B2.3

Question 1

Stem Cells

What is a morphogen?

Answer 1

• A signal molecule controlling cell differentiation
• Can accumulate in different conc. in various regions of the embryo and the conc. determines what the cells in that area will differentiate into
• Play an important role early in cell specialization

Question 2

Stem Cells

What is a stem cell?

Answer 2

• Has the ability to divide endlessly and differentiate into various cell types
• Undifferentiated cells with the potential to be many different types of specialized cells
• In early embryonic development - all cells are stem cells

Question 3

Stem Cells

What is a stem cell niche?

Answer 3

• A location in adults where stem cells are present in high numbers as a result of proliferation but maintain the ability to differentiate.
• Often done through cell division - daughter cell self-renews thus stays as a stem cell while the other differentiates

Question 4

Stem Cells

What are the steps between gametes and an Infant?

Answer 4

• GAMETES (sperm and eggs): join together through fertilization to form a ZYGOTE.
• After five-ish days - some specialized cells - EMBRYO
• After 4-8 weeks into development - FOETUS, a term used until it becomes an INFANT

Question 5

Stem Cells

What is the role of cell signalling on cell differentiation?

Answer 5

• Cell signalling can trigger the expression of certain genes
• In cell differentiation - signal directs which genes are expressed, leading to the cell becoming specialized
• Early embryonic development - done with morphogens that accumulate in conc. in different areas of embryo

Question 6

Stem Cells

What are the two unique properties of stem cells?

Answer 6

• Self renewal: can be done either by one self-renewing and the other differentiating/ sometimes both.
• Recreation of a functional tissue: able to differentiate into a specialized cell that carries out important functions.

Question 7

Stem Cells

What are the locations of human stem cell niches?

(two stem cell niches that are functionally important)

Answer 7

• In the bone marrow: stem cells that differentiate into different blood cells - red, white and platelets - able to move into blood stream.
• Hair follicle: there are epithelial stem cells at the bottom of follicles - differentiate & carry out functions like skin and hair renewal and oil production.

Question 8

Stem Cells

What is the totipotent stem cell?

Answer 8

• Capable of continued division and can produce any tissue type
• Only found in early stages of an embryo

Question 9

Stem Cells

What is the pulripotent stem cell?

Answer 9

• Once the stem cell begins specializing within the embryo
• Can differentiate into most cell types but not all

Question 10

Stem Cells

What is the multipotent stem cell?

Answer 10

• Has the ability do differentiate into several cell types
• Distinct form specialized cells but are much more limited than pluripotent cells
• Found in adults i.e., haematopoetic stem cells in bone marrow

Question 11

Stem Cells

What are the cell size benefits of the egg cell?

Answer 11

• Largest volume 110micrometers in diameter and spherical shape.
• Large volume enables storage of food in cytoplasm

Question 12

Stem Cells

What are the cell size benefits of the sperm cell?

Answer 12

• Longer human cell at 50 micrometers long, but cell is narrow so has small volume
• Slender shape and small volume aid in movement for sperm to swim to egg
• Contain few organelles

Question 13

Stem Cells

What are the cell size benefits of red blood cells?

Answer 13

• Red blood cells have 6-8 micrometre diameter (small cells) but also have a biconcave shape (1micrometre thick)
• Shape makes moving through vessels earier and provides a larger SA:V for efficient loading and unloading of oxygen onto haemoglobin

Question 14

Stem Cells

What are the cell size benefits of white blood cells?

Answer 14

• B-lymphocytes change in size between inactive state and when actively secreting antibodies
• Inactive - 10 micrometres, when active - 30 micrometres with extra rough ER & golgi to produce and package antibodies (proteins)

Question 15

Stem Cells

What are the cell size benefits of neurons?

Answer 15

• Contain soma (20micrometre diameter)/ cell body large enough to meet needs of the long cell.
• Contain long axons - less synapses and quicker neural transmission

Question 16

Stem Cells

What are the cell size benefits of striated muscle fibres?

Answer 16

• Larger than normal cells, diameter of 20-100 micrometers and up to 100milimeteres in length
• Length allows for greater flexibility and force for movement

Question 17

Cell Size and SA:V

Meaning of Surface Area to Volume ratio

Answer 17

• SA: area of the perimeter – measures the amount of cell membrane
• Volume: internal space – amount of cytoplasm.
• This ratio indiactes the amount of membrane relative to cell’s size.

