Making Links 1 – Stem Cells
Making links and interpreting data in unfamiliar contexts is something that students are now increasingly asked to do in assessments so it is vital that they are able to apply their knowledge. Using a wider range of examples means making links across different areas of biology instead of teaching isolated topics.
Plants can really help students to make links because so many of the same processes that are seen in animals also take place in plants. The fact that students often focus on the differences between animals and plants can be a hindrance to them making links between them. By encouraging students to make links and explore examples of biological concepts in plants as well as animals, they will gain a greater understanding of universal biological processes and how they can apply their knowledge of them.
In this article and our second article on making links, using content from an online course developed by SAPS and STEM Learning, we will introduce teaching and learning strategies that will help you and your students to make links between the topic of stem cells and other areas of the curriculum. To be clear, we are not talking about the cells in the stem of a plant, we are talking about the cells in the regions of a plant where cell division is occurring.
A fifteen-year-old student asks you this question:
“If a whole plant can be grown from a piece of leaf that’s left on a window sill in a jar of water, why can’t we grow a complete human from a piece of a finger?”. How would you answer this amazing question? Which areas of biology would you link to in your explanation?
The activities and information in these sections will help you to:
- Develop your subject knowledge of plant stem cells.
- Consider how the use of concept mapping can encourage students to make links, address misconceptions and discover inspiring contexts to support learning.
- Explore practical work which develops students’ understanding of key concepts and enables them to make links to other areas of the biology curriculum.
Teachers’ perspectives: making connections
Over the years we collect strategies for helping students to make links between topics. Which strategies have you developed?
Why make links?
Encouraging students to make links and explore examples of biological concepts in plants as well as animals allows them to gain greater understanding of universal biological processes. Here, we dip into the science of learning to explore why this is such an important part of teaching.
In school children, up to late teenage years, regions of the brain which are responsible for making connections are known to be relatively immature, and this can disadvantage them in making use of prior knowledge even when they possess it. Their neural circuitry for this connection-making process is still developing.
It is, therefore, important that teachers encourage and help students to make connections with their prior knowledge. This helps make new knowledge meaningful and memorable. A connection between a new concept and what has been taught before may seem obvious to an adult teacher but is perhaps not to a child whose brain is still developing.
Before we think of ways in which we can use the topic of stem cells to make links to other areas of the biology curriculum, let’s summarise some key information about stem cells.
What are stem cells?
Unicellular organisms consist of a single cell that carries out all the processes needed to keep that organism alive. Examples include bacteria, the amoeba and some algae.
Multicellular organisms are composed of many different types of cells which each have a different job to do. These are called specialised cells. The structure of a specialised cell is adapted to carry out its specific function. Examples include nerve cells (which are very long), muscle cells (which can contract) and root hair cells.
A stem cell is a cell which has the ability to divide and produce different types of specialised cells in an organism. Once a cell has become specialised, we say it has differentiated. A stem cell is undifferentiated.
Stem cells can divide to form more stem cells, or they can differentiate into specialised cells. This division of cells is called mitosis. The type of specialised cell that a stem cell differentiates into is controlled by the genes inside its nucleus.
The early embryos of animals contain stem cells. These very early stem cells are ‘totipotent’, meaning that they have the potential to differentiate into any of the specialised cells that are found in the body of an adult. In other words, an entire body can be grown from totipotent stem cells. Stem cells can also be found in certain tissues within the adult’s body, such as the bone marrow. However, in animals, these adult stem cells can only differentiate into a few different types of specialised cell, having lost the ability to become any type of cell in the body (they are no longer totipotent). For example, the stem cells in bone marrow can produce specialised red blood cells.
In plants, stem cells are found in the growing tips of roots and shoots, in specialised structures called meristems. These stem cells can differentiate into any of a plant’s specialised cell types, allowing the plant to form different tissues as it grows.
Unlike animals, many mature plant cells remain totipotent, able to differentiate into any type of cell. This is why a fragment of a mature plant, such as part of a leaf, can be used to regenerate an entire plant, whereas animals cannot regenerate an entire individual from a fragment of an organ.
What prior knowledge will your students need before they begin to learn about stem cells?
