Reproduction in Plants Flashcards
what are flowering plants known as?
angiosperms
what are the features of an insect pollinated flower?
-Carpel (female parts):
•stigma
•style
•ovule
•ovary
-Stamen (male parts):
•petal
•filament
•anther
-sepal, nectary, receptacle
what does the stigma do?
Is sticky to trap pollen on its surface
What does the style do?
holds the sticky stigma where it can come into contact with insects
what is the ovule?
female gamete
What does the ovary do?
protects the ovule and becomes the fruit
What do the petals do?
Brightly coloured/scented to attract insects
What is the anther?
produces pollen with male gamete (made by mitosis)
What is the filament?
thin/stalk like and contains vascular tissue to produce anther with nutrients
What is the receptacle?
Part of the stalk where the flower is attached
what is the sepal?
Protect the flower when in bud- often green to aid in photosynthesis
what can having the carpel and stamen in the same flower do?
it can promote self pollination so there’s less genetic variation whereas plants that only have carpel or only stamen can completely prevent it
what is the collective name for the sepals?
the calyx
What is the Corolla?
all the petals on a flower
What are the features of a wind pollinated flower?
(carpel)
stigma
style
ovary
(stamen)
filament
anther
what are the features of insect pollinated and wind pollinated flowers?
Presence of petals, scent, nectar?
Location of anthers
Location of stigma
Type and quantity of pollen
Presence of petals, scent, nectar? (insect)
Petals are brightly coloured, produce scent and nectar to attract pollinating insects
Presence of petals, scent, nectar? (wind)
Absent or small. Green or dull in colour, often green. No scent or nectar
Location of anthers (insect)
Anthers within the flower so more likely to brush past an insect
Location of anthers (wind)
Anthers hang outside
flower so they can be blown in the wind
location of stigma (insect)
Within the flower.
Sticky to trap pollen.
Can secrete chemicals to stimulate pollen tube growth
location of stigma (wind)
Large and feathery, large surface area to catch pollen grains in the wind
Quantity of pollen (insect)
Small quantity.
Pollen has barbs/hooks on its surface to attach to the insect
Quantity of pollen (wind)
Large quantity as there is lower probability of successful pollination. Small, smooth and lightweight
what is a pollen grain?
male gamete
what are the features of the anther?
pollen sac
epidermis
fibrous layer
tapetum
pollen
pollen mother cells/microspore mother cell (diploid)
what does the tapetum do?
releases nutrients/proteins/lipids that flourish developing pardon
How are pollen grains formed?
In the answer by mitosis and meiosis
what does mitosis occur to produce and what do these do? (formation of a pollen grain)
-Mitosis occurs to produce large numbers of diploid pollen mother cells (called diploid microspore mother cells)
-The mother cells undergo meiosis to produce a tetrad (four) haploid cells. These cells (micropore) each form a pollen grains that contain the male gamete.
What is the tapetum and what does it do?
-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 does the vascular bundle in the filament do? (anther)
supplies water and sucrose to the answer
What are two sources of genetic variation in the formation of a pollen grain?
crossing over and independent assortment
what is the process of the formation of pollen grains?
A diploid (2n) pollen mother cell undergoes meiosis I to form 2 genentically different microspores (haploid)which undergo meiosis II to form a tetrad of pollen (haploid) which seperates into pollen grains
What happens inside each pollen grain (young pg) (formation of male gamete)?
a haploid nucleus undergoes mitosis to produce two nuclei: a generative nucleus and a pollen tube nucleus (mature pollen grain).
Generative nucleus itself later divides by mitosis to form two male gamete nuclei
What are the features of a mature pollen grain?
Pollen tube nucleus
generative
Exine (thick outer coat)
Intine (thin inner wall)
what is a pollen grain released from?
anther
what are the features of the pollen cell wall (exine),
-Exine has hooks/barbs in a characteristic pattern for that species.
-Resists drying out of pollen grain (desiccation of pollen grain)
-tough and resistant to chemicals
what else is pollen also resistant to (intrine)?
UV radiation meaning pollen can be carried at high altitudes without DNA mutation occurring
Pollen is also resistant to UV radiation, meaning pollen can be carried at high altitudes without DNA mutation occurring.
