Download LECTURE 6: EVOLUTION OF LAND PLANTS

LECTURE 6: EVOLUTION OF LAND PLANTS
Pre-lecture Vocabulary
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Alternation of generations - the succession of multicellular haploid and diploid phases in some
sexually reproducing organisms, notably plants
Gametophyte – in plants and photosynthetic protists with alternation of generations, the multicellular
haploid phase that produces the gametes (1n)
Sporophyte – in plants and protists with alternation of generations, the diploid phase that produces the
spores (2n)
Gametangia (gametangium) – Any plant of fungal structure within which a gamete is formed
Archegonium – the multicellular structure that produces eggs in nonvascular plants, ferns, and
gymnosperms
Antheridium – the multicellular structure that produces the sperm in nonvascular plants and ferns
Isogamy – the condition where male and female gametes are morphologically identical
Heterogamy – where the two gametes are dissimilar in appearance
Homosporous – producing a single type of spore that gives rise to a single type of gametophyte,
bearing both female and male reproductive organs
Heterosporous – Producing two types of spores, one of which gives rise to a female megaspore, and
the other to a male microspore
Lecture notes
The transition from water to land poses challenges to organisms
• Structural challenges
• Physiological challenges (the way in which a living organism or body part functions)
Structural changes needed:
1. to avoid dehydration of the body – waxy covering (cuticle)
2. to obtain water and nutrients from the soil and means to distribute them to all parts of the body – roots,
shoots, stomata etc, vascular system.
3. to benefit from higher intensity of light on land – increased photosynthetic surface area – leaves with
increased surface area
4. Mechanical strength to support their body mass – specialized with thick cell walls, e.g. xylem vessels,
tracheids, fibers, phloem sieve elements, colenchyma, sclerenchyma.
5. Apical growth and branching to achieve maximum growth.
6. With respect to reproduction:
i. Protect gametes, zygote and embryo from dehydration – archegonium, antheridium, protected
embryo, seed
ii. Retention of egg on the mother plant.
iii. Mechanisms to transfer male gamete to the female gamete – pollination and pollination vectors.
7. to cope with possible environmental stresses – evolve pigments to cope with increased UV light on
land.
All of the adaptations needed for flourishing on land did not arise at the same time during the course of evolution,
their sequential acquisition and be seen in various land plants
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Alternation of Generations
In the
sexually
reproducing
These changes will in turn affect
life cycle
of the plant
organisms, there is a
phenomenon called Alternation
Alternation of Generations of generations. A haploid form
• A haploid form called
withwith
one set
of
calledgametophyte
gametophyte
one
chromosomes alternates
with a diploid form
called
set of chromosomes
alternates
a diploid
form called
sporophyte withwith
two sets
of chromosomes.
sporophyte
with
twotosets
• Gametophyte produces gametes that fuse
formofzygote
chromosomes.
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that develops into sporophyte.
Gametophyte
produces
The latter forms haploid
spores through
meiosis.
gametes
that fuse to form
Each spore develops
into a gametophyte.
zygote that develops into
sporophyte. The latter forms
Green algae
haploid spores through
• Advanced green meiosis.
algae (eg Chara
and Coleochaete)
Each spore
develops are
into a gametophyte.
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ancestors of plants
o Gametes already protected in these ancestors
• All have
o Photosynthesis with chlorophyll a and b
o Cellulose cell walls
o Haploid dominant
• Pair of advanced groups jointly have
o Multicellular thallus growth form
o Antheridium & oogonium protect gametes
o Sporophyte (diploid) is
! Single celled
! Matrotrophic – mother eating
• Chara (and like alga)
o Taller, cells up to 5cm long
o Possesses branching growth pattern, and could serve as an ancestor for most land plants with
erect growth habit
• Coleochaete (and like alga)
o flat
o Could serve as an ancestor of thallus based land plants like liverworts
Adaptive changes that evolved for life on land also altered the pattern of alternation of generations
• Remember gametophye = haploid, and sporophyte = diploid **** important
Chlamydomonas
• Shows isogamy – the two gametes are similar in appearance
• Unicellular green alga
• Has sexual and asexual modes of reproduction
• Gametophytic phase is predominant
• Sporophytic phase is limited to just the zygote
• Asexual reproduction is just the multiplication of the haploid gametophytic phase
Liverwort
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In this plant the waxy cuticle has appeared to prevent drying
Shows heterogamy (the two gametes are dissimilar in appearance and are protected in the gametangia)
Shows homospory
The gametopyte is predominant and its body is called thallus – a flat mat-like structure.