A plant-based teaching and learning resource
This animation demonstrates how growth occurs at specific regions within plants, how cells divide by mitosis, and how cells become specialised into different tissues (differentiation). Explore the animation and then have a go at answering the questions in the quiz below?
Would this resource be helpful when you are teaching about stem cells?
Mitosis, growth and differentiation in plants quiz
Try this quiz, based on the animation above. Some questions may have more than one correct answer.
1. Plants have specific zones where growth can occur, as shown by the circles on the plant above. Which of the following statements are correct: (pick three)
a) Each zone contains a meristem
Correct answer
Each zone does contain a meristem that consists of a group of dividing cells, clusters of new cells which are increasing in size (elongation), and slightly older cells which become specialized into different tissues (differentiation).
b) Each zone contains plant stem cells
Correct answer
Each zone does contain stem cells within a meristem. The meristem consists of a group of dividing stem cells, clusters of new cells which are increasing in size (elongation), and slightly older cells which become specialized into different tissues (differentiation).
c) Each zone can only produce specialised cells of one type
Incorrect answer
The mersitems that are found in each of the zones consist of a group of dividing stem cells, clusters of new cells which are increasing in size (elongation), and slightly older cells which become specialized into different tissues (differentiation). A stem cell in the meristem can differentiate into any type of plant cell.
d) Each zone contains cells that are beginning to differentiate into specialised cells
Correct answer
The mersitems that are found in each of the zones consist of a group of dividing stem cells, clusters of new cells which are increasing in size (elongation), and slightly older cells which become specialized into different tissues (differentiation).
2. The cells in the zone of division are small and unspecialized. They divide by:
a) Meiosis
Incorrect answer
Cells in the zone of division divide by Mitosis, forming two identical nuclei, before the cytoplasm divides between the nuclei and a new cell wall is formed. The cell then undergoes a period of growth before dividing once more. Cell division by Meiosis will only occur in the tissues that are dividing to form pollen (male plant gametes) and ovules (female plant gametes).
b) Mitosis
Correct answer
Cells in the zone of division divide by Mitosis forming two identical nuclei, before the cytoplasm divides between the nuclei and a new cell wall is formed. The cell then undergoes a period of growth before dividing once more.
c) Binary fission
Incorrect answer
Eukaryotic cells divide by mitosis, forming two identical daughter cells. Prokaryotic cells, such as bacteria, divide by binary fission.
d) Budding
Incorrect answer
Cells in the zone of division divide by Mitosis, forming two identical nuclei, before the cytoplasm divides between the nuclei and a new cell wall is formed. The cell then undergoes a period of growth before dividing once more. Cell division by budding is observed in yeast (a unicellular fungus), but not in plant cells in the zone of division.
3. The final scene in the root tip sequence illustrates how chromosomes behave during mitosis. Each chromosome consists of a pair of chromatids. These are pulled apart by microtubules within the cell. The separate chromatids are then replicated to form new chromosomes, ensuring that each new cell formed is genetically identical to every other cell within the plant. The phase of mitosis when the chromatids are pulled apart by microtubules is:
a) Metaphase
Incorrect answer
During metaphase, the chromosomes (which consist of a pair of chromatids), attach to microtubules and line up across the middle of the cell.
b) Telophase
Incorrect answer
Once the daughter chromosomes have reached the opposite poles of the cell (during anaphase), the dividing cell is said to be in telophase. The daughter chromosomes start to unwind and become long and thin again and a new nuclear membrane forms around each group of daughter chromosomes.
c) Anaphase
Correct answer
Each chromosome consists of a pair of chromatids. During anaphase these are pulled apart by microtubules within the cell.
d) Prophase
Incorrect answer
During prophase, the DNA condenses into chromosomes and each chromosome can be seen to consist of two sister chromatids, held together by a centromere. The microtubule spindle forms during prophase, but the chromosomes are not attached to it. The chromosomes, attach to microtubules and line up across the middle of the cell during metaphase.
