Biology -- Week 2

Amborella

basal angiosperm because xylem tissue lacks vessel elements, unlike all other extant angiosperms; shrubby tree found in southwest Pacific.

fruits

a ripened ovary; houses the seeds; important for seed dispersal

double fertilization

A mechanism of fertilization in angiosperms, in which two sperm cells unite with the egg and the two nuclei in the megagametophyte, respectively, to form the zygote (2n) and endosperm (3n).

abiotic dispersal (fire)

.serotinous cones in gymnosperms are sealed by resins that only melt in really high temperatures, allowing for the ovulate cones to release seeds that can then germinate

How does the angiosperm ovule differ from the gymnosperm ovule?

1. 2 integuments enclose the megasporangium 2. The megasporangium has no archegonia and is much smaller than that of the gymnosperm ovule 3. The ovule is not exposed like in the gymnosperm, but is covered with the ovary. 4. The 3n endosperm developed via double fertilization, NOT the remains of the megagametophyte, provides the nutrition for the developing embryo.

Life cycle of heterospores

1. Diploid sporophyte (dominant) produces mega and micro sporangia, which are located on sporophylls (leaves that bear the spores). 2. The sporangia form spore mother cells which undergo meiosis to form haploid mega and micro spores. 3. Haploid mega and micro gametophytes form via mitosis, releasing egg and sperm respectively. 4. Fertilization leads to the formation of a diploid zygote, which matures into the diploid sporophyte.

Gingkos (Gingkophyta)

1. Fan-like, bilobed venation, dichotomously forks from the base to tip of blade. 2. extinct currently 3. deciduous leaves dropped before winter 4. found in urban environments because of resistance to pollution/insects 5. dioecious: male and female organs on separate plants 6. females have paired ovules that secrete a sticky fluid to attract pollen. Polinated ovules will develop into seeds protected by sarcotesta, which secretes foul butanoic acid. Prehistoric animals must have found this attractive and carries these seeds. 7. endophytic green alga; unknown whether alga benefits from cumulative photosynthesis or is a commensal (benefitting from protection of leaf tissue) or flourishes when leaves drop

Cycads

1. Gymnosperms that grow in tropical areas 2. look like palm trees with strobili (male and female cones); unbranched stems 3. only produces either micro or mega sporangia 4. compound leaves similar to ferns 5. not really common anymore

Two primary cells of the microgametophyte (in angiosperms)

1. Pollen tube: undergoes cell growth as it makes its way down the stye to deliver sperm to the ovule in the ovary 2. The second cell travels through the pollen tube and mitotically produces two sperm cells right before they fertilize the ovule. (so in total, the microgametophyte is 3 cells big)

describe the development of a male gametophyte (pollen grain) in angiosperms

1. The anther houses the microsporangium, which contains 2n microsporocytes. 2. These mother cells undergo meiosis to form 4 haploid microspores 3. These undergo mitosis to form the immature pollen grain (n), which contains tube and generative cells protected by a sporopollenin coat. 4. During fertilization, the generative nucleus forms 2 sperm and the pollen tube germinates in the style.

Describe the development of the female gametophyte (embryo sac) in angiosperms

1. The ovule is protected by integument and contains the megasporangium, which houses the 2n megasporocytes. 2. These mother cells undergo meiosis to form 4 haploid megaspores, one of which usually survives. 3. The megaspore undergoes 3 rounds of mitosis to form: 3 antipodal cells, 2 polar nuclei, 2 synergids, and an egg (all haploid). This is a total of 8 nuclei and 7 cells.

basic structure of a leaf

1. cuticle 2. epidermis 3. mesophyll (internal parenchyma cells) that consist of palisade and spongy mesophyll layers 4. veins: vascular bundle tissues that facilitate transport of water/photosynthates throughout 5. stomata: facilitate gaseous exchange

describe the development of seed and embryo in angiosperms

1. endosperm and zygote formed within the integument 2. cotyledons appear and are nourished by the endosperm 3. meristematic tissue of the roots/shoots 4. mature seed protected by seed coat

abiotic dispersal (air)

1. mostly gymnosperms, small percentage of angiosperms rely on wind-pollination (eg: hazel, willow) 2. seeds may "helicopter" with the aid of "wings" (maple), or they may parachute to slow rate of fall and increase chances of being swept away opposite to the pull of gravity (dandelion seeds)

What advantages did seeds provide for plant life on land?

