Chapter 12 Out Line

1)      Reproduction

a)      Is the basic function of all living organisms.  In order for organisms (species) to live they have to reproduce. 

b)      Some organisms reproduce individually (asexually) and some organisms reproduce sexually.

2)      Cell Division and reproduction

a)      Asexual reproduction

i)        This requires a single parent.  One or more of the organisms cells form a genetically identical offspring.

ii)       A clone is a group of genetically identical cells or organism(s) produced through asexual reproduction.  Many organisms reproduce asexually.

iii)     Prokaryotes reproduce by dividing into two.  This is called binary fission.  Some Eukaryotes also reproduce by dividing in two.  Only one-celled Eukaryotes do this.  Others reproduce asexually.

iv)     Hydra reproduces by a process called budding, the buds grow to adult and detach to new individuals.  Planaria reproduces by a process called fragmentation which is breaking into pieces each piece is a new worm which can  reproduce sexually.

v)      Asexual reproduction in plants is called vegetative reproduction.  This reproduction is used to fill a space with plants. 

vi)     Potatoes grow from new eyes on underground stems.

vii)   Aspen trees reproduce from the roots of older trees making an "aspen clone."

b)      Chromosome Numbers

i)        Every species has a characteristic number of chromosomes.

ii)       Prokaryotes (bacteria & cyanobacteria) have only one major chromosome; it has a single circle of DNA.

iii)     Eukaryote number of chromosomes varies by species.  Humans have 46 chromosomes, turkeys have 82 chromosomes, and giant redwoods have 22 chromosomes.  It is not the number that is important but what is on the chromosomes.

iv)     Cells of most organisms that reproduce sexually have similar chromosomes.

v)      A diploid cell is a cell that carries a double set of chromosomes.  We call this 2n and most human body cells are diploid.  Haploid cells have just one set of chromosomes.  We say these are 1n (or just n) and these are our gametes (egg and sperm cells).

vi)     Homologous chromosomes are the 2 chromosomes of a homologous pair.  They have the same genes on each chromosome.  Diploid organisms have these.  [humans have 22 pairs of homologous chromosomes and one pair of sex chromosomes that are not homologous in human males- XY]

vii)   Homologues chromosomes have the same genes, but their DNA sequences may be different.

viii) Asexual reproduction: the parent and the offspring have the same set (identical) of chromosomes. 

ix)     Sexual reproduction two parents contribute to the offspring’s chromosomes.

x)      Somatic cells are body cells.  They come from the individual and are diploid.  The sexual reproductive cells of diploid organisms are haploid.

xi)     In sexual reproduction of animals, the male gametes are sperm and female gametes are ova or eggs.  In plants, they are pollen (male gametes) and ova. 

xii) In fertilization the female and male haploid gametes join and their nuclei fuse together to form a diploid nuclei.  A new organism develops from the diploid fertilized egg or zygote.

xiii)  Meiosis is a special cell division process in which a haploid gamete is produced.

xiv)  In fungi and simple plants meiosis produces different types of haploid cells called spores.  Spores can develop into haploid organisms without fertilization.  Spores can often survive harsh conditions and germinate at some future time when conditions are good.

xv)  Meiosis produces haploid gametes.  An exception: Desert whiptail lizard’s eggs develop without being fertilized, they are all females!  This is quite unusual in the animal world. 

c)      Cloning

i)        In 1970 scientists developed ways to insert DNA sequences into bacteria and other cells.  This process is known as cloning a gene. (or genetic engineering).

ii)       People have cloned crops, but artificial cloning is still a new idea.

iii)     The first cloned animal was a frog.  In Scotland they cloned the famous sheep known as Dolly.  Many species of animals have been cloned.

iv)     Artificial cloning is when scientist transfers a somatic cell’s nucleus from one sheep to the ovum of a different sheep.  The resulting embryo in then implanted into the uterus of a host mother sheep and the lamb that is born is an "identical twin" or a clone of the sheep whose nucleus was used.

d)      Meiosis and the Production of Gametes

i)        Meiosis is different from mitosis in several ways such as

(1)   Cells divide twicemeiosis

(2)   Meiosis distributes a random mixture of maternal and paternal chromosomes to each gamete.

(3)   Meiosis involves two nuclear divisions.  Meiosis 1 and meiosis 2.

          (4) Produces haploid gametes.

