Cell Specialisation

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Stem Cells: Key Properties

A stem cell is a cell that can divide by mitosis an unlimited number of times.
Each new cell produced when a stem cell divides can either remain a stem cell or develop into a specialised cell by differentiation.
The two key properties of stem cells are self-renewal (capacity to divide) and the ability to differentiate.
After differentiation, a cell is no longer considered a stem cell.
Some stem cells remain in specific locations in the body called stem cell niches, giving tissues the capacity to regenerate and repair.

Stem Cell Niches

A stem cell niche is a specific location in the body where stem cells remain after differentiation.
Bone marrow provides a niche for stem cells used to replace red blood cells, white blood cells and platelets, which are required indefinitely.
The hair follicle niche is located at the root of the hair and promotes continual hair growth.
The niche environment must be able to maintain an inactive state of stem cells and also stimulate proliferation and differentiation.

Stem Cell Potency

Potency is the ability of stem cells to differentiate into more specialised cell types.
Totipotent stem cells can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta).
The zygote formed when a sperm cell fertilises an egg cell is totipotent; embryonic cells up to the 16-cell stage are also totipotent.
Pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but not into extra-embryonic cells.
Multipotent stem cells are adult stem cells that can differentiate into closely related cell types, e.g. bone marrow stem cells differentiate into different blood cells.
Unipotent stem cells are adult cells that can only differentiate into their own lineage, e.g. heart muscle cells (cardiomyocytes) can generate new cardiomyocytes; most cells in animal bodies are unipotent.

Development of Specialised Cells

In complex multicellular organisms, eukaryotic cells become specialised for specific functions, also referred to as the division of labour.
Specialisation occurs after fertilisation to allow development of different tissues within the embryo.
Specialised cells develop specific adaptations for their role, enabling them to function more efficiently.
Structural adaptations include the shape of the cell and the organelles the cell contains (or doesn’t contain).
For example, cells that make large amounts of proteins contain many ribosomes (the organelle responsible for protein production).
During differentiation, cell sizes can vary drastically; size is a feature of adaptation.

A red blood cell

Examples of Cell Specialisation

Red blood cells are small to allow movement through narrow capillaries.
Active white blood cells are larger than inactive white blood cells to allow space for rER and Golgi apparatus for protein (antibody) synthesis.
Sperm cells are long to allow movement towards the egg cell and have narrow streamlined heads to reduce resistance.
An egg cell body has the largest volume of all cells to allow for stored food reserves.
A nerve cell has a large cell body to allow protein synthesis to maintain the structure of the long axon for rapid delivery of impulses.
Muscle cells are larger than normal cells; their length and diameter are designed to exert force during muscle contraction.

Surface Area to Volume Ratio and Cell Size

For cells to survive, metabolic reactions must occur; these rely on materials being constantly exchanged across the plasma membrane.
The metabolic requirements of a cell vary depending on the volume or mass of cytoplasm (where reactions take place).
As cells increase in size, their surface area to volume ratio (SA:V) decreases.
An increase in volume increases metabolic requirements, but the ability to exchange with the environment does not increase at the same rate.
Single-celled organisms have a high SA:V ratio; they can survive by exchanging substances by simple diffusion at the cell surface.
Their metabolic requirements are relatively low, the surface area is large enough for sufficient absorption and secretion, and the small volume means short diffusion distances.
For larger cells, the SA:V ratio is too small for survival using only diffusion at the cell surface; growth must stop and cells must divide.

Adaptations of the small intestine

Constraints on Cell Size

As cells get larger, the SA:V ratio decreases, so the surface area is not large enough to allow a sufficiently high rate of exchange.
The large volume means the diffusion distance to the centre of the cell is long, so substances cannot diffuse quickly enough to reach organelles.
Once the SA:V ratio becomes too small, growth must stop and the cell must divide, giving rise to multicellular organisms.
Multicellular organisms have evolved adaptations to facilitate exchange, such as gas exchange systems and digestive systems.
They also have efficient transport of substances within their bodies, e.g. circulatory systems.
As an organism gets larger, its SA:V ratio decreases, making it more difficult to gain enough oxygen and nutrients at its cell surface.

