Digestion starts with your first bite. Each type of tooth has a job, and all that chewing gives enzymes more to work on.
🍎 Physical digestion
Physical digestion breaks food into smaller pieces without any chemical change to the molecules. It increases the surface area of food for enzymes to act on.
incisors: chisel-shaped, biting and cutting
canines: pointed, gripping and tearing
premolars: chewing and grinding
molars: chewing and grinding
the stomach also churns food, which is physical digestion
🖼️ See it
Physical digestion breaks food up without changing its molecules.
🔬 Inside a tooth
A tooth is embedded in the bone and gums. Enamel is the hard outer layer, with dentine beneath it. The central pulp holds nerves and blood vessels, and cement helps anchor the root.
Bile also helps. It emulsifies fats into small droplets, which is physical digestion too, because the fat molecules do not change.
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Definition
Physical digestion is the breakdown of food:
The molecules do not change.
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Why chew?
Chewing helps chemical digestion by:
Smaller pieces, more surface.
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Incisors
Incisors are used for:
The front teeth.
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Molars
Molars are used for:
The big back teeth.
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Structure
The hard outer layer of a tooth is the:
The part you can see.
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Pulp
Nerves and blood vessels are found in the:
The soft centre.
✍️ Type your answer · 7 of 8
Each half of an adult’s upper jaw typically has 2 incisors, 1 canine, 2 premolars and 3 molars.
How many teeth is that in one half of the jaw?
Enter an exact answer, without rounding.
Add them up.
✍️ Type your answer · 8 of 8
A full adult set has 8 teeth in each of the four quarters of the mouth.
How many teeth is that altogether?
Enter an exact answer, without rounding.
Multiply by 4.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Canines are mainly used for:
Question 2 of 5
Which is an example of physical digestion?
Question 3 of 5
Dentine is found:
Question 4 of 5
Teeth are embedded in the:
Question 5 of 5
Bile emulsifying fat is:
Lesson 2 · Disease
🦠 Cholera
One bacterium in dirty water can kill a person within days, simply by making the body lose water. The cure can be as simple as clean water and salts.
💧 How cholera spreads
Cholera is a disease caused by a bacterium that is transmitted in contaminated water. It spreads where sewage mixes with drinking water.
prevention:
clean water supply
proper sewage treatment
good hygiene and hand-washing
vaccination
🖼️ See it
The bacterium does not need to destroy the gut. Moving ions is enough to make the body lose water.
⚙️ How the toxin works
The bacterium produces a toxin, which causes a chain of events in the gut.
1. the toxin causes chloride ions to be secreted into the small intestine
2. this lowers the water potential in the gut
3. water moves into the gut by osmosis
4. this causes severe diarrhoea
5. the result is dehydration and loss of ions from the blood
Link it to osmosis. Water follows the ions, moving from the blood into the gut.
✏️ Quick check · 1 of 8
Cause
Cholera is caused by a:
It makes a toxin.
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Spread
Cholera is transmitted in:
Think about sewage.
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Toxin
The cholera toxin causes secretion of which ions into the small intestine?
Part of table salt.
✏️ Quick check · 4 of 8
Water
Water enters the gut during cholera by:
Water follows the ions.
✏️ Quick check · 5 of 8
Effect
The severe diarrhoea causes:
What is the body losing?
✏️ Quick check · 6 of 8
Prevention
Which best prevents cholera in a city?
Break the route of spread.
✍️ Type your answer · 7 of 8
A cholera patient loses 12 litres of water in 2 days, at a steady rate.
How many litres is that per day?
Enter an exact answer, without rounding.
litres
Divide.
✍️ Type your answer · 8 of 8
Of 200 people drinking contaminated water, 15% develop severe cholera.
How many people is that?
Enter an exact answer, without rounding.
Find 15% of 200.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
The cholera bacterium harms the body mainly by:
Question 2 of 5
Where does the cholera toxin act?
Question 3 of 5
Why is cholera dangerous?
Question 4 of 5
Which treatment replaces what cholera removes?
Question 5 of 5
Chloride ions in the gut lower the:
Lesson 3 · Coordination
👁️ The Eye & Pupil Reflex
Your eyes refocus and adjust to brightness all day without you thinking about it. Each part has a precise job.