A thallus produces male or female umbrella-shaped structures which produce antheridia (containing
sperms) or archegonia (containing egg).
After fertilization, the zygote grows right on the umbrella-shaped structure and produces spores
through meiosis.
Each spore produces male or female thallus (different gametes, process starts over)
Moss
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Stomata appear for first time in evolution
Gametes are produced in multicellular protective gametangia
Each archegonium produces a single egg
Each antheridium produces millions of sperms
o Fertilization in non-vascular land plants requires water so sperm can swim to egg
The sporophyte is matrotrophic – is attached and nutritionally dependent on the gametophyte
Shows heterogamy
Hornwort
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One of the three groups of bryophyts, share common ancestry with vascular plants
Anthoceros is a hornwort
o The cylindrical sporophyte can be nearly 8” tall and is matrotrophic
Gametophytes are plate plates a few cell walls thick
Heterospory first appears n the earliest vascular plants – the Pteridophytes – club-mosses, ferns and horsetails
• Dissimilar spores –
o Megasporangium (2n) " (meiosis) " megaspore (n) " megagametophyte (egg)
o Microsporangium (2n) " (meosis) " microspore (n)" microgametophyte (sperm)
! produced in astronomical quantities, as it is the motile one
• Instead of sporangium " spore mother cell (2n) " spore (n) " gametophyte which creates both
sperm (in antheridium) and egg (in archegonium)
Leaves
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Evolution of microphylls and megaphylls to maximize light interception
Microphylls
o Simple leaves with a singular vascular projection
A sporangium evolved into this simple leaf
Megaphylls
o Expanded leaves with many vascular veins
o Webbing is large and complex
o A branching system became progressively reduced and flattened, where flat plates of
photosynthetic tissue developed between the branches
Selaginella (early vascular plant related to ferns)
• A heterosporous pteridophyte
• Microphylls appear
• Shows both heterospory and heterogamy
• It produces microspores giving rise to male gametophyte , and megaspores giving rise to female
gametophyte.
• After fertilization, in some species, the zygote undergoes dormancy before germinating (as in seeds).
Common Fern
• Ferns include both homosporous
and heterosporous species
• Megaphylls appear
• Xylem and phloem appear
o Vascular cells that
transport nutriends to the
top
• Stem is microscopic
Horsetail
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Up to here, sperms have flagella
and are motile
From now on they are not
Gymnosperm (eg conifer)
• 300 ft tall sporophyte
• same tree bears strobili and female cones
• naked ovuole developes a naked seed
• polyembryony: several embryos develop within one seed
• sperms are not motile
• no flowers
• no xylem vessels
• gametophyte is now matrotrophic
Gymnosperm life cycle
Naked ovule borne on the scale
sporophyte
e bears male strobili
e cones
ule develops into a
ed
yony: several
develop within one
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Angiosperm
• Male gametophyte is represented by mature pollen grains consisting of two cells
• Female gametophyte is represented by 8-celled embryo scar. One of those cells is the egg
• Gametophyte is matrotrophic
• Has double fertilizaton – which results in a 2n zygote and a 3n endosperm (the part of the seed that
provides food for the developing embryo)
• Only one embryo per seed **
• Seed dormancy present
Higher plant vasculature
• Xylem vessels and tracheids
o Dead cells used to transport water
o Tracheids in gymnosperms
o Xylem and vessel elements in angiosperms ?
