Gametes, Chromosomes and Egg Cells

Gametes

• Gametes are special cells adapted for reproduction.
• Egg cells and sperm cells are examples of gametes.
• Fertilization happens when the sperm cell nucleus fuses with the egg cell nucleus, the cell is now called a zygote.
• Gametes contain half the number of chromosomes that other cells have.
• Sperm cells are made in the testes and travel along the sperm duct into the urethra. Egg cells are made in the ovaries and travel along the oviduct, where they may be fertilised, and the zygote travels into the uterus, where it develops into a baby.

Chromosomes

• Every cell has chromosomes in its nucleus.
• Chromosomes are long, thread-like structures made of genetic material.
• Chromosomes contain information about how the cell will develop.
• Body cells have 46 chromosomes, while gametes have 23 chromosomes.

Egg Cells

• Egg cells are the female gametes.
• They are bigger than most other cells, about the size of the full stop at the end of the sentence.
• Their large size is to make space for food stores in their cytoplasm.

Sperm Cells

• Sperm cells are the male gametes.
• Sperm cells are smaller than most other cells and have a small amount of cytoplasm.
• They have a long tail for swimming.

Fertilization

• When a sperm cell meets an egg cell, the head of the sperm cell enters the egg cell.
• The nucleus of the sperm cell and the nucleus of the egg cell join together through fertilization.
• The result of fertilization is a new cell called a zygote.

Male Reproductive System

• Sperm cells are produced in the testes.
• Sperm cells travel along the sperm duct into the urethra.
• Seminal vesicles and the prostate gland produce a sugary fluid, giving sperm cells energy to swim.

Female Reproductive System

• Egg cells are produced in the ovaries.
• Approximately once a month, one egg cell leaves one of the ovaries, known as ovulation.
• The egg cell goes into the oviduct, where tiny hair-like structures called cilia move the egg cell along.
• Fertilization can happen in the oviduct if sperm cells are present.
• The zygote that forms from fertilization travels down the oviduct to the uterus, where the embryo develops into a baby.

Conception and Development

• Conception is the moment when the zygote is formed, marking the beginning of a new life.
• After fertilization in the oviduct, the cell is called a zygote.
• The zygote divides, becoming a little ball of cells called an embryo.
• The embryo takes days to travel into the uterus.
• Once the embryo sinks into the wall of the uterus, it develops into a foetus.

What Happens if the Egg Cell is Not Fertilized

• Most egg cells are not fertilized and die as they travel along the oviduct.
• One egg cell is usually released from an ovary each month.
• The uterus prepares for receiving a fertilized egg by thickening its lining.
• If the egg is not fertilized, the thick lining breaks down and is lost through the vagina through menstruation, or a period.
• The monthly pattern of thickening and loss of the uterus lining describes the menstrual cycle.

Placenta and Amnion

• The embryo sinks into the thick and spongy lining of the uterus, where will remain for nine months.
• The placenta is an special organ that develops and allows the embryo to get food and oxygen from its mother's blood.
• The embryo is attached to the placenta by the umbilical cord.
• The amnion is a fluid-filled bag surrounding the embryo.
• The amniotic fluid supports the embryo and protects it from bumps.

Foetal Development and Birth

• By 6 weeks, the embryo is about 4 mm long, with major organs beginning to grow.
• By 8 weeks, the embryo is about 13 mm long and starts to move.
• By 11 weeks, the embryo develops all body organs and becomes a foetus about 50 mm long and moves vigorously.
• From 11 weeks onward, the foetus grows steadily.
• Around 38 or 39 weeks after fertilisation, the foetus finishes growing and developing and is ready to be born.
• Before birth, the baby usually turns so that it is lying head downwards.
• The muscles in the wall of the uterus contract and widen the opening to allow the baby to pass through.
• Then the muscles contract again, pushing the baby out through the opening of the uterus and the vagina.

Growth and Development

• Soon after fertilisation, the zygote begins to divide, from one cell to two, then four, and so on, where Growth takes place as cells grow and divide.
• Development involves the change from a zygote to an adult.
• The tiny embryo forms its organs gradually.
• Even after birth, development of the new born continues.
• Each person develops in slightly different ways and at a different pace.

Adolescence

• Adolescence marks the time when a child gradually develops into an adult at puberty.
• During adolescence, the reproductive organs and the brain undergo major changes.
• Often, there is a growth spurt, a sudden and rapid period of growth, when the individual body undergoes changes.

Changes in the Reproductive Organs

• In girls, menstruation begins.
• Hormones cause changes in body shape, breasts develop, and hips widen.
• Hair starts to grow in the armpits and other parts of the body.
• In boys, sperm production begins.
• Hormones produced by the reproductive organs cause body shape changes, the shoulders broaden, and the voice deepens.
• Hair begins to grow on the face, armpits, and other parts of the body.

Changes in the Brain

• The brain undergoes significant reorganization.
• The ability to make decisions, plan ahead, and think logically improves.
• Emotions become stronger, and people may worry more.
• The period of adolescence sees potential for strong emotions, new romantic feelings, and increased self-awareness.
• During adolescence, there is generally a strong need for approval by friends and others.

Lifestyle and Health

• Genes from parents contribute to difference in people unless they have an identical sets of genes, such as identical twins.
• Factors like diet, illnesses, and drug use affect one's appearance and personality.
• A drug is something that affects the function of the body.
• Antibiotics are drugs that kill harmful bacteria in the body.
• Caffeine is a drug that can make you feel more alert and awake.
• Nicotine is a drug in cigarette smoke that has harmful effects on health.

Effects of Nicotine

• Both men and women nicotine lowers chance of getting pregnant.
• Nicotine crosses to the foetus in a smoking pregnant woman, stunting proper growth of the foetus.
• The brain of the foetus may get impacted by nicotine which could hinder proper development.
• A foetus exposed to nicotine increase the chances of developing diabetes even through breast feeding given a smoking mother.