chapter 17 reproduction in plants Flashcards
what is asexual reproduction
⤷ process resulting in production of genetically identical offspring (clones) from one parent
⤷ does not involve the fusion of the nuclei of gametes but involves mitosis
advantages and disadvantages of asexual reproduction
→ advantages of asexual reproduction:
Only one parent is required
Fusion of gametes is not required
All beneficial qualities can be passed down to offspring
Faster method of producing offspring compared to sexual reproduction -> colonise area quickly
→ disadvantages of asexual reproduction:
No genetic variation in offspring -> species are not well adapted to changes in environment
what is sexual reproduction
⤷ process involving the fusion of the nucleus of the male gamete and the nucleus of the female haploid gamete, which are produced in meiosis, to form a diploid zygote
⤷ produces genetically dissimilar offspring
pros and cons of sexual reproduction
→ advantages:
Offspring may inherit (more) beneficial qualities from both parents
Greater genetic variation in offspring -> species are better adapted to changes in environment
→ disadvantages:
Two parents are required (except for bisexual flowers)
Fusion of gametes is required
Slower method of reproducing
what are male parts of flower + functions
→ anther: produces the gamete pollen grains
- Consists of 2 lobes that contain 2 pollen sacs: contain the pollen grains
- Contains vascular bundle: help to transport needed substances (eg water, manufactured food) -> help in producing pollen grains (eg glucose to use in respiration to release energy to produce pollen grains)
- Splits open when mature to release pollen grains
→ filament: holds the anther in a suitable position to disperse the pollen (longer the filament, further the distance dispersed)
→ pollen grain: haploid sex cell produced via meiosis - Male gamete is present in nucleus of pollen grain (not whole pollen grain)
what are female parts of flower (5) + functions
→ stigma: swollen structure at end of style
- Receives pollen grains in pollination
- Secretes sugary fluid when mature: stimulates pollen grains to germinate (No sugary fluid = no germination)
→ style: holds stigma in suitable position to trap pollen grains (like filaments)
→ ovary: produces and protects the ovule(s)
- Develops into fruit after fertilisation by mitosis = will be genetically similar
→ ovule: produces ovum (female gamete) by meiosis
- Ovule develops into seed after ovum is fertilised (one ovule, one seed)
- Not all pods in ovary will have same number of seeds: not all ovules in a pod get fertilised/are mature enough to further develop
- Seeds will be genetically dissimilar as they are formed after fertilisation
→ ovum: haploid sex cell - Gamete is the nucleus of the ovum
what is self pollination
transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant (the plant has multiple flowers) = so to allow nuclei of male and females gametes to fuse together
– Self pollination ≠ asexual reproduction! Self pollination still involves fertilisation between a male and female gamete whereas asexual reproduction has no fertilisation at all
– SP can still involve insects or wind as pollinators (but not necessarily), as long as the pollen grain is being transferred in the same plant
features favouring self pollination
Flowers are bisexual -> anthers and stigmas should mature at the same time
Stigma is situated directly below the anther -> pollen grain can fall directly on the stigma
Certain plants which their bisexual flowers never open (cleistogamous) -> only able to receive pollen grains of their own flower
pros of SP
Only one parent plant is needed
Offspring inherits genes from same parent plant -> beneficial qualities more likely to be passed down to offspring
Do not have to depend on external factors like insects or wind for pollination
Higher probability of pollination (in general) occurring -> stigma and anthers of same flower are very close to each other
Less pollen and energy are wasted -> more pollen is likely to land directly on stigma = less pollen waster, shorter distance for pollen to have to travel = less energy used to transfer pollen
cons of SP
Less genetic variation in offspring (as compared to cross pollination) = species less well adapted to environment
Higher probability of harmful recessive genese being expressed in offspring
Continued self-pollination can lead to offspring becoming weaker, smaller and less resistant to diseases
what is cross pollination
transfer of pollen grains from anther of one plant to the stigma of a flower in another plant of the same species
– if cross pollination occurs between 2 flowers of different species = produces hybrid plant (if the pollen grain actually manages to germinate and not die after landing on stigma)
features favouring cross pollination
Bisexual flowers where the stigma and anther mature at different times
Bisexual flowers where the stigma is situated some distance away for pollen grains from anther to drop directly
Plants which only bear entirely female and male flowers on separate trees, and have their separate male and female trees (dioecious plants)
pros of CP
Offspring produced may have inherited beneficial qualities from both parents
More varieties of offspring can be produced (greater gene combinations from 2 parents = greater genetic variation
Higher chance of species surviving changes in environment -> one change in environment cannot destroy all varieties in a species
increased probabilities of offspring being heterozygous (alleles controlling trait are different)
Lower likelihood of harmful recessive alleles being expressed in offspring
More viable seeds are produced (seeds capable of surviving longer before germination)
cons of CP
Two parent plants are needed
Lower probability pollination will occur -> pollen grains have to travel a further distance between anther of one flower and stigma of another flower
More energy (further dispersing distance) and pollen (pollen may drop while being dispersed from one flower to another) wasted
Depends on external factors, leading to insect-pollination and wind pollination
pollination process in insect pollinated flower
(first assuming the insect has already visited another flower before visiting this flower)
- insect lands on standard petal, follows nectar guide into flower
- insect forces itself in between wing petals, moves in to collect nectar (in reproductive organs in keel petals)
- Insect’s back forces the keel petal upwards, exposes stigma and anthers, insect’s back brushes against anthers and stigma
- Brush against anther = some pollen grains stick onto hairy back of insect (to be transferred to another flower)
- Brush against stigma = pollen grains from other flower get transferred onto sticky stigma
- insect leaves flower, keel petal springs back to original position, encloses reproductive organs again