• Phloem sieve tubes
o Used to transport nutrients made in the leaves
• Compainion cells (to phloem)
o Take food (photosynthesis products) from surrounding tissue and then loads into phloem
tubes and goes to base of plant
Evolution of Alternations of generations
1. Mosses – gametophyte (n) predominant and nourishes smaller sporophyte
2. Ferns – gametophyte much smaller than sporophyte, but both live independently
3. Seed plants – sporophyte predominant, and nourishes the hidden an inconspicuous gametophyte
Sporophyte success
• Diploidy (2 copies of each gene) plays huge role
• Gene-dosage effect
o 2x genes = 2x proteins = 2x purpose/size
• provides a cushion against harmful mutations
Plants and motility
• Didn’t need to develop motility
• Sun and soil come to them
• Symbionic relationships with animals and insects bring needed supplies to them
LECTURE 7: PLANT BODY – STRUCTURE AND NUTRITION
LECTURE NOTES
Two Major Groups of Angiosperms
• Dicots (Eudicots)
o Root syetm: tap roots (one main vertical root, with branch roots)
o Leaf base: petiole
o Leaf venation: reticulate
• Monocts
o Root system: fibrous roots (equally important roots)
o Leaf base: sheath
o Leaf venation: parallel
• Leaves sprout from nodes, in between is the internode
• The apical bud is the bud at the top, all others are axillary buds
Stem modifications
• Modified to store food, eg potatoe
• “runners” for horizontal stems
• cacti modified to store water, no leaves (= spines), become green and carry out photosynthesis
Root modifications
• Carrots, etc
• Fibrous roots
• Prop roots on corn, can grow new ones above water level to take in oxygen
Root ! stem
• Transition occurs at the crown of the plant
• Goes from centrally located vascular tissue system, to peripherally located vascular system
• Vascular bundles are the “transport highways” – they conduct water and solutes throughout the plant
• The dermal Internal
tissue system is thestructutre
outer covering of the of
plant primary root
• the ground tissue system in leaves carries out photosynthesis, stores photosynthetic products, and
helps support the plants
Vascular bundles in stems
Note the difference in
• In a cross-section of the stem, vascular bundles are arranged differently in dicots (in a ring) and
the arrangement of
monocots (scattered).
vascular system in a
• In dicots, each year, the cambium of adjacent vascular bundles gets joined together, forming a cambial
dicot
ring. and a monocot
primary
root.activity of the cambial ring forms with the xylem towards the inside and the phloem
• The cell division
towards outside, constituting secondary growth.
• Thus you can determine the age of a tree by counting the number of rings in its cross section
• Within and annual ring, cells formed during wet seasons are larger than cells formed during drier
seasons. (this an examination of annual rings in tree cross-sections can tell us about past climate)
Internal structure of the primary root
• There is a large difference in the
arrangement of the vascular system
in a eudicot and a monocot primary
root
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Leaves
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Simple leaves – those with a single blade, with an axillary bud at the axil of that leaf
Complex leaves – many leaflets arranged along a central axis. Also can have further division of the
axis resulting in a doubly compound leaf
Has cells for photosynthesis
o palisade mesophyll cells
o bundle sheath cells
! Bundle-sheath cells are photosynthetic cells arranged into tightly packed sheaths
around the veins of a leaf. They form a protective covering on leaf veins, and consist
of one or more cell layers, usually parenchyma
Cells for transport
o Xylem
o Phloem
Cells for gas exchange (CO2, O2, water vapour)
o Guard cells, stoma – usually found on the underside of the leaf
! On monocots, as the leaves are more or less vertical, it is found on both sides
Movement of water and mineral ions
• Diffusion – the movement of molecules due to their internal thermal/kinetic energy
• Osmosis – diffusion across a selectively permeable membrane
• Two ways for water and minerals to mover from the soil to the root xylem
o Apoplastic pathway
! Water and ipns travel into and trhough cell walls and intercellular spaces in the
apoplast
! They never cross membranes or enter the cytoplasm – the cortex has large enough
intercellular spaces for water molecules
o Symplastic pathway
! Water and ions cross membranes, and go through the cells to get to the stele
• The stele, containing the pericycle, xylem and phloem is surrounded by endodermis, which has a
waxy coating on radial sides, which prevents molecules from passing through the intercellular space
