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| Question | Answer |
|---|---|
| Why does an organism need new cells? | to grow and to replace worn out or damaged cells |
| What is a gene? | a gene is a section of the chromosome that controls a characteristic or part of a characteristic |
| What is a gene made of? | a gene is made of the chemical DNA |
| What is DNA? | it is a special chemical used to build chromosomes and genes |
| Where are the chromosomes? | in the nucleus of the cell |
| What is a chromosome? | a chromosome is a set of genes connected together that carry genetic information and is made of DNA |
| What determines a characteristic of an organism? | some characteristics are the result of a single gene but most characteristics are the result of many different genes working together |
| What is the relationship between chromosomes and genes? | genes are grouped together to form chromosomes with a single chromosome often carrying several hundred or even thousands of genes |
| How many chromosomes are in the human cell? | 46 organised into 23 pairs |
| Where does each member of a chromosome pair come from? | 1 chromosome from each parent |
| Name the two human gametes? | sperm and ovum cells |
| How many chromosomes in a human gamete? | 23 single chromosomes |
| What is the cell cycle? | cells grow and divide in a series of stages called the cell cycle |
| What is the process of cell division called? | mitosis |
| What does mitosis produce? | two genetically identical cells called the daughter cells |
| Why do organisms need to do mitosis? | to produce new cells for growth or to replace worn out or damaged cells |
| How many parents are there in asexual reproduction? | just one |
| How many parents are there in sexual reproduction? | two |
| How does asexual reproduction happen? | offspring are produced by mitosis by a single parent |
| Why are offspring genetically identical to the parent in asexual reproduction? | because the offspring are produced by mitosis and mitosis produces genetically identically cells |
| How long does it take for the cell cycle to complete? | it varies taking anywhere from 24 hours to several years depending on the type of cell |
| How many stages are there in the cell cycle? | three |
| Describe the first stage of the cell cycle | • the longest stage • cells grow bigger and increase their mass • they replicate their DNA to create copies of all chromosomes • they increase the number of organelles like mitochondria and chloroplasts |
| Describe the second stage of the cell cycle | • mitosis starts • one set of chromosomes is to pulled to each side of the cell • the cell is dividing |
| Describe the third and final stage of the cell cycle | • the cytoplasm divides • the cell membranes divides • two daughter cells are formed |
| What is formed when a cell undergoes mitosis? | two genetically identical daughter cells |
| Compare cell division in a child and an adult | • in a child, cell division produces new cells faster than the old ones die • in an adult, cell division produces new cells at roughtly the samre rate as the old ones die |
| What is the average number of cell deaths per minute in humans? | about 300 million body cells die every minute |
| Question | Answer |
|---|---|
| How many cells are there in the human body? | Estimates range from 15 to 100 trillion |
| Why are the cells of a multicellular organism different? | as cells divide and grow, they differentiate |
| What are the undifferentiated cells of the early embryo called? | stem cells |
| How does a stem cell differentiate? | some genes are turned off and are switched on |
| Name some differentiated cells in humans. | nerve, skin, or muscle cells |
| When muscle cells divide by mitosis, what type of cells do they produce? | once a cell differentiates, it can only produce cells of the same kind by mitosis, so muscle cells |
| Can all differentiated cells divide by mitosis? | no - most can but not all |
| Name two differentiated cells that cannot divide by mitosis? | red blood cells and skin cells |
| How do red blood cells and skin cells reproduce to produce new cells for growth and repair? | adult stem cells produce new blood cells and skin cells |
| How do nerve cells divide to produce new nerve cells? | nerve cells do not divide once they are differentiated and there are no adult stem cells to produce new nerve cells so when nerve cells are damaged they are not replaced |
| Can differentiated animal cells redifferentiate? | no, once a muscle cell, always a muscle cell |
| Can adult plant cells redifferentiate? | unlike animal cells, most plant cells can differentiate all their lives - differentiation in plants cells is not permanent |
| Where are undifferentiated cells in plants? | they are generated at active regions in the roots and the stems called meristems |
| What happens in the meristems? | mitosis takes place continuously |
| How long do plants grow for? | all their lives |
