B2 topic 1 notes

Question	Answer
I know why light microscopes and electron microscopes are useful when studying cells.	It is because most cells are too small to be seen with the naked eye. In a light microscope, a beam of light is passed through the cells. In an electron microscope, a beam of electrons is passed through. They enable us to see the cells in much more detail.
I can carry out simple magnification calculations.	Total magnification=magnifying power of eyepiece lens x magnifying power of objective lens. Or The length of the object=the length of the magnified object/the magnification
I can explain why the development of modern microscopes has enabled us to see cells with more clarity and detail.	An electron microscope can magnify a specimens up to 2000000 times, and a light microscope can magnify a specimen more than 1500 times. With magnifications like this, we can see observe very small structures inside cells. These microscopes have resolving power(wavelength/2) which means that they can make objects that are close together seem further apart. The greater the resolving power, the clear the image showing more detail.
I can name the main components in plant and animal cells.	Animals and Plant cells both have: a nucleus cytoplasm cell membrane Mitochondria Only Plant Cells have: A cell wall Vacuole Chloroplasts
I can describe the functions of each cell component.	(Remember the song you made in year 9 to Bridgit Mendler's 'ready or not'.) A nucleus this controls what the cell does and contains the chloroplasts. Cytoplasm-this the jelly like stuff where all the chemical reactions happen. A cell membrane- a thin skin around the cell it holds the cells together and also controls the chemicals that go in and out. Mitochondria-where sugars are broken down to release energy. Plant Cells: Cell Wall- A supportive layer of cellulose, it strengthens the cell. Vacuole- A large space filled with cell sap, it keeps the cell turgid. Chloroplasts- contain chlorophyll used for photosynthesis.
I can explain the role of mitochondria and chloroplasts.	Most of the chemical reactions involved in cellular respiration happen in the mitochondria. A mitochondrion is shaped perfectly to maximize its efforts. Mitochondria are very small organelles(number of organized or specialized structures within a living cell). Chloroplasts are the food producers of the cell. When the energy from the Sun enters a chloroplast, chlorophyll (inside the chloroplasts) uses that energy to combine carbon dioxide and water to make oxygen and glucose. This nutrients for the cell and energy.
I know what a gene is and describe the basic structure of DNA.	A gene is strand of DNA (double stranded molecule twisted into a spiral called a double helix, they carry genetic codes) which carry the information in the sequence of it's amino acids (building blocks that make a protein) to produce a protein.
I can describe the structure of a DNA.	DNA is a long molecule made up of 2 twisted strands of the bases Adenine, Thymine, Cytosine and Guanine that forms a double helix. The two strands are held together by hydrogen bonds between pairs of bases.
I know how DNA can be extracted.	Use a detergent/salt mixture to break up the membrane of the cells and release the chromosomes. Use a protease enzyme(protein digestive enzyme) to break down the protein part of the chromosones, releasing their DNA. Add cold methanol, which precipitated the DNA(makes it come out of solution). The strands can be clearly seen.
I can explain what we mean by complementary base pairing.	The arrangement where the two strands of a DNA molecule are joined together through their bases. T-A G-C remember this as Tigers Are Great Cats.
I know that the work of Scientists Watson, Crick, Franklin and Wilkins helped discover the structure of DNA	In the 1950's Franklin and Wilkins beamed x-rays at purified DNA and used photos to record how the molecule scattered the x-rays. They discovered the arrangement of atoms in a DNA molecule. In 1953, Watson and Crick used this information to propose that the structure of a molecule of DNA is a double helix.
I can evaluate the roles of Watson, Crick, Franklin and Wilkins in the discovery.	Watson and Crick model was based on the images produced by Franklin, which was secretly given to them by Maurice Wilkins. Franklin's role is probably the most important because it was her data that she complied that aided Crick and Watson discover the double helix. When Watson and Crick published their paper, their only reference to Franklin and Wilkins' team was a footnote. Eventually their contributions were recognized. They were all awarded a noble piece prize, but sadly Franklin died four years before.
I understand what the Human Genome Project process was.	The genetic information in an organism is called its genome. The Human Genome Project began in 1989, the HGP used the DNA of several people to get an average sequence, but each person has a unique sequence. The scientists broke up chromosomes of cells to get their DNA. Copies of the DNA were placed inside machines called sequences, which display the most likely order of the bases. Computers were used to help match the base sequences of genes with the proteins for which they code. Aims: To work out the order or sequence of all the three billion base pairs in the human genome To identify all the genes To develop faster methods for sequencing DNA
I can evaluate the implications of the Human Genome Project.	Positive Implications: mproved genetic testing Location of genes that might be linked to increased chances of inheriting a disease New gene therapy treatments New knowledge of how humans have evolved Personalised medicines. However the ethical concern is that the human genome revealed that some races are more or less vulnerable to certain diseases than others. Some people are concerned that if genetic data identifying ethnicity were available it might encourage discrimination against certain groups of people.
