations
- Multicellular, dependent embryos
- Walled spores produced in sporangia
- Multicellular gametangia –multicelluar organs
that produce gametes - Apical meristems
Alteration of generations
Unlike animals in plants after meiosis the
haploid cells can develop into independent
organisms rather than gametes
Alternation of generations:
- Gametophytes (haploid)
- Sporophytes (diploid)
Where does meiosis occur in plants?
In meiosis, sexual cell division, one diploid (2n) meiocyte (a.k.a. germline cell) divides to produce four haploid (n) daughter cells.
These are further processed to become sex cells (gametes).
In plants this occurs in the archegonia in females and in the antheridia in males.
In plants, walled spores are produced by sporangia
Plant spores are haploid reproductive cells that grow into gametophytes by mitosis.
Sporopollenin makes the walls of spores very tough and resistant to harsh environments.
Multicellular organs called sporangia are found on the sporophyte and produce spores.
○ Within sporangia, diploid cells called sporocytes undergo meiosis and generate haploid
spores.
The outer tissues of the sporangium protect the developing spores until they are ready to be released into the air
Plant gametophytes produce gametes within multicellular organs called gametangia.
A female gametangium, called an archegonium, produces a single egg cell in a vase-shaped
organ.
○ The egg is retained within the base.
Male gametangia, called antheridia, produce and release sperm into the environment.
In many major groups of living plants, the sperm have flagella and swim to the eggs though a
water film.
Each egg is fertilized within an archegonium, where the zygote develops into the embryo.
The gametophytes of seed plants are so reduced in size that archegonia and antheridia have
been lost in some lineages.
What is a gymnosperm?
Gymnosperms are called “naked seed” plants because their seeds are not enclosed in
chambers.
What is an angiosperm?
Angiosperm seeds develop inside chambers called ovaries, which originate within
flowers and mature into seeds.
Walled Spores Produced in Sporangia
The sporophyte produces spores in organs
called sporangia.
Spore walls contain sporopollenin, which makes
them resistant to harsh environments
Plant spores are haploid reproductive cells that
can grow into multicellular haploid gametophytes
by mitosis.
Multicellular Gametangia
Gametes are produced within organs called
gametangia
• Female gametangia, called archegonia, produce
eggs and are the site of fertilization
• Male gametangia, called antheridia, produce
and release sperm
Moss life cycle
A spore germinates into a gametophyte
composed of a protonema and gamete-producing gametophore
• The height of gametophytes is constrained by
lack of vascular tissues
• Rhizoids anchor gametophytes to substrate
• Mature gametophytes produce flagellated
sperm in antheridia and an egg in each
archegonium
• Sperm swim through a film of water to reach
and fertilize the egg
The Ecological and Economic
Importance of Mosses
Mosses are capable of inhabiting diverse and
sometimes extreme environments, but are
especially common in moist forests and wetlands
• Some mosses might help retain nitrogen in the
soil
• Many mosses can exist in very cold or dry
habitats because they are able to lose most of
their body water and then rehydrate and
reactivate their cells when moisture again
becomes available.
What are the characteristics of vascular plants?
Life cycles with dominant sporophytes
Vascular tissues called xylem and phloem
Well-developed roots and leaves
Transport in Xylem and Phloem
Vascular plants have two types of vascular tissue: xylem and
phloem
• Xylem conducts most of the water and minerals and includes
dead cells called tracheids
• Water-conducting cells are strengthened by lignin and
provide structural support
• Phloem consists of living cells and distributes sugars, amino
acids, and other organic products
• Vascular tissue allowed for increased height, which provided
an evolutionary advantage
Sporophylls and Spore Variations
Milestone in the evolution of plants was the
emergence of sporophylls – modified leaves that
bear sporangia
• Sori are clusters of sporangia on the undersides of
sporophylls
• Strobili are cone-like structures formed from groups
of sporophylls
Heterospory: The Rule Among Seed Plants
A heterosporous species produces two kinds of spores.
- megaspores, which develop into female gametophytes.
- microspores, which develop into male gametophytes.