Crossing over is a process when cells exchange corresponding pieces of DNA during meiosis.  Pieces of homologous chromosomes are essentially "cut and pasted" with each other.

iii)     Each division includes the same four stages as mitosis from (prophase to telophase).

iv)     The results of meiosis in humans.  In males, meiotic division usually results in four equal sized sperm, each with 23 chromosomes.  In females, two polar bodies form, and only one egg cell results.  "Goal" for males: mass sperm production.  "Goal" for females: one large, high quality ova.

v)      Meiosis I contains prophase 1, metaphase 1, anaphase 1, and telophase 1.  Meiosis II contains prophase 2, metaphase 2, anaphase 2, and telophase 2. 

vi)     Polar bodies are two small cells in female animals whose function is to remove extra chromosomes so the single ova can be haploid.  The polar bodies die during or soon after meiosis.

3)      Sexual Reproduction

a)      Sexual Reproduction in microorganisms:

i)        Prokaryotes reproduce asexually through cell fission.  They also exchange genetic information occasionally.

ii)       Conjugation is when a tube of cytoplasm temporarily connects some bacterial cells, DNA passes through this tube.  This can be considered a form of bacteria "sexual reproduction."

iii)     Microorganisms that reproduce sexually and asexually include many unicellular or colonial green algae. (Protists)

iv)     Alternation of generations is the life cycles of these organisms include both haploid and diploid stages.

v)      Plasmodium, the organism that causes malaria, infects one species during the diploid stage and another during the haploid stage. (A protist pathogen with a flagella)

vi)   Stress and poor nutrition induce sexual reproduction in many organisms that normally use asexual reproduction.

vii)  Most fungus consists of filaments of haploid cells in the soil (fungal hyphae).  Some fungi have particularly complicated sexual reproductive cycles, some only reproduce asexually.  The mushroom is the spore producing body of many types of fungi.

b)      Sexual reproduction in Plants



i)        Higher  p
lants generally reproduce sexually.  Some can reproduce asexually.

ii)       Plant life cycles involve alternation of generations.

iii)     More complex plants are adapted to live in a wider variety of environments.  These plants have larger diploid structures.

iv)     Wind or symbiotic animals carry the sperm inside tough protective pollen grains to the female organs. (pollen are male gametes).

v)      The most successful plants are the flowering plants.  Each flower may produce sperm, ova, or both.

vi)     At the center of an ovum producing flower, one or more modified leaves called carpels fuse edge to edge, forming a hollow structure.

vii)   The ovary is the base of this structure.  Inside are one or more small structures called ovules (eggs).

viii) Within each ovule, a specialized cell undergoes meiosis.

ix)   Cells in the anther undergo meiosis.  Then produce four haploid cells (pollen).

x)     Sexual reproduction begins as the anthers shed pollen.

xi)    Pollination is the transfer of pollen from anther to carpel.  Many pollinators are insects but, many plants (such as grasses) use the wind to pollinate.

xii)   Some insects and flowering plants have become so completely dependent on each other that neither can reproduce without that other.  Example: Yucca plant and moth.

xiii)  Fertilization occurs when one sperm nucleus fuses with the egg.

xiv)  The second sperm nucleus fuses with the two polar nuclei, forming a triploid cell that develops into the endosperm. (food for the plant/seed, usually contains much starch).

xv)   Then fertilization occurs this ends the short haploid stage in the life cycle of a flowering plant.

xvi)   Auxin produced by the seeds stimulates the ovary to enlarge and develop into a fruit.  The function of a fruit is to disseminate the seeds.

xvii)  Many seeds are carried by the wind.

xviii) The female reproductive structures of many plants release chemical signals that attract sperm or animals that carry pollen.

xix)   Flowering plants adaptations:

(1)   The dominance of the diploid stage in the life cycle, which allows development of complex structures.

(2)   The evolution of pollen, which allows transfer of sperm for plant to plant without the need for water. (pollen do not need a liquid environment therefore, are more advanced than animals sperm).

(3)   The evolution of the seed, which protects the dormant embryo and provides food and protection for the young plant.

(4)   A variety of adaptations that promote pollen and seed dispersal.

c)      Sexual Reproduction in Animals.

i)      A large portion of animals reproduce sexually.

ii)     Animals that reproduce sexually have organs called gonads that produce haploid gametes.

iii)   Ovaries produce ova and testes produce sperm.

iv)   In simple animals like the planaria and earth worm, each individual produces both eggs and sperm.

v)    Few vertebrates produce both eggs and sperm.

vi)   The simplest animals are aquatic.

vii)   External fertilization or spawning is the release of large numbers of gametes into the open. (most fish and amphibians)

viii)  Many fail to live.

ix)     During internal fertilization, a male releases sperm into a female reproductive organ.

x)      Amphibians and vertebrates are intermediate between internal and external fertilization.

xi)     Internal fertilization is more efficient on land.

xii)   Mammals that have hair and produce milk include many of the most extreme examples of this trend.

xiii)   Humans and elephants usually only produce one offspring at a time.

xiv)  In most animals, sperm are much smaller that the egg.

xv)   Animal sperm can not live long after it is produced. (Human males produces billions of sperm cells a day)

xvi)  If sperm reaches an egg both must be shed at about the same time and place.

xvii)   Internal fertilization is more efficient but still many sperm must be produced because:

(1)   Fertilization must occur in a brief time.

