Reproduction Humans and Plants

Reproduction Individual organisms do not live forever. Therefore the continuity of a species relies on individuals reproducing. There are two types of reproduction: asexual reproduction and sexual reproduction.

Two Types of Reproduction Asexual Offspring are produced by a single parent Found in stable environments to which they are very well suited No sperm and egg Sexual Involves the fusion of two gametes (sex cells), one from a male and the other from a female Diversity allows adaptation to changing environment Egg and Sperm

Asexual Reproduction Methods There are several ways an organism may reproduce asexually: Fission and Budding Fragmentation Spore Formation Vegetative Reproduction Parthenogenesis

Fission and Budding Fission is common among unicellular organisms such as bacteria occurs when a parent cell splits into two daughter cells forming a new organism Budding can be seen in unicellular organisms and small multicellular animals similar to fission except that the division of the cytoplasm is unequal and the new individual arises from an outgrowth, or bud, from the parent

Fission and Budding

Fragmentation Fragmentation occurs in multicellular organisms when the body of the organism breaks into two or more parts each of which will form a new organism common in flatworms, marine worms, and echinoderms (starfish) With worms and new individual may form when the worm gets so long that it simply falls apart forming new organisms.

Spore Formation Spores are formed by fungi and are often contained within a structure known as a sporangium which will disintegrate releasing the spores into the environment When a spore lands in a suitable environment it will germinate forming a new fungus. Spores are formed by budding.

Vegetative Reproduction Many plants are capable of vegetative reproduction which is the separation of one plant to form a new, independent plant Vegetative reproduction may arise from many parts of a plant including the leaves and underground stems

Parthenogenesis Parthenogenesis is the development of an unfertilized egg into a new individual that is a clone of the parent In order to obtain the needed diploid set of chromosomes the egg will often duplicate by mitosis and then fuse to give the egg two sets of chromosomes. Animals that are parthenogenic include bees, wasps, ants, and some species of birds and lizards.

Parthenogenesis The fertilized eggs of bees, wasps and ants will develop into females A population of these organisms in some regions may be composed entirely of female organisms An unfertilized egg however will duplicate by mitosis, fuse to form a diploid cell, then further divide and form into males

Hermaphrodite Both male and female sex organs

Sexual Reproduction Sexual reproduction involves: Gamete production by a type of cell division called meiosis Normal body cells have a diploid number of 46 chromosomes Gametes have the haploid number of 23 chromosomes When the gametes fuse, they form a zygote with the diploid number of 46 chromosomes Further mitotic divisions allow the zygote to grow and produce a large number of cells that differentiate to form the various different types of tissues that make up the new individual

Reproductive Systems Reproductive systems are composed of primary and secondary sex organs In animals the primary sex organs which produce the gametes are the ovaries in females and the testes in males Secondary sex organs include: various glands that produce nutrition and lubrication for gametes ducts and chambers that provide areas for storage and development of the gametes organs for mating and protection of the developing embryo

Fertilization Fertilization can be: Internal: reptiles, birds and mammals External: most fish and amphibians

Process of Fertilization in Animals Upon meeting the ovum, sperm start to break down the jelly coated membrane Only one sperm head containing the nucleus will enter the egg Once the sperm has entered the egg, the membrane changes so that no other sperm can enter is the fusion of gametes to produce a new organism.

Human Reproduction

Development of Gametes

Male Gametes Male gametes are called sperm and are produced in the testes acrosome – releases enzymes to penetrate egg nucleus – contains DNA mitochondria – energy to swim tail – to swim - delivers sperm - stores sperm - produces sperm and testosterone - keeps sperm 1–2 ° lower than body temperature

fluids for transport and nutrition of sperm Structure of Male Reproductive System kidney urinary bladder ureter urethra seminal vesicle prostate gland vas deferens penis scrotum epididymis testis (testes) fluids for transport and nutrition of sperm

Female Gametes Female gametes are called ova (eggs) and are produced in the ovaries Cytoplasm – storage of food for ovum Nucleus – contains DNA Membrane – hardens after one sperm enters to keep others out - where baby develops - muscle that opens for baby to be born - receives sperm produces eggs - and hormones egg fertilization and travel - - where embryo implants

Structure of Female Reproductive System kidney ureter fallopian tube ovary urinary bladder uterus urethra cervix vagina

Egg Development in Ovary Females are born with all the egg cells they will ever have, but they are not completely developed By puberty, a female’s ovaries contain about 400,000 follicles, each containing a primary oocyte (egg cell) Every 28 days or so hormones cause one follicle and egg to mature, break open and the oocyte is released

Human Egg Fertilization

Male Gamete Female Gamete   Male Gamete Female Gamete Size Relatively smaller Relatively larger Key Structures Head (nucleus and acrosome) Middle piece (mitochondria) Tail (flagellum) Nucleus Outer membrane (jelly coat) Large amount of cytoplasm Relative Numbers 50 million - 500 million sperms released during ejaculation 1 ovum matured and released each month Motility Motile (able to move by propelling its tail) Mobile (Passive movement due to action of cilia and peristalsis of oviduct wall) X or Y Chromosomes Each sperm contains either an X or a Y chromosome All ova contain only the X chromosome

Plant Reproduction

Alternation of Generations All land plants undergo alternation of generations. In this process, individuals have a multicellular haploid phase called the gametophyte and a multicellular diploid phase known as the sporophyte. The two phases of the life cycle are connected by distinct types of reproductive cells—gametes and spores.

