Examples of Different Life Cycles
Joe Wolfensohn
Teacher
What is the difference between mitosis and meiosis?
- Mitosis produces genetically identical diploid cells for growth and repair.
- Meiosis produces genetically varied haploid cells (gametes or spores) through two divisions.
- Meiosis separates homologous paris of chromosomes, this does not happen in mitosis.
What does “haploid” and “diploid” mean?
- Haploid (n): 1 single set of chromosomes.
- Diploid (2n): 2 sets of chromosomes, one from each parent (chromosomes are in pairs)
Topic Explainer Video
Check out this @JoeDoesBiology video that explains examples of different life cycles or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Life Cycles of Different Organisms
Humans have a simple life cycle, meiosis produces the gametes and then after fertilisation mitosis produces all other cells, other organisms are not so simple. You need to be able to recognise at what stages of a life cycle mitosis and meiosis are occurring and when fertilisation happens. To recognise meiosis look for when haploid cells (n) are produced, it is not always to produce gametes. To recognise when fertilisation occurs look for when two cells fuse together, and then everything else will be mitosis.
Moss Life Cycle (Alternation of Generations)
- Haploid-dominant lifecycle.
- Key Stages:
-
- Gametophyte (n): Dominant generation; produces gametes by mitosis.
- Gametes fuse (Fertilisation): Zygote (2n).
- Zygote undergoes Mitosis: Sporophyte (2n).
- Sporophyte undergoes Meiosis: produces haploid spores (n).
- Spores undergo mitosis: New gametophyte (n).
Where is Mitosis in this example?
- Gamete production (in gametophyte).
- Growth of zygote into sporophyte.
Where is Meiosis in this example?
- In sporophyte to produce haploid spores.
Plasmodium (Malaria Parasite) Life Cycle
Host 1: Human (Asexual Reproduction)
- Sporozoites (n) (from mosquitoes) enter the liver: divide by mitosis.
- Infect red blood cells: mitosis to form merozoites (n).
- Some merozoites become gametocytes (n).
Host 2: Mosquito (Sexual Reproduction)
- Gametocytes fuse (fertilisation) in the mosquito gut: zygote (2n).
- Zygote undergoes meiosis: haploid sporozoites (n).
- Sporozoites travel to salivary glands to infect the next human.
Where is Mitosis in this example?
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In human Liver and Red Blood Cells: clonal expansion.
Where is Meiosis in this example?
- In mosquito: zygote undergoes meiosis to introduce genetic variation.
Key Terms
- Mitosis: Cell division producing genetically identical, diploid cells.
- Meiosis: Cell division halving chromosome number to produce haploid cells.
No answer provided.
Exam Tips
Meiosis halves the number of chromosomes, diploid to haploid. Mitosis produces genetically identical cells, haploid cells can still divide by mitosis (the cells produced would also be haploid!).
You do not need to memorise the examples provided here. However, you may need to be able to spot where meiosis and mitosis are taking place in an unfamiliar life cycle.
In the moss life cycle, haploid spores divide to produce haploid gametophytes. State and explain what type of cell division this is. (2 marks)
- Mitosis.
- Division produces cells with the same number of chromosomes as parent cell.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!