GCSE Core Science - Edexcel - B1

Asha Harney
Flashcards by Asha Harney, updated more than 1 year ago
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All the key things to learn for B1
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What is a gene? The basic unit of genetic material inherited from our parents. A gene is a section DNA which controls part of a cells chemistry - particualry protein production.
Where are genes found? Genes are found in our chromosomes,which parents pass on to offspring in their sex cells in reproduction. Different versions of the same gene are called alleles, and these can determine features like eye colour, and the inheritance of disorders.
What are choromosomes? Chromosomes are structures found in the nucleus of most cells. They consist of long strands of a substance called deoxyribonucleic acid, or DNA for short.
What is a section of DNA that has a genetic code for making a particular protein? A section of DNA that has the genetic code for making a particular protein is called a gene. The proteins can either be: structural proteins such as the ones found in muscles and hair enzymes, such as proteases and other digestive enzymes.
Describe what is meant by the term 'variation': Individuals differ in all sorts of ways, even when they are offspring of the same parents. These differences are called variation. Most characteristics, such as height, are determined by several genes working together.
What are environmental factors? Things such as climate, diet, culture and lifestyle determine variation. For example, an individual might inherit a tendency to tallness, but a poor diet during childhood will result in poor growth and a shorter individual.
Why are identical twins a good example of the interaction between inheritence and environment? Identical twins are genetically the same and yet an identical twin who does regular exercise will have better muscle tone than one who does not exercise. All of the differences between identical twins are due to differences in their experiences or environment.
How many pairs of chromosomes do human bodies contain? Human body cells each contain 23 pairs of chromosomes. Parents pass on their genes to their offspring in their sex cells.
What do a pair of chromosomes carry? A pair of chromosomes carry the same genes in the same place, on each chromosome within the pair. However, there are different versions of a gene called alleles. These alleles may be the same on each pair of chromosomes, or different.
What do sex cells only contain one of from each pair? Sex cells only contain one chromosome from each pair. When an egg cell and sperm cell join together, the fertilised egg cell contains 23 pairs of chromosomes. One chromosome in each pair comes from the mother, the other from the father.
Is the chromosome we get from each pair completely random or not? Which chromosome we get from each pair is completely random. This means different children in the same family will each get a different combination. This is why children in the same family look a little like each other and a little like each parent, but are not identical.
What happens to when the sex cells form? When sex cells form, the pairs of sex chromosomes (XX and XY) are separated. Females carry XX, males XY. This means all normal egg cells produced by a human ovary have an X chromosome and half the sperm carry an X chromosome, and half a Y.
How is a human baby's gender determined? A human baby’s gender is determined by the sperm that fertilises the egg cell. The baby will be a girl if it carries an X chromosome. It will be a boy if the fertilising sperm carries a Y chromosome.
What are some arguments in favour of using IVF? Some people think parents should be able to choose the sex of their future children, especially if they had a child that died, or already have three or four children of the same sex
What are some arguments against the use of IVF? Some people think we should not be able to choose, because this could affect the balance of males and females in society, or because they believe it is against God or nature.
Descibe the term 'values': Science can provide information and data, but it cannot answer questions about values. Values often result in different people coming to different decisions. This is why some people think we should be able to choose the sex of our children while others don't.
Descibe the Y Chromosome: The Y chromosome carries a gene called the ‘sex-determining region Y’, or SRY for short. The SRY gene causes testes to develop in an XY embryo. These produce androgens: male sex hormones. Androgens cause the embryo to become a male: without them, the embryo develops into a female.
What are alleles? Different versions of the same gene are called alleles. They can be either recessive or dominant. Genetic testing can determine whether a person is carrying the alleles that cause genetic disorders. But there are limits to the testing.
What is a recessive allele? A recessive allele only shows if the individual has two copies of it. For example, the allele for blue eyes is recessive. You need two copies of this allele to have blue eyes.
What is a dominant allele? A dominant allele always shows, even if the individual only has one copy of it. For example, the allele for brown eyes is dominant. You only need one copy of it to have brown eyes. Two copies will still give you brown eyes.
What is the genotype? Genotype describes the genetic make-up of an organism (the combination of alleles).
What is a phenotype? Phenotype describes the observable, physical characteristics that an organism has. This is often related to a particular gene.
Describe cystic fibrosis: Cystic fibrosis is caused by a recessive allele.People with CF produce abnormally thick and sticky mucus in their lungs and airways. They are more likely to get respiratory infections.
What does the disease CF do and how you relieve some of the side effects? The disease blocks tubes that take enzymes to the gut meaning food is not digested properly, leaving the person short of essential nutrients. Daily physiotherapy helps to relieve congestion, while antibiotics can fight infection.
