Edexcel IGCSE Biology 复习笔记 1.1.6 Living Organisms: Reproduction & Growth
Reproduction
- Reproduction is the process that leads to the production of more of the same kind of organism
- Reproduction is fundamental to the survival of a population and ultimately, the species
- There are different types of reproduction: sexual and asexual
Sexual Reproduction
- In this type of reproduction, the male and female gametes fuse together
- In humans, the male gamete is the sperm and the female gamete is the egg
- In plants, the male gamete is in the pollen grains and the female gamete is the ovule
- The DNA of the offspring is composed of both maternal and paternal DNA
Sexual reproduction involves the fusing of two gametes to form a zygote that contains DNA from both parents
Asexual reproduction
- Cells or whole organisms can also reproduce using asexual reproduction
- Mitosis is an example of asexual reproduction
- There is only one parent involved so an exact clone is produced
- The DNA of offspring is identical to parental DNA
- Plants can reproduce asexually through tubers, budding or runners
- Single-celled organisms such as bacteria or amoeba reproduce asexually
Asexual reproduction in bacteria involves creating exact copies of the parent cell
Growth
- Growth is defined as a permanent increase in size
- In animals, an individual grows larger between the zygote and adult stage with changes in proportion or shape
- In plants, an individual grows larger throughout their whole life with new shoots, leaves, branches etc forming year after year
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