Plant Reproduction Flashcards
What are flowering plants called?
angiosperms
What ploidy level are most flowering plants?
diploid
Where does meiosis take place in plants, what does it produce?
within the reproductive tissues
produces haploid spores which contain gametes
What is the male spore? produced where?
pollen grains, produced in the anther
What is the female spore? produced where?
embryo sac, produced in the ovule, in the ovary
What do many species of flowers contain? (reproductive organs) making them what?
hermaphroditic, the flowers contain both male and female parts
What is the general pattern seen in all flowers?
a flower is four sets of modified leaves arising from the receptacle at the base of the flower
What is the calyx?
the outermost ring of structures, which comprises the sepals.
They are usually green and protect the flower bud.
Where is the corolla located? what is it?
inside the sepals, a ring of petals
These range from abscent to small and pale green to large and brightly coloured
What is the stamen?
male parts of the flower, consists of a filament supporting an anther
What does the filament contain and do?
contains vascular tissue
transports sucrose, mineral ions, and water to the developing pollen grains
What does the anther contain? how many? what happens when mature?
4 pollen sacs arranged in 2 pairs
when mature the pollen sacs dehisce (open and release the pollen)
What structure is located in the centre of the flower?
the carpel, which are female parts of the flower
What structures does the carpel consist of?
stigma
style
ovary
What is the function of the stigma?
attract the pollen grains
What is the function of the style?
connects the stigma to the ovary, is where the pollen tube grows
What is the function of the ovary?
hold egg cells, contains ovules waiting to be fertilised by pollen
How do insect pollinated flowers distribute their pollen?
They attract pollinators like Bees, through colourful petals, scent, and nectar. As the bee enters the flower the anthers brush against it’s lorax and legs leaving sticky pollen behind
What happens when the bee carrying pollen enters another flower?
it brushes some of the pollen against the ripe stigma, cross-pollination has taken place
How do wind pollinated flowers distribute their pollen?
their anthers hang outside the flower so that the wind can blow away the small, smooth, and light pollen.
How do wind pollinated flowers adapt to receive pollen?
The feathery stigmas hang outside the flowers and provide a large surface area for catching pollen grains that are blown into their path.
What undergoes meiosis in the pollen sacs of the anther? forming? (development of the male gamete)
diploid pollen mother cells, each forms a tetrad congaing four haploid cells
What is the tapetum, what does it do?
a layer of cells around the pollen sac, provides nutrients and regulatory molecules to the developing pollen grains
has a significant role in the formation of the pollen cell wall
What properties does the cell wall of the pollen grains have?
is tough and resistant to chemicals
resists desiccation
UV light cannot penetrate pollen grains
What do pollen grains resisting desiccation allow?
so pollen grains can be transferred from one plant to another without drying out
What does UV light being unable to penetrate pollen grain cell wall do?
the DNA in pollen that is carried at high altitude is protected from mutation
What does the haploid nucleus in the pollen grain undergo? producing what?
mitosis, producing 2 nuclei (a generative nucleus and a tube nucleus
What is produced when the generative nucleus undergoes mitosis? (male gamete)
2 male nuclei
What happens when the pollen is mature?
outer layers of anthers dry out
What does the drying out of the anthers when pollen is mature cause?
tension in lateral grooves
until eventually dehiscence occurs in which tension pulls the walls of the anther apart and the edges of the pollen sacs curl away
What is the opening called that exposes the pollen grains during dehiscence, what then happens?
the stomium
exposes the pollen grains and they are carried away by insects or by wind
What is dehiscence?
the opening of the anther, releasing pollen grains
What happens in the ovule in development of the female gamete?
a megaspore mother cell undergoes meiosis making four haploid cells
How many of these 4 haploid cells disintegrate? (female gamete) (meiosis of megaspore mother cell)
3
What happens to the remaining haploid cell? (female gamete) (meiosis of megaspore mother cell)
Undergoes 3 rounds of mitosis, producing eight haploid nuclei, one of which is the female gamete, 2 fuse to form polar nucleus, 3 antipodals, 2 synergids
What can the female gamete also be called?
egg cell or oosphere
What happens to 2 of the haploid nuclei produced in mitosis of haploid cell? (female gamete)
they fuse to make a diploid nucleus called the polar nucleus
What is the nucellus?
a layer of cells which provides nutrients
What are integuments?
two layers of cells around nucellus
protective layer
What is a gap in the integument called?
a micropyle
What is a micropyle
small opening in the ovule through which pollen tube penetrates
What is pollination?
the transfer of pollen grains from the anther to the mature stigma of a plant of the same species
What is self-pollination?
the pollen from the anthers of a flower is transferred to the mature stigma of the same flower or another flower of the same plant
What is cross-pollination?
pollen is transferred from the anthers of one flower to the mature stigma of another flower on another plant of the same species
What are the results of self fertilisation?
less genetic variation
greater chance of 2 potentially harmful recessive alleles being brought together at fertilisation
can preserve successful genomes that are suitable to a relatively stable environment
What are the results of cross fertilisation? (advantages)
more genetic variation
reduces chances of harmful allele combinations
may allow species to survive in a changing environment, as there are likely to always be some members of a population with suitable alleles/phenotypes
What is protandry?
the stamens of a flower ripen before the stigmas
How do plants ensure cross-pollination occurs?
protandry
anther is below stigma so pollen cannot fall onto it
genetic incompatibility
separate male and female flowers on the same plant
separate male and female plants
What is fertilisation?
the fusion of a female gamete and male gamete forming a zygote
What happens when a compatible pollen grain lands on the stigma?
it germinates in the sucrose solution secreted by the stigma and produces a pollen tube
How does the pollen tube grow?
out of the pollen grain through a gap in the cell wall (pit)
down the style up a gradient of chemoattractants
What does the pollen tube nucleus code for? to digest through what?
codes for the production of hydrolases, including cellulases and proteases
digest its way through the tissues of the style
What are the products of the digestion of the tissues of the style used for?
growth of the pollen tube
Where does the pollen tube grow through and to?
