Reproduction in Plants Flashcards
what are flowering plants known as?
angiosperms
give the labels of an insect-pollinated flower
there are 15 to label and briefly describe
stigma (sticky to trap pollen)
style (holds the stigma)
petal (brightly coloured/scented to attract insects)
anthem (produces pollen - male gamete)
filament (thin, contains vascular tissue to provide anther with nutrients)
stamen (both filament and anthem together known as this)
ovules (female gamete)
ovary (protects ovule)
nectaries
receptacle (part of the stalk where flower is attached)
sepal (protects flower when in bud - often green to aid photosynthesis)
carpel (female reproductive parts of a plant)
stamen (male reproductive parts of a plant)
the collective name for the sepals is the calyx
the corolla is all the petals on a flower
give the labels of a wind-pollinated flower
stigma, style and ovary (carpel)
filament and anther (stamen)
describe the features of an insect-pollinated flower in terms of petals, locations of anther and stigma and type and quantity of pollen
petals: often scented, large brightly coloured conspicuous petals, nectar present
anther: anthers fixed to filaments and positioned inside flower to come into contact with visiting insects
stigma: small stigma enclosed within the flower and positioned to come into contact with visiting insects
pollen: less pollen produced, grains are larger, barbs for hooking onto insects
describe the features of a wind-pollinated flower in terms of petals, locations of anther and stigma and type and quantity of pollen
petals: no scent, small inconspicuous petals and sometimes absent and if present then not brightly coloured, no nectar
anther: anthers outside of flower so pollen easily dispersed
stigma: large stigma, often branched and feathery, hanging outside the flower to trap pollen
pollen: pollen produced in large quantities, light, smooth pollen grains
give the labels of an anther of a plant
epidermis
fibrous layer
pollen sac
tapetum
pollen mother cells (2n)
pollen
filament (contains vascular bundle supplying water and sucrose to the anther)
groove is where the anther splits to release pollen
how is a pollen grain (male gamete) formed?
pollen grains are formed in the anther by mitosis and meiosis
mitosis occurs to produce large numbers of diploid pollen mother cells
the mother cells undergo meiosis to produce a tetrad (four) haploid cells
these cells form pollen grains that contain the male gamete
the tapetum is a layer of cells around the pollen sac
it provides nutrients to the developing pollen grains and produces a waterproof coat for the pollen grain
what happens next after the pollen grains are formed?
inside each pollen grain the haploid nucleus undergoes mitosis to produce two nuclei: a generative nucleus and a pollen tube nucleus
the generative nucleus will later undergo mitosis to give rise to two male nuclei
describe and name the pollen cell wall
exine
it is tough and resistant to chemicals
it resists desiccation - drying out
what is pollen also resistant to?
UV radiation
meaning pollen can be carried at high altitudes without DNA mutation occurring
what type of pollen dispersal method is being resistant to UV radiation particularly important in?
wind pollination
pollen can be carried to high altitudes by the wind
describe the process of dehiscence
the outer layers of the anther dry out, causing tension
dehiscence occurs - tension pulls the walls of the anther apart and the edges of the pollen sacs curl away (creating the stomium)
an opening called the stomium exposes the pollen grains and they are carried away by insects or the wind
what does open grooves mean in the anther?
the pollen grain has matured
describe the process of developing the ovule
the ovule contains the female gamete and is formed in the ovary by mitosis and meiosis
the megaspore mother cell in the nucellus undergoes meiosis to produce four haploid megaspores
three of the megaspore cells degenerate and only one grows and develops
this one megaspore undergoes three mitotic divisions to produce eight haploid nuclei within the embryo sac of the ovule
give the labels of the female gamete
wall of ovary (funicle)
integuments
nucellus (may provide nourishment to the developing embryo)
embryo sac (megaspore mother cell 2n)
micropyle
describe embryo sac devlopement
the eight haploid nuclei inside each embryo sac includes one female gamete, two polar nuclei, two synergids and three antipodal cells
what do the antipodals and synergids provide?
antipodals - provide nourishment to the fertilised egg
synergids - are involved in pollen tube guidance
define micropyle
a gap in the integuments for the male nuclei to enter the embryo sac
define integuments
protect the embryo sac
define funicle
attaches the ovule to the ovary wall
define polar nuclei
fuse with a male nucleus in double fertilisation to form a triploid endosperm
define female gamete
fuses with a male nucleus to form a zygote
define pollination and why is it necessary
it is the transfer of pollen grains from the anther to the stigma
necessary so that the pollen grains containing the male gametes are brought into contact with the female part of the flower so that fertilisation can be achieved
what is self-pollination?
