Before studying cells, systems, or ecosystems, it helps to know exactly what separates something "alive" from something that isn't.
📋 MRS GREN
All living things share 7 characteristics, often remembered with the mnemonic MRS GREN: Movement, Respiration (releasing energy from food), Sensitivity (responding to surroundings), Growth, Reproduction, Excretion (removing waste), and Nutrition (taking in food or energy).
📝 Worked examples
M Movement — a plant turns toward light
R Respiration — releasing energy from food
S Sensitivity — responding to the environment
G Growth — getting bigger
R Reproduction — making offspring
E Excretion — removing waste
N Nutrition — taking in food
A car moves and uses fuel, but it cannot grow or reproduce → not living.
An object must show ALL seven characteristics to be called living.
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The mnemonic
The mnemonic used to remember the 7 characteristics of living things is:
Its letters stand for Movement, Respiration, Sensitivity…
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A shared characteristic
Which of these is one of the 7 shared characteristics of all living things?
Which option is something every living thing does, from bacteria to whales?
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Excretion
"Excretion" refers to:
Ex- means out. What does the body get rid of?
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MRS GREN represents the 7 characteristics of living things.
How many total characteristics are shared by all living things?
Enter an exact answer, without rounding.
Count the letters in the mnemonic: each one is a characteristic.
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List the characteristics in order: Movement(1), Respiration(2), Sensitivity(3), Growth(4), Reproduction(5), Excretion(6), Nutrition(7).
Which position number is Growth in this list?
Enter an exact answer, without rounding.
Count along the list until you reach Growth.
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A car moves and releases energy from fuel, a bit like movement and respiration. It shows none of the other MRS GREN characteristics.
How many of the 7 characteristics does the car NOT show?
Enter an exact answer, without rounding.
Take the two it shows away from 7.
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Excretion
Excretion in living things means:
The E in MRS GREN.
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Sensitivity
A plant bending toward a window shows which characteristic?
It responds to a stimulus.
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The mnemonic MRS GREN lists the characteristics of living things.
How many characteristics does it list?
Enter an exact answer, without rounding.
Count the letters, and R appears twice.
✍️ Type your answer · 10 of 10
A seedling grows from 2 cm to 5 cm.
How many centimetres did it grow?
Enter an exact answer, without rounding.
cm
Subtract the starting height.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Respiration in living things:
Question 2 of 5
Which of these is NOT living?
Question 3 of 5
Nutrition means:
Question 4 of 5
Reproduction is the ability to:
Question 5 of 5
Which characteristic does a seed show when it starts to germinate?
Lesson 2 · Cells
🧫 Cell Structure & Function
Every living thing is made of cells — the basic unit of life. Plant cells and animal cells share some parts, but each has special structures suited to how it lives.
🔍 Plant cells vs. animal cells
Both cell types have a nucleus (the control centre), mitochondria (the powerhouse that releases energy), and a cell membrane (which controls what enters and exits). Plant cells also have a rigid cell wall, chloroplasts for photosynthesis, and a large vacuole for storage. Filling the rest of the cell around these organelles is the cytoplasm — a jelly-like substance that holds the organelles in place and is where many chemical reactions take place.
The cell is the basic unit of structure and function in living things.
All cells come from other, pre-existing cells.
📝 Worked examples
Nucleus → controls the cell, holds DNA
Mitochondria → release energy (respiration)
Cell membrane → controls what enters and leaves
Cytoplasm → where reactions happen
Ribosomes → make proteins
PLANT cells also have: cell wall, chloroplasts, large vacuole
Animal cells have none of the three extra structures. The cell wall gives plant cells a fixed shape, and chloroplasts contain chlorophyll for photosynthesis.
Which organelle is known as the "control centre" of the cell?
It holds the DNA, the cell’s instructions.
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Powerhouse of the cell
Which organelle is known as the "powerhouse" of the cell?
It releases energy from food in respiration.
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Plant-only structures
Which structure is found in plant cells but NOT in animal cells?
It is a rigid outer layer that gives plants their shape.
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Think about cell theory.
What is the minimum number of cells a living thing must have?
Enter an exact answer, without rounding.
Some living things, like bacteria, are just one cell.
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Look back at the diagram of the two cell types.
How many of these organelles appear in BOTH plant and animal cells: nucleus, mitochondria, cell membrane?
Enter an exact answer, without rounding.
Check each of the three: is it in the plant cell and the animal cell?
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Cell wall, chloroplast, and large vacuole are structures unique to plant cells.
How many of those three structures are unique to plant cells?
Enter an exact answer, without rounding.
The question tells you all three are plant-only.
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Powerhouse
Which organelle releases energy from glucose?
Think "powerhouse".
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Only plants
Which structure is found in plant cells but NOT animal cells?
Photosynthesis happens only in plants.
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Plant cells have a cell wall, chloroplasts and a large vacuole that animal cells lack.
How many structures is that?
Enter an exact answer, without rounding.
Count the structures in the list.
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A plant cell is 0.1 mm long.
How many such cells fit in a row across 1 mm?
Enter an exact answer, without rounding.
Divide the length by the cell size.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
The cell membrane:
Question 2 of 5
Chlorophyll is found in:
Question 3 of 5
Genetic material (DNA) is found in the:
Question 4 of 5
Chemical reactions in a cell take place mostly in the:
Question 5 of 5
The cell wall in a plant cell provides:
Lesson 3 · Cells
🔎 Microscopes & Magnification
Scientists use microscopes to see structures far too small for the naked eye — understanding how they work and calculating magnification is a key skill in biology.
🔬 Lenses and magnification
A light microscope has an eyepiece lens (where you look through) and an objective lens (closest to the specimen, usually a choice of several on a rotating nosepiece). Total magnification = eyepiece magnification × objective magnification. For example, an eyepiece of 10x with an objective of 40x gives a total magnification of 400x. When preparing a slide (a "wet mount"), you place the specimen on a slide, add a drop of water or stain, and cover it with a coverslip — then view it starting at low power before switching to higher power lenses.
📝 Worked examples
total magnification = eyepiece × objective
10× eyepiece with 40× objective → 400×
magnification = image size ÷ actual size
8 mm image of a 0.02 mm cell → 8 ÷ 0.02 = 400
1 mm = 1000 µm (micrometres)
Always start with the lowest-power objective, focus with the coarse knob, then switch up and use only the fine focus.
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Calculating total magnification
Total magnification of a microscope is calculated by:
The two lenses magnify one after the other, so their powers multiply.
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Closest to the specimen
Which lens is closest to the specimen being viewed?
It hangs just above the slide.
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Viewing order
Before viewing a specimen at high magnification, you should:
Low power shows more of the slide, which makes it easier to find and focus.
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A microscope has an eyepiece of 10x and an objective lens of 40x.
What is the total magnification?
Enter an exact answer, without rounding.
Multiply the eyepiece by the objective: 10 × 40.
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A microscope has an eyepiece of 10x and an objective lens of 4x.
What is the total magnification?
Enter an exact answer, without rounding.
Multiply the eyepiece by the objective: 10 × 4.
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A microscope has an eyepiece of 15x and an objective lens of 100x.
What is the total magnification?
Enter an exact answer, without rounding.
Multiply the eyepiece by the objective: 15 × 100.
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Total magnification
A 10× eyepiece and a 40× objective give a total magnification of:
Multiply the two lenses.
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Starting
When you first view a slide you should use:
Start low.
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Eyepiece 10×, objective 10×.
What is the total magnification?
Enter an exact answer, without rounding.
Multiply.
✍️ Type your answer · 10 of 10
The image of a cell is 8 mm and its actual size is 0.02 mm.
What is the magnification?
Enter an exact answer, without rounding.
Magnification = image ÷ actual.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
2 mm is equal to how many micrometres (µm)?
