Sexually transmitted infections — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

Section 1 of 29Sexually transmitted infections

STI

STI an infection transmitted through sexual contact.

• Unprotected intercourse can pass pathogens through the exchange of body fluids.

HIV

• HIV the human immunodeficiency virus is a pathogen that causes an STI.

AIDS

• HIV infection may lead to acquired immunodeficiency syndrome.

Section 2 of 29Other STIs

Infection	Pathogen	Treatment
Chlamydia	Bacterium	Antibiotics
Gonorrhoea	Bacterium	Antibiotics
Genital herpes	Virus	Antiviral drugs relieve symptoms
HIV	Virus	Antiretroviral drugs control it; no cure

Section 3 of 29Transmission of HIV

Sexual intercourse

• Sexual intercourse through exchange of body fluids.

Sharing needles

• Sharing needles with an infected person.

Blood transfusion

• Blood transfusion with infected blood.

Mother to baby

• Mother to baby through the placenta, and in breast milk.

Section 4 of 29How HIV affects the immune system

1

HIV enters the body and often causes mild flu-like symptoms.

2

The symptoms pass and the person may not know they are infected.

3

HIV infects a type of lymphocyte and uses its machinery to multiply.

4

HIV avoids recognition by repeatedly changing its protein coat.

5

The number of lymphocytes and the antibodies they make fall.

6

The immune system weakens and opportunistic infections occur, leading to AIDS.

Section 5 of 29Controlling the spread

Method	How it helps
Limit the number of sexual partners	Reduces exposure
Use condoms	Barrier to body fluids; also prevent pregnancy
Get tested after unprotected sex	Allows early treatment
Screen blood donations	Removes infected blood
Do not share needles	Stops blood transfer
Education programmes	Raise awareness

Section 6 of 29More from the specification

1

Pathogen invasion of mucosal epithelial cells

• Pathogen invasion of mucosal epithelial cells sexually transmitted bacteria and viruses adhere to and invade genital epithelial cells, triggering inflammatory responses.

2

Pituitary gland

• The master gland whose hormones control other glands.

3

Structural adaptation

• An adaptation of body form.

4

Pathogenesis and Impact of Human Immunodeficiency Virus (HIV) — HIV infects and progressively destroys CD4+ helper T lymphocytes, impairing the adaptive immune system and eventually leading to Acquired Immune Deficiency Syndrome (AIDS).

5

Transmission Routes of Sexually Transmitted Infections

• Pathogens causing STIs are transmitted through unprotected sexual intercourse, exposure to contaminated blood, needle sharing,
  • and vertically from mother to foetus during childbirth or breastfeeding.
  • (such as HIV, gonorrhea, and chlamydia)

6

Prevention and Management Strategies for STIs

• Transmission rates are effectively minimized through the consistent use of barrier contraceptives (condoms), comprehensive public screening, prophylactic antiretroviral therapies,
  • and contact tracing.

7

Hormone

• A chemical substance produced by a gland and carried by the blood that alters the activity of specific target organs.

8

Variation

• Differences between individuals of the same species.

9

Germination

• The start of growth of a seed.

10

Oestrogen

• The main female sex hormone, made in the ovaries.

11

Progesterone

• A hormone that maintains the uterus lining.

12

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

13

Menstrual cycle

• A monthly series of changes in the female reproductive system controlled by hormones.

14

Genetically identical

• Having the same alleles

15

Pollen

• Grains made by plants, each type with a different shape.

16

Fertilisation

• The fusion of the nuclei of a male and a female gamete.

17

Reproduction

• The processes that make more of the same kind of organism.

18

Gamete

• A haploid sex cell.

19

Uterus

• The organ in which the foetus develops.

20

Pollination

• Transfer of pollen from an anther to a stigma.

Section 7 of 29What an STI is

STI

STI an infection passed from an infected person to another during sexual contact.

Pathogens

• Pathogens live in body fluids such as semen, vaginal fluid and blood.

Entry

• Entry they enter through the delicate lining of the reproductive tract.

Section 8 of 29Common STIs

Infection	Pathogen	Features	Treatment
Gonorrhoea	Bacterium	Discharge, pain on urination; can cause infertility	Antibiotics
Chlamydia	Bacterium	Often no symptoms; can cause infertility	Antibiotics
Syphilis	Bacterium	Sores, later organ damage	Antibiotics
Genital herpes	Virus	Painful blisters that recur	Antiviral drugs relieve symptoms
HIV	Virus	Attacks the immune system; leads to AIDS	Antiretroviral drugs

• Bacterial STIs are treated with antibiotics; viral STIs cannot be cured by antibiotics.

Section 9 of 29Other STIs

HPV

• HPV a virus causing genital warts and cervical cancer; a vaccine is available.

Hepatitis B

• Hepatitis B a virus affecting the liver, spread in blood and body fluids; a vaccine is available.

