B2

Question 1

What information is in your cells?

Answer 1

• Each of your cells has a nucleus that contains chromosomes.
• Chromosomes carry the genes that contain the instructions for making both new cells and all the tissues and organs needed to make an entire new you.
• A gene is a small packet of information that controls a characteristic, or part of a characteristic of your body. It is a section of DNA, the unique molecule that makes up your chromosomes.
• You have 46 chromosomes in the nucleus of you body cells. They are arranged in 23 pairs.
• In each pair of chromosomes, one chromosome is inherited from the father and one from the mother.

Question 2

What is the cell cycle and mitosis?

Answer 2

• Body cells divide in a series of stages known as the CELL CYCLE.
• Cell division in the cell cycle involves a process called MITOSIS and it produces two identical cells.
• Cell division by mitosis produces the additional cells needed for growth and development in multicellular organisms, and for the replacement of worn or damaged cells

Question 3

What is asexual reproduction?

Answer 3

• Asexual reproduction, is when the cells of an offspring are produced by mitosis from the cells of their parent.
• This is why they contain exactly the same genes as their parent with little genetic variation.

Question 4

What is the cell cycle?

Answer 4

• The cell cycle is short as a baby develops before it is born, when new cells are being made all the time.
• In adults there are regions where there is continued growth or regular replacement of cells. These include hair, skin, blood and the lining of the digestive system.
  The cell cycle, in normal, healthy cells follows a regular pattern:
• Stage 1: this is the longest stage in the cycle. The cells grow bigger, increase in mass, and carry out normal cell activities. Most importantly they replicate their DNA to form to copies of each chromosome ready for cell division. They also increase the number of sub-cellular structures such as mitochondria, ribosomes and chloroplasts ready for the cell to divide.
• Stage 2: Mitosis: in this process one set of the chromosomes is pulled to each end of the diving cell and the nucleus divides.
• Stage 3: this is the stage during which the cytoplasm and the cell membrane also divide to form two identical daughter cells.

Question 5

Why do cells differentiate?

Answer 5

• The cells of your body, or any complex multi cellular organism, are not all the same.
• They are not the same as the original cell either. This is because, as cells divide, grow and develop, they also begin to differentiate.

Question 6

What is differentiation in animal cells?

Answer 6

• In the early development of animal and plant embryos, the cells are unspecialised.
• Each one of them (known as a STEM CELL) can become any type of cell that is needed.
• Most specialised cells can divide by mitosis, but they can only form the same sort of cell.
• Some differentiated cells, such as red blood cells and skin cells, cannot divide at all and so ADULT STEM CELLS replace dead or damaged cells.
• Nerve cells do not divide once they have differentiated and they are not replaced by stem cells. As a result, when nerve cells are damaged they are not usually replaced.

Question 7

What is differentiation in plant cells?

Answer 7

• In contrast to animal cells, most plant cells are able to differentiate all through their lives.
• Undifferentiated cells are formed as active regions of the stems and roots, known as the meristems. In these areas, mitosis takes place almost continously.
• The cells then elongate and grow before they finally differentiate.

Question 8

What is cloning in plants?

Answer 8

• Producing identical offspring is known as CLONING.
• Huge numbers of identical plant can be produced from a tiny piece of leaf tissue. This is because, in the right conditions, a plant cell will become unspecialised and undergo mitosis many times.
• Each of these undifferentiated cells will produce more cells by mitosis.

Question 9

What is the function of stem cells?

Answer 9

• An egg and a sperm cell fuse to form a ZYGOTE, a single new cell. That cell divides and becomes a hollow ball of cells - the embryo.
• The inner cells of this ball are the EMBRYONIC STEM CELLS that differentiate to form all of the specialised cells of your body.
• Even when you are an adult, some of your stem cells remain.
• An adult stem cell is an undifferentiated cell of an organism that can give rise to many more cells of that same type.
• Certain other types of cell can also arise from stem cells by differentiation.
• Your bone marrow is a good source of ADULT STEM CELLS.
• Many of your differentiated cells can divide to replace themselves.
• Then they start dividing to replace the different types of damaged cell.

Question 10

How could stem cells be used?

Answer 10

• We might be able to grow whole new organs from embryonic stem cells.
• These could then be used in transplant surgery.
• Conditions from infertility to dementia could eventually be treated using stem cells.

Question 11

How are stem cells used in plants?

Answer 11

• The stem cells from plant meristems can be used to make clones of the mature parent plant very quickly and economically.
• This is important as it gives us a way of producing large numbers of rare plants reliably and safely.
• We may be able to save some rare plants from extinction in this way.
• Plant cloning also gives us a way of producing large populations of identical plants for research. This is important as scientists can change variables and observe the effects on genetically identical individuals.
• Cloning large numbers of identical plants from stem cells in plant meristems is also widely used in horticulture producing large numbers of plants such as orchids for sale.

Question 12

What are the problems with embryonic stem cells?

Answer 12

• Some people question the use of a potential human being as a source of cells, even to cure others.
• Some people feel that, as the embryo cannot give permission, using it is a violation of its human rights.
• The religious beliefs of others mean they cannot accept any interference with the process of human reproduction.
• Some people feel that a great deal of money and time is being wasted on stem cell research that would be better spent on research into other areas of medicine.
• Yet in spite of all these concerns, there is a lot of investment into stem cell research as many scientists and doctors are convinced stem cells have the potential to benefit many people.

Question 13

What is the future of stem cell research?

Answer 13

• An area of stem research that is being developed is known as therapeutic cloning, which has much potential but is proving very difficult.
• It involves using cells from an adult to produce a cloned early embryo of themselves.
• This would provide a source of perfectly matched embryonic stem cells.
• In theory, these could then be used for medical treatments such as growing new organs for original donor.
• The new organs would not be rejected by the body because they have been made from the body’s own cells and have the same genes.
  At the moment, after years of relatively slow progress, hopes are high again that stem cells will change the future of media. Currently, in the UK, stem cell research is being carried out into potential therapies to treat:
• spinal cord after injuries
• diabetes
• heart after damage in a heart attack
• eyesight in the blind
• damaged bone and cartilage.