Biology Unit 4/5- Eukaryotes (Protists+ Fungi)

What are the general charactericts of eukaryotic cells?

They have a nucleus, membrane-bound organelles, and generally multiple linear chromosomes.

What is the endosymbiotic theory?

The theory that mitochondria and plastids originated from bacteria that were engulfed by ancestral eukaryotic cells.

What happened during endosymbiosis?

An ancestral eukaryotic cell engulfed a bacterium, but instead of digesting it, the bacterium lived inside the cell and eventually became an organelle.

What evidence supports the endosymbiotic theory?

Mitochondria and plastids have their own DNA, ribosomes, double membranes, and reproduce by division.

Mitochondria originated from aerobic bacterium and plastids + chloroplasts from photosynthetic bacteria

How has endosymbiosis shaped the evolution of eukaryotic cells?

In photosynthetic endosymbionts, the host was able to “steal” a proportion of the sugars being made by algae through photosynthesis until overtime the algae was reduced to an organelle

What is the relationship between membrane infolding and eukaryotic cells?

Infolding of the ancestral cell membrane may have produced internal compartments such as the nucleus and endomembrane system.

What are protists?

A diverse collection of eukaryotic organisms that are not classified as animals, plants, or fungi which include organisms from multiple evolutionary lineages (uni, multicellular or colonial)

What are the nutritoonal modes of portists?

Photoautotrophs: contain chloroplasts, get energy from light

Heterotrophs: absorb organic molecules or ingest larger food particles

Mixotrophs: combine photosynthesis and heterotrophic nutrition

How do protists reproduce asexually and sexually?

Aseually: through cell division or fragmentation

Sexually: production and fusion of gametes during fertilization

What are algae and their importance?

A diverse group of primarily photosynthetic organisms traditionally classified as protists.

Green algae are closely related to land plants (unicellular, colonial, plant-like bodies), found in freshwater, marine

Red algae are separate evolutionary lineages and possess different photosynthetic pigments mostly found in marine warm waters

What is the clade excavata?

Features: Often unicellular and flagellated, typically featuring a pronounced feeding groove on the cell surface. Many have modified or reduced mitochondria.

Key Groups: Diplomonads, parabasalids, and euglenozoans (including photosynthetic euglenids and parasites like Trypanosoma

What features do diplomonads have?

Found in anaerobic environments and thus get energy from anaerobic biochemical pathways

Have reduced mitochondria (mitosomes)—lack electron transport chains and cannot use oxygen to help extract energy from carbs and organic molecules

Have two equal sized nuclei and multiple flagella

What features do parabasalids have?

Reduced mitochondria called hydrogenosomes—generate some energy anaerobically, release hydrogen gas as a byproduct

What features do euglenozoans have?

Group includes predatory heterotrophs, photosynthetic autotrophs, mixotrophs and parasites

Main morphological feature: presence of rod with either a spiral or a crystalline structure inside their flagella

What are the two groups of euglenozoans?

Kinetoplastids: have single large mitochondrion containing mass of DNA composed by kinetoplasts. Includes a species that feed on prokaryotes in freshwater, marine, and moist ecosystems

Euglenids: has a pocket at one end of cell from which two flagella emerge. Some are mixotrophs, many others engulf prey by phagocytosis

What is the SAR supergroup?

A proposed monophyletic supergroup of protists identified through whole-genome DNA sequence analysis.

Includes Stramenopiles, Alveolates, and Rhizarians

What are the key SAR groups?

Stramenopiles: Includes diatoms, brown algae (kelp), and water molds (oomycetes) that often possess "hairy" flagella.

Alveolates: Includes dinoflagellates, ciliates (Paramecium), and apicomplexans (like Plasmodium, which causes malaria), defined by membrane sacs (alveoli) beneath the plasma membrane.

Rhizarians: Includes foraminiferans and radiolarians, which are mostly amoeboid with thread-like or needle-like pseudopodi

What is the archaeplastida supergroup?

Characterized by plastids (like chloroplasts) derived from an ancient primary endosymbiosis event with a cyanobacterium (monophyletic)

Key groups: Red algae, green algae (chlorophytes and charophytes), and land plants (embryophytes)

What is the amoebozoans supergroup?

