Prokaryotes Protists And Fungi

Prokaryotes Everything else

(Bacteria)

Prokaryotic cells have a variety of shapes 

The three most common of which are spheres (cocci), rods (bacilli), and spirals

1 µm (a) Spherical (cocci)

2 µm (b) Rod-shaped (bacilli)

(c) Spiral

5 µm

Cell-Surface Structures 

One of the most important features of nearly all prokaryotic cells 

24.2

Is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment

Using a technique called the Gram stain 

Scientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gramnegative Lipopolysaccharide

Cell wall

Peptidoglycan layer

Cell wall

Outer membrane

Peptidoglycan layer Plasma membrane

Plasma membrane

Protein

Protein Grampositive bacteria

Gramnegative bacteria 20 µm

Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye, which masks the added red dye.

24.2/3

Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between the plasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added.

The cell wall of many prokaryotes 

Is covered by a capsule, a sticky layer of polysaccharide or protein 200 nm

Capsule

24.1

Some prokaryotes have fimbriae and sex pili 



Fimbriae allow them to stick to their substrate or other individuals in a colony Sex pili allow two bacteria to join and exchange DNA during conjugation

Fimbriae

24.1

200 nm

Motility



Most motile bacteria propel themselves by flagella 

Which are structurally and functionally different from eukaryotic flagella Flagellum Filament 50 nm Cell wall

Hook Basal apparatus

24.1

Plasma membrane

The typical prokaryotic genome 

Is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region Chromosome

24.1

1 µm

Many prokaryotes form endospores 

Which can remain viable in harsh conditions for centuries Endospore

0.3 µm

24.1

Major nutritional modes in prokaryotes

24.4

Prokaryotic metabolism also varies with respect to oxygen 

Three types of oxygen metabolism 

Obligate aerobes 



Facultative anaerobes 



Can survive with or without oxygen

Obligate anaerobes 

24.5

Require oxygen

Are poisoned by oxygen

Protists

Single-celled Eukaryotes (mostly)

Overview: A World in a Drop of Water • Even a low-power microscope – Can reveal an astonishing menagerie of organisms in a drop of pond water

Figure 28.1

50 µm

Protists, the most nutritionally diverse of all eukaryotes, include – Photoautotrophs, which contain chloroplasts – Heterotrophs, which absorb organic molecules or ingest larger food particles – Mixotrophs, which combine photosynthesis and heterotrophic nutrition

24.6

Chlorohyta phacus

Protist habitats are also diverse in habitat • And including freshwater and marine species

There is now considerable evidence • That much of protist diversity has its origins in endosymbiosis

Diversity of plastids produced by secondary endosymbiosis

Objectives 24.7 and 24.8 will be covered in a class project

Plasmodial Slime Molds • Many species of plasmodial slime molds – Are brightly pigmented, usually yellow or orange 4 cm

24.9

At one point in the life cycle – They form a mass called a plasmodium 1 The feeding stage is a multinucleate plasmodium that lives on organic refuse.

3 The plasmodium erects stalked fruiting bodies (sporangia) when conditions become harsh.

2 The plasmodium takes a weblike form.

Feeding plasmodium Zygote (2n)

Mature plasmodium (preparing to fruit) Young sporangium

SYNGAMY

1 mm Amoeboid cells (n)

Flagellated cells (n) 7 The cells unite in pairs (flagellated with flagellated and amoeboid with amoeboid), forming diploid zygotes.

6 These cells are either amoeboid or flagellated; the two forms readily convert from one to the other.

Germinating spore

Mature sporangium Spores (n)

Key

MEIOSIS

Haploid (n) Diploid (2n) Stalk

5 The resistant spores disperse through the air to new locations and germinate, becoming active haploid cells when conditions are favorable.

4 Within the bulbous tips of the sporangia, meiosis produces haploid spores.

24.9

Cellular Slime Molds • Cellular slime molds form multicellular aggregates – In which the cells remain separated by their membranes

24.9

• The life cycle of Dictyostelium, a cellular slime mold 1 In the feeding 9 In a favorable environment, amoebas stage of the life emerge from the spore cycle, solitary haploid coats and begin feeding. amoebas engulf bacteria. 8 Spores are released.

