a-sec-shual Flashcards
Reproductive success
An organisms ability to produce fertile offspring that survives to sexual maturity and produces offspring
similarities of asexual and sexual reproduction
- passes on DNA (method of heredity)
- produces offspring
- involves plants, fungi and animals
- forms of reproduction
differences of sexual and asexual reproduction
Sexual: 2 parents
- cells divide by meiosis
- genetic variation in offspring
- gametes produced
- generally produces minimum of 1 offsping
- found in higher organisms (mammals)
Asexual: one parent
- cells divide by mitosis, budding or fragmentation
- little chance of genetic variation
- no need to produce gametes
- generally produces minimum of 2 offspring
- found in lower organisms (bacteria)
Pros of sexual reproduction
- speeds up evolution due to genetic variation
- high genetic variability = less susceptibility to genetic disease, increases the genetic health of the species
- facilitates adaptation
Pros of asexual reproduction
- greatest increase in fitness for each individual (non taxing on either sex)
- saves energy: the process requires more energy to achieve the result
- courtship is a non-issue: less consumption of time and resources
Cons of sexual reproduction
- energy costly
- courtship is time / resource consuming
- usually sacrifices the fitness of one sex to the other - can lead to death
Cons of asexual reproduction
- less genetic variability (highly susceptible to genetic diseases)
- adaptation to environments is difficult (lack of suitable options)
- inhibits adaptation
Process of sexual reproduction
- cells enter meiosis in both parents and form gametes
- fertilisation occurs and a zygote forms - contains all the genetic information
- blastocyte forms as zygote divides by mitosis to form cells
- foetus stage is when it is sufficiently developed for life outside the uterus
Internal and External fertilisation: points to remember
- number of gametes
- location of union
- conception mechanism
- chance of fertilisation
- environment for zygote
- number of offspring
- breeding frequency
- parental investment
- examples
Internal and external: gametes
External: larger number of gametes produced as they are less likely to be fertilised
Internal: less gametes because of higher success rate. Higher number of male gametes produced.
Similarities: male and female gametes required.
Internal and external: union
Ext: aquatic environment
Int: inside the reproductive tract of female
Similarities: sperm fertilises egg when united
Internal and external: conception mechanism
Ext: simultaneous release of gametes (spawning events) regulated by environmental cues
Int: copulation
Sim: fertilisation when coming into close proximity - water environment required
Internal and external: chance of fertilisation
Ext = lower (released in large open area)
Int: higher (confined space)
Sim: if in close proximity, will fertilise
Internal and external: environment for zygote
Ext: aquatic environment - vulnerable to environmental elements
Int: protected environment, less vulnerable
Sim: requires a watery environment for development
Internal and external: number of offspring
Ext: larger number (low success rate - i.e small amount of offspring survive to sexual maturity)
Int: Usually smaller number
Internal and external: Breeding frequency
Ext: more frequent (lower fertilisation success rate)
Int: less frequent due to higher success rate
Sim: depends on requirements of species and favourability of environmental conditions
Internal and external: parental investment
Ext: usually no parental investment
Int: parental care of eggs / developing young
Sim: parental investment is indirectly proportional to number of gametes produced
Example of external fertilisation
Bony fish: produces eggs in large batches where they fuse with sperm in spawning events.
