Syllabus coverage
- Describe and compare the structure of a plant cell with an animal cell, limited to: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria and vacuoles
- Describe the structure of a bacterial cell, limited to: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA and plasmids
- Identify the cell structures listed above in diagrams and images of plant, animal and bacterial cells
- Describe the functions of these structures in plant, animal and bacterial cells
- State that new cells are produced by division of existing cells
- State that specialised cells have specific functions, limited to: (a) ciliated cells - movement of mucus in the trachea and bronchi; (b) root hair cells - absorption; (c) palisade mesophyll cells - photosynthesis; (d) neurones - conduction of electrical impulses; (e) red blood cells - transport of oxygen; (f) sperm and egg cells (gametes) - reproduction
- Describe the meaning of the terms cell, tissue, organ, organ system and organism as illustrated by the examples given in the syllabus
- State and use the formula: magnification = image size / actual size, and calculate magnification and the size of biological specimens using millimetres as units
- Convert measurements between millimetres (mm) and micrometres
Part of the IGCSE Biology syllabus 0610 / 0970.
The eight structures inside a cell
Cambridge limits cell structure to eight parts: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria and vacuoles. Five of them are found in both plant and animal cells. The other three are the ones that make a plant cell different.
Never learn a structure on its own. A diagram question asks you to identify the part, and the very next question asks what it does, so learn each structure as a pair: the name and the job. That single habit answers most of the marks in this topic.
Look at where each structure sits as well as what it does. The cell membrane is the outer boundary in an animal cell but sits just inside the cell wall in a plant cell, and the nucleus is a large, dark, rounded structure inside the cytoplasm.
| Structure | Found in | Function |
|---|---|---|
| Cell membrane | All cells (plant, animal and bacterial) | A thin, partially permeable layer that controls what enters and leaves the cell |
| Cytoplasm | All cells | A jelly-like substance in which the cell's chemical reactions take place; it contains the enzymes and the other structures |
| Nucleus | Plant and animal cells only | Contains the DNA (chromosomes), which controls the activities of the cell |
| Ribosomes | All cells | The site of protein synthesis - the place where proteins are made |
| Mitochondria | Plant and animal cells only | The site of aerobic respiration, where energy is released from glucose |
| Chloroplasts | Plant cells only, in the green parts | Contain chlorophyll, which absorbs light energy for photosynthesis |
| Cell wall | Plant and bacterial cells | An outer layer that strengthens and supports the cell and gives it a fixed shape; in a plant cell it is made of cellulose |
| Vacuoles | Plant cells have one large permanent vacuole; animal cells may have small temporary ones | Filled with cell sap; keeps the cell firm (turgid) and helps to support the plant |
Plant cells and animal cells compared
A plant cell and an animal cell contain the same basic machinery - membrane, cytoplasm, nucleus, mitochondria and ribosomes - but they differ in three structures: the cell wall, the chloroplasts and the vacuole.
Each difference exists for a reason, and stating the reason is what turns one mark into two. Plants have no skeleton, so the cellulose cell wall gives each cell strength and a fixed shape, and the large permanent vacuole filled with cell sap presses outwards and makes the cell turgid, which holds the plant upright. Chloroplasts are there because plants make their own food by photosynthesis.
Animal cells have none of these three structures. Instead they have a flexible membrane and an irregular shape, which is why cells such as white blood cells can squeeze through narrow capillaries. Do not go looking for a chloroplast or a cell wall in an animal cell diagram - they will not be there.
| Feature | Plant cell | Animal cell |
|---|---|---|
| Cell wall | Present - an outer layer of cellulose, outside the cell membrane | Absent |
| Chloroplasts | Present in the green parts of the plant | Absent |
| Vacuole | One large permanent vacuole filled with cell sap | None, or only small temporary vacuoles |
| Shape | Fixed, usually a regular rectangular shape | Irregular and flexible, so the cell can change shape |
| Cell membrane, cytoplasm, nucleus, mitochondria, ribosomes | All present | All present |
The bacterial cell
A bacterium is a single-celled organism, and its cell is built on a different plan. It is much smaller than a plant or animal cell and it has no nucleus, so its genetic material is not enclosed in a membrane.
Instead, a bacterium carries a single loop of circular DNA lying free in the cytoplasm, and it may also carry small extra rings of DNA called plasmids. Cambridge limits the bacterial cell to six structures: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA and plasmids.
Notice what is missing. There is no nucleus, no mitochondrion and no chloroplast, so a bacterium cannot photosynthesise and it releases energy using enzymes in its cytoplasm rather than inside mitochondria. Its cell wall is also not made of cellulose, unlike a plant cell wall.