Through the gap in the integuments (the micropyle) and passes into the embryo sac
What happens to the pollen tube nucleus when the pollen tube reaches the embryo sac?
It disintegrates
What happens to the pollen tube when it reaches the embryo sac?
the tip of the pollen tube opens, releasing 2 male gametes into the embryo sac
What then happens to the male gametes released into embryo sac?
one male gamete fuses with the female gamete (oosphere), to form a zygote which is diploid
the other male gamete fuses with the diploid polar nucleus forming a triploid nucleus
What is the triploid nucleus? what happens to it? what does this do?
the endosperm nucleus
divides repeatedly by mitosis
generates the endosperm tissue which takes over from the nucellus in providing nutrition for the developing embryo
what is double fertilisation?
when 2 fusions have occured one to form the zygote, one to form the endosperm, it is unique to seed plants.
After fertilisation In fruits and seeds what happens to the diploid zygote?
it divides by mitosis, becoming an embryo which consists of a plumule, a radicle and one or 2 cotyledons
What is the plumule?
the developing shoot
What is the radicle?
the developing root
what is the cotyledon?
embryonic seed leaf
After fertilisation in fruits and seeds what happens to the triploid endosperm nucleus?
it develops into a food store, providing food for the developing embryo
What does the seed coat (testa) form from?
the drying out of outer integuments which harden and become waterproof with deposits of lignin
What is the seed that is formed comprised from? |(double fertilisation)
the ovule (consisting of the embryo, endosperm and testa)
What is the fruit formed from?
the ovary
What is an example of a dictoyledon?
broad bean, seeds have 2 cotyledons (seed leaves)
What is an example of a monocotyledon?
maize
What does dormant mean in seeds?
describes a seed when its active growth is suspended. Germination will only occur when specific conditions are met
What are the methods of seed dispersal?
wind, transport, rolling, bursting, water, carrying
What is wind seed dispersal?
seed is carried by the wind to a new area
dandelion fruits have a parachute of stiff hairs
What is transport seed dispersal?
Birds eat seeds that pass through the digestive system and are dispersed in the faeces (mammals, reptiles and fish can also sometimes do this) testa is weakened by digestive system acid and enzymes, some seed species can only distribute in this way
What is rolling seed dispersal?
Horse Chestnut tree - fruit of tree breaks open releasing conker which falls to the ground and rolls away from the parent tree
What is bursting seed dispersal?
When legume pods dry they split and scatter seeds. In many species the pods rotate as they burst open sending the seeds in many different directions
What is water seed dispersal?
seeds that when they fall into water they float because their air cavities make them buoyant and water carries them away (coconut palms)
What is carrying seed dispersal?
hooked seeds attach to animal coats and are carried away (burdock)
How do dormant seeds survive very cold weather?
they have a low metabolic rate
How does the testa help the seed survive?
it is chemically resistant and so can survive adverse chemical conditions
can physically protect the embryo
What do endosperms or cotyledons do for seed survival?
provide a supply of nutrients, which lasts until the emerging seedling can photosynthesise adequately
How is seed dispersal a good method of species/seed survival?
they can be dispersed great distances so they don’t compete with parent plant
allows the colonisation of new habitats
What is germination?
the biochemical and physiological processes through which a seed becomes a photosynthesising plant
Water are the 3 main elements for successful germination?
suitable temperature
water
oxygen
How does a suitable temperature affect germination?
at optimum temperature of enzymes involved in process germination happens at it’s best. Optimum varies from species to species but is usually between 5C and 30C
How does water affect germination?
it mobilises enzymes for transport in the xylem and phloem and to vacuolate cells cells making them turgid
How does oxygen affect germination?
aerobic respiration releases energy, which fuels metabolism and growth
In Broad beans germination what happens when suitable conditions are met?
water is taken up rapidly by the seed through the micropyle. causing the tissues to swell and provides suitable conditons for enzyme activity
Why must food reserves in seeds be broken down to be transported to the embryo?
they are insoluble in water
What enzymes break down food reserves in seeds?
amylase hydrolyses starch into maltose
proteases hydrolyse proteins to amino acids
What are the products of broken down food reserves used for?
Sugars are used for aerobic respiration and energy release
and are converted into cellulose for cell wall synthesis
Amino acids are used to synthesise new proteins
What happens when the testa splits?
radicle emerges and grows downwards
then plumule emerges and grows upwards
What happens to the plumule after it emerges, how is it adapted?
it elongates rapidly
the end is hooked over as it pushes through soil to avoid damage to tip by soil abrasion
What happens to the plumule when it breaches the soil surface?
the hooked end unfurls and produces leaves which begin to photosynthesise
What are gibberellins used in the brewing industry for?
speed up germination so that barley seeds need to be kept warm for less time and more malted barley can be produced
What does gibberellic acid do when it is secreted by a plant growth regulator?
switches on genes in the cells of the aleurone layer, resulting in transcription and translation, producing enzymes including protease and amylase
What do the proteases that are formed from gibberellic interaction do?
hydrolyse protein in the aleurone layer to amino acids, which are used to make amylase and maltase
What are carbohydrases produced as a result of gibberellic interaction do?
diffuse out of the aleurone layer and hydrolyse the starch stored in the endosperm cells
What is produced as a result of hydrolysis of starch in the endosperm cells? what are they used for?
sugars that diffuse back through endosperm to the plumule and radicle, they are respired for energy, which fuels biosynthesis and cell division, bringing the seed out of dormancy
