CHAPTER 9: REPRODUCTIVE STRATEGIES Jacaranda Chapter 9 pg 510 - 559 UNIT 2 AOS 2 K E Y K N O W L E D G E REPRODUCTION: WHAT IS IT? Reproduction: the creation of a new generation of single cells, single celled organisms or multicellular organisms. Asexual reproduction: type of reproduction that does not require the fusion of gametes, where offspring arise from a single parent and are genetically identical to that parent. Sexual reproduction: the fusion of two distinct haploid gametes to produce single diploid zygote composed of two sets of chromosomes. ASEXUAL REPRODUCTION • Involves only one parent • Offspring genetically identical to parent • Involves regular body cells (somatic) • Its quick SEXUAL REPRODUCTION • Involves two parents • Offspring genetic mix of both parents hence allows variation • Involves specialized sex cells (gametic) • Its slow REPRODUCTION: IMPORTANT TERMS GAMETES: are sex cells (egg and sperm) involved in sexual reproduction (contains n). SOMATIC CELLS: cell that is not a reproductive cell (contains 2n). ZYGOTE: immediate result of fertilisation after fusion of gametes. DIPLOID: describes a cell or organism that has a genome comprising two copies of each chromosome (2n). HAPLOID: describes a cell or organism that has a genome that contains one copy of each chromosome (n). HOMOLOGOUS CHROMOSOMES: a pair of chromosomes that have the same size, shape and genes. Asexual and sexual reproduction • https://youtu.be/fcGDUcGjcyk TOPIC 1: ASEXUAL REPRODUCTION • • • • What is asexual reproduction Types of asexual reproduction • Prokaryotes (bacteria and archaea) • binary fission • Eukaryotes (animals, plants and fungi) • Mitosis • Vegetative propagation • Budding • Fragmentation • Parthenogenesis Advantages Disadvantages Summary of the different methods of asexual reproduction ASEXUAL REPRODUCTION: BINARY FISSION - Prokaryotes “binary” – two; “fission” - splitting • Common is single-celled bacteria and protozoans. • Involves: • • • • Replication of the circular molecule of DNA off the cell Attachment of the two DNA molecules to the plasma membrane Lengthening of the cell Division of the cell into two via a constriction across the middle of the cell and the formation of a septum, so that each new cells contains once circular molecule of DNA Sample Problem (page 512) Bacteria can have a detrimental effect on the human body. E.coli is a regular cause of food poisoning and Neisseria meningitidis (meningococcus) can cause life-threatening sepsis. With so many bacteria causing illness, how can bacteria have a symbiotic relationship with humans? (4 marks) THINGS to THINK about: • What role do bacteria play in the body? • What does symbiotic mean? • How do both humans and bacteria benefit from the relationship? ASEXUAL REPRODUCTION: BINARY FISSION - Eukaryotes “binary” – two; “fission” - splitting • UNICELLULAR EUKARYOTES • e.g. amoeba • Process is different to the process in bacteria as it involves MITOSIS • MULTICELLULAR EUKARYOTES • e.g. flatworms, anemones and coral • Asexually split in two FUN FACT: Amoeba can also undergo MULTIPLE DIVISION – process of division in which multiple cells are produced from a single starting cell Sample Problem (page 515) Compare and contrast binary fission in prokaryote and eukaryotes? (2 marks) THINGS to THINK about: • Similarities and differences • Two modes of reproduction • So similarities of two modes • And differences of two modes ASEXUAL REPRODUCTION: MITOSIS- Eukaryotes 1. Replacement of body cells 2. Spore formation in algae and some fungi • Spores are hardy, self-contained single-cell capsules that contain the DNA instructions required to produce a new plant in times of rain. • Spores are dispersed and develop into new organisms genetically identical to each other and the parent • FUN FACT: IF spores are produced by MEIOSIS (some plants e.g. mosses and ferns) they are not genetically identical and not ASEXUAL ASEXUAL REPRODUCTION: MITOSIS- Eukaryotes 3. Vegetative propagation – main types RUNNERS CUTTINGS RHIZOMES TUBERS BULBS CORMS PLANTLETS SEE NEXT SLIDE FOR EXAMPLES ASEXUAL REPRODUCTION: MITOSIS- Eukaryotes 4. Fragmentation A form of asexual reproduction where an organism is split into fragments and each fragment can develop into a mature organism Example: filamentous cyanobacteria, moulds, sponges, sea stars, flatworms, annelid worms, plant tubers ASEXUAL REPRODUCTION: MITOSIS- Eukaryotes 5. Budding • A form of asexual reproduction where a new organism develops, through cell division, from an outgrowth of the parent. • Example – sponges where each sponge is made of thousands of cells but has no specialised organs or nervous system. ASEXUAL REPRODUCTION: MITOSIS- Eukaryotes 6. Parthenogenesis PARTHENOGENESIS – “virgin birth” defined as reproduction without fertilisation and almost always involves the development of an unfertilised egg – no sperm is necessary. Offspring are identical to the female parent. Example – aphids, Komodo dragons, whiptail lizards, some shark species Result in typically all female populations ASEXUAL REPRODUCTION: ADVANTAGES vs DISADVANTAGES ADVANTAGES DISADVANTAGES • Can reproduce quickly • No energy expended finding a mate • Do not have to rely on other organisms/means to spread pollen/seeds • Well-suited to the environment • Able to colonise cleared areas rapidly • Lack of genetic variation reduces the chance of a population adapting to new environmental conditions • Pressure on availability of resources • If conditions change, entire population can be lost ASEXUAL REPRODUCTION: Online ACTIVITIES AND WORKSHEETS (9.1 and 9.2)