Investigating Surface Area to Volume Ratio

Scientists use models to represent real-world ideas that cannot be easily investigated; models are simplified versions of complex systems.
Agar cubes can model the effect of changing surface-area-to-volume ratio on the rate of ion diffusion.
Coloured agar is cut into cubes of different dimensions (e.g. 0.5 cm, 1 cm, 2 cm cubes).
The cubes are placed into a diffusion solution such as dilute hydrochloric acid; the acid diffuses into the agar and changes the colour of the indicator.
Measurements can be taken of the time taken for the acid to completely change the colour, or the distance travelled by the acid in a given time.
The rate of diffusion can be calculated and graphed against the surface area : volume ratio of the agar cubes.

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Practice questions

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1.Which of the following is not a source of stem cells?
Easy
- AUmbilical cord blood
- BBone marrow
- CAn embryo
- DBlood plasma
2.What happens to the surface area:volume ratio of a cell as the cell grows and increases in size?
Easy
- AIt does not change
- BIt increases
- CIt decreases
- DIt doubles as the cell doubles in size
3.Which of the following is true of stem cells? I. Cells in early-stage animal embryos are totipotent. II. Stem cells in adult tissue are multipotent. III. Pluripotent stem cells are formed in adult tissue.
Easy
- AI and II only
- BII and III only
- CI and III only
- DII only
4.Which property of stem cells makes them suitable for use in medicine?
Medium
- AThey can differentiate into specialised cells
- BThey can produce chemicals that destroy viruses
- CThey can form gametes when they divide by mitosis
- DThey have chromosomes that are suitable for gene transfer
5.The cube below has sides that measure 2 cm in length. Which of the following represents the correct surface area : volume ratio of this cube?
Medium
- A1:1
- B6:1
- C3:1
- D2:1
6.Current research is making great advances in the therapeutic use of stem cells. Embryonic stem cells are delivering promising results in treating diseases such as Stargardt’s disease due to their unique characteristics. Which of the following are not characteristics of embryonic stem cells?
Hard
- AThey have the potential to develop into any type of tissue if taken within the first few days after fertilisation
- BThey can be stimulated in a laboratory setting to develop into any specialised cell type
- CA small number remain in many tissues of the body, such as bone marrow, skin and the liver to replace damaged or dead cells
- DThey can divide an unlimited number of times to produce a large number of cells that can become specialised
7.The cells of bacteria are on average 1-5 μm long, whereas human cells are on average 100 μm in diameter. What is the main limiting factor preventing the bacterial cells from growing to the same size as human cells?
Medium
- AThe rate of cell division would be too slow to allow colonisation of new areas
- BThe structure of bacterial cell walls limits the size of the cell
- CA larger size would limit cell motility
- DThe rate of diffusion at the cell surface does not increase quickly enough
8.Which of the following statements about stem cells are true? (select all that apply)
Medium
- AStem cells can divide by mitosis an unlimited number of times.
- BAfter differentiation, a cell is still considered a stem cell.
- CTotipotent stem cells can differentiate into extra-embryonic cells such as the placenta.
- DMultipotent stem cells can differentiate into any cell type in the body.
- EUnipotent stem cells can only differentiate into their own cell lineage.