(2)   The sperm must swim to the egg.  Few sperm reach the egg.

(3)   The enzyme activity of many sperm is required to penetrate the membranes and layers of cells around the egg.

xviii)    Many insects avoid these problems by storing sperm in a pouch inside the female.

xix)   Female bees and ants, may store sperm from a single mating for an entire life span and use it to produce thousands of eggs.

4)      Reproduction in Humans

a)      Egg Production and the Menstrual Cycle

i)   In human females, the ovaries are located inside the body cavity.

ii)  The egg travels through one of two tubular structures, called oviducts, to the uterus.

iii)  In birth, strong muscular contractions push the baby out of the uterus through the vagina.

iv)  The menstrual cycle is the egg releasing cycle.

v)   The first day of menstrual flow marks the first day or the menstrual cycle.

vi)  The hypothalamus monitors and helps adjust the level of hormones in the circulatory system.

vii)   The start of the menstrual flow, estrogen and progesterone, hormones released into the bloodstream by the ovaries, is very low.

viii)  Gonadotropin-releasing hormone (GnRH) follicle-stimulating hormone (FSH), luteinizing hormone (LH) are all involved.

ix)   FSH causes an egg to start maturing inside a fluid filled sac, or follicle, in the ovary.

x)   Ovulation occurs when LH from the pituitary gland causes the follicle to burst and release the egg into oviduct.

xi)     The ruptured follicle forms into a corpus luteum.

xii)   The hypothalamus detects the increased levels of estrogen and progesterone, if the egg is not fertilized, the approximate 28 day menstrual cycle starts again.

xiii) If pregnancy occurs the corpus luteum functions for the first 3 months of gestation, or development of the embryo within the uterus. It releases high levels of est. and prog. to maintain the pregnancy.

xiv)   After 3 months the placenta takes over the release of these hormones and maintains the pregnancy.

xv)  Soon after birth, the placenta separates from the uterine wall is called "afterbirth".

xvi)   Menstruation is a characteristic of female primates.

xvii)  Menstrual cycles, estrus cycles, and ovulation at intercourse are all adaptations that help ensure reproductive success within different species.

b)      Sperm Production

i)   In human males, the testes are located in the scrotum, an out pocketing of the body wall.

ii)  Human sperm needs a slightly cooler environment to develop normally.

iii)   During ejaculation, sperm and seminal fluid are released, together called semen.

iv)  LH stimulates cells between those tubules to secrete androgens, a group of male hormones.

v)   The major androgen secreted by the testes is testosterone.

c)    Secondary Sex Characteristics

i)        Females produce more estrogen, and males produce more androgens.

ii)       Hormones control the development of secondary sex characteristics.

iii)     Changes begin at puberty, the beginning of sexual maturation.

iv)     Androgens control the development of secondary sex characteristics in males such as facial hair and deeper voices.

v)      Most males enter puberty later than most females.

d)      Infertility and Contraception

i)        Blocked oviducts can prevent fertilization.

ii)       Hormone treatments can sometimes establish regular ovulation.

iii)     Invitro fertilization can help women with blocked oviducts to conceive.

iv)     After external fertilization the embryos are implanted in the mother’s uterus. ("test tube babies")

v)      Some methods of contraception provide a physical barrier between the egg and sperm.

vi)     The condom is a sheath that is slipped over the penis prior to intercourse.

vii)   A diaphragm is a flexible cup that is inserted through the vagina to cover the cervix, along with a spermacide.

viii)  Other methods of contraception prevent ovulation (the pill).

ix)     Norplant implanted in the upper arm.

x)     Depo-provera is an inject able drug.

xi)    Taking pills regulates estrogen and progesterone (the pill).

xii)   Other contraceptives include foams or jellies that immobilize sperm.

xiii)  Surgical sterilization is another form of contraception.

xiv) The sperm ducts can be cut and tied in a process called a vasectomy.

xv)   The oviducts can also be cut and tied in a process called a tubule legation.

The only 100% reliable method of birth control is abstinence from intercourse. HOME     Back To Lesson Plans    

By:  Samantha C.  3-21-06,