Dumb Bio Test

Mechanisms preventing self fertilization

• Dioecious plants- separate female and male plants

• timing of flower development

• Self incompatibility- plant rejects its own pollen

Flowers

the reproductive shoots of the angiosperm sporophyte

4 floral organs  

1. Sepals

2. Petals

3. Stamens

4. Carpels

Sepals

protect the flower in the bud

Petals

surround the reproductive parts

Stamens

male reproductive structure

Carpels

female reproductive structure

Incomplete flowers

lack 1 or more of the floral organs

Production of male gametophyte

1. male gametes are produced in the anther of the stamen from diploid cells called microsporocytes

2. Microsporocytes undergo meiosis to produce 4 haploid microspores

3. Each microspore divides once via mitosis to produce two cells ( a generative cell and a tube cell)

4. This two celled structure is usually encased in a thick wall and is the pollen grain

5. Male gametophyte in polle grain

Pollination and Fertilization

1. pollen grain lands on the stigma of a compatible plant

2. the tube cell grows and burrows through the stigma and down the style

3. the generative cell then divides via mitosis and the two sperm travel down the pollen tube

4. the pollen tube enters the micropyle

5. one sperm fertilizes the egg

6. the other joins with the other two polar nuclei forming a triploid cell

7. that cell gives rise to the endosperm or food storing material

(pollination does not always lead to fertilization)

Production of female gametophyte

1. In the ovule a megasporocyte undergoes meiosis producing megaspores (egg and central cell)

2. The megaspore undergoes three mitotic divisions (8 nuclei partitioned into 7 cells)

3. 1 egg with 2 synergids, 3 antipodal cells, 1 remaining cell w/2 nuclei

pollen tube

• provides an appropriate environment and path for the sperm

• highly species specific and prevents interspecific fertilization

double fertilzation

• produces zygote and endosperm

• ensures nutrients are supplied only to eggs thats have been fertilized

Costs of Sexual Reproduction

• requires twice the fitness

• loss of “ideal” individuals

• less efficent

• slower population growth rate

Vicar of Bray Hypothesis

• sexual reproduction increases variation which means a greater chance of gathering more fit traits

• more variation is beneficial in changing environments

The Red Queen Hypothesis

• evolutionary arms race between hosts and pathogens

• pathogens adapt to common host genotypes

• sexual reproduction produces rare hosts genotypes

• increased host variation makes it difficult for pathogens to specialize

External Reproduction

• often associated with aquatic animals

• release eggs and sperm into water, sperm swims to eggs

• many have a planktonic larval stage

Gonochorism

separate sexes

Problems associated with sexual reproduction

• must exclude self fertilization and gametes from other species

• must bring gametes together

• must produce gametes

• must limit fertilization to two gametes

Male reproductive structures

• male gametes (sperm) are produced in the testes

• Sperm pass into the epididymis from the seminiferous tubules (highly coiled tubes in the testes)

Leydig cells

produce testosterone

Sertoli cells

provide nutrients for developing sperm

Spermatogenesis

• the process cells move from the outer edge of the tubules toward the center

• Spermatogonia (diploid) through mitosis

• the cells undergo meiosis (spermatocytes) (initially diploid)

• produce haploid spermatids

• mature into final sperm cells (haploid)

• cells mature in the epididymis

Sperm passage

• During ejaculation, sperm are propelled from the epididymis through the vas deferens and out through the urethra

• three sets of glands add secretions to the sperm to form the semen:

• Seminal Vesicle: fructose (60% of total vol.)

• Prostate gland: anticoagulant enzymes and citrate

• Bulbourethral gland: neutralizes the acidic environment of the urethra

Female Reproductive Structures

• the ovaries are composed of an outer covering surrounding up to 400,000 follicles (present at birth)

• from puberty to menopause follicles mature and egg cells are released (ovulation)-monthly

• the remaining cells of the follicle form the corpus luteum

• the egg moves into the oviduct and travels along to the uterus.

• travel aided by cilia

Oogenesis

• Oogonia (diploid) enter meiosis and become primary oocytes

• But stop in prophase I of meiosis (prior to birth)

• After puberty FSH stimulates one or more primary oocytes to complete the first meiotic division and pause in Metaphase II

• At the time of ovulation, the egg is in Metaphase II of meiosis

• The mature follicle ruptures, releasing the secondary oocyte from the ovary

• After a sperm cell penetrates the egg, it is triggered to complete meiosis

Fertilization in Mammals

• sperm travel through an outer layer of cells to reach the zona pellucida, the extracellular matrix of the egg

• when the sperm binds to a receptor in the zona pellucida, it triggers a slow block to polyspermy

• no fast block to polyspermy has been identified in mammals

Fertilization

if fertilized the developing embryo will implant in the thickened lining of the uterus (endometrium)

Hormonal Regulation Males

Hypothalamus: GnRH (gonadotropin releasing hormone)

Anterior Pituitary: FSH and LH (follicle stimulating hormone and luteinizing hormone)

Testes: FSH acts on Sertolli cells supporting spermatogenesis, LH stimulates Leydig cells to produce androgens (testosterone- also needed for spermatogenesis)

Hormonal Regulation in Females

Hypothalamus: GnRH (gonadotropin releasing hormone)

Anterior Pituitary: FSH and LH (follicle stimulating hormone and luteinizing hormone)

Ovaries: FSH stimulates maturation of follicle (estrogen), LH stimulates ovulation and development of corpus luteum (progesterone)

