Sexual Reproduction In Flowering Plants Flashcards
What are the four layers of microsporangium?
Epidermis, Endothecium, middle layers and Tapetum
What is the function of the first three layers of the microsporangium?
Protection and dehiscence of anther
Describe Tapetum. What is the function of the Tapetum?
Nourishes the developing pollen grains it has a dense cytoplasm and more than one nucleus. It is the innermost layer.
Sporogeneous cells are also called?
Microspore mother cell or pollen mother cell
Two layers of pollen grain are called
Exine and intime
The exine made up of highly resistant material is called
Sporopollenin
Apertures in Exine layer are called
Germ pores where sporopollenin is absent
What are the two cells in a mature pollen grain?
Vegetative cell and generative cell
Describe intine wall of pollen
The inner wall that is thin and continuous made of cellulose and pectin
Viability of pollen grains of rice and wheat
30 mins
Single and more than one pistil present are respectively called
Monocarpellary and multicarpellary
Economic importance of pollen
Rich in nutrients
Pollen tablets are used as food supplements which are syrups and tablets which increase sports performance of athletes and racehorses
Stored for years in liquid nitrogen at -196°C
Pollen are stored in pollen banks for crop breeding programs
Viability of solanaceae, rosaceae, leguminoseae
Months
Where is the generative cell and how is it shaped
Floats in cytoplasm of vegetative cell and spindle shaped with dense cytoplasm
Example of allergic pollen
Parthenium- carrot grass causes chronic respiratory disorders- asthma bronchitis, etc
Parts of pistil
Style, stigma, ovary
What is the cavity inside ovule called?
Ovarian cavity - locule
Where do ovules arise from
Placenta which is present in locule
Examples of plants with one ovule
Wheat, mango, paddy
Examples of plants with many ovules
Watermelon, papaya, orchids
The stalk by which the ovule is attached to the placenta is called
Funicle
What is hilum
The junction between the ovule and the funicle
What are integuments
Each ovule has one or two protective envelopes called integuments except at the tip where a small opening called. The micropyle is present.
What is micropyle?
The small opening where integuments aren’t present.
Basal part of ovule
Opposite to the micropylar end is called chalaza
Female gametophyte is also known as
Embryo sac
Nucellus
Mass of cells, enclosed within the integuments are called nucellus. These cells contain reserve food material.
What is present inside nucellus
Embryo sac (Female gametophyte)
What is the ploidy level of the mega poor mother cell before meiosis?
Diploid
What type of cell divisions occur in the megaspore mother cell to produce megaspores
Meiosis
What is free nuclear cell division?
Nuclear divisions are not followed immediately by cell wall formation
What are synergids?
two specialized, short-lived cells located near the egg cell, that play a crucial role in guiding pollen tubes which contain filiform apparatus
What is the filiform apparatus?
Special cellular thickenings at the micropylar tip which play an important role in guiding the pollen tubes into the synergid.
What is the egg apparatus
group of three cells located at the micropylar end consisting of one egg cell and two synergids
What are antipodals?
Three cells at the chalazal end
Define autogamy
transfer of pollen grains from the anther to the stigma of the same flower
What does autogamy require?
Synchrony in pollen release and stigma receptivity, and also the anther and the stigma should lie close to each other.
Examples of Autogamy
Viola, oxalis, commelina,
Open anther flowers are called
Chasmogamous
Flowers which don’t open at all are called
Cleistogamous
Geitonogamy
Transfer of pollen grains from the anther to the stigma of another flower at the same plant
Functionally cross pollination but genetically similar to autogamy
Xenogamy
Transfer of pollen grains from the anther to the stigma of a different plant
Wind pollination requires
Pollen grains that are light and non sticky, exposed stigma, feathery stigma.
