A

Reproduction in Flowering Plants and Animal Reproduction

Reproduction in Flowering Plants

UNIT 1–5 overview

  • Content focus: Sexual and asexual reproduction in plants; Flowers, pollination, fertilisation; Crop improvement through evolution, artificial selection, and genetic engineering; Seed banks for biodiversity; Growth regulators in modern agriculture.

  • Key terms to know: asexual reproduction, sexual reproduction, stamen, anther, filament, pollen grains, pistil (carpel), stigma, style, ovary, ovules, perianth (calyx and corolla), pollination, fertilisation, polyploidy, mutagenesis.

Terminology (from transcript)

  • Asexual reproduction – Production of a new generation of the same species from one parent.

  • Sexual reproduction – Production of a new generation of the same species by combining gametes of two parents.

  • Stamen – Male part of flower; consists of anthers and filaments; pollen grains produced in anthers.

  • Pistil (carpel) – Female part of a flower; comprises stigma, style, and ovary; ovules produced in ovaries.

  • Perianth – Calyx (sepals) and corolla (petals) of the flower.

  • Pollination – Transfer of pollen from anther to stigma.

  • Fertilisation – Fusion of male and female gametes (sperm and egg).

  • Polyploidy – Presence of more than two homologous sets of chromosomes in a cell.

  • Mutagenesis – DNA changes in a plant resulting in heritable gene mutations, potentially altering protein function and phenotype.

Asexual reproduction

  • No seeds produced.

  • Plants can form roots from cuttings placed in water.

  • Examples: potato plants can grow anew from stems; runners form new plants; bulbs form new individuals; general “split asexually.”

  • Practical implications: rapid multiplication; useful for clonal propagation of desirable traits; can occur in diverse environments.

Benefits of asexual reproduction

  • No mates required.

  • Rapid reproduction; large numbers in short time.

  • Positive genetic influences (e.g., beneficial mutations) can be passed to successive generations.

  • Occurs across various environments.

  • Question posed in notes: What are possible disadvantages? (e.g., lack of genetic diversity, vulnerability to widespread threats.)

Asexual reproduction & crop improvement

  • Activity prompt: Do internet research on grafting of common crops (example: orange on lemon).

  • Implication: grafting combines desirable rootstock and scion traits to improve yield, disease resistance, or vigor.

Sexual reproduction

  • Involves two organisms; gametes produced by meiosis; fertilisation leads to unique genetic combinations.

  • Key processes in flowering plants:

    • Meiosis in reproductive cells produces haploid gametes (n).

    • Pollen grain contains sperm; formed in anthers via meiosis.

    • Pollen tube grows toward the ovule; sperm used to fertilise the egg in the ovule.

    • Zygote forms (diploid, 2n) and develops into the embryo via mitotic divisions.

    • Endosperm forms as a result of fertilisation and triple fusion (in many angiosperms) leading to a nucelus with 3n genetic content.

  • Key structural components:

    • Ovary, ovule, embryo sac, stigma, style, and other flower parts involved in fertilisation and seed formation.

    • Diagram cues include: pollen grain (n) fertilises egg to form zygote (2n); endosperm (often 3n) results from fusion of polar nuclei with sperm.

Flower structure (parts and positions)

  • 1 Ovary

  • 2 Style

  • 3 Stigma

  • 4 Pistil

  • 5 Anther

  • 6 Filament

  • 7 Stamen

  • 8 Petal

  • 9 Sepal

  • 10 Ovule

  • 11 Receptacle

Asexual vs Sexual reproduction (comparative)

  • Asexual: one parent; no gametes; offspring genetically identical; mitotic cell division; rapid, large numbers.

  • Sexual: two parents; gametes via meiosis; offspring genetically variable; fertilisation leads to zygote; usually fewer offspring but greater variation and potential for adaptation.

Pollination

  • Transfer of pollen from anther to stigma.

  • Pollination can be aided by various pollinators: birds, insects, wind, etc.

Self-pollination vs cross-pollination

  • Self-pollination: pollen transferred to stigma from the same plant.

  • Cross-pollination: pollen transferred between different plants via a pollinator or wind; increases genetic diversity.

Fertilisation

  • Fusion of male and female gametes; occurs in the ovary (after pollen tube delivers sperm to embryo sac).

  • Results in zygote and subsequent seed development.

Benefits of sexual reproduction

  • Generates genetic diversity, visible in phenotype.

  • Increases survival rate across varying environments due to variation.

  • May reduce vulnerability to diseases due to heterozygosity and adaptation.

Sexual reproduction & crop improvement

  • Hybrid crops: produced by cross-pollinating two inbred parents with dissimilar genotypes.

