5.1.1 Mechanisms of Reproduction Flashcards
Importance of Reproduction
4
- Maintain balance between the birth and death rate
- Increase the number of species in the ecosystem
- Transmit genes from parents to offspring
- Facilitate evolution and genetic variation to increase survival
Reproductive Success
Ability of an individual to produce fertile offspring that survive to reproductive maturity and produce offspring of their own.
Biological Fitness
A measure of an individual allele’s reproductive success, calculated as the average contribution to the gene pool by a certain genotype and the relative likelihood that those alleles will appear in future generations.
Sexual Reproduction
Involves two parents giving rise to an offspring, inheriting genetic material from both parents.
Asexual Reproduction
A single parent involved, with no mixing of genetic information or exchange of gametes, making the offspring is an exact clone of the parent.
Advantages of Sexual Reproduction
3
- New gene combinations are created, allowing further survival in sudden environmental change.
- Harmful mutations may be removed from the population.
- Offspring may differ in their requirements due to variation, allowing for less competition for the same resources among a population.
Disadvantages of Sexual Reproduction
2
- Takes time, energy and bodily resources.
- Two parent organisms are required (less efficient).
Advantages of Asexual Reproduction
4
- Enables organisms to reproduce quickly without a mating partner.
- Can be a competitive advantage to be genetically identical.
- Some selection pressures make asexual reproduction more advantageous such as shortage of resources and small mating population.
- Does not require mobility of parent organism.
Disadvantages of Asexual Reproduction
2
- Little to no variation, making them particularly vulnerable to sudden changes in environment.
- Large numbers of offspring may compete for resources.
Vegetative Propogation
Plant Reproduction
Asexual
A new plant grows from a fragment of the parent plant or a specialised reproducing structure, which differs depending on the species of plant.
Runners
Vegetative Propagation: Reproductive Structures
Modified stems that grow along the surface of soil for new plants to grow on.
E.g. strawberries, spinifex
Rhizomes
Vegetative Propagation: Reproductive Structures
Modified, underground, horizontal stems that give rise to a new shoot at each node.
E.g. ginger, bracken fern, many grasses
Suckers/Sprouts
Vegetative Propagation: Reproductive Structures
Modified roots produced by plants to give rise to new plants, even when the parent shrub dies, allowing for rapid regrowth.
E.g. reeds, wattles, blackberries
Bulbs
Vegetative Propagation: Reproductive Structures
Rounded, underground storage organ that contains the shoot of a new plant.
E.g. onions, tulips, daffodils
Stem Tubers
Vegetative Propagation: Reproductive Structures
The thickened part of an underground stem with buds from which new plant shoots grow.
E.g. potatoes
Perennating Organs
Vegetative Propagation: Reproductive Structures
Underground organs that contain enough stored food to sustain the plant in a dormant state, allowing the plant to survive adverse conditions such as extreme cold or drought.
The plant above ground may die in the process and regrow during favourable conditions.
E.g. onion, carrot
Apomixis
Vegetative Propagation
Some plants are able to produce offspring from special generative tissues. The generative tissue may be gametes or non-reproductive tissue, but it gives rise to plantlets that can produce asexual seeds that grow into individuals genetically identical to their parent.
Multiplication by apomixis is rapid and the platelets assist in seed dispersal. However, it still lacks the variation that sexual reproduction allows.
Natural Vegetative Propagation
- The natural development of a new plant without human intervention
- Occurs through roots, bulbs, corms, tubers, suckers, rhizomes, runners and plantlets
- Helps avoid physical barriers that prevent sexual reproduction
Artificial Propagation
- The artificial development of new plants by means of human intervention
- Occurs through budding, grafting, layering, cutting and tissue culture
- Helps maintain desirable characteristics over generations
Pollination
Plant Reproduction
Sexual
Some plants produce structures called flowers, which are the sexual organ of a plant. These produce pollen, and when pollen from two flowers come in contact, it produced a seed, which can grow into a new plant with traits of both parents, but different and unique.
Flowering depends on external biotic and abiotic agents of pollination and seed dispersal. It can also occur as self-pollination and cross-pollination.
Petals
Parts of a Flower
A whorl of brightly coloured leaves modified to increase the likelihood of pollination by attracting pollinators and facilitating entry for particular pollinators.
Receptacle
Parts of a Flower
The reinforced base of the flower, which supports the weight of all reproductive structures.