Question 2 of 5
An image is 20 mm and the specimen is 0.5 mm. What is the magnification?
Question 3 of 5
The stage of a microscope:
Question 4 of 5
Which part focuses light from the lamp?
Question 5 of 5
Resolution is the ability to:
Lesson 4 · Cells
🔄 Cell Division: Mitosis & Meiosis
Cells don't last forever — they divide to help the body grow, repair damage, and (in a special case) create sex cells for reproduction.
🔬 Two types of division
Mitosis produces 2 identical daughter cells, each with the full set of chromosomes (same as the parent cell) — used for growth and repair. Meiosis produces 4 daughter cells, each with HALF the number of chromosomes — these are gametes (egg and sperm cells), used for sexual reproduction. Human body cells have 46 chromosomes (23 pairs); human gametes have 23.
Mitosis (2 identical cells)
Meiosis (4 gametes, half chromosomes)
Mitosis: 2 identical cells, full chromosome setMeiosis: 4 gametes, half the chromosomes
📝 Worked examples
Mitosis: 1 cell (46) → 2 cells (46 each), identical
used for growth and repair
Meiosis: 1 cell (46) → 4 cells (23 each), different
makes sperm and egg cells (gametes)
1 → 2 → 4 → 8 → 16 (4 rounds of mitosis)
Stages of mitosis: Prophase, Metaphase, Anaphase, Telophase (PMAT)
Fertilisation: egg (23) + sperm (23) = zygote (46). That is why meiosis halves the number.
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Result of mitosis
Mitosis results in:
Mitosis makes copies for growth: one cell becomes two.
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Result of meiosis
Meiosis results in:
Meiosis makes sex cells, which need half the chromosomes.
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Purpose of mitosis
Mitosis is mainly used for:
Think of what your body needs when you grow or cut your skin.
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Human body cells (not gametes) contain a full set of chromosomes.
How many chromosomes does a human body cell have?
Enter an exact answer, without rounding.
It is 23 pairs.
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Human gametes (egg and sperm cells) have half the chromosomes of a body cell.
How many chromosomes does a human gamete have?
Enter an exact answer, without rounding.
A gamete has half of a body cell’s 46.
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Think about how many cells meiosis produces from 1 starting cell.
How many daughter cells does meiosis produce?
Enter an exact answer, without rounding.
Meiosis divides twice: 1 → 2 → ?
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Growth
Which type of cell division is used for growth and repair?
Which keeps the full set of chromosomes?
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Gametes
Meiosis produces cells that are:
Eggs and sperm.
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A cell divides by mitosis 4 times in a row.
How many cells are there?
Enter an exact answer, without rounding.
Double the cells each round.
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A human body cell has 46 chromosomes.
How many chromosomes are in a human sperm cell?
Enter an exact answer, without rounding.
Half of 46.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
After mitosis, the two daughter cells are:
Question 2 of 5
How many daughter cells does one meiosis make?
Question 3 of 5
Which stage of mitosis comes first?
Question 4 of 5
In which stage do the chromosomes line up in the middle?
Question 5 of 5
Haploid means a cell has:
Lesson 5 · Organisation
🧩 Levels of Organisation
Living things are organised in levels, each one built from the level before it — from a single cell all the way up to a complete organism.
📈 From cell to organism
A cell is the smallest unit of life. Similar cells working together form a tissue. Different tissues working together form an organ. Organs working together form an organ system. All the organ systems together make up an organism.
❤️ A real example
Muscle cells group together to form muscle tissue. Muscle tissue combines with other tissues to build the heart (an organ). The heart works with blood vessels to form the circulatory system (an organ system). All your organ systems together make up you — the organism.
📝 Worked examples
cell → tissue → organ → organ system → organism
Cardiac muscle cell → cardiac muscle tissue → heart → circulatory system → human
A tissue is a group of similar cells doing one job. An organ is made of different tissues working together. An organ system is a group of organs with a shared function.
Cell is the smallest unit of life. Each level is built from the one before it.
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Smallest level
Which is the smallest level of organisation?
Everything else is built from this building block.
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Definition of a tissue
A group of similar cells working together is called a:
Muscle and nerve are examples. They are one step up from cells.
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Organ system example
The heart and blood vessels working together to move blood is an example of a(n):
Several organs working together for one job.
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Count the levels: cell, tissue, organ, organ system, organism.
How many total levels are in this hierarchy?
Enter an exact answer, without rounding.
Count each word in the list.
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Think about the full hierarchy from cell to organism.
How many levels sit between a single cell and a full organism (tissue, organ, organ system)?
Enter an exact answer, without rounding.
Count only the levels in between, not the cell or the organism.
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An organ, like the heart, is built from multiple tissue types.
At least how many different tissue types combine to form an organ?
Enter an exact answer, without rounding.
An organ is made of more than one tissue type.
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Tissue
A group of similar cells that do the same job is called a:
Between cell and organ.
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Organ
Which is an example of an organ?
Several tissues together.
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Levels: cell, tissue, organ, organ system, organism.
How many levels of organisation are listed?
Enter an exact answer, without rounding.
Count them.
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Number the levels with cell = 1.
What number is the organ level?
Enter an exact answer, without rounding.
Count up from the cell.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
The smallest unit of life is the:
Question 2 of 5
The lungs are an example of an:
Question 3 of 5
A group of organs working together is a(n):
Question 4 of 5
Which order is correct (smallest to largest)?
Question 5 of 5
Blood is considered a:
Lesson 6 · Energy
🌿 Photosynthesis & Cellular Respiration
Plants capture sunlight and turn it into food through photosynthesis. Almost all living cells then break that food down for energy through cellular respiration — two processes that are nearly opposite of each other.
☀️ Photosynthesis
Plants use sunlight, water, and carbon dioxide to make glucose (sugar) and release oxygen. This happens inside the chloroplasts.
6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
💥 Cellular respiration
Cells break down glucose using oxygen to release usable energy, giving off carbon dioxide and water as waste. This happens inside the mitochondria.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
Photosynthesis (chloroplast)
Respiration (mitochondria)
📝 Worked examples
Photosynthesis:
6CO₂ + 6H₂O --light--> C₆H₁₂O₆ + 6O₂
Respiration:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
One glucose needs 6 CO₂ and 6 H₂O and gives off 6 O₂.
Photosynthesis happens in chloroplasts and needs light, carbon dioxide and water. Respiration happens in mitochondria in all living cells, including plants.
The two reactions are opposites. The products of one are the reactants of the other.
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Where photosynthesis happens
Photosynthesis takes place inside which organelle?
It is green and found only in plant cells.
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Where respiration happens
Cellular respiration takes place inside which organelle?
It is the “powerhouse” of the cell.
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Gas released by photosynthesis
Which gas do plants release during photosynthesis?
It is the gas animals breathe in.
✍️ Type your answer · 4 of 10
Look at: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.
How many oxygen molecules are produced?
Enter an exact answer, without rounding.
Read the number in front of O₂ on the right-hand side.
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Look at: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.
How many carbon dioxide molecules are needed as a reactant?
Enter an exact answer, without rounding.
Read the number in front of CO₂ on the left-hand side.
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Think about photosynthesis and cellular respiration together.
How many total processes are described in this lesson as being nearly opposite of each other?
Enter an exact answer, without rounding.
One process stores energy and the other releases it.
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Reactants
Which are the reactants in photosynthesis?
What goes in?
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Oxygen
Which gas is released during photosynthesis?
It is the gas we breathe.
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Look at 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
How many molecules of CO₂ are needed to make one glucose?
Enter an exact answer, without rounding.
Read the coefficient.
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Look at 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
How many molecules of O₂ are made per glucose?
Enter an exact answer, without rounding.
Read the coefficient.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Photosynthesis takes place in:
Question 2 of 5
Respiration releases:
Question 3 of 5
Do plants respire?
