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Table of Contents
Life cycles are the stages of development that all living organisms, including plants and animals, go through before dying. This generally consists of three stages, beginning with a fertilized egg or seed, progressing to an immature juvenile, and finally transforming into an adult, which is a stage for reproduction to give birth to the next generation, which is assumed to go through the same stages.
See the fact file below for more information about Life Cycles, or download the comprehensive worksheet pack, which contains over 11 worksheets and can be used in the classroom or homeschooling environment.
Key Facts & Information
Life Cycle
- It is a biological series of changes that occur as a species progresses through its developmental stages.
- It refers to the generation of an organism through sexual or asexual reproduction.
- It may refer to an organism’s development from conception to maturity when it is capable of producing another of its kind.
- Depending on the species, it may include additional stages. For example, humans progress through seven distinct stages, namely fetus, infancy, toddler years, childhood, adolescence, adulthood, and old age. However, infancy and toddler years are collectively called as “baby stage” making the human life cycle a six-staged cycle.
- In insects, the development cycle is known as metamorphosis, which can be classified as complete or incomplete. The complete metamorphosis cycle consists of four stages: egg, larva, pupa, and adult. Meanwhile, incomplete metamorphosis includes only the egg, nymph, and adult stages.
- The seven-year life cycle is a concept based on the claims of biologists that human cells are replaced every seven to ten years.
Discovery
- Many botanists and zoologists attempted to study organism reproduction and development.
- Wilhelm Hofmeister demonstrated a generational change in plants in 1851.
- Nils Svedelius proposed the haplobiont and diplobiont life cycle descriptions initially used for algae. The terms were then used to describe other organisms.
- Karl Gottlieb Grell coined autogamy and gamontogamy to describe protist life cycles.
- In the 1840s and 1850s, proposed descriptions of complex life cycles contributed to the debunking of ideas of spontaneous generation.
Sexual Life Cycle
- Reproduction is a property of life in which an offspring is created to carry on the genetics of the parents. This can be done asexually or sexually.
- Sexual life cycles vary between different types of eukaryotic organisms that reproduce sexually. These life cycles regulate not just how the organism produces offspring but also how the cells within the multicellular creature replicate themselves.
- The sexual life cycle specifies the number of chromosomal sets that each cell in the organism will have.
- Haploid contains a single set of chromosomes and forms through, while diploid contains two sets of chromosomes and forms through mitosis.
- A diploid organism is required for sexual reproduction because each parent organism distributes one set of chromosomes.
- The only haploid cells in the human body are the egg and sperm cells.
Haplontic Life Cycle
- Mitosis occurs only in the haploid phase of this cycle. Mitosis is the process by which cells replicate their chromosomes.
- The zygotes, the cycle’s only diploid cell, undergo meiosis immediately after the fusion of two cell nuclei. This results in several haploid cells that divide mitotically to form more prominent, multicellular individuals or even more haploid cells. As a result, opposite types of gametes, such as male and female, develop into individuals or fuse to form a zygote.
- Haplonts are individuals or cells produced by mitosis, including some green and golden algae, many dinoflagellates, some euglyphids, some parabasalids, and Dictyostelium, and the majority of fungi.
Diplontic Life Cycle
- Instead of producing haploid cells, the zygote divides mitotically to produce a multicellular diploid individual or a group of unicellular diploid cells in this cycle.
- After meiosis, haploid cells or gametes were formed from the cells of diploid individuals. These haploid cells may divide mitotically again to produce more haploid cells.
- Mitosis occurs only during the diploid phase for some reasons, one of which is that gametes typically form quickly and fuse to produce diploid zygotes.
- Diplonts are multicellular diploid organisms that include some green and brown algae, opalines, ciliates, parabasalids, fungi, and animals.
Haplodiplontic Life Cycle
- In sporic meiosis, the zygotes divide mitotically to produce a multicellular diploid sporophyte.
- Spores are formed from sporophytes via meiosis, which also divides mitotically to produce small and short-lived haploid individuals known as gametophytes.
- Gametophytes produce gametes via mitosis. b
- Red algae, some green algae, most brown algae, myxogastrids, some fungi, and haptophytes are all haplodiplonts.
