B2.3 Cell specialization

How can cells in a multicellular organism differentiate?

A. They express some of their genes but not others.

B. They all have a different genetic composition.

C. Different cells contain a different set of chromosomes.

D. Different cells do not have some of the genes.

Answer: A

A. Correct. Differentiated cells perform specialized functions because they express only some of their genes and not all of the others. This process is called differentiation, in which cells selectively use certain genes while suppressing others.

B. Incorrect. Cells in a multicellular organism all contain the same genome or genetic code because they originate from a single zygote that divides by mitosis.

C. Incorrect. Differentiation does not change the chromosome set.

D. Incorrect. Cells suppress the expression of unnecessary genes, but they still retain the full genetic information.

When compared to other body cells, which characteristic of stem cells is the most important for therapeutic uses?

A. Less differentiation

B. Less excretion

C. Lower rate of reproduction

D. Lower rate of metabolism

Answer: A

A. Correct. Correct. Stem cells are defined as undifferentiated, which is the most important feature for therapeutic use. They can differentiate into needed cell types (e.g., retinal cells for treating Stargardt’s disease).

B. Incorrect. Although stem cells participate in metabolism, sources do not indicate that reduced excretion is the most important characteristic making them suitable for therapy.

C. Incorrect. A key feature of stem cells is their ability to divide continuously. They can divide repeatedly without limit. A rapid rate of cell division (mitosis) is necessary to generate enough cells for therapy or to replace lost cells.

D. Incorrect. Sources do not support the claim that a low metabolic rate is the most important characteristic for therapeutic purposes. Differentiation ability and cell division are the key factors.

Scientists are investigating the potential use of embryonic stem cells to repair spinal cord injuries in humans. What would be an advantage of using embryonic rather than adult stem cells?

A. More cell types can be obtained. 

B. Possibilities of rejection are lower. 

C. The risk of stem cells forming malignant tumours is lower.

D. Unlimited numbers of cells can be extracted from the umbilical cord.

Answer: A

A. Correct. Embryonic stem cells are pluripotent or totipotent, meaning they can develop into all cell types of an adult organism. In contrast, adult stem cells are multipotent and can produce only a limited range of cell types.

B. Incorrect. There is no indication that embryonic stem cells have a lower rejection risk.

C. Incorrect. Embryonic stem cells often carry a higher risk of tumor formation due to their high differentiation potential.

D. Incorrect. Although the umbilical cord is a stem cell source, the main advantage of embryonic stem cells is their ability to differentiate into many cell types.

How do cells in multicellular organisms differentiate?

A. Some cell types divide by mitosis more often than others.

B. They express some of their genes but not others.

C. Some of their proteins denature but not others.

D. Their DNA content changes with time.

Answer: B

A. Incorrect. This relates to growth or replacement rates, not the mechanism of differentiation.

B. Correct. Cell differentiation occurs because different cell types express different sets of genes, achieved through selective gene expression and gene suppression.

C. Incorrect. Protein denaturation is caused by factors like heat or pH, not part of the differentiation mechanism.

D. Incorrect. All cells in a multicellular organism contain the same genetic material.

How would surface area, volume and surface area to volume ratio of a cell change as the cell becomes bigger, if the cell does not change shape?

Answer: B

• Surface area (Increases): As a cell grows, its surface area increases.

• Volume (Increases): As a cell grows, its volume also increases.

• Surface area : Volume ratio (Decreases): As the cell grows larger, the volume increases faster than the surface area. Therefore, the surface area to volume ratio decreases.

Therefore B is correct.

A,C, and D. Incorrect

Which sequence has the cells arranged according to their ability to differentiate, starting from the least able?

A. bone marrow, neuron, embryonic, umbilical 

B. neuron, bone marrow, umbilical, embryonic 

C. umbilical, embryonic, bone marrow, neuron

D. embryonic, umbilical, bone marrow, neuron

Answer: C

The sequence should go from least differentiation potential to highest.

A. Incorrect. Neurons are highly specialized and have the least differentiation potential.

B. Correct 

• Neuron: Highly differentiated, cannot divide or differentiate into other cell types; least potential. 
• Bone marrow: Contains adult stem cells, multipotent, can differentiate into a limited range of cells (e.g., blood cells). 
• Umbilical: Stem cells from the umbilical cord have higher differentiation potential than adult stem cells like bone marrow.
• Embryonic: Contains embryonic stem cells, pluripotent, able to develop into all adult body cell types; highest potential in these options.

