AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The use of hormones to treat infertility (HT only): The fertilised eggs develop into embryos.
In fertility treatment, eggs are collected from the mother and fertilised outside the body.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In fertility treatment, eggs are collected from the mother and fertilised outside the body. Each fertilised egg, now a single cell called a zygote, divides by mitosis to form a small group of identical cells. This early stage is an embryo. The word 'develop' covers this cell division and the gradual formation of a ball of cells, not just one division. For example, a zygote divides into 2 cells, then 4, then 8, forming a tiny ball within a few days. Only healthy-looking embryos are chosen for the next step. Understanding this stage explains why treatment must be timed carefully and why several embryos may be produced. Note that IVF and infertility treatments are Higher Tier only content.
What earns the marks
- A fertilised egg is a single cell formed when a sperm nucleus fuses with an egg nucleus.
- The fertilised egg divides by mitosis to produce genetically identical cells.
- Repeated division produces a small ball of cells called an embryo.
- Development happens outside the mother's body in this fertility treatment.
- Several fertilised eggs may develop, giving more than one embryo.
Common mistakes and how to put them right
Saying the embryo forms immediately at fertilisation.
Put it right by stating that the fertilised egg must first divide by mitosis to become an embryo.
Confusing an embryo with a fetus.
Put it right by noting that an embryo is the early ball of cells, while a fetus is a much later stage.
Writing that the egg develops into an embryo without fertilisation.
Put it right by stating that fertilisation by a sperm is needed first.
Exam tips
- Use the sequence fertilisation, mitosis, ball of cells, embryo in your answer.
- Link the word 'develop' to cell division, not to growth in size alone.
Try the lesson
The start of the The use of hormones to treat infertility (HT only): The fertilised eggs develop into embryos. lesson, made from checked teaching notes for this specification point.
Have a go first
In fertility treatment, what do fertilised eggs develop into?
Listen
In fertility treatment, eggs are collected from the mother and fertilised outside the body. Each fertilised egg, now a single cell called a zygote, divides by mitosis to form a small group of identical cells. This early stage is an embryo. The word 'develop' covers this cell division and the gradual formation of a ball of cells, not just one division. For example, a zygote divides into 2 cells, then 4, then 8, forming a tiny ball within a few days. Only healthy-looking embryos are chosen for the next step. Understanding this stage explains why treatment must be timed carefully and why several embryos may be produced. Note that IVF and infertility treatments are Higher Tier only content. A strong answer earns marks for these points. A fertilised egg is a single cell formed when a sperm nucleus fuses with an egg nucleus. The fertilised egg divides by mitosis to produce genetically identical cells. Repeated division produces a small ball of cells called an embryo. Development happens outside the mother's body in this fertility treatment. A common slip: Saying the embryo forms immediately at fertilisation. Instead, stating that the fertilised egg must first divide by mitosis to become an embryo. Exam tip: Use the sequence fertilisation, mitosis, ball of cells, embryo in your answer.
See it
Put it in order
Put these steps in the order they happen.
- 1. Divides by mitosis
- 2. Repeated division
- 3. Small ball of cells
- 4. Embryo
- 5. Fertilised egg
Key words
Say what each word means before you turn the card.
Fertilisation
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Cell division by mitosis
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Embryo development
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Infertility treatment
Try answering aloud or in your head before turning the card.
See every definition
- Fertilisation
- The process in which a sperm nucleus fuses with an egg nucleus to form a fertilised egg, which is a single cell.
- Cell division by mitosis
- The process by which the fertilised egg divides to produce genetically identical cells.
- Embryo development
- Repeated division produces a small ball of cells, and the word 'develop' covers this cell division and the gradual formation of a ball of cells.
- Infertility treatment
- A treatment in which eggs are collected from the mother and fertilised outside the body, and several fertilised eggs may develop.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
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