Question 4 of 5
The products of respiration are:
Question 5 of 5
The energy source for photosynthesis is:
Lesson 7 · Plants
🌱 Plant Structure & Function
Plants have specialized parts that each play a specific role in helping the plant survive, grow, and reproduce.
🌿 Parts of a plant
Roots absorb water and nutrients from the soil and anchor the plant. The stem supports the plant and transports water and nutrients through tissues called xylem and phloem. Leaves are where most photosynthesis happens, and have tiny pores called stomata for gas exchange. Each stoma is opened and closed by a pair of guard cells, which control how much gas moves in and out, while the tightly-packed palisade layer near the top of the leaf holds most of the chloroplasts responsible for photosynthesis. Flowers are the plant's reproductive structures, eventually producing seeds.
📝 Worked examples
Roots: anchor the plant and absorb water and minerals
Stem: supports; xylem carries water UP, phloem carries sugars
Leaves: photosynthesis; stomata let gases in and out
Transpiration: water evaporates from leaves, pulling more up the xylem.
A plant losing 4 mL/h loses 4 × 6 = 24 mL in 6 hours.
Guard cells open and close the stomata. Root hairs have a large surface area to absorb water. Palisade cells are packed with chloroplasts.
Xylem = water up. Phloem = food (sugar) around.
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Absorbing water and nutrients
Which plant part absorbs water and nutrients from the soil?
This part is under the ground.
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Main site of photosynthesis
Which plant part is the main site of photosynthesis?
These are flat and green to catch the light.
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Gas exchange openings
The tiny openings on a leaf used for gas exchange are called:
They are tiny pores, mostly on the underside of the leaf.
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The plant diagram labels roots, stem, leaves, and flower.
How many main plant parts are labeled in the diagram?
Enter an exact answer, without rounding.
Count the four labels.
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Xylem and phloem are the two tissues that transport materials through the stem.
How many types of transport tissue are named?
Enter an exact answer, without rounding.
Xylem carries water and phloem carries sugar.
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A plant has 4 leaves, and each leaf has 100 stomata.
How many stomata does the plant have in total?
Enter an exact answer, without rounding.
Multiply 4 leaves by 100 stomata.
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Xylem
What does xylem carry?
It goes up from the roots.
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Stomata
What is the function of stomata?
They are tiny pores.
✍️ Type your answer · 9 of 10
A plant has three main vegetative organs: roots, stem and leaves.
How many is that?
Enter an exact answer, without rounding.
Count them.
✍️ Type your answer · 10 of 10
A plant loses 4 mL of water per hour through transpiration.
Flowers aren't just decorative — they're the plant's reproductive organs, built specifically to make seeds that grow into new plants.
🌺 Flower parts & pollination
A flower's parts each have a job: Petals attract pollinators with colour and shape. Sepals protect the bud before it opens. The stamen is the male part, which produces pollen. The carpel (also called the pistil) is the female part, containing the ovary and ovule.
Pollination is the transfer of pollen from the stamen to the carpel — it can happen via insects (attracted by bright petals, scent, and nectar) or via wind (small, plain flowers producing lots of light pollen). Fertilisation happens when pollen fuses with the ovule, which eventually develops into a seed. Germination is when a seed begins to grow into a new plant, needing water, oxygen, and a suitable temperature.
📝 Worked examples
Male parts (stamen): anther (makes pollen) + filament
Female parts (carpel): stigma + style + ovary (contains ovules)
Pollination → pollen lands on the stigma
Fertilisation → pollen nucleus joins the egg in the ovule
Ovule → seed Ovary → fruit
8 fruits × 50 seeds each = 400 seeds
Insect-pollinated flowers are bright and scented. Wind-pollinated flowers are small and make lots of light pollen. Seeds are dispersed by wind, water, animals or explosion.
Germination needs water, oxygen and a suitable temperature. Light is not needed until the shoot emerges.
✏️ Quick check · 1 of 8
The male part of the flower
The male part of a flower that produces pollen is called the:
It has an anther on top of a filament.
✏️ Quick check · 2 of 8
The female part of the flower
The female part of a flower that contains the ovary is called the:
It has a stigma, a style and an ovary.
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Wind pollination
Wind-pollinated flowers are typically:
Wind does not need to attract insects, so there is no need for colour or scent.
✍️ Type your answer · 4 of 8
Germination requires 3 main conditions: water, oxygen, and a suitable temperature.
How many main conditions does a seed need to germinate?
Enter an exact answer, without rounding.
Count the conditions in the list.
✏️ Quick check · 5 of 8
Pollen
Where is pollen produced?
It is part of the male structure.
✏️ Quick check · 6 of 8
Fruit
After fertilisation, the ovary develops into a:
It protects the seeds.
✍️ Type your answer · 7 of 8
A flower has 6 stamens.
How many male reproductive parts does it have?
Enter an exact answer, without rounding.
Count the stamens.
✍️ Type your answer · 8 of 8
A plant produces 8 fruits, each with 50 seeds.
How many seeds is that in total?
Enter an exact answer, without rounding.
Multiply.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Pollination is the transfer of pollen from:
Question 2 of 5
Wind-pollinated flowers are usually:
Question 3 of 5
Which of these is a method of seed dispersal?
Question 4 of 5
Which does NOT help a seed germinate?
Question 5 of 5
Fertilisation in plants takes place in the:
Lesson 9 · Body Systems
🫀 Human Body Systems
Your body is organised into systems, each made of organs that work together to keep you alive — from pumping blood to breathing to thinking.
🧠 A quick tour of the body
System
Main Job
Key Organ
Digestive
Breaks down food for energy
Stomach
Circulatory
Transports blood and nutrients
Heart
Respiratory
Exchanges oxygen and carbon dioxide
Lungs
Nervous
Controls and coordinates the body
Brain
Skeletal
Supports and protects the body
Bones
Muscular
Produces movement
Muscles
📝 Worked examples
Circulatory — heart, blood vessels → transport
Respiratory — lungs → gas exchange
Digestive — stomach, intestines → break down food
Nervous — brain, nerves → fast signals
Skeletal — bones → support, protection
Muscular — muscles → movement
Excretory — kidneys → remove waste
Endocrine — glands → hormones
Immune — white blood cells → defence
Systems work together: during exercise the muscles move, the lungs and heart supply oxygen, and the nervous system coordinates it all. At rest the heart beats about 70 times per minute: 70 × 10 = 700 beats in 10 minutes.
No system works alone. Muscle movement needs oxygen from the respiratory and circulatory systems.
✏️ Quick check · 1 of 10
The circulatory system
Which system transports blood throughout the body?
Circulate means to move around.
✏️ Quick check · 2 of 10
The respiratory system
Which system is responsible for breathing and gas exchange?
Respire relates to breathing.
✏️ Quick check · 3 of 10
The pump of the circulatory system
Which organ pumps blood through the circulatory system?
It is a muscle in your chest that beats.
✍️ Type your answer · 4 of 10
Look at the table of body systems above.
How many body systems are listed?
Enter an exact answer, without rounding.
Count the rows in the table.
✍️ Type your answer · 5 of 10
Think about the structure of the human heart.
How many chambers does the human heart have?
Enter an exact answer, without rounding.
Two atria and two ventricles.
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Think about the adult human skeletal system.
How many bones does an adult human commonly have?
Enter an exact answer, without rounding.
It is just over 200.
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Brain
The brain is part of which system?
It controls the body.
✏️ Quick check · 8 of 10
Kidneys
The kidneys belong to the:
They make urine.
✍️ Type your answer · 9 of 10
The resting heart beats 70 times per minute.
How many beats happen in 10 minutes?
Enter an exact answer, without rounding.
Multiply.
✍️ Type your answer · 10 of 10
Two adults each have 206 bones.
How many bones do they have in total?
Enter an exact answer, without rounding.
Multiply.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Which system provides support and protection?
