Angiosperms Life cycle

Angiosperms Life cycle

 Introduction: In this chapter, Angiosperms Life cycle, we will discuss in detail. Angiosperms bear seeds inside fruits. Flowering plants are highly evolved. The first flowering plant was recorded in China and Canada. Most flowering plants are found on earth.

Image: Angiosperm

Characteristic features:

• Angiosperms are found in hills and plains also.
• Microsporophylls and megasporophylls are present.
• Filament and anther are components of microsporophyll.
• Stigma, Style, and ovary are components of megasporophyll.
• The female gametophyte is an embryo sac formed by meiosis.
• Mainly insects help in pollination.
• Eight nucleate state is formed by female gametophyte.
• Egg apparatus, antipodal cells, and two polar nuclei are present in the embryo sac.
• Double fertilization: one male gamete + egg cell→ zygote and second male gamete + diploid secondary nucleus→ Primary endosperm nucleus (3n).
• Triploid primary Endosperm→ form→ the triploid endosperm.
• Endosperm gives nourishment to the embryo.
• Seeds are found in fruit and fruit provide protection in dispersal.
• Xylem and phloems are present.

Image: life-cycle-angiosperm

Structure of Flower:

• The modified shoot is a flower.
• Flowers have different colors, sizes, shapes, and smells.
• A flower developed on a mature plant.
• The flower contains sepals, petals, carpels, and stamens.
• Stamens (androecium) and Carpel (Gynoecium).
• The Accessory organs are sepals and petals.

Image: Flower

See Also: Angiosperms Pollination

Diversity Living World

Stamen: Male organ

• It is the male organ of a flower.
• Stamen contains anther and filament.
• The filament is long and stalk structure in the stamen.
• Anther shows fertility and broader in size.
• When one anther lobe is present, known as monothecous and two-lobe is present, known as dithecous.
• Groove help to the separation of two anther lobes.

Image: Stamen

Structure of Anther:

• It is a fertile portion in the stamen.
•  It is a bilobed structure.
• Every lobe consists of microsporangia.
• Bisporangiate is monothecous stamen.
• Tetrasporangiate is dithecous.
• Four microsporangia parallel to each other.
• Archesporial cells have parietal cells and sporogenous cells.
• Consists of the endothecium, middle layer, and tapetum.

Microsporangium:

• The outer wall and sporogenous tissue are the part of microsporangium.
• The epidermis, endothecium, middle layer, and tapetum are layers of the microsporangial wall.
• Large cells are present in endothecium and tapetum.
• Endothecium consists of fibrous thickenings.
• When middle layers are corrupt then they help in the protection of microspore mother cells.
• Tapetal cells consist of protoplasmic contents.
• Functions of Tapetum: provide nourishment to microspore mother cell and pollen grain, Amoeboid tapetum help in the exine formation of pollen grains, Secretory tapetum increase thickness of exine.

Microsporogenesis: (Formation of microspores or pollen grain)

• Microsporogenesis: microspore mother cell ➡ develop callose ➡ break plasmodesmal connections ➡ mother cell separate ➡ meiosis occurs ➡ produce haploid tetrad ➡ microspores (pollen grains). 

Anther Dehiscence:

• Mature anther ➡ contains two cavities 
• By loss of water ➡ endothecium contract ➡ form concave shape ➡ anther lobe ruptures ➡ Line of dehiscence observed ➡ yellow powdery mass ➡ appears in case of Mustard.

Structure of Pollen Grain:

• Diameter approx. 30-50 μm.
• The starch is found in the cytoplasm.
• Sporoderm is the covering of pollen grain.
• The inner layer is Intine containing pecto-cellulose.
• Sporopollenin found in Exine.
• Strong acid, alkali, enzymes, and high temperature cannot affect the sporopollenin.
• Ektexine and Endexine are components of Exine.
• The foot layer, baculate layer, and tectum are further components of Ektexine.
• Tectum provides in the design of pollen surface.
• Pollenkit consists of yellow, viscous layer, lipid, and carotenoids.
• In dicots, pollen grains contain three germ pores.
• In monocots, pollen grains contain a single germ furrow.
• Pollen grain has the ability to retain germination ability.
• Potato, brinjal, chilly, legumes, etc. have in the month of viability.
• Wheat has less than an hour of viability.
• Liquid nitrogen is used to preserve the pollen grains.
• Pollen causes Asthma and bronchitis-like disorders.
• Pollen contains protein, carbohydrates, and fats, hence they intake in form of tablets and syrups.

Image: Pollen grain

See also: Biological Classification

Protista Protozoan Plasmodium

Microgametotogenesis:

• Male gametophyte start ➡ in the microsporangium➡ young pollen grain embedded➡ into the cytoplasm➡ vacuoles push pollen grain➡ towards the wall➡ protoplast divide mitotically➡ form generative and vegetative cell➡ callose separates the cell➡ generative cell divides➡ into two male gametes (nonmotile).
• Pollen tube carries male gametes.
• Pollen tube secretes hormones.
• Pollen tube takes food.

Image: Microgametogenesis

Female reproductive organ: Pistil

• The female organ is a gynoecium of a flower.
• It can contain monocarpellary, bicarpellary, tricarpellary and multicarpellary.
• When carpels are separate then gynoecium is apocarpous.
• If carpels are not separate means they are fused then gynoecium is syncarpous.
• The pistil consists stigma, style, and ovary.
• Stigma help as a landing purpose for pollens.
• The pistil contains swollen parts i.e ovary.
• In wheat and rice single ovule is present in the ovary.
• Watermelon contains many ovules in the ovary.

Image: Gynoecium

Structure of Ovule:

• Ovule develops into the seed after the fertilization process.
• It is attached to the placenta.
• Funiculus is the stalk of an ovule.
• Orthotropous, anatropous, circinotropous, hemitropous, amphitropous and campylotropous are different types of ovules.
• The mass of parenchymatous cells present in the ovule is called nucellus.
• Micropyle is a narrow pore and present at end of the ovule.
• Chalaza is the place of origin.

Megasporogenesis: development of ovule

• Mound of nucellus ➡ over placenta ➡ integument develop ➡  from base ➡ primary archesporial cell ➡ develop ➡ archesporial cell divides into ➡ primary parietal and primary sporogenous cellm➡ primary sporogenous cell works as ➡ megaspore mother cell➡  then meiosis occurs ➡ form 4 haploid megaspore ➡ megasporogenesis.
•  Only chalazal megaspore performs functions. 

Megagametogenesis: Development of female gametophyte

• Cell enlarges ➡ mitotic division occurs ➡ produce 2 nucleate embryo sac ➡ both nuclei shift ➡ towards ends ➡ divide ➡ 4 nucleate and 8 nucleate ➡ one nucleus in middle ➡ polar nuclei ➡ 3 nuclei at ends ➡ 3 celled apparatus ➡ at the micropylar end ➡ 3 antipodal cells ➡ at chalazal end.

Structure of Embryo sac

•  Oval-shaped structure.
• It consists of 3 micropylar,3 chalazal, and 1 central.
• It consists of eight nuclei.
• Three mitosis and one meiosis occur.
•  Egg apparatus present at micropylar end.
• Antipodal cells are present at the chalazal end.

Image: Embryo sac

Conclusion: Angiosperms are cosmopolitan. Firstly angiosperm fossils were founded in China. They contain mostly bisexual flowers.

This article contains Angiosperms Life cycle with images and well explanation.