Form 4 · Common mistakes

Cell Biology and Organisation, common mistakes

The mistakes SPM students make on Cell Biology and Organisation, why each one loses marks, and the correct version.

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The mistakes, why they lose marks, and the fix

Common mistake	Why it loses marks	What earns the mark
Saying the vacuole is found only in plant cells.	Animal cells can contain small, temporary vacuoles; it is the large permanent vacuole that is unique to plant cells.	State that a plant cell has one large permanent vacuole, while an animal cell has at most small temporary ones.
Writing that the 'cell membrane' is a feature unique to animal cells.	Both animal and plant cells have a plasma membrane; the term describes the same structure in every cell.	Both cell types have a plasma membrane; only the plant cell adds a cellulose cell wall outside it.
Calling the cell wall the outer boundary of an animal cell.	Animal cells have no cell wall at all, so it cannot be their boundary.	The outer boundary of an animal cell is the plasma membrane; the cell wall belongs only to plant cells.
Using 'tissue' and 'organ' as if they mean the same thing.	A tissue is a group of similar cells; an organ is made of more than one tissue working together.	Blood is a tissue, whereas the heart, built from more than one tissue, is an organ.
Saying the nucleus is found only in plant cells.	Both animal and plant cells have a nucleus, which controls the activities of each equally.	State that the nucleus is present in both cell types and controls their activities.
Describing the mitochondrion as the site of photosynthesis.	Mitochondria carry out respiration; only chloroplasts carry out photosynthesis.	The mitochondrion is the site of respiration; the chloroplast is the site of photosynthesis.
Assuming a unicellular organism is too simple to perform every life process.	A single cell such as an Amoeba still carries out nutrition, respiration, excretion, growth, movement and response by itself.	State that a unicellular organism performs all life processes using its one cell, relying on diffusion because of its large surface area to volume ratio.
Treating a chloroplast and a mitochondrion as doing the same job.	A chloroplast traps light energy to make food, while a mitochondrion releases energy from food; they work in opposite directions.	The chloroplast stores energy by photosynthesis; the mitochondrion releases it by respiration.
Naming an organelle in a labelled diagram without stating its function.	This content standard assesses structure and function together, so a name with no function earns only part of the mark.	Always pair the organelle with its role, such as 'ribosome, site of protein synthesis'.
Thinking a larger organism is made of larger cells than a smaller one.	A larger organism has more cells of a similar size, not bigger cells; cell size stays broadly the same.	Larger organisms are made of a greater number of cells, which is why they need division of labour among tissues and organs.
Using 'chlorophyll' and 'chloroplast' interchangeably.	Chlorophyll is the green pigment; the chloroplast is the organelle that contains it.	The chloroplast is the structure, and chlorophyll is the pigment inside it that absorbs light.

How to avoid these mistakes

Draw and fully label both an animal cell and a plant cell from memory, then check each organelle name against a textbook diagram.
Build a two-column comparison table listing every structure shared by both cell types and every structure unique to plant cells.
Learn the five levels of organisation in order, with one human example for each level, from cell to organism.
List at least four specialised cells together with the one structural feature that suits each cell to its particular function.
Compare, process by process, how Amoeba and a human carry out the same life process, such as excretion or respiration.
Practise naming an organelle correctly straight from a description of its function, before checking the answer against a diagram.

Frequently asked questions

What is the difference between a plant cell and an animal cell?

A plant cell has a rigid cellulose cell wall, chloroplasts for photosynthesis and one large permanent vacuole. An animal cell has none of these, its outer boundary is the plasma membrane, and any vacuoles are small and temporary. Despite these differences, both cell types carry out the same basic life processes using a nucleus, cytoplasm and mitochondria.

What are the levels of organisation?

From simplest to most complex: cell, tissue, organ, system and organism. Similar cells form a tissue, tissues form an organ, organs form a system, and systems together form the whole organism. The blood, for example, is a tissue, the heart is an organ built from several tissues, and the circulatory system links the heart to every blood vessel in the body.

Why do cells become specialised?

Specialised cells have shapes and structures suited to one job, which makes multicellular organisms efficient. For example, a nerve cell is long to carry impulses and a red blood cell is biconcave to carry more oxygen. Without specialisation, every cell would need to perform every function poorly, rather than one function very well.