Life cycles in Phaeophyceae

Question 1

How do Phaeophyceae reproduce?

Answer 1

Species reproduce asexually and sexually in a haplodiplontic life cycle with sporic meiosis

Phaeophyceae generally are haplodiplont
- isomorphic (in the most primitive orders)
- heteromorphic: mostly with dominance of sporophyte

Question 2

What is the significance of heteromorphic life cycles in Phaeophyceae?

Answer 2

Heteromorphic life cycles, with dominance of the sporophyte phase, are hypothesized to be a response to seasonal changes, allowing different phases to develop in different periods of the year.

Question 3

What is the characteristic of the life cycle of the order Ectocarpales?

Answer 3

The life cycle of Ectocarpales is haplodiplontic and isomorphic, meaning both haploid and diploid phases exhibit the same morphology.

Question 4

What types of sporangia does the diploid sporophyte of Ectocarpales bear, and what controls their formation?

Answer 4

The diploid sporophyte of Ectocarpales bears two different types of sporangia. The formation of these sporangia is controlled by temperature;
1. unilocular sporangia or unilocular zoidangia (At 13°C)
2. plurilocular sporangia or plurilocular zoidangia (At 20°C)

Question 5

Unilocular sporangia or unilocular zoidangia

Answer 5

• Produced at 13°C
• Round to oval form
• Lack cross walls
• A meiosis takes place, followed by many mitosis processes
• Many haploid meiospores are produced. Each of them develops a gametophyte.
• The haploid meiospores give rise to haploid gametophytes (about 50% male gametophytes, 50% female gametophytes)

Question 6

What occurs during meiosis in the diploid sporophyte of Ectocarpales?

Answer 6

During meiosis in the diploid sporophyte of Ectocarpales, genes for both female and male occur at the same locus but are separated on homologous chromosomes.

Question 7

Describe the characteristics of the plurilocular sporangia or plurilocular zoidangia

Answer 7

• Produced at 20°C.
• Elongated, tapering sporangia or zoidangia divided by walls into several chambers.
• Each chamber produces a single diploid zoospore, contributing to the formation of a new sporophyte.

Question 8

What occurs in sporophytes between 13°C and 20°C in terms of zoidangia production?

Answer 8

Between 13°C and 20°C, sporophytes produce both types of zoidangia, indicating a transitional period where both plurilocular and unilocular zoidangia are formed.

Question 9

What do the arrows point at?

Answer 9

• Both arrows on the right point out plurilocular sporangium
• The arrow on the right points out unilocular sporangium

Question 10

Life cycle of Ectocarpus sp.

Answer 10

Question 11

Gametophyte vs Sporophyte

Answer 11

Question 12

What are the characteristics of thalli in the order Dictyotales?

Answer 12

Thalli in the order Dictyotales exhibit a parenchymatous structure and are widely distributed in tropical oceans and temperate waters

e.g.: Dictyota dichotoma

Question 13

Describe the sexual fusion in the haplodiplontic isomorphic life cycle of Dictyotales.

Answer 13

• In the haplodiplontic isomorphic life cycle of Dictyotales, sexual fusion is oogamous.
• Male gametes possess a single, anterior, pleuronematic flagellum, while each sporangium in the sporophyte produces four non-flagellate spores

Question 14

Answer 14

Very similar morphology

Difficulat to distinct

Question 15

What characterizes the macrothallus of the sporophytic phase in the typical heteromorphic life cycle of Phaeophyceae?

Answer 15

The macrothallus of the sporophytic phase bears unilocular sporangia that produce haploid zoospores.

Question 16

Describe the development of haploid zoospores in the typical life cycle of Phaeophyceae.

Answer 16

Haploid zoospores develop into microscopic filamentous gametophytes capable of photosynthesis, resembling a reduced form of Ectocarpus.

Question 17

What occurs during gametogenesis in the typical heteromorphic life cycle of Phaeophyceae?

Answer 17

The gametophyte phase forms gametes, with reproductive methods varying from isogamous to oogamous.

Question 18

What is the outcome of the fusion of gametes in Phaeophyceae?

Answer 18

The fusion of gametes results in the formation of a zygote, often giving rise to a plethysmothallus—a filamentous juvenile phase capable of reproducing through diploid zoospores formed in plurilocular sporangia.

Question 19

Under what conditions does the plethysmothallus of Phaeophyceae grow into a macrothallus?

Answer 19

Under favorable environmental conditions, the plethysmothallus grows, developing into a macrothallus.

This enables the sporophytic phase to encompass both the macrothallus and the juvenile phase (microthallus).

Question 21

Haplodiplontic heteromorphic life cycle

Answer 21

Question 22

What trend is recognized in the evolution of Phaeophyceae regarding generational alternation?

Answer 22

In the evolution of Phaeophyceae, there is a trend of alternation between heteromorphic generations, generally with sporophyte dominance over gametophyte, and rarely with gametophyte dominance over sporophyte.

Question 23

An increased structural complexity of the sporophyte vs gametophyte

Answer 23

Question 24

How does Laminaria sp. reproduce?

Answer 24

Laminaria sp. reproduces only sexually.

Question 25

What are the irregular areas found on the lamina of the diploid sporophyte of Laminaria sp., and what do they contain?

Answer 25

The irregular areas are called dark brown sori, which contain unilocular sporangia mixed with sterile paraphyses.

Question 26

What occurs within the unilocular sporangia of Laminaria sp.?

Answer 26

Within the unilocular sporangia of Laminaria sp., meiosis occurs, giving rise to haploid zoospores.

