Sexual Reproduction in Flowering Plants Flashcards
Structure of typical anther
- A typical anther has two anther lobes
- Each anther has two pollen chambers (microsporangia) which has many microspores
Epidermis in anther- structure + function
It is the outermost layer in a mature anther and is composed of tangentially stretched cells
The cells are tangentially stretched so that at the time of maturation, the anther can rupture easily and release pollen grains
Endothecium (anther)- structure + function
It is the second layer of the mature anther and is composed of columnar cells with fibrous thickened bands
They are fibrous for elasticity and thickened for protection
Middle layers of the anther
Third layer of a mature anther and they degenerate before pollen mother cells undergo meiosis
Tapetum- structure + function
The tapetum is the 4th and innermost layer of a mature anther
It is composed of cytoplasmic cells which are multinucleate
Serves as nutritive tissue for pollen mother cells and microspores/pollen grains/male gametophyte
Microsporogenesis
Formation of microspores from sporogenous tissue.
Name the two walls of the pollen grain
Exine and intine
Exine- structure
Composed of sporopollenin- oxidative polymer of carotenoid esters. Hardest substance seen in a plant
* Resistant to physical and biological decomposition
* Checks the natural decay of pollen
Give reason why the exine is resistant to heat and acid
It is composed of sporopollenin, which is the hardest substance seen in a plant, making the exine resistant to physical and biological decomposition/ heat and acid
Intine- structure + function
Structure: Inner layer that is composed of pectin and cellulose
Function: Gives rise to pollen tube at the time of pollen germination
Which two cells does a pollen grain divide into?
- A larger vegetative cell
- And a smaller generative cell which divides mitotically to form 2 non-motile male gametes
Pollination- definition
Transger of pollen grains from the anther to the stigma of a flower is called pollination
Self pollination- definition
Transfer of pollens from the anther of a flower to the stigma of the same flower (bisexual) (autogamy) or another flower of the same plant (geitonogamy).
Adaptation/contrivances for self pollination
Homogamy- Anthers and stigma mature at the same time
Chasmogamous flowers- Flowers with exposed anthers and stigma
Cleistogamous flowers- Completely closed flowers
Cross pollination- definition
Transfer of pollens from the anther of a flower to the stigma of another flower of another plant of the same species (allogamy/xenogamy)
Adaptation/contrivances for cross pollination
- Self sterility- Pollens of flowers do not grow or grow slowly
- Dichogamy- Maturation of pollens and stigma of a flower at different times
- Herkogamy- In some bisexual flowers, the style is longer than the stamens. Pollens fail to reach the stigma
- Heterostyly- In dimorphic flowers, the styles are of different lengths (long styled flowers and short styled flowers)
What is the nucellus
Parenchymatous body of the ovule/mega sporangium
What are integuments
Sheaths that cover the nucellus of the ovule
What is the micropyle
Small opening at one end of the ovule that facilitates the entry of the pollen tube
What is the funicle
The stalk that attaches the ovule to the placenta
What is the chalaza
The basal part of the ovule where the nucellus, integuments and funicle merge
Megasporogenesis
Development of megaspore within the ovule is called Megasporogenesis
Functions of Antipodal cells
- They nourish the embryo sac
- growth and nourishment of the endosperm
Functions of Synergid cells
- It helps in guiding the pollen tube towards the ovule
- It releases substances that stop the growth of the pollen tube and help in the release of male gametes from the pollen tube
Types of entry of pollen tube (Name)
- Porogamy
- Chalazogamy
- Mesogamy
Porogamy
When the pollen tube wnters through the micropyle, it is the most common type of entry of pollen tube
Chalazogamy
Entry of pollen tube from the chalazal end.
E.g. plants like Casuarina
Mesogamy
Entry of pollen tube through integuments
E.g. plants like Cucurbita
Syngamy
Fusion of gametes is called Syngamy
Fertilization
Fusion of male and female gametes is called fertilization
Triple fusion/Double fertilization
In angiosperms, one of the male gametes fuses with the egg cell to form the zygote (2n) and the other fuses with the diploid polar nuclei forming the endosperm (3n). This is known as triple fusion or double fertilization
Who discovered triple fusion/double fertilization
S.G. Nawaschin
What is the endosperm?
- Endosperm (triploid nucleus) is a nutritive tissue formed by 3 halploid nuclei, 2 from the female gametophyte and one from the male gametophyte.
- It provides nourishment to the growing embryo
Nuclear endosperm
- Seen in polypetalous dicots
- Nucleus division is not followed by wall formation
- Nuclei formed remain free in the embryo sac
- Watery endosperm of coconut contains growth promoting coconut milk factor Used as nutrient medium in culture experiments
- E.g. coconut
Cellular endosperm
- Seen in gamopetalous dicots
- Wall formation begins along with first division of nucleus, transversely.
- Subsequent divisions are irregular
Helobial endosperm
- Seen in members of order- Helobiales of monocots
- Nucleus division is accompanied by wall formation
- This is followed by free nuclear and wall divisions
Is it n, 2n, 3n-
1. Vegetative parts of a plant
2. Endosperm
3. Antipodal cell, synergid cell, egg cell, male gamete
4. Nucellus
- Vegetative parts of a plant- DIPLOID (2n)
- Endosperm- TRIPLOID (3n)
- Antipodal cell, synergid cell, egg cell, male gamete- HAPLOID (n)
- Nucellus- DIPLOID (2n)
Embryogenesis
Development of mature embryo from diploid zygote is called embryogenesis
Fate of the ovary
fruit
Fate of the ovary wall
pericarp
Fate of the ovule
seed
Fate of the funicle
stalk of seed
Fate of the nucellus
perisperm
Fate of the integuments
seed coat
Fate of the egg cell
embryo
Fate of the secondary nucleus
endosperm
Define fruit
Fruit is a ripened ovary
True fruit
When a fruit develops exclusively from the ovary
E.g. Mango
False fruit
When other parts like tepals or thalamus take part in the formation of a fruit in addition to the ovary
E.g. Apple (fleshy thalamus)
Parthenocarpy
Development of fruits without fertilisation
Polyembryony
The condition where more than one embryo are present in the seed
Apomixis
Substitution of sexual process by asexual methods
Albuminous seeds
Endosperm persists to nourish the young seedling
E.g. Dicot: Castor, Custard apple
Monocot- Cereals, pulses
Exalbuminous seeds
Non-endospermic, cotyledons store food for nourishment
Dicot- Pea, bean, mango
Monocot- Orchids, Vallisneria