Section 10 of 29Transmission routes

Sexual contact

• Sexual contact through exchange of body fluids, or skin contact for herpes.

Blood

• Blood shared needles and contaminated blood products.

Mother to baby

• Mother to baby across the placenta, at birth or in breast milk.

HIV is not spread by touching, hugging, sharing food or toilet seats.

Section 11 of 29Symptoms and testing

Symptoms

• Symptoms unusual discharge, pain when urinating, itching, sores or blisters, and lower abdominal pain.

Silent infection

• Silent infection many STIs, especially chlamydia, have few or no symptoms, so people pass them on unknowingly.

Tests

• Tests a urine sample or swab, and blood tests for HIV and syphilis.

Section 12 of 29Complications if untreated

Chlamydia and gonorrhoea

• Chlamydia and gonorrhoea can cause pelvic inflammatory disease, scarring of the oviducts, infertility and ectopic pregnancy.

Men

• Men can suffer inflammation of the epididymis.

Syphilis

• Syphilis can damage the heart and brain years later.

Babies

• Babies of infected mothers may suffer eye infections or other serious illness, so screening in pregnancy is common.

Another STI

• Another STI damaged tissue and inflammation make infection with another STI, such as HIV, more likely.

Section 13 of 29More from the specification

1

Gametes and Fertilisation in Plants

• In flowering plants, male gametes contained within pollen grains fertilise the female egg cells located inside the ovules of the flower ovary.

2

Flower Adaptations for Pollination

• Insect-pollinated flowers have large petals and sticky pollen to facilitate pollen transfer,
• whereas wind-pollinated flowers produce abundant, aerodynamic pollen grains.

3

Human Fertilisation and Embryo Implantation

• In human reproduction, mobile sperm cells travel to fertilise the female ovum;
  • the resulting embryo implants into the endometrial lining of the uterus.

4

STI Transmission and Prevention

• Sexually transmitted infections are pathogens passed during sexual intercourse that can damage reproductive organs and are prevented by barrier contraception.
  • (including the female uterus)

5

Pituitary gland

• The master gland whose hormones control other glands.

6

Structural adaptation

• An adaptation of body form.

7

Hormone

• A chemical substance produced by a gland and carried by the blood that alters the activity of specific target organs.

8

Variation

• Differences between individuals of the same species.

9

Germination

• The start of growth of a seed.

10

Oestrogen

• The main female sex hormone, made in the ovaries.

11

Progesterone

• A hormone that maintains the uterus lining.

12

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

13

Menstrual cycle

• A monthly series of changes in the female reproductive system controlled by hormones.

14

Genetically identical

• Having the same alleles

15

Pollen

• Grains made by plants, each type with a different shape.

16

Fertilisation

• The fusion of the nuclei of a male and a female gamete.

17

Gamete

• A haploid sex cell.

18

Uterus

• The organ in which the foetus develops.

19

Pollination

• Transfer of pollen from an anther to a stigma.

Section 14 of 29HIV and AIDS

HIV

HIV the human immunodeficiency virus, which infects and destroys lymphocytes (T helper cells) that coordinate the immune response.

AIDS

AIDS acquired immune deficiency syndrome, the late stage when the body can no longer fight infections and certain cancers.

Section 15 of 29Course of infection

Stage	Features
Early infection	Flu-like symptoms within weeks, then often none
Latent period	The virus multiplies; lymphocytes slowly fall; often lasts years
AIDS	Severe infections such as tuberculosis and pneumonia, weight loss, certain cancers

• The person can pass on the virus at every stage, including when feeling well.

Section 16 of 29How HIV defeats immunity

Normal response

• Normal response lymphocytes make antibodies and destroy infected cells.

Entry

• HIV enters T helper cells using surface proteins and copies its genetic material inside them.

Release

• Release new viruses burst out and infect more cells.

Reduced immunity

• Reduced immunity destroying T helper cells lowers the efficiency of the whole immune system.

Avoiding recognition

• HIV repeatedly changes its protein coat, so antibodies for one form may not recognise another.

Section 17 of 29Transmission

Can spread HIV	Cannot spread HIV
Unprotected sex	Hugging or shaking hands
Sharing needles or syringes	Sharing cups or food
Infected blood transfusion	Toilets or swimming pools
Mother to baby in pregnancy, birth or breast milk	Insect bites

Section 18 of 29Control and treatment

Control and treatment

Antiretroviral drugs

• Antiretroviral drugs slow replication so people stay healthy for years and are much less likely to pass it on.

Combined drugs

• Combined drugs used because a single drug lets resistant viruses survive.

Undetectable viral load

• Undetectable viral load daily treatment can reduce the virus to undetectable levels.

Condoms

• Condoms reduce the risk of sexual transmission.

Screening donated blood and sterile needles

• Screening donated blood and sterile needles protect others.