Question 27

What is the fate of the zoospores released from the unilocular sporangia in Laminaria sp.?

Answer 27

Half of the zoospores grow into male gametophytes, while the other half grow into female gametophytes.

Question 28

What conditions are required for the formation of gametangia in Laminaria sp.?

Answer 28

The formation of gametangia in Laminaria sp. requires low temperatures.

Question 29

What structures do male and female gametophytes of Laminaria sp. bear?

Answer 29

Male gametophytes bear small unicellular antheridia, while female gametophytes bear unicellular oogonia.

Question 30

Describe the process of fertilization in Laminaria sp.

Answer 30

• After release, the zoospores of Laminaria sp. grow into male and female gametophytes.
• The egg cell, located within the oogonium, secretes a pheromone called lamoxirene, attracting spermatozoids produced by the antheridia.
• After successful fertilization, a zygote is produced on the female gametophyte.
• The presence of lamoxirene increases the chances of successful fertilization.

Question 31

Laminaria saccharina life cycle

Answer 31

Question 32

What type of life cycle characterizes the order Cutleriales?

Answer 32

The order Cutleriales exhibits a haplodiplontic heteromorphic life cycle, with dominance of the gametophyte phase.

Question 33

Describe the gametophyte of Cutleria multifida.

Answer 33

The gametophyte of Cutleria multifida displays a laminar thallus composed of flattened axes, with tufts of hair present at the apex of the axes.

Question 34

What does the sporophyte of Cutleria multifida resemble, and to what genus was it previously attributed?

Answer 34

• The sporophyte of Cutleria multifida exhibits an amorphous globose thallus, adhering to the substrate.
• In the past, it was attributed to the genus Aglaozonia.

Question 35

Haplodiplontic heteromorphic life cycle of Cutleria sp.

Answer 35

Question 36

What characterizes the order Scytosiphonales in terms of gametophyte structure?

Answer 36

The order Scytosiphonales exhibits parenchymatic gametophytes, with small, prostrate, uniseriate filaments forming compact discs as microthalli, and large, erect macrothalli growing up to 45 cm high as conspicuous parenchymatous structures.

Question 37

Describe the distribution and growth pattern of Scytosiphon sp.

Answer 37

Scytosiphon sp. has a global distribution in the coasts of temperate zones and develops in spring.

It forms erect tubular macrothalli with plurilocular reproductive structures (gametophytes), alternating with crustose microthalli bearing unilocular sporangia (sporophytes).

Question 38

What is the pattern of alternation of generations in Scytosiphon sp.?

Answer 38

Scytosiphon sp. exhibits an alternation of heteromorphic generations with dominance of gametophyte.

Flagellate stages formed by the tubular gametophyte more commonly develop through parthenogenesis, directly forming the crustous thallus.

Gamete copulation and meiosis only occur in some populations.

Question 39

Life cycle of Scytosiphon lomentaria

Answer 39

Question 40

What factors influence the formation of micro- or macrothalli in some populations?

Answer 40

The formation of micro- or macrothalli in some populations is influenced by factors such as photoperiod and temperature.

Question 41

What do flagellate cells formed in plurilocular structures of the erect tubular macrothalli produce?

Answer 41

Flagellate cells formed in plurilocular structures of the erect tubular macrothalli produce…

Question 42

What is the order of algae characterized by generations without an autonomous haploid phase?

Answer 42

The order Fucales includes algae with generations lacking an autonomous haploid phase.

Question 43

Describe the surface features of the thallus in Fucus sp.

Answer 43

The surface of the thallus in Fucus sp. is characterized by cryptostomata, which are sterile cysts containing tufts of phaeophycean hair, and receptacles, the fertile tips of the thallus.

Question 44

What structures are found within the conceptacles of Fucus sp.?

Answer 44

The conceptacles of Fucus sp. contain phaeophycean hairs and sexual reproductive structures, including oogonia in female thalli and antheridia in male thall

Question 45

What determines whether Fucus species are monoecious or dioecious?

Answer 45

Whether Fucus species are monoecious or dioecious depends on the species.

Question 46

Meaning of monoecious vs dioecious

Answer 46

• Monoecious: In plants, monoecious (from the Greek words “monos” meaning “single” and “oikos” meaning “house”) refers to a species where both male and female reproductive organs (stamens and pistils) are found on the same individual plant.
• Dioecious: In contrast, dioecious (from the Greek words “di” meaning “two” and “oikos” meaning “house”) describes a plant species in which male and female reproductive organs are borne on separate individual plants. Each plant is either male or female, and both are required for sexual reproduction to occur.

Question 47

Describe the process of gamete formation in Fucus sp.

Answer 47

• Each antheridium undergoes meiosis followed by various mitoses, resulting in the formation of a cluster of 64 spermatozoids.
• Each oogonium undergoes meiosis followed by one mitosis, forming a cluster of 8 egg cells.

Question 48

What attracts spermatozoids to the egg cells in Fucus sp.?

Answer 48

Spermatozoids in Fucus sp. are chemotactically attracted to the egg cells by fucoserratene produced by the eggs.

Question 49

Describe the process of fertilization and zygote formation in Fucus sp.

Answer 49

Once liberated in seawater, spermatozoids attach themselves to egg cells.

After penetration by a spermatozoid, the fertilized egg cell surrounds itself with a wall, forming a zygote.

The zygote secretes an adhesive substance to attach itself to the substrate and grows into a new diploid sporophyte.

Question 50

Life cycle of Fucus sp.

Answer 50

There is no alternation of generations recognizable haploid phase is reduced to a few cells