Staghorn coral: colony of invertebrate marine polyps which achieve fertilisation by shedding millions of gametes into the sea (triggered and synchronised by environmental cues)
Reptiles + birds: internal
Reptiles: protects gametes from dehydration on land and other environmental stress such as predation
Birds; most male birds do not have a penis so during copulation the male and females rub the opening to their cloaca for fertilisation
Mammals: internal
Monotreme - oviparous (lay eggs after internal fertilisation)
Marsupials: develop internally briefly then continue embryonic development in a pouch
Placentals: develop in a specialised organ of the uterus
Pollination
transfer of the gametes from the male to the female
cross pollination
transfer of the pollen from anther of one plant to the stigma of another plant (more desirable as it increases variation within the species)
self pollination
transfer of pollen from the anther to the stigma of the same plant
germination
the development of a plant from a seed or spore
fertilisation
when the pollen grain fuses with the ovule
Process of pollination
- Pollination occurs, resulting in a pollen on the stigma of the plant
- pollen tube germinates and grows down the style (carrying inside it the pollen grain) before arriving at the ovule
- fertilisation occurs internally in the ovary
Lifecycle
- production of gametes occurs in the anther (male) and the stigma (female)
- meiosis occurs, pollen and egg, followed by pollination
- pollen tube delivers pollen to ovule in ovary (fertilisation)
- embryo is produced and seeds start developing
- seed dispersal occurs in order for the plant to colonise other areas
- seed germination occurs
Parts of a plant
Anther on the filament
Stigma on the style on the ovary
Sepal encloses the bud
Receptacle where the flower grows
Seed dispersal strategies: Wind
- small, dull coloured petals or no petals at all (e.g. grasses)
- scent + nectar = unnecessary
- anthers = long, protrude outside of the flower
- stigma = sticky to hold onto pollen, long and bigger for increased SA
- increased production of pollen as there is lower success rate. very small, light, powdery grains
Seed dispersal strategies: bird
- tend to be larger and colourful, some flowers change colours as an indicator
- birds have no / poor sense of smell therefore scent is unnecessary
- large amount of nectar, typically at the bottom of a tube of petals
- animals brush against the anther, the pollen sticks to its body as it reaches in with a long beak. Enclosed within flower, lower than stigma.
- the pollen sticking to its body will brush against the stigma
- pollen has a rough surface to stick to pollinator
seed dispersal strategies: insect
- use of colour and guiding marks (e.g. u.v. marks that cannot be seen by people), shaped to provide a landing platform or to resemble the mate of the pollinator
- scent attracts insects - important as colours cannot be seen in the dark
- nectar production
- filaments are short, lower than stigma, enclosed by petals
- relatively large grains, often sticky, small amounts produced
Seed dispersal - animals
- seeds covered in hooks / spines which attach the seed to the animal’s fur / feathers, before being carried and thus dispersed
- produce their seeds inside fruits that get eaten (seeds pass through the digestive tract)
- animals bury seeds to save for later (often get left there and grow)
Seed dispersal - wind
- small seeds with ‘wings’ or hair/feather like structures
- production of large amounts of seeds
- examples: dandelion or milkweed
Seed dispersal - Self seed
- pods that explode when ripe and shoot out seeds (peas, beans, mistletoe)
- explosive force is used to fling the seeds away
- sandbox tree has exploding capsules that launch seeds 100m away
- some exploding fruits utilise built up water pressure (squirting cucumber) while others employ tension from drying fruits (violets)
Seed dispersal - water
- aquatic plants have seeds that can float and are carried by water
- coastal plants are typically very tolerant of salt water (coconuts, e.g.)
- certain mangrove species produce propagules that survive up to a year in salt water
Asexual Reproduction types
Binary Fission, Budding, Spores
Fragmentation and Regeneration:
- Vegetive propagation: Natural (bulbs, runners, rhizomes, tubers) and artificial (cuttings)
- Animal regeneration: starfish + earthworms
Binary Fission
Asexual reproduction used by bacteria, protists and amoebae (unicellular organisms)
Cell goes through the stages of mitosis; however, when it reaches cytokinesis it splits into two different organisms. Newly formed cells are ‘clones’ of the parent and parent identity is lost.
Budding
Completed by: yeast, jellyfish, sea anemones
(uni + multicellular)
A new organism (bud) grows off the original organism. As soon as the bud is capable of surviving on its own, it separates itself from the original organism. Only one daughter cell (smaller than the parent) is formed at a time (parent identity is maintained)
Spores
ferns, algae, mosses
reproductive cell capable of developing into a new individual without fusion (fertilisation) with another reproductive cell
Vegetive propagation: natural - bulbs
Formed from fleshy leaves which surround a small stem. This stem grows to become a new plant. Small bulbs may form around parent bulb. Example = daffodil, onion
Vegetive propagation: runners
A stolon / runner is a stem that grows horizontally on the surface of the parent plant with a small terminal offspring. When the stolon breaks off, a new individual plant is formed. Example = strawberry and some grasses
Vegetive propagation: rhizomes
Horizontal, underground stems, with buds rising from these stems to the surface and growing into a new plant. Example = mint, iris, ginger, couch grass
Vegetive propagation: tubers
Thickened underground stem bearing buds, from which new plants grow. Tubers contained stored food material. Example = potato, dahlia
Fragmentation and Regeneration: VG artificial: grafting
A technique used where a cutting is attached to another plant (called the new stock). The stock provides the root system and lower support for the new plant.
