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Plant Reproduction and Responses. By Michael Hohl,Sam Melville, Jordan Petersen, and Matt Rosenthal. Life Cycles of Plants. Main Idea: plants cycle through haploid(n) gametophyte and diploid(2n) sporophyte generations.

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Plant reproduction and responses
Plant Reproductionand Responses

By Michael Hohl,Sam Melville, Jordan Petersen, and Matt Rosenthal

Life cycles of plants
Life Cycles of Plants

  • Main Idea: plants cycle through haploid(n) gametophyte and diploid(2n) sporophyte generations.

  • the sporophyte undergoes meiosis to produce haploid spores that undergo mitosis to produce multicellular gametophytes- the male and female plants that produce gametes

  • fertilization= the fusion of gametes that ultimately results in new sporophytes forming

Now let’s take a closer look at angiosperms to understand how plants go through this cycle…

Angiosperm structure function
Angiosperm Structure & Function

  • Male parts make up the stamen

    Anther= produce pollen in microsporangia chambers

    Filament= long stalk that is capped off by the anther

  • Female parts make up the carpel (a single carpel or multiple fused carpels are called the pistil)

    Ovary= forms the base of the carpel and holds the ovules

    Ovules= holds the embryonic sac (female gametophyte) and the egg

    Style= the long slender neck of the carpel

    Stigma= sits atop the style and captures pollen

Now see if you can figure out which arrow points to what floral organ in the picture on the left. (carpel and stamen arrows not shown).

The answers are on the next slide.

Angiosperm structure
Angiosperm Structure

  • Parts of an angiosperm: (See which ones you got correct!)

  • Complete flowers have the four basic floral organs (sepals, petals, stamens, and carpels)

  • Incomplete flowers lack one or more of the four basic floral organs

    - Unisexual flowers lack either stamens or carpels

Development of gametophytes in angiosperms
Development of Gametophytes in Angiosperms

  • Development of male gametophytes in pollen grains

    -anthers contain diploid cells called microsporocytes which undergo meiosis to form many haploid microspores. These microspores undergo cell division to create a pollen grain (which houses the male gametophyte)

  • Development of female Gametophytes (Embryo Sacs)

    - occurs in the tissue of the ovule (called megasporangium)

    - a cell called the megasporocyte undergoes meiosis, creating 4 haploid megaspores (“mother cells”), only one of which survives.

    -after three mitotic divisions, the embryo sac is formed inside the ovary

Pollination fertilization
Pollination & Fertilization

  • pollination= the transfer of pollen from an anther to stigma by wind water or animals

  • fertilization= the fusion of gametes that ultimately results in new sporophytes forming

  • Angiosperms undergo double fertilization.

    - If pollination is successful, the pollen grain will germinate, producing a pollen tube that grows towards the ovary

    • The generative cell of the pollen grade undergoes mitosis to produce two sperm

    • The two sperm enter the embryo sac. One fertilizes the egg, forming the zygote. The other combines with two polar nuclei in the embryo sac, forming an endosperm, which stores food inside the seed.

Click video to begin

Development of seed fruit
Development of Seed & Fruit

  • After double fertilization, the ovules develop into seeds and the ovary encases the seeds by developing into a fruit.

    • the seeds gather nutrients such as oils, proteins, and starch in the endosperm

    • a fruit protects the seeds and aids in their dispersal by animals or wind

  • dormancy= the period when the seed is almost full grown and the embryo stops growing.

  • the seed will begin to germinate when it takes in water

  • imbibition= the soaking up of water as a result of low water potiential. Imbibition will cause the seed to germinate.

Germinating seed

Forms of angiosperm reproduction
Forms of Angiosperm Reproduction

Angiosperms can reproduce sexually, asexually, or both

  • Asexual reproduction= where offspring result from one parent without the fusion of sperm and egg. (aka vegetative reproduction in plants)

    • fragmentation= “the separation of parent plants into parts that develop into whole plants.” pg 812

    • apoximis= the production of seeds without fertilization or pollination

  • Prevention of Asexual reproduction

    -Dioecious species= plants that lack either carpels or stamens

    -Self-incompatibility= the inability of a plant to accept its own pollen (and sometimes the pollen of closely related plants)

Reception transduction response
Reception, Transduction, Response


  • Reception: Signals are first detected by receptors, embedded into the plasma membrane, which are proteins that change in shape in response to a certain stimulus.

