Plant Reproduction Flashcards
What are all the parts of a dicotyledonous insect-pollinated flower?
receptacle, calyx, sepal, corolla, petal
stamen (male parts): anther and filament
carpel (female parts): stigma, style, ovary and ovule
What is the function of a sepal?
they protect the flower when it is in a bud
What is the calyx?
Outermost ring of structures, collective term for all of the sepals
What is the corolla?
A ring of petals (collective name)
- may be a nectary at the base (releasing nectars to attract pollinators)
What is the function of a petal?
Colourful to attract insects
- the inner sterile whorl of a flower
What is the function of the anther?
where pollen is produced
- consists of 4 pollen sacs that split and release pollen
What is the function of the filament?
vascular tissue that supports the anther
- transports food materials needed for formation of pollen grains
What is the function of the stigma?
sticky part that receives pollen from the anther
What is the function of the style?
pollen grows a tube down the style to the ovule
What is the function of the ovary?
Fertile part of the carpel, meiosis occurs here to produce haploid ovules
What is the function of the ovule?
contains an egg that after fertilisation forms the seed
What is the function of the stamen?
male part of the flower, consisting of the anther and the filament
What is the function of the carpel?
female part of the flower, consisting of the stigma, style, ovary and ovule
Insect-pollinated flower vs wind-pollinated: pollen
insect: produces small quantities of sticky, sculptured pollen, larger pollen grains (less wastage of pollen)
wind: produces large quantities of smooth, small pollen (most pollen doesn’t reach another flower)
Insect-pollinated flower vs wind-pollinated: anther and stigma
insect: both within the flower, anther positioned to rub pollen onto the back of insects (e.g. bees)
wind: hang outside the flower so they can be exposed to wind (wind carry pollen away), feathery to increase SA for catching pollen
Insect-pollinated flower vs wind-pollinated: petals
insect: colourful petals to attract insects
wind: absent
Insect-pollinated flower vs wind-pollinated: nectar
insect: usually contain nectar (sucrose)
wind: no nectar
Insect-pollinated flower vs wind-pollinated: scent
insect: produce a scent
wind: no scent
Insect-pollinated flower vs wind-pollinated: attracting insects
insect: attracts
wind: no need to attract insects
What are the 2 distinct phases of the life cycle in flowering plants?
the diploid sporophyte
- the haploid gametophyte
What is the diploid sporophyte phase?
Produces haploid spores by meiosis
- spores develop into haploid gametophyte, which produces haploid gametes by meiosis
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 advantages of self-pollination?
diversity only arises from independent assortment and crossing over
suited to stable environments
preserves genes well suited to that environment
What are the advantages to cross-pollination?
prevents inbreeding (form of outbreeding)
harmful recessive alleles less likely to be expressed
allows species to survive in a changing environment (can withstand environmental change)
How do flowers prevent self-pollination?
stigma is above the stamen (pollen can’t fall onto it)
stigma and anther mature at different times (protandry or protogyny)
separate male and female plants (dioecious)
What is pollination?
The transfer of pollen grains from anther to the mature stigma of a plant of the same species
What are the labels of the cross section of an anther?
Pollen sac
filament (contains vascular bundle)
epidermis
fibrous layer
tapetum
pollen
Describe the cross section of the anther?
cross section of anther shows 4 chambers called pollen sacs
each pollen sac is enclosed by a protective epidermis and fibrous layer
inside the fibrous layer is the tapetum (food store providing energy for cell divisions)
What happens when the pollen has matured?
The anther dries out, splits open at the weakest part/stomium, this exposes the pollen grains
This process is called dehiscence
What is dehiscence?
The opening of the anther, releasing pollen grains
Draw a simple flow chart of pollen formation
Diploid cell -meiosis I and II-> tetrad of microspores (n) -mitosis and development of exine and intine layer-> 4 pollen grains (n)
Describe the process of pollen formation in the anther?
- each pollen sac is filled with diploid cells containing large nuclei
- the anther grows and each cell goes through meiosis forming a tetrad of microspores (young pollen grains)
- the nucleus of each pollen grain undergoes mitosis to produce 2 nuclei: a generative nucleus (n) and a tube nucleus (n)
- when pollen grains are mature, outer layers of anther dry out and split open at the weakest point (in dehiscence) and releases pollen for pollination to occur
- the generative nucleus (n) will later divide by mitosis to form 2 male gametes
Describe the development of the female gamete?
- in each ovule a megaspore mother cell (2n), surrounded by cells of the nucellus, divides by meiosis forming 4 haploid cells (megaspores)
- three of these cells disintegrate the remaining nucleus of the megaspore undergoes 3 meiotic divisions producing 8 haploid nuclei one of which is the female gamete (oopshere)
- the entire structure is called the embryo sac
How many ovules does an ovary contain?
one or more
Draw and label an embryo sac
(at the top) 3 antipodals nuclei (n)
(in the middle) 2 polar nuclei (n)
(at the bottom) 2 synergids nuclei (n) on either side of the oopshere (n)
What are all the labels of the female structure in plants?
stigma
style
ovary wall
funicle
2 integuments
micropyle
ovule
embryo sac
nucellus
What does the ovule consist of?
The outer integuments surrounding the nucellus and an embryo sac containing seven nuclei
What is the nucellus?
