Plant Reproduction

mechanisms by which flowering plants reproduce asexually

vegetative propagation, division, budding

flowers, seeds, fruits

flowers: produce gametes, attract pollinators, nourish embryos, develop seeds and fruit

seeds: embryo, stores nutrients, protective coat

fruits: develop into flower and contain seeds

plant asexual reproduction- rhizomes, corms, plantlets,

produce clones

rhizomes: horizontal stem which roots and shoots emerge

corms: modfied stems which grow under surface of soil

plantlets: form along margins of plant leaves

apoxmixis

mature seeds can from without ferilziaiton

downside of asexual reproduction

• disease causing agents infect platns offspring

• lack genetic diversity to generate disease fighting

sexual reproduction;

• meiosis and fertilization

• produce genetically different offspring

life cycle of land plant- angiosperms

1. meiosis occurs in sporophytes, sporangia produce

sepal function, entire group of sepals is called

attached to receptacle in whorl, enclose and protect flower bud as it grows, calyx

corolla

group of petal in flower

wind pollination

angiospersm (oaks, birches, grasses) have small petals/ no petals

wind polinated species lack nectaries, do not invest in strcitures that are not

imperfect flowers

contain either stames or carpels, not both

monoecious plants

separate male and female reproductive organs on the same individual plant (corn)

diocieious plant

cannabis- produce only male or female flowers

how are female gametophytes produced

• . Ovule Structure

  • Each ovule is located inside the ovary of a carpel (female reproductive organ of a flower).

  • Within each ovule is a diploid (2n) cell called the megasporocyte (or megaspore mother cell), located inside a tissue called the megasporangium (also known as the nucellus).

  2. Meiosis of the Megasporocyte

  • The megasporocyte (2n) undergoes meiosis, a type of cell division that reduces the chromosome number by half.

  • This results in four haploid (n) megaspores, but typically only one survives; the other three degenerate.

  3. Development of the Female Gametophyte (Embryo Sac)

  • The surviving megaspore undergoes three rounds of mitosis, producing eight haploid nuclei.

  • These nuclei are arranged into a seven-celled structure known as the mature embryo sac (female gametophyte).

  4. Structure of the Mature Embryo Sac

  • Three antipodal cells at the chalazal end.

  • Two synergid cells and one egg cell at the micropylar end.

  • One central cell with two polar nuclei in the center.

ovary vs ovule

ovary contains the ovules, develop into a fruit after fertilization.

ovules, which are located inside the ovary, develop into seeds

outcrossing

sperm and eggs from diff individuals combine, results from cross pollinations

more genetically diverse

selfing

successful pollination all time

offspring are less genetically diverse

how plants prevent selfing

temporal avoidance: male and female gametophyte within perfect flower mature at different times

spatial avoidance: dioecious species w perfect flowers have anthers and stigmas so par apart, self pollination unlikely

molecular matching: plants recognize self and non self tissues= self incompatible

pollination syndromes: bird, moth

suites of flower associated with certain types of pollinators

• birds: red, unscented, day

• moth/bat: white, strongly scented, night

  • bees: purple

pollinators can be inferred from flower structure and color

extremely long probacis, with orchid

how many cotyledons do monocots and eudicots have, what are they

1, 2’; take up nutrients from endosperm and sotre

describe similatries between eudicot and monocot

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seeds become dormant when

mature, becomes dry embryo becomes dormant, pe

pericarp

fruit protects seeds, formed from tissues derived from mother

simple fruits

single flower single carpel/ several fused carpels- grapes, cherries

aggregate

single flower, many seperate carpels/ ovaries (blackberry), strawberry

multiple fruits

many flowers many carpels pineapple

accessory fruits

fruits come from ovaries and receptale; apple, oear, pineapple, strawberry

2 funtiosn of fruits

aid in seed dispersal, protect seedstwe

tewksbury and nabhan hypotheisis

does capsacin prmote seed dispersal by thrashers and deter seed preedation by mice? curve ate all three, germinated, mice ate fewwer, did not germinate

ABA

stomata closure, seed dormancy, and abscission

conditions to germinate

o2 water warm temp, seed coat sacrificed,

in monocots, what emerges first, in eudicots?

1. radicle root emerge first, develop into mature root system

   1. eudioct: shoots and cotyledon emerge after radical gone

   2. monotocots: coleoptile protects shoot

   3. no longer relies on food reserve endopserm/coteyleodn

vegetative development

non reproductive portions of plant body- roots, leaves stemsem

embryogenesis

2n Zygote = fertilized egg divides into 2 cells:

Bottom cell → makes suspensor (helps move nutrients)

apical cell → becomes the embryo

first division of zygote

• The apical cell divides to form (globular) mass of cells.

• Cells begin to differentiate.

Protoderm (future epidermis) is established.

4. Heart Stage

• The embryo begins to show bilateral symmetry.

• Formation of cotyledons (embryonic leaves).

Primary meristems become visible:

• Protoderm → epidermis

• Ground meristem → ground tissue

• Procambium → vascular tissue

5. Torpedo Stage

• Cotyledons elongate.

6. Mature Embryo Stage

• Contains fully developed shoot apical meristem (SAM) and root apical meristem (RAM).

• The embryo is ready for dormancy inside the seed until germination.

How Embryogenesis Leads to Meristems:

• Shoot Apical Meristem (SAM):

  • Formed at the tip of the embryo above the cotyledons.

  • Produces all above-ground tissues (stems, leaves, flowers).

• Root Apical Meristem (RAM):

  • Formed at the opposite end of the embryo.

  • Generates all root tissues.