Question 2 of 5
Which system moves the body?
Question 3 of 5
Hormones are produced by the:
Question 4 of 5
White blood cells belong to the:
Question 5 of 5
Which system removes waste from the blood?
Lesson 10 · Nutrition
🍎 Nutrition: A Balanced Diet
Your body needs a mix of different nutrients in the right amounts — a balanced diet — to grow, repair itself, and have energy for everything you do.
🍎 The main nutrients
Carbohydrates are the body's main energy source (bread, rice, pasta). Proteins support growth and repair of body tissue (meat, beans, eggs). Fats (lipids) store energy and insulate the body (oils, butter). Vitamins are needed in small amounts for specific body functions (e.g. Vitamin C). Minerals support specific functions too (e.g. calcium for bones, iron for blood). Fibre helps digestion move smoothly, even though it isn't absorbed. Water is essential for nearly every process in the body.
📝 Worked examples
Energy per gram (approx.):
carbohydrate 4 kcal/g
protein 4 kcal/g
fat 9 kcal/g
20 g carbohydrate → 20 × 4 = 80 kcal
5 g fat → 5 × 9 = 45 kcal
Carbohydrates give quick energy, proteins build and repair tissue, fats store energy, vitamins and minerals keep the body working, fibre aids digestion and water carries nutrients.
Deficiency diseases: vitamin C → scurvy, vitamin D → rickets, iron → anaemia.
✏️ Quick check · 1 of 10
Main energy source
Which nutrient is the body's main source of energy?
Bread, rice and pasta are rich in it.
✏️ Quick check · 2 of 10
Growth and repair
Which nutrient is most important for growth and repair of body tissue?
Meat, fish, eggs and beans are rich in it.
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The role of fibre
Fibre is important in the diet mainly because it:
Your body cannot digest it, but it keeps food moving through the gut.
✍️ Type your answer · 4 of 10
A balanced diet is often described using 7 main components: carbohydrates, proteins, fats, vitamins, minerals, fibre, and water.
How many main components are listed?
Enter an exact answer, without rounding.
Count the items in the list.
✍️ Type your answer · 5 of 10
Calcium (for bones) and iron (for blood) are the mineral examples named in this lesson.
How many mineral examples are named?
Enter an exact answer, without rounding.
Count the minerals named.
✍️ Type your answer · 6 of 10
Vitamin C is the one vitamin example named in this lesson.
How many specific vitamin examples are named?
Enter an exact answer, without rounding.
Only one vitamin is named.
✏️ Quick check · 7 of 10
Growth
Which nutrient is needed for growth and repair?
Think muscles.
✏️ Quick check · 8 of 10
Scurvy
A lack of vitamin C causes:
Sailors used to get it.
✍️ Type your answer · 9 of 10
Carbohydrates give about 4 kcal per gram.
How many kcal are in 20 g of carbohydrate?
Enter an exact answer, without rounding.
kcal
Multiply grams by 4.
✍️ Type your answer · 10 of 10
Fat gives about 9 kcal per gram.
How many kcal are in 5 g of fat?
Enter an exact answer, without rounding.
kcal
Multiply grams by 9.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Fibre helps the body by:
Question 2 of 5
Which mineral is important for strong bones?
Question 3 of 5
A lack of iron can cause:
Question 4 of 5
Which nutrient gives the most energy per gram?
Question 5 of 5
A balanced diet contains:
Lesson 11 · Digestion
🍅 The Digestive System
Digestion breaks food down into nutrients small enough for your body to absorb and use, through both physical and chemical processes.
🍅 The path of food
Mechanical digestion is the physical breakdown of food (chewing in the mouth, churning in the stomach). Chemical digestion uses enzymes to break large food molecules into smaller ones — for example, amylase in saliva breaks down starch. Path of food: Mouth → Esophagus → Stomach → Small Intestine (where most nutrient absorption happens) → Large Intestine (water absorption, waste forms here).
📝 Worked examples
mouth → oesophagus → stomach → small intestine → large intestine → anus
Mouth: amylase begins digesting starch
Stomach: acid + protease digest protein
Small intestine: final digestion + ABSORPTION through villi
Large intestine: absorbs water
Small intestine ≈ 6 m, large intestine ≈ 1.5 m → total ≈ 7.5 m
Enzymes are biological catalysts: amylase (starch), protease (protein), lipase (fats). Bile from the liver emulsifies fats.
Villi give the small intestine a huge surface area for absorbing nutrients.
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Chewing food
Chewing food in the mouth is an example of:
Physically breaking food into smaller pieces, without chemicals.
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How enzymes work
Enzymes work by:
They are biological catalysts that break things down.
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Where absorption happens
Most nutrient absorption happens in the:
It is long and lined with villi to take in nutrients.
✍️ Type your answer · 4 of 9
Food travels through 5 main organs in order: mouth, esophagus, stomach, small intestine, large intestine.
How many main organs does food pass through in the digestive tract?
Enter an exact answer, without rounding.
Count the organs in the list.
✍️ Type your answer · 5 of 9
Amylase, found in saliva, is the one enzyme example named, and it breaks down starch.
How many specific enzyme examples are named in this lesson?
Enter an exact answer, without rounding.
Only amylase is named.
✏️ Quick check · 6 of 9
Absorption
Most nutrients are absorbed in the:
It is lined with villi.
✏️ Quick check · 7 of 9
Enzyme
Which enzyme breaks down starch?
Starts with A.
✍️ Type your answer · 8 of 9
Food passes through: mouth, oesophagus, stomach, small intestine, large intestine.
How many parts are listed?
Enter an exact answer, without rounding.
Count them.
✍️ Type your answer · 9 of 9
The small intestine is 6 m long and the large intestine is 1.5 m.
What is their combined length in metres?
Enter an exact answer, without rounding.
m
Add them.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Stomach acid helps by:
Question 2 of 5
Bile does what to fat?
Question 3 of 5
Which organ absorbs the water left over after the small intestine?
Question 4 of 5
Villi are:
Question 5 of 5
Enzymes are:
Lesson 12 · Respiration
🫁 The Respiratory System & Gas Exchange
Breathing brings oxygen into your body and removes carbon dioxide, but breathing itself is different from the cellular process that actually uses that oxygen for energy.
🫁 Breathing vs. cellular respiration
Air travels: Nose/Mouth → Trachea → Bronchi → Bronchioles → Alveoli (tiny air sacs where gas exchange happens: oxygen moves into the blood, carbon dioxide moves out). Breathing is the physical, mechanical movement of air in and out of the lungs. Cellular respiration is the chemical reaction inside cells that releases energy from glucose using oxygen: Glucose + Oxygen → Carbon Dioxide + Water + Energy. Breathing supplies the oxygen that cellular respiration then uses — the two work together but are not the same process.
📝 Worked examples
nose/mouth → trachea → bronchi → bronchioles → alveoli
Inhale: diaphragm contracts and moves DOWN, ribs move up and out
Exhale: diaphragm relaxes and moves UP
Air is about 21% oxygen: in 200 mL → 200 × 0.21 = 42 mL
Breathing 15 times/min for 4 min → 60 breaths
Gas exchange occurs in the alveoli: oxygen diffuses into the blood and carbon dioxide diffuses out. Their walls are thin and surrounded by capillaries.
Smoking damages the cilia that sweep dirt out of the airways, and tar damages the alveoli.
✏️ Quick check · 1 of 10
Where gas exchange happens
Gas exchange (oxygen in, carbon dioxide out) happens in the:
Tiny air sacs at the very end of the airways.
✏️ Quick check · 2 of 10
Defining breathing
Breathing is best described as:
Breathing is about moving air.
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Defining cellular respiration
Cellular respiration is best described as:
Respiration happens inside cells and releases energy.
✍️ Type your answer · 4 of 10
The equation Glucose + Oxygen → Carbon Dioxide + Water + Energy starts with glucose and oxygen as its starting materials.