1. seeds contain embryos in dormant state and provide it with nourishment and protection (seed coat) for optimal development. The embryos are heterotrophs in early stages where they are below ground and do not receive sunlight, thus depending on the seed for nutrition. They resume growth during germination. 2. Pollen grains are immature male gametophytes that are meiotically produced from microsporocytes on pollen cones (male strobili). They consist of a haploid microspore protected by sporopollenin (derived from diploid sporophytic tissue) from desiccation/UV rays, as well as air-filled wings so they can survive long journeys to the ovule/stigma of another plant.. They later form microgametophytes via mitosis. Unlike pteridophytes/bryophytes, they don't require water for fertilization. 3. seeds = sources of nutrition for animal/human life

types of fruit

1. simple: 1 flower with 1 ovary (plum, peaches, legumes) 2. aggregate: 1 flower with multiple ovaries (blackberries) 3. multiple: many flowers with combined ovaries (pineapples!!) 4. accessory: derived from non-ovarian tissue (apple is derived from stem tissue, known as the receptacle)

The unfertilized ovule contains...

2n megasporangium that contains the 2n megasporocytes and is protected by integument

The gymnosperm seed consists of...

2n seed coat that encloses the remains of megasporangium and megagametophyte, within which the 2n embryo is developing and which serves as the nutrition source for when the seed germinates.

sporocyte

A diploid cell, also known as a spore mother cell, that undergoes meiosis and generates haploid spores.

Magnoliids

A flowering plant clade that evolved later than basal angiosperms but before monocots and eudicots. Extant examples are magnolias, laurels, black pepper/nutmeg/cinnamon plants.

sporangium

A multicellular organ in fungi and plants in which meiosis occurs and haploid spores develop.

Which kind of pollination do angiosperms rely on the most?

Animals. hummingbirds, bats (esp for night-growing plants), flesh flies, male wasps

What are the four main groups of gymnosperms?

Cycads, Ginkgos, Gnetales, Conifers

perianth

Calyx (sepals) & Corolla (petals), which are the outermost whorls and are sterile.

Gnetophyta

Ephedra: shrub in sunny/dry settings; mormon tea/ephedrine Gnetum: tree/shrub/vine in the wet tropics Welwitschia: two huge strap-like leaves in Southwest African deserts; dioecious; long/thick taproots; stout woody trunks; insects attracted to the pollen of male cones and transfer to female cones closely classified with angiosperms because they have vascular tissue including vessel elements/tracheids as well as flower-like structures sister taxa to conifer group

star anise

Illicium verum

What are the two types of spores produced by heterospores?

Megaspores that produce megagametophytes, held in ovules/seeds, which only bear eggs. Microspores produce microgametophytes, contained in pollen grains, which release sperm

Differences between monocots and dicots

Monocots: floral structures in multiples of 3, fibrous roots (instead of a central tap root), vascular bundles scattered throughout the stem, leaves have parallel veins, monophyletic group, have a single cotyledon (orchids); pollen with one opening Eudicots: floral structures in multiples of 4 or 5, distinct central taproot, vascular bundles arranged in a ring around the stem, leaves have net-like veins, paraphyletic group, two cotyledons (roses, oaks, maples, birches, legumes); pollen with 3 openings

spatial separation of sex organs

Monoecious plants with perfect flowers produce short and long-styled flowers to create a gap between anthers and stigma. Those with imperfect flowers spatially separate staminate and carpellate flowers on the same plant.

Compare and contrast the sperm in gingkos and cycads

SIMILARITIES: both have flagellated sperm that rely on motility for fertilization. Male gametes swim through fluid to fertilize the female gametes, marking a transition from bryophytes/ferns to land plants. The microgametophyte produces a tube through which it takes up nutriment from the nucellus (megasporangium) and two sperm cells with cilia that allow them to swim through fertilization fluid released by the nucellus. DIFFERENCES: Gingko has posterior ciliary band through which sperm swim, whereas the band is (r in cycads.

Why is examining the production of secondary xylem NOT a great way to estimate the age of a tree in tropical areas where water is abundant year-round?

Secondary xylem cells typically demonstrate larger diameters and thinner cell walls, and as water conduction in the trees is maximized, the secondary xylem cells produced later are smaller and have thicker cell walls. This creates a distinctive ring. However, since the trees are receiving water year-round, the ring will not be as visible since the contrast between smaller and larger cells is less prominent.

how do plants avoid self-fertilization (selfing)?

Spatial separation of sex organs; Temporal separation of sex organs; Self-incompatibility alleles (S-genes). These mechanisms prevent genetic disease or inbreeding depression

apomixis

The ability of some plant species to reproduce asexually through seeds without fertilization by a male gamete. (dandelions)

style

The stalk of a flower's carpel through which the pollen tube germinates

stigma

The sticky part of a flower's carpel, which receives pollen grain.