How are people born with CF? You need to inherit two copies of the faulty allele to be born with CF. If you have just one copy, you are a carrier, but will not experience any symptoms. If two carriers have a child together, there is a one-in-four chance of passing on the disorder.
What is Huntington's disorder cause by? Huntington’s disorder is caused by a dominant allele, written as H. The symptoms usually develop in middle age, and include tremors, clumsiness, mood changes, memory loss and the inability to concentrate.
How do you get Huntington's disorder? You only need to inherit one copy of the faulty allele to have Huntington’s disorder, unlike cystic fibrosis. You can inherit Huntington’s disorder if one or both of your parents carry the faulty allele, because it is a dominant allele.
Describe what's going on on this example of a Punnett Square: ae517ddc-d03a-4e1f-b373-72cf79b50431.gif (image/gif) In this example one parent carries one copy of the Huntington’s allele and has the disorder. The father does not carry the Huntington’s allele, so he does not have the disorder. There is a 1 in 2 or 50 per cent chance of the couple producing a child with the disorder.
What is the key thing to remember about Huntington's disease? Note that in any individual family with a carrier parent, by chance, all the children may inherit Huntington's disorder or none at all.
Why is there an issue regarding cystic fibrosis? Scientists are now able to test adults and foetuses for alleles that can cause genetic diseases. However, the scientific information produced raises many issues that science cannot address. For example, should a couple with a one-in-four risk of having a child with cystic fibrosis take the gamble, or decide not to have any children at all? If a woman becomes pregnant with a child that is going to have cystic fibrosis, should she have the child, or consider having an abortion? These are questions about values that science cannot answer. Different people will have different views.
Describe genetic testing: Genetic testing involves analysis of a person’s DNA to see if they carry alleles that cause genetic disorders. It can be done at any stage in a person’s life. There are several types of genetic testing, including testing for the purpose of medical research.
What is Antenatal testing? This is used to analyse an individual’s DNA or chromosomes before they are born. At the moment, it cannot detect all inherited disorders. Prenatal testing is offered to couples who may have an increased risk of producing a baby with an inherited disorder. Prenatal testing for Down’s syndrome, which is caused by a faulty chromosome, is offered to all pregnant women.
What is Neonatal testing? This is used just after a baby has been born. It is designed to detect genetic disorders that can be treated early. In the UK, all babies are screened for phenylketonuria, congenital hypothyroidism and cystic fibrosis. Babies born to families that are at risk of sickle cell disease are also tested.
What is Pre-implantation genetic diagnosis? Pre-implantation genetic diagnosis (PGD) is a procedure used on embryos before implantation. Fertility drugs are taken by the female so that several eggs are released and collected by a doctor. These eggs are then fertilised in a Petri dish by sperm, either from the father or a donor. This is known as in vitro fertilisation (IVF). Once the embryos have reached the eight-cell stage, one cell is removed from each.The cells are tested for the allele posing a risk (for example the Huntington’s allele). This is known as PGD. Embryos that don’t contain the unwanted allele are then implanted into the uterus to hopefully create a lower risk, full-term pregnancy.
What is carrier testing? This is used to identify people who carry a recessive allele, such as the allele for cystic fibrosis. Carrier testing is offered to individuals who have a family history of a genetic disorder. It is particularly useful if both parents are tested, because if both are carriers there is an even greater risk of producing a baby with a genetic disorder. The cells are tested for the allele posing the risk (for example the Huntington’s allele). This is known as PGD. Embryos not containing the unwanted allele are then implanted into the uterus.
What is predictive testing? This is used to detect genetic disorders where the symptoms develop later in life, such as Huntington’s disorder. Predictive testing can be valuable to people who have no symptoms but have a family member with a genetic disorder. The results can help to inform decisions about possible medical care.
Describe some of the limits of genetic tests: Genetic tests are not available for every possible inherited disorder. And they are not completely reliable. They may produce false positive or false negative results, which can have serious consequences.
When does a fake positive occur? A false positive occurs when a genetic test has wrongly detected a certain allele or faulty chromosome. The affected individual or family could believe something is wrong when it is not, which may lead them to decide against starting a family or considering an abortion in order to avoid having a baby with a genetic disorder
When does a false negative occur? A false negative happens when a genetic test has failed to detect a certain allele or faulty chromosome. The affected individual or family would be wrongly reassured, which may lead them to decide to start a family or continue with a pregnancy that they otherwise would have avoided.
What is meant by the term 'distinguish questions'? You will need to use your ideas about science to distinguish questions that can be answered using a scientific approach from those that cannot. For example, science can answer the question, 'What are the chances of my child having cystic fibrosis?'. However, it cannot answer the question, 'Should I have my pregnancy terminated?'