In a diagram, the giveaway is the shape - a rod, a sphere or a spiral - with a cell wall, no nucleus, and a single dark loop of DNA in the middle of the cytoplasm.
| Structure | Function in the bacterial cell |
|---|---|
| Cell wall | A rigid outer layer that gives the cell its shape and protects it; it is not made of cellulose |
| Cell membrane | A partially permeable layer that controls what enters and leaves the cell |
| Cytoplasm | The jelly-like substance where the cell's chemical reactions take place |
| Ribosomes | The site of protein synthesis - where proteins are made |
| Circular DNA | A single loop of DNA that carries the bacterium's genetic information and controls its activities |
| Plasmids | Small rings of extra DNA, separate from the main loop, that may carry useful genes such as those for antibiotic resistance |
Specialised cells and their adaptations
A specialised cell has a structure adapted to one particular job. During development each cell switches on only the genes it needs, so a red blood cell makes haemoglobin and nothing else, while a palisade mesophyll cell fills itself with chloroplasts.
Cambridge names six specialised cells you must know. For each one, learn the feature and the benefit: a question that asks how the cell is adapted wants both halves, and 'it has a long extension' on its own will not score.
The rule to follow in every answer is the same: feature -> how it helps. The root hair cell's long, thin extension increases the surface area, which lets the cell absorb more water and mineral ions from the soil. The red blood cell loses its nucleus, which leaves more room for haemoglobin, so it can carry more oxygen.
| Specialised cell | Where it is found | Adaptation | Function |
|---|---|---|---|
| Ciliated cell | Lining the trachea and bronchi | Tiny hair-like cilia on its surface that beat in a coordinated wave | Moves mucus, which traps dust and bacteria, away from the lungs |
| Root hair cell | Near the tip of a plant root | A long, thin extension that greatly increases the surface area | Absorbs water and mineral ions from the soil |
| Palisade mesophyll cell | In the upper part of a leaf | Packed with chloroplasts and shaped like a tall box, so the cells fit closely together | Absorbs light for photosynthesis |
| Neurone (nerve cell) | Throughout the nervous system | A very long fibre that carries a signal a long distance without it fading | Conducts electrical impulses |
| Red blood cell | In the blood | No nucleus, a biconcave disc shape and packed with haemoglobin | Transports oxygen |
| Sperm and egg cells (gametes) | In the reproductive system | Sperm: a tail to swim and many mitochondria for energy. Egg: a food store for the developing embryo | Reproduction |
New cells come from existing cells
The syllabus states that new cells are produced by division of existing cells. Cells never appear from nowhere: every cell in your body is descended from a cell that divided before it.
Before a cell divides it copies its DNA, so each of the two new cells receives a complete set of genetic information. The cell then splits to form two new cells, and each one can grow and divide again.
This is how an organism grows, and it is also how an adult repairs itself. Cell division adds the new cells that make up new tissue, replaces cells that wear out - skin cells and red blood cells are replaced constantly - and closes a wound when you cut yourself.
It also explains why growth needs food. Growth is a permanent increase in size and dry mass, and dry mass can only come from new cells and the materials they are built from.
From cell to organism: the levels of organisation
In a multicellular organism, cells are not scattered at random. Similar cells are grouped into tissues, tissues into organs, organs into organ systems, and the organ systems together make the whole organism.
A tissue is a group of similar cells working together to carry out the same function, such as blood tissue, which contains red blood cells, white blood cells and plasma. An organ is a group of different tissues working together for a particular job, such as the heart or a leaf. An organ system is a group of organs working together, such as the circulatory system, and the whole living thing - the human, or the bean plant - is the organism.
Run the chain with one example until it is automatic. In a human: red blood cell -> blood tissue -> heart -> circulatory system -> human. In a plant: palisade mesophyll cell -> palisade mesophyll tissue -> leaf -> transport system of xylem and phloem -> bean plant.
| Level | Definition | Example in a human | Example in a plant |
|---|---|---|---|
| Cell | The basic unit of all living organisms | Red blood cell | Palisade mesophyll cell |
| Tissue | A group of similar cells working together to carry out the same function | Blood tissue | Palisade mesophyll tissue |
| Organ | A group of different tissues working together for a particular function | Heart | Leaf |
| Organ system | A group of organs working together to carry out a major function | Circulatory system | Transport system (xylem and phloem) |
| Organism | A whole living thing, made of organ systems working together | Human | Bean plant |
Measuring cells: magnification and units
Cells are far too small to measure with a ruler directly, so you measure them from a drawing, a photograph or a microscope image and work back to the real size using the magnification formula: magnification = image size / actual size.
