Biology 6.6-Sexual+Asexual Reproduction

• Reproduction is the production of offspring sexually or asexually.
• Plants can reproduce sexually and asexually.
• Most animals rely on sexual reproduction.
• Bacteria, fungi and plants reproduce asexually.
• Sexual reproduction is the fusion of male and female gametes and the mixing of genetic information (fertilisation).
• Sexual reproduction involves two parents, therefore, the offspring will be genetically different.
• There is variation over generations due to sexual reproduction.
• Gametes contain half the number of chromosomes in a normal human cell (23 chromosomes in a gamete).
• Gametes in humans are sperm in males and eggs in females.
• In plants, the female gamete is eggs and the male gamete is pollen.
• Gametes are made through a process called meiosis.
• Meiosis contains 2 cell divisions, and produces 4 genetically different daughter cells which have half the number of chromosomes of a normal human cell (23 chromosomes).
• Asexual reproduction involves only one parent.
• Asexual reproduction contains no mixing of genetic information therefore the offspring will be genetically identical (clones).
• Prokaryotic cells like bacteria asexually reproduce by binary fission.
• Eukaryotic cells like some animals, fungi and plants asexually reproduce by mitosis.
• Mitosis is required for a continuous supply of new cells for growth, development and repair.
• The stages of mitosis include growth, duplication and division (cytokinesis).
• In mitosis, the cell grows in size to increase the number of sub-cellular structures.
• In mitosis, the DNA duplicates itself so that each of the new cells have a full set of DNA.
• When the cell is not dividing, the DNA is spread out in long strings.
• Once it starts to divide, the DNA condenses into chromosomes.
• Chromosomes are tight coils of DNA.
• The cell duplicates each chromosome during mitosis, which stays attached to the original chromosome (forming an X shape).
• All 46 chromosome line up along the centre of the cell before the first division in mitosis.
• In mitosis, fibres from either side of the cell attach to the respective half of each chromosome, and pull the arms to opposite side of the cells (called the poles).
• During Cytokinesis (cell division in mitosis), the cell membrane and cytoplasm divide and form two daughter cells (which have the same DNA and are genetically identical).
• Binary fission is the process which prokaryotic organisms like bacteria divide and reproduce.
• Bacterial cells have a cell wall, cell membrane, cytoplasm, a flagellum (to move), large circular strands of DNA and small circles of DNA (plasmids).
• The large, circular strand of DNA contains the important genes of the bacteria.
• The plasmids contain non-essential genes of the bacteria.
• In binary fission, the bacteria cell divides into two.
• Binary fission is a type of asexual reproduction (as bacteria is single celled and will therefore produce a cloned 'offspring')
• The Bacteria cell grows to give rise to two new cells in binary fission.
• During binary fission, the bacterium replicates its chromosome so that there are now two copies inside the cell.
• The two large circular strands produced after replication in binary fission move to opposite sides of the cell while the plasmids are arranged randomly.
• The bacteria cell grows a new cell wall along the middle of the cell in binary fission, allowing the two halves to pull apart.
• Bacteria reproduces and divides rapidly by binary fission.
• The reproduction of bacteria is sped up by optimum conditions such as warmth, moisture and a plentiful supply of nutrients.
• Sexual reproduction is more time consuming and complicated.