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Minne Life Cycles and Adaptations of Marine organisms > Life cycles Diatoms > Flashcards

Life cycles Diatoms Flashcards

1
Q

How do diatom cells reproduce?

A

Diatom cells reproduce both asexually and sexually

Species that reproduce sexually have:
- a diplontic life cycle with gametic meiosis

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2
Q

How do diatoms primarily reproduce asexually?

A

Diatoms reproduce asexually primarily by cell division:

  1. Before division, the cell contents swell, forcing the epitheca and hypotheca apart.
  2. The mitosis takes place
  3. Protoplast division

After mitosis, the formation of new wall elements in each daughter cell takes place.

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3
Q

Describe the process of new theca (cell wall) formation in daughter diatom cells.

A

Each daughter cell inherits one of the thecae from the mother cell and forms the new theca inside by the deposition of silica, facilitated by vesicles.

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4
Q

What is the result of the unique type of cell division in diatoms?

A

One daughter cell is the same size as the parent cell (upper cell in picture), while the other daughter cell is slightly smaller (lower cell in picture)

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5
Q

How does inheritance of the parental epitheca (upper part of cell) and hypotheca (lower part of cell) affect the size of daughter diatom cells?

A
  • The daughter cell inheriting the epitheca is the same size as the parent cell,
  • while the daughter cell inheriting the hypotheca is slightly smaller, as it reforms the internal theca.
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6
Q

So at each division half the daughter cells are smaller than their parents, what is the consequence of this?

A

Average cell size in a population decreases with each successive round of cell division

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7
Q

asexual reproduction scheme

A
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8
Q

What triggers sexual reproduction in diatoms?

A
  • Sexual reproduction in diatoms is triggered when the size of individual cells reaches approximately 30% of their original diameter.
  • Meiosis occurs to produce gametes
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9
Q

What is the genetic status of vegetative cells in diatoms?

A
  • Vegetative cells in diatoms are diploid, containing two sets of chromosomes.
  • The only haploid phase in the life cycle of the diatoms are gametes
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10
Q

Taxonomy of Diatoms based on..

A

The taxonomy of Diatoms
- valve simmetry
- kind of sexual reproduction

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11
Q

Centric diatoms

A
  • Radial symmetry
  • Oogamous sexual reproduction
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12
Q

When do centric diatom cells become potentially sexual and capable of producing gametes?

A

Centric diatom cells become potentially sexual and will produce gametes when they reach minimal sizes, if environmental conditions are suitable

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13
Q

All the potentially sexual cells (gametangia) can form either female or male gametes.
What determines whether a centric diatom cell produces male or female gametes?

A
  • Smaller cells usually produce male gametes
  • Larger cells typically produce female gametes.
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14
Q

What happens to the very smallest cells in the population?

A

They cannot be induced to form gametes and these tiny cells continue to divide and become smaller still until they die

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15
Q

What process occurs in male gametangia of centric diatoms before meiosis?

A

Male gametangia undergo two or three rapid mitotic divisions in rapid succession before meiosis occurs.

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16
Q

What are the characteristics of the four spermatozoids produced during meiosis in centric diatoms?

A

The spermatozoids produced during meiosis are characterized by the presence of a pleuronematic flagellum, which aids in their motility.

17
Q

What are the two meiotic processes involved in the formation of female gametes in centric diatoms?

A
  • Meiosis I
  • Meiosis II.

After the meiosis I one of two nuclei degenerates. The remaining nucleus undergoes to meiosis II and again one of the daughter nuclei degenerates.

18
Q

What happens after the meiotic divisions in the formation of female gametes in centric diatoms?

A

After the meiotic divisions, a single egg cell containing one functional egg nucleus is produced.

After a resting period of about 5-8 hours, the egg cell begins to expand and mature, becoming ready for fertilization.

19
Q

What is the initial step in the development of the auxospore in centric diatoms?

A

After the sperm and egg come into contact, the sperm injects its nucleus into the egg cell, resulting in fertilization and the formation of a zygote.

20
Q

What are the key processes involved in the formation of the auxospore in centric diatoms after fertilization?

A
  • After fertilization, the protoplast of the zygote contracts, surrounded by a polysaccharidic wall with silica scales.
  • There’s an increase in turgor pressure, leading to the growth of the auxospore.
  • The zygote nucleus undergoes mitotic processes to form the new thecae (epitheca and hypotheca), completing the first frustule of the new generation.
  • A mitosis is necessary for the formation of each theca
21
Q

Sexual reproduction oogamy

A
22
Q

Life cycle centric diatom

A
23
Q

Sexual reproduction diatom

A
24
Q

Sexual reproduction in Biddulphia sp.

A
24
Q

Pennate diatoms

A
  • Bilateral symmetry
  • Isogamous sexual reproduction
25
Q

Sexual reproduction in Melosira sp.

A
26
Q

What triggers sexual reproduction in pennate diatoms, and what happens if cells fail to find a partner?

A
  • Sexual reproduction is initiated when pennate diatom cells reach minimal sizes after repeated divisions.
  • If cells fail to find a partner, they continue dividing vegetatively.
27
Q

Describe the process of sexual reproduction in pennate diatoms after encountering a partner cell.

A
  1. Partner cells surround themselves with a common mucilaginous envelope, called copulation papilla
  2. They undergo reduction meiotic divisions to produce two haploid gametes.
  3. During these meiotic divisions there is production by the cells of mucilaginous material to form a conjugation canal
  4. The gametes fuse after migrating through the canal
  5. Resulting in the production of two zygotes, each of which may give rise to an auxospore representing a new vegetative cell.

In some species one of the zygotes degenerates

28
Q

Life cycle pennate diatom

A
29
Q

Sexual reproduction in Rhopalodia sp.

A
30
Q

Sexual reproduction in Cocconeis sp.

A
31
Q

In some centric diatoms there is a vegetative enlargement:

A

the frustule splits open and the protoplast is extruded, it enlarges and subsequently re-forms a new enlarged frustule

32
Q

Under what conditions do some diatoms produce resting spores, and how long can these spores last?

A

Some diatoms produce resting spores in response to nutrient deficiencies or adverse environmental conditions.

These spores can last for decades in conditions that reduce metabolic demand, germinating in the presence of light when nutrient concentrations increase.

33
Q

Describe the characteristics of resting spores in diatoms.

A

Resting spores are short cells with thick cell walls, differing in structure from vegetative cells.

These walls are heavily silicified, allowing the spores to sink to the sea bottom.

Resting spores are not an obligate stage of the diatom life cycle.

34
Q

Life cycle of genus Chaetoceros

A
  1. Vegetative Cell Division:
  • Vegetative cells divide by binary fission.
  • Each division results in one larger and one smaller daughter cell.
  1. Sexual Reproduction:
  • Small vegetative cells differentiate into gametes.
  • Gametes fuse to form a zygote.
  • The zygote develops into an auxospore, restoring cell size.
  1. Resting Spore Formation:
  • Environmental stress induces resting spore formation.
  • Resting spores germinate when conditions improve, resuming vegetative growth.
  • This cycle ensures the survival and genetic diversity of Chaetoceros, allowing it to thrive in various marine environments.

some species have oogamous, others isogamous sexual reproduction

Minne Life Cycles and Adaptations of Marine organisms (14 decks)

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