B2.3 Cell Specialization

Question 1

what is a zygote?

Answer 1

a zygote = an unspecialized cell produced from fertilization

Question 2

What is the difference between a multicellular and unicellular organism?

Answer 2

• Multicellular organisms are made of many cells working together
• Unicellular organisms consist of one cell which conducts all major life process

Question 3

List the differences between a plant and animal cell

Answer 3

Plant cells have chloroplast, cell wall, large central vacuole, animal cells don’t

Question 4

• All the cells within one organism contain _________
• However, not all cells of an individual will ______
• This difference in gene expression is ______

Answer 4

• All the cells within one organism contain identical sequences of DNA (except for gametes)
• However, not all cells of an individual will express the same genes at the same time
• This difference in gene expression is what determines the type of cell that is formed

Question 5

what is differentiation?

Answer 5

the process by which cells become specialised to carry out specific functions

Question 6

Outline the impact of chemical gradients on gene expression within an early-stage embryo

Answer 6

• Chemical gradients in an early-stage embryo are created by molecules called morphogens

–> morphogens = secreted by certain cells and diffuse through surrounding tissue

• As morphogens spread, they form a concentration gradient
• Cells in the embryo detect their position within this gradient using surface receptors, and this determines which genes are turned on or off
• SO, cells begin to differentiate based on the morphogen concentration they are exposed to

–> This system ensures that even though all cells have the same DNA, they express different sets of genes

Question 7

Advantages of specialisation?

Answer 7

increased efficiency in carrying out specific functions by specialised cells in multicellular organisms

Question 8

what is a stem cell?

Answer 8

an undifferentiated cell of a multicellular organism that can form more cells of the same type for an unspecified period

Question 9

Outline two properties of stem cells

Answer 9

• Self-renewal: stem cells they continuously dividing and replicating
• Potency: stem cells having the capacity to differentiate into specialised cell types (depending on the type of stem cell, they can form all, many, or one type of cell)

Question 10

what are the 4 different types of stem cells?

Answer 10

• Totipotent
• Pluripotent
• Multipotent
• Unipotent

Question 11

Totipotent stem cells can? (define)
+ give example

Answer 11

Totipotent stem cells can:

• differentiate into any type of cell (including placental cells)
• give rise to a complete organism

EXAMPLE: a zygote

Question 12

Pluripotent stem cells can? (define)
+ give example

Answer 12

Pluripotent stem cells can:

• differentiate into all body cells
• BUT! they cannot give rise to a whole organism

EXAMPLE: embryonic stem cells

Question 13

Multipotent stem cells can? (define)
+ give example

Answer 13

Multipotent stem cells can:

• differentiate into a few closely related types of body cells

EXAMPLE: umbilical cord stem cell, bone marrow

Question 14

Unipotent stem cells can? (define)
+ give example

Answer 14

Unipotent stem cells can:

• Only differentiate into their associated cell type

EXAMPLE: liver stem cells only being able to make liver cells

Question 15

which stem cells are most prevalent in the early embryonic development of a multicellular organism?

explain why.

Answer 15

pluripotent stem cells!

because they have the ability to differentiate into all body cells needed to form the entire organism

• Although they cannot form extra-embryonic tissues like the placenta, they can give rise to the three germ layers (endoderm, mesoderm, and ectoderm) from which all the body’s tissues and organs develop

–> this makes them essential during the early stages of development when the embryo is beginning to form all of its complex structures

Question 16

what type of stem cells are the cells at the morula stage?

Answer 16

they are totipotent stem cells

BC they not only can differentiate into any cell of the organism, but they can also give rise to the embryo, the placenta and the embryonic sac tissues

BUT, as the morula develops into a blastocyst, the cells become less adaptable + start to lose their totipotency (later, pluripotent stem cells take over, which is why they are the “most prevalent” in the early embryonic development of a multicellular organism)

Question 17

what happens at fertilisation?

Answer 17

the diploid single cell called a zygote begins dividing

• Once it becomes a solid ball of about 16 to 32 cells, it is called a morula
• After another 6 more days the morula becomes a hollow ball of cells called a blastocyst
• The outer cells (trophoblast) will become the placenta. The inner cell mass (ICM) will become the embryo

Question 18

define stem cell niche

Answer 18

The microenvironment within the organism in which the stem cells exist and receive their instructions

Question 19

what does the stem cell niche do? how does it do this?