What type of pollen dispersal method is this particularly important in?
-wind pollination.
-Pollen can be carried to high altitudes by the wind so they must be able to resist higher UV radiation levels and resist drying out
what is dehiscence (to burst open)
the release of pollen
What is the process for the release of pollen?
-When pollen grains are mature, the outer layers of the anthers dry out and tensions are set up in lateral grooves
-Dehiscence occurs, tension pulls the walls of the anther apart and edges of pollen sacs curl away
-An opening called the stomium exposes the pollen grains and they are carried to the stigma by insects or by wind
what is the ovule contain?
the female gamete
where is the ovule formed?
In the ovary by mitosis and meiosis
how is the ovule developed?
-embryo (megaspore mother cell 2n) undergoes meiosis to produce four haploid megaspores
-three of the megaspore cells degenerate and only one grows and develops in an embryo sac
-The one megaspore undergoes three mitotic divisions to produce eight haploid nuclei (in female gamete) within the embryo sac (one cell) of the ovule
-five of the haploid nuclei degenerate leaving three haploid polar nuclei within the embryo sac of the ovule and one becomes a female gamete
What are the features of an ovary?
-wall of ovary
-integuments (form seed coat)
-Embryo sac (megaspore) mother cell (2n)
-Nucellus
-Micropyle
How is an embryo sac developed?
-A diploid megaspore mother cell undergoes meiosis, forming four haploid megaspores; three disintegrates, leaving one functional.
-The functional megaspore undergoes three rounds of mitosis to produce 8 nuclei
-The eight nuclei organise into:
3 antipodals
2 synergids
1 temale gamete
2 polar nuclei
when an embryo sac develops what do the eight haploid nuclei inside each include?
include one female gamete, two polar nuclei, two synergids and three antipodal cells.
What happens once an of ovule mature is in an ovary and pg lands on stigma?
•Tube nucleus + generative nucleus.
•Generative nucleus divides by mitosis to from 2x male gamete nuclei.
-3 antipodal cells degenerate
-2 synergid cells degenerate
what is the definition of micropyle?
a gap in the integuments for the male nuclei to enter the embryo sac
what do integuments do?
protect the embryo sac = becomes the seed coat (testa)
What does the funicle do?
Attaches the ovule to the ovary
what does the polar nuclei do?
fuse with a male nucleus in double fertilisation to form a triploid endosperm
what does the female gamete do?
fuses with a male nucleus to form a diploid zygote
what is the definition of pollination?
the transfer of pollen grains from the anther to the mature stigma of a plant of the same species
why is pollination 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 must pollen grains be transferred from?
Pollen grains must be transferred from the anther to the receptive/mature stigma of a plant from same species.
What does it mean as the pollen grain contains two mate gamete nuclei?
double fertilisation
When does self pollination occur?
when pollen is transferred from the anther onto the stigma of the same flower (or onto the stigma of another flower on the same plant resulting in self fertilisation)
(some genetic variation through crossing over an independent assortment)
What are the advantages of self pollination?
•Only one parent needed.
•Can help maintain genotypes which are well adapted to the current environment
What are the disadvantages of self pollination?
•Reduces genetic variation (no mixing of genotypes from different individuals)
•Inbreeding = Increases the chance of offspring being homozygous for recessive alleles which could lead to genetic diseases
What is cross pollination?
Transfer of pollen grains from an anther to a stigma of a different plant of the same species.
what are the advantages of cross pollination
-Increased genetic variation through crossing over, independent assortment and mixing of parental
genotypes when haploid gametes fuse.
-It 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 ensures that cross pollination occurs?
- 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 male and female sex organs so can’t self pollinate.
What is the process of fertilisation?
-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.
what will only germinate on the stigma? (fertilisation)
Only compatible pollen grains will germinate on the stigma: the stigma releases sucrose to stimulate pollen germination
How does the pollen tube grow and what does the tube nucleus genes code for? (fertilisation)
Pollen tube grows towards chemicals produced from ovule (chemo-trophism): tube nucleus genes code for hydrolytic enzymes that digest the style tissue
where do two male nuclei originate from? (fertilisation)
these originate from mitosis of the generative nucleus
what happens in 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 nucleus.
what are the similarities between fertilisation in humans and flowering plants?
