Biology - CH 2 - Reproduction

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Reproduction: Process by which an organism propetuates itself and its species.
Cell Division: Cell doubles its organelles and cytoplasm.

Cell replicates its DNA.

Then divides in two.
Purpose of Cell Division for unicellular/multicellular organisms:: Unicellular organisms - Reproduction

Multicellular organism - method of growth, development, and replacement of worn-out cells.
Mitosis: Division and distribution of cell's DNA to its two daughter cells (exact copy)

Karyokinesis - Nuclear Division, followed by:

Cytokinesis - Cell division

Prior to initiation of mitosis, cell undergoes period of growth and replication of DNA called interphase
Karyokinesis: Nuclear Division
Cytokinesis: Cell Division
Mitosis Acronym: I nterphase
P rophase
M etaphase
A naphase
T elophase
C ytokinesis
Mitosis - Interphase: 90% of life

Chromosome is replicated

Individual chromosome is not visible

DNA uncoiled called chromatin
Sister Chromatids: After replication the chromosomes consist of two identical sister chromatids held together at a central region called the centromere.
Centromere: After replication the chromosomes consist of two identical sister chromatids held together at a central region called the centromere.
Chromatin: DNA is uncoiled
Mitosis - Prophase: Chromosomes Condense

Centriole pairs separate and move towards the opposite poles of the cell

Spindle apparatus forms between them

Nuclear membrane dissolves, allowing the spindle fibers to interact with the chromosomes.
Mitosis - Metaphase: Centriole pairs now at opposite poles of the cell

Fibers of spindle apparatus attach to each chromatid at the centromere to align the chromosomes at the center of the cell (equator) forming the metaphase plate.
Metaphase plate: Fibers of spindle apparatus attach to each chromatid at the centromere to align the chromosomes at the center of the cell (equator) forming the metaphase plate.
Mitosis - Anaphase: Centromeres split so that each chromatid has its own distinct centromere (each chromatid has own centromere) allowing separation

Sister chromatids pulled to opposite poles by shortening of spindle fibers

Spindle fibers are composed of microtubules
Mitosis - Telophase: Spindle apparatus dissapears.

Nuclear membrane forms around each set of newly formed chromosomes.

Each nucleus contains diploid (2n), same as parent.

Chromosomes uncoil assuming interphase form
Mitosis - Cytokinesis: Near end of telophase, cytoplasm divides into two daughter cells each with nucleus and organelles.

Cleavage furrow forms and the cell membrane indents along equator of the cell and finally pinches through the cell, seperating the two nuclei.
Mitosis for Plants: Two major differences:
1) Plant cells lack centrioles
2) Plant cells are rigid and can't form cleavage furrow. Divide via cell plate.
Mitosis in a Nutshell: Prophase: Chromosomes condense; spindles form

Metaphase: chromosomes align

Anaphase: sister chromatids seperate

Telophase: new nuclear membranes form
Meiosis: Sexual Reproduction

Sexual Reproduction occurs via fusion of gametes (produced by mesiosis)

Meiosis produces haploid (1N)

Meiosis involves two divisions of primary sex cells resulting in four haploid cells called gametes.
Meiosis - Interphase: As in mitosis.

Parent cell's chromosomes and replicated during interphase resulting in 2N number of sister chromatids.
Meiosis - First Meiotic Division: Prophase I: Chromatin condenses into chromosomes

Spindle apparatus forms

Nucleoli and nuclear membrane dissapear

Homologous chromosomes (chromosomes that code for the same traits, one from each parent), come together and intertwine in a process called synapsis.

Each chromosome consists of two sister chromatids, each synaptic pair of homologous chromosomes contains four chromatids, and is therefore often called a tetrad.

Crossing over can occur.
Meiosis - First Meiotic Division: Anaphase I: Homologous pairs separate and are pulled to opposite poles of the cell.

Process is called disjunction.
Meiosis - First Meiotic Division: Telophase I: Nuclear membrane forms around each new nucleus.

Each chromosome still consists of sister chromatids joined at the centromere.
Meiosis - Second Meiotic Division: Second division very similar to mitosis, without preceding chromosomal replication.

The chromosomes align at the equator, seperate and move to opposite poles, and are surrounded by a reformed membrane.

New cells have haploid number of chromosomes.

In females, only 1 of these daughter cells becomes a functional gamete.
Asexual Reproductive Mechanisms: Production of offspring without fertilization.

Fission
Budding
Regeneration
Parthenogenesis

Prokaryotes reproduce asexually

In animals, invertabrates are more common to reproduce asexually

All plants reproduce asexually in some form
What is Fission and by whom?: Prokaryotic organisms reproduction method

DNA replicates and a new plasma membrane and cell wall grow inward along the midline of the cell dividing into two equal parts.

Very similar process occurs in primitive eukaryotic organisms.

amoebae, paramecia, algae, bacteria
What is Budding and by whom?: Replication of the nucleus followed by unequal cytokinesis.

