Cell division

The cell cycle

Cells divide in a series of stages. Te genetic material is doubles and divided into two identical cells.

What does a cel have t do before it can divide? (interphase/growth phase)

• It needs to grow and ncrease the number of sub-cellular structures such as ribosome and mitochondria

• the DNA replicates to form two copies of each chromosome

What happens in mitosis?

one set of each chromosome is pulled to each end of the cell and the nucleus divides

What happens in the last stage of cell cycle? (cytokinesis)

The cytoplasm and cell membrane divides to form two identical cells

reasons why mitosis is important

for growth and development of multi cellular organisms

for repair of damaged cells

what is a stem cell?

A stem cell is an undifferentiated cell of an organism which is capable of giving rise to mny more cells of th same type, and from which certain other cells can arise from differentiation.

How to calculate the length of time in different stages in mitosis. (From a pie chart)

lenth of time in stage= (observed number of cells in stage/ total numbers of cells observed) x total time of cell cycle

Benefits of therapeutic cloning in plants

• Rare species can be cloned to protect from extinction

• crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers

• crops with resistance to pest can be cloned

Why is theraputic cloning/ the method of peroducing stem cells opposed by many people?

The embryo may die in the process

if implanted, the embroyo would develop into a clone of the patient

religious/moral/ethical beliefs

Disadvantage of using stem cells from meristem in plants

there will be low genetic diversity in the cloned plants

Difference between embryonic stem cell differs from adult stem cells

• Embroyonic stem cells have not differentiated and can differentiate into most types of human cells

• adult stem cells can form many but not all types of cells (e.g. blood cells)

• Embryonic stem cells are only found in embryos / early is develoment

• Adult stem cells are present in humans regardless of age

The pros of embrtnic stem cells

• can be used to treat a wide variety of diseases

• Embryonic stem cells are sourced from embryos made in IVF and more are usually made than are used

• The potential benefits of being able to treat more conditions and diseases with embryonic stem cells (to prevent human suffering) outweighs the consequences, especially as many embryos produced during IVF treatment are just discarded without having a use

Disadvantages of using stem cells

The long-term effects of embryonic stem cells are not known

Using embryos as a source of embryonic stem cells is controversial as some consider the practice to cause harm to an embryo which cannot give consent

Disadvantages of adult stem cells

• they can only differentiate into fewer types of specialised cells and may only be useful in treating a smaller number of disease

• very painful operation

• there are hazards if an operation to consider

Advantages of adult stem cells

• no ethical issues to consider if an adult consents to donating their bone marrow

• has been used as a source of stem cells for treatment for much longer and is more tried and tested (and therefore reliable);

Outlined process by which a cell divides by mitosis

• After the chromosomes are duplicated

• the chromosomes separate

• cytokynesis occurs (the cell membrane and cytoplasm divides)

• two genetically identical daughter cells are formed

Why can you use therapeutic cloning to treat disease but not to produce a baby

• Any baby produced in this way would be a clone as the genetic material only came from one individual which is illegal

• Cloning has many ethical issues; is a clone the property of the person it was cloned from or its own individual with its own rights?

• The cells would be used to treat disease and not used to make a baby

• Many different types of cells could be produced and used for research to help treat many diseases

• Any cells produced would have the same genetic makeup as the patient

• so there would be no issues of tissue rejection

How can embryonic stem cells treat paralysis

• Paralysis is caused by damage to neurones in the spinal cord (which cannot be repaired);

• Embryonic stem cells are unspecialised and could be manipulated to differentiate into neurones / nerve cells / their supporting cells;

• Which could be used to replace the cells damaged in the spine;

How does a foetus form through mitosis from a zygote ?

Mitosis increases the number of cells

cell differentiation occurs

to create speacialise dcells which carry out particular fuctions

How can embryonic cells be used to treat a heart attack when the coronary artery becomes blocked .

Stem cells can be removed from an ealy embryo.

Could be stimulated to develop into heart muscle tissue

these stam cells could then be transferred/implanted int the patient

to repair the damaged tissues/cells