•Both involve the fusion of haploid gametes to form a zygote
•Both involve internal fertilisation in the female
•Both involve the secretion of digestive enzymes to digest a path for the male gamete to reach the female gamete
what are the differences between fertilisation in humans and flowering plants?
•Double fertilisation occurs in plants
•Pollen tube formation in plants / acrosome reaction in humans
•Male gamete is able to swim in humans / pollen
how is the seed and fruit formed?
-The ovule (once fertilised) becomes the seed
-The ovary becomes the fruit (a fruit is a mature ovary that may contain seeds)
what does a diploid zygote undergo when the seed and the fruit are being formed?
mitosis- Diploid embryo, consisting of plumule (developing shoot), radicle (developing root) and one or two cotyledons.
what does the triploid nucleus endosperm undergo when the seed and the fruit are being formed?
mitosis- Endosperm tissue, an important food storage tissue in cereal grains, e.g. wheat & maize. (the tissue containing food reserves: starch = amylose/amylopectin)
what does the ovule become when the seed and the fruit are being formed?
the seed (embryo plant inside seed)
what does the ovary wall become when the seed and the fruit are being formed?
Develops into a fruit wall enclosing the seeds.
what do the integuments become when the seed and the fruit are being formed?
Develop into the testa (seed coat) (tough outer coat of the seed = prevents drying out/resists frost)
what does the micropyle become when the seed and the fruit are being formed?
remains as a pore in the testa (allows water to enter which is needed for germination of seed)
what are the features of a seed and fruit
-ovule wall
-plumule
-funicle
-micropyle
-radicle
-cotyledon
-testa
What does the funicle form?
a scar on the seed called the hilum
what is a cotyledon?
a seed leaf
what are monocotyledons?
seeds with one cotyledon, e.g. maize and wheat
What are dicotyledons?
seeds with two cotyledons, e.g. broad beans
what are the features of maize (a cotyledon?
-testa and ovary wall fused
-endosperm
-coleoptile (plumule sheath)
-pumule
-radicle
-cotyledon- (embryo seed leaf£
-funicle
what is the plumule?
embryo plant shoot (becomes stem)
what is the radicle?
embryo plant root (becomes root)
what is the testa fused with and what does this mean?
The testa is fused with the ovary wall, so the maize has a one seeded fruit
Why are broad beans dicotyledons?
they have two cotyledons with the embryo lying between them
what do broad bean seeds use cotyledons as and what does this mean?
food storage tissue meaning they do not have an endosperm and so are non-endospermic
In broad bean seeds what happens to the endosperm and what does this mean?
Endosperm (food store) is absorbed by the seed leaves, so the cotyledon is the primary food store
What are the differences between monocotyledons and dicotyledons?
Mono:
-One cotyledon
-Veins usually parallel
-Vascular bundles usually complexly arranged
-Fibrous root system
-Floral parts usually in multiples of three
Di:
Two cotyledons
-Veins usually netlike
-Vascular bundles usually arranged in ring
-Taproot usually present
-Floral parts usually in multiples of four or five
What are seed adaptions for life on land?
-testa is chemically resistant and so seeds survive adverse chemical conditions and it also provides physical protection
-Endosperm/cotyledons provide a supply of glucose/amino acids/lipids until the first true leaves are formed that can then photosynthesise
-Dormant seeds have a low metabolic rate so they can survive cold weather
-Very low water content needed to survive very dry conditions
Why is seed dispersal important for plants ?
-Reduces intra-specific competition (nitrate ions / phosphate ions / oxygen..) with the parent plant and other offspring plants
-Allows for colonisation of new areas
Why are fruit important in seed dispersal?
-Fruits are eaten by animals, the seeds pass through the animals digestive system and then egested. This disperses the seeds.
-Fruit may be adapted for specific mode of dispersal e.g. hooked to attach to animals
what are the three main requirements for successful germination?