o Casparian strips prevent water in the apoplast from passing between the endodermal cells
into the stele
• Molecules travelling both ways must actually pass through the cell walls to access the stele via the
symplast
• This acts as the “immigration check point”, and only ions matching an ion pathway can enter
Pathway of water movement through plants
• Plants take up immense quantities of water from the soil and throw 99% of it back up to the
atmosphere though transpiration
o Loss of water from average human = 1 L/day
o Corn plant ~ 2 L/day , average tree = 1000 L/day
• They make use of the strong cohesive properties of water
• Through transpiration water vapor diffuses through the stomata
• Water evaporates from the mesophyll cell walls, and tension pulls the ater from the veins into the
apoplast of the mesophyll cells
• Tension pulls the water column upward, all the way from the roots (where it entered through osmosis)
through the xylem
• Apoplastic and symplastic motion happens simultaneously
Plants as primary producers
• Plants take CO2 (unsaturated C) from the air, E from light, H2O and mineals from the soil and can creat
their own food with O2 as waste
• We have to eat complex, organic food made by other organisms (saturated C aka reduced C)
• Plants reduce C by adding H through photosynthesis (H comes from water) in leaves
• Other modifications to C
o Carbohydrates are always made first, but can be further modified
o N added ! becomes amino acid
o Add other components ! becomes fatty acids
• When the food is transferred, it must be converted to sucrose which is the most stable form of
carbohydrates, and is thus the only transportable form
Transport of photosynthetic products
• The plant moves the photosynthetic products (mainly sugars) from the source tissue (leaves) to the
sink tissues (growing organs)
• Both xylem and phloem are involved.
• Source leaves are rich in sugar and load sugars into upper phloem cells
o Upper phloem cells are now high solute concentration and thus absorb water from xylem
through osmosis
o This develop high turgor pressure and the sugar/water moves down to lower phloem cells
• Sink cells unload sugars from lower phloem cells
o This creates a low solute concentration in the lower phloem, so water returns to the xylem
o This creates low tugor pressure which helps move the sugar/water down the phloem
• Thus transport of photosynthetic products in the phloem is purely pressure-driven.
• We discovered that these were transferred in the phloem by using aphids
Mineral elements required by plants to complete their lifecycle. Some
others in much
Mineral
elements
minerals
are needed in large quantities (Macronutrients),
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Mineral
elements
are required by plants to complete their life cycle
smaller quantities
(micronutrients)
• Macronutrients – minerals needed in large quantities
• Micronutrients – minerals needed in much smaller quantities
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Mineral deficiencies and symptoms
• Calcium - growing points die back; young leaves are yellow and crinkly
• Iron – young leaves are white or yellow
• Magnesium – older leaves have yellow in stripes between veins
• Manganese – younger leaves are pale with green veins
• Nitrogen – oldest leaves turn yellow and die prematurely; plant is stunted
• Phosphorus – plant is dark green with purple veins and is stunted
• Potassium – older leaves have dead edges
• Sulfur – young leaves are tallow to white with yellow veins
• Zinc – young leaves are abnormally small; older leaves have many dead spots
Absorption of water and minerals by the root
• Root hairs increase the absorptive surface area of the root.
• Water and minerals enter the root hair by osmosis (Symplast).
• Note that root hair is an extension of a single epidermal cell.
• Water and minerals can also enter the root up to endodermis, through cell wall and intercellular spaces
between adjacent cells (apoplast).
• Soils favorable to plant growth contain both clay and larger mineral particles as well as water, air, and
organic matter.
• Cationic minerals (K+, Ca2+), due to their electric charges are adsorbed on to the surface of clay
particles, which are negatively charged.
• Anions are generally leached down with rainwater and are less stably available to the root (lost more
easily)
• The cations are exchanged for hydrogen ions obtained from carbonic acid (H2CO3) or from the plant
itself
Fixation of atmospheric N2
• Atmospheric nitrogen is a diatomic gas with a strong triple bond between the 2 nitrogen atoms.
• Specific bacteria living in root nodules fix N2 gas into nitrogenous compounds which are then
transported to all parts of the plant.
