Life cycle: Difference between revisions

Latest revision as of 11:16, 23 March 2025

Life Cycle[edit]

The term "life cycle" refers to the series of changes in the life of an organism, including reproduction. It encompasses the entire sequence of stages in the life of an organism, from the initial stage of development to maturity and eventual death. Life cycles vary significantly among different species, reflecting the diversity of life on Earth.

Types of Life Cycles[edit]

Life cycles can be broadly categorized into several types based on the organism's reproductive strategy and developmental stages.

Simple Life Cycles[edit]

In simple life cycles, organisms undergo a straightforward sequence of stages. For example, many bacteria and unicellular organisms reproduce through binary fission, a process where a single cell divides into two identical daughter cells. This type of life cycle is characterized by rapid reproduction and minimal differentiation between stages.

Complex Life Cycles[edit]

Complex life cycles involve multiple stages with distinct forms and functions. These are common in many invertebrates, amphibians, and plants. For instance, the life cycle of a butterfly includes the egg, larva (caterpillar), pupa (chrysalis), and adult stages.

Alternation of Generations[edit]

Some organisms, particularly plants and certain algae, exhibit alternation of generations, where the life cycle alternates between a multicellular diploid phase (sporophyte) and a multicellular haploid phase (gametophyte). This is a key feature in the life cycles of ferns, mosses, and other non-flowering plants.

Life Cycles in Cnidarians[edit]

Cnidarians, such as jellyfish, corals, and sea anemones, have fascinating life cycles that often include both asexual and sexual reproduction.

Polyp and Medusa Stages[edit]

Many cnidarians exhibit a life cycle that alternates between a polyp stage and a medusa stage. The polyp is typically sessile and asexual, while the medusa is free-swimming and sexual.

In the polyp stage, the organism is attached to a substrate and reproduces asexually by budding. This stage is exemplified by corals and sea anemones.

A medusa of the species Aglantha digitale

The medusa stage is free-swimming and typically reproduces sexually. Jellyfish are well-known for their medusa stage, where they release gametes into the water for external fertilization.

Coral Life Cycle[edit]

Corals are colonial organisms composed of numerous polyps. Each polyp is capable of budding to form new polyps, contributing to the growth of the coral colony.

Corals also engage in sexual reproduction, releasing eggs and sperm into the water column, where fertilization occurs. The resulting larvae, known as planulae, settle on a substrate and develop into new polyps.

Life Cycles in Other Cnidarians[edit]

Sea Anemones[edit]

Sea anemones are primarily polypoid throughout their life cycle. They reproduce both sexually and asexually, with some species capable of splitting into two individuals through a process called fission.

Box Jellyfish[edit]

The box jellyfish, or sea wasp, has a life cycle that includes both polyp and medusa stages. The medusa stage is notorious for its potent venom.

Stalked Jellyfish[edit]

Stalked jellyfish are unique among jellyfish as they remain attached to substrates throughout their life cycle, resembling a polyp more than a typical medusa.

Related Pages[edit]