  • Transduction: Many signals or receptors are very weak and need amplification by way of transduction, or the use of small ions or molecules (second messengers) that amplify and transfer a signal from receptor to other proteins that carry out the response.

  • Response: Ultimately, second messengers regulate a cell activity, generating a response. Can be post translational modification or transcriptional regulation.

    • Post- translational modification activates pre-existing enzymes already constructed using RNA.

    • Transcriptional regulation increases or decreases the synthesis of mRNA encoding a specific enzyme.

Plant hormones
Plant Hormones

  • Plant hormones are unlike human and animal hormones in that many have overlapping uses.

  • Tend to stimulate growth/processes:

    • Auxin

    • Cytokinins

    • Gibberellins

  • Tend to inhibit growth/processes:

    • Abscisic acid (ABA)

    • Ethylene

Stimulating hormones
Stimulating Hormones

  • Auxin (IAA): hormone responsible for stimulating stem elongation,

  • root and fruit formation, and functions in phototropism and gravitropism.

  • Cytokinins: synthesized in roots, regulate cell cell division in shoots and roots.

  • Gibberellins: synthesized in meristems of buds, roots and leaves, stimulate stem elongation, pollen development, seed development, and fruit growth.

Inhibiting hormones
Inhibiting Hormones

  • Abscisic acid (ABA): synthesized in all plant cells, inhibits growth of plant in stem and roots.

  • Ethylene: gaseous hormone produced in most parts of plant, promotes ripening of fruit and root and root hair formation.

Responses to light
Responses to Light

  • Tropism: any growth response that results in plant organs curving toward or away a stimulus.

  • Phototropism: The growth of

    a shoot towards or away from

    light (positive or negative


Click video to begin

Response to gravity mechanics environment
Response to Gravity, Mechanics, Environment

  • Gravotropism occurs as soon as a seed germinates, ensuring root grows into soil and stem up.

  • Statoliths, or dense cytoplasmic components, settle under the influence of gravity in a cell which triggers calcium redistribution and lateral transport of auxin.

  • Thigmomorphosis: changes in form that result from mechanical perturbation(i.e. wind).

  • Directional growth in response to touch is called thigmotropism.

  • Environmental Stresses can be divided into two categories: abiotic (non-living) and biotic(living).

  • Plants have the ability to respond to changes in temperature, salt, and water concentration.

Response to herbivores
Response to Herbivores

  • Plants have physical defenses (i.e. thorns),

  • …or chemical defenses (i.e. production of distasteful or toxic compounds).

  • Some plants can "recruit" predatory animals

  • that feed on herbivores by releasing attractants.

  • Called “recruitment”

Response to pathogens
Response to Pathogens

  • In response to many pathogens, a plant often reaches a compromise with virus, so that both may survive instead of one killing the other and then dying with no host. Called avirulent pathogens.

  • Plants can initiate a hypersensitive response that causes tissue death near infection site.

  • Plants can also initiate a systemic acquired resistance which arises from entire plant and produces methylsalicylic acid, which is converted to salicylic acid that is transported to infected areas and triggers an immune response there and thus produces an acquired resistance.

Plant reproduction and responses



Plant Reproduction and Response: Reece, Jane B., and Neil A. Campbell. Campbell Biology. AP 9th ed. Boston: Benjamin Cummings / Pearson Education, 2011. Print.

Plant horomones and responses:

lecture notes

Images and video:

Double fertilization video:

Phototropism video:

Plant life cycle picture:,r:2,s:0,i:137

Pollen grain picture:

picture of flower on opening slide:,r:12,s:0,i:95

germinating seed picture:,r:1,s:0,i:135

apple picture:,r:5,s:0,i:91

parts of a flower picture:,r:5,s:0,i:77

Plant reproduction and responses

5-hour energy picture:,r:2,s:0,i:145&biw=1280&bih=627

stop sign picture:

Reception, transduction, and Response picture:,+Transduction,+Response&um=1&hl=en&client=safari&rls=en&biw=1280&bih=627&tbm=isch&tbnid=namqn_Ik_KM4sM:&imgrefurl=,r:1,s:0,i:69

Cytokinins picture:,r:1,s:0,i:109

Gibberellins picture:,r:0,s:0,i:81

Auxin picture:,r:2,s:0,i:111

Abscisic acid picture:,r:2,s:0,i:91&tx=105&ty=20

Ethylene picture:,r:0,s:0,i:120