OCR GCSE Biology B (J257) — Human Physiology
Imagine a central heating thermostat that turns off the boiler when the house gets too warm. Your body uses a similar "switch-off" system to control fertility. By introducing synthetic hormones, contraceptives can trick the reproductive system into pausing its normal cycle, preventing pregnancy.
Hormonal contraceptives contain synthetic oestrogen and/or progesterone. High levels of these hormones in the blood trigger a negative feedback mechanism that targets the pituitary gland.
This negative feedback stops the pituitary gland from releasing two crucial hormones: FSH (Follicle Stimulating Hormone) and LH (Luteinising Hormone). This creates a three-step barrier to pregnancy:
Different hormonal methods deliver these chemical signals in various ways:
Non-hormonal methods rely on physical barriers, chemical sperm-killers, or avoiding intercourse during fertile windows. They do NOT cause systemic hormonal side effects.
When evaluating contraceptives, you must consider efficacy (perfect vs. typical use), side effects, STI protection, and invasiveness.
Typical vs. Perfect Use: Methods like LARC have a typical failure rate of because they remove user error. Barrier methods rely on correct usage every time, leading to higher typical failure rates (e.g., to for condoms, and to for diaphragms).
Forming a Reasoned Judgement: In an evaluation question, you must weigh the pros and cons and provide a final conclusion. For example:
"While the combined pill is highly effective at preventing pregnancy (moderate typical failure rate of -), it offers no protection against STIs and can cause side effects like mood swings. Therefore, condoms are the better overall choice for preventing the spread of STIs, despite having a higher typical failure rate (-). For maximum protection against both pregnancy and STIs, a combination of a LARC (like an implant) and a condom is the most effective strategy."
Examiners often ask you to calculate the number of pregnancies in a population based on failure rates.
Question: If women use a contraceptive method with a typical failure rate of , how many pregnancies would be expected in a year?
Step 1: Convert the percentage to a decimal.
Step 2: Multiply the population size by the decimal failure rate.
Step 3: State the final answer.
| Feature | Hormonal (Pill/Patch) | Barrier (Condom) | Diaphragm (+ Spermicide) | Copper IUD |
|---|---|---|---|---|
| STI Protection | No | Yes | No | No |
| Main Side Effects | Mood swings, headaches, blood clot risk | Latex allergy | Irritation from spermicide | Heavier/painful periods |
| Reliability (Typical) | Moderate (Pill: - failure) | Lower (- failure) | Low (- failure) | Very High ( failure) |
| Invasiveness | Low | Non-invasive | Non-invasive | Invasive (medic required) |
Students often state that all barrier methods protect against STIs. This is incorrect; while condoms do, diaphragms do NOT provide significant STI protection.
When answering an 'Explain' question on hormonal contraception, OCR mark schemes require a clear causal chain: you must state that the hormones inhibit the pituitary gland, which stops FSH/LH, which then prevents egg maturation and ovulation.
Always use the specific failure rate data provided in the exam paper's table for your calculations, as these percentages can vary slightly between different past papers.
Remember to mention the exact effects of progesterone: use the phrasing 'thickens cervical mucus to prevent sperm reaching the egg' and 'thins the uterus lining to prevent implantation'.
Oestrogen
A female reproductive hormone used in combined contraceptives that helps trigger negative feedback to inhibit FSH and LH.
Progesterone
A female reproductive hormone that thickens cervical mucus and thins the uterine lining to prevent pregnancy.
Negative feedback
A regulatory mechanism where a stimulus (such as high hormone levels) causes a response that does the opposite (stopping the production of further hormones).
Pituitary gland
A small gland in the brain that releases FSH and LH, which are inhibited by hormonal contraceptives.
FSH
Follicle Stimulating Hormone; a hormone released by the pituitary gland that causes an egg to mature in the ovary.
LH
Luteinising Hormone; a hormone released by the pituitary gland that triggers ovulation.
Follicle
A ball of cells inside the ovary that contains and protects a developing egg cell.
Ovulation
The release of a mature egg from a follicle in the ovary into the fallopian tube.
Cervical mucus
Fluid produced by the cervix that is thickened by progesterone to create a physical block against sperm.
Endometrium
The mucous membrane lining the uterus, which is thinned by progesterone to prevent an embryo from attaching.
Fertilisation
The fusion of the nuclei of a sperm and an egg.
Implantation
The stage of reproduction where a fertilised egg (embryo) adheres to the wall of the uterus.
Transdermal
A route of administration where ingredients (like hormones in a patch) are absorbed across the skin directly into the bloodstream.
LARC
Long-Acting Reversible Contraception (e.g., implants or IUDs) that are highly effective because they do not rely on daily user compliance.
IUS
Intrauterine System; a small, plastic, T-shaped device inserted into the uterus that releases progesterone.
Condoms
Barrier methods (male or female) that prevent sperm from entering the vagina; the only contraceptive method that protects against STIs.
STIs
Sexually Transmitted Infections (e.g., HIV, Chlamydia) that are spread through sexual contact.
Diaphragm
A non-hormonal barrier method consisting of a silicone dome placed over the cervix before sex; must be used with spermicide.
Spermicide
A chemical substance that disables or kills sperm, often used alongside barrier methods like diaphragms.
Put your knowledge into practice — try past paper questions for Biology B
Oestrogen
A female reproductive hormone used in combined contraceptives that helps trigger negative feedback to inhibit FSH and LH.
Progesterone
A female reproductive hormone that thickens cervical mucus and thins the uterine lining to prevent pregnancy.
Negative feedback
A regulatory mechanism where a stimulus (such as high hormone levels) causes a response that does the opposite (stopping the production of further hormones).
Pituitary gland
A small gland in the brain that releases FSH and LH, which are inhibited by hormonal contraceptives.
FSH
Follicle Stimulating Hormone; a hormone released by the pituitary gland that causes an egg to mature in the ovary.
LH
Luteinising Hormone; a hormone released by the pituitary gland that triggers ovulation.
Follicle
A ball of cells inside the ovary that contains and protects a developing egg cell.
Ovulation
The release of a mature egg from a follicle in the ovary into the fallopian tube.
Cervical mucus
Fluid produced by the cervix that is thickened by progesterone to create a physical block against sperm.
Endometrium
The mucous membrane lining the uterus, which is thinned by progesterone to prevent an embryo from attaching.
Fertilisation
The fusion of the nuclei of a sperm and an egg.
Implantation
The stage of reproduction where a fertilised egg (embryo) adheres to the wall of the uterus.
Transdermal
A route of administration where ingredients (like hormones in a patch) are absorbed across the skin directly into the bloodstream.
LARC
Long-Acting Reversible Contraception (e.g., implants or IUDs) that are highly effective because they do not rely on daily user compliance.
IUS
Intrauterine System; a small, plastic, T-shaped device inserted into the uterus that releases progesterone.
Condoms
Barrier methods (male or female) that prevent sperm from entering the vagina; the only contraceptive method that protects against STIs.
STIs
Sexually Transmitted Infections (e.g., HIV, Chlamydia) that are spread through sexual contact.
Diaphragm
A non-hormonal barrier method consisting of a silicone dome placed over the cervix before sex; must be used with spermicide.
Spermicide
A chemical substance that disables or kills sperm, often used alongside barrier methods like diaphragms.
