Biology: Sexual and Asexual Reproduction

• This fascicle is the paper version of the "La Reproducció" multimedia learning unit of Science Bits
• The content comes from a multimedia digital work available at science-bits.cat
• The goal is to complement digital content with a physical paper format, useful in classrooms without student computers

Reproduction

• All living beings originate from the reproduction of other living beings
• Reproduction has two forms: sexual and asexual

Asexual Reproduction

• A single organism generates descendants as identical copies or clones

Sexual Reproduction

• Two organisms cooperate to generate descendants
• Descendants' traits are a mix from the progenitors

Asexual Reproduction: Identical Offspring

• Asexual reproduction results in a new organism genetically identical to its progenitor
• These organisms are clones
• Asexual Reproduction is rapid and effective when environmental conditions are stable
• The progenitor organism doesn't need to find a compatible partner to reproduce
• Well-adapted progenitors produce well-adapted descendants

Asexual Reproduction: Organisms

• Bacteria and other prokaryotes reproduce asexually
• Eukaryotic unicellular organisms: protozoa, unicellular algae, and yeasts
• Many fungi, multicellular algae, animals, and plants reproduce this way under certain conditions
• Types include fission, budding, fragmentation and sporulation

Sexual Reproduction: Combining Traits

• When organisms reproduce sexually their offspring share characteristics with both parents and aren't identical to either
• Sexual reproduction results in varied organisms better adapted to environmental changes than clones
• With few exceptions, all eukaryotic cell organisms reproduce sexually, be they unicellular or multicellular
• Bacteria, and prokaryotes generally, don't reproduce sexually

Sexual Reproduction: Cellular Perspective

• Sexual reproduction involves specialized cells called gametes
• Animals and plants produce two types of gametes: male and female
• Sexual reproduction depends on a female gamete and a male gamete fusing to form a single cell
• Resulting cell is a zygote, the first cell of the new organism

Germ Cells

• Gametes or sex cells are produced inside specialized reproductive organs
• Female gametes are large cells, usually spherical, with cytoplasm containing reserve substances as an energy source during initial zygote development
• Male gametes are relatively small cells with nuclei occupying most of the cytoplasm, specialized to reach the female gamete
• Nucleus contains half the genetic material versus other animal or plant cells

Fertilization

• Male and female gamete produce a new cell called zygote during a process called fertilization
• The zygote is the first cell of a sexually reproduced organism
• During fertilization, the genetic materials of the male and female nuclei unit together

Embryonic development

• Through embryonic development, the zygote transforms into a multicellular organism, which forms all tissues and bodies
• Besides embryonic growth, processes have significance
• The zygote's genetic material duplicates and its cellular membrane constricts which forms two cells with genetic material copies
• The process (mitosis) repeats until creating billions of cells
• Cell Differentiation: At the start of development, cells are identical
• Depending on position in the embryo, each cell develops uniquely to become specific, providing structure and function
• Organisms are embryos during development produced inside specialized structures
• The uterus of mammals and the eggs of many animals exemplify these structures

Biological cycle

• A organism completes its embryonic development, it is ready to abandon its protective structure with this being its birth
• After birth, organisms aren't ready to reproduce
• They are considered juveniles or immatures
• Tadpoles, fry, nymphs, caterpillars exemplify immature organisms

Animals' Reproduction

• Though simple animals reproduce asexually (budding or fragmentation), usually animals reproduce sexually
• To conduct sexual reproduction, animals create gametes inside reproductive organs called gonads
• Gonads include testicles, which produce male gametes (spermatozoa)
• Gonads also form ovaries, producing female gametes (egg cells)
• A species has one or both types of gonads, and can be unisexual or hermaphroditic:
• Unisexual species have male or female gonads with separate individuals
• Some animals are sexually dimorphic
• Hermaphroditic species have both types of gonads either at the same time or at disparate moments in development but don't self-fertilize
• For fertilization to happen, the male gametes' sperm needs to be released into a matching water medium
• Following the water medium they're released into, fertilization can be: -Fecundación can be internal, occurring in a female’s body that requires male gametes (organ copulador)

Developement of Embryo

• Direct development: juvenil presents a similar aspect to the one of adults, and they will need to develop their reproductive system.
• Indirect developemt : the juvenil is borned as a very diferent larva, and the maturation will need a series of changes called metamorphosis

Reproduction in Plants

• Asexual Reproduction is more frequent in plants than it is in animals.
• Sexial Reproduction will take place in flowers where seeds also develop.
• We call these plants ''Espermatofites'' or plants with seeds (sperma-seed; y phyto-plants)