🔎 Parts of the eye
Sense organs are groups of receptor cells that respond to specific stimuli, such as light, sound, touch, temperature and chemicals.
cornea: refracts light
iris: controls how much light enters the pupil
lens: focuses light on to the retina
retina: contains light receptors
optic nerve: carries impulses to the brain
blind spot: where the optic nerve leaves; no receptors
🖼️ See it
The optic nerve then carries impulses from the retina to the brain.The two sets of muscles are antagonistic: when one contracts, the other relaxes.
☀️ The pupil reflex
In bright light the pupil gets smaller, protecting the retina. In dim light it gets larger, letting more light in. This works through two antagonistic muscles in the iris.
Accommodation means changing the shape of the lens to focus. Rods work in dim light; cones detect colour and fine detail, and are packed into the fovea.
near object: ciliary muscles contract, ligaments slacken, lens fatter
far object: ciliary muscles relax, ligaments tighten, lens thinner
Near means fat. A nearby object needs a fatter lens to bend the light more.
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Cornea
The cornea’s function is to:
It bends the light.
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Iris
The iris controls:
The coloured part.
✏️ Quick check · 3 of 8
Retina
Light receptors are found in the:
At the back of the eye.
✏️ Quick check · 4 of 8
Blind spot
The blind spot has no receptors because it is where the:
The nerve exits here.
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Bright light
In bright light, the pupil:
Protect the retina.
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Muscles
In bright light, the circular muscles of the iris:
Circular narrows.
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Receptors
Which receptors detect colour?
C for colour.
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Near
To focus on a nearby object, the lens becomes:
More bending is needed.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Which part focuses light on to the retina?
Question 2 of 5
The optic nerve carries:
Question 3 of 5
The fovea is packed with:
Question 4 of 5
Muscles that work in opposite ways are described as:
Question 5 of 5
To focus on a far object, the ciliary muscles:
Lesson 4 · Plant responses
🌱 Tropisms & Auxin
Plants have no muscles or nerves, yet shoots still find the light and roots still find the soil. A single chemical makes this happen.
🌻 Tropic responses
Phototropism is growth towards or away from the direction of light. Gravitropism is growth towards or away from gravity.
shoots: grow towards light, away from gravity
roots: grow away from light, towards gravity
Investigation: put seedlings in a box with light from one side.
The shoots bend towards the light.
A control group gets even light or none.
🖼️ See it
These responses take shoots to the light and roots down to water and minerals.The shaded side grows faster, so the shoot curves towards the light.
🧪 How auxin works
Auxin is a plant growth regulator. It is made in the shoot tip and diffuses through the plant. It stimulates cell elongation, so the side with more auxin grows longer and the shoot bends.
phototropism in a shoot:
1. auxin collects on the shaded side
2. cells on the shaded side elongate more
3. the shoot bends towards the light
gravitropism in a horizontal shoot:
auxin collects on the lower side, and the shoot bends upward
Common mistake: the cells on the lit side do not shrink. The shaded side simply grows faster.
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Phototropism
Phototropism is a growth response to:
Photo means light.
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Gravitropism
Gravitropism is a growth response to:
Gravi- for gravity.
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Shoots
A plant shoot shows:
Shoots need light.
✏️ Quick check · 4 of 8
Roots
A plant root grows:
Think about soil.
✏️ Quick check · 5 of 8
Source
Auxin is made in the:
At the very top.
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Effect
Auxin makes shoot cells:
Cells get longer.
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Which side?
In a shoot lit from one side, auxin collects:
The side away from light.
✍️ Type your answer · 8 of 8
In a test, 25 seedlings were lit from the left, and 80% bent to the left.
How many seedlings bent to the left?
Enter an exact answer, without rounding.
Find 80% of 25.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
Which is the best description of auxin?
Question 2 of 5
A shoot tip is removed, then the plant is lit from one side. The shoot will:
Question 3 of 5
A shoot placed horizontally in the dark will:
Question 4 of 5
Why does a shoot benefit from phototropism?
Question 5 of 5
In a phototropism experiment, the control group has:
Lesson 5 · Reproduction
👶 Human Reproduction
Every human life begins as a single cell. This lesson follows it from the two gametes to a fetus ready to be born.
🧬 The reproductive systems
Each part of the reproductive system has a specific function.
MALE
testes: make sperm and testosterone
scrotum: holds the testes
sperm ducts: carry sperm
prostate gland: adds fluid to make semen
urethra: carries semen out through the penis
FEMALE
ovaries: make egg cells and hormones
oviducts: carry the egg; site of fertilisation
uterus: where the fetus develops
cervix: the ring of muscle at the neck of the uterus
vagina: where sperm are received; the birth canal
🖼️ See it
Each gamete is adapted to its job, and each holds half the usual number of chromosomes.The two blood supplies stay separate, and substances cross the placenta.