Sepals
Parts of a Flower
A whorl of modified leaves that protect the unopened bud.
Stamen
Parts of a Flower
The male parts of the flower which release pollen to pollinate other plants, including anther and filament.
Anther
Parts of a Flower
Where pollen grains are formed.
Filament
Parts of a Flower
The stalk that carries the anther, the length of which determines whether the anthers are for insect pollination or wind pollination.
Carpel
Parts of a Flower
The female parts of the flower which receive pollen from other flowers, including the stigma, style and ovary.
Stigma
Parts of a Flower
The sticky top surface of the flower for pollen to adhere to, which can be small and smooth for insect pollinators or large and feathered for wind pollinating.
Style
Parts of a Flower
Connection of the stigma to the ovary.
Ovary
Parts of a Flower
Where ovules are formed.
Petals of Wind Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Small, inconspicuous, dull
Petals of Bird Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Large, colourful (red/orange) and tubular (sometimes no petals)
Petals of Insect Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Large, colourful (yellow/blue), specific shapes to encourage pollinators
Scent of Wind Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
None
Scent of Bird Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Rare (birds can’t smell)
Scent of Insect Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Often (insects smell)
Nectar of Wind Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
None
Nectar of Bird Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Large amounts produced at base of flower
Nectar of Insect Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Sometimes produced at base of flower to insects to enter
Anthers of Wind Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Produces pollen abundantly and protrudes outside so pollen can be blown off
Anthers of Bird Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Produces little pollen, commonly lower than stigma, colourful, and may be enclosed
Anthers of Insect Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Produces little pollen, enclosed and lower than stigma
Stigma of Wind Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Long, feathery, sticky and protruding to increase surface area for trapping pollen
Stigma of Bird Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Higher than anthers, colourful and sometimes not enclosed
Stigma of Insect Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Enclosed, sticky and commonly higher than anthers
Pollen of Wind Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Small, light and powdery
Pollen of Bird Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Sticky or powdery
Pollen of Insect Pollinated Flower
Comparison of Wind, Bird and Insect Pollinated Flowers
Large, sticky
Conifers (Gymnosperms)
Example of Pollination
Conifers utilise their cones rather than flowers to pollinate and fertilise. Male cones produce enormous amounts of pollen to be blown by the wind into female cones, which have ovules at the centres.
After fertilisation, the zygote-containing ovules develop into seeds that are released from the scales of the cone.
Parthenogenesis
Animal Reproduction
Asexual
The most complicated form of asexual reproduction and the only kind capable of animals, where the female egg gamete can develop into an embryo without a sperm.
E.g. Aphids, Bees, Ants, Wasps, Crayfish, Komodo Dragons, Geckos
Internal Fertilisation
Animal Reproduction
Sexual
- Does not occur in many aquatic species, but it allows less energy to be spent on producing mass numbers of gametes and instead caring for the young and increasing the likelihood of their survival.
- A large number of male gametes is produced but fewer female gametes. This allows the male gamete to travel into the reproductive tract of the female parent through copulation, where the male inserts his sperm. The chance that the egg fertilises at this point is very high, as is the likelihood of surviving to maturity as parental care is common.
- In terrestrial species, internal fertilisation is the only practical option for reproduction. It can occur in three ways: oviparous, viviparous, ovo-viviparous
Oviparous Reproduction (+ Three Examples)
Animal - Internal Fertilisation
Internally fertilised egg develops a shell and is laid to complete development eternally, often by reptiles and birds.
Saltwater Crocodiles:
* Most reptiles lay eggs after internal fertilisation, allowing a nest to be built to care for the eggs until they hatch.
* The Saltwater Crocodile (Crocodylus porosus) lays a small number of eggs and build a nest on sandbanks to care for them until they hatch.
Maleefowl:
* Birds are rigorous nest builders in order to control the temperature and maintain optimum development of their eggs.
* The Malleefowl makes their nest from a mound of twigs, soil, sand and leaf litter.
Platypus and Echidna:
* Monotremes lay eggs after internal fertilisation, caring for their eggs in burrows or a pouch to be fed by lactation from their mother’s body.
Viviparous Reproduction (+ Two Example)
Animal - Internal Fertilisation
Fertilised egg becomes an embryo and is nurtured inside of the female parent to obtain nutrients through placenta and be born alive to most mammals.
