1. The sperms journey By Emily Brealey Fertilisation and reproduction

2. Reproducing For mammals, flowering plants and fungi, reproduction is a sexual process. It involves the female sex cell (ovum/egg) and the male sex cell (sperm) to fuse together inside the oviduct to reproduce. To reproduce this way, a female and a male must have sexual intercourse. When this takes place, the males penis becomes stiffer, harder and longer (because the erectile tissue in his penis fills with blood) so it can easily enter the vagina. The vagina becomes most with lubricating fluid so intercourse becomes easier. After a short period of time, semen, which contains millions of sperm cells, is pumped through the penis into the vagina. This is how the reproduction process begins.

3. The sperm cell Tail The sperm cell has a long tail to help it swim to the ovum. It also has chemicals in the head called acrosomes that allow it to enter the egg cell. Millions of male gametes are released with the semen into the vagina to ensure that at least one sperm will survive the long journey through the uterus and successfully reach the egg.

4. The ovum (egg) cell Sperm cells The human egg cell (ovum) is hundreds of times larger than the sperm. It contains a large food store and many chemicals. Some chemicals help the male and female sex cells fuse together during fertilisation whilst others harden the jelly like coat around the cell once one sperm cell has entered the ovum. Ovum are created inside the ovaries. From around the age of 12 to 50, females will release one egg cell from one of the ovaries every month/28 days. Once the egg is released from the ovary, it is sucked into the oviduct/fallopian tube.

5. The journey for the sperm Uterus Millions of sperm are released into the vagina because only a few will make it to the fallopian tube/oviduct to fertilise the ovum. As the sperm are around 0.005mm small, the journey to the ovum is massive. It usually takes around ten hours for the sperm cell to reach the fallopian tubes and ovum. However, sometimes it can take as little as three hours or up to three days to swim all the way to the egg cell. Every sperm is different so there is no exact amount of time for sperm to meet the ovum in the oviduct. The sperm will usually meet the ovum about here but it could find it anywhere in the fallopian tube. It cannot get into the ovary and fertilise a new egg that has not yet been released.

6. Fertilisation Once inside the fallopian tubes, after making the long journey through the uterus, the sperms are attracted to the ovum. However, some sperm cells will swim down the wrong tube thus not meeting the egg. Once the sperm find the egg, they fight to break through the egg's outer wall (the zona pellucida). It takes dozens, sometimes even hundreds of sperm cells, to release their enzymes which help "eat away" at the wall. This will clear a pathway for one sperm to fuse its cell membrane to the membrane of the egg. Once the membranes are combined, the sperm enters the egg, losing its tail as it does so. The zona pellucida hardens as soon as one sperm is inside the ovum to stop other sperm cells getting in. It is impossible for more than one sperm to get inside the egg. Ovum Sperm enters egg

7. The embryo Once the sperm is inside, the nuclei of the egg and sperm combine to make one new cell. This is the first cell of the young and is known as the zygote. The zygote then divides to make a ball of about a hundred cells. This is called an embryo.

8. Implantation For the next step of reproduction, the embryo moves down the fallopian tube or oviduct to the uterus. It sinks into the thick lining of the uterus. This is called implantation. The embryo gets food and oxygen from the blood vessels in thee lining of the uterus/womb. This allows it to grow into a baby. Over the next 9 months, the embryo will continue to grow into a baby, its heart beating at 24 days old and finally, at 48 days old, beginning to look like a human being with limbs, a head, eyes, ears and the early stages of a brain. This is called a foetus. And it all started off as a tiny sperm cell and one small ovum. 48 days after implantation