• Bacterium gets photosynthates from the plant.
• A root nodule (large round bumps) develops as a result of bacterium-plant interactions.
• Plant hemoglobin is 20x stronger than human hemoglobin in binding oxygen
• Some plants living in nitrogen poor habitats obtain protein and phosphorous supplements from insects.
• There are carnivorous plants
o Insectivores (like venus fly trap and sundew) secrete enzymes to digest the insect. Only the
insect exoskeleton is left at the end
o Rat-Eating Pitcher Plant even digest bones
• And one that create mutualistic relationships
o A species of pitcher-plant has discovered rich nutrition in tree-shrew droppings
o To entice the shrew, the lid of the pitcher secretes copious amounts of nectar
• Parasitic plants
o Parasitic plants obtain photosynthetic products, water and minerals by parasitizing other
plants
o Cuscuta or dodder is shown parasitizing golden rod plants.
! Cuscuta produces flowers and seeds.
! The young seedling establishes connection with host plant and loses its connection
the soil.
! It sends haustoria or pegs into the host plant to contact its xylem and phloem.
! A single cuscuta plant can parasitize more than one plant and can transfer soluble
material from one plant to another (can make 2nd plant flower if 1st plant is)
LECTURE 8: GROWTH, DEVELOPMENT AND RESPONSES
TO ENVIRONMENTAL STRESSES
Pre-Lecture Vocabulary:
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Abscission – the process by which leaves, petals, and fruits separate from plants
Adventitious – a root growing directly from a stem or upper part of a plant
Cotyldons – a “seed leaf.” An embryonic organ that stores and digests reserve materials’ may expand
when seed germinates
Epicotyl – that part of the plant embryo or seedling that is above the cotyldons
Hypocotyl – that part of the embryonic or seedling plant shoot that is below the cotyldons
Coleoptile – a sheath that surrounds the and protects the shoot apical meristem and young primary
leaves of a grass seedling as they move through the soil
Lecture Notes:
Before we start.. what do we mean by growth and development?
• Growth – irreversible quantitative increase – ie irreversible increase in height, volume, (dry) weight,
or number in the case of populations
• Development – qualitative changes in body structure or function – ie development of organs
(organogenesis), achieving final shape and size (morphogenesis), juvenile phase, adult phase (sexual
maturity), flowering, senescence (the condition or process of deteriorating with age) or physiological
aging
Phytohormones (plant hormones)
• Abscisic acid – maintains seed dormancy and winter dormancy; closes stomata
• Gibberellins – promote seed germination, stem growth, and fruit development; break winter
dormancy; mobilize nutrient reserves in grass seeds. (Antagonistic hormone to abscisic acid, the
balance will determine if a seed germinates or not)
• Auxins – promote stem elongation, adventitious root initiation, and fruit growth; inhibit axillary bud
outgrowth and leaf abscission
• Brassinosteroids – promote stem and pollen tube elongation; promote vascular tissue differentiation
• Cytokinins – inhibit leaf senescence; promote cell division and axillary bud outgrowth; affect root
growth
• Ethylene – promotes fruit ripening and leaf abscission; inhibits stem elongation and gravitropism
Seed germination
• Qualitative change
• Seeds are generally dormant just after being shed. They won’t germinate even if temperature, soil and
moisture conditions are optimal. This is seed dormancy.
• Hormonal seed dormancy - seed dormancy is most frequently due to the presence of the hormone
abscisic acid (ABA). ABA has to degrade or leach out before the seed will germinate
• Mechanical seed dormancy - Sometimes seed dormancy is due to the seed coat being mechanically too
strong. The seed coat has to be cracked by freeze-thaw cycles in nature or weakened by microorganisms.
• Small wild seeds frequently need a light signal to make them germinate. Because the small seeds have
only a small amount of stored food, they have to germinate close to the soil surface. If they “see” the
light, they think they are close to the soil surface. If they germinated deep down below the soil surface,
their food material would run out before they could come above the soil and start photosynthesis
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Some desert plants have a built in rain gauge, where there is only a 3 week period where there is
enough water. The amount of rain that is sufficient for the plant to complete its lifecycle is the same
amount of water it takes to wash out the abscisic acid.
