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sexual reproduction in plants without flowers

Introduction 

Plants without flowers (algae, mosses, and ferns) are plants that have neither flowers nor seeds. They present a varied group such as ferns, mosses, algae, and lichens. They can colonize various environments, terrestrial or aquatic. During the period of sexual reproduction, these plants produce both male and female gametes. Usually, the male gametes are released into the water to fertilize the female gametes

- Where are the reproductive organs located in plants without flowers?

- How does sexual reproduction take place in these plants?

Reproduction in algae

Algae are chlorophyllous plants that live in
aquatic or humid environments. They have no roots
neither stem nor leaves nor flowers, such a vegetative apparatus is called"thallus". Algae can be unicellular or haploid or diploid multicellular.

sexual reproduction in Bladder Wrack

Bladder Wrack

image 1: sexual reproduction in Bladder Wrack

The reproductive organs of the Bladder Wrack

The reproductive organs of Bladder Wrack
-The male reproductive system is made up of receptacles, and organs located at the end of the mature thallus, each receptacle is made up of numerous cavities called conceptacles.
- Inside the conceptacles are branched hairs
  bearing antheridia (place of formation of antherozoids)
-The female reproductive system consists of greenish receptacles located at the end of the mature thallus. Each receptacle is formed of several cavities called conceptacle
- Inside the conceptacle are oogonia (place of formation of oospheres) carried by small filaments, not fertile branches.

Gametogenesis in bladderwrack

- Within the antheridia, a parent cell (2n) undergoes meiosis and gives rise to 4 haploid cells.
-The haploid cells undergo 4 mitoses and then a differentiation to give 64 antherozoids.
-The antherozoids are released into the seawater after the opening of the conceptacle.

- Within the oogonium, a mother cell (2n) undergoes meiosis

  to give 4 haploid cells (n).

-These cells undergo mitosis giving 8 cells that differentiate into female gametes called oospheres.

-The oospheres are large and immobile and are released into the seawater after opening the conceptacle female.

-After releasing into seawater, each oosphere is surrounded by a large number of sperm (Anthozoa)

-Only one of the spermatozoa manages to cross the membrane of the oosphere

-The 2 male and female nuclei come together and merge

thus giving rise to a diploid (2n) cell called a zygote, it is fertilization

-The zygote undergoes several mitoses giving rise to an embryo that attaches itself to a rocky substrate by holdfasts

-The embryo develops and gives a young male fucus or female

N.B: the male gametes are attracted by a chemical substance emitted by the female gametes, this is the phenomenon of chemotropism.

Bladderwrack development cycle

The cycle represents only one generation which
diploid (thallus) the haploid phase is reduced to gametes, so it is a diplophasic monogenetic cycle.

Sexual reproduction in the spirogyra

The characteristics of the spirogyra

-The conjugation is done through bridges that are formed between two neighboring and parallel filaments which allow the passage of the male nucleus (n) to the female nucleus (n) to form the zygote (2n).
-The male gamete corresponds to the cell that has moved and the female gamete to the one that has remained in place.
-The egg thus formed undergoes meiosis to give 4 spores (n) of which 3 degenerate and the remaining spore passes into slowed life.
-When conditions become favorable the spore germinates to then form a new filament of spirogyra

The development cycle of the spirogyra

The biological cycle of spirogyra is very simple: all cells are haploid except the diploid zygote. It is a monogenetic haplophasic cycle.

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