3 - EUKARYOTIC MICROBES: FUNGI & PROTISTS

What defines a eukaryotic cell?

A membrane-delimited nucleus containing the genetic material.

Why is the nucleus important in eukaryotic cells?

It protects DNA and separates transcription from translation.

What special structures do eukaryotic cells have that prokaryotes lack?

Membrane-bound organelles.

Give examples of membrane-bound organelles in eukaryotes.

Mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes.

What is the intracytoplasmic membrane complex?

An internal membrane system used for transport and compartmentalisation.

Why is compartmentalisation important in eukaryotic cells?

It allows different processes to occur efficiently in separate areas.

How do eukaryotic cells compare in size to prokaryotic cells?

They are typically much larger.

What is the function of the plasma membrane?

Acts as a mechanical boundary, selectively permeable barrier, and is involved in transport, cell adhesion, secretion, and signal transduction.

What is the cytoplasm made of and what does it do?

Made of cytosol and organelles; site of many metabolic processes.

What structures make up the cytoskeleton?

Actin filaments, intermediate filaments, and microtubules.

What is the function of the cytoskeleton?

Provides cell shape, structure, and movement.

What is the role of the endoplasmic reticulum?

Transport of materials and lipid synthesis.

What is the function of ribosomes?

Protein synthesis.

What does the Golgi apparatus do?

Packages and secretes materials and forms lysosomes.

What is the function of lysosomes?

Intracellular digestion.

What is the main function of mitochondria?

Energy production (ATP) via the TCA cycle, electron transport chain, and oxidative phosphorylation.

What do chloroplasts do?

Carry out photosynthesis, converting CO₂ and water into carbohydrates using light energy.

What is the function of the nucleus?

Stores genetic information (DNA)

What happens in the nucleolus?

rRNA synthesis and ribosome construction.

What is the role of the cell wall and pellicle?

Strengthens and gives shape to the cell.

What is the function of cilia and flagella?.

Cell movement

What are the functions of vacuoles?

Temporary storage, transport, digestion, and water balance (contractile vacuole).

What theory explains the origin of mitochondria and chloroplasts?

The endosymbiotic theory.

According to the endosymbiotic theory, how did mitochondria and chloroplasts originate?

From bacterial cells ingested by ancestral eukaryotic cells.

Which organelles are thought to have bacterial origins?

Mitochondria, hydrogenosomes, and chloroplasts.

Which bacteria are mitochondria most similar to?

Purple non-sulphur bacteria.

Which bacteria are chloroplasts most similar to?

Cyanobacteria.

How do endosymbiotic organelles compare in size to bacteria?

They are similar in size.

What is special about the inner membranes of mitochondria and chloroplasts?

They contain prokaryotic-like proteins and transport systems.

How do mitochondria and chloroplasts replicate?

By binary fission.

What type of DNA do these organelles contain?

Circular DNA that replicates independently of the nucleus

What type of ribosomes do mitochondria and chloroplasts contain?

70S ribosomes, similar to prokaryotes.

How do these ribosomes differ from eukaryotic ribosomes?

Eukaryotic ribosomes are 80S, not 70S.

What is the main function of mitochondria?

ATP production through aerobic respiration.

Which metabolic pathway occurs in the mitochondria?

The tricarboxylic acid (TCA) cycle.

Where does oxidative phosphorylation occur?

On the inner mitochondrial membrane.

What role does the electron transport chain play in mitochondria?

It transfers electrons to generate a proton gradient used to make ATP.

How is ATP generated in mitochondria?

By oxidative phosphorylation using energy from electron transport.

Why is oxygen important for mitochondrial function?

Oxygen acts as the final electron acceptor in aerobic respiration

What are hydrogenosomes?

Energy-conserving organelles found in anaerobic protists.

In what type of environment do hydrogenosomes function?

Anaerobic (oxygen-free) conditions.

How do hydrogenosomes produce ATP?

Through fermentation, not oxidative phosphorylation.

Do hydrogenosomes use oxygen to make ATP?

No, they function without oxygen.

What is the evolutionary origin of hydrogenosomes?

They are derived from a common mitochondrial ancestor.

How many membranes do hydrogenosomes have?

A double membrane.

What mitochondrial feature is absent in hydrogenosomes?

Cristae.

Do hydrogenosomes contain DNA?

Often no DNA (unlike mitochondria).

What are chloroplasts?

A type of plastid that contains pigments and is essential for photosynthesis.

