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6 (a) Sperm cells and egg cells are needed for human sexual reproduction - Edexcel - GCSE Biology - Question 6 - 2012 - Paper 1
Question 6
6 (a) Sperm cells and egg cells are needed for human sexual reproduction. Describe in detail the type of cell division that produces sperm cells. (b) The diagram sh... show full transcript
Worked Solution & Example Answer:6 (a) Sperm cells and egg cells are needed for human sexual reproduction - Edexcel - GCSE Biology - Question 6 - 2012 - Paper 1
Step 1
Describe in detail the type of cell division that produces sperm cells.
Answer
Sperm cells are produced through a process called meiosis, which is a specialized form of cell division.
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Meiosis Overview: This process involves two successive divisions (meiosis I and meiosis II) from one parent cell, resulting in four unique sperm cells at the end.
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Haploidy: The cells produced are haploid, meaning they contain half the number of chromosomes, specifically 23 chromosomes in humans. This is crucial for sexual reproduction, as it ensures that when the sperm and egg unite, the resulting zygote has the correct diploid number of chromosomes.
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Genetic Variation: Meiosis introduces genetic variation through processes such as crossing over and independent assortment, resulting in genetically different sperm cells.
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Final Outcome: The final outcome of meiosis is four genetically distinct sperm cells, with each having unique genetic material.
Step 2
Using the diagram and your own knowledge, describe the processes that take place in the formation of the fetus from a sperm cell and an egg cell.
Answer
The formation of a fetus from a sperm cell and an egg cell can be described through several key processes:
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Fertilization: The process begins with the fertilization of the egg cell (ovum) by the sperm cell. This fusion of nuclei results in the formation of a diploid zygote, which contains genetic material from both parents.
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Zygote Development: The zygote undergoes rapid mitotic divisions, a process known as cleavage, where it divides into multiple cells without increasing in size. Initially, it becomes a two-cell embryo, followed by further divisions leading to a four-cell, then an eight-cell structure.
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Embryonic Growth: As the mitotic divisions continue, these cells begin to differentiate into various cell types, forming the foundational layers and organs of the body.
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Fetal Development: The embryo eventually develops into a fetus, which grows in mass and height, undergoing further specialization and development of systems necessary for life.
Step 3
State two differences between sexual reproduction and asexual reproduction.
Answer
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Genetic Variation: Sexual reproduction results in offspring that are genetically different from the parents due to the combination of genetic material from both parents, while asexual reproduction produces genetically identical offspring (clones).
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Gametes Formation: In sexual reproduction, gametes (sperm and egg cells) are formed through meiosis, whereas asexual reproduction does not involve gamete formation and can occur through processes like mitosis or budding.