6.5 - Stem Cells Flashcards
What is a stem cell?
Undifferentiated cells that can divide indefinitely and differentiate into a range of specialised cells
Name 4 types of stem cells
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
Define a totipotent cell
•Are able to differentiate into any type of cell found in the body
• Aldi into extra embryonic cells such as those in the placenta
• these cells are found in the embryo at an early stage called the blastocyst
Define multipotent
Can differentiate into a number of closely related cell types within a certain type of tissue
Eg. Haematopoeitic adult stem cells in the bone marrow give rise to different types of blood cells
Define unipotent
Cannot differentiate, but are capable of self renewal
What are embryonic stem cells?
Stem cells found in embryos and can develop into almost every cell type under the right conditions in a lab
- present a very early stage of embryo development
- embryonic stem cells are totipotent before 7 days and pluripotent after the blastocyst forms
What are some advantages of embryonic stem cells?
- can treat a wide variety of diseases
- can become any cell tyoe
What are some disadvantages of embryonic stem cells?
- possible harm/death of the embryo
- human rights / ethical issues the embryo cannot give consent
- unreliable as this is not a well tested method
What are some advantages of adult stem cells?
- no ethical issues as adult can give consent for the stem cells to be collected
- safer as this is a well tested method
What are some disadvantages of adult stem cells?
- 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 )
- can be very painful
What are adult tissue stem cells?
- found in adult tissues eg. Bone marrow, brain , muscle
- can only differentiate into the same type of cell as the tissue they came from
- present throughout life from birth
- could be artificially triggered to become pluripotent
- can be harvested from umbilical cords of newborn babies
- in animals adult stem cells are used to replace damaged cells
Where are plant stem cells found?
Meristems
Where is the cambium in meristems in plants ?
Between xylem and phloem - a layer of meristem cells - they divide to produce new xylem and phloem
What is the role of xylem in meristems in plants?
- transports water and minerals within plant
- meristem cells produce small cells which elongate
- walls are reinforced with waterproof lignin
- ends of cells break down
- this forms a long continuous tubes with a wide lumen
- provides support for the plant
What is the role of phloem in meristem in plants?
- transports products of photosynthesis within a plant
- structure consists of sieve tubes and companion cells
- meristem tissue produces cells that elongate and line up to form end to end tubes
- ends do not break down completely
- form sieve played in between cells
- sieve plates allow for the movement of material up or down tube
- next to each sieve cell is a companion cell providing support