transfer of pollen grains from an anther to a stigma of the same plant
some genetic variation through crossing over and independent assortment
what are advantages of self-pollination?
only one parent needed
can help maintain genotypes which are well adapted to the current environments
disadvantages of self-pollination
reduces genetic variation - offspring may be less likely to survive changes in the environment
increases the chance of offspring being homozygous for recessive alleles, which could lead to genetic diseases (many genetic diseases are caused by mutations resulting in defective recessive alleles)
describe cross-pollination
transfer of pollen grains from an anther to a stigma of a different plant of the same species
increased genetic variation through crossing over, independent assortment and mixing of parental genotypes when haploid gametes fuse
cross pollination is of greater evolutionary significance than self-pollination because it increases genetic variation, so a species can adapt to environmental change through natural selection
how could cross-pollination be prevented during plant reproduction experiments?
prevent the transfer of pollen from one flower to another by enclosing or isolating the flower in a bag
where do insect-pollinated flowers have their nectaries located?
why is this an advantage?
below the anther/stigma
this promotes insects transferring pollen grains as they will brush past the anther/stigma when going down to the nectaries
what process ensures that cross pollination occurs?
1) the stamen and stigma ripen at different times
even if pollen produced by the anther lands on the stigma it will not germinate and form a pollen tube
no pollen will fall onto the ripe stigma as it is not being produced by the anther
2) the anther is below the stigma so that pollen cannot fall from the anther onto the stigma
3) genetic/chemical incompatibility e.g. red clover
pollen is unable to germinate on the stigma of the flower which produced it
4) separate male and female plants (unisexual) e.g. holly
the plant does not have both make and female sex organs so can’t self pollinate
describe the process of fertilisation in a plant
when a compatible pollen grain lands on a stigma, the stigma secretes a sugary solution
the pollen grain then germinates, and the pollen tube nucleus controls the growth of a pollen tube
the pollen tube nucleus codes for hydrolytic enzymes that digest through the tissues of the style
the products of digestion are used by the pollen tube
the pollen tube nucleus is at the tip of the pollen tube with the two male nuclei behind
the pollen tube enters the embryo sac through the micropyle
the pollen tube nucleus now disintegrates, and the tip of the pollen tube opens, releasing the two male nuclei into the embryo sac
are you able to map out the path of the pollen tube to the embryo sac?
page 11 in booklet
describe double fertilisation
both male gametes are involved in separate fertilisation events:
one male gamete fuses with the female gamete to produce a diploid zygote
the second male gamete fuses with the two polar nuclei to form a triploid primary endosperm (3n) nucleus
what are the similarities and differences between fertilisation in humans and fertilisation in flowering plants?
similarities:
both involve the fusion of haploid gametes to form a zygote
both involve internal fertilisation in the female
both involve secretion of digestive enzymes to digest a path for the male gamete to reach the female gamete
differences:
double fertilisation occurs in plants
pollen tube formation in plants/acrosome reaction in humans
meiosis is not followed by mitosis in humans but it is in plants
describe briefly the formation of the seed and fruit
the ovule becomes the seed
the ovary becomes the fruit - a fruit is a mature ovary that may contain seeds
how does each structure in an ovary transform into the structures of a seed? there are 6
diploid zygote -> mitosis -> diploid embryo, consisting of plumule (developing shoot), radicle (developing root) and one or two cotyledons
triploid endosperm nucleus -> mitosis -> endosperm tissue, an important food storage tissue in cereal grains, e.g. wheat & maize
ovule -> seed
ovary wall -> develops into a fruit wall enclosing the seeds
integuments -> develop into the testa (seed coat)
micropyle -> remains as a pore in the testa
give the labels of the seed
ovule wall
plumule
funicle - forms a scar on the seed called the hilum
micropyle
radicle
cotyledon
testa
what is a cotyledon? and describe the different types
cotyledon = a seed leaf
seeds with one cotyledon are called monocotyledons, e.g. maize & wheat
seeds with two cotyledons are called dicotyledons, e.g. broad beans
describe maize/monocotyledons
and give labels
the endosperm acts a food store therefore maize is endospermic
testa and ovary wall fused
endosperm
plumule sheath
plumule
radicle
cotyledon
funicle
describe broad beans/dicotyledons
broad beans have the embryo lying between the two cotyledons
broad beans use the cotyledons as food storage tissue
this means they do not have an endosperm (its been absorbed into the cotyledons) so are non-endospermic
(labels: seed coat, cotyledon)
what have seeds evolved as?