Cells that surround the embryo sac and provide nutrition for growth of the ovule
What is the small opening in the integuments called and what does it do?
called the micropyle
where water enters
What is fertilisation?
the fusion of a female and a male gamete, producing a zygote
What happens when the pollen reaches another flower in double fertilisation?
compatible pollen grain lands on the stigma, it germinates in sucrose solution secreted by the stigma
produces a pollen tube
pollen tube nucleus at the tip secretes enzymes to digest cells of the style as it grows
2 male nuclei behind it control growth of the tube (these nuclei originate from the generative nucleus)
What happens when the pollen tube reaches the ovule in double fertilisation?
pollen tube grows through the gap in the integuments (micropyle), passing into the embryo sac
pollen tube nucleus disintegrates, top of the pollen tube opens, releasing the 2 male gametes into the embryo sac
What happens in the double fertilisation phase?
one of the two male gametes fuses with the oopshere (female gamete) to form a diploid zygote
the other male gamete fuses with both polar nuclei to form the triploid endosperm nucleus
a double fertilisation has occured (2 fusions)
a zygote eventually develops into an embryo and grows into a new plant
What type of fertilisation occurs in flowering plants only?
double fertilisation
What are the labels of a fruit and seed?
Ovary (fruit)
Embryo plant (plumule and radicle)
Funicle
Micropyle
Testa
Cotyledon
What is the plumule?
Embryo plant shoot
What is the radicle?
Embryo plant root
What is the testa?
The tough/protective outer covering of the seed
often has outgrowths which keep in dispersal of the seed
also called the seed coat
What is the cotyledon?
Food store
What happens after fertilisation?
the fruit and the seed develop
stamen and the sepals fall off
ovule turns into a seed
fertilised egg inside develops into an embryo plant
What does the zygote turn into?
divides by mitosis into the embryo consisting of the plumule and radicle
as well as one of two cotyledons
What does the triploid endosperm nucleus develop into?
into a food store providing food for the developing embryo
What happens to the micropyle?
remains as a pore in the seed
What happens to the outer integuments?
dries out, hardens and becomes waterproof
- becomes the seed coat (testa)
What does the funicle of the ovule develop into?
Funicle of the seed
What does the ovary develop into?
becomes the fruit
What does the ovule develop into?
becomes the seed
What is the fruit?
A structure developing from the ovary wall, containing one or more seeds
What is the seed?
structure developed from fertilised ovule, containing an embryo and food store enclosed within a testa
What is meant by dormant?
describes a seed when its active growth is suspended, germination will only occur when specific conditions are met
What does a seed do to become dormant?
Dehydrates itself, water content falls below 10%
- this reduces metabolic rate
What 3 things provide nutrition to the developing embryo?
the nucellus
the endosperm
one or two cotyledons
What 2 groups are flowering plants divided into?
- monocotyledons, have on cotyledon only (includes cereals)
- dicotyledons, they have 2 seed leaves or 2 cotyledons (broad beans)
What is the eternal structure of a seed?
testa
endosperm
coleophile (plumule sheath)
hypocotyl -> plumule and radicle
cotyledon
funicle
What is the embryo of a seed?
- consisting of a radicle (gives rise to the root) and a plumule (growing part of a shoot)
- part containing both of these is the hypocotyl
- one or two seed leaves (cotyledons) grow from the hypocotyl
What is the food-store of the seed?
the reserve of food which supplies the embryo and growing plant until it can make its own food through photosynthesis
may be in the cotyledon or in the endosperm
these add nutritional value to seeds for animals and humans
What is the endosperm?
Tissue produced inside the seeds of the most flowering plants
surrounds the embryo
act as a food store for the seed
found in monocots
not photosynthetic
What is the cotyledon?
provides nutrition to developing embryo within seed of the plant
found in dicots
are photosynthetic
Why is the dormancy of seeds important?
allows the seed to survive in unfavourable conditions
ensures that it ensures it germinates in favourable conditions
allows seed to avoid competition with its parent
provides time for seed to be dispersed
What are the adaptations of seeds for dormancy?
- low metabolic rate
- testa physically protects by providing a hard outer coating
- testa is chemically resistant (survive adverse chemical reactions)
- low water content allows it to be resistant to desiccation
- endosperms/cotyledon provide a source of nutrients
Describe the sequence of events that take place during fertilisation [4 marks]
- pollen tube grows through the style controlled by the pollen tube nucleus
- enzymes digest a path through the style to the micropyle
- one male nucleus fuses with female gamete to form the zygote
- second male nucleus fuses with female gamete to form the zygote
What are the different ways of transportation/seed dispersal?
rolling
carrying
bursting
wind
water
animals (either disperse them in faeces or require scarification)
What is scarification?
the digestive system of an animal weakens the testa by physical attack
What are the 3 optimum temperatures needed for seed germination?
Water, Oxygen and Temperature
Why is the optimum amount of water required for seed germination?
nutrients in the dry tissue need to be rehydrated
mobilises enzymes for transport in xylem and phloem
cracks testa so that roots can grow out
Why is an optimum amount of oxygen required for seed germination?
aerobic respiration releases energy which fuels metabolism and growth
Why is an optimum temperature needed for seed germination?
optimum temperature for enzymes involved in the process (enzyme action)
however this temperature varies between species as they may grow best at different times of year (seasonal variation)