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-{{multiple image
+== Life Cycle ==
-|direction=vertical |
-| header    = [[Endopterygota|Most insects]] go through sharply defined stages in their life cycle
-| width     = 150
-| image1 = Monarch egg lgbg cutted.png
-| caption1  = Egg
-| image2    = Danaus plexippus caterpillar.jpg
-| caption2  = [[Caterpillar]] larva
-| image3    = Monarch Butterfly Cocoon 3.jpg
-| caption3  = [[Pupa]]
-| image4    = Danaus plexippus emerging from chrysalis 04.jpg
-| caption4  = Butterfly: [[imago|adult insect]]
-}}
-'''Life cycle''' means the stages a living thing goes through during its life.
-In some cases the process is slow, and the changes are gradual. Humans have various stages of growth during their lives, such as [[zygote]], [[embryo]], [[child]] and [[adult]]. The change from a child to an adult is slow and continuous. In many [[society|societies]] it is marked by ceremonies at [[puberty]].
+The term "life cycle" refers to the series of changes in the life of an organism, including reproduction. It encompasses the entire sequence of stages in the life of an organism, from the initial stage of development to maturity and eventual death. Life cycles vary significantly among different species, reflecting the diversity of life on Earth.
-In most [[insect]]s the transition is sharp and well-defined: [[ovum|egg]] > [[larva]] > [[pupa]] > [[imago]] (adult).
+== Types of Life Cycles ==
-== Different generations have different forms ==
+Life cycles can be broadly categorized into several types based on the organism's reproductive strategy and developmental stages.
-In some animals, the parent generation looks different from the child. The most common case is that there are two different forms. One form will have [[sexual reproduction]], the others might not reproduce, or might reproduce [[asexual reproduction|asexually]].
-=== Parasites ===
+=== Simple Life Cycles ===
-[[Parasitism|Parasites]] are organisms that benefit from harming  other organisms. The organism they profit from is usually called [[Host (biology)|host]]. Many parasites have complex life cycles, where they need different hosts for different stages of their development. As an example, the cycle egg > [[snail]] host > [[mammal]] host is common for parasites of [[Herbivore|herbivorous]] mammals. [[Malaria]] is caused by single-celled parasites. These parasites go through two stages in their development. One stage is in the [[blood]] of [[mosquito|mosquitoes]], the other in the blood of [[human|humans]].
-=== Cnidaria ===
+In simple life cycles, organisms undergo a straightforward sequence of stages. For example, many [[bacteria]] and [[unicellular organisms]] reproduce through binary fission, a process where a single cell divides into two identical daughter cells. This type of life cycle is characterized by rapid reproduction and minimal differentiation between stages.
-Examples of this can also be found in the [[Cnidaria]]. These animals live in the [[sea]] or in [[freshwater]] and the structure of most is relatively simple. Some live as single animals, others form [[Colony (biology)|colonies]]. In a colony, many animals live together. Often, each animal in a colony is specialized, and needs the other animals of the colony to survive.
-==== Complete cycle ====
+=== Complex Life Cycles ===
-A well-known example where different generations have different forms is the [[jellyfish]]. It has two:
-* One is called [[medusa (biology)|medusa]]: it reproduces sexually, and is what most people associate with the word jellyfish.Very ofen the medusa is free-floating.
-* The other form is called [[polyp]]. It does not reproduce sexually, and is usually [[sessile]]. Polyps are generally attached to the sea floor or another hard surface in the water. [[Coral reef]]s are colonies of polyps.
-In a complete cycle, the offspring of a medusa will develop into a polyp, and the offspring of a polyp will be a medusa.
-<gallery>
-File:Polypen_einer_Gorgonie.jpg|Polyps
-File:HydomedusaeAglanthaDigitale.jpg|A medusa
-</gallery>
-==== Incomplete cycle and variations ====
+Complex life cycles involve multiple stages with distinct forms and functions. These are common in many [[invertebrates]], [[amphibians]], and [[plants]]. For instance, the life cycle of a [[butterfly]] includes the egg, larva (caterpillar), pupa (chrysalis), and adult stages.
-Sometimes the cycle is modified or incomplete. [[Anthozoa]] is a group of the Cnidaria which contains [[sea anemone|sea anemones]] and [[coral|corals]]. In the anthozoa, there is only a polyp stage, and no medusa stage.
-The  [[box jellyfish]] form another small group in the Cnidaria.  In the box jellyfish, the polyp transforms into the medusa. In some cases, only part of the polyp transforms, the part that is left [[Regeneration|regenerates]] to form a new polyp. People have also talked about the box jellyfish because many of them produce [[poison]] that is very effective, and that can be dangerous to humans.
+=== Alternation of Generations ===
-In the [[Staurozoa|stalked jellyfish]], there is only one form, which has been interpreted as a sessile medusa. <gallery>
+Some organisms, particularly [[plants]] and certain [[algae]], exhibit alternation of generations, where the life cycle alternates between a multicellular diploid phase (sporophyte) and a multicellular haploid phase (gametophyte). This is a key feature in the life cycles of [[ferns]], [[mosses]], and other non-flowering plants.
-File:Acanthastrea_lordhowensis.jpg|Single polyp of a coral
-File:PillarCoral.jpg|A Coral
-File:Urticina_piscivora_1.jpg|A sea anemone
-File:Avispa_marina.jpg|The [[sea wasp]], a box jellyfish
-File:Haliclystus_stejnegeri_1.jpg|A stalked jellyfish.
-</gallery>
-== Related pages ==
+== Life Cycles in Cnidarians ==
-*[[Metamorphosis]]
-*[[Parasitism]]
-*[[Life cycle (computing)]]
-*[[Alternation of generations]] - A process happening in plants. Two generations are also different because one is [[haploid]], and the other one [[diploid]].
+[[Cnidarians]], such as [[jellyfish]], [[corals]], and [[sea anemones]], have fascinating life cycles that often include both asexual and sexual reproduction.
+=== Polyp and Medusa Stages ===
+Many cnidarians exhibit a life cycle that alternates between a polyp stage and a medusa stage. The polyp is typically sessile and asexual, while the medusa is free-swimming and sexual.
+[[File:Polypen_einer_Gorgonie.jpg|Polyps of a gorgonian coral|thumb|right]]
+In the polyp stage, the organism is attached to a substrate and reproduces asexually by budding. This stage is exemplified by corals and sea anemones.
+[[File:HydomedusaeAglanthaDigitale.jpg|A medusa of the species Aglantha digitale|thumb|left]]
+The medusa stage is free-swimming and typically reproduces sexually. Jellyfish are well-known for their medusa stage, where they release gametes into the water for external fertilization.
+=== Coral Life Cycle ===
+[[Corals]] are colonial organisms composed of numerous polyps. Each polyp is capable of budding to form new polyps, contributing to the growth of the coral colony.
+[[File:Acanthastrea_lordhowensis.jpg|Single polyp of a coral|thumb|right]]
+Corals also engage in sexual reproduction, releasing eggs and sperm into the water column, where fertilization occurs. The resulting larvae, known as planulae, settle on a substrate and develop into new polyps.
+[[File:PillarCoral.jpg|A Coral colony|thumb|left]]
+== Life Cycles in Other Cnidarians ==
+=== Sea Anemones ===
+[[Sea anemones]] are primarily polypoid throughout their life cycle. They reproduce both sexually and asexually, with some species capable of splitting into two individuals through a process called fission.
+[[File:Urticina_piscivora_1.jpg|A sea anemone of the species Urticina piscivora|thumb|right]]
+=== Box Jellyfish ===
+The [[box jellyfish]], or sea wasp, has a life cycle that includes both polyp and medusa stages. The medusa stage is notorious for its potent venom.
+[[File:Avispa_marina.jpg|The sea wasp, a box jellyfish|thumb|left]]
+=== Stalked Jellyfish ===
+[[Stalked jellyfish]] are unique among jellyfish as they remain attached to substrates throughout their life cycle, resembling a polyp more than a typical medusa.
+[[File:Haliclystus_stejnegeri_1.jpg|A stalked jellyfish of the species Haliclystus stejnegeri|thumb|right]]
+== Related Pages ==
+* [[Reproduction]]
+* [[Metamorphosis]]
+* [[Cnidaria]]
+* [[Coral reef]]
 [[Category:Biology]]
+[[Category:Life cycles]]