Organismal Biology: Reproduction and Development

• Organismal Biology covers reproduction and development.
• This is from the Final term, Week 1.

Phylogeny Recap

• In Phylogeny, The Principle of Parsimony means the best hypothesis needs the fewest evolutionary changes.
• Polypheletic clade does not consist of the ancestor species and all its descendants.
• The derived character state is not the form of character that was present in the common ancestor of the group

Objectives

• To define plant and animal reproduction and development.
• To differentiate between sexual and asexual reproduction.
• To identify different types of animal development and types of sexual and asexual reproduction.
• To compare and contrast plant and animal reproduction by creating a Venn-Diagram.

Reproduction

• A biological process by which offspring are produced from a parent or parents.
• There are two types of reproduction: Asexual and sexual.

Asexual Reproduction

• No gametes are involved; parts of a mature organism develop int new individuals.
• Offspring are genetically identical to the parent.
• Binary Fission is the separation of the body into two new bodies and is common in single-celled organisms.
• Budding occurs when a new organism develops as an outgrowth or bud from the parent body.
• Fragmentation occurs when the parent body breaks into several pieces, and each piece grows into a new individual.
• Vegetative Reproduction means a plant part such as stems, leaves, roots, or turions are used in plant reproduction.

Sexual Reproduction

• Involves the use of sex cells, or gametes.
• The fusion of male and female gametes makes a zygote.
• Results in genetic variability.

Male Reproductive System

• The testes and male reproductive organs create sperm via the seminiferous tubules, which is spermatogenesis.
• The system is regulated by the hormones GnRH, FSH, and LH.

Female Reproductive System

• The ovaries produce eggs via oogenesis, or the development of ovarian follicles, and they secrete estrogen and progesterone.
• The fallopian tubes, or oviducts are the area where fertilization occurs.
• The uterus contains the endometrium and myometrium.

Animal Development

• Gametogenesis is the formation of gametes
• Fertilization is sperm fertilizing an egg
• Implantation is the attachment of the fertilized egg to the uterine wall.
• Gastrulation is the formation of the three germ layers
• The Embryonic Stage creates four membranes that support, protect, and nourish the embryo. These membranes are the yolk sac, allantois, amnion, and chorion.
• Development of the placenta and organs also occurs
• During the Fetal Stage, the organs differentiate further and grow.

Hormonal Regulation of Animal Reproduction

• Gonadotrophin-releasing hormone (GnRH) stimulates the release of two hormones:
  • Luteinizing Hormone (LH)
  • Follicle-Stimulating Hormone (FSH)
• The Pituitary Gland secretes two gonadotropic hormones:
  • Follicle Stimulating Hormone (FSH)
  • In males it causes the testes to produce sperm.
  • In females it causes growth of an ovarian follicle and it causes the follicle cells to secrete estrogen.
  • Luteinizing Hormone (LH)
  • In males it causes the testes to secrete testosterone.
  • In females it causes ovulation and it causes secretion of progesterone.

Plant Reproduction - Flower Structure

• The stamen is the male portion of a flower composed of an anther and a filament.
• The anther produces haploid pollen grains by meiosis.
• Most flowers have multiple stamens.
• The carpel or pistil is the female portion of a flower.
• The stigma on it is sticky to trap pollen.
• The style is a hollow tube that connects the stigma and ovary.
• The ovary produces female gametes or ovules.

Monoecious and Dioecious Plants

• Monoecious plants have stamens and pistils that occur on separate flowers but on the same plant.
• Dioecious plants have staminate and pistillate flowers occur on separate plants

Plant Development

• It involves alternation between a diploid sporophyte and a haploid gametophyte generation.

Angiosperm Life Cycle - Male Gametophyte

• Inside the anthers' microsporangia, male gametophytes divide by meiosis to generate haploid microspores which then undergo mitosis and give rise to pollen grains.
• Each pollen grain contains a generative cell and a cell that will become the pollen tube cell.

Angiosperm Life Cycle - Female Gametophyte

• The ovule inside the ovary contains the megasporangium.
• Within each megasporangium, a megasporocyte undergoes meiosis, generating four megaspores: three small and one large.

Pollination and Fertilization

• Pollination transfers pollen from an anther to a receptive stigma, aided by animals, wind, water, or humans.
• During fertilization, one sperm and an egg combine, forming a diploid zygote that develops into the embryo.
• A double fertilization happens when another sperm fuses with the 2n polar nuclei, which then forms a triploid cell that develops into endosperm, which becomes a food reserve.

Plant Embryo Development

• Ovules become the seed.
• The ovary matures into the fruit.

Plant Seed Germination and Growth

• Germination restarts growth and development following a period of seed dormancy.

Hypogeous Germination

• Cotyledons remain inside seed coat.

Epigeous Germination

• Hypocotyl elongates,
• Cotyledons emerge above ground.

Hormonal Regulation of Plant Growth and Development

• Auxins stimulate elongation of cells in the stem, control phototropism, gravitropism, and thigmotropism, stimulate root growth from stem cuttings, and suppress growth of lateral buds.
• Cytokinins stimulate cell division in seeds, roots, young leaves, and fruits and delay the shedding of leaves,
• Gibberellins stimulate cell division and elongation in roots, shoots, and young leaves and break seed dormancy.
• Ethylene hastens fruit ripening, stimulates the shedding of leaves, flowers and fruits, and participates in thigmotropism.
• Abscisic acid inhibits shoot growth, maintains bud dormancy, induces and maintains seed dormancy, stimulates protein storage in seeds, and stimulates closure of stomata.

This lesson defines plant and animal reproduction and development. It differentiates between sexual and asexual reproduction. Different types of animal development and types of sexual and asexual reproduction are explored.