reproduction in plants Flashcards
tissue culture
-a piece of tissue is taken from parent plant, called the explant
-the explant is surface sterilised and placed into growth media
-the plant cells divide to form clumps of totipotent cells called calluses
-each callus can grow shoots, if they are placed in suitable growth media
-the shoots can be transferred to a different growth medium to grow roots
-the plantlets are transferred to soil
-eventually, the plants can be transferred to the field
definition of sexual reproduction
-the reproductive process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring
definition of asexual reproduction
-the reproductive process which results in the production of genetically identical offspring from one parent
characteristics of asexual reproduction
-requires only 1 parent
-no fertilisation involved
-offspring are genetically identical to parent/ there is no genetic variation amongst offspring
-larger number of offspring produced in a short time
characteristics of sexual reproduction
-requires 2 individuals for reproduction to form a zygote
-involves fusion of gametes/ fertilisation
-offspring is genetically dissimilar from parents
-smaller number of offspring
advantages of asexual reproduction
-less time and energy consuming
-does not require a mate
-many offspring can be produced
-beneficial traits from parents are passed onto offspring
disavatanges of asexual reproduction
-less genetic variety in offspring
-more likely for a disease or environmental change to wipe out the whole species
-non-beneficial traits from parents are passed onto offspring
advantages of sexual reproduction
-genetic variety in offspring
-increased adaptations in offspring
-reduces chances of a disease or environment change from wiping out the whole species
disadvantages of sexual reproduction
-time and energy consuming
-required to find a mate
-beneficial traits may not always be passed onto offspring
receptacle
-enlarged end of flower stalk/ pedicel that attaches flower to part of the stem
sepal
-usually green
-protects the flower when in bud
-support petals when in bloom
petal
-brightly-coloured in insect-pollinated flowers
-attract pollinators
-act as a landing platform for insects
stigma
-structure with sticky fluid for pollen to land on
style
-stalk that holds the stigma in position to trap pollen grains
ovary
-may contain one or more ovules
-each ovule produces a female gamete
-each ovule develops into a seed after fertilisation
anther
-male reproductive structure containing pollen grains
-consists of two lobes containing two pollen sacs
filament
-stalk that holds the anther in a suitable position to disperse pollen
pollination
-the process in which pollen is transferred from the anther to the stigma of flowers of the same species
self-pollination
-the transfer of pollen from the anther to the stigma of the same flower, or stigmas on flowers of the same plant and same species
cross-pollination
-the transfer of pollen from the anther to the stigma of the flower of a different plant, but same species
-usually involves insect-pollination, or wind-pollination
advantages of self-pollination
-only 1 parent is required
-offspring inherits genes from parent plant, so beneficial genes are more likely to be passed to offspring
-does not depend on external factors like insects or wind for pollination
-anthers are close to stigma, so high probability of pollination
-less pollen is wasted to cross pollination
disadvantages of self-pollination
-less genetic variation, so offspring is less adapted to changes in the environment
-higher probability of harmful recessive alleles being expressed
-continued self pollination may result in weaker, smaller offspring that is less resistant to diseases
advantages of cross-pollination
-offspring inherit beneficial qualities from both parents
-increased genetic variation in offspring, which increases the chances of survival in an environment that is constantly changing
-increased probability of offspring being heterozygous, so less harmful recessive alleles are expressed
-more viable seeds are produced
disadvantages of cross-pollination
-2 parents are required
-depends on external factors like insect or wind for pollination
-lower probability of cross pollination occurring as compared to self pollination
-more pollen in wasted compared to self pollination
insect-pollination characteristics
petals
-brightly-coloured petals
-serve as landing platform for insects
scent
-scent produced by flowers serves to attract appropriate pollinator
nectar
-production of nectar by nectary, serves as a reward for pollinators
-nectar guides may be present to lead insect to the nectar
stigma
-compact and not feathery
-produces a sugary fluid to trap pollen grains from pollinators, which also stimulates the germination of pollen grains
stamen
-anthers are found inside the flower
pollen grains
-pollen is produced in moderate amounts
-larger, with rough surfaces so that they can easily cling onto pollinators
wind-pollination characteristics
petals
-small and dull petals
scent
-usually do not have a scent
nectar
-nectar is absent
-nectar guide is absent
stigma
-large and feathery
-large surface area to trap pollen grains
stamen
-anthers tend to hang outside the flower on long thin filaments, to be exposed to the wind
-stamens are pendulous so that pollen is released when the anthers are shaken
pollen grains
-pollen is produced in extremely large amounts
-small and smooth surfaces
-light to be easily blown about by the wind
double fertilisation
-after pollination, the pollen grains on the stigma will germinate in response to the sugary fluid containing enzymes and glucose secreted by the mature stigma
-a pollen tube grows out from the pollen grain. the pollen tube grows down the style towards the ovary, guided by the vegetative nucleus
-the generative nucleus also travels down inside the pollen tube
-the pollen tube secretes enzymes to digest tissues of the stigma and style
-the generative nucleus divides to form two male gametes
-the pollen tube reaches the ovule through the micropyle
-the tip of the pollen tube absorbs sap and bursts to release male gametes
-the nucleus of one male gametes fuses with the female gamete to form a diploid zygote/ fertilisation
-the nucleus of the other male gamete fuses with two polar nuclei to form the triploid endosperm
development of flower to fruit
-ovary - fruit, provides protection for the enclosed seeds and sometimes aid in their dispersal
-ovary wall - fruit wall/ pericarp
-ovule - seed