Kangaroo:
* Marsupials have pouches to protect their young.
* Kangaroos have three stages of development: one in womb, one in pouch and one at the side of its parent.
Placental Mammals:
* Eutherians complete their embryonic development entirely internally, inside the female parent’s uterus which nurtures and protects the embryo.
* The live, mature young that are born have a greater chance of survival.
Ovo-Viviparous Reproduction
Animal - Internal Fertilisation
Eggs with yolk for nourishment are nurtured inside of the female parent’s body and newly hatched young are born alive, such as sharks and snakes.
Internal Fertilisation in an Aquatic Environment
- Usually successful.
- Energy efficient as fewer gametes required.
- Water needs to pass over gills for hydration.
Internal Fertilisation in a Terrestrial Environment
- Used to overcome the need for water in fertilisation.
- Direct transfer of gametes avoids loss.
- Very high success rates as internal environment protects.
External Fertilisation (+ One Example)
Animal Reproduction
Sexual
- Occurs in open water environment and is often highly successful
- Pressures of predation, disease and dispersal means that large numbers of gametes must be produced. Given that these threats are avoided, fertilisation is likely to occur as long as the gametes meet (syngamy)
- Not cared for by parents, meaning few make it to adulthood even if they fertilise.
- Simultaneous release of large numbers of both male and female gametes, producing a similarly large number of zygotes, though many do not survive.
Amphibians:
* Reproductive process by eternal fertilisation that holds them to the marine environment.
* The Southern Gastric Brooding Frog (Rheobatrachus silus) was a unique case where the eggs were eternally fertilised but then swallowed by the female parent to develop internally before being born out of the mouth.
External Fertilisation in an Aquatic Environment
- Usually highly successful as gametes are completely hydrated.
- Must produce high numbers of gametes to lessen threat of selection pressures.
External Fertilisation in a Terrestrial Environment
Not successful due to the lack of hydration, meaning gametes will desiccate.
Fungi
Fungus is a multicellular organism made up of threads or filaments called hyphae, which branch and interconnect to form the mycelium, the main body. They colonise in aerobic, damp and dark environments where there is less competition for resources, such as underground or in dead/decaying matter.
Fungi can be:
- Saprophytic - obtain nutrients from dead/decaying matter
- Parasitic - obtain nutrients from a living host
Budding
Fungi Reproduction
Asexual
A unicellular or multicellular organism may form an outgrowth or bud at a particular site of its body due to increased cell division. When the bud becomes fully mature, it will detach from the parent body and become a singular independent organism.
E.g. Corals, Sponges, Acoel Flatworms, Yeast, Echinoderm Larvae, Amoeba, Sea Anemone, Hydra
Fragmentation
Fungi Reproduction
Asexual
A multicellular organism will split into fragments, each of which will regenerate into a matured individual genetically identical and even morphologically identical to the original.
Sea Star:
* Capable of both sexual and asexual reproduction, but they asexually reproduce through fragmentation.
* A part of their arm and central disk will become detached from the parent and develop into an independent sea star.
Spores
Fungi Reproduction
Asexual AND Sexual
- In favourable conditions, the fungi’s sporangia, which are specialised tips on the hyphal threads, will release a large number of spores, which are single cells of the parent organism.
- Numerous haploid nuclei develop microscopic spores, which appear as a white powder when released as they clump together, but are able to travel by the wind, water or animals.
- In a suitable location and conditions, they will ripen into a black colour, germinate, undergo nuclear division and grow into a new mycelium.
- The hyphae of two different mating types of fungi can fuse, forming a fruiting body capable of sexually reproducing. The spores that this organ produces includes a combination of genetic material.
Rhizopus Nigricans:
Rhizopus nigricans is a black mould similar to Mucor (pin-head mould) and Penicillium (antibiotic-producing mould), in that they are multinucleate, meaning they have many nuclei in the hyphae and no cross walls to separate them into individual cells.
Binary Fission
Bacteria Reproduction
Asexual
- An organism duplicates its genetic material (one chromosome of DNA) and grows larger to divide into two parts through cytokinesis to create two organisms, each with a copy of the original DNA.
This is NOT the same as mitosis, which is used for growth/development rather than reproduction and is much more complicated as it is undergone by eukaryotic cells. Being performed by prokaryotes means that there is less DNA to duplicate and internal structures are much simpler (not membrane-bound).