🔬 Gametes and fertilisation
Fertilisation is the fusion of the nuclei of a sperm and an egg cell. The resulting zygote forms an embryo, a ball of cells that implants in the lining of the uterus.
sperm: flagellum to swim, mitochondria for energy,
acrosome enzymes to enter the egg
egg: energy stores, jelly coat that changes at fertilisation
COMPARED
size: sperm tiny, egg far larger
movement: sperm swim, egg does not
numbers: sperm in millions, egg usually one a month
🤰 Developing fetus
The placenta exchanges glucose, oxygen, water and ions from the mother with carbon dioxide and urea from the fetus. The umbilical cord joins the fetus to the placenta. The amniotic sac and fluid protect the fetus.
The placenta is a barrier, but not a perfect one. Some pathogens and toxins can cross it. This is why alcohol and smoking are harmful in pregnancy.
✏️ Quick check · 1 of 8
Testes
The testes produce:
Male gametes.
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Oviduct
Fertilisation normally takes place in the:
The tube from the ovary.
✏️ Quick check · 3 of 8
Definition
Fertilisation is the fusion of:
Sperm and egg.
✏️ Quick check · 4 of 8
Sperm
A sperm cell has many mitochondria to:
They respire.
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Acrosome
Enzymes in the acrosome allow the sperm to:
Getting inside.
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Placenta
Which passes from fetus to mother across the placenta?
Waste products.
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Amnion
The amniotic fluid’s role is to:
A cushion.
✍️ Type your answer · 8 of 8
A body cell has 46 chromosomes and a gamete has half that number.
How many chromosomes are in a human egg cell?
Enter an exact answer, without rounding.
Halve it.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Which structure joins the fetus to the placenta?
Question 2 of 5
The embryo implants in the:
Question 3 of 5
Compared with a sperm cell, an egg cell is:
Question 4 of 5
The prostate gland:
Question 5 of 5
Why should pregnant women avoid alcohol?
Lesson 6 · Reproduction
📅 Sex Hormones & STIs
Hormones drive the changes of puberty and run a monthly cycle. Understanding them also helps you protect your health.
🌱 Puberty
Testosterone (made in the testes) and oestrogen (made in the ovaries) control the development and regulation of secondary sexual characteristics during puberty.
testosterone: facial hair, deeper voice, muscle growth
oestrogen: breast development, wider hips, start of periods
both: body hair, growth spurt
🖼️ See it
If the egg is not fertilised, progesterone falls and the cycle starts again.
🔄 The menstrual cycle
The menstrual cycle lasts about 28 days. It involves changes in the ovaries and in the lining of the uterus, under the control of four hormones.
day 1–5: the uterus lining breaks down (menstruation)
FSH (pituitary): an egg develops in the ovary
oestrogen (ovary): rebuilds the lining
LH (pituitary): triggers ovulation at about day 14
progesterone (ovary): maintains the lining
no fertilisation: progesterone falls and the cycle restarts
pregnancy: the placenta makes progesterone and oestrogen
🛡️ Sexually transmitted infections
A sexually transmitted infection (STI) is an infection that is transmitted through sexual contact. HIV is a pathogen that causes an STI, and HIV infection may lead to AIDS.
HIV is transmitted by:
unprotected sexual contact
shared needles
infected blood
mother to baby
STIs are controlled by:
condoms
testing and treatment
not sharing needles
screening donated blood
HIV is not spread by everyday contact such as hugging or sharing a meal.
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Oestrogen
Oestrogen is made mainly in the:
The female gonads.
✏️ Quick check · 2 of 8
Testosterone
Testosterone causes the development of:
During male puberty.
✏️ Quick check · 3 of 8
FSH
FSH stimulates:
F for follicle.
✏️ Quick check · 4 of 8
LH
A surge of LH triggers:
Release of the egg.
✏️ Quick check · 5 of 8
Progesterone
Progesterone’s main job is to:
It keeps things ready.
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HIV
HIV infection may lead to:
The immune system fails.
✏️ Quick check · 7 of 8
Control
Which helps to control the spread of STIs?
A barrier method.
✍️ Type your answer · 8 of 8
A menstrual cycle lasts 28 days, and ovulation happens halfway through.
On about which day does ovulation happen?
Enter an exact answer, without rounding.