All Land Plants Undergo Alternation of Generations 2. FERTILIZATION Gametophyte (n; multicellular, haploid) MITOSIS MEIOSIS Sporophyte (2n; multicellular, diploid) Spores (n) Haploid (n) Diploid (2n) Gametes (n) Zygote (2n) 1. 3. 5. 4. Alternation of generations always involves the same five key events: (1) Haploid gametophytes produce haploid gametes by mitosis. (2) Two gametes unite during fertilization to form a diploid zygote. (3) The zygote divides by mitosis, developing into a multicellular, diploid sporophyte. (4) The sporophyte produces haploid spores by meiosis. (5) Spores divide by mitosis and develop into a haploid gametophyte.

Gametophyte-Dominated Life Cycles Evolved Early Haploid (n) Diploid (2n) Eggs form in archegonia Sperm form in antheridia Sperm swim to egg Spores (n) are produced in sporangia by meiosis, dispersed by wind Mature sporophyte     (2n) Egg (n) Zygote (2n) Developing sporophyte (2n) Archegonium Mature gametophyte (n) Developing gametophyte Spore (n) FERTILIZATION MITOSIS MEIOSIS Mosses: Gametophyte is large and long lived; sporophyte depends on gametophyte for nutrition.

Sporophyte-Dominated Life Cycles Evolved Later Ferns: Sporophyte is large and long lived but, when young, depends on gametophyte for nutrition. Spore (n, dispersed by wind) Mature gametophyte (n, underside) Sperm develop in antheridia 1 mm Eggs develop in archegonia Sperm swim to egg Zygote (2n) Sporophyte (2n; develops on gametophyte) Developing gametophyte (n) Spores are produced in sporangia Gametophyte (n; side view) Mature sporophyte (2n) FERTILIZATION MITOSIS MEIOSIS Archegonium

Heterospory Another important innovation found in seed plants is heterospory, the production of two distinct types of spores, male and female. The two types of spore-producing structures in heterosporous species are microsporangia and macrosporangia. Microsporangia produce microspores that develop into male gametophytes that produce sperm. Macrosporangia produce megaspores that develop into female gametophytes that produce eggs. Thus, the gametophytes of seed plants are either male or female, but never both.

Pollen When pollen evolved, heterosporous plants lost their dependence on water for fertilization. Seeds Seeds allow embryos to be dispersed to a new habitat, away from the parent plant. Seeds are often dispersed by wind, water, or animals. The evolution of heterospory, pollen, and seeds triggered a dramatic increase of seed plants starting about 290 million years ago.

Heterospory (micro- and megaspores) in Gymnosperms Mature sporophyte (2n) Developing sporophyte Seed (disperses via wind or animals) Embryo (2n) Ovules (contain megasporangia) Ovulate cone Female gametophyte (n) Archegonia Eggs (n) Mother cell (2n) Pollen produces sperm Cones with microsporangia Microspore (n) forms pollen grain Pollen grain (male gametophyte Megasporangium Pollen grain Megaspore divides to form female gametophyte (n), which produces archegonia and eggs by mitosis. (Only one egg is fertilized and develops.) Note that the red dots here and elsewhere represent nuclei Pollen grains disperse via wind Four meiotic products; one is large and forms the megaspore (n) Three meiotic products die MEIOSIS MITOSIS POLLINATION FERTILIZATION MITOSIS

Flowers Flowering plants, or angiosperms, are the most diverse land plants living today. About 250,000 species have been described, and more are discovered each year. The success of angiosperms in terms of geographical distribution, number of individuals, and number of species revolves around a reproductive organ: the flower. Flowers contain two key reproductive structures: stamen and pistils (carpels). The stamen contains the anther, where microsporangia develop. The pistil (carpel) contains the ovary in which the ovules are found. Ovules contain the megasporangia.

Heterospory in Angiosperms Megasporangium Sperm travel down growing pollen tube to reach egg Pollen lands near female gametophyte; produces pollen tube and sperm Pollen grains disperse via wind or animals (the red dots here and elsewhere are nuclei) Nutritive tissue Embryo (2n) Developing sporophyte Seed (disperses via wind or animals) Zygote (2n) Endosperm (3n) forms nutritive tissue in seed Mature sporophyte flower (2n) Flower Ovule Ovary Carpel Stamen Anther Microspore (n) forms pollen grain Pollen grain (male gametophyte) Egg Megaspore (n: retained in ovary) Female gametophyte (n: retained in ovary) MEIOSIS MITOSIS POLLINATION FERTILIZATION

Flowers Flowers vary in size, structure, scent, and color in order to attract different pollinators. The evolution of the flower made efficient pollination possible. Fruits For the Discovery Channel Video Plant Pollination, go to Animation and Video Files A fruit is a structure that is derived from the ovary and encloses one or more seeds. The evolution of fruit made efficient seed dispersal possible.

Flower Parts

Pistil and Stamen STAMEN consists of: Filament: positions the anther to release pollen Anther: makes pollen (male gametes) Ovary: contains ovules which contain the egg cell (female gamete) Style: positions the stigma to receive pollen Stigma: receives pollen PISTIL (carpel) consists of:

Pollination Pollination is the transfer of pollen from the anther to the stigma Cross-pollination occurs when the pollen from one flower lands on the stigma of a different flower This is ideal and creates variation in genetics Self-pollination occurs when the pollen of one flower lands on the stigma of the same flower Not as desirable since it reduces variation Flowers will prevent self-pollination by having the stigma higher than the stamen or by having the stamen and stigma mature at different times

Life Cycle of an Angiosperm