Pollination by water is limited to how many genera
30 mostly monocots
Examples of water pollinated plants
Vallisneria and hydrilla
In water pollinated plant, pollen grains are protected from wetting by
Mucilaginous covering
Insect pollinated flowers are
Large, colorful, fragrant and rich in nectar
Relationship of plant providing place to lay eggs
Moth and yucca
Moth deposits its eggs in the locule of the ovary and the flower in turn gets pollinated by the moth.
Continuous self pollination can cause
Inbreeding depression
Devices developed by plants to discourage self pollination
• Pollen release and stigma receptivity are not synchronized
• Anther and stigma placed at different positions
•self incompatibility (inhibits pollen germination or pollen growth)
•production of unisexual flowers
If both sexes are present in different flowers but same plant then which typo of pollination can and cannot occur? Examples?
Autogamy cannot occur but geitonogamy can occur
Ex: Maize and corn
Species that have female and male flowers on different plants
Papaya which prevents autogamy and geitonogamy
Method of pollen pistil interaction?
Pollen does not guarantee transfer of right type of pollen.
Pistil has the ability to recognize right type of pollen growth
This is the continuous dialogue between pollen grain and the pistil
What is pollen-pistil interaction?
Events from pollen deposition on the stigma until pollen tubes enter the ovule are pollen-pistil interaction
What if pollen is right type?
Then position accepts and promotes post pollination events
What if pollen is of wrong type?
Pistil rejects pollen by preventing pollen germination
What is artificial hybridization
Crossing different species and often genera to combine desirable characters to produce commercially superior varieties.
What happens after the pollen tube enters the synergid?
The pollen tube releases 2 male gametes into the cytoplasm of the synergid. One male gamete fuses with the egg cell nucleus (syngamy) to form a diploid zygote, and the other fuses with two polar nuclei (triple fusion) to form the triploid primary endosperm nucleus (PEN).
Why is fertilization in flowering plants called double fertilization?
Because it involves two types of fusions: syngamy (formation of zygote) and triple fusion (formation of PEN).
What happens to the central cell after triple fusion?
It becomes the primary endosperm cell (PEC) and develops into the endosperm, while the zygote develops into an embryo.
What are the main post-fertilization events?
Development of the endosperm and embryo, maturation of ovules into seeds, and the ovary into a fruit.
What is the function of the primary endosperm cell (PEC)?
It divides repeatedly to form triploid endosperm tissue, which stores nutrients for the developing embryo.
What is free-nuclear endosperm?
It is endosperm formed by successive nuclear divisions without cell wall formation, such as the tender coconut water.
Describe the stages of embryo development.
Zygote → Pro-embryo → Globular → Heart-shaped → Mature embryo.
What structures are found in a dicotyledonous embryo?
An embryonal axis, two cotyledons, epicotyl (ending with plumule), and hypocotyl (ending with radicle).
What is the scutellum in monocotyledonous embryos?
The single cotyledon located lateral to the embryonal axis.
What are the types of seeds based on endosperm presence?
Non-albuminous seeds: No residual endosperm (e.g., pea, groundnut). Albuminous seeds: Retain part of the endosperm (e.g., wheat, maize).
What is perisperm?
Remnants of nucellus persistent in some seeds (e.g., black pepper, beet).
What forms the seed coat in mature seeds?
The integuments of the ovule harden to form tough protective seed coats.
How does water and oxygen enter a seed during germination?
Through a small pore in the seed coat called the micropyle.
Give examples of true fruits and false fruits.
True fruits: Mango, guava, orange. False fruits: Apple, strawberry, cashew.
What are parthenocarpic fruits, and how are they induced?
Parthenocarpic fruits develop without fertilization, and they can be induced using growth hormones. Examples: Banana.
What is dormancy in seeds, and what conditions break it?
Dormancy is a state of inactivity with low metabolic activity. Favorable conditions like moisture, oxygen, and suitable temperature can break dormancy and trigger germination.
Why are dehydrated seeds advantageous?
Dehydration reduces water content to 10–15%, slowing metabolic activity, allowing seeds to be stored and used later.
