2.6.10 Stem Cells In Animals & Plants

Question 1

Stem Cells in the Bone Marrow

Answer 1

The stem cells found in bone marrow are multipotent adult stem cells
- this means they can only differentiate into erythocrytes (red blood cells), monocytes, neutrophils and lymphocytes

Question 2

Erythrocytes

Answer 2

Erythrocytes are red blood cells, the main function of which is the transport of oxygen around the body (and also the transport of carbon dioxide)
As red blood cells lack a nucleus, they cannot constantly being formed from bone marrow stem cells in order to maintain the red blood cell count in the blood
- this process is known as erythropoiesis

Question 3

Structure and Function of Erythrocytes

Answer 3

During erythropoiesis, changes occur that adapt the structure of the original stem cell to enable it function as an erythrocytes
These captions include
- the changing of the cell into a biconcave shape which has a larger surface area, allowing fore more oxygen to be absorbed through the cell surface
- the building up of the haemoglobin in the cytoplasm: haemoglobin is the pigment that binds with oxygen and only realises it when oxygen concentrations decreases below a certain level
- the ejection of the nucleus (and other organelles including mitochondria, endoplasmic reticulum and Golgi apparatus) which creates more room in the cytoplasm for haemoglobin, increasing the oxygen-carrying capacity
- an elastic membrane which allows erythrocytes to change shape and therefore squeeze through narrow capillaries

Question 4

Neutrophils

Answer 4

The same stem cells from the erythrocytes also form neutrophils (a type of white blood cell)
As the stem cells differentiate into neutrophils, the main changes that occur include:
- indentations form in the nucleus, giving it a lobed structure
- granules accumulate (these are lysosomes that contain hydrolytic enzymes)

Question 5

Structure and Function of Neutrophils

Answer 5

Neutrophils are the first white blood class to arrive at an infection site on or in the body
They exit the blood through tiny gaps in the capillary walls and collect around foreign bodies (e.g. pathogens)
They then destroy these by engulfing them (phagocytosis) and digesting them using their hydrolytic enzymes
The adaptions of neutrophils include:
- a flexible shape and a flexible nuclear membrane which allows them to fit between the capillary wall cells and to form pseudopodia (the extensions of the cytoplasm that engulf foreign bodies during phagocytosis)
- containing many lysosomes which contain digestive enzymes that destroy invading cells

Question 6

Meristems

Answer 6

Xylem vessels and phloem sieve tubes form the transport systems of plant and are found throughout their roots and stems
The xylem and phloem are formed from stem cells that are found in the tissue between the
- this is known as the cambium
The cambium is a meristem, which is the temp given to any undifferentiated tissue in an plant that has the ability to give rise to new cells
- for example, there are also meristems located at the tip of shoots and roots that prove new cells to these growing parts of the plant

Question 7

The Cambium

Answer 7

In the roots and stems of the plants, the stem cells at the inner edge of the cambium differentiate into xylem cells and the stem cells at the outer edge of the cambium differentiate into phloem cells
- cambium cells that differentiate to form the xylem close their cytoplasm, deposit lignin in the cell walls and lose their end cell wall
- cambium cells that differentiate to form the phloem lose some of their cytoplasm and organelles, and develop sieve plates (located at end of the cells)
This cell differentiation is stimulated by hormones (the balance of different hormones can determine whether xylem or phloem tissue is produced)

Question 8

Embryonic Stem Cells Summary

Answer 8

Found on the inside layer of an embryo
Undifferentiated/unspecialised
Can produce all the different types of specialised cells in the body

Question 9

Adult Stem Cells Summary

Answer 9

1. Bone marrow - limited ability to differentiate/partially specialised - can produce mainly cells of the blood (red blood cells, cells of the immune system)
2. Skin - limited ability to differentiate/partially specialised - can produce cells found in different layers of the skin and hair follicles
3. Other organs such as the liver and brain - limited ability to differentiate/partially specialised - can produce cells found in these organs
4. Umbilical cord - limited ability to differentiate/partially specialised - can produce cells of the blood (red blood cells, white blood cells), muscle and nerve tissue

Question 10

Meristem Cells Summary

Answer 10

Found in tips of roots and shoots (growing regions of plants)
Fully undifferentiated
One cell has the ability to divide to produce a whole new plant