22 Plant reproduction Flashcards
what is the definition of pollination?
the transfer of pollen grains from male reproductive structures to female reproductive structures of another plant prior to fertilisation
what is self-pollination?
pollen is transferred to a stigma of the same flower/another flower on the same plant
what is the advantage of self-pollination?
more reliable than cross-pollination
what is the disadvantage of self-pollination?
less genetic variation –> inbreeding –> disadvantageous recessive characteristics more likely to be passed on
how is self-pollination avoided?
male and female parts mature at different times (protandry and protogyny)
physical separation of male and female parts
some flowers are monoecious (i.e. only male/female)
chemicals on stigma prevent pollen grains from same plant producing pollen tube (self-incompatibility)
what is cross-pollination?
pollen is transferred from one plant’s anther to another plant’s stigma
what are the features of plants that are pollinated by insects?
colourful, scented petals (can mimic female insects)
nectar produced
short stamen with firmly attached anthers
small, sticky pollen grains
small, sticky stigma
what are the features of plants that are pollinated by the wind?
small and inconspicuous petals
long stamen with loosely attached anthers
large, smooth, light pollen
large, feathery stigma
what are the advantages of cross-pollination?
increases variation and widens gene pool
more heterozygous plants ∴ allele frequency of advantageous genes increases ∴ less susceptible to disease
better chance of adaptation to environment
what are the disadvantages of cross-pollination?
requires a pollinating agent
waste of energy
transmission of disease more likely
takes longer
fewer offspring produced
outline the first stage of fertilisation in angiosperms
pollen grain lands on stigma, completes development and matures
pollen tube grows a cytoplasmic extension down the style (chemotropism), controlled by tube nucleus
pollen tube enters the ovary through the micropyle
tube tip bursts to release male gametes
outline the second stage of fertilisation in angiosperms
double fertilisation:
- one sperm nucleus fuses with ovum –> zygote
- one sperm nucleus fuses with 2 polar nuclei within embryo sac –> 3n endosperm tissue –> embryo food supply
ovules develop into seeds (containing embryo and endosperm)
ovary develops into fruit
what is the genetic advantage of fertilisation in angiosperms?
restores chromosome number to diploid
increases genetic variation
what are the features of a seed’s embryo?
plumule = shoot
hypocotyl = simple stem
radicle = root
1 or 2 cotyledons
what are the three main features of an endospermic seed?
embryo
endosperm
testa
why might a seed lack an endosperm?
to prevent it from germinating in the autumn/winter by reducing its metabolic rate
what would a seed have instead of an endosperm?
seed leaves - absorb nutrient reserves from the endosperm
what is the function of the micropyle?
to allow the entry of water and nutrients to the seed
what is the definition of germination?
plant growth from a seed, including the growth of an embryo root and shoot
what are gibberellins?
plant ‘hormones’ required for germination as growth regulators and cell signalling molecules
outline the process of germination
exposure to water causes rehydration of the seed
water washes out enzyme that was inhibiting growth
metabolic rate reactivated
insoluble starch in endosperm hydrolysed to maltose by a-amylase and then to G/S by maltase
gibberellins induce synthesis of amylase –> initiates break down of starch
how does water affect germination?
enters by osmosis and softens testa to allow it to rupture
mobilises food reserves in the endosperm
activates enzymes
required for hydrolysis and as a solvent
washes out germination/growth inhibitors
how does temperature affect germination?
increased metabolic rate
optimum for enzymes
digests food reserves
moderates respiration and growth
how does oxygen affect germination?
required for aerobic respiration
required for oxidation of glucose and lipids as respiratory substrates
what are the three vegetative structures?
root
stem
leaves
what are triggers for development to the reproductive phase?
temperature
duration of dark period
what is unique in each flowering plant that causes it to flower?
the proportions of Pr and Pfr
what are the two isomers of phytochrome?
Pr - 660nm
Pfr - 730nm
what is photoperiodism?
the reactions of Pr Pfr that occur in daylight and darkness
which phytochrome accumulates in darkness?
Pr
how is day length measured by the plant?
the conversion rate of Pr –> Pfr
how is the apical meristem triggered to its development phase?
active form of phytochrome
causes transcription of flowering time gene
FT mRNA transported in phloem to shoot apical meristem
translated to FT protein
protein binds to transcription factor
activation of flowering gene –> reproductive meristems
give an example of a cereal
rice
maize
wheat
why are cereals used as a source of food by humans?
rich in starch
what is the definition of global supply?
the annual production of a specific crop, plus stockpiles of it carried over from previous years
what is the effect of the increasing human population on cereal production?
increasing use
demand exceeding supply
why is sustainability of food increasingly more difficult?
population increasing
BUT available land and water decreasing
+ increasing costs
