IQ1: Reproduction

• sexual reproduction is the fusion of male and female gametes to form a zygote
• Advantages of sexual reproduction are

  • Genetic diversity (continuity of life at the species level), allowing species to survive and reproduce in varied and changing environments
  • Greater adaptability and evolutionary potential in changing conditions
  • Elimination of unfavourable traits and facilitates selection of beneficial traits
• Disadvantages of sexual reproduction

  • Finding and competing for a mate is time consuming, energetically costly and risk
  • Mating is potentially harmful, competition between males
  • Substantial investment of time and resources to provide parental care and protection of offspring
• Internal fertilisation is when gametes fuse internally in the female's body (Human intercourse)
• External fertilisation is when the gametes fuse outside either male or female
• Advantages of animals that are hermaphrodites (each individual has both male and female reproductive organs)

  Low population, ensures reproduction despite lack of mate around them
• Disadvantage of hermaphrodites

  Energy costing to have two sets of reproductive organs
• The internal environment protects gametes from dehydration, protects loss to external elements and the fertilised eggs and developing young from immediate predatio
• why is external fertilisation better suited to organisms that reproduce in aquatic or moist environments?

  Moisture in the environment keeps the gametes from dehydrating as it is important that the eggs and sperm can move around freely to meet and fuse
• Advantage of external fertilisation

  Wide dispersal of young, reduction of competition for food and living space, more rapid
• Advantage of internal fertilisation

  less gametes have to be produced, higher success rate, gametes and zygotes are protected from predation and disease
• Disadvantage of external fertilisation

  No control over the gametes once released, decreased change of successful fertilisation and must take place in an aquatic environment
• Disadvantages of internal fertilisation

  Potential for STD, energetically costly and parental care for young may be lengthy and demanding
• Male parts of the flower

  Stamen

  • Anther - pollen grains are formed and where male gametes are found
  • Filament - stalk that carries the anther
• Female parts of the flower

  Carpel

  • Stigma - sticky surface where pollen adheres to
  • Style - joins the stigma to the ovary
  • Ovary - where ovules are formed
• The process of gamete transfer is called pollination
• Male gametes inside pollen must be carried from the anthers down the style to the ovary. Once pollen has been deposited on the stigma, a pollen tube germinates and grows down the style, carrying inside it the sperm to an ovule contacted in the ovary. 
• Plants depend on wind, water and animals to carry their pollen, from the anthers of one flower to the stigma of a flower either on another plant (cross pollination) or on the same plant (self pollination).
• • Cross pollination ensures greater variation in the offspring. 
• It is an advantage for seeds to be dispersed over a wide distance as this helps present overcrowding and competition for light, water and soil nutrients.
• Germination


  The plant embryo inside a seed is in a dehydrated form and is dormant, to allow the seed to survive adverse conditions. If the seed lands on suitable soil that provides sufficient water, oxygen and warmth, it germinates. 
• Fertilisation


  1. the sperm cell that was transferred by the pollen tube fuses with the egg cell inside the ovule in the female part of the flower 
• Asexual reproduction is the production of identical offspring from just one parent and are produced via mitosis. Each daughter cell receives a copy of every chromosome and therefore, the offspring are genetically identical copies to the parent
• Advantages of asexual reproduction

  • efficient form of reproduction
  • amount of time and energy to produce offspring is minimal
  • population sizes can increase rapidly in optimal environments
  • there is no need to find a sexual partner
  • offspring are genetically identical to the parent cell, so they are well suited to a stable environment
• Disadvantages of asexual reproduction

  • rapid population growth can lead to overcrowding and increased competition for resources
  • the lack of genetic variation in a population can cause death of the entire population if conditions change (e.g. a disease pathogen arrives or a severe drought) because they are not adaptable to new environmental conditions
• Fission: splitting one cell into two (binary fission) or many (multiple fission)
• Budding: a new individual is produced from the parent plant by splitting off a small part of the parent plant
• Fragmentation: of body parts, or of a whole organism, into smaller pieces
• Spore formation is the process of producing spores, which are tiny, dormant, and non-reproductive cells
• Vegetative propagation in plants: The process of producing new plants from a single parent plant by producing new plants from its roots, stems, or leaves
• Parthenogenesis in some female animals
• • Binary fission is an exponential process because the population doubles after every cycle of division. 
• • Bacteria are unicellular, microscopic prokaryotes that reproduce asexually. Due to the lack of organelles and smaller amount of DNA, cell replication in prokaryotes occurs more quickly than in eukaryotes. 
• Binary fission process in bacteria:

  • Prokaryotic cell grows to full adult size
  • Replicates its single DNA molecule
  • Each copy of the DNA attaches to opposite ends of the cell membrane
  • A new cell wall is synthesised . 
• Protists are eukaryotic organisms that live in aquatic or moist environments. They can be unicellular or multicellular.
• protists can reproduce by binary fission but it’s different to bacteria as protists have a membrane bound nucleus that needs to be replicated.
• • Some fungi reproduce asexually by spores (mould, mushrooms, puffballs) releasing from fruiting bodies or they reproduce by budding (yeast). 
• Budding process of Fungi

  • Parent yeast cell produces a small outgrowth that grows larger and forms a bud.
  • The nucleus of the parent cell splits off a smaller daughter nucleus, which migrates into the daughter cell. 
  • Bud detaches from the parent by pinching inwards at the base.
  • The bud is much smaller than the parent but is genetically identical.
  • Repeated budding forms a chain of connected but independent cells.
• • Spores are tiny, unicellular reproductive cells that are produced in great numbers by organisms such as fungi.
• Vegetative propagation examples

  Runners (modified stems)

  • Long thin modified stems that grow along the surface of the soil (e.g. strawberries can be produced at very alternate node on a stem runner)
  • Advantage: Enables reproduction in harsh climates and is rapid

  Rhizomes (modified stems, underground)

  • They give rise to a new shoot at each node, farmers often propagate them by splitting the rhizomes (e.g. ginger)