Halve it.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Menstruation is the breakdown of the:
Question 2 of 5
During pregnancy, progesterone and oestrogen are made by the:
Question 3 of 5
FSH and LH are both released by the:
Question 4 of 5
HIV can be transmitted by:
Question 5 of 5
Which change is caused by oestrogen?
Lesson 7 · Biotechnology
🧫 Biotechnology & Genetic Modification
Yeast raises your bread, enzymes clean your clothes, and bacteria make the insulin that keeps millions of people alive.
🍞 Everyday biotechnology
Yeast respires anaerobically, producing ethanol and carbon dioxide. Enzymes are used to make many useful products.
biofuel: yeast makes ethanol from sugar
bread: yeast makes CO₂, and the dough rises
fruit juice: pectinase breaks down cell walls, giving more juice
washing powder: enzymes remove stains at low temperature
lactose-free milk: lactase breaks down lactose
🖼️ See it
Using the same restriction enzymes gives matching sticky ends.Keeping these steady gives the microbes the best conditions to grow.
🏭 Fermenters
Fermenters grow bacteria and fungi on a large scale to make products such as insulin, penicillin and mycoprotein. Conditions must be carefully controlled.
temperature: too hot denatures enzymes; a water jacket cools it
pH: kept at the best value for enzymes
oxygen: needed for aerobic respiration
nutrients: supply the energy and materials for growth
waste products: removed so they do not poison the microbes
✂️ Genetic modification
Genetic modification changes an organism’s genetic material by removing, changing or inserting individual genes. Examples include human proteins made by bacteria, and pest-resistant or vitamin-enriched crops.
making a human protein:
1. cut out the human gene with restriction enzymes, forming sticky ends
2. cut a bacterial plasmid with the same enzymes
3. join them with DNA ligase, forming a recombinant plasmid
4. put the recombinant plasmid into bacteria
5. the bacteria multiply and make the human protein
GM crops can raise yields and reduce pesticide use, but they raise concerns about cost to farmers, seed dependence and effects on wild plants and insects.
✏️ Quick check · 1 of 8
Yeast
When bread is made, yeast produces a gas that:
The bubbles in bread.
✏️ Quick check · 2 of 8
Biofuel
Yeast is used to produce the biofuel:
An alcohol.
✏️ Quick check · 3 of 8
Pectinase
Pectinase is used to:
It helps release juice.
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Lactase
Lactase is used to produce:
It digests milk sugar.
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Fermenter
A water jacket on a fermenter is used to control the:
Respiration gives off heat.
✏️ Quick check · 6 of 8
Product
Which is made in a fermenter?
An antibiotic.
✏️ Quick check · 7 of 8
Enzymes
In genetic modification, restriction enzymes are used to:
Molecular scissors.
✏️ Quick check · 8 of 8
Ligase
DNA ligase is used to:
It joins pieces.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
Genetic modification means:
Question 2 of 5
Biological washing powders contain:
Question 3 of 5
Why are waste products removed from a fermenter?
Question 4 of 5
A recombinant plasmid contains:
Question 5 of 5
Which is a concern about GM crops?
Final Challenge
🏆 14-Question Challenge Quiz
Questions from every topic in this course. Pick an answer for each one, then hit Check My Answers.
0 / 14
💪 Keep practicing — go back through the lessons and retake the quiz!
Q1 · Teeth & Physical Digestion
Physical digestion mainly increases food’s:
Q2 · Teeth & Physical Digestion
Which tooth is chisel-shaped for cutting?
Q3 · Cholera
Cholera is transmitted through:
Q4 · Cholera
During cholera, water moves into the gut by:
Q5 · The Eye & Pupil Reflex
In dim light, the pupil:
Q6 · The Eye & Pupil Reflex
Rods are best suited to vision in:
Q7 · Tropisms & Auxin
Auxin is made in the shoot tip and moves by:
Q8 · Tropisms & Auxin
A shoot bends towards light because cells on the shaded side:
Q9 · Human Reproduction
Which feature helps a sperm to swim?
Q10 · Human Reproduction
A fertilised egg is called a:
Q11 · Sex Hormones & STIs
Falling progesterone at the end of a cycle leads to:
Q12 · Sex Hormones & STIs
An STI is an infection that is transmitted through:
Q13 · Biotechnology & Genetic Modification
Insulin for people with diabetes can be made by:
Q14 · Biotechnology & Genetic Modification
Which condition is NOT usually controlled in a fermenter?