In which organisms are chloroplasts found?.

Plants and algae

: How many membranes surround a chloroplast?

Two membranes (double membrane).

What are thylakoids?

Flattened membrane sacs inside the chloroplast.

What are stacks of thylakoids called?

Grana.

Where do the light reactions of photosynthesis occur?

In the thylakoid membranes (within the grana).

How did the chloroplast ancestor first enter a eukaryotic cell?

A plastid-less phagotrophic eukaryote engulfed a cyanobacterium.

Why was the cyanobacterium not digested by the host cell?

The relationship was beneficial to the host, so it was retained.

What was the outcome of this beneficial relationship?

The endosymbiont became established as an organelle, increasing in frequency over time.

What is secondary endosymbiosis?

When a eukaryote containing a plastid is engulfed by another eukaryotic

What type of organisms are engulfed during secondary endosymbiosis?

Red or green algae.

How many membranes surround plastids formed by secondary endosymbiosis?

Three membranes.

What is tertiary endosymbiosis?

When a eukaryote engulfs another eukaryote that already contains a plastid.

How many membranes surround plastids formed by tertiary endosymbiosis?

Four membranes.

How do eukaryotic flagella move?

They move with a wave-like, undulating motion.

What is the typical length of eukaryotic flagella?

100–200 µm.

What is the structure of eukaryotic flagella?

They are membrane-bound cylinders about 2 µm in diameter.

What is the axoneme in flagella?

A core of microtubules arranged in a 9+2 pattern.

What is the function of the basal body in flagella?

It directs the assembly of the flagellum from the base.

How do cilia move?

They beat in two coordinated phases.

What is the typical length of cilia?

5–20 µm.

What is the axoneme in cilia?

The core of microtubules arranged in a 9+2 pattern.

What role does the basal body play in cilia?

It directs the assembly of the cilium from the base.

Where are fungi mainly found?

Primarily terrestrial, with some aquatic species.

How widespread are fungi?

They have a global distribution, from polar to tropical regions.

Do fungi carry out photosynthesis?

No, fungi are not photosynthetic.

Why can’t fungi photosynthesise?

They lack chloroplasts and plastids.

How many fungal species have been described?

About 90,000 species.

What is the estimated total number of fungal species?

More than 1.5 million species.

What type of nutrition do fungi have?

Chemoorganoheterotrophic – they obtain energy from organic chemicals and cannot photosynthesize.

What is osmotrophy in fungi?

Fungi secrete enzymes to digest food outside their cells and then absorb the nutrients through their cell wall.

What are saprophytes?

Fungi that feed on dead or decaying matter, acting as biodegraders in nutrient cycles.

What are pathogenic fungi?

Fungi that survive inside a host and can cause disease.

What are mutualistic fungi?

Fungi that form beneficial relationships, e.g.,

• Mycorrhizae with plant roots

• Lichens with algae or cyanobacteria

How do fungi generally produce energy

Most are aerobic and use oxygen for respiration.

What are facultative anaerobes?

Fungi that can switch between aerobic and anaerobic respiration depending on oxygen availability.

What are obligate anaerobes?

Fungi that die in the presence of oxygen.

Are there exceptions to fungi being aerobic?

Yes, some yeasts can be facultative or obligate anaerobes.

Why are fungi important industrially?

Yeast fermentation is vital in many industrial processes, like bread, alcohol, and biotechnology.

What is the general term for the body of a fungus?

Thallus (plural: thalli)

What are thalli made of?

Long, branched filaments called hyphae.

What is a network of hyphae called

Mycelium

How does fungal size vary?

From microscopic unicellular yeasts to massive multicellular fungi covering miles

Are yeasts unicellular or multicellular?

Unicellular fungi, often forming colonies.

How do yeasts appear in Gram staining?

They retain purple dye but are not Gram-positive since they have a fungal cell wall, not a bacterial one.

What is the typical shape of yeast cells?

Oval or egg-shaped, and larger than bacteria.

How many nuclei do yeast cells possess?

A single nucleus.

Name the main reproductive mechanisms of yeast.

Binary fission, budding (asexual), and spore formation (sexual).

What is budding in yeast?

A small cell forms on the side of the mother cell, grows, and then separates.

Do yeast cells have flagella or cilia?

No, they lack flagella and cilia.

Do yeast cells have organelles?

Yes, they contain essential eukaryotic organelles.

What are filamentous fungi commonly called

Molds

Are molds unicellular or multicellular?

Multicellular