Life cycles Chlorophyta Flashcards
What is the status of knowledge regarding life cycles in Chorophyta?
Knowledge of life cycles is still limited for many green algae.
What type of life cycle do most green algal groups have?
Most green algal groups have a haplontic life cycle.
What is unique about the nucleus of the zygote in haplontic life cycles?
In haplontic life cycles, the only nucleus of the zygote is diploid.
Do some Chlorophyta exhibit a different life cycle? If so, what is it called?
Yes, some Chlorophyta also show a haplodiplontic life cycle:
- Isomorphic (in primitive algae)
- Heteromorphic
What 3 basic types of life cycle do Chlorophyta show?
- Haplontic life cycle
- Haplodiplontic life cycle
- Diplontic life cycle
Haplontic life cycle in chlorophyta
- The primitive condition
- The vegetative cells are haploid, the zygote is the only diploid stage
- Zygotic meiosis
- Often the zygote is characterized by a resting stage
Haplodiplontic life cycle
- Presents alternation of generation
- A haploid vegetative phase alternates with a diploid phase –> sporic meiosis.
- These phases can be isomorphic or heteromorphic.
Diplontic life cycle
- rare in algae
- The vegetative phase is diploid,
- Gametes are the only haploid cells
- Gametic meiosis
What characterizes a haplontic life cycle?
In a haplontic life cycle, vegetative cells are haploid and reproduce asexually to form two or a multiple of two small daughter cells.
How do vegetative cells respond to stress conditions? (Haplontic life cycle)
Under stress conditions, such as limited nitrogen concentrations, vegetative cells divide to form gametes of opposite sexes
How do gametes differ from vegetative cells at the TEM level? (haplontic life cycle)
- Gametes show the presence of mating structures near the apex of the cells, which are oval areas in the plasmalemma,
- Gametes bear many agglutinin molecules on their flagella.
What distinguishes the mating structures of gametes of different sexes?
- In the mating structure of gametes of one sex (+), there are two darkly stained layers beneath the plasmalemma,
- In the other sex (-), there is only one layer.
Life cycle in Chlamydomonas reinhardtii
- The flagella of each gamete are covered with an agglutinin
- The gametes (-) have an agglutinin typical of the (-) sex.
- The (+) and (-) agglutinins are complementary: If agglutinins of a gamete (+) come into contact with those of gamete (-), they will stick together.
What happens during fertilization in the haplontic life cycle?
During fertilization, the fusion of gametes occurs at the mating structures, where agglutinin molecules play a role in the adhesion of flagella of opposite mating types.
Fusion of gametes
Life cycle of Ulva sp.
What distinguishes the “Codiolum” phase in Chlorocystis cohnii?
The “Codiolum” phase in Chlorocystis cohnii is cudgel-shaped with a basal part of wall material consisting of annular constrictions
Life cycle of Chlorocystis cohnii
What is the characteristic organization of thalli in the Order Dasycladales?
Thalli in the Order Dasycladales have a siphonous organization.
Each thallus consists of a single giant, multinucleated cell containing a thin layer of cytoplasm and a central vacuole.
Life cycle Acetabularia acetabulum