What does it mean to clearly state the issue at heart of any debate? Find the ethical issue. In a debate about treating genetic diseases with gene therapy, some people think that altering our DNA is against nature or God. The ethical issue is whether scientists should be allowed to use gene therapy.
What is meant by 'access to our genetic profile'? Some people believe employers should have access to our genetic profile when we apply for a job. In the future, they may be able to use this information to determine how much time we are likely to take off due to illness, and use this information to help decide whether or not to offer us a job. Insurance companies may also want access to our genetic profile. They could use this information to see how long we are expected to live, and possibly refuse to give us insurance or only provide it at an increased cost.
What is the difference between genetic testing and values? Genetic testing is an example of what is technically feasible, ie what can be done. But the decisions we take on how to use this information are an example of values, and cannot be ‘answered’ by science. A common argument when discussing ethical issues like this is that the right decision is the one that leads to the best outcome for the majority of those involved. Society is going to have to decide who has access to our genetic profile. For example, should we all be on a DNA database to help the police catch criminals? Or is this a step too far, because in the future it could allow employers and insurance companies to access to data that we would rather they did not see?
Describe what is meant by 'changing values': Scientific data does not change according to who is reading it. But values can change, especially in different environmental and social contexts. For instance, many Roman Catholics think abortion is a sin, but many other people do not and choose to have an abortion because they think it is the right thing to do.
What are clones? Clones are genetically identical individuals. Bacteria, plants and some animals can reproduce asexually to form clones that are genetically identical to their parent. Identical human twins are also clones: any differences between them are due to environmental factors.
Whats is asexual reproduction? Asexual reproduction only requires one parent, unlike sexual reproduction, which needs two. Since there is only one parent, there is no fusion of gametes, and no mixing of genetic information. As a result, the offspring are genetically identical to the parent, and to each other - so they are clones.
Describe asexual reproduction in plants: Asexual reproduction in plants can take a number of forms. Many plants develop underground food-storage organs that later develop into the following year’s plants. Potato plants and daffodil plants do this. Some plants produce side branches with plantlets on them. The Busy Lizzie plant does this. Others, such as strawberry plants, produce runners with plantlets on them
Describe artificial cloning: It is possible to make clones artificially. The cloning of animals has many important commercial implications. It allows an individual animal that has desirable features, such as a cow that produces a lot of milk, to be duplicated several times.
Describe the two types of cells: There are two types of stem cells: adult stem cells - these are unspecialised cells that can develop into many (but not all) types of cells embryonic stem cells - these are unspecialised cells that can develop into any type of cell. During the development of an embryo, most of the cells become specialised (cells with modifications to structure according to the task they have to perform). They cannot later change to become a different type of cell.
Describe embryonic stem cells: But embryos contain a special type of cell called stem cells. These embryonic stem cells can grow into any type of cell found in the body so they are not specialised. Stem cells can be removed from human embryos that are a few days old, for example, from unused embryos left over from fertility treatment. Here are some of the things stem cells could be used for: making new brain cells to treat people with Parkinson’s disease rebuilding bones and cartilage repairing damaged immune systems making replacement heart valves.
What is Therapeutic cloning? If you were to receive medical treatment with cells grown from stem cells, your body’s immune system would recognise the cells as foreign, and they would be rejected and die. But this would not happen if you received cells with the same genes as your own. This could be done by cloning one of your cells to produce an embryo, then taking stem cells from this.
What are the teps involved in Therapeutic cloning? 1. Nucleus taken out of a human egg cell 2. Nucleus from a patient's cell put into the egg cell 3. Egg cell stimulated to develop into an embryo 4. Stem cells taken from the embryo 5. Stem cells grown in a container of warm nutrients 6. Stem cells treated to develop into required cell types.
Decribe the process of embryo transplants: A developing embryo is removed from a pregnant animal at an early stage, before its cells have had time to become specialised. The cells are separated, grown for a while in a laboratory then transplanted into host mothers. When the offspring are born, they are identical to each other and to the original pregnant animal. They are not identical to their host mothers because they contain different genetic information.
What is fusion cell clothing? Fusion cell cloning involves replacing the nucleus of an unfertilised egg with one from a different cell. The replacement can come from an embryo. If it is from an adult cell, it is called adult cell cloning.
Who was Dolly the sheep and how was she produced? Dolly the sheep' was the first mammal to be cloned using adult cell cloning. She was born in the UK in 1996 and died in 2003. Here is how she was produced: An egg cell was removed from the ovary of an adult female sheep, and its nucleus removed The nucleus from an udder cell of a donor sheep was inserted into the empty egg cell The fused cell then began to develop normally, using genetic information from the donated DNA. Before the dividing cells became specialised, the embryo was implanted into the uterus of a foster mother sheep. The result was Dolly, who was genetically identical to the donor sheep.
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