1.Oxygen = aerobic respiration in cells of embryo to produce ATP = more cell division (mitosis)
2.Optimum temperature for enzymes (e.g. amylase, maltase, protease) involved in germination
3.Water = mobilise enzymes for transport, enters cells by osmosis (down a water potential gradient) to make them turgid = important in growth
what do the first steps of germination involve?
-what is imbibed (taken in) through the micropyle
-the tissues then swell, spitting or softening the testa, allowing entry of more oxygen
-oxygen can be used in aerobic respiration to produce ATP energy for metabolism
Whilst germinating what does the plant use to provide energy for growth?
-the plant uses food stores in cotyledons (for dicotyledon plants) or the endosperm (for monocotyledon plants)
-The seedling can now photosynthesise and make its own GLUCOSE
why is the plumule initially bent over? (germination)
to protect from soil abrasion
Explain the relative changes in the dry mass of the embryo/seedling and endosperm. (diagram)
•Endosperm- starch hydrolysed to maltose (and then maltose hydrolysed to glucose by maltase) and loss of carbon dioxide in respiration;
•Embryo- glucose used by growing regions of the embryo
•Seedling- increase as first leaves produced start to photosynthesis.
what would be the control experiment?
boil seeds to denature enzymes
why is germination different in non-endospermic seeds?
endosperm has been absorbed into the cotyledons
what is 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 & 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 photosynthesis. The plant is now independent of food stores in the seed.
In endospermic seeds what is involved in the process of germination?
gibberellin (a plant hormone)
What does the endosperm contain?
starch, proteins and fats
What is 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 then 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 and fatty acids & 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.
what are starch and proteins examples of? (germination)
food reserves found in seeds
describe the breakdown of starch and proteins into soluble products including the enzymes used (germination)-
•Starch hydrolysed to maltose (2x a-glucose linked by an al-4 glycosidic bond) by amylase; maltose is then hydrolysed to a-glucose by maltase;
• Proteins hydrolysed to amino acids by proteases (endoproteases + exoproteases)
In what vessels are the soluble products transported in the plumule and radicle?
Phloem tissue (in sieve tubes - translocation e.g. sucrose + amino acids)
Give examples of the uses of these soluble products in plant cells. (germination)
• Maltose is hydrolysed to a-glucose for respiration or it is converted to B-glucose to form cellulose to make cell walls
• 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 the seeds indicate amylase activity.
• Boiled then cooled seeds are set up as a control. (a) Describe how you would develop and refine this practical procedure to determine whether treatment of seeds with a 0.1 mmol dm-3 solution of gibberellic acid increased production of amylase.
Soak some seeds in gibberellic acid
Measure clear area/ compare size of clear zone
Any two from:
Same type of seed
Soaked for same time
Same conc./depth 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
what is the tapetum?
A layer of cells around the pollen sac. It provides nutrients and regulatory molecules to the developing pollen grains
What is the pollen tube nucleus?
A nucleus containing genetic information coding for hydrolytic enzymes to digest a path through the style
what is the generative nucleus?
A nucleus which undergoes mitosis to form two male nuclei (gametes)
what is exine?
The tough cell wall of a pollen grain
what is dehiscence?
Release of pollen when the anther dries out, tension pulls the walls of the anther apart and the edges of the pollen sacs curl away
what is a megaspore?
A haploid cell which undergoes mitosis three times to form 3 antipodals, 2 synergids, 2 polar nuclei and 1 female gamete
what is pollination?
Transfer of pollen from an anther to a stigma
what is double fertilisation?
When one male gamete fuses with the female gamete to produce a diploid zygote and the second male gamete fuses with the two polar nuclei to form a triploid primary endosperm nucleus.
What is the endosperm?
An important food storage tissue. Fuses with the cotyledons in dicotyledons
What is the testa?
The tough outer coat of a seed, formed from the integuments.
Resistant to chemical digestion.
what is a cotyledon?
A seed leaf. In dicotyledons these fuse with the endosperm to act as the main food store for the seed.
What are gibberellins?
Plant hormones involved in germination of monocotyledons
what is the aleurone layer?
A protein layer found in monocotyledon seeds which is digested to provide amino acids for protein synthesis
why is maize endospermic?
endosperm acts as a seed coat
