Stem Cells

Question 1

What are stem cells?

Answer 1

Unspecialised cells that can develop into different types of cells.

Question 2

What’s the difference between stem cells and adult stem cells?

Answer 2

Stem cells in early embryos can develop into any type of human cell. Stem cells in adults can develop into a limited range of cells.

Stem cells are found in early embryos and in a few places in adults.

Question 3

How do stem cells differentiate in animals?

Answer 3

In animals, adult stem cells are used to replace damaged cells. E.g. to make new skin or blood cells.

Question 4

How do stem cells differentiate in plants?

Answer 4

Plants are always growing, so stem cells are needed to make new shots and roots throughout their lives. Stem cells in plants can differentiate into various plant tissues including xylem and phloem.

Question 5

Cells in Bone Marrow differentiate into Blood Cells.

Answer 5

Marrow is found in the centres of the main bones.
Adult stem cells divide and differentiate to replace worn out blood cells - erythrocytes (red blood cells) and neutrophils (white blood cells that help fight infection).

Question 6

Cells in the Meristems differentiate into Xylem and Phloem.

Answer 6

In plants, stem cells are found in the meristems.
In the roots and stem, stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes.

Question 7

How are Neutrophils (white blood cells) specialised for their function? (Animal cell)

Answer 7

• Flexible shape allows them to engulf foreign particles or pathogens.
• Many lysosomes in their cytoplasm contain digestive enzymes to break down engulfed particles.

Question 8

How are Erythrocytes (red blood cells) specialised for their function? (Animal cell)

Answer 8

• Bioconcave disc shape provides a large surface area for gas exchange.
• No nucleus so there more room for haemoglobin, the protein that carries oxygen.

Question 9

How are Epithelial cells specialised for their function? (Animal cell)

Answer 9

• Cells are joined by interlinking cell membranes and a membrane at their base.
• Ciliated epithelia (in airways) have cilia that beat to move particles away.
• Squamous epithelia (in lungs) are very thin to allow efficient diffusion of gases.

Question 10

How are Sperm cells specialised for their function? (Animal Cell)

Answer 10

• Flagellum (tail) so they can swim to the egg.
• Lots of mitochondria to provide energy to swim.
• Acrosome (tip) contains digestive enzymes so sperm can penetrate surface of the egg.

Question 11

How are Palisade mesophyll cells specialised for their function? (Plant cell)

Answer 11

• They do most of the photosynthesis in leaves.
• Contain many chloroplasts, so they can absorb a lot of sunlight.
• Walls are thin, so carbon dioxide can easily diffuse into the cell.

Question 12

How are Root hair cells specialised for their function? (Plant cell)

Answer 12

• Large surface area for absorption.
• Thin, permeable cell wall, for entry of water and ions.
• Extra mitochondria in cytoplasm to provide energy needed for active transport.

Question 13

How are Guard cells specialised for their function? (Plant cell)

Answer 13

• Found in pairs, with a gap between them to form a stoma. (Used for gas exchange)
• In light, guard cells take up water and become turgid.
• Thin out walls and thickened inner walls force the, to bend outwards, opening the stomata.

Question 14

What are the 4 types of potency of stem cells?

Answer 14

Unipotent, multipotent, pluripotent, totipotent.

Question 15

What does unipotent mean?

Answer 15

Can not differentiate, but are capable of self renewal (e.g. progenitor cells, muscle stem cells).

Question 16

What does multipotent mean?

Answer 16

Can differentiate into a number of closely related cell types within a certain type of tissue (e.g. haematopoeitic adult stem cells in bone marrow give rise to different types of blood cells).

Question 17

What does pluripotent mean?

Answer 17

Pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells (the cells that make up the placenta).

Question 18

What does totipotent mean?

Answer 18

Totipotent stem cells that are able to differentiate into any type of cell found in body including into extra embryonic cells such as those in the placenta. These cells are found in the embryo at an early stage called the blastocyst. The ‘total’ individual. E.g. zygote

Question 19

How long are zygotes totipotent for?

Answer 19

These embryonic cells are totipotent up to day 16 after fertilisation.

Question 20

How long are embryonic stem cells totipotent for?

Answer 20

Embryonic stem cells are totipotent before 7 days and pluripotent after the blastocyst (very early embryo) forms.

Question 21

Where are adult stem cells found?

Answer 21

In adult tissues such as bone marrow, brain, muscles, liver, breast, testicles, surface of eye, intestines.

Question 22

What type of stem cells are found in bone marrow?

Answer 22

Multipotent adult stem cells.
- This means they can only differentiate into erythrocytes (red blood cells), monocytes,
neutrophils and lymphocytes.