Advantages of Reduced Gametophytes
The gametophytes of seed plants are microscopic
• The gametophytes of seed plants develop within the
walls of spores that are retained within tissues of the
parent sporophyte
• This arrangement protects the developing
gametophyte from environmental stress and enables
it to obtain nutrients from the sporophyte
Pollen and Production of Sperm
Microspores develop into pollen grains, which contain the male
gametophytes
• Pollination is the transfer of pollen to the part of a seed plant
containing the ovules – contrast with bryophytes and seedless v
plants
• Pollen eliminates the need for a film of water and can be
dispersed great distances by air or animals
• If a pollen grain germinates, it gives rise to a pollen tube that
discharges sperm into the female gametophyte within the ovule
Seeds provide some evolutionary advantages over
spores
Spores are single celled, seeds are multicelled.
– They may remain dormant for days to years, until
conditions are favorable for germination
– Seeds have a supply of stored food
– They may be transported long distances by wind or
animals
The Angiosperm Life Cycle
The flower of the sporophyte is composed of both male and
female structures
• Male gametophytes are contained within pollen grains
produced by the microsporangia of anthers
• The female gametophyte, or embryo sac, develops within an
ovule contained within an ovary at the base of a stigma
• Most flowers have mechanisms to ensure cross-pollination
between flowers from different plants of the same species
Development of Male Gametophytes
in Pollen Grains
Pollen develops from microspores within
the microsporangia, or pollen sacs, of anthers
• Each microspore undergoes mitosis to produce two cells: the
generative cell and the tube cell
• A pollen grain consists of the two-celled male gametophyte and
the spore wall
• If pollination succeeds, a pollen grain produces a pollen tube
that grows down into the ovary and discharges two sperm cells
near the embryo sac
Development of Female
Gametophytes (Embryo Sacs)
The embryo sac, or female gametophyte, develops within the
ovule
• Within an ovule, two integuments surround a megasporangium
• One cell in the megasporangium undergoes meiosis,
producing four megaspores, only one of which survives
• The megaspore divides, producing a cell partitioned into a
multicellular female gametophyte, the embryo sac
Double Fertilization
One sperm fertilizes the egg, while the other combines with two
nuclei in the central cell of the female gametophyte and initiates
development of food-storing endosperm
• The triploid endosperm nourishes the developing embryo
• Within a seed, the embryo consists of a root and two seed
leaves called cotyledons
Fruit Form and Function
A fruit develops from the ovary
• It protects the enclosed seeds and aids in seed
dispersal by wind or animals
• A fruit may be classified as dry, if the ovary dries
out at maturity, or fleshy, if the ovary becomes
thick, soft, and sweet at maturity
Fruits are also classified by their development
– Simple, a single or several fused carpels
– Aggregate, a single flower with multiple separate
carpels
– Multiple, a group of flowers called an
inflorescence
What are the 2 angiosperm groups?
Monocots (one cotyledon)
Eudicots (two dicots)
Different Whorl Combos
Whorl 1=sepal, A genes
Whorl 2=petal, A+B genes
Whorl 3=stamen, B+C genes
Whorl 4=carpel, C genes
Flowering time is regulated by coordinated
genetic changes that respond to:
Photoperiod
- Temperature
- Plant hormone signals
The 2 Processes of Photosynthesis
The light reactions (photo) convert solar energy to chemical energy.
○ The Calvin cycle (synthesis) uses energy from the light reactions to incorporate CO2 from the
atmosphere into sugar.
What is an Autotroph?
Autotrophs sustain themselves without
eating anything derived from other organisms
• Autotrophs are the producers of the
biosphere, producing organic molecules from
CO2 and other inorganic molecules
• Almost all plants are photoautotrophs, using
the energy of sunlight to make organic
molecules
What is the reaction for photosynthesis?
6CO2 + 12H2O –> C6H12O6 + 6O2 + 6H2O
The light reactions (in the thylakoids)
Split H2O – Release O2 – Reduce NADP+ to NADPH – Generate ATP from ADP by photophosphorylation
Info on Calvin cycle
The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH.
The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules
What is a photosystem?