C. Incorrect. Order is reversed.

D. Incorrect. Order is reversed.

 What features of a cell favour efficient removal of waste products?

Answer: B

A. Incorrect. Waste production depends on cell volume. High volume produces more metabolic waste. Even with high surface area, if the SA:V ratio is low, efficiency is limited.

B. Correct.The rate at which materials (including waste) leave a cell depends on surface area (SA). The rate of waste production depends on the cell volume (V). Efficient waste removal requires a high surface area to volume ratio, achieved by high surface area and low volume.

C. Incorrect. Low SA:V ratio means waste cannot be removed quickly enough to maintain metabolism.

D. Incorrect. Low volume reduces waste, but low surface area slows exchange and is not optimal for efficiency.

Which process is required for development of specialized tissues in a multicellular organism?

A. Expression of some genes in the genome but not others

B. Production of memory cells

C. Signals either from nerves or from hormones

D. Cell replacement

Answer: A

A. Correct. The development of specialized tissues requires cell differentiation, which occurs because cells selectively express (turn on) some genes and suppress (turn off) others in their genome.

B. Incorrect. Memory cells are specialized immune cells and are the result of differentiation, not a general process required for all specialized tissues.

C. Incorrect. Chemical signals (like morphogens) influence how cells differentiate, but differentiation itself is controlled by selective gene expression.

D. Incorrect. Cell replacement is a function of stem cells and cell division (mitosis), but generating specialized cells initially requires differentiation via selective gene expression.

Describe the characteristics of stem cells that make them potentially useful in medicine. [5]

Any five of the following:

a. (stem cells) have/retain the capacity to divide;

b. can be used to produce cell cultures/large number of identical cells;

c. can be used to repair/replace damaged/lost cells/tissue;

d. (stem cells) are undifferentiated / have not yet differentiated/specialized;

e. can differentiate/specialize in different ways / are pluripotent/totipotent;

f. can be used to form a variety of different tissues / form organs;

g. used in medical research;

h. used in treatment of (named) disease;

Sample answer:

Stem cells are potentially useful in medicine because they retain the capacity to divide [1], allowing them to generate a continuous supply of new cells. They can be used to produce large numbers of identical cells [1] in culture, which is valuable for research and therapeutic applications. As they are undifferentiated and have not yet specialized [1], stem cells have the ability to differentiate in different ways, being pluripotent or totipotent, which allows them to develop into many types of cells. This capacity enables them to repair or replace damaged or lost cells and tissues and even form a variety of different tissues or organs [1]. Additionally, stem cells are widely used in medical research [1] to study disease mechanisms and to develop potential treatments for conditions such as Parkinson’s disease or diabetes.

Research is being conducted into treatment for diabetes based on stem cells. Discuss the ethical issues involved in stem cell research. [3]

Any three of the following: 

a. suffering of patients could be reduced / diseases could be cured / better treatments developed / might replace treatment with cure;

b. (possibly) less cost than treating disease/diabetes; 

c. specific example of ethical conflict; (e.g. patient groups support use of embryonic stem cells but religious groups oppose / different views on the moral status of an embryo)

d. restrictions on research in some countries due to cultural/religious traditions; 

e. still in experimental stages / risk to patient;

f. specific example of risk; (e.g. stem cells developing into tumours / rejection /need for immunosuppressants);

g. death of early-stage embryos / production of embryos for stem cell research;

h. use of stem cells from adults/patients could overcome these objections;

Sample answer: 

Research into stem cells, particularly for the treatment of diseases such as diabetes, raises complex ethical issues that must be carefully considered. In the early phases of research, there is significant potential to reduce patient suffering and possibly cure diseases or replace existing treatments with a definitive cure [1]. However, ethical concerns emerge in the phases involving embryos, as the death of early-stage embryos or creation of embryos solely for stem cell research can occur. This creates a phase of ethical conflict [1], where patient groups may support the use of embryonic stem cells, but religious groups oppose it due to differing views on the moral status of the embryo. During the experimental phases of therapy, there are risks to patients, including the potential for stem cells to develop into malignant tumors or be rejected by the body. Finally, in later application phases, the use of stem cells from adult patients [1] could help overcome some of these ethical objections.