5.1 Part 1 - A/Sexual Reproduction Flashcards
Why reproduction
Heredity and reproduction is the most important aspect of all life. Reproduction ensures the continuity of species as offspring counter the death rate, and result in production of more offspring to maintain the species population.
Asexual reproduction - animals
Budding: polyps form at the side of parent polyps and “bud” off to form new colonies. E.g. corals, hydra (freshwater)
Fragmentation: new organisms are formed from fragments of an animal that is broken or cut into pieces. E.g. corals, starfish
Agamogensis - without fertilisation by a male gamete. Most common form - Parthenogensis: new organism developing from a unfertilised egg. E.g. gecko
Required condition for fertilisation
As life originated in the ocean, fertilisation retains the primitive requirement of a water body to occur.
E.g. acquatic environment, internal water of a parent’s body.
Fertilisation - animals
Fusion of male and female gametes
External: gametes are made large in number and produced in water. Gametes and zygotes do not dry out in aquatic environments, therefore highly successful. However, loss of gametes by predators, disease or unsuitable environments -> larger number of gametes.
In terrestrial environments, rarely successful as gametes dessicate.
Internal: Some acquatic species, as they do not produce massive numbers of gametes. Less energy expended and more spent caring on a smaller number of young.
Majority of terrestrial animals - appropriate environment for gametes to fertilse.
Compare External and Internal fertilisation
External: syngamy occurs in external medium
Internal: syngamy occurs inside the body of the organism
External: synchrony between sexes - time of release of gametes triggered by shared environmental conditions.
Internal: motile (spontaneous movement) sperm seeks the egg.
External: Large number of gametes into surrounding medium to increase the chance of syngamy/fertilisation
Internal: Reduced number of gamete production as there is a higher chance of fertilisation due to the direct transfer of gametes and protection from external environment (predation, disease, dessication)
External: fish, algae, amphibians, coral
Internal: reptiles, birds, mammals, angiosperms and gymnosperms
Similarities:
* Both forms of sexual reproduction requiring the fusion of male and female gametes
* Both need a body of water to occur
Aquatic v Terrestrial
Terrestrial: generally external fertilisation is not successful
* Need for a watery environment is bypassed by using internal body water
Aquatic: generally internal fertilisation is not successful, as the need for water to continually pass over the gills. However some species are evolving, as this is more energy efficient. E.g. horn shark
External fertilisation in Australian animals
In the GBR: coral species acheive fertilisation by shedding millions of gametes into the sea. As there is no parental care, only a few live to adulthood.
Amphibians: semiterrestrial, using water for external fertilisation.
* Some amphibians do parental care - Gastric Brooding Frog
Internal Fertilisation types
The only option for terrestrial species
Oviparous: interally fertilised egg develops a shell and is laid in the external environment, where it completes its development as nourishment lies within the egg. E.g. reptiles, birds
Viviparous: born alive, as the embryo has developed fully within the parent, obtaining nutrients through the placenta. E.g. mammals
Ovo-viviparous: the egg is retained in the mother’s body, and hatches inside the body.
Similary to viparious fertilisation, the embryo develops inside the body but is not nourished by the female’s placenta but from yolk sac in shelled egg.
Or hatches outside, only with complete development.
E.g. sharks, snakes
Tips and tricks:
Ovi comes from the word ovum, meaning egg. Therefore oviparous involved shelled eggs
Ovo-viviparous combines the words “egg” and “live”, so ovo-viviparous is a hybrid between shelled eggs and the birthing of live young
Reptile reproduction
Internal oviparous fertilisation (generally)
Reptiles care for the egg, not offspring.
Hatchlings crawl from the sandback they are born into the water to find food/fend for themselves
Temperature determines the sex of the eggs. Female hormones are functional at higher temperatures. Genetically male eggs will hatch as females and can reproduce as such.
E.g. saltwater crocodile
Bird reproduction
Internal oviparous fertilisation
Nest builders, trying to control the temperature of the nest with constant maintenance to optimise development of the egg.
Birds care for their young after hatching.
Mammals
Monotremes - internal oviparous: lay eggs. Eggs are cared for in burrows and fed milk from the mother. e.g. platypus, echidna
*Marsupial *- internal viviparous: pouch-bearing animals to care for young. E.g. Kangaroo females can have three infants at different stages (womb, pouch, side). If conditions are not favourable, the development of babies will be halted.
