1.4 Cellular Differentiation

Question 1

What is differentiation?

Answer 1

a basic unspecialised cell becomes altered to have a specific structure and function through the expression of certain genes

Question 2

TOPTIP

Answer 2

Differentiation = Specialisation

Question 3

What is gene expression?

Answer 3

the transcription and translation of genes to produce proteins

Question 4

Expression of Essential genes?

Answer 4

essential genes that code for proteins vital to all cells e.g. respiratory enzymes are ‘switched on’ - expressed

Question 5

Expression of cell specific genes?

Answer 5

cell specific genes that code for proteins allowing the cell to specialise to perform a function are ‘switched on’ - expressed

Question 6

Expression of unnecessary genes?

Answer 6

Unnecessary genes to the function of the particular cell are ‘switched off’ - not expressed

Question 7

TOP TIP

Answer 7

specialised cells can be somatic (body cells) or gametes (sex cells)

Question 8

LOOK AT DIAGRAM

Answer 8

…

Question 9

TOP TIP

Answer 9

When writing about specific genes being ‘switched on’ and others being switched off make sure you dont refer to a gene as being switched on and off - it gives the wrong idea completely

Question 10

What are meristems?

Answer 10

undifferentiated cells dividing by mitosis are found in specific regions of a multicellular plant called meristems
meristems are the only places that growth can occur in multicellular plants
cells produced in meristems then become specialised to form differentiated tissue

Question 11

What is totipotent?

Answer 11

meristematic cells are said to be totipotent which means they can form all the types of differentiated cells of the organism

Question 12

What are the two types of meristems?

Answer 12

apical

lateral

Question 13

What are apical meristems?

Answer 13

an apical meristem is found at the apex or tip of the roots and shoots of a plant
the growth and increase in length of the roots and shoots depends on three cells dividing, elongating, and becoming specialised for a particular function

Question 14

zones of a root tip?

Answer 14

root cap - protects the root as it forces its way downwards through the soil particles
zone of cell division - meristem - where new cells are formed
zone of elongation - the cells stretch and vacuoles form
zone of specialisation

Question 15

How do you calculate the mitotic index?

Answer 15

no. of cells undergoing a stage of mitosis
- ————————————————————-
no. of cells in field of views

Question 16

What are annual plants?

Answer 16

annual plants complete their life cycle in one year and then they die. They do not need particularly thick stems to support the plant as the plant will not grow very tall in one year.

Question 17

What are perennial plants?

Answer 17

perennial plants grow year after year and must develop thicker stems in order to support the new growth each year

this increases in girth of the plant is produced by lateral meristems

Question 18

What are lateral meristems responsible for?

Answer 18

responsible for making sure that enough new xylem is formed so that the plant gets enough support and is able to transport enough water and minerals to the living parts of the plant

Question 19

How are annual rings formed?

Answer 19

xylem is produced every year leading to the formation of annual rings

Question 20

Size of annual rings
spring into summer?
summer into autumn?

Answer 20

spring into summer - large thin walled xylem vessels allow for increased flow of water + minerals
summer into autumn - small thick walled xylem provide greater support

Question 21

what is the width of each ring dependent upon growing conditions present during that year?

Answer 21

a) wider rings produced by warm or wet weather

b) narrow rings are produced by cold or dry conditions

Question 22

What is mericloning?

Answer 22

plants such as orchids can be cloned by a process called mericloning
this involves removing the shoot tip of a parent plant containing the meristem
the cells are cultured in laboratory and grown into new plants
the plants produced by mericloning are identical to the parent plant from which the meristem cells were taken
this process allows many copies of a desirable plant to be produced.

Question 23

What is tissue culture?

Answer 23

the growth of tissues or cells separate from the organism

meristem is a type of plant that would be useful in tissue culture

Question 24

Where are the two locations of meristematic regions in a plant?

Answer 24

root and shoot tips (apical)

cambium between xylem and phloem in vascular bundles (lateral)

Question 25

How do scientists use tissue culturing techniques to create a clone of a plant?

Answer 25

tiny pieces of plant tissues are cut from the parent plant and grown on a medium containing nutrients and growth regulators (plant hormones) in aseptic conditions (free contamination)
The cells multiply and form a mass of undifferentiated cells called callus
in the presence of the correct balance of hormones in the growth medium, the callus tissue differentiates into plantlets with roots and shoots
when these plantlets are transferred to potting compost, they develop into normal, complete plants
thousands of genetically identical offspring (clone) can be obtained from a single plant by subdividing the calluses as they grow

Question 26

What can tissue culturing of plants used for?

Answer 26

production of clones of commercially important plants such as ornametals e.g. rose and orchid, crops including pineapple and oil palm and forests e.g. pine trees
regeneration of transgenic plants following genetic modification
Multiplication of plants that have been cleared of pathogens, for use in horticulture and agriculture

Question 27

What is a stem cell?

Answer 27

A stem cell is a master cell that is found in multicellular organisms
they are undifferentiated and have a unique property in that they can not only make new copies of themselves (self renewal) but can differentiate to become a specific cell type

Question 28

What are embryonic stem cells?

Answer 28

are totipotent - have the potential to become any type of body cell.

Question 29

What are the two sources of stem cells?

Answer 29

embryonic and adult tissues

Question 30

What are sources of stem cells?

Answer 30

donated embryos
amniotic fluid
induced pluripotent stem cells

Question 31

Donated embryos?

Answer 31

patients undergoing infertility treatment may agree to donate any extra embryos that are not required for their treatment to medical science
these very early embryos proved an immediate source of embryonic stem cells from donated embryos
these sources are limited, restricting the research that can be done on embryonic stem cells

Question 32

Amniotic fluid?

Answer 32

stem cells can be harvested from the fluid removed from pregnant women for amniocentesis tests
the stem cells obtained are multipotent the advantage is that no human embryos are destroyed in this procedure

Question 33

Induced pluripotent stem cells?

Answer 33

induced pluripotent stem cells are not true stem cells. they are differentiated cells that have been genetically reprogrammed using transcription factors to switch some of their switched off genes back on again
as a result they act as stem cells and can be used for research

Question 34

Moral ethical issues?

Answer 34

unused blastocysts from embryonic stem cells lines and cytoplasmic hybrid cells are destroyed as they are not allowed to develop beyond day 14 of the development stage. this is when the embryo would normally implant in the uterus and develop into a foetus.

Question 35

Health ethical issues?

Answer 35

a complete medical history of adult stem cell donors is required to minimise the chance of recipients developing other medical problems

Question 36

Safety ethical issues?

Answer 36

stem cells must be safe to use in the treatment of patients i.e. they should not cause other conditions or diseases such as tumours caused by certain types of IPSCs. It is for this reason that ongoing research and thorough testing is vital.

Question 37

What are therapeutic uses of stem cells?

Answer 37

New skin can be grown in the laboratory from the stem cells of burns patients for grafting
As the new skin has been grown from the patients own stem cells, it will not be rejected by the body

Bone marrow transplants give patients suffering from cancer of the blood (leukemia) the ability to make healthy blood cells from the stem cells within the donated bone marrow

Corneal transplants in the eye can be achieved by growing new corneal tissue from a patients eye stem cells which replaces damages cornea, restoring light.