How many total reactants (starting materials) are in this equation?
Enter an exact answer, without rounding.
Count what comes before the arrow.
✍️ Type your answer · 5 of 10
Air passes through 4 main structures before reaching the alveoli: nose/mouth, trachea, bronchi, bronchioles.
How many main airway structures are listed before air reaches the alveoli?
Enter an exact answer, without rounding.
Count the structures in the list.
✍️ Type your answer · 6 of 10
Cellular respiration produces 2 waste products according to the equation: carbon dioxide and water.
How many waste products does cellular respiration produce?
Enter an exact answer, without rounding.
Look after the arrow, leaving out energy.
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Gas exchange
Where does gas exchange take place in the lungs?
Tiny air sacs.
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Diaphragm
When you inhale, the diaphragm:
The chest gets larger.
✍️ Type your answer · 9 of 10
A person breathes 15 times per minute.
How many breaths do they take in 4 minutes?
Enter an exact answer, without rounding.
Multiply.
✍️ Type your answer · 10 of 10
Air is 21% oxygen. Enter the oxygen volume as a number of mL.
How much oxygen is in 200 mL of air?
Enter an exact answer, without rounding.
mL
Find 21% of 200.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Which tube carries air from the throat to the bronchi?
Question 2 of 5
Exhaled air contains more ___ than inhaled air.
Question 3 of 5
Alveoli are well suited to gas exchange because they have:
Question 4 of 5
Cilia in the airways:
Question 5 of 5
Oxygen is carried in the blood by:
Lesson 13 · Circulation
🩸 The Circulatory System
Your circulatory system is the transport network that carries oxygen, nutrients, and waste throughout your entire body, powered by your heart.
🩸 Vessels and blood
Arteries carry blood away from the heart (usually oxygen-rich, with thick walls to handle high pressure). Veins carry blood back to the heart (usually oxygen-poor, and contain valves to keep blood flowing one way). Capillaries are tiny vessels connecting arteries and veins, where exchange with body tissues actually happens. Blood itself is made of: red blood cells (carry oxygen), white blood cells (fight infection), platelets (help blood clot), and plasma (the liquid part that carries everything else).
Blood vessels
Blood components
📝 Worked examples
Heart: 4 chambers (2 atria, 2 ventricles)
Arteries: carry blood AWAY from the heart, thick walls
Veins: carry blood TO the heart, valves
Capillaries: tiny, thin walls → exchange of materials
Blood: red cells (oxygen), white cells (defence), platelets (clotting), plasma (liquid)
75 beats/min × 60 min = 4500 beats per hour
Double circulation: the right side pumps blood to the lungs; the left side pumps oxygenated blood to the body.
✏️ Quick check · 1 of 9
Away from the heart
Blood vessels that carry blood AWAY from the heart are called:
A for Arteries, A for Away.
✏️ Quick check · 2 of 9
Back to the heart
Blood vessels that carry blood BACK to the heart are called:
These have valves to stop blood flowing backwards.
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Fighting infection
Which blood component's main job is fighting infection?
They are part of your immune system.
✍️ Type your answer · 4 of 9
Blood has 4 main components: red blood cells, white blood cells, platelets, and plasma.
How many main components make up blood?
Enter an exact answer, without rounding.
Count the components in the list.
✍️ Type your answer · 5 of 9
Capillaries are the smallest blood vessels, connecting arteries to veins.
How many types of larger vessels do capillaries connect?
Enter an exact answer, without rounding.
They join arteries on one side to veins on the other.
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Arteries
Arteries carry blood:
A for Away.
✏️ Quick check · 7 of 9
Red cells
Which blood cells carry oxygen?
They are red because of haemoglobin.
✍️ Type your answer · 8 of 9
The human heart has two atria and two ventricles.
How many chambers is that in total?
Enter an exact answer, without rounding.
Add the atria and ventricles.
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A heart beats 75 times per minute.
How many beats per hour?
Enter an exact answer, without rounding.
Multiply by 60.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Veins have valves to:
Question 2 of 5
Platelets help to:
Question 3 of 5
White blood cells:
Question 4 of 5
The right side of the heart pumps blood to the:
Question 5 of 5
Capillaries are suited to exchange because they:
Lesson 14 · Genetics
🧬 Genetics & Heredity
Traits are passed from parents to offspring through genes, which are sections of DNA. Understanding how genes combine helps us predict what offspring might look like.
🔬 Genes, alleles & DNA
A gene is a section of DNA that controls a trait. Each gene can have different versions called alleles. A dominant allele (capital letter, like B) shows up even if only one copy is present. A recessive allele (lowercase, like b) only shows up if both copies are recessive.
DNA double helix
Punnett square: Bb × Bb
Shows dominant trait (BB or Bb)Shows recessive trait (bb)
📝 Worked examples
A = dominant (tall), a = recessive (short)
Aa × Aa: AA, Aa, Aa, aa → 25% aa (short)
Aa × aa: Aa, Aa, aa, aa → 50% Aa
AA × aa: all Aa (100% heterozygous)
Genotype = the alleles Phenotype = the visible trait
Genes are sections of DNA on chromosomes in the nucleus. Humans have 46 chromosomes (23 pairs), with one of each pair from each parent.
A recessive trait shows only if the genotype is homozygous recessive (aa).
✏️ Quick check · 1 of 10
Representing a dominant allele
A dominant allele is usually represented by:
Dominant alleles are written big, like B.
✏️ Quick check · 2 of 10
Shape of DNA
DNA is famously shaped like a:
Two strands twisted together like a ladder.
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Where alleles come from
For each gene, an offspring receives one allele from:
You get half your genes from each parent.
✍️ Type your answer · 4 of 10
Look at the Punnett square for Bb × Bb above.
Out of the 4 boxes, how many show BB?
Enter an exact answer, without rounding.
Find the box where B meets B.
✍️ Type your answer · 5 of 10
Look at the Punnett square for Bb × Bb above.
Out of the 4 boxes, how many show Bb?
Enter an exact answer, without rounding.
Find the boxes that mix one B and one b.
✍️ Type your answer · 6 of 10
Look at the Punnett square for Bb × Bb above.
Out of the 4 boxes, how many show bb?
Enter an exact answer, without rounding.
Find the box where b meets b.
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Allele
An allele is:
Versions of a gene.
✏️ Quick check · 8 of 10
Phenotype
The phenotype is:
Physical features.
✍️ Type your answer · 9 of 10
Cross Aa × Aa.
What percentage of offspring are aa?
Enter an exact answer, without rounding.
%
Draw a Punnett square.
✍️ Type your answer · 10 of 10
Cross Aa × aa.
What percentage of offspring are Aa?
Enter an exact answer, without rounding.
%
Draw a Punnett square.
📝 Lesson quiz · 5 questions
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Question 1 of 5
AA × aa gives offspring that are all:
Question 2 of 5
A recessive allele is expressed when:
Question 3 of 5
DNA is found in the:
Question 4 of 5
How many chromosomes do human body cells have?
Question 5 of 5
The genotype Aa is:
Lesson 15 · Classification
🐾 Classification of Living Things
Scientists sort every living thing into a system of nested categories, from very broad down to very specific, so that any organism can be identified precisely.
📈 The seven levels
From broadest to narrowest: Kingdom, Phylum, Class, Order, Family, Genus, Species. A common way to remember the order is "King Philip Came Over For Good Soup."
Human example: Animalia → Chordata → Mammalia → Primates → Hominidae → Homo → sapiens
📝 Naming species
Every species gets a two-part scientific name called binomial nomenclature: the genus (capitalized) followed by the species (lowercase), like Homo sapiens.
