Reproduction and development

Reproduction and development

Subject

#1 Gametes

#2 The human reproductive system

#3 What happens to the egg cell?

#4 From embryo to baby

#5 Growth and development

#1 Gametes

• Your body is made of millions of cells. But you began your life as a single cell.

  That single cell was made when two very special cells joined together. 

  The special cells were egg cell and sperm cell.

Chromosomes

Every cell has chromosomes in its nucleus.

Chromosomes are long, thread-like structures. They are made up of the genetic material, which contains information about how the cell will develop.

Egg cells

Egg cells are the female gametes.

They are bigger than most other cells. 

Egg cells need to be quite large to make space for food stores in their cytoplasm.

Largest diameter - 0.12mm

Sperm cells

Sperm cells are the male gametes.

They are smaller than most other cells. 

They have only a tiny amount of cytoplasm. They have a long tail, so that they can swim.

50 μm long (10000 x smaller than the egg)

Fertilisation

When a sperm cell meets an egg cell, the head of the sperm cell goes into the egg cell.

The nucleus of the sperm cell and the nucleus of the egg cell join together.

This is called fertilisation.

The new cell that is produced is called a zygote.

Multiple Choice

How many chromosomes do humans have?

• 22

• 23

• 42

• 46

Multiple Choice

What is the joining of a sperm and egg cell called?

• fertilization

• cellular respiration

• crossing over

Multiple Choice

List three ways in which an egg cell differs from other cells in the human body.

• It is larger. It has food stores in its cytoplasm. It has

  only 23 chromosomes instead of 46.

• It is smaller. It has food stores in its cytoplasm. It has

  only 23 chromosomes instead of 46.

• It is larger. It does not have much cytoplasm. It has only

  23 chromosomes instead of 46.

Multiple Choice

What would indicate a human female?

• XX

• XY

The human reproductive system

#2

The male reproductive system

Sperm cells are made in the testes (singular: testis).

They travel along the sperm duct, into the urethra.

The seminal vesicles and the prostate gland make a sugary fluid for the sperm cells to swim in.

The sugar helps to give the sperm cells energy to swim.

Multiple Choice

These are the major male sex organs that produce sperms.

• Penis

• Testes/testicles

• Ovary/ovaries

• seminal vesicle

Multiple Choice

The two male reproductive organs that produce most of the fluids that make up semen are called

• seminal Vesicle & prostate gland

• urethra & penis

• testis & sperm duct

The female reproductive system

Egg cells are made in the ovaries. 

In an adult woman, one egg cell leaves one of the ovaries approximately each month. This is called ovulation.

The female reproductive system

The egg cell goes into the oviduct. 

Tiny hairlike structure on the oviduct walls, called cilia, move the egg cell slowly along the oviduct. 

This is where fertilisation can happen, if there are any sperm cells there.

Multiple Choice

These are the major female sex organs that produce ova or eggs.

• Testes/testicles

• Ovary/ovaries

• Oviduct

• uterus

Multiple Choice

Where does the egg need to be fertilized for successful pregnancy?

• Ovary

• Uterus

• Oviduct

• Vagina

#3 What happens to the egg cell?

What happens if an egg is fertilised

The moment at which the zygote is formed is called conception. It is the start of a new life.

It takes several days for the zygote to become an embryo, and to travel into the uterus. When the embryo has sunk into the wall of the uterus, the woman is pregnant.

It takes about nine months for the tiny embryo to develop into a foetus and then a baby.

If the egg cell is not fertilised, this thick lining is not needed. It breaks down, and is lost through the vagina. In an adult woman, this takes about five days and happens about once a month.

The loss of the uterus lining through the vagina is called menstruation, or a period.

Multiple Choice

If an egg cell is fertilised, the zygote divides to produce an embryo. The embryo travels to the uterus where it sinks into the uterus lining and develops into a foetus.

• true

• false

Multiple Choice

If an egg cell is not fertilised, it dies. The thick, spongy uterus lining is not needed, so it breaks down and is lost through the vagina. This is called menstruation.

• true

• false

Multiple Choice

What is an embryo?

• The nucleus of the sperm cell and nucleus of the egg cell join together

• A little ball of cells that forms after the zygote divides.