| What is producing identical offspring called? | cloning |
| Can new plants be produced from a leaf? | yes, under the right conditions a plant cell will become undifferentiated so a leaf can be split into small sections each of which will form a new tiny plant that is gentically identical |
| Which are easy to clone, plants or animals? | plants are easy to clone while animals are very difficult to clone. |
| Question | Answer |
|---|---|
| What happens when an egg meets a sperm? | they fuse to form a single cell called a zygote |
| What happens to the zygote? | it divides by mitosis until it forms a hollow ball of cells called an embryo |
| What are the inner cells of the embryo called? | embryonic stem cells |
| What happens to embryonic stem cells? | they differentiate to form specialised cells |
| What is an adult stem cell? | adults have a small number of stem cells known as adult stem cells |
| Can an adult stem cell differentiate? | yes, it can differentiate to form specialised cells |
| Where in humans can adult stem cells be found? | bone marrow is a good scource of stem cells in humans |
| Why can spinal injuries cause paralysis? | because nerve cells cannot repair or replace themselves |
| What is the cause of type 1 diabetes? | specialised cells in the pancreas that are supposed to produce insulin are not working |
| How is it hoped that stem cells can help spinal injuries? | it is hoped that stem cells will differentiate and replace the damaged nerve cells |
| How is it hoped that stem cells can cure type 1 diabetes? | it is hoped that the stem cells will differentiate into working cells that produce insulin to replace the damaged cells in the pancreas |
| Name 3 conditions that may benefit from stem cells other than paralyis and diabetes? | dementia, infertility, and new organs for transplant |
| How are plants best cloned? | by taking cells from the meristems large numbers of plants can be made quickly and economically |
| Name industries that use plant cloning? | horticulture, agriculture, and research |
| How could cloning be used to combat plant extinction? | cloning can be used to produce very large numbers of rare plants |
| What is the value of cloning plants to research? | it produces large numbers of identical cells for scientist to test with |
| How does plant cloning assist agriculture? | large numbers of plants with special features like fruit colour and shape or disease resistance can be produced as in the banana trade |
| How has plant cloning affected horticulture? | orchids are hard to grow, grow very slowly, and used to be rare but are now available cheaply in large numbers because plant cloning can produce large large numbers of plants cheaply and quickly |
| Question | Answer |
|---|---|
| Where do large numbers of stem cells come from? | aborted embryos and spare embryos from fertility treatment |
| What are the issues with stem cell research? | • ethical and religious views about embryos • the slow pace of progress with research • the possiblity that stem cells may cause cancer • the concern that adult stem cells may be infected with viruses • the view that there are more important areas of medical research |
| What are the objections to sourcing stem cells from embryos? | • some people are uncomfortable with making use of a potential human beings • some people do not like the fact that the embryo cannot give permission to be used • some people's religious beliefs prohibit abortion and the use of embryos |
| What has progress been like in stem cell research? | relatively slow, difficult, expensive and hard to control over 20 years of research, in paticular, the signals that control differentiation are not yet understood |
| Why is there a concern that stem cells may cause cancer? | because this has been observed in the treatment of mice and some autoimmune diseases in humans |
| What are the concerns about using adult stem cells? | • they may be infected by viruses • they may trigger an immune response and be rejected |
| Where can embryonic stem cells be found other than in embryos? | in the blood of the umbilical cord and the amniotic fluid |
| What is the benefit of using embryonic stem cells from the blood of the umbilical cord? | it overcomes the ethical and religious objections to using embryos for stem cells |
| What is the benefit of using adult stem cells? | it overcomes the ethical and religious objections to using embryos for stem cells |
| What is therapeutic cloning? | it involves using cells from an adult to produce a cloned embryo |
| What is the benefit of therapeutic cloning? | the stem cells are genetically identical to the recipient so any new organs produced should not be rejected by the patient |
| What potential therapies are being considered with stem cell research? |
• spinal cord injuries • diabetes • heart damage due to heart attack • eyesight for blind people • damaged bone and cartilage |
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