A photosystem consists of a reaction -center complex (a type of protein complex) surrounded by light -harvesting complexes • The light -harvesting complexes (pigment molecules bound to proteins) transfer the energy of photons to the reaction center
2 Types of photosystems
Photosystem II (PS II) functions first (the numbers
reflect order of discovery) and is best at absorbing
a wavelength of 680 nm
• The reaction-center chlorophyll a of PS II is called
P680
• Photosystem I (PS I) is best at absorbing a
wavelength of 700 nm
What is linear electron flow?
Linear electron flow, the primary pathway,
involves both photosystems and produces ATP
and NADPH using light energy
• This is the ‘canonical’ process of the lightdependent reactions
What is Cyclic electron flow?
Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH • No oxygen is released • Cyclic electron flow generates surplus ATP, satisfying the higher demand in the Calvin cycle
What are C4 plants?
C4 plants minimize the cost of photorespiration by
incorporating CO2
into four-carbon compounds in
mesophyll cells
• This step requires the enzyme PEP carboxylase
• PEP carboxylase has a higher affinity for CO2
than
rubisco does; it can fix CO2 even when CO2
concentrations are low; O2 does not compete.
• These four-carbon compounds are exported to
bundle-sheath cells, where they release CO2
that is
then used in the Calvin cycle
C4 photosynthesis
Primary CO2
fixing enzyme: PEP carboxylase (phosphoenol pyruvate carboxylase) which has higher affinity for
CO2
(in fact, almost no affinity for O2)
• Needs bundle sheath anatomy
• Advantageous in high light, high temperature, high
evaporation conditions
But requires high energy
CAM Plants
Some plants, including succulents, use crassulacean
acid metabolism (CAM) to fix carbon
• CAM plants open their stomata at night, incorporating
CO2
into organic acids
• Stomata close during the day, and CO2 is released from
organic acids and used in the Calvin cycle
CAM Plants photosynthesis
Primary CO2
fixing enzyme:
PEP carboxylase as in C4
• Separates CO2 uptake and temporary storage (during
night) from final CO2
fixation (during day)
• Survival mechanism in arid regions (eg deserts)
• High ‘water use efficiency’ (ratio of CO2
fixed to water
lost)
What are the functions of a root?
– Anchoring the plant
– Absorbing minerals and water (from the soil)
– Storing carbohydrates (from the leaves)
Eudicots and gymnosperm root system
Most eudicots and gymnosperms have a taproot
system, which consists of:
– A taproot, the main vertical root
– Lateral roots, or branch roots, that arise from the
taproot
Monocot root system
Most monocots have a fibrous root system, which
consists of:
– Adventitious roots that arise from stems or
leaves
– Lateral roots that arise from the adventitious roots
What are the 5 types of modified roots?
- Prop roots
- Storage roots
- Strangling/Aerial roots
- Buttress roots
- Pneumatophores
What are the 3 Meristematic tissues of a plant?
Dermal: epidermis, periderm
Vascular: xylem, phloem
Ground: pith and cortex
What is Dermal tissue?
In nonwoody plants, the dermal tissue system
consists of the epidermis
• A waxy coating called the cuticle helps prevent
water loss from the epidermis
• Trichomes are outgrowths of the shoot epidermis
and can help with insect defense
Ground tissue
Tissues that are neither dermal nor vascular are
the ground tissue system
• Ground tissue internal to the vascular tissue is
pith; ground tissue external to the vascular tissue
is cortex
• Ground tissue includes cells specialized for
storage, photosynthesis, and support
Vascular tissue
The vascular tissue system carries out long-distance transport
of materials between roots and shoots
• The two vascular tissues are xylem and phloem
• Xylem conveys water and dissolved minerals upward from roots
into the shoots
• Phloem transports organic nutrients from where they are made to
where they are needed
Parenchyma Cells
– Have thin and flexible primary walls – Lack secondary walls – Large vacuole – Are the least specialized – Perform the most metabolic functions – Retain the ability to divide and differentiate – Can regenerate
Collenchyma Cells
Collenchyma cells are grouped in strands and
help support young parts of the plant shoot
• They have thicker and uneven cell walls
• They lack secondary walls
• These cells provide flexible support without
restraining growth
Sclerenchyma Cells
Sclerenchyma cells are rigid because of thick
secondary walls strengthened with lignin
• They are dead at functional maturity
• There are two types:
– Sclereids are short and irregular in shape and
have thick lignified secondary walls
– Fibers are long and slender and arranged in
threads
2 types of plant growth.