All seeds must absorb water to become metabolically active
Light requirements for seed germination
• With small seeds, light sensitivity is of great economical value
• First question to ask: What is the action spectrum? ie what is the light which stimulate the process
• A study was done with lettuce seeds, where red light (663 nm) and far-red light (730 nm) was shown
on the seeds
• The last light shown on the seeds would determine if it would germinate
• Red light caused germination, and far-red light, inhibits germination = 663 nm is the action spectrum
• Second question to ask: What is the absorption spectrum? Ie What is the pigment which absorbs the
light to stimulate germination?
o The action and absorption spectrum must match – only the pigment which absorbs the same
wavelength which is found to stimulate the process can be responsible for that process
• The found that there is a single pigment that has two conformational forms to absorb two different
wavelengths of light: phytochrome
• Pr is a phytochrome that absorbs red light and is TURNED INTO Pfr
o Then Pfr interacts with the seed
o Stimulates seed germination, stimulates chlorophyll synthesis, hook unfolding, leaf expansion
o Inhibits stem growth/ plant height (sturdy, green and shorter)
• Pfr is a phytochrome that absorbs far red light and is TURNED INTO Pr
o Then Pr interacts with seed
o If the seed has already germinated, plant will grow tall, spindly, pale, and (in eudicots) the
apical hook will not unfold, and cotyldon leaves will remain protected
Hypogeal and Epigeal Germination:
In Hypogeal, epicotyl elongates;
In Epigeal, hypocotyl elongates
Monocot
Hypogeal and Epigeal Germination
• In hypogeal growth, the epicotyl elongates
• In epigeal growth, the hypocotyl elongates
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Hypogeal
Dicot – Bean
Epigeal
Dicot – Pea
Hypogea
Auxin
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Auxin controls plant shape by controlling the growith of the lateral branches through apical dominance
If you remove the shoot apex (apical bud), side branches start growing (this is the basis of pruning)
If you put an agar block with auxin on the remaining stem, the plant will continue growing as before
Darwin discovered that the very tip of the coleoptile reacts to the light (positive phototropism)
o The isolated hormone was auxin
o More auxin = more growth,
o auxin moves to the shaded side of the plant, so the side of the plant that is farthest from light
grows more, so that it bends towards the light
negative geotropism
o shoots show negatively geotropic growth – they bend away from gravity
o auxin produced in the tip moves toward the lower side and stimulates cell growth on the
underside, bending the shoot upward
positive geotropism
o roots exhibit the opposite phenomenon
o we don’t have to know this mechanism
REPRODUCTION IN ANGIOSPERMS
Asexual reproduction
• Vegetative or asexual reproduction: parts of the vegetative body regenerates shoots and roots
• Potato tuber (?)
o Is an underground stem modified for storage of food materials
o Potato “eyes” are actually axillary buds in the axils of scale leaves
o Under appropriate conditions, the bud grows out into shoots. This is how the potato crop is
planted
• Onion
o Bulbs are short stems with large buds that store nutrients and can give rise to new plants
• Kalanchoe
o New plantlets can form on the margin of leaves
o They will fall to the ground and become independent plants
Flowers The structure of dicot angiosperm
• The structure of a dicot angiosperm flower:
The pistil consisting of:
One or more carpals.
Each carpel has an
ovary, style and
stigma. Each ovary has
one or more ovules.
Carpals are generally
fused together.
