Angiosperm Reproduction and Plant Traits Quiz

Plant Reproduction and Growth

• Angiosperms (flowering plants) can reproduce asexually or sexually.
• Asexual reproduction is advantageous in stable environments, as it allows for rapid cloning from parts of the parent plant.
• Vegetative reproduction is a type of asexual reproduction, resulting in new individuals.
• Asexual reproduction requires less energy than sexual reproduction.
• Various forms of vegetative reproduction include runners (e.g., strawberries), rhizomes (e.g., irises, potatoes), suckers (e.g., cherry, apple), and adventitious plantlets (e.g., Kalanchoë).

Angiosperm Reproduction (Sexual)

• Sexual reproduction involves an alternation of generations.
• The diploid sporophyte generation gives rise to a haploid gametophyte generation contained within sporophyte tissues.
• Male gametophytes are pollen grains, developing from microspores.
• Female gametophyte is the embryo sac, developing from megaspores.
• These gametophytes are formed in specialized structures within the angiosperm flower.
• Angiosperm reproductive organs are developed seasonally.

Flower Structure

• Most flowers contain male (stamens) and female (carpels) parts.
• Stamens have anthers (at the tip) containing microspore mother cells.
• Carpels consist of an ovary (lower bulge), style (slender stalk), and stigma (sticky tip).
• Imperfect flowers contain only male or only female parts.
• Monoecious plants have both male and female imperfect flowers on the same plant.

Pollen Formation

• Pollen sacs within anthers contain microspore mother cells.
• Meiosis in microspore mother cells form four haploid microspores.
• Mitosis in these microspores produces pollen grains, with generative and tube cell nuclei.
• The tube cell nucleus forms the pollen tube.
• The generative cell divides to form two sperm cells.

Egg Formation

• Ovules inside the ovary contain diploid megaspore mother cells.
• Meiosis in megaspore mother cells produces four haploid megaspores.
• One surviving megaspore undergoes repeated mitotic divisions forming eight haploid nuclei.
• These nuclei are precisely arranged within the embryo sac.

Pollination

• Pollination is the transfer of pollen from anther to stigma.
• Self-pollination occurs when pollen from a flower's anther lands on the same flower's stigma.
• Many angiosperms utilize animals (pollinators) for cross-pollination, often rewarded with food (nectar).
• Flower color and form have been shaped by evolution to attract specific pollinators.
• Effective animal pollination requires pollinators to visit multiple plants of the same species.
• Wind pollination is common in some angiosperms and all gymnosperms. Often small, green, and odorless flowers are wind-pollinated.

Fertilization

• Pollen grains adhere to the stigma, germinating and growing a pollen tube to reach ovules in the ovary.
• Upon reaching the embryo sac, the pollen tube releases two sperm cells.
• One sperm fertilizes the egg, the other fuses with polar nuclei to form endosperm (food supply for the embryo).
• This process is called double fertilization.

Seed Development

• After fertilization, active cell division forms the embryo.
• Early embryo development halts, becoming dormant due to drying.
• Embryo development stops after apical meristems and seed leaves (cotyledons) develop.
• The outer covering of the ovule develops into a seed coat which protects the dormant embryo.

Seed Germination

• Germination is the resumption of metabolic activities leading to growth.
• Water intake and oxygen accessibility are essential for germination.
• Germination occurs when conditions are favorable to the plant’s survival.
• The roots emerge first, followed by the shoot in dicots, and the coleoptile in monocots.

Fruit Development

• The flower ovary develops into a fruit during seed formation.
• Fruits vary considerably in form and are dispersed in diverse ways, including animals (fleshy fruits), wind, and water.

Plant Hormones

• Plant growth and differentiation are influenced by plant hormones, originating from various tissues.
• Some plant cells have the ability to rediscover hidden genetic information, influenced by environmental cues.
• Growth is largely reversible in plants.
• Examples of plant hormones include auxin, gibberellins, cytokinins, ethylene, and abscisic acid.

Auxin

• Auxins are crucial for plant growth responses, including phototropism (growth toward light).
• Experiments by Darwin explored the role of a substance (later identified as auxin) causing plant bending in response to light.
• Frits Went’s work elaborated on how auxin concentrations vary across the seedling depending on light location, causing directed growth.
• Synthetic auxins control weeds by inducing rapid growth followed by death.

Photoperiodism and Dormancy

• Photoperiodism is a mechanism used by organisms to measure seasonal changes in day and night lengths.
• Plant flowering responses are categorized into long-day plants (flower in long days), short-day plants (flower in short days), and day-neutral plants (flower regardless of day length).
• Dormancy is a plant’s ability to halt growth when conditions are unfavorable.
• In temperate zones, dormancy is linked to winter.

Tropisms

• Tropisms are directional and irreversible growth responses to external stimuli.
• Phototropism is growth towards light.
• Gravitropism is growth in response to gravity, with stems growing upwards and roots downwards.
• Thigmotropism is the response of plants to touch.