Pollination

The transfer of pollen from anther to stigma. Pollen contains the haploid microgametophyte that has the sperm.

The gymnosperm seed represents which three generations?

a 2n seed coat from the original sporophyte, the n megagametophyte, and the 2n embryo (next generation sporophyte)

integument

a layer of parental sporophytic tissue around the megasporangium which will become the seed coat.

Major clades of angiosperms

amborella, coontails, water lilies, star anise, magnoliids, monocot, eudicot,

root system

anchoring, absorb and transport minerals and water, and store water and carbohydrates irregular branching, can perform photosynthesis, penetrate tissues of hosts, or serve as above-ground support fibrous: mat of thin roots that spread uniformly at shallow depths below the soil surface; found in most monocots; interconnected net of roots that provides access to water and minerals in upper soil layers and provides resistance to being uprooted by grazing animals taproots: a large and vertical root that branches laterally into smaller roots; absorption of nutrients and water occur at the tips of lateral roots, while the main axis facilitates anchorage and often stores food. examples include beets and carrots adventitious roots: occasionally arise from positions along the stems

root apical meristem

at the very tip of root, protected by the root cap. The cells continuously divide to later form more specialized cells. Three main regions become identifiable in the root: zone of elongation, zone of cell division, and zone of maturation (differentiation)

shoot system

can be reproductive (flowers) or vegetative stems: consist of nodes (where leaves and axillary buds are attached) separated by internodes (leafless segments). support leaves and flowers, main storage structure for carbs and water. buds: short embryonic regions, found in axillary (where leaf meets stem) or apical (at apex of shoot) buds. Axillary buds can form new vegetative/reproductive shoots (branches), and apical buds can produce flowers or allow for elongation of the vegetative shoot. leaves: main photosynthetic organ; grow from the nodes and originate from bud; reach maturity and cease growth, unlike stems; consist of a blade and petiole

meristems (meristematic tissue)

comprised of meristematic cells which regenerate via mitosis and are generally unspecialized, though some may generate specialized cells/tissues meristems involved in elongation are protected by the leaf primordia in a structure called the bud

Spermatophytes (seed plants)

consist of ANGIOSPERMS and GYMNOSPERMS 1. they have dominant photosynthetic sporophytes 2. the gametophytes are very reduced (only a few cells) and nutritionally dependent on the sporophyte 3. they are heterosporous (i.e. they produce two types of spore) 4. they have seeds (unlike all other plants)

Archaefructus

evidence suggests this is the ancestor of flowering plants, suggests they were herbaceous rather than woody; discovered with fish fossils, therefore might have evolved from aquatic plants; still uncertain

Johann Wolfgang von Goethe

father of morphology; interprets individual forms in universal archetypes; finds plant archetype in the leaf; challenged by Evo-Devo theorists

abiotic dispersal (water)

floating, tape grass (reproduces vegetatively via below-ground runner or reproduces sexually to give rise to small flowers and tiny seeds that float elsewhere), coconut palm (floats onto shores where it uses its food stores to germinate/establish a root system before floating off elsewhere)

Angiosperms

flowering plants defined by flowers, double fertilization, fruits, and ovaries

eudicots

grew in close relationship with fungi/insects.

water lilies

include three clades of aquatic plants

carpel (pistil)

located in the center of the flower, carpels are megasporophylls. Consists of the stigma, style, and ovary.

Stamen

located inside of the perianth, stamens are microsporophylls. Consist of anthers (4 chambers of microsporangia) and a filament (supporting stalk)

temporal separation of sex organs

male and female organs mature at different times

The fertilized ovule contains...

megasporangium that contains the n multicellular megagametophyte and is protected by integument. The megagametophyte is dependent on the sporophyte for nutrition, especially because it doesn't have exposure to sunlight or any chlorophyll.

floral organs

modified shoots and leaves that consist of carpels/stamens (fertile organs) and petals/sepals (sterile organs) sterile organs do NOT produce spores and primarily attract pollinators

What are the major groups of angiosperms?

monocots and Eudicots

Monocots

orchids, bamboo, found in prairies/grasslands as well as aquatic environments, wheat/oat/barley

primary meristems

originate during embryonic development, facilitate primary growth in length (creating new organs), present in all plants, consist of shoot apical and root apical meristems protoderm, ground meristem, procambium

Secondary meristems (lateral meristems)

originate later in the life cycle of a plant, facilitate secondary growth in thickness, not present in all plants but is found in woody plants (pines, magnolias, roses)

pollen germination

pollen grain takes in water from the stigma, the sporopollenin coating is broken open, and the pollen tube emerges

molecular mechanisms to avoid selfing

pollen grains coated with proteins that serve as genetic fingerprints, so when they do land on the stigma of a closely related plant, the common genotype is mutually realized and fertilization doesn't occur.