What adaptations make seeds advantageous?
Dependable formation, dispersal ability, food reserves, embryo protection, genetic diversity, and storability due to dehydration and dormancy.
What is the oldest viable seed known?
A 10,000-year-old lupine seed from the Arctic Tundra.
What part of the coconut is the free-nuclear and cellular endosperm?
Tender coconut water is free-nuclear endosperm, and the surrounding white kernel is the cellular endosperm.
What structures enclose the shoot apex and root cap in monocot embryos?
The shoot apex is enclosed in the coleoptile, and the root cap is enclosed in the coleorrhiza.
What is apomixis?
Seed production without fertilization, mimicking sexual reproduction (e.g., Asteraceae and grasses).
What is polyembryony?
The occurrence of more than one embryo in a seed, often due to nucellar cell division (e.g., Citrus, mango).
Why is apomixis important in the hybrid seed industry?
It prevents segregation in hybrid progeny, allowing farmers to reuse hybrid seeds without losing hybrid characters.
What is double fertilization in flowering plants?
Double fertilization is the process where one male gamete fuses with the egg cell (syngamy) to form a zygote, and the other fuses with two polar nuclei (triple fusion) to form the primary endosperm nucleus (PEN).
What happens to the central cell after triple fusion?
It becomes the primary endosperm cell (PEC), which develops into the endosperm.
Define syngamy.
Syngamy is the fusion of one male gamete with the egg cell to form a diploid zygote.
What is triple fusion?
Triple fusion is the fusion of one male gamete with two polar nuclei in the central cell, forming a triploid primary endosperm nucleus (PEN).
Why is double fertilization unique to angiosperms?
Because it involves two fusions—syngamy and triple fusion—in the same embryo sac.
What is the role of endosperm in seed development?
The endosperm provides nutrition to the developing embryo.
What is free-nuclear endosperm?
Free-nuclear endosperm is formed by repeated nuclear divisions without cell wall formation, as seen in tender coconut water.
What are the stages of embryo development?
Zygote → Pro-embryo → Globular → Heart-shaped → Mature embryo.
Describe the structure of a dicot embryo.
It has an embryonal axis, two cotyledons, an epicotyl (ending in plumule), and a hypocotyl (ending in radicle).
What is the function of the scutellum in monocots?
The scutellum is a single cotyledon that absorbs nutrients from the endosperm.
What are albuminous and non-albuminous seeds?
Albuminous seeds retain part of the endosperm (e.g., wheat), while non-albuminous seeds consume all the endosperm (e.g., pea).
What is the significance of seed dormancy?
Seed dormancy helps seeds survive unfavorable conditions and enables long-term storage.
What is perisperm?
Perisperm is the persistent nucellus found in some seeds, such as black pepper.
What are true fruits and false fruits?
True fruits develop from the ovary alone (e.g., mango), while false fruits involve other floral parts (e.g., apple).
What are parthenocarpic fruits?
Fruits that develop without fertilization, such as bananas. They are usually seedless.
What is apomixis?
Apomixis is the formation of seeds without fertilization, mimicking sexual reproduction (e.g., some grasses).
What is polyembryony?
Polyembryony is the occurrence of more than one embryo in a seed, as seen in citrus and mango.
Why is apomixis important in agriculture?
Apomixis allows hybrid traits to be preserved across generations, reducing the cost of hybrid seed production.
How does the ovary develop into a fruit?
The ovary wall transforms into the pericarp, and ovules become seeds.
What is the role of the micropyle in seeds?
The micropyle allows water and oxygen to enter the seed during germination.
What factors are essential for seed germination?
Moisture, oxygen, and suitable temperature.
Give an example of the oldest viable seed.
A 10,000-year-old lupine seed found in the Arctic Tundra.
What is the significance of seeds in angiosperms?
Seeds enable survival in adverse conditions, assist in dispersal, and contain stored food for the developing plant.