Question 18

Cell Size and SA:V

Nephron?

Answer 18

• A specialized cell with increased SA:V
• A nephron is a functional filtering loop within the kidney
• It’s purpose is to move substances between blood & urine, hence a high SA:V is beneficial.

Question 19

Cell Size and SA:V

Alveoli?

Answer 19

• Located in the lungs in the airways which branch into individual air sacs where gasses are exchanged between the bloodstream and lungs.
• Many small air sacs/alveoli increases the SA:V area of lung tissue to faciliate faster gas diffusion.

Question 20

Cell Size and SA:V

What are the challenges of a larger cell?

Answer 20

• Larger cells have more volume
• Means it takes longer for needed matierals to get where they are needed & wastes longer to exit
• Waste can accumulate and be toxic

Question 21

Cell Size and SA:V

What are the steps to calculate SA:V?

Three steps

Answer 21

1. Calculate the SA of the object following the formula
2. Calculate the volume of the object using the formula for its shape
3. Divide the surface area by the volume to get the ratio

Question 22

Cell Size and SA:V

What is the relationship between SA:V and cell size?

Answer 22

• Small cells have LARGER SA:V ratios (i.e., have more membrane for amount of cytoplasm)
  Vice versa with large cells

Question 23

Cell Size and SA:V

What are some cell modifications that increase SA:V?

Answer 23

• Change in shape - long and thin
• Having projections (made of membrane)
• Localise functions that rely on transport close to membrane
• Cell junctions that aid in material transport

Question 24

Cell Size and SA:V

What are the SA:V adaptations for Erhythocytes?

Blood cells

Answer 24

• Biconcave disc shape of red blood cells allows for a larger SA:V ratio by decreasing volume
• Cytoplasm is closer to the cell membrane, helping oxygen move in and out of the cell quicker.

Question 25

# Cell Size and SA:V What are the SA:V adaptations for Proximal Convoluted Tubule Cells? | Nephron, kidney

Answer 25

* Cube shape to **pack together** * **Microvilli** towards the inside, creating 'brush border' to increase SA:V with more membrane * Lots of **mitochondira** for active transport * Folds in opposite membrane as well

Question 26

# Cell Size and SA:V What are the SA:V adaptations for Type 1 pneumocytes? | 95% of alveoli is Type 1 pneumocytes, create a one cell thick layer

Answer 26

* Thin and flat to increase SA:V, contain minimal organelles. * Surrounded by **one cell thick capillaries** for efficient exchange * Tight junctions between 2 cells to prevent fluid entry

Question 27

# Cell Size and SA:V What are the SA:V adaptations for Type 2 pneumocytes? | 5% of alveolus, produce surfactant (fluid reducing surface tension)

Answer 27

* Cube shape with more **volume for organelles**, like secretory vesicles * Microvilli facing the alveolus * An irregular shape from frequent exocytosis

Question 28

# Cell Size and SA:V What are the SA:V adaptations for Cardiac Muscle cells? | Small, cubical Y shape

Answer 28

* Banding to **connect to multiple cells** * Intercalated **discs** as junctions between cells for **transmission of signals** * Branching for connection

Question 29

# Cell Size and SA:V What are the SA:V adaptations of Striated Skeletal Muscle Cells? | Muscle fibres are a single long "cell"

Answer 29

* These cells contain **multiple nuclei** and visable bands, related to shortening and lengthening for movement * **Long and thing** cells have a high SA:V ratio.

Question 30

# Cell Size and SA:V What are the SA:V adaptations of sperm cells? | Specifically for helping them penetrate an egg cell

Answer 30

* Receptors able to bind to the glycoproteins of the zona pellucida * **Acrosome** - sac of enzymes that digest the zona pellucide to allow sperm it * Binding proteins to faciliate **the fusion of membranes** for nuclear entry

Question 31

# Cell Size and SA:V What are the SA:V adaptations of egg cells? | Speficially to ensure only one sperm penetrates it

Answer 31

* **Zona pellucida** - layer of glycoprotiens with ZP3 receptors that chemically change post-fertilization * Binding proteins in plasm membrane that allow sperm in * **Cortical granules** - vesicles of enzymes around plasm membrane that release contents after fertilization to make **zona pellucida impenetrable**