The formula can be rearranged for whichever value the question leaves out: actual size = image size / magnification and image size = actual size x magnification. Write the formula down first and substitute the numbers - most lost marks here come from putting the wrong value on the top line.
Keep the units consistent. If the question works in millimetres, give the answer in millimetres. To convert millimetres into micrometres, multiply by 1000, and to convert micrometres back into millimetres, divide by 1000.
- magnification = image size / actual size
- actual size = image size / magnification
- image size = actual size x magnification
- 1 millimetre (mm) = 1000 micrometres, so mm x 1000 gives micrometres
- Worked example: a cell measures 40 mm across in a photograph magnified 2000 times. Actual size = 40 mm / 2000 = 0.02 mm, which is 0.02 x 1000 = 20 micrometres.
Key terms you must be able to define
- Cell
- The basic unit of all living organisms; the smallest structure that can carry out all the processes of life.
- Tissue
- A group of similar cells working together to carry out the same function, such as blood tissue or palisade mesophyll tissue.
- Organ
- A group of different tissues working together to carry out a particular function, such as the heart or a leaf.
- Organ system
- A group of organs working together to carry out a major function in the body, such as the circulatory system.
- Organism
- A whole living thing, made of organ systems working together, for example a human or a bean plant.
- Specialised cell
- A cell whose structure is adapted to carry out one particular function, such as a red blood cell, a neurone or a root hair cell.
- Plasmid
- A small ring of extra DNA found in the cytoplasm of a bacterial cell, separate from the main loop of circular DNA; plasmids often carry useful genes such as those for antibiotic resistance.
- Magnification
- How many times larger an image is than the actual specimen: magnification = image size / actual size.
Applied to the real world
Cambridge sets biology in unfamiliar contexts - a hospital, a farm, a water-treatment plant. Use these as models for how to apply the science, then write your own.
A mature red blood cell has no nucleus at all. Losing it makes room for more haemoglobin, the red pigment that binds oxygen, and the biconcave disc shape gives the cell a large surface area for oxygen to diffuse in and out. The cell pays for this: with no nucleus it cannot divide or repair itself, which is why red blood cells are replaced by new ones made in the bone marrow.
The ciliated cells lining the trachea and bronchi sweep mucus, dust and bacteria away from the lungs. Tar in cigarette smoke paralyses and destroys the cilia, so the mucus can no longer be moved upwards. It collects in the airways, which is why smokers develop a persistent cough, and the trapped bacteria make chest infections much more likely.
A plant left in a dark cupboard grows tall and spindly with small, pale yellow leaves. Light is needed for chloroplasts to develop, so a plant grown in the dark builds very few of them and makes little chlorophyll. With fewer chloroplasts there is less photosynthesis, so the plant has less sugar to build new tissue and its leaves stay small and pale.
Plasmids are the tool that makes bacteria useful for genetic engineering. The human gene for insulin is cut out and inserted into a plasmid, which is then put into a bacterium. The bacterium divides and its circular DNA and plasmids are copied with it, so a huge population of identical bacteria is produced, all of them reading the human gene and making human insulin that can be collected and given to people with diabetes.
Flashcards
Click a card to flip it. Mark honestly — the tracker uses this.
Exam-style questions
9 questions, 27 marks. Write your answer, then reveal the mark scheme and tick each point you actually made. Answering honestly here is what makes the rest of the site useful.
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Mark scheme — tick each point you actually made
Exam technique for this topic
- When you compare a plant cell with an animal cell, give the difference and the reason: 'the plant cell has a cell wall made of cellulose, which gives it a fixed shape and support' scores more than 'it has a cell wall'.
- Never write that an animal cell has no cell membrane. Every cell has a cell membrane; a plant cell simply has a cell wall outside it as well.
- For bacterial cell questions, stay with the six syllabus structures, and remember that the DNA is a loop of circular DNA lying free in the cytoplasm, plus plasmids - there is no nucleus.
- Identify questions want the name of the structure only. Function questions want what it does, not where it is, so read the command word before you start writing.
- Adaptation answers must come in pairs: the feature and the benefit. 'A root hair cell has a long extension that increases the surface area for absorbing water' earns both marks; 'it has a long extension' earns one.
- For magnification, write the formula first and substitute into it, then convert the units at the end. Dividing the magnification by the image size is the single commonest error in this topic.
Why students lose marks here
Where this fits in IGCSE Biology
This page is one topic of Cambridge IGCSE Biology 0610 / 0970. IGCSE Biology is the course home: every area and every topic in Cambridge's own order, the papers you sit and what each one tests, and the exam-practice tools. The full topic list, with each topic linked to its revision page, is on the IGCSE Biology syllabus page.