Chloroplast Origin and Evolution

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Questions and Answers

What is the main difference between the cyanelles of Cyanophora paradoxa and regular plastids found in higher plants?

Production of photosynthetic enzyme (correct)

Type of starch stored

Location of the nucleus

Presence of flagellated cells

Where are the cyanelles of Cyanophora paradoxa thought to be similar in evolution to?

Chloroplasts (correct)

Glaucocystis

Cyanobacteria

Red algae

What is the unique characteristic of the ecological niche that the first red alga likely evolved into?

Low oxygen levels

High temperature

Low pH (correct)

High salinity

What is the main difference between the Rhodophyceae and other algal classes?

Absence of flagellated cells Signup and view all the answers

What is the characteristic of the thylakoids in the chloroplasts of Rhodophyceae?

They occur singly Signup and view all the answers

Who first proposed the endosymbiotic origin of chloroplasts?

Konstantin Mereschkowsky Signup and view all the answers

What is the main characteristic of the larger species of fleshy red algae?

They occur in cool-temperate areas Signup and view all the answers

What did Mereschkowsky liken plastids to in his theory?

Little green slaves Signup and view all the answers

What has reinforced Mereschkowsky's theory of endosymbiotic origin of plastids?

Cytological and biochemical studies Signup and view all the answers

What is the approximate number of species of Rhodophyceae?

4000 Signup and view all the answers

What has shown the similarity between cyanobacteria and plastids?

Nucleotide sequencing Signup and view all the answers

What is the characteristic of the Rhodophyceae that allows them to live at greater depths in the ocean?

Unique adaptation to low light conditions Signup and view all the answers

What is thought to represent intermediates in the evolution of the chloroplast?

Glaucophyta Signup and view all the answers

What was the likely outcome of the mutation that allowed the cyanobacterium to survive in the host flagellate?

The cyanobacterium secreted metabolites to the host flagellate Signup and view all the answers

What is unique about the symbiotic association in Glaucophyta?

The cyanobacterium is in the cytoplasm instead of a chloroplast Signup and view all the answers

What is the likely reason for the cyanobacterium's increased secretion of metabolites to the host flagellate?

The cyanobacterium lacked feedback inhibition Signup and view all the answers

Where does the fusion of one male nucleus and the carpogonial nucleus occur?

In the basal portion of the carpogonium Signup and view all the answers

What is the result of fertilization in the carpogonial branch?

Production of carpospores Signup and view all the answers

What is the function of the trichogyne in the reproductive process of red algae?

To facilitate contact with a spermatium Signup and view all the answers

What is the characteristic of the cell wall in the carpogonium after fertilization?

It becomes thicker Signup and view all the answers

What is the arrangement of tetraspores in a tetrasporangium?

All of the above Signup and view all the answers

What is the function of dictyosomes in the formation of tetraspores?

To lay down a wall inside the tetrasporangium Signup and view all the answers

What is the characteristic of spores in red algae?

They are motile by gliding Signup and view all the answers

How many classes are there in the Rhodophyta?

One Signup and view all the answers

What is the main difference between carrageenan and agar?

Carrageenan requires higher concentrations to form gels than agar Signup and view all the answers

What is the role of potassium ions in the formation of carrageenan gels?

They are required for the formation of gels Signup and view all the answers

What is the main use of carrageenans in the dairy industry?

As a stabilizer in milk and dairy products Signup and view all the answers

What is the advantage of carrageenans in instant puddings, sauces, and creams?

They do not require refrigeration to set Signup and view all the answers

What is the function of spermatia in the sexual reproduction of red algae?

They are the male gametes that are carried passively by water currents Signup and view all the answers

What is the difference between carpospores and tetraspores?

Tetraspores are generally larger than carpospores Signup and view all the answers

What is the function of gonimoblast filaments in the sexual reproduction of red algae?

They form the carposporangia and produce the diploid carpospores Signup and view all the answers

What is a property of carrageenans that makes them useful in pharmaceutical applications?