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flower
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An inflorescence is a branch that bears flowers
There are several types of inflorescence depending on the arrangement of flowers
o Compund umbel – each umble bears flowers on stalks that arise from a common center
o Head – in a head, each of the long, petal like-structures is a ray flower; the central portion of
the head consists of hundreds of disk flowers (eg sunflower)
o Spikes – eg fountain grass
Photoperiodism
• A condition in which physiological and behavioral changes (ie flowering) are induced by changes in
day length
• Depending on the species, a plant is induced to flower when a particular combination of day-length
and night-length in a 24-hour cycle is obtained
• A combination of light-length and day-length that induces a flower is an inductive photoperiodic cycle
• Some plants need only one and others several inductive cycles
• Exposure of a single leaf to inductive cycles can induce flowering. This some singal or hormone
moves from the inducedleaf to the shoot apex where the flowers are produced
• Such a flowering hormone was given a hypothetical name – florigen
• Florigen can travel across a graft union between two plants. If one of the plants is induced, the other
one also flowers
Short-day plants and long-day plants
• Short-day plants (SDP) – flower when the day length is less than (or when the night length exceeds) a
certain critical duration (critical photoperiod) in a 24-hour cycle
• Long-day plants (LDP) – flower only when day-length is longer than its critical photoperiod, or when
uninterrupted night-length is shorter than a critical length
• each flowering plant species has a defined critical photoperiod
• SDP and LDP have identical floigen
Fertilization in angiosperms
• Double fertilization – virtually unique to angiosperms, a process in which the nuclei of two sperm
fertilize one egg. One sperm’s nucleus combines with the egg nucleus to produce a zygote, while the
other combines with the same egg’s two polar nuclei to produce the first cell of the triploid endosperm
(the tissue that will nourish the growing plant embryo)
Responses to stressful environments
• Drought
o Desert ephemerals avoid drought by growing during the brief rainy season
o Large trees in the desert have deep tap roots to explore for water in a large and deep volume
of soil
• Flooding or hypoxia (oxygen deficiency)
o Roots produce pneumatophores that stick out of the water and take up air though tiny pores.
Oxygen is distributed to the entire root system
o Development of air spaces – aquatic plants have aerenchyma tissue (containing air-spaces).
o Other plants such as corn develop aerenchyma tissue during flooding
• Insect pests
o Biting by an insect sends a signal to the plant which activates genes to make protease
inhibitors which inhibit the protein digesting enzymes in the insect gut. The insect dies of
starvation
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Biting by a specific insect sends signals to the plant, which sends volatile chemical signals to
the predator of the insect pest. The insect predator come and eats the insect
Cutting or grazing by herbivores
o Cutting and herbivory grazing removes apical dominance by auxin. Therefore, side branches
come out from the bottom of the shoot
LECTURE 9: INTRODUCTION TO ANIMALS – SPONGES
Pre-lecture Vocabulary:
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Motile – capable of motion
Tissues – a group of similar cells organized into a functional unit; usually integrated with other tissues
to form part of an organ
Hermaphroditic – the coexistence of both female and male sex organs in the same organism
Lecture Notes:
Animal Characteristics:
1. Eukaryotic
2. Heterotrophic
3. Multicellularity
4. No cell walls
5. Motile at some life stage
6. Diploid somatic cells
7. Diplontic life cycle
8. * MOST animals have tissues
Eukaryotic
• Must have nucleus
• Membrane-bound organelles
Heterotrophic
• “different feeding”
• used pre-formed organic material as energy and carbon source
• modes of feeding
o predators
o herbivores
o filter feeders (sea fan, sponge, coral)
o parasites (tape worm)
o detritivores (worms, feed on dead organic matter)
o omnivores
• most animals have internal digestion
o most use internal processes to break down food (as opposed to fungi, who rely on external
digestion)
o most have an internal gut that is continuous with the outside environment and permits internal
digestion of food items
• prokaryotes, protists, fungi can all be heterotrophs. Not plants
Multicellularity
• Having multiple cells means
o Cells can become specialized to carry out specific functions
o Organisms can grow in size (and have more complex functions)
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!