More questions

9.The zygote formed when a sperm cell fertilises an egg cell is totipotent.
Easy
True or false?
10.Pluripotent stem cells can differentiate into extra-embryonic cells such as those that make up the placenta.
Easy
True or false?
11.Match each type of stem cell potency with its correct description.
Medium
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
- Can differentiate into any cell type including extra-embryonic cells
- Can differentiate into any cell type of the embryo but not extra-embryonic cells
- Can differentiate into closely related cell types
- Can only differentiate into its own cell lineage
12.Arrange the following levels of stem cell potency from highest to lowest.
Medium
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
13.Which of the following are features of a stem cell niche? (select all that apply)
Medium
- AIt can maintain stem cells in an inactive state
- BIt can stimulate stem cell proliferation and differentiation
- CIt is a location where stem cells remain after differentiation
- DIt is found only in embryonic tissues
- EIt prevents stem cells from dividing
14.Which of the following statements about cell specialisation are correct? (select all that apply)
Medium
- ASpecialised cells have specific adaptations that help them carry out their functions.
- BThe process by which cells become specialised is called differentiation.
- CAll specialised cells contain the same organelles in the same quantities.
- DCell size can vary drastically during differentiation.
- ESpecialised cells cannot carry out metabolic reactions.
15.Match each type of stem cell with its correct description.
Medium
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
- Can differentiate into any cell type in the embryo and extra-embryonic cells
- Can differentiate into any cell type in the embryo but not extra-embryonic cells
- Can differentiate into closely related cell types
- Can only differentiate into their own cell lineage
16.Which of the following are structural adaptations of specialised cells? (select all that apply)
Medium
- AThe shape of the cell
- BThe organelles the cell contains
- CThe organelles the cell does not contain
- DThe ability to divide by mitosis an unlimited number of times
- EThe presence of a cell wall in all animal cells
17.Match each specialised cell with its adaptation for function.
Medium
- Red blood cell
- Sperm cell
- Egg cell
- Nerve cell
- Small size to move through narrow capillaries
- Long, narrow streamlined head to reduce resistance
- Largest volume of all cells to store food reserves
- Large cell body for protein synthesis to maintain a long axon
18.A student investigates diffusion using agar cubes of different sizes. Which of the following statements about this investigation are correct? (select all that apply)
Hard
- AThe agar cubes model the effect of changing surface area to volume ratio on diffusion.
- BThe rate of diffusion can be calculated from the time taken for the acid to completely change the colour of the indicator.
- CThe same volume of dilute hydrochloric acid should be used in each boiling tube.
- DThe acid should have a lower molarity than the sodium hydroxide in the agar.
- EThe distance travelled by the acid into the block can be measured after a set time.
19.Which of the following is the best definition of differentiation?
Medium
- AThe process by which a cell becomes specialised for a specific function
- BThe process by which a cell divides by mitosis
- CThe process by which a cell increases in size
- DThe process by which a cell undergoes apoptosis
20.During an investigation using agar cubes, a 1 cm × 1 cm × 1 cm cube and a 2 cm × 2 cm × 2 cm cube are placed in acid. Which cube will take longer for the acid to completely change its colour, and why?
Medium
- AThe 2 cm cube, because it has a smaller surface area to volume ratio
- BThe 1 cm cube, because it has a smaller surface area to volume ratio
- CThe 2 cm cube, because it has a larger surface area to volume ratio
- DBoth cubes will take the same time because they are made of the same material
21.A student uses agar cubes to model diffusion into cells. A 0.5 cm × 0.5 cm × 0.5 cm cube and a 2 cm × 2 cm × 2 cm cube are placed in dilute hydrochloric acid. Which cube will take the shortest time for the acid to completely change the colour of the indicator throughout the cube?
Easy
- AThe 0.5 cm cube, because it has the highest surface area to volume ratio
- BThe 2 cm cube, because it has the largest surface area
- CBoth cubes will take the same time because they are made of the same agar
- DThe 2 cm cube, because it has the largest volume
22.A plant palisade mesophyll cell is approximately cuboid with dimensions 4 μm × 4 μm × 25 μm. Which of the following is the correct surface area to volume ratio of this cell?
Medium
- A1.2 : 1
- B2.1 : 1
- C3.3 : 1
- D6.3 : 1
23.As a cell increases in size, its surface area to volume ratio decreases.
Easy
True or false?