• This is a zygote

#4 From embryo to baby

The embryo sinks into the thick, spongy lining of the uterus. 

This will be its home for the next nine months.

The placenta and amnion

When it sinks into the uterus wall, the embryo is only the same size as the egg cell from which it was formed. It was not grown at all. 

However, it is now made up of many tiny cells, rather than one big cell. These little cells were made as the zygote divided, over and over again. 

The food stores in the egg cell provided energy for it to do this.

To grow and develop, the embryo now needs more food. A special organ develops that allows it to obtain food and oxygen from its mother’s blood. 

This is the placenta. 

The embryo is attached to the placenta by the umbilical cord.

The little embryo floats in its own private pond, containing amniotic fluid. 

This fluid is made by a bag or membrane called the amnion, which grows around the embryo. 

The amniotic fluid supports the embryo, and protects it from bumps and knocks.

Foetal development

By the time it is 6 weeks old, the embryo is about 4mm long. All its major organs have begun to grow.

At 8 weeks old, the embryo is about 13mm long. It is already beginning to move.

At 11 weeks old, all the body organs have developed. The embryo has now become a foetus. It is about 50mm long. It is moving quite vigorously now.

Multiple Choice

In which part of the body does the growing embryo develop?

• oviduct

• ovary

• vagina

• in the uterus

Multiple Choice

Explain how the growing embryo obtains food.

• From its mother’s blood, through the placenta.

• Uterus lining

• Amniotic fluid

Multiple Choice

How long after fertillisation does an embryo become a foetus?

• at 6 weeks

• at 8 weeks

• at 11 weeks

#5 Growth and development

Growth

Soon after fertilisation, the zygote begins to divide. The single cell divides to form two cells, then four and so on.

As the embryo grows into foetus, and the foetus grows into a baby, this cell division continues.

Each cell grows, then divides, grows, then divides - over and over again.

This carries on all through childhood, until a person has reached adulthood and stops growing.

Development

The change from a zygote to an adult does not involve only growth.

It also involves development.

As the tiny embryo develops, its organs gradually from. For example, it develops a heart, lungs and brain.

When a baby is born, it has all of its organs. But development continues.

Its muscles become stronger as it learns to crawl, walk and run.

Its brain develops, as it learns to talk and play with toys.

Each person is an individual. Each of us develops in slightly different ways, and at a slightly different pace. The chart shows the main stages in development that everyone passes through. Notice that there are no sharp change from one stage to another.

Adolescence

At around the age of 12 or 13 in boys, and 10 or 11 in girls, a big step in development takes place.

The reproductive organs and the brain undergo quite large changes. There is often a growth spurt (a sudden, rapid period of growth) at this time.

This time of change from childhood to adulthood is called adolescence.

Changes in the reproductive organs

In girls, menstruation begin. Hormones produced by the reproductive organs cause changes in body shape, as breasts develop and hips widen. Hair begins to grow in the armpits and other parts of the body.

Changes in the reproductive organs

In boys, sperm production begins. Hormones produced by the reproductive organs cause body shape changes, as shoulders broaden. The voice becomes deeper. Hair begins to grow on the face, armpits and other parts of the body.

Changes in the brain

The brain does not grow any larger during adolescence.

But there is quite a lot of reorganisation in the brain, which makes a person think and feel differently from when they were a child.

Changes in the brain

• The person becomes better at making decisions and planning ahead. The ability to think logically improves. This is a time when people find they can learn more quickly.

• Emotions may become stronger. People may worry more. They may begin to have romantic feelings. They become more self-aware.

• During adolescence, there is often a strong need for approval by friends and others. Young people may want to be like a role model. This can be stressful if they set themselves impossible standards, perhaps trying to be like someone they see on television.

Multiple Choice

Adolescence occurs AROUND the ages of...

• 8-13

• 10-19

• 18-25

Multiple Choice

______ is the stage in life when humans change from children to adults.

• Puberty

• Asynchrony

• Adolescence

• Teens

Multiple Choice

What causes puberty to occur

• Enzymes

• Hormones

• No one knows

Multiple Choice

Which changes occur at puberty to boys and girls

• Pubic hair grows

• Sexual organs grow and develop

• Underarm hair grows

• All are correct