  • Improvements from hybridisation (summary):

    • Improved pest and disease resistance

    • Early crop maturity

    • Increased yield

    • Quality improvement

Seed banks

  • Definition: facilities storing seeds from diverse wild plant and crop species to maintain biodiversity.

  • Millennium Seed Bank (Kew) is highlighted as an example (link provided in notes).

  • Importance: safeguard genetic diversity for future breeding, restoration, and resilience.

Animal Reproductive Strategies (overview)

  • This section introduces animal reproduction, including courtship behavior, fertilisation types, and developmental strategies.

Animal Reproductive Strategies

Terminology

  • Vertebrates – animals with a spinal cord/vertebral column (including humans).

  • Fertilisation – fusion of egg and sperm nuclei.

  • External fertilisation – fertilisation occurs outside the female’s body (e.g., many aquatic species).

  • Internal fertilisation – fertilisation occurs inside the female’s body.

  • Ovipary – eggs laid outside the body; eggs may be nourished by yolk; fertilisation can be internal or external; young hatch from eggs.

  • Ovovivipary – fertilised eggs retained inside the female; embryo nourished by yolk; eggs hatch inside the body; young appear alive.

  • Vivipary – fertilisation internal; embryos develop inside the uterus with nourishment via placenta; live birth.

  • Precocial development – offspring are relatively mature and mobile soon after birth/hatching.

  • Altricial development – offspring are immature and require care after birth.

  • Parental care – patterns of parental investment to improve offspring survival and future reproductive success.

Reproductive goals

  • Primary aim: produce the maximum number of surviving offspring while using the least energy.

  • Outcome: species survival and avoidance of extinction.

Courtship behaviour

  • Courtship rituals attract mates and can include:

    • Displaying beauty (e.g., male peacock plumage)

    • Fighting skills (e.g., lions, elephants)

    • Intricate dances, movements, vocalisations (e.g., fiddler crab)

    • Providing food resources (e.g., Pel’s fishing owl)

  • Purpose: to assess mate quality and coordinate mating.

External fertilisation

  • Water needed for fertilisation (e.g., frogs, salmon).

  • Advantages:

    • Increases genetic variation.

    • Produces a large number of offspring.

    • Gametes can drift, facilitating mate encounters.

  • Disadvantages:

    • Energetically wasteful; many eggs produced, few survive.

    • Low fertilisation success rate; environmental conditions influence hatching.

Internal fertilisation

  • Water not required for fertilisation (e.g., lions, crocodiles).

  • Advantages:

    • Higher probability of successful fertilisation.

    • Mates are selective.

    • Reduced desiccation risk for gametes.

    • Offspring often better protected and with higher survival chances.

  • Disadvantages:

    • Coordination of mating can be challenging; often fewer offspring per event.

    • Higher risk of sexually transmitted diseases in some species.

Three ways internal fertilisation produces offspring

  • Oviparity (oviparity): fertilised eggs laid outside the body; nutrients from yolk; examples include fish, amphibians, reptiles, birds.

  • Ovoviviparity: fertilised eggs retained inside the female; embryo nourished by yolk; hatch inside body; little or no parental care; examples include some sharks, lizards, snakes.

  • Viviparity: embryos develop inside mother and receive nourishment via placenta; live birth; typical of mammals and some reptiles.

Ovipary, Ovovivipary, Vivipary (summary)

  • Ovipary: external development; nourishment from yolk; eggs laid outside; parental care may be present or absent.

  • Ovoviviparity: internal fertilisation; eggs kept inside; embryo nourished by yolk; hatch inside; parental care may be present or absent.

  • Vivipary: internal fertilisation; embryo develops in uterus with maternal nourishment; live birth; parental care often present.

Amniotic egg (structure and significance)

  • Critical evolutionary development for terrestrial animals (birds, reptiles, some mammals).

  • Key features in the amniotic egg:

    • Shell, chalaza, air space, membranes, vitellus (yolk), albumen (egg white), amniotic fluid, developing embryo.

    • The yolk provides food; albumen provides water and nutrients; wastes exit via the allantois; oxygen diffuses through the shell regulated by the chorion.

  • Benefits: protects embryos from drying out, allows life in terrestrial habitats outside water.

Precocial vs Altricial development

  • Precocial development (e.g., chicken):

    • Young hatch or are born almost fully developed; eyes open; mobile; not nest-bound; energy is invested prenatally; higher chance of early survival due to mobility/self-feeding.

  • Altricial development (e.g., humans):

    • Born immature; often naked or downy; cannot walk or feed themselves; require parental care; energy goes into postnatal care.

  • Examples in transcript: precocial – Gallus gallus domesticus (domestic chicken); altricial – Homo sapiens (humans); other examples include parrots, songbirds, rheas, ducks, pelicans.