Features: Includes amoebas that move and feed using large, lobe-shaped pseudopodia (lobose pseudopodia) rather than thread-like ones. Most lack rigid cell walls. Heterotrophs, engulf particles

key groups: Tubuline amoebas, entamoebas, and cellular/plasmodial slime molds

What are the two types of slime moulds, and how do they differ?

Plasmodial slime moulds: form a large plasmodium—a single mass of cytoplasm containing many nuclei but no cell divisions between nuclei; feed by phagocytosis.

Cellular slime moulds: normally exist as individual cells, but when food is scarce, cells aggregate into a slug-like unit while remaining separate cells.

Both can form fruiting bodies for reproduction/spore dispersal.

What is the opisthokonta supergroup?

Features: Named for the single posterior flagellum found in flagellated cells (such as animal sperm cells or chytrid spores).

Key groups: Animals (Metazoa), fungi, and close protistan relatives like choanoflagellates and nucleariids

What is the fungal cell wall made of?

Chitin

What are hyphae?

Long, filamentous structures that make up bodies of most multicellular fungi

Septate: hyphae divided into compartments by septa

Coenocytic: hyphae that lack septa separating their cytoplasm into induvial cells

What is mycelium?

A network of hyphae that forms the main body of a fungus

How do fungi reproduce?

Asexual: It allows a single fungus to clone itself rapidly when environmental conditions are good.

Sexual: It mixes genetic material from two parents to create diversity, helping them survive harsh conditions.

What are the 4 main ways fungi reproduce asexually?

• Spore formation (making identical clones)

• Budding (a small cell pinches off a yeast parent)

• Fragmentation (broken pieces of hyphae grow into new fungi)

• Fission (one cell splits into two)

What is the heterokaryotic stage?

A stage in which genetically different nuclei coexist within the same cytoplasm

What are the 3 sequential steps of sexual reproduction in fungi?

Plasmogamy (cells cytoplasm fuse, but nuclei stay separate)

Karyogamy (the two nuclei fuse into one)

Meiosis (the cell divides to create diverse spores)

What type of nutrition do fungi use?

Chemoheterotrophic, absorptive nutrition

They secrete digestive enzymes into their surroundings and absorb the resulting small molecules.

What is external digestion?

Digestion that occurs outside the organism’s cells through secreted enzymes

What is a saprobe and parasites?

Saprobe: An organism that obtains nutrients from dead organic matter

Parasites: A fungus that obtains nutrients from a living host (plants, animals, other fungi)

What is a chytrid and why are they important in fungal evolution?

An early-diverging fungal lineage containing some flagellated forms

Some retain flagellated cells, whereas most other fungi lost the flagellum during evolution which helps understand evolution of fungi from aquatic to land forms

How are protists and fungi decomposers?

Protists: Break down organic matter and contribute to nutrient cycling

Fungi: break down organic matter using extracellular enzymes and recycle nutrients

How do protists serve as food for other organisms?

Protists are important food sources for organisms in aquatic and terrestrial food webs.

What ecological role do photosynthetic protists play?

They are primary producers that convert light energy into chemical energy and form the base of many aquatic food webs.

How can protists participate in mutualistic symbiosis?

Some protists live inside or alongside other organisms and exchange nutrients or other benefits with their hosts.

Mutualistic symbiosis of fungi

Lichen: association between a fungus and a photosynthetic partner, usually algae or cyanobacterium (provides structure, portection, water retention)

Mycorrhizae: association between fungi and plant roots (increase plants access to water and minerals)

Endophytes: live within plant tissues causing disease (improve resistance to herbivores, pathogens, drought etc)

How can fungi form mutualistic relationships with animals?

Some fungi live in association with animals and provide nutrients or aid digestion, while receiving nutrients or habitat in return.

Ex. fungi in gut of herbivores help digestion of plants

How can fungal diseases affect plants and animals?

Plants: They can damage tissues, interfere with nutrient transport, reduce growth, and potentially kill the plant

Animals: infect tissues and cause diseases ranging from superficial infections to serious systemic infections