📝 Worked examples
Kingdom → Phylum → Class → Order → Family → Genus → Species
"King Philip Came Over For Good Soup"
Human: Homo sapiens (genus Homo, species sapiens)
Binomial nomenclature: genus capitalised, species lower-case, both italic.
Five kingdoms: Animalia, Plantae, Fungi, Protista, Monera
A species is a group that can breed and produce fertile offspring. A dichotomous key identifies organisms using a series of yes/no questions.
The more levels two organisms share, the more closely related they are.
✏️ Quick check · 1 of 10
The broadest level
Which is the broadest (most general) level of classification?
King Philip Came Over For Good Soup: the first word.
✏️ Quick check · 2 of 10
The narrowest level
Which is the narrowest (most specific) level of classification?
King Philip Came Over For Good Soup: the last word.
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Right after Kingdom
Which level comes right after Kingdom?
King Philip Came Over For Good Soup: the second word.
✍️ Type your answer · 4 of 10
Count the levels in the diagram: Kingdom, Phylum, Class, Order, Family, Genus, Species.
How many total levels are there?
Enter an exact answer, without rounding.
Count each level in the list.
✍️ Type your answer · 5 of 10
Think about binomial nomenclature, like Homo sapiens.
How many words are used to name a species this way?
Enter an exact answer, without rounding.
Genus and species.
✍️ Type your answer · 6 of 10
Think about how Homo sapiens is written.
How many of the two name parts is capitalized?
Enter an exact answer, without rounding.
Only the genus gets a capital letter.
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Binomial
In the name Homo sapiens, "Homo" is the:
It is written with a capital letter.
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Most specific
Which level of classification is the most specific?
The five kingdoms are Animalia, Plantae, Fungi, Protista and Monera.
How many kingdoms is that?
Enter an exact answer, without rounding.
Count them.
📝 Lesson quiz · 5 questions
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Question 1 of 5
A species is a group of organisms that can:
Question 2 of 5
Which kingdom do mushrooms belong to?
Question 3 of 5
Vertebrates are animals that have:
Question 4 of 5
A dichotomous key uses:
Question 5 of 5
In a scientific name, the genus is:
Lesson 16 · Microorganisms
🦠 Microorganisms: Bacteria & Viruses
Not everything that affects living things is visible to the naked eye — bacteria and viruses are microscopic, and they behave very differently from each other.
🦠 Bacteria vs. viruses
Bacteria are single-celled living organisms without a nucleus (called prokaryotes). Some bacteria are helpful (aiding digestion, acting as decomposers), while others cause disease. Bacteria reproduce through binary fission, splitting one cell into two. Viruses are NOT considered fully alive by most scientists — they can't reproduce on their own and must invade a host cell to make copies of themselves.
Bacteria (prokaryote)
Virus (not fully alive)
📝 Worked examples
Bacteria: single-celled, no nucleus, can reproduce by binary fission
Viruses: tiny, need a host cell to reproduce
Fungi: yeast, moulds
Protists: e.g. amoeba
Bacteria that double every 20 minutes:
1 hour = 3 doublings → 2³ = 8
2 hours = 6 doublings → 2⁶ = 64
Antibiotics kill bacteria but do not work against viruses. Vaccines train the immune system to recognise a pathogen. Many microorganisms are useful: yeast makes bread and bacteria make yoghurt.
Prevent infection: wash hands, cook food well, keep wounds clean, and get vaccinated.
✏️ Quick check · 1 of 10
Describing bacteria
Bacteria are best described as:
They are tiny, made of one cell, and have no nucleus.
✏️ Quick check · 2 of 10
What viruses need
Viruses need a ___ in order to reproduce.
They take over another organism’s cells to make copies.
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Are viruses alive?
Are viruses generally considered fully alive by most scientists?
Can a virus reproduce on its own?
✍️ Type your answer · 4 of 10
Bacteria reproduce through binary fission, splitting into daughter cells.
How many cells does one bacterium split into during binary fission?
Enter an exact answer, without rounding.
Binary means two.
✍️ Type your answer · 5 of 10
A single bacterium divides by binary fission 3 times in a row: 1 → 2 → 4 → 8.
How many bacteria result after 3 rounds of division?
Round your answer as the question asks.
The number doubles each time: 1, 2, 4…
✍️ Type your answer · 6 of 10
Of the two microorganisms in this lesson (bacteria and viruses), only one is generally NOT considered fully alive.
How many of the two are described as not fully alive?
Enter an exact answer, without rounding.
Only viruses are in doubt.
✏️ Quick check · 7 of 10
Antibiotics
Antibiotics are effective against:
Flu is not treated with antibiotics.
✏️ Quick check · 8 of 10
Vaccine
A vaccine works by:
It prepares your defences.
✍️ Type your answer · 9 of 10
Bacteria double every 20 minutes, starting from 1 cell.
How many bacteria after 1 hour?
Enter an exact answer, without rounding.
60 ÷ 20 = 3 doublings.
✍️ Type your answer · 10 of 10
The same bacteria keep doubling every 20 minutes.
How many after 2 hours (6 doublings)?
Enter an exact answer, without rounding.
Compute 2 to the power 6.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Flu is caused by a:
Question 2 of 5
Yeast is a type of:
Question 3 of 5
Viruses can only reproduce:
Question 4 of 5
Pasteurisation is used to:
Question 5 of 5
Handwashing reduces infection by:
Lesson 17 · Ecosystems
🌳 Ecosystems & Food Chains
An ecosystem is a community of living things interacting with each other and their environment. Energy flows through that community along food chains, starting with the sun.
🌱 Producers, consumers & decomposers
Producers (like plants) make their own food using sunlight. Consumers get energy by eating other organisms. Decomposers (like fungi and bacteria) break down dead material, returning nutrients to the ecosystem.
A simple food chain
Energy pyramid
At each step up the pyramid, only about 10% of the energy passes on to the next level — the rest is used up or lost as heat.
Biotic factors are the living parts of an ecosystem, like plants, animals, and bacteria. Abiotic factors are the non-living parts, like water, sunlight, temperature, and soil — together they shape where and how living things survive.
📝 Worked examples
grass → rabbit → fox
producer → primary consumer → secondary consumer
Arrows show the direction of energy flow (toward the eater).
10% rule: only about 10% of energy passes up each level
5000 kJ at producers → 500 kJ at primary → 50 kJ at secondary
Producers make food by photosynthesis. Consumers eat other organisms (herbivores, carnivores, omnivores). Decomposers break down dead matter and recycle nutrients. A food web is many interlinked food chains.
Energy is lost as heat and in waste at every level, so food chains are rarely longer than 4–5 links.
✏️ Quick check · 1 of 10
Producers
Organisms that make their own food are called:
Plants make their own food by photosynthesis.
✏️ Quick check · 2 of 10
Consumers
Organisms that get energy by eating other organisms are called:
They consume, or eat, other living things.
✏️ Quick check · 3 of 10
Decomposers
Organisms that break down dead plants and animals are called:
Fungi and bacteria that rot dead things.
✍️ Type your answer · 4 of 10
Look at the food chain: Grass → Grasshopper → Frog → Snake → Hawk.
How many organisms are in this food chain?
Enter an exact answer, without rounding.
Count the organisms in the chain.
✍️ Type your answer · 5 of 10
Think about the energy pyramid.
About what percent of energy transfers from one trophic level to the next?
Enter an exact answer, without rounding.
%
Most energy is lost at each step; only about a tenth passes on.
✍️ Type your answer · 6 of 10
In Grass → Grasshopper → Frog → Snake → Hawk, the grasshopper is the 1st consumer.
Which consumer number is the frog?
Enter an exact answer, without rounding.
Count the consumers from the grasshopper onwards.
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Producer
Which organisms are producers?
They photosynthesize.
✏️ Quick check · 8 of 10
Arrow direction
In a food chain, an arrow means:
It points to what gets the energy.
✍️ Type your answer · 9 of 10
Producers contain 5000 kJ. Use the 10% rule.