If you are one large cell, you have a diffusion problem due to low SA:V ratio
Materials can diffuse throughout smaller cells more quickly
No cell walls
• Types of structural support:
o Hydrostatic skeleton
! Muscles contract against fluid-filled cavity (worms)
o Exoskeleton
! Exo=internal
! Nonliving covering that does not grow with the animal
! Ecdysozans – molting animals, eg dragonflies
o Endoskeleton
! Internal support
! Vertebrates – use living tissue
! Invertebrates – non-living, CaCO3
Motile at some life stage
• Movement reduces competition, enhance genetic diversity
o Eg barnicels are animals, they are motile as larva
Diploid somatic cells
• Somatic (body) cells are diploid (2n)
• Gametes are n
Animals are diplontic
• Most of the life-cycle is in the diploid phase
Animals
• Haploid gametes
are tiny and matrotrophic
Tissues
• About 35 phyla
• Tissues – groups of similar cells organized into a functional unit
o Muscular – for movement
• About ~1 million species classified (likely
o Nervous – transmitting electrical signals, or protecting them
millions exist)
o Connective – bone, cartilage, blood, adipose (fat)
Epithelial – line outer and internal surfaces
• 97% areoinvertebrates
• can function together as organs to complete more complex tasks (ex: digestion, absorption)
• Note: imbalance in lecture distribution
ANIMALS!
• About 35 phyla
• About ~1 million species classified (likely millions exist)
• 97% are invertebrates
• note: imbalance in lecture distribution
Animal phylogeny
Sponges
Common
Ancestor
Cnidarians
Lophotrocozoans
Arthropods
Echinoderms
Hemichordates
Chordates
Animals are monophyletic
• Although most of their characteristics are shared with some other groups, no groups share all of these
characteristics
• There are several lines of evidence that animals are monophyletic (one common ancestor)
o Similar gene sequences
! Ex: Hox genes; genes that act in development and control the identity of different
body parts
o Unique types of junctions between cells
o Similar extracellular matrix molecules (collagen, proteoglycans)
• Closest living relative to ancestral animal is the colonial choanoflagellate protozoan
o Note in a colony, some cells are specialized, but are not living in a coordinated fashion
Animal diversification
• “Cambrian explosion”
• 543-490 MYA
• rapid diversification
• many new phyla formed
• Burgess Shale, BC
SPONGES (Phylum Porifera)
• Poifera meas “pore bearing”
• ~9000 species, mostly marine
• Sessile as adults, motile as larvae
• Spicules (CaCO3, Silica, protein fibers) and a network of elastic fibers for support
• Size range: ~2mm to 2 meters
• Sponge morphology is highly variable
o Matches environment, tital sponges are flat and close to rock (purple encrusting sponge)
Basic form
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Cell types
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Osculum – excurrent pore
Spongeocoel – internal cavity/atrium
Ostia – incurrent pore
o Water moves in ostia and out the osculum
Cells are imbedded in a jelly matrix – mesoglea
o No true tissues or organs (no muscles or nerves)
which means there is no coordinating structure
o Non cellular
o Some support
Spicules
o In mesoglea
o Provide rigidity
o CaCO3 or SiO2
Spongin
o Protein fibers
o Provide flexible support in mesoglea
o Think bath sponge, but also “glass sponge” with high SiO2 content
Choanocytes
o “collar cells”
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o line interior
o flagellated
o create currents
o trap food particles
o Note similarity to choanoflagellates, and thus genetic link
Amoebocytes
o Amoebid movement
o Reside in jelly matrix
o Transfer food to other cells
Epidermal cells
o Flattened
o Line exterior
Porocytes
o Form channel for water flow (line incurrent pore)
o Not always present
Feeding
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Choanocytes beat their flagella and create a current to bring food particles into the spongecoel
They get trapped on the collar of the choanocyte
the particles are taken up by the cellular portion of the choanochyte
Are digested through phagocytosis OR transferred to amoebocyte through exocytosis
Reproduction
• Asexual reproduction
o Fragmentation
! Not-self induced
! Brought on by waves or predators
o Budding
! Clone of parent buds off
• Sexual reproduction
o Is Hermaphroditic
o Sperm and eggs are produced in the choanocytes or amoebocytes
o Broadcast sperm
o Filter in different sperm (cannot self fertilize)
o Eggs become fertilized and develop in mesoglea
o Larvae released (motile)
o Settle on suitable substrate
Sponge Origins
• Evolved ~700 MYA
• Ancestor ~ choanoflagellates
Limitations of Sponges
• Very successful, but have limitations
• Unable to feed on larger prey as digestion is intracellular
• Unable to achieve greater organization or coordination between body parts
o Cellular level of organization