Download Cells and tissues - Unpicking misconceptions

Biology
Topic 1 Cells and tissues
Unpicking misconceptions
1 Identifying misconceptions
When students start this topic they may come with numerous misconceptions. This is due in part
to the very nature of the topic – a study of the invisible (to them at least) world of cells and cell
structure. They may also find the concept of cell theory a difficult one to envisage – it took
humankind a very long time before we finally accepted the idea that cells form the building blocks
that define life.
 Key questions to ask to identify misconceptions
How big (or small) are cells?
Ensure that teaching involves the use of microscopes and models to emphasise cell size, including
the relative sizes of cells.
How do we know if something is living?
Students will know from Key Stage 2 that living things show certain ‘characteristics of life’. By
asking students to define life, including that at cellular level, we can ensure that they have a clear
understanding of the importance of cells in that definition.
What are living things made from?
It is important that students are aware of the idea of cell theory. This may also be an opportunity to
ensure that students are aware that many diseases (fungi, bacteria) are also cells.
Where do cells come from?
The idea of spontaneous generation (the development of living organisms from non-living matter)
should be discussed, together with an emphasis on the role of the nucleus in passing on
information to allow future generations of cells.
2 Common misconceptions

“Respiration is the same as breathing.”
Students will often confuse the terms respiration and breathing, partly because they are
unclear of the processes involved, but also because we refer to the lungs and trachea as
the ‘respiratory system’ when we mean the ‘gas exchange system’ that is used for
breathing. In order to avoid this, students need to be guided to automatically link respiration
with a biochemical reaction, but breathing with physiological gas exchange.

“Excretion is the same as egestion.”
Another characteristic of life that is often misunderstood is excretion – confused instead with
egestion. Egestion is the ejection of solid waste from the body through the anus – the result
of food digestion. A good way to remember this is that egestion sounds like digestion.
Excretion is the removal of metabolic waste products from the body – usually through the
kidney.
Teach Better KS3 Biology Dynamic Learning © Hodder and Stoughton 2013
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Biology • Topic 1 • Cells and tissues

“Cells are too small to see.”
Because of the very small nature of cells and the difficulty in visualising them, students often
have misconceptions regarding the actual sizes of cells or the relative sizes of different
specialised cells (egg and sperm in particular). The use of scale models or scale diagrams
is a good way of showing relative sizes of cells. If a red blood cell were the size of a football,
an amoeba would be as large as a bus, and a human would be 55 km tall – that’s halfway to
space. You could show students the interactive scale at
http://learn.genetics.utah.edu/content/begin/cells/scale/.

“Root hair cells are animal cells that make hair grow.”
One specialised cell that causes a great deal of confusion is the plant root hair cell. Because
of its name, students often regard this as an animal cell linked to hair.

“Specialised DNA is found in specialised cells.”
A very common misconception is the link between the structure of the cell and the
information found in the nucleus. When asked, many students will state that a nerve cell
contains only the genetic information needed to make another nerve cell. Students should
be aware that every cell in the body contains information for ‘making’ every other cell in the
body.

“Bacteria will grow in sterile milk if left long enough.”
Because we rarely keep food or drinks in completely sterile conditions, it will inevitably ‘go
bad’ as a result of microbial growth. This leads to the misconception that some cells
(diseases and decomposers in particular) simply ‘appear’ rather than multiply as a result of
cell division. Discussion of experimental work by Pasteur should help dispel this
misconception.

“Clear round structures under the microscope are cells.”
When preparing slides, air bubbles will often get trapped under the cover slip, and students
commonly mistake these distinctive structures for cells. When placing a cover slip onto a
specimen it is important to gently lower it from one side to exclude air bubbles. Students
could be shown what air bubbles look like under the microscope before they start to make
their own observations.
3 Overcoming the big misconceptions
In Topic 1 Unpicking Misconceptions you will find presentations on overcoming these two big
misconceptions:
► Misconception 1: Respiration is the same as breathing
► Misconception 2: Specialised DNA is found in specialised cells.
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Biology • Topic 1 • Cells and tissues
Once you have listened to the presentations, you can use the content of the slides to work through
the misconceptions with your students.
Teach Better KS3 Biology Dynamic Learning © Hodder and Stoughton 2013
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