2 During sexual reproduction, two haploid amoebas fuse and form a zygote.

SYNGAMY

7 Other cells crawl up the stalk and develop into spores.

Emerging Spores amoeba (n) Solitary amoebas (feeding stage)

600 µm

Zygote (2n)

SEXUAL REPRODUCTION MEIOSIS Amoebas

Fruiting bodies

ASEXUAL REPRODUCTION

4 The resistant wall ruptures, releasing new haploid amoebas.

Aggregated amoebas

5 When food is depleted, hundreds of amoebas congregate in response to a chemical attractant and form a sluglike aggregate (photo below left). Aggregate formation is the beginning of asexual reproduction.

Migrating aggregate

6 The aggregate migrates for a while and then stops. Some of the cells dry up after forming a stalk that supports an asexual fruiting body.

24.9

3 The zygote becomes a giant cell (not shown) by consuming haploid amoebas. After developing a resistant wall, the giant cell undergoes meiosis followed by several mitotic divisions.

Key 200 µm

Haploid (n) Diploid (2n)

Fun gi

Also pronounced “fun guy”

Mig hty Mu sh r ooms Fungi  Are diverse and widespread  Are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

T he O rig in o f Fungi 

Molecular evidence 



Supports the hypothesis that fungi and animals diverged from a common ancestor

Fungi probably evolved 

Before the colonization of land by multicellular organisms

Fossi l Evi dence  The oldest undisputed fossils of fungi  Are only about 460 million years old

Nu trit ion a nd Fungal Lif est yle s  Fungi are heterotrophs (consumers)  But do not ingest their food

 Fungi secrete  exoenzymes that break down complex molecules and then they absorb the remaining smaller compounds as nutrients.

24.10/11

 Fungi exhibit diverse lifestyles  Decomposers  Parasites  Mutualistic symbionts

24.10/11

Ba sid io mycetes  Decomposers (b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat

 Breakdown organic material using enzymes to obtain nutrients

(a) Fly agaric (Amanita muscaria), a common species in conifer forests in the northern hemisphere

(d) Puffballs emitting spores (c) Shelf fungi, important decomposers of wood

24.10-11 24.14

Pathogens  About 30% of known fungal species  Are parasites, mostly on or in plants

24.10-11 24.14

(a) Corn smut on corn

(b) Tar spot fungus on maple leaves

(c) Ergots on rye

Lic hens

(m utu alis tic )

 Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae

(a) A fruticose (shrub-like) lichen

24.10-11 24.14

(b) A foliose (leaf-like) lichen

(c) Crustose (crust-like) lichens

Bo dy St r uctu r e  The morphology of multicellular fungi  Enhances their ability to absorb nutrients from their surroundings Reproductive structure.

The mushroom produces tiny cells called spores. Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae.

Spore-producing structures

20 µm

24.12 Mycelium

Fungi c onsist o f  Mycelia, networks of branched hyphae adapted for absorption  Most fungi have cell walls made of chitin (polysaccharide - also found in the exoskeleton of many insects and arthropods)

24.12

Network of Hyphae

Fungi p ropa ga te themsel ves 

By producing vast numbers of spores, either sexually or asexually LIFE CYCLE

24.13

Many f ungi t ha t can r epr oduce ase xuall y  Grow as mold, sometimes on fruit, bread, and other foods Orange

2.5 µm

24.13/14

Ot her ase xual f ungi ar e yeasts  That inhabit moist environments  Which reproduce by simple cell division 10 µm

Parent cell

Bud

24.14

Fungus- Animal Symb iosis  Some fungi share their digestive services with animals  Helping break down plant material in the guts of cows and other grazing mammals

24.14

Pr actic al Use s o f Fungi

 Humans eat many fungi

 And use others to make cheeses, alcoholic beverages, and bread

24.15

Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open.

The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards.

Antibiotics pr oduced by fungi  Treat bacterial infections Staphylococcus Penicillium

Zone of inhibited growth

24.15

Fair y Ri ngs  Folklore holds that fairy rings are doors into the fairies' world, transporting people to other places or making people appear in the same place in a different time.

Extra Credit – write 1/2 page describing how fairy rings form