as a survival strategy for a terrestrial mode of life
give the seed adaptations for life on land
the testa is chemically resistant, so seeds survive adverse chemical conditions, it also provides physical protection
endosperm/cotyledons provide a supply of nutrients until photosynthesis can occur
dormant seeds have a low metabolic rate so they can survive over winter in time for higher temperatures in spring/summer
very low water content to survive dry conditions
plants have developed different mechanisms to enable the dispersal of seeds
why is seed dispersal important for plants?
reduces competition with the parent plant and other offspring plants
allows for colonisation of new areas
why are fruit important in seed dispersal?
seeds from fruit eaten by animals pass through the digestive system and out
non edible fruits have other adaptations for dispersal e.g. hooks to attach to animals
state three seed dispersal mechanisms and how it works
water - coconut seeds can float as air cavities make them buoyant
wind - light seeds that can be easily carried by the wind, may have parachute-like or feathery structures
animals - spikes means seeds attach to animals
when will seeds germinate?
after a period of dormancy and when environmental factors are favourable, stored food will mobilise and the seed will germinate
what are the three main requirements for successful germination?
suitable temperature - optimum for the enzymes, differs between species
water - needed for mobilisation of enzymes, vacuolation of cells and transport
oxygen - aerobic respiration releases ATP energy required for metabolism and growth
what do the first steps of germination involve?
water is imbibed (taken in) through the micropyle
the tissues then swell, splitting or softening the testa, allowing entry of more oxygen
oxygen can then be used in aerobic respiration to produce ATP energy for metabolism
the graph shows changes in the dry mass of seeds as they are germinating, the dry mass of the endosperm (food reserve), embryo as it develops into a seedling and the total for. the seed (page 16)
explain the relative changes in the dry mass of the embryo, seedling and endosperm
embryo - uses the glucose for growth
seedling - as first leaves produced, starts to photosynthesise, increasing in mass
endosperm - decreases as food reserves are hydrolysed by enzymes (starch -> maltose/glucose) and used in respiration (CO2 lost)
describe the process of germination in non-endospermic seeds
mobilised enzymes hydrolyse large, insoluble food stores:
amylase hydrolyses starch into maltose
lipase hydrolyses lipids into fatty acids and glycerol
protease hydrolyses proteins into amino acids
these soluble products are transported to the plumule and the radicle for use in respiration
aerobic respiration can then produce ATP energy for mitosis and growth
the plumule grows upwards
the radicle grows downwards
the plumule emerges from the soil, the leaves unfurl and begin to photosynthesise
the plant is now independent of food stores in the seed
what hormone is involved in germination of endospermic seeds and what does the endosperm contain?
gibberellin
endosperm contains starch, proteins and fats
describe the process of germination in endospermic seeds
following imbibition of water, gibberellin is released by the embryo and diffuses to the aleurone layer
gibberellins cause transcription and translation to occur, producing hydrolytic enzymes e.g. protease
protease digests the proteins in the aleurone layer to form amino acids, these can be used in further enzyme synthesis e.g. amylase
amylase diffuses into the endosperm and hydrolyses the starch stored there into maltose
proteins and fats in the endosperm are also hydrolysed into amino acids, fatty acids and glycerol
maltose, glucose and other nutrients diffuse to the embryo where they are used in aerobic respiration to provide ATP for the growth of the plumule and radicle
describe the breakdown of starch and proteins into soluble products including the enzymes used
starch -> amylase (+maltase) -> maltose (+glucose)
proteins -> protease -> amino acids
in what vessels are the soluble products transported in the plumule and radicle
phloem
give examples of the uses of the soluble products, produced in germination, in plant cells
maltose hydrolysed to glucose for respiration, or converted to cellulose for cell wall protection
amino acids for protein synthesis
as maize seeds germinate, they produce the enzyme amylase which hydrolyses starch in the endosperm into maltose
this can be demonstrated in the laboratory using the following method:
maize seeds are soaked in water
seeds are cut in half and placed onto starch agar
after 24 hours the seeds are removed and iodine solution added to the starch agar
clear zones around the position of seeds indicate amylase activity, boiled then cooled seeds are set up as a control
describe how you would develop and refine this practical procedure to determine whether treatment of seeds with a 1.0 mmol dm^-3 solution of gibberellic acid increased production of amylase
independent variable - some seeds soaked in gibberellic acid and water and some soaked in just water
dependent variable - measure clear are/compare size of clear zone
control variable - any two from: same type/variety/age/size/mass of seed
soaked for same time
same concentration/depth of starch agar
same temperature/light
the plumule is positively phototropic and negatively geotropic
the radicle is negatively phototropic and positively geotropic
explain this statement
plumule grows towards light and against gravity
radicle grows away from light and towards gravity
