IB Biology Topic A2.2.9 Atypical Cell Structure in Eukaryotes Revision Notes (SL/HL)

IB Biology Topic A2.2.9 Atypical Cell Structure in Eukaryotes Revision Notes (SL/HL) | RevisionDojo

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Some Eukaryotic Cells Break the One-Nucleus-Per-Cell Rule

Most cells follow cell theory, with a single nucleus controlling one cell.
Some specialised cells break this pattern in ways that suit their function.
There are four key examples covered in this article.

Note

Aseptate fungal hyphae form one continuous cytoplasm with many nuclei.
Skeletal muscle fibres are single fibres holding many nuclei.
Mature red blood cells have no nucleus at all.
Phloem sieve tube elements lose their nucleus and rely on companion cells.

Aseptate Fungal Hyphae: One Continuous Cytoplasm Without Cross-Walls (Septa)

Fungi grow as thread-like structures called hyphae.
Most hyphae are divided into compartments by internal cross-walls called septa.
In aseptate hyphae these internal septa are missing, though the hypha still has an outer cell wall.
The result is a coenocyte, a single continuous cytoplasm containing many nuclei.

Definition

Coenocyte

A coenocyte is a multinucleated cell-like structure formed by repeated nuclear divisions without cell division.

Why Missing Septa Helps

Without internal cross-walls, nuclei and cytoplasm can flow freely along the hypha.
1. This lets the fungus grow faster and move nutrients where they are needed.
2. It makes the fungus more efficient at spreading across large areas and absorbing nutrients.

Analogy

Aseptate hyphae work like an open-plan office with no internal walls.
Nutrients and nuclei move freely wherever they are needed.

Skeletal Muscle Fibres Are Multinucleate Syncytia

Skeletal muscle fibres are long cells packed with multiple nuclei.

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Some Eukaryotic Cells Break the One-Nucleus-Per-Cell Rule

Most cells follow cell theory, with a single nucleus controlling one cell.
Some specialised cells break this pattern in ways that suit their function.
There are four key examples covered in this article.

Note

Aseptate fungal hyphae form one continuous cytoplasm with many nuclei.
Skeletal muscle fibres are single fibres holding many nuclei.
Mature red blood cells have no nucleus at all.
Phloem sieve tube elements lose their nucleus and rely on companion cells.

Aseptate Fungal Hyphae: One Continuous Cytoplasm Without Cross-Walls (Septa)

Fungi grow as thread-like structures called hyphae.
Most hyphae are divided into compartments by internal cross-walls called septa.
In aseptate hyphae these internal septa are missing, though the hypha still has an outer cell wall.
The result is a coenocyte, a single continuous cytoplasm containing many nuclei.

Definition

Coenocyte

A coenocyte is a multinucleated cell-like structure formed by repeated nuclear divisions without cell division.

Why Missing Septa Helps

Without internal cross-walls, nuclei and cytoplasm can flow freely along the hypha.
1. This lets the fungus grow faster and move nutrients where they are needed.
2. It makes the fungus more efficient at spreading across large areas and absorbing nutrients.

Analogy

Aseptate hyphae work like an open-plan office with no internal walls.
Nutrients and nuclei move freely wherever they are needed.

Skeletal Muscle Fibres Are Multinucleate Syncytia

Skeletal muscle fibres are long cells packed with multiple nuclei.

Definition

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Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

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Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic A2.2.9: Atypical Cell Structure in Eukaryotes Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Some Eukaryotic Cells Break the One-Nucleus-Per-Cell Rule

Aseptate Fungal Hyphae: One Continuous Cytoplasm Without Cross-Walls (Septa)

Why Missing Septa Helps

Skeletal Muscle Fibres Are Multinucleate Syncytia

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Some Eukaryotic Cells Break the One-Nucleus-Per-Cell Rule

Aseptate Fungal Hyphae: One Continuous Cytoplasm Without Cross-Walls (Septa)

Why Missing Septa Helps

Skeletal Muscle Fibres Are Multinucleate Syncytia

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account