Life Processes

Section: Biology | Syllabus: Cambridge Primary Science (0846)

Physical Changes During Puberty

Puberty is the stage in life when you continue to grow and develop into an adult
- these changes are caused by chemicals in the body called hormones
Timing: usually starts around 11 for girls and 13 for boys
Growth spurt: fast growth in height
- girls can grow up to 12 cm a year, boys up to 10 cm
Skin: becomes oilier, and many get pimples
Body odour: sweat glands become more active, so body odour can develop - regular washing helps control it
Body hair: starts to grow in the armpits and other parts
- boys also grow hair on the face
Voice: becomes deeper for both, though more noticeable in boys
Body shape: boys' shoulders broaden; girls' hips widen and breasts develop
Menstruation: starting about a year after puberty begins, girls start having periods (see the Human Reproductive System topic for details)

Question: what causes the physical changes that happen during puberty?
- Answer: the changes are caused by chemicals in the body called hormones

Diseases stop our bodies from working properly - infectious diseases are caused by tiny living things that infect, grow and reproduce on or in our bodies
A parasite is any living thing that lives on or in the body of another living thing
A host is the living thing that a parasite infects

A parasite lives on or in its host, such as a mosquito on skin or a tapeworm in the gut

Type of Pathogen	Details & Examples
Bacteria	Very small, seen with a microscope. Cause cholera and pneumonia (not all are harmful)
Viruses	Smaller than bacteria. All are harmful. Cause flu, chicken pox and measles
Fungi	Some are parasites. Cause ringworm and athlete's foot
Other parasites	Organisms that cause diseases like malaria and dysentery

Good hygiene means keeping yourself and the things around you clean, to help prevent diseases from spreading

Good hygiene: wash hands with soap and water before eating, after the toilet, and after handling animals, then dry them well
Safe food: wash raw fruits and vegetables, keep raw and cooked food separate, keep food covered, chill/refrigerate food that spoils easily, check expiry dates, and don't leave food at room temperature in hot weather
- bacteria grow fastest in food kept between about 5°C and 60°C - most bacteria are killed once food is cooked to 65-75°C, and a fridge (around 0°C) slows their growth
Clean surfaces: keep kitchens and toilets clean, and wash knives and surfaces with hot soapy water
Safe water: drink only clean water - boil water from rivers or treat it with bleach
Respiratory hygiene: cover your nose and mouth with a tissue or your elbow when coughing or sneezing, wear a mask if you are unwell, and avoid close contact with others when sick
Wound care: keep wounds covered with a plaster

Some serious diseases, like malaria and yellow fever, are spread by mosquitoes
- these insects are vectors - they spread the parasite but don't get the disease themselves
To prevent bites: sleep under bed nets, wear long sleeves, use insect repellent, and keep doors/windows closed at night

Simple ways to prevent insect bites and the diseases they can spread

Question: what is an insect vector?
- Answer: an insect that spreads a disease parasite when it bites you, but does not get the disease itself (e.g. a mosquito spreading malaria)

The body has natural ways to keep pathogens out:

Skin: a barrier that stops germs from getting into the body
Stomach acid: kills any germs in food we have eaten
Mucus: sticky liquid in the nose, windpipe and air passages that traps germs
Tears: contain a chemical substance that kills some bacteria
White blood cells: part of the body's immune system - if germs do get into the body, white blood cells destroy them, including by making antibodies that target specific germs

❌ Thinking stomach acid "digests" germs
- ✓ stomach acid actually kills germs, because it is a very strong acid

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