How much energy reaches the primary consumers?
Enter an exact answer, without rounding.
kJ
Take 10%.
✍️ Type your answer · 10 of 10
Food chain: grass → rabbit → fox.
How many trophic levels are there?
Enter an exact answer, without rounding.
Count the organisms.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Decomposers:
Question 2 of 5
A herbivore eats:
Question 3 of 5
Energy is lost between trophic levels mostly as:
Question 4 of 5
An apex predator is:
Question 5 of 5
A food web differs from a food chain because it:
Lesson 18 · Ecosystems
🤝 Symbiosis & Species Interactions
Species in an ecosystem don't just eat each other — many form close, long-term relationships called symbiosis, which can help, harm, or have no effect on each partner.
🤝 Three types of symbiosis
Mutualism: both species benefit (e.g. bees pollinate flowers and get nectar in return). Commensalism: one species benefits and the other is unaffected (e.g. a bird nesting in a tree). Parasitism: one species benefits while the other is harmed (e.g. a tick feeding on a dog).
Mutualism
Commensalism
Parasitism
📝 Worked examples
Mutualism (+ , +) clownfish and sea anemone; bees and flowers
Commensalism (+ , 0) barnacles on a whale
Parasitism (+ , −) tapeworm in a gut; ticks on a dog
Competition (− , −) two plants competing for light
In mutualism both species benefit. In commensalism one benefits and the other is unaffected. In parasitism the parasite benefits and the host is harmed. Lichens are a mutualism between a fungus and an alga.
Read the signs: + helped, − harmed, 0 not affected.
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Both species benefit
In a relationship where both species benefit, this is called:
Mutual means shared by both.
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One benefits, one harmed
In a relationship where one species benefits and the other is harmed, this is called:
A parasite lives off its host and harms it.
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One benefits, one unaffected
In a relationship where one species benefits and the other is unaffected, this is called:
One gains, and the other neither gains nor loses.
✍️ Type your answer · 4 of 10
Mutualism, commensalism, and parasitism are the three main types of symbiosis described.
How many main types of symbiosis are described in this lesson?
Enter an exact answer, without rounding.
Count the types in the list.
✍️ Type your answer · 5 of 10
In mutualism, both species involved gain something from the relationship.
How many species benefit in a mutualistic relationship?
Enter an exact answer, without rounding.
In mutualism, does either side lose out?
✍️ Type your answer · 6 of 10
In parasitism, one species benefits while the other is harmed.
Out of the two species in a parasitic relationship, how many are harmed?
Enter an exact answer, without rounding.
Only the host is harmed.
✏️ Quick check · 7 of 10
Parasite
A tick living on a dog and feeding on its blood is an example of:
One benefits, one is harmed.
✏️ Quick check · 8 of 10
Mutualism
Bees collecting nectar and pollinating flowers is:
Both benefit.
✍️ Type your answer · 9 of 10
In a parasitic relationship, one species benefits and one is harmed.
How many species benefit?
Enter an exact answer, without rounding.
Count the winners.
✍️ Type your answer · 10 of 10
In a mutualistic relationship both species benefit.
How many species benefit?
Enter an exact answer, without rounding.
Count the winners.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
Barnacles on a whale are an example of:
Question 2 of 5
Two species fighting for the same food is:
Question 3 of 5
Lichens are a partnership of:
Question 4 of 5
Which organism is a parasite?
Question 5 of 5
Oxpecker birds eat ticks from large animals. This is mostly:
Lesson 19 · Ecosystems
🐇 Predator-Prey Population Dynamics
Predator and prey populations don't stay constant — they rise and fall together in repeating cycles that reveal how tightly connected species really are.
📈 Boom-and-bust cycles
When a prey population increases (more food available), the predator population tends to increase soon after. As predators increase, they eat more prey, causing the prey population to decrease. With less prey available, the predator population then decreases too, allowing the prey population to recover — and the cycle repeats. This creates a repeating boom-and-bust pattern when graphed over time, with predator peaks lagging slightly behind prey peaks.
Prey populationPredator population (peaks lag behind prey)
📝 Worked examples
Prey increases → more food for predators → predators increase
Predators eat more prey → prey decreases
Less prey → predators starve and decrease → prey recover…
The prey peak comes BEFORE the predator peak.
Population 200 grows 10%: 200 × 1.10 = 220
Carrying capacity 500, population 350: room for 500 − 350 = 150 more
The carrying capacity is the maximum population an environment can support. Limiting factors such as food, water, space and disease keep populations in check.
Removing a predator can lead to prey overpopulation, which can then overgraze the habitat.
✏️ Quick check · 1 of 9
Prey increases
When a prey population increases, the predator population usually:
More prey means more food for predators.
✏️ Quick check · 2 of 9
Too many predators
When predators become too numerous, the prey population usually:
More predators means more prey get eaten.
✏️ Quick check · 3 of 9
Reading the graph
On a predator-prey population graph, the predator population's peaks typically:
Predators need time to breed after their food increases.
✍️ Type your answer · 4 of 9
The cycle has 4 main stages in order: prey increases, predators increase, prey decreases, predators decrease (then it repeats).
How many main stages make up one full cycle?
Enter an exact answer, without rounding.
Count the stages in the list.
✍️ Type your answer · 5 of 9
A prey population graph shows peaks at year 2, year 6, and year 10 — a pattern repeating at a constant interval.
How many years pass between each repeating peak?
Enter an exact answer, without rounding.
Subtract one peak year from the next.
✏️ Quick check · 6 of 9
Which peaks first?
In a predator–prey cycle, which population peaks first?
Predators depend on prey.
✏️ Quick check · 7 of 9
Carrying capacity
The carrying capacity is:
Think maximum.
✍️ Type your answer · 8 of 9
A population of 200 grows by 10%.
What is the new population?
Enter an exact answer, without rounding.
Multiply by 1.10.
✍️ Type your answer · 9 of 9
The carrying capacity is 500 and the current population is 350.
How many more individuals can the environment support?
Enter an exact answer, without rounding.
Subtract.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
When prey numbers fall, predator numbers will:
Question 2 of 5
Which is a limiting factor?
Question 3 of 5
A population graph that levels off at the carrying capacity is called:
Question 4 of 5
Competition happens when organisms:
Question 5 of 5
Removing the predators from an area often causes the prey to:
Lesson 20 · Ecosystems
🌎 Human Impact on Ecosystems
Human activity can dramatically reshape ecosystems — for better or worse — and understanding these impacts is key to protecting the natural world.
⚠️ Reshaping the natural world
Deforestation is cutting down large areas of forest, destroying habitats and reducing biodiversity. Pollution is releasing harmful substances (chemicals, plastic, waste) into air, water, or soil, harming living things. Habitat destruction means converting natural areas (wetlands, forests, grasslands) into farms, cities, or roads, leaving species without a place to live. Conservation refers to efforts to protect ecosystems and species, such as national parks, recycling, and sustainable farming.
Before
After human impact
📝 Worked examples
Deforestation → habitat loss, less CO₂ absorbed
Burning fossil fuels → more CO₂ → global warming
Pollution → harms water, soil and air quality
Overfishing → fish stocks collapse
Invasive species → outcompete native species
1000 hectares of forest losing 5% per year → 1000 × 0.05 = 50 hectares
Conservation includes protected areas, recycling, planting trees and using renewable energy. The 3 Rs are Reduce, Reuse, Recycle.
Biodiversity is the variety of living things in an area. More biodiversity makes an ecosystem more stable.
✏️ Quick check · 1 of 9
Deforestation
Cutting down large areas of forest is called:
De- means removing, and forest is in the word.
✏️ Quick check · 2 of 9
Pollution
Releasing harmful substances into air, water, or soil is called:
Harmful substances released into air, water or soil.