Eutherians (placental mammals) - internal viviparous: young completes its embryonic development inside the mother (uterus) with nutrients derived from placental connection. Mature upon birth, and have a greater chance of survival. E.g. bears, tigers
Sexual reproduction in animals procon
Advantages: sexual reproduction of combining two chromosomes increases genetic diversity
* External: large no. of gametes are produced resulting in more offspring. Does not require mating rituals (simpler behavioural process)
* Internal: Increased likelihood of fertilisation as egg and sperm are in close proximity, in high protection from the environment.
Disadvantages: dependent on syncing of fertility cycles, less prolific/rapid than asexual
* External: extra energy expended on large numbers of gametes. Requries watery environment (difficult for amphibians)
* Internal: Fewer offpspring are produced, more difficult contact between females and males. STI risk increases.
Sexual reproduction in plants - external and internal
Fertilisation occurs externally and internally
External: requires the presence of water, damp environment. E.g. mosses and ferns.
- Spores need dampness to quickly germinate and start growing. More primitive than seeds.
Internal: gymnosperms (cone-producing plants) and angiosperms (flowering plants)
- Gymnosperms: pollen in male cones, wind blows the pollen to the female scale with ovules at the centre containing egg cells. A fluid-filled pollen tube grows down the centre to the ovule. After this fertilisation seeds are produced and released from the scales of the cone.
- Angiosperms: Petals attract pollinators. Stamen (male part) and carpel (female part).
After fertilisation, the petals fall off and the ovule becomes a seed, the ovary becomes fruit.
Moss and fern reproduction
Asexual
- Haploid spores grow into tiny gametophytes once finding appropriate damp environment.
- Mitosis - haploid gametes
Sexual:
- Male and female haploid gametes fuse at fertilisation forming a zygote
- Zygote grows into a diploid sporophyte that produces haploid spores by meiosis.
Gymnosperms sexual reproduction steps
Conifers are male (thin) and female (thicker). Male cones are near the base of the tree, and female cones in the tops. This avoid self pollination.
1. Male cones produce massive amounts of pollen, female cones have ovules in scales.
2. Wind blows pollen from male to female cone
3. Fluid-filled (watery environment) pollen tube grows from the surface to the ovule.
4. Sperm swins to the egg cell
5. Ovules develop into seeds that are released from scales of the cone when mature.
Self pollination vs cross pollination
Pros/cons
Self pollination: pollen from the anther of a plant is transferred to a stigma from the same plant
- Pros: don’t need structures to attract pollinators e.g. nectar, brightly coloured flowers → less energy spent; don’t need pollinators → can grow in remote areas where insects and pollinating animals are scarce
- Cons: gametes sourced from the same plant → less genetic diversity, which lowers population resilience
Cross pollination: pollen from the anther of a plant is transferred to the stigma of another plant
- Pros: gametes are from different individuals → more genetic diversity and variation in the offspring, which increases population resilience against environmental changes
- Cons: relies on agents of pollination e.g. wind, animals, insects, water → successful pollination relies on favourable conditions; must attract pollinators → energy expended on maintaining structures like brightly coloured flowers, sweet fruits, and nectar
Pollination by wind
Pros/cons + example
A large number of pollen grains are dispersed by wind to reach the stigma of another tree.
- Pros: as pollen is carried by the wind, pollen can be spread over a great distance → wide distribution of offspring; large numbers of pollen grains can be dispersed at the same time
- Not dependent on animal/insect pollinators and do not need to expend energy to create attractive structures.
- Cons: reliant on favourable wind conditions; large energy expenditure on producing copious numbers of gametes to offset gamete loss; no guarantee that pollen will reach the right part of another individual of the same species → high risk of wasting gametes
E.g. Confiers like cyprus, Christmas tree, and juniper
Pollination by animals
Pros/cons + example
Pollen is dispersed by the help of animals e.g. birds, bees, butterflies. Pollen sticks to the bodies of the animals. As animals visit different flowers to feed, pollen is deposited on the stigma of female flowers.
- Pros: more reliable than pollination by wind because pollinators visit many different flowers to feed → ensures that pollen will be transferred to the stigma of another plant; with specialised plants that only a few or one pollinator species can access, transfer of pollen to another plant of the same species is guaranteed
- Cons: dependent on there being a healthy population of pollinators → drops in pollinator population can adversely decrease pollination rate; high energy expenditure in maintaining nectar, brightly coloured flowers to attract pollinators
E.g. Specialisation: hammer orchids mimic the shape of a female wasp, deceiving male wasps into visiting the flower to “mate with it”. When this happens, the flower “hammers” the male wasp with its pollen capsule
Hummingbirds, with their elongated beak shape, can access the nectar of honeysuckles better than other species.
