Archegonium - Structure & Defination

What is Archegonium?

Archegonium is the female reproductive organ seen in non-flowering plants like bryophytes, ferns, and some gymnosperms. It is flask-shaped and has a single egg cell at the base. The neck part forms the passage by which the male gametes swim to fuse with the egg for fertilisation. The archegonium develops in the gametophyte generation of the plant and plays an important role in sexual reproduction in lower plant groups.

Structure of Archegonium

Fertilisation takes place inside the archegonium. Until the fertilised egg converts into a sporophyte, it stays inside the archegonium. The plant's spore-producing structure is known as a sporophyte. The sporophyte is released by the archegonium after its complete development. The basic structure of Archegonia is discussed below:

• The gametophyte is applied and is an important part of the plant.

• The venter is a bulb-like structure which is used for storing and developing the eggs.

• After maturity, the inner cell of the neck disintegrates, and it creates a pathway for the sperm to reach the eggs.

• The sporophyte or the spore-producing structure remains inside the archegonium until complete fertilisation occurs.

• They also remain inside until there is complete development.

• Once the complete development is done, the sporophyte is released from the archegonium.

Placement of Archegonium in Plants

For archegonia, there is no specific location within a plant. Archegonia are usually found on the thallus surface. However, they are deeply lodged inside hornworts. Archegonia are not embedded but rather are found on top of the leafy gametophyte, as in moss Physcomitrella patens.

• Sperm in bryophytes and other cryptogams travel through water films to access the archegonium.

• The sperm is delivered by a pollen tube in Pinophyta and Angiosperms, while the pollen is carried by wind or animal vectors.

• The archegonium of gymnosperms is severely reduced and incorporated into their megagametophytes.

• The megasporangium (nucellus) of the ovule's diploid megasporangium cells performs the job of protecting the gamete.

• The archegonium of gymnosperms develops during pollination within female conifer cones.

Role of Archegonium in Sexual Reproduction

The importance of Archegonium is discussed below:

Archegonium in Different Plant Groups

The archegonium is the multicellular female sex organ found in bryophytes, pteridophytes, and gymnosperms but absent in angiosperms. Its structure is flask-shaped in all groups, but the size, position, and protective adaptations vary across plant groups.

Archegonium NEET MCQs

Q1. Given below are two statements:

One is labeled as Assertion A, and the other is labeled as Reason R.

Assertion A: In gymnosperms, the pollen grains are released from the microsporangium and carried by air currents.

Reason R: Air currents carry the pollen grains to the mouth of the archegonia, where the male gametes are discharged, and the pollen tube is not formed.

In the light of the above statements, choose the correct answer from the options given below:

1. Both A and R are true and R is the correct explanation of A

2. Both A and R are true, but R is not the correct explanation of A.

3. A is true, but R is false.

4. A is false but R is true.

Correct answer: 3) A is true, but R is false.

Explanation:

Assertion A is true. Gymnosperms are plants that produce naked seeds, and their pollen grains are typically released from the microsporangium (pollen sacs) and are dispersed by air currents. This is known as anemophily, which is a common mode of pollination in gymnosperms.

Reason R is false. Air currents do carry the pollen grains, but they are not specifically directed to the mouth of the archegonia. In gymnosperms, the male gametes are discharged from the pollen grains and are transported to the female reproductive structures called ovules. The male gametes typically travel through a pollen tube to reach the archegonia, where fertilization takes place.

Therefore, while assertion A is true, reason R is incorrect as it does not provide a correct explanation for assertion A.

Hence, the correct answer is Option 3) A is true, but R is false.

Q2. Given below are the stages in the life cycle of pteridophytes. Arrange in correct sequence:

A. Prothallus stage

B. Meiosis in spore mother cells

C. Fertilisation

D. Formation of archegonia and antheridia in the gametophyte

E. Transfer of antherozoids to the archegonia in the presence of wate

1. E, D, C, B, A

2. B, A, D, C, E

3. B, D, C, A, E

4. D, E, C, A, B

Correct answer: 2) B, A, D, C, E

Explanation:

The pteridophyte life cycle shows alternation of phases between the sporophytic (diploid) and gametophytic (haploid) generations. The proper sequence is:

B. Meiosis in spore mother cells → Takes place in sporangia of the sporophyte to form haploid spores.

A. Prothallus stage → The spores germinate to produce a haploid gametophyte, called a prothallus.

D. Archesgon and antheridial formation in gametophyte → Male (antheridia) and female (archegonia) sex organs are formed in the prothallus.

C. Fertilisation → Takes place when male gametes reach and merge with egg cells in archegonia.

E. Antherozoids transferred to the archegonia when in the presence of water → Needs water for the antherozoids (sperm) to swim and release the egg.

Hence, the correct sequence is option 2) B, A, D, C, E.

Q3. Which one of the following pairs is wrongly matched?

1. Salvinia - Prothallus

2. Viroids - RNA

3. Mustard - Synergids

4. Ginkgo - Archegonia

Correct answer: 1) Salvinia - Prothallus

Explanation:

Prothallus - Spores germinate to give rise to small, multicellular, free-living, mostly photosynthetic thalloid gametophytes, called prothallus. Prothallus is a small, multicellular, free-living gametophyte that develops from the germination of spores in non-seed plants like ferns. It is usually thalloid, meaning it has a simple, undifferentiated body structure, and is primarily photosynthetic. The prothallus provides the necessary environment for the production of gametes (sperm and egg cells), which are essential for sexual reproduction. Once fertilization occurs, the zygote develops into the sporophyte, completing the plant's life cycle.

Hence, the correct answer is option 1) Salvinia - Prothallus

Also Read:

• MCQs on Characteristics and Classification of Gymnosperms

• Abiotic Agents of Pollination

• Endosperm

FAQs on Archegonium

Define archegonium.

An archegonium is the female reproductive organ in bryophytes, pteridophytes, and gymnosperms. It is a multicellular, flask-shaped structure that produces and protects the egg cell (female gamete). Archegonia are absent in angiosperms, where the embryo sac takes over this function. They play a key role in sexual reproduction of lower plants.

What is the structure of archegonium?

The structure ensures safe fertilization and development of the zygote. The archegonium is typically flask-shaped with three main parts:

• Neck – a narrow, elongated structure formed by neck cells.

• Venter – a swollen basal region containing the egg cell.

• Neck canal cells – located inside the neck, which disintegrate at maturity to form a passage for male gametes.

In which plants is archegonium found?

Archegonia are found in bryophytes (e.g., mosses, liverworts), pteridophytes (ferns and their allies), and gymnosperms (conifers like Pinus). They are not present in angiosperms (flowering plants), where the ovule contains the embryo sac instead. Thus, archegonia are characteristic of the lower land plants and some gymnosperms, representing an important evolutionary stage in reproduction.

What is the role of archegonium in reproduction?

The archegonium produces and houses the egg cell (female gamete) and provides a protective chamber for fertilization. After maturity, the neck canal cells disintegrate, releasing chemicals that guide the male gametes (sperm) towards the egg. Fertilization occurs inside the venter, and the zygote develops into an embryo within the archegonium. Thus, archegonium plays a vital role in ensuring successful fertilization and early development of the sporophyte.