Answer 19

it influences the stem cells and how they differentiate

it can do this because:

• there are numerous interactions that happen in the niche that can determine what happens to the stem cells
• The stem cells can interact with the extracellular matrix, with signalling molecules in the matrix either telling the cells to remain dormant or to activate gene expression

–> This leads to the creation of more stem cells or for the existing cells to differentiate

Question 20

what are two types of multipotent stem cells in an adult human body?

Answer 20

1. Haematopoietic (Blood) Stem Cells
2. Hair Follicle (Skin) Stem Cells

Question 21

what is the bone marrow? what is it made up of?

Answer 21

• it’s the soft, spongy centre of most bones that has many blood vessels associated with it
• made up of a combination of cells that make blood cells (haematopoietic) as well as those that are supportive cells

–> supportive cells regulate the function of the haematopoietic ones that generate the blood cells

Question 22

outline the location + function of Haematopoietic Stem Cells

Answer 22

LOCATION: in the bone marrow

FUNCTION:

• they produce all types of blood cells (red, white, platelets)
• they maintain a constant supply of functional blood cells throughout life

Question 23

outline the location + function of Hair Follicle Stem Cells

Answer 23

LOCATION: the ‘bulge’ area of hair follicles in the skin

FUNCTION:

• they are involved in the growth and regeneration of hair
• they contribute to the replacement of skin cells and the cyclical nature of hair growth, rest, and regeneration
• they help to maintain healthy skin and hair throughout life

Question 24

how are stem cells used in the treatment of leukaemia?

Answer 24

1. hematopoietic stem cells (HSC)s are harvested - they can be taken from bone marrow, peripheral blood or umbilical cord blood
2. the patient next undergoes chemotherapy and radiotherapy to get rid of the diseased white blood cells
3. the HSC’s are transplanted back into bone marrow, where they differentiate to form new healthy white blood cells

Question 25

what is leukaemia? what is it caused by + what is the effect?

Answer 25

- it's a type of cancer of the blood or bone marrow - it results in a high number of abnormal white blood cells - it's caused by mutations in genes that control cell division

Question 26

What is an advantage of treating leukaemia with hematopoietic stem cells (HSCs) taken from the patient’s own pelvic bone?

Answer 26

the chances of tissue rejection by the patient’s immune system is reduced since the HSCs are obtained from the patient’s own pelvic bone

Question 27

the name of the solid ball of totipotent cells formed soon after fertilisation?

Answer 27

morula

Question 28

what is the surface area to volume ratio?

Answer 28

- it is the ratio of the surface area of a cell to its volume - as the size or volume of a cell increases, the surface area to volume ratio reduces

Question 29

calculate surface area to volume ratios

Answer 29

proves that: as the size or volume of a cell increases, the surface area to volume ratio reduces

Question 30

The rate at which substances cross the plasma membrane depends on?

Answer 30

The rate at which substances cross the plasma membrane depends on **its surface area** so, SA = important BC a cell needs to import molecules and expel waste products through its plasma membrane in order to survive! (+ SA plays a role in increasing or decreasing that rate!)

Question 31

Single-celled organisms have a ____ surface area to volume ratio what is the implication of this?

Answer 31

Single-celled organisms have a **very large** surface area to volume ratio SO, they can obtain all the nutrients they need and remove all their waste products via simple diffusion

Question 32

relating back to SA:V ratios, why must a cell divide in order to survive?

Answer 32

- If a cell continues to grow, the cell's surface area will become too small compared to its volume (BC its volume increases faster than its surface area) + not enough of the necessary molecules can get in and not enough waste can get out --> meaning: a small SA:VOL ratio means may cause a cell to die (BC it causes a decreased rate of exchange) - SO a cell needs to divide in order to restore a larger surface area to volume ratio

Question 33

How do cells control their size within an organism?

Answer 33

- Cells use **control mechanisms** involving **cell surface receptors** and **growth factors** in their environment --> These signals help regulate growth + ensure that the maximum size of any given cell type is consistent within an organism

Question 34

Why is the surface area to volume ratio important when considering cell size?