- The haplodiploid sex-determination system of some animals is not related to this cycle.
Vegetative Meiosis
- It is a rare occurrence that can occur in both haplodiplontic and diplontic life cycles. Non-reproductive vegetative diploid cells undergo meiosis to produce vegetative haploid cells, which then undergo numerous mitoses to produce gametes.
- Vegetative or somatic meiosis occurs in some green and red algae.
- In some brown algae, a different phenomenon that involves interbreeding and is known as vegetative diploidization occurs. In a haploid plant, cells spontaneously duplicate their chromosomes to produce diploid tissue.
Parasitic Life Cycle
- This is a life process in which organisms known as parasites rely on one or more hosts for survival, and the more host species infected, the more complex the life cycle.
- Heartworm has a complex or indirect life cycle. A female mosquito must first consume microfilariae before it can develop into an infective larval stage. The infective larvae are then transmitted to the animal that was bitten by the mosquito and migrate to the pulmonary artery, where they mature into adults.
- Parasites that have direct life cycles infect only one species throughout their life. A canine hookworm develops to the infective larval stage in the environment and matures in the dog‘s small intestine after penetrating its skin.
- A parasite becomes the obligate parasite of the host, where it completes its life cycle.
- Facultative infection is when a parasite survives and completes its life cycle without infecting the host species.
Host
- Accidental hosts are species that do not complete the life cycle of the parasites even after being infected.
- A species in which parasites reproduce sexually is referred to as a definitive or primary host.
- Intermediate hosts are those in which parasites constantly progress to a new stage.
- Paratenic or transport hosts are species that do not allow parasites to develop. They are quite useful in transmitting parasites to potential hosts.
Evolution
- Haploid individuals most likely reproduced asexually in the past. Some eukaryotes, such as bacteria and archaea, are most likely not primitively asexual but rather have lost their sexual reproduction.
- Cells from organisms are said to be immortal, connecting life cycle generations even after the organisms die.
- According to Zhores Medvedev, a Russian biologist and historian, the immortality of germ lines cannot be explained solely by the accuracy of genome replicative and other synthetic systems. He believed that sexual reproduction indicates the presence of distinct information processes that take place during gametogenesis.
- Cells, rather than being immortal, are said to have multigenerational lineages. This depends on the maintenance of cell division potential, which can be lost in any lineage during development due to cell damage, terminal differentiation, or programmed cell death.
- The ability to divide cells is also dependent on the avoidance and accurate repair of cellular damage.
- The survival of the germline in sexual organisms is dependent on avoiding DNA damage and repairing it. In eukaryotes, homologous recombination allows for effective DNA repair.
Life Cycle Worksheets
This bundle contains 11 ready-to-use Life Cycle Worksheets that are perfect for students who want to learn more about Life cycle, which are the stages of development that all living organisms, including plants and animals, go through before dying.
List of Worksheets Included
- Life Cycle Facts
- Seasons in the South
- Animal Life Cycle – Three Stages
- Four Stages
- Meta-word Creator
- Plant Life Cycle – Growing Plant
- Life Cycle of a Man – My family Life Cycle
- More Life Cycle – Quick Quiz
- Facts of Life
- Reflection
- Key Answers
Frequently Asked Questions
What are the seven stages of human life?
For example, humans progress through seven distinct stages, namely fetus, infancy, toddler years, childhood, adolescence, adulthood, and old age.
What is a 4 stage life cycle called?
The complete metamorphosis cycle consists of four stages: egg, larva, pupa, and adult.
Is seven years a life cycle?
The seven-year life cycle is a concept based on the claims of biologists that human cells are replaced every seven to ten years.
How many life cycle do we have?
This generally consists of three stages, beginning with a fertilized egg or seed, progressing to an immature juvenile, and finally transforming into an adult, which is a stage for reproduction to give birth to the next generation, which is assumed to go through the same stages.
What are the six major stages in human life?
For example, humans progress through seven distinct stages, namely fetus, infancy, toddler years, childhood, adolescence, adulthood, and old age. However, infancy and toddler years are collectively called as “baby stage” making the human life cycle a six-staged cycle.
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Use With Any Curriculum
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