Root important functions:

• anchoring the plant

• absorbing minerals and water

• storing carbohydrates

Stems consist of

• nodes: points at which leaves are attached

• internodes: stem segments between nodes

• apical bud: causes elongation of a young shoot

• axillary bud: a structure that has the potential to form a lateral branch, thorn, or flower

Leaves

• main photosynthetic organ of most vascular plants

• leaves intercept light, exchange gases, dissipate heat, and defend the plant from herbivores/pathogens

• Blade and petiole (attached to node on stem)

• Monocots: have parallel veins

• Dicots: have branching veins

3 tissue types in plants

1. Dermal

2. Vascular

3. Ground

dermal tissue system

• in nonwoody plants, the dermal tissue system consists of the epidermis

• cuticle- waxy coating that helps prevent water loss from the epidermis

• in woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots

vascular tissue system

facilitates the transport of materials through the plant and provides mechanical support

Xylem: conducts water and dissolved minerals upward from roots to shoots

Pholem: transports sugars from where they are made (primarily leaves) to storage structures or sites of growth

ground tissue system

includes cells specialized for storage, photsynthesis, support, and transport

Water-conducting cells of the Xylem

• Vessel elements are common to most angiosperms, and a few gymnosperms and seedless vascular plants

• Vessel elements align end to end to form long pipes called vessels

• the end walls of of vessel elements have perforation plates that allow water to flow freely through the vessels

Sugar-conducting cells of the Pholem

• cells of the Pholem are alive at maturity, but lack organelles

• In angiosperms, sugars are transported in sieve tubes, chains of cells called sieve-tube elements

Pholem

sieve tubes, sieve tube elements, carbohydrates, from lead to other parts of plant

Xylem

vessels, vessel elements, water + minerals, from root to shoot

Primary growth

apical meristems are located at the tips of roots and shoots

• elongate shoots and roots, process is called primary growth

Secondary growth

• Lateral meristems add thickness to woody plants- secondary growth

• Vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary pholem

• Cork cambium replaces the epidermis with periderm, which is thicker and tougher

• Secondary growth occurs in gymnosperms and many eudicots, but is rare in monocots

Dedrochronology

analysis of tree ring growth patterns to study past climate change

• tree rings are present where late and early wood meet

• thick rings indicate a year with warm or wet growing conditions, thin rings indicate a cold or dry year

4 key stages of Animal Development

1. Fertilization

2. Cleavage

3. Morphogenesis

4. Organogenesis

acrosomal reaction

triggered when the sperm meets the egg

• the acrosome at the tip of the sperm releases hydrolytic enzymes that digest jelly coat surrounding the egg

• acrosomal process forms, grows, and develops the egg

• “lock and key” on plasma membrane

The Cortical Reaction

• Na+ rush in and the membrane depolarizes- creates an electric barrier to other sperm (separate from the cortical reaction)

• fusion of egg and sperm also initiates the cortical reaction

• seconds after the sperm binds to the egg, vesicles just beneath the egg plasma membrane release their contents and form a fertilization envelope

• the fast block of polyspermy (seconds)

• the fertilization enevelop also acts as a slower block to polyspermy 30-60 seconds

• the cortical reaction requires a high concentration of calcium ions in the egg

• the reaction is triggered by a change in calcium ion concentration

• calcium ions spread across the egg correlates with the appearence of the fertilzation envelope

Fertilization

• egg activation- activates a sharp rise in metabolic processes

• in humans this stimulates the oocyte to complete meiosis

• fusion of haploid nuclei into diploid nucleus

• the fertilization stage ends with a zygote

Cleavage

• a series of mitotic divisions

• results in the formation of a fluid-filled ball of cells, Blastula

• each cell is called a blastomere

• the fluid filled space is the blastocoel

Morphogenesis

• involves large scale movement of cells

• involves cell movement, and cell shape changes

• Establishment of: three primary tissue types, anterior/posterior axis, digestive system

• begins with gastrulation

• involves invagination: cells at one end of the blastula begin to migrate inside the blastocoel generating a tube within a tube

Organogenesis

• regions of the three germ layers develop into the rudiments or organs

• the mechanisms of organogenesis involve folds, splits, and dense cell clustering

• this must occur in the proper location (pattern formation)

pattern formation

the process governing the arrangement of tissues and organs, largely controlled by chemical cues

determination

refers to the process by which a cell or group of cells become committed to a particular fate

differentiation

refers to the resulting specialization in structure and function

fate maps

diagrams showing organs and other structures that arise from each region of an embryo

positional information

the molecular cues that control pattern formation, this information tells a cell where it is with respect to the body axes

Formation of the Vertebrate Limb

• one limb bud regulating region is the apical ectodermal ride (AER)

• The AER secretes a protein signal called fibroblast growth factor (FGF) that promotes limb-bud outgrowth

• the second region is the zone of polarizing activity (ZPA)

• ZPA regulates development along anterior/posterior axis of the limb

• cells nearest the ZPA form posterior structures, and those furthest form anterior structures

• sonic hedgehog is a secreted signal produced by the ZPA

• the production of a forelimb or a hindlimb depends on patterns of Hox gene expression

• BMP-4, FGF, hedgehog, and Hox proteins are examples of a larger set of molecules governing cell fates in animals

• Higher concentration of sonic hedgehog determines posterior side (long digits)

• Lower concentration of sonic hedgehog determines anterior side (short digits)