24.A patient with a spinal cord injury was treated using stem cell therapy. Stem cells were collected from the patient's own tissues, cultured in the laboratory for one month, and then injected into the injury site where they developed into nerve cells. Which of the following properties of stem cells made this therapy possible?
Medium
- AThey can divide by mitosis an unlimited number of times and can differentiate into specialised cells.
- BThey can produce antibodies to destroy damaged cells.
- CThey can form gametes when they divide by mitosis.
- DThey have chromosomes suitable for gene transfer.
25.
A student measures the time taken for acid to completely change the colour of the indicator in agar cubes of different sizes. The results are shown in the table below.
Cube size (cm) Time (s)
0.5 120
1.0 480
2.0 1920
Which of the following best describes the relationship between cube size and the rate of diffusion?
Hard
- AAs cube size increases, the rate of diffusion decreases because the surface area to volume ratio decreases.
- BAs cube size increases, the rate of diffusion increases because the surface area increases.
- CAs cube size increases, the rate of diffusion remains constant because the concentration gradient is the same.
- DAs cube size increases, the rate of diffusion decreases because the volume decreases.
26.In the agar cube diffusion investigation, why is the same volume of dilute hydrochloric acid measured into each boiling tube?
Medium
- ATo ensure the acid concentration is the same in each tube so the only variable affecting diffusion is the cube size
- BTo make sure the acid completely covers the agar cubes
- CTo keep the total surface area of the agar cubes the same
- DTo prevent the indicator changing colour too quickly
27.A student places a 1 cm × 1 cm × 1 cm agar cube and a 2 cm × 2 cm × 2 cm agar cube into separate boiling tubes containing the same volume of dilute hydrochloric acid. The time taken for the acid to completely change the colour of the indicator is recorded. Which statement correctly predicts and explains the result?
Medium
- AThe 1 cm cube will take longer because it has a smaller volume
- BThe 2 cm cube will take longer because it has a smaller surface area to volume ratio
- CBoth cubes will take the same time because they are made of the same agar
- DThe 2 cm cube will take longer because it has a larger surface area
28.In the agar cube investigation, which measurement would allow you to calculate the rate of diffusion directly?
Medium
- AThe distance travelled by the acid into the block in a given time
- BThe initial mass of the agar cube
- CThe volume of acid used
- DThe concentration of the sodium hydroxide in the agar
29.Which of the following are valid conclusions from an agar cube diffusion experiment where cubes of different sizes are placed in acid? (select all that apply)
Hard
- AThe rate of diffusion per unit surface area is similar for all cubes.
- BThe smallest cube changes colour completely in the shortest time.
- CThe surface area to volume ratio decreases as cube size increases.
- DThe rate of diffusion is directly proportional to the volume of the cube.
- EThe largest cube has the greatest surface area to volume ratio.
30.In the agar cube experiment, the acid diffuses into the cube and the indicator changes colour, allowing the rate of diffusion to be measured.
Easy
True or false?
31.Which of the following is the independent variable in this investigation?
Medium
- AThe size of the agar cubes
- BThe time taken for the colour change
- CThe volume of acid used
- DThe concentration of the acid
32.Which of the following is the dependent variable in this investigation?
Medium
- AThe time taken for the colour change
- BThe size of the agar cubes
- CThe volume of acid used
- DThe temperature of the acid
33.Which of the following variables should be controlled in this investigation? (select all that apply)
Hard
- AThe volume of dilute hydrochloric acid used
- BThe concentration of the dilute hydrochloric acid
- CThe temperature of the acid
- DThe size of the agar cubes
- EThe time taken for the colour change
34.Which of the following is the correct definition of a stem cell?
Easy
- AA cell that can divide by mitosis an unlimited number of times and can differentiate into specialised cells
- BA cell that has lost the ability to divide and carries out one specific function
- CA cell that can only divide by meiosis to produce gametes
- DA cell that cannot differentiate but can divide a limited number of times
35.Which of the following is the correct definition of differentiation?
Easy
- AThe process by which a cell becomes specialised for a specific function
- BThe process by which a cell divides to produce two identical daughter cells
- CThe process by which a cell loses its nucleus
- DThe process by which a cell increases in size
36.Which of the following correctly describes a totipotent stem cell?
Easy
- AIt can differentiate into any cell type found in an embryo, as well as extra-embryonic cells such as those that make up the placenta