Parental care

  • Patterns of care can be prenatal and post-natal:

    • Prenatal: guarding eggs, building nests, incubating, placental nourishment.

    • Post-natal: feeding, protecting, teaching offspring.

  • Trade-offs:

    • Little to no parental care: many eggs, high mortality, few reach reproductive age (e.g., many fish, amphibians, insects, most reptiles).

    • High parental care: fewer offspring, higher survival to reproductive age (e.g., mammals, birds, some reptiles).

Reproductive Strategies: K- and r-strategists

  • K-strategists:

    • Stable environments; low fecundity; few offspring with high parental investment; slow growth and long life expectancy; examples: humans, elephants.

  • r-strategists:

    • Unstable, unpredictable environments; high fecundity; little investment in any one offspring; rapid growth to maturity; short life spans; examples: salmon, many insects.

Survivorship curves

  • Type I: high survival into adulthood; mortality increases in old age; small litter sizes and high parental care (K-selected).

  • Type II: constant mortality rate across ages; relatively small litter sizes and parental care (often K-selected).

  • Type III: high infant mortality; larger litters with little to no parental care; many offspring die early (r-selected).

  • Link: Type I and II align with K-selected; Type III aligns with r-selected.

Practice questions (selection from transcript)

  • The structure in the amniotic egg that removes waste products:

    • A) Yolk sac

    • B) Chorion

    • C) Amnion

    • D) Allantois

  • The type of reproduction in which young develop from eggs kept in the mother's body but do not receive nutrition from the mother:

    • A) Vivipary

    • B) Ovipary

    • C) Ovovivipary

    • D) Altricial

  • Seahorses question: fertilisation takes place in the pouch; which fertilisation and reproductive strategy does this represent?

    • A) External fertilisation and vivipary

    • B) Internal fertilisation and vivipary

    • C) External fertilisation and ovipary

    • D) Internal fertilisation and ovipary

  • Terms to fill in (from subsequent slides):

    • The finger-like projections from the outer extra-embryonic membrane:

    • A type of reproduction in humans where the foetus develops inside the uterus:

    • The structure in the amniotic egg that stores wastes:

    • The type of fertilisation associated with viviparous reproduction:

    • Embryo nourished by yolk found in the egg:

    • Foetus attached to the mother's uterus:

    • The type of development in birds in which offspring are capable of moving soon after hatching: or

    • Precocial vs Altricial development: which applies to birds or humans (fill with the appropriate term)

  • More practice (from slides 1.3.x and 1.3.1–1.3.6):

    • Requires production of a large number of gametes to ensure survival of the species: External fertilisation vs Internal fertilisation

    • A type of development in birds where hatchlings are helpless: Precocial vs Altricial

    • Forms the placenta: Chorionic villi vs Endometrium

    • Reproductive strategy in birds where hatchlings are helpless and cannot move or feed themselves: Precocial vs Altricial

    • Type of reproduction in vertebrates: Vivipary vs Ovovivipary

    • Nutrition provided by the egg: Ovipary vs Ovovivipary

    • A developmental type where young can move soon after hatching: Precocial vs Altricial

  • Notes on equations and quantities mentioned in diagrams:

    • Haploid number: n

    • Diploid number: 2n

    • Triploid endosperm (in many angiosperms): 3n

    • Zygote is formed by fusion of gametes (sperm + egg) to yield 2n.

Connections to foundational concepts and real-world relevance

  • Seed banks preserve genetic diversity, enabling breeding resilience against climate change and emerging pests.

  • Hybrid crops demonstrate how combining diverse genotypes can yield improved pest resistance, earlier maturity, and higher yields, informing modern agricultural practices.

  • Understanding different fertilisation modes informs conservation biology, aquaculture, and poultry industries.

  • Amniotic egg evolution highlights key adaptations that allowed terrestrial colonisation by reptiles, birds, and some mammals.

  • Parental care strategies illustrate trade-offs between offspring quantity and survival probability, shaping life-history theory.

Ethical, philosophical, and practical implications

  • Seed banks raise questions about access, benefit-sharing, and bioprospecting versus protecting biodiversity.

  • Genetic engineering and artificial selection in crops can balance food security with ecological impact and cultural considerations.

  • Animal reproductive strategies reflect energy allocation decisions; human interventions (breeding, domestication) influence natural selection pressures and ecosystem dynamics.

Mathematical references and notation used in the notes

  • Haploid number: n

  • Diploid number: 2n

  • Triploid endosperm: 3n

  • Zygote formation: fertilisation yields 2n

  • Gametogenesis and chromosomal sets are assumed per standard meiosis and mitosis conventions.