Modifications for vegetative propogation/asexual reproduction

rhizomes: modified below-ground stems that can produce new shoots; can give rise to clonal quaking-aspen tree colonies stolons: modified above-ground stems that can turn into new shoots¸ flowers¸ and fruits. tubers: modified stems that can turn into organs of vegetation reproduction or storage. stump sprouts; brood bodies in bryophytes

cotyledons

seed leaves that develop along with meristematic tissue to provide embryo with nutriment; can photosynthesize and live for a while after the seed germinates or die after food reserves are depleted; also found in gymnosperms!

ovules

seeds develop from the ovule, an immature seed in which fertilization occurs and the egg is formed. Ovules on megasporangiate cones in gymnosperms are unprotected and exposed, unlike in angiosperms.

4 types of foliar appendages on flowers

sepals, petals, stamen, carpels

shoot apical meristem

shape of a dome at the very tip of the shoot, protected by leaf primordia (young leaves). The cells produced by the apical meristem either differentiate into different specialized tissues or remain inactive in a structure called the axillary bud. Axillary buds can later become the shoot apical meristem of a developing branch in case of damage to the main stem or during the normal course of development.

Synapomorphy

shared derived character

simple vs compound leaf

simple: one blade attached to petiole which meets the stem at the axillary bud compound: multiple leaflets stem from the petiole. the leaflets do not have axillary buds at their base

coontails

sister to eudicots; only 4 living species found in ponds/freshwater/streams; native to all continents and important for fish/invertebrates; create abundant oxygen

leaf adaptations and modifications

spines, tendrils, succulents, trapping

describe the structure of a young stem

stem has an epidermis that is green due to the presence of chlorophyll. stomata are present for gas exchange and the stem can perform photosynthesis. center of the stem is the pith, which consists of living parenchyma cells. Between pith and cortex is the vascular bundle which consists of primary xylem (towards center) and primary phloem (towards the outside). Procambium (layer of undifferentiated cells) are between the primary xylem and phloem. In a young stem, the vascular bundles are still intact.

modified shoots

stolons (runners): grow on the ground surface, have long internodes to reach farther rhizomes: grow underground, thick horizontal stems that serve as storage for carbon-based food tubers: rounded, swollen underground stems specialized for storing foods These modified shoots serve as means of asexual reproduction via propagation

describe the structure of a mature stem

the interfascicular and fascicular layers become the vascular cambium, which produces secondary xylem (wood) towards the inside of the stem. The secondary xylem cells are dead at maturity but continue transporting water and minerals from roots upward. The vascular cambium will also divide towards the outside to form secondary phloem which will continue to transport photosynthates to roots. Diameter of stem increases as more secondary vascular tissue is formed, pushing the epidermis, cortex and primary phloem outwards to be sloughed. The primary xylem will remain within the center of the stem.

Conifers

the largest group in gymnosperms, not monophyletic, commonly found in forests in the Northern Hemisphere, but also found in rainforests/deserts/boreal forests 1. first appeared in Paleozoic era 2. cones: reproductive structures; megasporangiate (produce ovules) and microsporangiate (produce pollen) consisting of the spore, sporangium, and gametophyte 3. in ovulate cones, the scales are the sporophylls on which sporangia produces megasporocytes (cells). These cells undergo meiosis to form megaspores. 3. megasporangiate cones: extra layer of protection for ovules which develop at axils (woody structure where fertilization occurs; opens when seeds are ready to disperse 4. microsporangiate cones: contain huge amounts of pollen; smaller and spongier and far more abundant than female counterparts 5. needle/scale leaves retained year-round in evergreens; can withstand harsh conditions 6. vascular system only consists of tracheids!

cork cambium

the second type of lateral meristematic tissue formed during secondary growth in a stem. it is formed in the outer cortex layers and divides to form cork cells that are dead at maturity and whose cell walls contain suberin, a waxy substance that prevents water loss. bark: everything external to the vascular cambium, including periderm/cork cambium/secondary phloem.

Palynology

the study of fossil pollen grains and spores to reconstruct past climates and human behavior