Pregnant women

• Pregnant women treatment greatly lowers the risk to the baby.

No cure

• No cure there is no cure or widely available vaccine because HIV mutates quickly.

Section 19 of 29Testing and living with HIV

Testing

• Testing antibody tests show infection, though antibodies may take a few weeks to appear.

Early diagnosis

• Early diagnosis with lifelong treatment a person can expect a near-normal lifespan.

Monitoring

• Monitoring viral load and lymphocyte numbers are checked regularly.

Stigma

• Stigma discourages testing, so confidentiality and education are important.

Section 20 of 29More from the specification

1

Sexual Reproduction in Flowering Plants

• Pollen grains containing male gametes are transferred to female flower structures during pollination,
• leading to fertilisation within the ovary.

2

Gamete Adaptations in Plants and Animals

• Male plant pollen is adapted for transport by wind or insects,
• whereas human sperm cells possess flagella and mitochondria to swim towards the female ovum.

3

Human Fertilisation and Gestation

• Following fertilisation of an ovum by a sperm cell, the diploid zygote divides and implants in the wall of the female uterus to undergo embryonic development.

4

Reproductive Health and STIs

• Sexually transmitted pathogens can cause pelvic inflammatory disease and scarring of the fallopian tubes or uterus, impairing natural fertilisation and fertility.

5

Pituitary gland

• The master gland whose hormones control other glands.

6

Structural adaptation

• An adaptation of body form.

7

Hormone

• A chemical substance produced by a gland and carried by the blood that alters the activity of specific target organs.

8

Variation

• Differences between individuals of the same species.

9

Germination

• The start of growth of a seed.

10

Oestrogen

• The main female sex hormone, made in the ovaries.

11

Progesterone

• A hormone that maintains the uterus lining.

12

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

13

Menstrual cycle

• A monthly series of changes in the female reproductive system controlled by hormones.

14

Genetically identical

• Having the same alleles

15

Pollen

• Grains made by plants, each type with a different shape.

16

Fertilisation

• The fusion of the nuclei of a male and a female gamete.

17

Reproduction

• The processes that make more of the same kind of organism.

18

Gamete

• A haploid sex cell.

19

Uterus

• The organ in which the foetus develops.

20

Placenta

• The organ where substances are exchanged between mother and foetus.

21

Pollination

• Transfer of pollen from an anther to a stigma.

Section 21 of 29Principles of prevention

Break the chain

• Break the chain reduce contact with infected fluids, find and treat infected people, and educate.

Combination

• Combination no single method is perfect, so several are used together.

Section 22 of 29Methods and how they work

Method	How it works	Limit
Condoms	Barrier stops body fluids passing between partners	Must be used correctly every time
Abstinence or one faithful uninfected partner	Avoids exposure	Relies on trust and honesty
Not sharing needles	Stops blood contact	Needs clean equipment
Screening blood donations	Removes infected blood	Cost
Testing and treatment	Cures bacterial STIs and controls viral ones	People may avoid testing
Vaccination	Prevents hepatitis B and HPV	None for HIV

• Hormonal contraceptives, withdrawal and natural methods do not protect.

Section 23 of 29Partner notification and education

Partner notification and education

Treatment

• Treatment an infected person is tested and treated.

Contact tracing

• Contact tracing recent partners are traced and offered testing.

Education

• Education programmes explain risks, safer sex and how infections spread.

Confidential clinics

• Confidential clinics encourage people to attend.

Pregnant women

• Pregnant women treatment prevents infection of the baby.

Section 24 of 29Vaccination

HPV vaccine

• HPV vaccine given to adolescents, greatly reduces cervical cancer risk.

Hepatitis B vaccine

• Hepatitis B vaccine part of many routine immunisation schedules.

HIV

• HIV research on vaccines continues, and pre-exposure drugs can protect people at high risk.

Section 25 of 29Evaluating strategies

Evaluating strategies

Condoms

• Condoms cheap, widely available and effective, but depend on behaviour.

Treatment of bacterial STIs

• Treatment of bacterial STIs effective, but growing antibiotic resistance makes gonorrhoea harder to treat.

Antiretroviral therapy

• Antiretroviral therapy lowers viral load, improves health and reduces transmission, but is lifelong and expensive.

Best approach

• Best approach combines education, condom use, testing, treatment and a safe blood supply.

Barriers

• Barriers stigma, cultural beliefs, poverty and access to clean needles.

Section 26 of 29Prevention in different settings

1Schools

• Schools teach about safe sex and the risks of drug misuse.

2Clinics

• Clinics offer free confidential testing.

3Governments

• Governments run public campaigns and provide condoms freely.

4Limited health care regions

• Limited health care regions aim to make testing and treatment accessible and affordable.