4. In a plant, increasing the diameter of the stem enables the plant to grow taller. The dividing cells within the stem of the plant are found in meristems: (pick two)
a) In the xylem and the phloem
Incorrect answer
In a plant stem, the dividing cells are located inside the vascular bundle in meristems called cambium.
b) In the cambium between the xylem and the phloem
Correct answer
The dividing cells are located inside the vascular bundle in meristems called cambium.
c) In the cortex
Incorrect answer
The dividing cells are located inside the vascular bundle in meristems called cambium.
d) Inside the vascular bundles
Correct answer
The dividing cells are located inside the vascular bundle in meristems called cambium.
5. Small, undifferentiated cells in the cambium divide and are pushed outwards. They enlarge and start to differentiate. The enlargement of the cells as they differentiate is brought about by: (pick two)
a) An increase in cellular respiration
Incorrect answer
The cell’s rate of respiration may increase as it differentiates, allowing the transfer of energy from glucose to processes inside the cell that are important in differentiation, such as protein synthesis. However, the increase in the cell’s volume is brought about by the movement of water molecules into the cell’s vacuole by osmosis, from a dilute solution/higher water potential outside the cell to a more concentrated solution/lower water potential inside the cell, down a water concentration/water potential gradient.
b) Gene expression
Incorrect answer
The regulation of gene expression allows the cell to differentiate into a specialised cell with a specific structure and function. However, the increase in its volume is brought about by the movement of water molecules into the cell’s vacuole by osmosis, from a dilute solution/higher water potential outside the cell to a more concentrated solution/lower water potential inside the cell, down a water concentration/water potential gradient.
c) Uptake of water by osmosis
Correct answer
The increase in the cell’s volume is brought about by the movement of water molecules into the cell’s vacuole by osmosis, from a dilute solution/higher water potential outside the cell to a more concentrated solution/lower water potential inside the cell, down a water concentration/water potential gradient.
d) An increase in volume of the cell’s vacuole
Correct answer
The increase in the cell’s volume is brought about by the movement of water molecules into the cell’s vacuole by osmosis, from a dilute solution/higher water potential outside the cell to a more concentrated solution/lower water potential inside the cell, down a water concentration/water potential gradient.
In your lessons you will use a variety of ways to find out what students already know in order to inform your teaching. For example, you may ask students to draw a mind map of what they already know about a new topic.
But what about those students who find this too difficult – those who may have the prior knowledge, but don’t realise that it links to the new topic or can’t recall it? How do you support those students to make those all-important connections?
The value of concept mapping
A concept map is a diagrammatic tool that allows students to organise subject knowledge, visualise links between different concepts and promote meaningful learning. It begins with a main idea (concept) and then shows how the main idea can be broken down into specific topics. The ideas are linked by words or phrases that explain the relationship between them. A concept map is hierarchical, unlike a mind map which has the main idea at the centre of the map with expanded ideas radiating outwards. When constructing a concept map, students are having to make decisions and order the concepts as well as making links.
The example of a concept map below links together some of the ideas about stem cells from across the biology curriculum.
This example clearly shows that:
- Main concepts appear at the top of the map and more specific concepts appear lower down
- Each concept appears only once on the map
- Links have arrow heads to show the direction in which concepts should be read
- Links are given meaning by words or phrases
- There can be any number of links going to or coming from a concept box
- The overall layout is clear and uncluttered
(The above bullet points were summarised from The active use of concept mapping to promote meaningful learning in biological science by Ian M. Kinchin School of Educational Studies, University of Surrey. Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy within the School of Educational Studies. © I.M.Kinchin September 2000.)
Could you make a concept map for osmosis (or another topic) using ideas from across the biology curriculum?
Conclusion – Stem cells and barriers to learning
The topic of stem cells is a fascinating one that enables biological concepts to be taught in ‘real world’ contexts. However, the topic can also present barriers to learning such as lack of prior knowledge, complex vocabulary and accessible practical work may be limited. Concept mapping of key ideas following a taught introduction to the topic can help to address the first two of these. In the next section (making links, part two), we will introduce you to plant-based practical investigations that can provide your students with first-hand experience of stem cell biology, allowing them to think scientifically about this important part of the biology curriculum.
This article was written using reworked content from the course Teaching Biology: Inspiring Students with Plant Science codeveloped by SAPS and STEM Learning.
This article was written using reworked content from the course Teaching Biology: Inspiring Students with Plant Science codeveloped by SAPS and STEM Learning.
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