Gametes and fertilisation

What is a gamete?A sex cell, such as a sperm or an ovum. Features of a gamete include a haploid nucleus.How is a sperm cell adapted?Flagellum- Tail, enables the sperm to move.Collar with many mitochondria- The vast amount of mitochondria means it provides a lot of energy for the sperm to move.Haploid nucleus- Chromosomes will fuse with haploid nucleus of ovum forming a diploid nucleus.Acrosome- Specialized lysosome, containing digestive enzymes. Capable of breaking down the zona pellucida.How is an ovum adapted?Haploid nucleus- Chromosomes will fuse with haploid nucleus of sperm forming a diploid nucleus.Lipid and protein food reserves- Food for developing an embryo.Zona pellucida- Can be broken down by digestive enzymes. Can thicken when ovum releases chemicals.The process of fertilization- Sperm swim through the uterus (assisted by muscular contractions of the uterus wall) When sperm reaches the zona pellucida, the acrosome swells and fuses with the sperm cell surface membrane. Acrosome releases digestive enzymes which break down the zona pellucida. This is called an acrosome reaction. Sperm fuses with ovum membrane and sperm nucleus enters. Enzymes released from lysosomes in the ovum thicken the zona pellucida preventing polyspermy. This is called a cortical reaction. Nuclei of the ovum and sperm fuse, forming a fertilized egg (zygote). Dictionary-Sperm- Male sex cell, with a haploid nucleus.Ovum- Female sex cell, with a haploid nucleus.Haploid- Half the amount of chromosomes than in a systematic cell.Diploid- Full amount of chromosomes like found in a systematic cell.Mitochondria- Creates energy (ATP) for cellular processes. The site of the later stages of aerobic respiration.Lysosome- Spherical sacs containing digestive enzymes. Involved i the breaking down of unwanted cellular organelles.Acrosome reaction- The process at which the chromosome swells releasing digestive enzymes in response breaking down the zona pellucida.Polyspermy- The sperm at which would enter the ovum after the first sperm has entered.Cortical reaction- The process at which lysosomes release chemicals which thickens the zona pellucida, preventing further sperm from entering the ovum.Zygote-Facts to know Fertilization normally takes place in the Fallopian tube. The fertilized ovum is a zygote when it is one cell. 2 cell's + is classed as an embryo. 8 weeks after fertilization + is classed as a fetus.

Questions How does the size of a sperm cell aid the fertilization process? (2 marks) How is an acrosome (a specialized lysosome) different to a lysosome? (2 marks) Why does the sperm not attempt to enter any other cell other than the ovum? (3 marks) If a sperm cell contains 23 chromosomes how many chromosomes does a fertilized egg hold? (1 mark) What is an acrosome reaction? (1 mark) What is a cortical reaction? (1 mark) What is the purpose of a flagellum on a sperm? (1 mark) What is the cell division that forms gametes? (1 mark) How does the size of an ovum aid the fertilization process? (1 mark) (Total marks= 13)

Answers Sperm is small- Enables it to move better (1) More energy efficient (1). An acrosome has a specific job, acrosome contains digestive enzymes which break down the zona pellucida (1). Whereas a lysosome generally breaks down unwanted organelles (1). The ovum releases chemicals which attract the sperm (1) Sperm follow concentration gradient of the chemical (1) Swim towards high concentration of the chemicals by the ovum (1). 46 chromesomes (23 pairs) Where the acrosome swells and releases digestive enzymes which break down the zona pellucida (1). Where lysosomes release chemicals which thicken the zona pellucida prevent further sperm from entering the ovum (preventing polyspermy) (1). The flagellum enables the sperm to move (1). Meiosis (1). Egg is big, because it needs to be able to be wafted along the uterus (by cillia) (1).