Section 27 of 29More from the specification

1

Pollen adaptations in flowering plants

• Pollen adaptations in flowering plants insect-pollinated flower species produce sticky, spiked pollen grains that adhere readily to visiting pollinators during sexual reproduction.

2

Plant sexual fertilisation and gametes

• Plant sexual fertilisation and gametes transfer of haploid pollen nuclei down styles enables fertilisation with female egg cells within plant ovules.

3

Mammalian gamete fusion and uterus implantation

• Mammalian gamete fusion and uterus implantation haploid gamete cells fuse during internal fertilisation,
  • forming blastocysts that travel towards the female uterus wall.

4

Sexually Transmitted Infections

• Pathogenic viruses and bacteria that cause STIs are transmitted primarily through intimate sexual contact, contact with infected bodily fluids,
• or vertically to developing embryos in the female uterus.

5

Human Fertilisation and Uterine Development

• Human sexual reproduction requires the fusion of male and female haploid gametes during fertilisation in the oviduct, followed by embryo implantation and growth in the uterus.

6

Floral Structure and Pollination

• In flowering plants, sexual reproduction begins when pollen grains are transferred from anthers to the female stigma of a flower by wind or animal pollinators.

7

Gametes and Fertilisation Across Kingdoms

• Both flowering plants and mammals produce haploid gamete cells that unite during fertilisation to form a diploid zygote that divides to form a new individual.

8

Pituitary gland

• The master gland whose hormones control other glands.

9

Structural adaptation

• An adaptation of body form.

10

Pollination

• Transfer of pollen from an anther to a stigma.

11

Variation

• Differences between individuals of the same species.

12

Germination

• The start of growth of a seed.

13

Oestrogen

• The main female sex hormone, made in the ovaries.

14

Progesterone

• A hormone that maintains the uterus lining.

15

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

16

Menstrual cycle

• A monthly series of changes in the female reproductive system controlled by hormones.

17

Genetically identical

• Having the same alleles

18

Pollen

• Grains made by plants, each type with a different shape.

19

Fertilisation

• The fusion of the nuclei of a male and a female gamete.

20

Reproduction

• The processes that make more of the same kind of organism.

21

Gamete

• A haploid sex cell.

22

Uterus

• The organ in which the foetus develops.

23

Placenta

• The organ where substances are exchanged between mother and foetus.

Section 28 of 29Key terms

Term	Meaning
STI	An infection passed on by sexual contact.
HIV	A virus that attacks lymphocytes of the immune system.
AIDS	The late stage of HIV infection when the immune system cannot fight infections.
Lymphocyte	A white blood cell of the immune system.
Condom	A barrier that reduces the spread of STIs.
Antiretroviral drug	A drug that controls HIV infection.

Term	Meaning
STI	An infection passed on by sexual contact.
Chlamydia	A bacterial STI that often has no symptoms.
Gonorrhoea	A bacterial STI treated with antibiotics.
Genital herpes	A viral STI causing recurrent blisters.
Ectopic pregnancy	A pregnancy outside the uterus, often in the oviduct.
Infertility	Inability to have children.

Term	Meaning
HIV	A virus that infects lymphocytes and weakens the immune system.
AIDS	The late stage of HIV infection.
T helper cell	A lymphocyte that coordinates the immune response.
Antibody	A protein made by lymphocytes that attaches to pathogens.
Viral load	The amount of virus in the blood.
Opportunistic infection	An infection that takes hold because immunity is weak.

Term	Meaning
Condom	A barrier that prevents body fluids passing between partners.
Screening	Testing blood or people to find infection.
Contact tracing	Finding and testing the recent partners of an infected person.
Vaccination	Giving a vaccine to prevent infection.
Antiretroviral therapy	Drug treatment that controls HIV.

Section 29 of 29Exam technique

1

Saying HIV and AIDS are the same — HIV is the virus and AIDS is the late syndrome.

2

Saying antibiotics treat HIV — antibiotics do not affect viruses.

3

Saying HIV spreads by touch or hugging — it spreads by body fluids and blood.

4

Saying treatment cures HIV — antiretroviral drugs control it.

1

Saying antibiotics treat viral STIs — antibiotics act only on bacteria.

2

Saying you can tell by looking at a person — many infections show no symptoms.

3

Saying HIV spreads by mosquitoes or hugging — it does not.

4

Saying only women are affected — both sexes can be infected.

1

Treating HIV and AIDS as the same thing — HIV is the virus, AIDS is the syndrome.

2

Saying HIV spreads by touching — it does not.

3

Saying drugs cure HIV — they control it.

4

Saying infected people always look ill — there may be no symptoms for years.

1

Thinking the pill is safe sex — it gives no protection against STIs.

2

Saying treatment alone stops transmission — prevention methods are also needed.

3

Ignoring that bacterial STIs can become resistant — antibiotic resistance may make treatment fail.

4

Saying one method is enough — a combination of measures works best.