- BIt can differentiate into any cell type found in an embryo but not into extra-embryonic cells
- CIt can differentiate into a closely related group of cell types only
- DIt can differentiate into only one specific cell type
37.Which of the following correctly describes a pluripotent stem cell?
Medium
- AIt can differentiate into any cell type found in an embryo but cannot differentiate into extra-embryonic cells
- BIt can differentiate into any cell type including extra-embryonic cells
- CIt can differentiate into only closely related cell types
- DIt can differentiate into only its own cell lineage
38.Which of the following correctly describes a multipotent stem cell?
Medium
- AIt can differentiate into closely related cell types, such as bone marrow stem cells forming different blood cells
- BIt can differentiate into any cell type found in an embryo
- CIt can differentiate into any cell type including extra-embryonic cells
- DIt can differentiate into only one specific cell type
39.Which of the following correctly describes a unipotent stem cell?
Medium
- AIt can only differentiate into its own cell lineage, such as heart muscle cells generating new heart muscle cells
- BIt can differentiate into any cell type found in an embryo
- CIt can differentiate into closely related cell types only
- DIt can differentiate into extra-embryonic cells only
40.A stem cell can divide by mitosis an unlimited number of times.
Easy
True or false?
41.What term describes a cell that can divide by mitosis an unlimited number of times and has the potential to differentiate into specialised cells?
Easy
42.An adult has a total alveolar surface area of 5.2 × 10⁷ mm². One alveolus has a surface area of 0.104 mm². Calculate how many alveoli this person has in each lung. Give your answer as an ordinary number.
Medium
43.Complete the sentence about cell specialisation.
Easy
The process by which a stem cell becomes a specialised cell is called ____.
44.State how the surface area to volume ratio changes as the Amoeba proteus grows.
Easy
45.Gaseous exchange allows the Amoeba to carry out aerobic respiration. State which aspect of the surface area to volume ratio has the greater effect on the rate of gaseous exchange.
Medium
46.The contractile vacuole of the Amoeba helps to maintain its osmotic equilibrium by excreting excess water from the cell. State which aspect of the surface area to volume ratio would depend on this organelle.
Medium
47.Calculate the surface area to volume ratio of a cube with sides of 3 cm. Give your answer as a whole number.
Medium
48.Complete the sentence about stem cell potency.
Easy
Stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells such as those that make up the placenta, are described as ____.
49.A cuboidal cell measures 2 μm × 2 μm × 6 μm. Calculate its surface area to volume ratio. Give your answer to 1 decimal place.
Medium
50.Calculate the surface area to volume ratio of a cube with sides of 5 cm. Give your answer as a decimal to one decimal place.
Medium
51.A cuboidal cell measures 3 μm × 3 μm × 12 μm. Calculate its surface area to volume ratio. Give your answer as a decimal to two decimal places.
Medium
52.A cell has a surface area of 96 μm² and a volume of 64 μm³. Calculate its surface area to volume ratio. Give your answer as a decimal to two decimal places.
Medium
53.Define the term stem cell.
Medium
54.Define the term totipotent.
Medium
55.Explain why surface area to volume ratio is an important factor in limiting cell size.
Hard
56.Explain why the surface area to volume ratio is important in limiting cell size.
Hard
57.Explain why the surface area to volume ratio is an important factor in limiting cell size.
Hard
58.An adult has a total alveolar surface area of 5.2 × 10⁷ mm². One alveolus has a surface area of 0.104 mm². Calculate how many alveoli this person has in each lung. Give your answer as an ordinary number.
Medium
- A225000000 alveoli
- B250000000 alveoli
- C275000000 alveoli
- D300000000 alveoli
59.Calculate the surface area to volume ratio of a cube with sides of 3 cm. Give your answer as a whole number.
Medium
- A3
- B2
- C1
- D4
60.A cuboidal cell measures 2 μm × 2 μm × 6 μm. Calculate its surface area to volume ratio. Give your answer to 1 decimal place.
Medium
- A2.3
- B7.0
- C0.4
- D3.5
61.Calculate the surface area to volume ratio of a cube with sides of 5 cm. Give your answer as a decimal to one decimal place.
Medium
- A2.2
- B0.2
- C1.2
- D3.2
62.A cuboidal cell measures 3 μm × 3 μm × 12 μm. Calculate its surface area to volume ratio. Give your answer as a decimal to two decimal places.
Medium
- A0.17
- B1.17
- C2.17
- D3.17
63.A cell has a surface area of 96 μm² and a volume of 64 μm³. Calculate its surface area to volume ratio. Give your answer as a decimal to two decimal places.
Medium
- A3.5
- B1.5
- C0.5
- D2.5

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Cube size (cm)	Time (s)
0.5	120
1.0	480
2.0	1920