Answer 34

As a cell grows, its volume increases faster than its surface area, which can limit the efficiency of nutrient uptake and waste removal (a small SA:V ratio might even cause the cell to die) --> so this ratio = super important to consider!

Question 35

Put the following cells found in humans in order from smallest largest: - Egg (ovum) - Red blood cell - Fat cell - Sperm cell - Cardiac cell

Answer 35

1. Sperm 2. Red blood cell 3. Cardiac cell 4. Fat cell 5. Egg (ovum)

Question 36

Outline the activities occurring in the volume and at the surface of the cell

Answer 36

**Volume (inside the cell):** - metabolic activities occur - organelles within the cytoplasm carry out essential processes like protein synthesis, energy production, and waste management - the larger the volume, the more space is available for these activities **Surface (cell membrane):** - the surface = involved in the exchange of materials with the environment (ex. nutrient intake, oxygen absorption, and removal of waste products) - the membrane also contains receptors for communication and control mechanisms

Question 37

Explain the benefits of using cubes to model the surface area and volume of a cell

Answer 37

- Simplicity: Cubes have straightforward, measurable dimensions that make calculating surface area and volume easy - Visual clarity: They help students understand how increasing size affects surface area and volume differently - Scalability: They clearly demonstrate the mathematical relationship between surface area and volume

Question 38

Explain the limitations of using cubes to model the surface area and volume of a cell

Answer 38

- Shape difference: Real cells are rarely perfect cubes - Complexity of membranes: Real cell membranes are not flat surfaces and have complex structures - Function and structure diversity: Real cells have internal organelles and structures that are not represented in a cube model

Question 39

Describe the relationship between cell size and the SA:V ratio of the cell why does this relationship matter?

Answer 39

As a cell grows in size, its volume increases faster than its surface area --> meaning: the SA:V ratio decreases This relationship matters BC larger cells have a smaller surface area relative to their volume, which makes it harder for it to efficiently exchange materials with its environment

Question 40

Explain why cells are often limited in size by the SA:V ratio

Answer 40

they are limited in size BC: - A smaller SA:V ratio means slower and less efficient exchange of nutrients, gases, and waste across the cell membrane - If a cell becomes too large, its surface area may not be able to support the metabolic demands of its volume - To stay alive, cells must maintain a balance by remaining small or dividing once they reach a certain size (which limits its size)

Question 41

Relate the size of a sperm cell to its specialized function

Answer 41

**Size:** - One of the smallest human cells **Function:** - to deliver DNA to the egg **Relation to size:** - Small size and streamlined shape help the sperm move quickly and efficiently toward the egg - Carries minimal cytoplasm because it doesn't need nutrients

Question 42

Relate the size of an egg cell to its specialized function

Answer 42

**Size:** - One of the largest human cells **Function:** - Provides the nutrients and cellular machinery needed for the early development of the embryo **Relation to size:** - Large volume allows storage of nutrient-rich cytoplasm, which supports the embryo

Question 43

Relate the size of a red blood cell to its specialized function

Answer 43

**Size:** - Small, with a biconcave shape **Function:** - Transports oxygen throughout the body **Relation to size:** - Small size and high surface area-to-volume ratio allows for efficient gas exchange - Lack of a nucleus makes room for more haemoglobin

Question 44

Relate the size of a white blood cell to its specialized function

Answer 44

**Size:** - Larger than red blood cells **Function:** - Part of the immune system + fights infections **Relation to size:** - Larger size and presence of a nucleus help these cells store and use genetic instructions for creating immune responses

Question 45

Relate the size of a nueron to its specialized function

Answer 45

**Size:** - Can be very long (some axons are over 1 metre long) **Function:** - Transmits electrical signals over long distances in the body **Relation to size:** - Long, slender shape allows for rapid and direct communication between the brain/spinal cord and distant body parts

Question 46

Relate the size of striated muscle fibers to their specialized function

Answer 46

**Size:** - Large, multinucleated, and can be extremely long **Function:** - Contracts to produce movement **Relation to size:** - Large size provides the force and coordination needed for powerful muscle contractions - Multiple nuclei help manage the high demand for protein production along the length of the fibre

Question 47

what feature of red blood cells enables them to be deformed and return to their original shape as they squeeze through small gaps?

Answer 47

Their highly flexible membrane (it allows them to spring back to shape)