✏️ Quick check · 3 of 9
Conservation
Efforts to protect ecosystems and species, like national parks and recycling, are called:
It means protecting and preserving.
✍️ Type your answer · 4 of 9
National parks, recycling, and sustainable farming are 3 examples of conservation efforts named in this lesson.
How many conservation effort examples are named?
Enter an exact answer, without rounding.
Count the examples in the list.
✍️ Type your answer · 5 of 9
A forest with 100 trees loses 40 trees to deforestation.
How many trees remain in the forest?
Enter an exact answer, without rounding.
Take 40 from 100.
✏️ Quick check · 6 of 9
Greenhouse gas
Which gas is the main greenhouse gas added by burning fossil fuels?
Burning carbon makes it.
✏️ Quick check · 7 of 9
Sustainable
Sustainable use of resources means:
Think about the future.
✍️ Type your answer · 8 of 9
A forest of 1000 hectares loses 5% each year.
How many hectares are lost in a year?
Enter an exact answer, without rounding.
ha
Find 5% of 1000.
✍️ Type your answer · 9 of 9
Reduce, Reuse, Recycle are called the 3 Rs.
How many Rs is that?
Enter an exact answer, without rounding.
Count them.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Recycling helps by:
Question 2 of 5
Biodiversity is:
Question 3 of 5
An invasive species is one that:
Question 4 of 5
Acid rain is mainly caused by:
Question 5 of 5
Which action helps conserve energy?
Lesson 21 · Reproduction
🥚 Reproduction: Asexual & Sexual
Living things reproduce in two main ways: asexual reproduction, needing just one parent, and sexual reproduction, which combines genetic material from two parents.
⚖️ Comparing the two
Asexual (1 parent)
Sexual (2 parents)
Asexual: offspring are identical clonesSexual: offspring have a mix of both parents' genes
Fertilisation can be external (frogs, fish) or internal (mammals, birds). Mammals nourish the developing embryo in the uterus through the placenta.
Variation from sexual reproduction helps populations survive environmental change.
✏️ Quick check · 1 of 10
Genetic identity in asexual reproduction
Offspring from asexual reproduction are:
With only one parent, where could different genes come from?
✏️ Quick check · 2 of 10
Sexual reproduction
Sexual reproduction combines genetic material from:
A mother and a father.
✏️ Quick check · 3 of 10
Binary fission
Binary fission (a single cell splitting into two) is an example of:
Only one cell is involved, and it splits.
✍️ Type your answer · 4 of 10
Think about asexual reproduction.
How many parents are needed?
Enter an exact answer, without rounding.
A- means without: no partner needed.
✍️ Type your answer · 5 of 10
Think about sexual reproduction.
How many parents are needed?
Enter an exact answer, without rounding.
It needs a male and a female.
✍️ Type your answer · 6 of 10
Think about how similar asexual offspring are to their parent.
What percent of DNA do asexual offspring share with their single parent?
Enter an exact answer, without rounding.
%
The offspring are exact copies of the parent.
✏️ Quick check · 7 of 10
One parent
Which type of reproduction needs only one parent?
No gametes are needed.
✏️ Quick check · 8 of 10
Zygote
A zygote is formed when:
Two gametes join.
✍️ Type your answer · 9 of 10
A bacterium divides 3 times by binary fission.
How many bacteria are there?
Enter an exact answer, without rounding.
Double three times.
✍️ Type your answer · 10 of 10
A human egg has 23 chromosomes and a sperm has 23.
How many chromosomes does the zygote have?
Enter an exact answer, without rounding.
Add them.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Binary fission is used by:
Question 2 of 5
A disadvantage of asexual reproduction is:
Question 3 of 5
Which is an example of internal fertilisation?
Question 4 of 5
The placenta provides:
Question 5 of 5
Strawberry plants that spread by runners reproduce:
Lesson 22 · Evolution
🦋 Adaptations & Natural Selection
An adaptation is a trait that helps an organism survive in its environment. Natural selection, proposed by Charles Darwin, explains how helpful adaptations become more common in a population over generations.
🍿 The peppered moth example
Before pollution darkened tree trunks, light-coloured moths were camouflaged and dark moths stood out to predators. As soot darkened the bark, the advantage flipped — dark moths became camouflaged instead. This is natural selection: organisms best suited to their environment survive and reproduce more.
Light bark (before pollution)
Dark bark (after pollution)
Camouflaged moths survive and reproduce more — shifting the population over generations.
📝 Worked examples
Variation → some individuals have helpful traits
Survival → they survive and breed more
Inheritance → they pass the traits on
Result → the helpful trait becomes common
Polar bear: thick fur and fat (structural)
Bird migration: behavioural
Camel stores fat in its hump, conserves water (physiological)
Charles Darwin developed the idea of natural selection after observing finches on the Galápagos Islands with different beak shapes suited to different foods.
Individuals do not "try" to adapt. Populations change over many generations because some variants survive better.
✏️ Quick check · 1 of 10
Summarising natural selection
Natural selection is often summarised by the phrase:
The organisms best suited to their environment survive.
✏️ Quick check · 2 of 10
Defining an adaptation
A trait that helps an organism survive in its environment is called a(n):
Adapt means to fit your surroundings.
✏️ Quick check · 3 of 10
The peppered moth example
The peppered moth example illustrates:
Dark moths on sooty trees were hidden from birds.
✍️ Type your answer · 4 of 10
In a population of 100 moths, 30% are dark-coloured.
How many moths are dark-coloured?
Enter an exact answer, without rounding.
Find 30% of 100.
✍️ Type your answer · 5 of 10
In a population of 100 light-coloured moths, 60 are eaten by predators.
How many light-coloured moths survive?
Enter an exact answer, without rounding.
Take 60 from 100.
✍️ Type your answer · 6 of 10
Charles Darwin is the scientist most credited with proposing natural selection.
How many scientists are named in this lesson as proposing natural selection?
Enter an exact answer, without rounding.
Only Darwin is named.
✏️ Quick check · 7 of 10
Adaptation
An adaptation is:
It helps survival.
✏️ Quick check · 8 of 10
Darwin
Darwin studied finches with different beaks on which islands?
Off the coast of Ecuador.
✍️ Type your answer · 9 of 10
A beetle population has 200 beetles and 30% are green.
How many are green?
Enter an exact answer, without rounding.
Find 30% of 200.
✍️ Type your answer · 10 of 10
A population has 200 beetles and 30% are green. Birds eat all the green ones.
How many beetles remain?
Enter an exact answer, without rounding.
Subtract the green beetles.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Camouflage is an example of a:
Question 2 of 5
Natural selection acts on:
Question 3 of 5
Hibernation is a:
Question 4 of 5
Which is needed for natural selection?
Question 5 of 5
Over many generations, natural selection can lead to:
Final Challenge
🏆 32-Question Challenge Quiz
One question from every topic you just learned. Pick an answer for each question, then hit Check My Answers.
0 / 32
💪 Keep practicing — go back through the lessons and retake the quiz!
Q1 · Cell Structure
Which organelle is known as the "powerhouse of the cell"?
Q2 · Levels of Organisation
How many total levels are in the hierarchy from cell to organism?
Q3 · Photosynthesis & Respiration
Photosynthesis takes place inside which organelle?
Q4 · Human Body Systems
The heart is the main organ of which body system?
Q5 · Genetics & Heredity
In a Bb × Bb cross, what fraction of offspring show the recessive trait (bb)?
Q6 · Classification
Binomial nomenclature names a species using how many words?
Q7 · Ecosystems
Organisms that make their own food are called:
Q8 · Reproduction
How many parents are needed for asexual reproduction?
Q9 · Adaptations
Natural selection is often summarised by the phrase:
Q10 · Cell Theory
According to cell theory, all living things are made of:
Q11 · Characteristics of Living Things
Which characteristic does a seed show when it starts to germinate?