Cell membrane pinches inward to form a new cell that is smaller in size but genetically identical to the parent cell and will grow to adult size.

May separate immediatly or grow as an outgrowth.

Hydra, yeast
Regeneration and by whom?: Regrowth of a lost or injured body part

Replacement occurs via mitosis.

Hydra, starfish, salamanders, tadpoles
Parthenogenesis: Development of an unfertilized egg into an adult organism

Occurs naturally in some lower species.

Artificial parthenogenesis can occur in some species.
Asexual reproduction in Plants Types: Spore Formation
Vegetative propagation
Asexual Reproduction in Plants - Spore Formation: All plants exhibit alternation of generations in which a diploid generation is succeeded by a haploid generation

Diploid sporophyte generation produces haploid spores which develop into the haploid gametophyte generation.
Spores: Specialized cells with hard coverings that prevent loss of water.
Asexual Reproduction in Plants - Vegetative Propagation: Undifferentiated tissues in plants, called meristems, provide a source of cells that can develop into an adult plant.

Introduces no genetic variation
Meristems: Undifferentiated tissues in plants
Asexual Reproduction in Plants - Natural Vegetative Propagation: Bulbs split to form several bulbs. Occurs in tulips and daffodils.

Tubers are underground stems with buds, like the eyes of potatoes, that can develop into adults plants.

Runners are stems running above and along ground, extending from main stem. Can produce new roots and upright stems as they do in strawberry and lawn grasses.

Rhizomes (stolons) are woody, underground stems. They can develop new upright stems as they do in ferns and iris plants.
Asexual Reproduction in Plants - Artificial Vegetative Propagation: Humans may use in agriculture

A cut piece of stem can develop new roots in water or moist ground. Geranium and willow. Synthetic plant hormones called auxins can be used to accelerate root formation.

Layering - Stems of certain plants (blackberry and raspberry) will take root if bent to the grounded and covered in soil.

The stem of one plant called the scion can be attached to the rooted stem of another closely related plant called the stock. The cambium tissue of both stems must in contact.
Pathway of Sperm: S eminiferous tubules
E pididymis
V as Deferens
E jaculatory Duct
N othing
U rethra
P enis
Female reproductive Anatomy: Once a month, an immature ovum is released from the ovary into the abdominal cavity and drawn into the nearby ovidcut.
Ovaries: Abdominal Cavity, below digestive system

Ovaries consist of thousands of follicles.

All eggs for lifetime of woman are present at birth.
Follicles: Multi-layered sac of cells that contains, nourishes, and protects an immature ovum.

Follicle cells produce estrogen.
Uterus: Site of fetal development
Cervix: Lower end of uterus, connects to vagina
Female Sex Hormones: Overies synthesize and secrete the female sex hormones including estrogens and progesterone.

Secretion of both is regulated by LH and FSH, both of which are regulate by GnRH.
Estrogens: Steroid hormones for female maturation.

Stimulate development of the female reproductive tract and contribute to the development of secondary sex characteristics and sex drive.

Responsible for thickening of the endometrium (uterine wall).

Secreted by the ovarian follicles and corpus luteum
What causes thickening of endometrium: Endometrium (uterine wall) thickens due to Estrogens.
Progesterone: Steroid hormone secreted by corpus luteum during luteal phase of the menstrual cycle.

Stimulates the development and maintenance of the endometrial walls in preparation for implantation.
Menstrual Cycle: Hormonal secretions of the ovaries, hypothalamus, anterior pituitary play important roles in the female reproductive cycle.

Cycle divided into: follicular phase, ovulation, luteal phase, menstruation.
The Menstrual Cycle in a Nutshell: Follicles mature during follicular phase (FSH, LH)

LH surge at midcycle triggers ovulation

Ruptured follicle becomes corpus luteum and secretes estrogen and progesterone to build up uterine lining in preparation for implantation; LH and FSH inhibited

If fertiliazation doesn't occur, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again.
Menstrual Cycle - Follicular Phase: Begins with the cessation of the menstrual flow from previous cycle

FSH from anterior pituitary promotes development of the follicle, whech grows and begins to secrete estrogen
FSH: Follicle Stimulating Hormone

Anterior pituitary

Promotes development of follicle
Menstrual Cycle - Ovulation: Midway through the cycle ovulation occurs

Mature ovarian follicle bursts and releases ovum.

Caused by surge in LH, preceded by peak in estrogen levels.
Menstrual Cycle - Luteal Phase: LH induces ruptured follicle to develop in the corpus luteum, with secretes estrogen and progesterone.
LH: Luteinizing Hormone
Menstrual Cycle - Menstruation: No fertilization -> Corpus luteum atrophies -> drop in progesterone and estrogen -> endometrium sloughing -> menstrual flow
Menses: Menstrual Flow
Menstrual Cycle - Fertilization: Developing placent produces hCG (human chorionic gonadotrophin), maintaining corpus luteum and thus, supply of estrogen and progesterone -> maintains uterus until placenta takes over production of hormones
Sexual Reproduction in Plants: Life cycles characterized by alternation of the diploid sporophyte generation and the haploid gametophyte generation.