Primary for growth in height
Secondary for growth in diameter
Water loss from plants
Plants take up large quantities of water
• > 90% of the water taken in by roots is lost from the plant as water
vapour.
• Very little is ‘used’ in any biochemical process
• The loss of water from the plant is termed transpiration
• Terrestrial plants lose water as an unavoidable consequence of
having to take up CO2
• Dehydration is always a risk
• But transpiration stream does distribute minerals
What are the 3 transport routes between cells?
Three transport routes for water and solutes are
– The apoplastic route, through cell walls and extracellular spaces
– The symplastic route, through the cytosol, on the inside
– The transmembrane route, across cell walls
Short-Distance Transport of Solutes
Across Plasma Membranes
Plasma membrane permeability controls short-distance
movement of substances
• Both active and passive transport occur in plants
• In plants, membrane potential is established through
pumping H by proton pumps
Bulk flow
Efficient long distance transport of fluid requires bulk
flow, the movement of a fluid driven by pressure
• Water and solutes move together through tracheids and
vessel elements
Water-Conducting Cells of the Xylem
The two types of water-conducting cells, tracheids and vessel
elements, are dead at maturity
• Tracheids are found in the xylem of all vascular plants
• Vessel elements are common to most angiosperms and a few
gymnosperms
• Vessel elements align end to end to form long micropipes called
vessels
Bulk Flow Transport via the Xylem
Xylem sap, water and dissolved minerals, is transported from
roots to leaves by bulk flow
• The transport of xylem sap involves transpiration, the
evaporation of water from a plant’s surface
• Transpired water is replaced as water travels up from the roots
Pulling Xylem Sap: The Cohesion-Tension
Hypothesis
According to the cohesion-tension hypothesis, transpiration
and water cohesion pull water from shoots to roots
• Xylem sap is normally under negative pressure, or tension
How does bulk flow differ from diffusion?
It is driven by differences in pressure potential, not solute potential
– It occurs in hollow dead cells, not across the membranes of living
cells
– It moves the entire solution, not just water or solutes
– It is much faster
Sugar-Conducting Cells of the Phloem
Sieve-tube elements are alive at functional
maturity, though they lack organelles
• Sieve plates are the porous end walls that allow
fluid to flow between cells along the sieve tube
• Each sieve-tube element has a companion cell
whose nucleus and ribosomes serve both cells
What is water potential?
Water potential is a measurement that combines the effects of
solute concentration and pressure
• Water potential determines the direction of movement of water
• Water flows from regions of higher water potential to regions of lower
water potential
Role of rhizobacteria
Rhizobacteria can play several roles
– Produce hormones that stimulate plant growth
– Produce antibiotics that protect roots from disease
– Absorb toxic metals or make nutrients more available to roots
Nitrogen fixing bacteria
Ammonifying bacteria produce NH3 by breaking down nitrogen in proteins and other organic compounds in humus. Nitrogen-fixing bacteria convert N2 into NH3 In the soil, NH3 picks up another H+ to form NH4 (which plants can absorb) • Plants acquire nitrogen mainly in the form of NO3 – • Soil NO3 - formed by two step processes called nitrification. – Nitrifying bacteria oxidize NH3 to nitrite (NO2 – ) then nitrite to nitrate (NO3 – ) (2 different bacteria) • Nitrogen is lost to the atmosphere when denitrifying bacteria convert NO3 – to N2
Fungi and Plant Nutrition
Mycorrhizae (fungus roots) are mutualistic associations of fungi
and roots
• The fungus benefits from a steady supply of sugar from the host
plant
• The host plant benefits because the fungus increases the
surface area for water uptake and mineral absorption
• Mycorrhizal fungi also secrete growth factors that stimulate root
growth and branching and produce antibiotics that protect the
root.
Ectomycorrhizae
In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the
surface of the root
• These hyphae form a network in the apoplast, but do not penetrate the root cells
• Ectomycorrhizae occur in about 10% of plant families including pine, spruce, oak,
walnut, birch, willow, and eucalyptus
