Stem Cells

Question 1

What are gametes?

Answer 1

Gametes are the sex cells that fuse together during sexual reproduction. Gametes have haploid nuclei, so in humans both egg and sperm cells contain 23 chromosomes.

Question 2

What is a zygote?

Answer 2

The fertilized egg cell. It is therefore is a diploid (2N - N being 23 chromosomes) cell containing two of each chromosome.

Question 3

How do cells differentiate?

Answer 3

All cells of an individual organisms share an identical genome - each cell contains the entire set of genetic instructions for that organism. BUT not all genes are activated. Newly formed cells receive signals from morphogens which deactivate (or more rarely activate) genes,
The fewer active genes a cell possesses the more specialized it will become
Some cells lose the ability to divide once specialized, such as nerve and muscle cells

Question 4

What are totipotent stem cells?

Answer 4

Capable of continued division and possesses the ability to produce any tissue in the organisms. Only exist in the very early stages of embryo development. Could produce a whole organism

Question 5

What are pluripotent stem cells?

Answer 5

Only exist in early embryonic stage. Can mature into almost all the different cell types. Would not be able to produce a whole organism

Question 6

What are multipotent stem cells?

Answer 6

Can differentiate into a few closely-related types of cell. Occur later in the embryo development and are present during the remainder of an organism’s life

Question 7

What are unipotent stem cells?

Answer 7

Can regenerate but can only differentiate into their associated cell type (ex. liver stem cells can only make liver cells).

Question 8

What are the two types of stem cells?

Answer 8

Embryonic stem cells can differentiate into any kind of cell. They are considered pluripotent
Tissue stem cells (sometimes called “adult stem cells”) exist within specialized tissue. They are only able to differentiate into certain types of cells.

Question 9

What two properties are unique to stem cells?

Answer 9

They can self-renew: This means they can divide and become more stem cells, or a mixture of stem and differentiated. This allows stem cells to be maintained
They can recreate functional tissues. Signalling will turn on and off certain genes to cause the cells to become differentiated

Question 10

What is therapeutic cloning?

Answer 10

Stem cells can be used to replace damaged or diseased cells with healthy, functioning ones
This process requires:
The use of biochemical solutions to trigger the differentiation of stem cells into the desired cell type
Surgical implantation of cells into the patient’s own tissue
Suppression of host immune system to prevent rejection of cells (if stem cells are from foreign source)
Careful monitoring few cels to ensure they do not become cancerous

Question 11

What is therapeutic cloning used for?

Answer 11

Leukaemia: Bone marrow transplants for cancer patients who are immunocompromised as a result of chemotherapy
Paraplegia: Repair damage caused by spinal injuries to enable paralysed victims to regain movement Diabetes: Replace non-functioning iset cells with those capable of producing insulin in type I diabetics
Burn victims: Graft new skin cells to replace damaged tissue

Question 12

Ethical issues of stem cells

Answer 12

The ethical considerations associated with the therapeutic use of stem cells will depend on the source
The greatest yield of pluripotent stem cells comes from embryos, but requires the destruction of a potential living organism
The source of these embryonic stem cells comes from laboratories carrying out in vitro fertilization. Not all fertilized eggs are implanted so the rest will be used for research.

Question 13

What is size of cells dictated by?

Answer 13

Basic processes of cell physiology, such as need for materials to move in and out o the cell. This usually involves the surface area to volume ratio
Cell division apparatus. If cells are too large or too small, the mitotic spindle will not function properly

Question 14

Properties of red blood cells

Answer 14

Red blood cells transport oxygen throughout the body
* Contain hemoglobin that combine and release oxygen
* They have a biconcave disc shape which increases surface area for absorption
* They lack a mitochondria and a nucleus
* They are flexible and size limited because they need to move through narrow blood capillaries

Question 15

Properties of white blood cells

Answer 15

White blood cells mainly function as a defence against infections.
* They retain their nucleus
* There are several different types of white blood cells each with specific functions
* Posses vesicles with enzymes to kill microrganisms and break down their cellular debris that they obtain through phagocytosis

Question 16

Properties of neurons

Answer 16

There are several types of neurons each with distinct adaptations for their functions.
Motor neurons carry impulses from the brain or spinal cord to muscles and glands. They have long fibers called axons that can carry impulses up and down the body over long distances
Axons can extend up to 1 m

Question 17

What is striated muscle fibre

Answer 17

Striated muscle fibres make up skeletal muscle
Each fibre is its own cell, and it contains membranes that allows signal propagation.
They can be up to 12 cm long and are longer than cardiac and smooth muscle cells
Each band represents a unit of contraction
* They can have multiple nuclei

Question 18

Why the surface area to volume ratio is important

Answer 18

As the size of a cell is increased, the ratio between the surface area and the volume decreases.
This means that as the cell grows, the surface area is too small to allow enough substances into or out of the cell.
This rate of exchange limits the cell’s activities.
If the ratio is too small then substances will not enter the cell as quickly as they are needed and the waste products will accumulate since they are produced faster than they are removed.

Question 19

How do Organisms Maximize SA:Vol Ratio?

Answer 19

As organisms grow, cells divide. Two small cells are more efficient that one large cell.
Cells compartmentalize- They use membranes to care out metabolic processes. In eukaryotes, these are called organelles.
Organelles themselves, like mitochondria, are also made of membranes-maximizing the surface area for reactions.
Examples:
Intestines → fold up to make food absorption more efficient
Alveoli in the Lungs→ thin membranes to maximize surface area for gas exchange
Root hairs → maximize surface area for water absorption from the soil