They inhibit human immunodeficiency virus (HIV) replication Signup and view all the answers

What is the characteristic of the thalli of Red Algae in intertidal or shallow subtidal environments?

They are delicate and thread-like Signup and view all the answers

Which pigments are responsible for the red coloration of Red Algae?

Phycoerythrin and phycocyanin Signup and view all the answers

What is the characteristic of the morphology of Red Algae in Order Batrachospermales?

Filamentous or branched Signup and view all the answers

Where are Red Algae in Order Nemaliales typically found?

In marine environments, particularly in intertidal and subtidal regions Signup and view all the answers

What is the characteristic of the thalli of Red Algae in Order Corallinales?

Calcified with calcium carbonate deposits Signup and view all the answers

What is the characteristic of the reproduction of Red Algae?

Either sexually or asexually by spores or filament fragmentation Signup and view all the answers

What is the characteristic of the color of Red Algae in Order Corallinales?

Red, pink, purple, yellow, or blue Signup and view all the answers

Where are Red Algae in Order Corallinales typically attached to?

Hard substrates such as rocks, shells, or coral reefs Signup and view all the answers

Study Notes

Endosymbiotic Origin of Chloroplasts

Konstantin Mereschkowsky proposed the endosymbiotic origin of chloroplasts in 1905.
He likened plastids to "little green slaves" working for their host cells to produce food from sunshine.
Nucleotide sequencing has shown the similarity between cyanobacteria and plastids, supporting the endosymbiotic origin theory.
All plastids evolved from a single endosymbiotic event.

Evolution of Chloroplasts

A cyanobacterium was taken up by a phagocytic organism into a food vesicle, leading to an endosymbiotic relationship.
The cyanobacterium evolved into a chloroplast surrounded by two membranes of the chloroplast envelope.

Glaucophyta

Glaucophyta includes algae that have endosymbiotic cyanobacteria in their cytoplasm instead of chloroplasts.
They are thought to represent intermediates in the evolution of chloroplasts.
The cyanelles of Cyanophora paradoxa are similar to chloroplasts in evolution, but are primitive in regard to where photosynthetic enzymes are produced.

Rhodophyta

Rhodophyta is a division of red algae that comprises the class Rhodophyceae.
Rhodophyceae are probably one of the oldest groups of eukaryotic algae.
They are directly descended from a cyanome in the Glaucophyta.
The first red alga likely evolved into an ecological niche unoccupied by cyanobacteria, in waters with a pH less than 5.

Characteristics of Rhodophyceae

Lack flagellated cells
Have chlorophyll a, phycobiliproteins, Floridian starch as a storage product, and thylakoids occurring singly in the chloroplast
Most species are found in marine environments, particularly in intertidal zones
Reproduce sexually and asexually by spores or filament fragmentation

Carrageenan

Carrageenan is a phycocolloid similar to agar but with a higher ash content and requiring higher concentrations to form gels.
It is obtained from wild populations of Irish moss and is used extensively for many purposes, including stabilizing emulsions and stiffening milk and dairy products.

Red Algae Reproduction

In sexual reproduction, gamete cells have no flagella and spermatia are carried passively by water currents to the female organ, the carpogonium.
Fertilization stimulates the production of polyamine spermine, which steers the carpogonial branch toward the production of carpospores.
Tetrasporangia form four tetra spores, either in a row, crosswise, or in a tetrad.

Asexual Spores

Monosporangia and parasporangia produce asexual spores that re-form the parent thallus.
Spores, whether monospores, tetraspores, or carpospores, of almost all red algae are capable of motility by gliding.

Red Algae Classification

Rhodophyta has a single class, the Rhodophyceae.
The Rhodophyceae was previously divided into two subclasses, the Bangiophycidae and the Florideophycidae.
There are several orders of red algae, including Batrachospermales, Nemaliales, and Corallinales, each with distinct characteristics.

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Description

Learn about the endosymbiotic origin of chloroplasts, first proposed by Konstantin Mereschkowsky. Discover how plastids work with host cells to produce food from sunlight.