Evolutionary trend has been towards an increased dominance of the sporophyte generation.
Alteration of generations in Plants cycle: Sporophyte (2N) -> Spore (1N) -> Gametophyte (1N) -> Fertilization (2 * 1N) Gametes -> Sporophyte (2N)
Gametophyte Generation: Haploid gametophyte generation produces gametes by mitosis.

Union of male and female gametes at fertilization restores the diploid sporophyte generation.
Do gametophytes and sporophytes reproduce sexually or asexually?: Sporophytes (2N) - Asexually
Gametophytes (1N) - Sexually
Gametophyte Generation - Mosses: Mosses, gametophyte is dominant generation

Sporophyte is smaller, short-lived, depends on gametophyte for energy and nutrients.

Sporophytes grow on top of gametophytes and produce spores that develop into gametophytes.
Sporophyte Generation: Diploid sporophyte generation produces a haploid (monoploid) spore by meiosis. Spores divdide by mitosis to produce haploid or gametophyte generation
Sporophyte Generation - Ferns: Sporophyte is dominant, familiar form.

Sporophyte releases spores from undersides of leaves -> develop into small heart shaped gametophytes.
Sporophyte Generation - Angiosperms: Flowering plants or angiosperms have gametophytes consisting of few cells and very short lived.

The woody plant that is seen (maple, rose) is the sporophyte stage.
What is the reproductive structure in angiosperms: Flower
What two types of flowers are there?: Those with stamens (male plants) and those with pistils (female plants)
Stamen: Male organ of flower

Thin stalk-like filament with a terminal sac called the anther.

Anther produces monoploid spores wich develop into pollen grains.
Pistil: Female organ of flower.

Three parts:
1) Stigma - Sticky top part of pistil wich catches pollen
2) Style - Tuve-like strucutre connecting thestigma to the ovary at base of pistil
3) Ovary - Enlarged base of the pistil. Contains 1 or more ovules each containing a monoploid egg nucleus.
Petals: Specialized leaves

Surround and protect pistil

Colors and odors attract insects which transfer pollen between plants allowing for fertilization
Sepals: Green leaves that cover and protect the flower bud during early development
Fertilization of plants - Male Gametophytes: Male Gametophyte - Pollen Grain. Contains a tube nucleus and a generative nucleus formed by mitosis of microspore.

Pollen grains transferred from anther to stigma and generative nucleus divids to form sperm nuclei which are the male gametes.
Fertilization of plants - Female Gametophytes: Female Gametophyte - Develops in the ovule from one of four spores.

Gametophyte is the embryo sac and contains nuclei including two polar (endosperms) nuclei and an egg nucleus.
Fertilization of Plants: Fertilization occurs when the sperm nuclei enter the embryo sac.

One sperm nucleus fuses with the egg nucleus to form the diploid zygote, which develops into the embryo.

Other sperm nucleus fuses with the 2 polar bodies to form the endosperm (triploid or 3N).

Endosperm provides food for the embryonic plant.

In dicotyledonous plants, the endosperm is absorbed by the seed leaves (cotyledons)
Fertilization of Plants in a Nutshell: 1 sperm nucleus + 1 egg nucleus -> zygote -> embryo

1 sperm nucleus + 2 polar nuclei -> 3N endosperm
Seed Formation: Zygote divides mitotically to form the cells of the mass of cells called the embryo.

Embryo consists of following parts:
Epicotyl
Cotyledons
Hypocotyl
Endosperm
Seed Coat
What does the embryo of a plant consist of?: Embryo consists of following parts:
Epicotyl - Precursor of upper stem and leaves
Cotyledons - Seed leaves. Dicots have two seed leaves, monocots have only one.
Hypocotyl - Develops in lower stem and root.
Endosperm - Grows and feeds the embryo. In dicots, the cotyledon absorbes the endosperm.
Seed Coat - Develops from the outer covering of the ovule. Embryo and seed coat together comprise the seed.
Seed Coat
Seed Dispersal: Fruit, in which seeds develop, fromed from the ovary walls, base of flower, and other consolidated pistil components.

Fleshy (tomatoe) or hard (nut)
Plant Development: Growth in higher order plants is restricted to the embryonic cells called meristem cells.
Meristem Cells: Undifferentiated plant cells.
Plant Development - Apical Meristem: Found in tips of roots and stems, growth in length only occurs at these points.
Plant Development - Lateral Meristem: AKA Cambium

Located between xylem and phloem.

Permits growth in diameter and can differentiate in new xylem and phloem.

Not active in monocots (grasses) or herbaceous dicots (alfalfa) but is predominant in woody dicots like oaks.

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