Question 23

Advantages of embryonic stem cells.

Answer 23

• Can treat a wide variety of diseases.
• Can become almost any cell type because they are pluripotent.

Question 24

Disadvantages of embryonic stem cells.

Answer 24

• Possible harm/death of the embryo.
• Human rights/ethical issues (the
  embryo cannot give consent).
• Unreliable as this is not a well-tested
  method.

Question 25

Advantages of adult stem cells.

Answer 25

- No ethical issues as adult can give consent for the stem cells to be collected. - Safer, as this is a well-tested method.

Question 26

Disadvantages of adult stem cells.

Answer 26

- Possibility of infection during extraction of stem cells. - Adult stem cells can only become one type of cell (same as the tissue it came from) as they are multipotent. - Can be very painful.

Question 27

What can totipotent embryonic stem cells differentiate into?

Answer 27

Pluripotent embryonic stem cells. They can either turn into Endoderm, Mesoderm or Ectoderm lines.

Question 28

What can pluripotent embryonic stem cells differentiate into? (Endoderm, Mesoderm, Ectoderm).

Answer 28

They turn into multipotent stem cells. - Endoderm stem cells can turn into lung or pancrease cells. - Mesoderm stem cells can turn into heart muscle or red blood cells. - Ectoderm stem cells can turn into skin of neuron cells.

Question 29

What can undifferentiated stem cells from bone marrow differentiate into?

Answer 29

Neutrophils (white blood cells). Erythrocytes (red blood cells).

Question 30

What happens during the process of erythropoiesis?

Answer 30

As red blood cells lack a nucleus, they cannot divide, meaning that new erythrocytes are constantly being formed from bone marrow stem cells in order to maintain the red blood cell count in the blood.

Question 31

What changes occur that adapt the structure of the original stem cell to enable it to function as an erythrocyte?

Answer 31

• The changing of the cell into a biconcave shape: this shape has a larger surface area, allowing for more oxygen to be absorbed through the cell surface. • The building up of haemoglobin in the cytoplasm: haemoglobin is the pigment that binds with oxygen and only releases it when oxygen concentrations decrease below a certain level. • The ejection of the nucleus (and other organelles including mitochondria, endoplasmic reticulum and Golgi apparatus): creates more room in the cytoplasm for haemoglobin, increasing the oxygen-carrying capacity. • An elastic membrane: this allows erythrocytes to change shape and therefore squeeze through narrow capillaries.

Question 32

What changes occurs in the differentiation into a neutrophil?

Answer 32

• A type of white blood cell. • Keep (lobed) nucleus. • Cytoplasm appears granular. • Large number of lysosomes produced. • This aids their role of ingesting invading microorganisms.

Question 33

What is Cambium?

Answer 33

A layer of meristem cells that lies in between xylem and phloem. They divide to produce new xylem and phloem.

Question 34

What different groups of tissues work together in the lungs?

Answer 34

- Squamous epithelial tissue in the alveoli. - Ciliated epithelial tissue in the bronchi. - Elastic connective tissue and vascular tissue in the blood vessels.

Question 35

What different groups of tissues work together in the leaves?

Answer 35

- Palisade tissue for photosynthesis. - Epidermal tissue to prevent water loss from the leaf. - Xylem and phloem tissue in the veins.

Question 36

Squamous epithelium functions.

Answer 36

- Single layer of flat cells lining a surface. - Found in may places including alveoli in lungs.

Question 37

Ciliated epithelium functions.

Answer 37

- Layer of cells covered in cilia. - Found on surfaces where things need to be moved. - Trachea, where cilia waft mucus along.

Question 38

Muscle tissue functions.

Answer 38

- Made up of bundles of elongated cells called muscle fibres. - 3 different types of muscle tissues: smooth, cardiac and skeletal. - Smooth (found on stomach lining). - Cardiac (found in the heart). - Skeletal (used to move).

Question 39

Cartilage functions.

Answer 39

- A type of connective tissue found in the joints. - Shapes and supports the ears, nose and windpipe. - Formed when cells called chondroblasts secrete extracellular matrix which they become trapped inside.

Question 40

Xylem tissue functions.

Answer 40

- Transports water around the plant. - Also supports the plant. - Contains hollow xylem vessels cells, which are dead, and living parenchyma cells.

Question 41

Phloem tissue functions.

Answer 41

- Transports sugars around the plant. - Arranged in tubes and is made up of sieve cells, companion cells, and some ordinary plant cells. - Each sieve cell has end walls with holes in them, so sap can move easily through them. - These end walls are called siege plates.