Seed dispersal
Seeds form after the ova have been fertilised. They are dispersed to allow offspring to grow away from the parent plant in conditions that are potentially more favourable.
Seeds can be dispersed by
- Wind
- Water
- Fruit: seeds are deposited in the faeces of animals
Angiosperm fertilisation steps
- Pollen is transferred to the stigma of a flower. Its dispersal from an anther to a stigma may be aided by a pollinator, e.g. bees, or it may occur through wind or water dispersal.
- The pollen’s tube cell creates a pollen tube from the stigma towards the ovary. The pollen’s generative cell travels down this tube and divides to form two sperm cells.
- The two sperm cells enter one of the ovules within the plant’s ovary.
- Inside the ovule, one sperm cell fertilises the egg. The other sperm cell combines with the polar nuclei to form the endosperm that helps provide nourishment for the zygote.
- After fertilisation, an ovule matures into a seed. The seed contains the fertilised egg (zygote) and the endosperm.
- The fertilised egg (zygote) develops into an embryo, which will grow into a new plant by cell division (mitosis) after the seed germinates.
Angiosperm double fertilisation
- One sperm fuses with the egg to form diploid zygote
- Other sperm fuses with two polar nuclei to create endosperm, which provides nourishment for the zygote during its development
Seed dispersal in edible vs inedible fruits
Fruits help seed dispersal.
- Edible fruits that are eaten by birds and animals have seeds that are indigestible and buried deep within dense fruits. The seeds are excreted in the animal’s droppings some distance away from the mother tree, allowing the species to grow in less competitive conditions.
- In non-edible fruits, fruits are designed to maximise natural agents of dispersion such as wind and water. Wind-dispersed fruits are lightweight and have wing-like appendages that help them be carried long-distance by the wind, or hairy, weightless structures, for example dandelion clocks. Seeds dispersed by water, like willows and silver birches, rely on buoyant, lightweight fruits that can float on water to a new germination ground.
Cross pollination
Transfer of pollen from the anther of one plant to the stigma of another plant from the same species
Increases genetic diversity
Mechanisms:
* In some angiosperms, the stamen (male part) and stigma (pollen receptacle on female part) ripen at different times so that the plant cannot pollinate itself
* In gymnosperms, female cones are located at the top of the tree and male cones at the bottom.
Anther
The top part of the stamen, produces pollen
Stamen
Male reproductive organ of plants, includes anther and filament
Carpel
Female reproductive organ of plants, includes stigma, style, and ovary
Ovule
Part of the ovary that can be fertilised to become a seed
Ovary
Base of the carpel, contains one or more ovules
Stigma
The sticky top part of the carpel, supported by the style
Gametophyte
Haploid plant structure
Sporophyte
Diploid plant sturcture
Above ground asexual reproduction
4
Cutting: pieces of stem/leaf is capable of growing leaves. E.g. geranium can grow in jars of water
Runner: new organisms growing from a central plant on the ground. E.g. strawberry, spinifex plants.
Suckers: formation of a new organism by developing a new stem and root system from the parent plant’s root or branch node. E.g. tomato and Australian wattle.
Layering: Branches make contact with soil, triggering root growth. E.g. blackberries
Underground asexual reproduction
4
Rhizomes: underground horiztonal stems with nodes that can give rise to new individuals. Underground runners. E.g. ginger
Bulbs: underground food storage organs with the capability to grow into separate plants (fleshy leaves). As the plant grows, new bulbs form and after developing into clumps each is able to grow a separate plant. E.g. onion, ginger
Corms: the same as bulbs, but wthout layers or rings, being a single piece of stem tissue. E.g. taro
Tubers: genetic copies can be propogated from sprouting nodes (“eyes”). Stores nutrients, fueling growth of new organisms. E.g. potatos, sweet potatos
Apomixis
Reproduction through specialised generative tissue. Does not require fertilisation or seeds. Embryos are developed from somatic cells directly, bypassing meiosis therefore maintaining chromosome number. E.g. Kentucky blue grass
Sexual reproduction in plants procon
Advtanges:
- Genetic diversity –> disease resistance and ability to adapt to changing conditions.
Disadvantages
- Can prevent favourable genes (if recessive) from being passed to offspring
- More difficult process to propogate. Less rapid.