I understand what we mean by genetic engineering.	The deliberate modification of the characteristics of an organism by manipulating its genetic material.
I can describe the stages of the genetic engineering technique on bacteria.	The first process of recombinant DNA technology (Genetic Engineering) is to identify the required gene. The gene is cut out using a restriction endonuclease enzyme. The same enzyme is used to cut out a section of the plasmid. This ensures it to have the correct bases and match the ends of the gene. The plasmid and gene are stuck together using a DNA ligase enzyme. The taking up of a gene by a bacterial cell can be done by using the process of temperature shock or electric shock treatment. This is to make the bacterial cell more permable and take up the gene. After this process, the bacterial cell is then able to make the protein instructed by the gene. Now, the bacteria can multiply and produce millions of identical clones all with the gene that codes for the amino acids required for the protein . For example, a bacteria containing the human gene for insulin are grown in a fermenter to make insulin. The insulin is then purified for use.
I know what a plasmid is.	Loops of DNA found in the cytoplasm of bacterial and yeast cells.
I can discuss the advantages and disadvantages of using genetically engineered insulin.	Advantages: Cheap Available in Large Quantities It is a human gene for insulin, therefore, users experience no allergic reactions or intolerances. It does not use animal products, and so is not a problem for certain religious groups and vegetarians. Disadvantages: Some people are concerned that GM organisms could have unknown and unforeseen effects on other organisms, including humans.
I understand why it is sensible to have only bacteria with modified plasmids in the fermenter.	The fermenter is expensive, the other non-modified bacteria would not be of any use to us, so it would waste nutrients. Moreover, it reduced contamination. Finally, the non-modified bacteria would compete with the modified bacteria and as a result, so, there would be less insulin.
I can state some uses of genetically modified crops and know some issues associated with them.	Some scientists have added genes to some plants to make them herbicide resistant. This can allow farmers to then destroy competing weeds without destroy the crop. GM crops include those that can produce their own fertiliser, herbicide resistant, resist diseases, grow in places with low rainfull. However, some people are concerned that it's not natural, so it could affect our health. It may harm wildlife and pollen from crops modified to resist herbicides may transfer to weeds.
I can evaluate the use of herbicide resistant crops.	Although this process might be incredibly effective, the potential disadvantages include the potential development of herbicide-resistant weeds Loss of biodiversity as fewer weed species survive as a food and shelter source for animals.
I can discuss the advantages and disadvantages of golden rice.	Scientists have added two extra genes to normal rice to make golden rice. Golden rice produces beta-carotene which is needed by humans to produce vitamin A. Vitamin A deficiency is common among millions of poorer people and can cause blindness. Arguments For: Human cells convert beta-carotene into vitamin A very efficiently. Golden Rice is not meant to be the only solution to the Vitamin A problem. Arguments Against: The people who most need this source of vitamin A might not be able to afford to buy the golden rice seed. It might crossbreed with wild plants and contaminate their DNA. There are concerns that eating GM foods might harm people. Some people say that the levels of beta-carotene in golden rice are not high enough to make much of a difference to children's health.
I know that mitosis results in two daughter cells identical to the parent cells, and that it is used for growth repair and asexual reproduction.	When the cell divides by mitosis, it produces two daughter cells, each with identical sets of chromosomes in the nucleus as the parent cell, this results in the formation of two genetically identical diploid body cells. It does not matter if the cells are different in size, the nucleus is the same meaning they are identical.
I can describe the process of mitosis. (Image)	Image: add_ocr_bimitosisa_v2.gif (image/gif)
I can describe the process of mitosis.	One pair of homologous(same) chromosones replicate to form two joined strands, in the process of DNA replication. The joined strands sperate and one complete set of chromosones begins to move to each side of the cell. A new nuclear membrane begins to form around each set of chromosones. Two new nuclei are formed and the cell begins to split and form two new cells.
I can describe the process of meiosis.	It starts with a cell with complete set of chromosome (23 pairs), each chromosome then replicates. This results with two identical strands of each chromosome, these are called chromatids. The chromosomes line up with their replicas in the centre of the cell. The chromatids are split in half . The chromatids exchange parts. The cells has divided to form four new cells each with half the chromosome number of the original cell.
I can define haploid and diploid.	Haploid- having a single set of unpaired chromosomes. Diploid- containing two complete sets of chromosomes, one from each parent.
I can recall that at fertilisation haploid gametes join to form a diploid zygote.	Diploid adult undergoes meiosis and produce 23 chromosones which then fertilise to produce a zygote with diploid cells. Therefore, it goes from diploid adult to haploid gametes to diploid zygote.At fertilisation, the nuclei of the sperm and an egg join to form the diploid zygote.
I can recall what meiosis produces.	Meiosis produces four daughter cells each with half the number of chromosones and this produces haploid gametes. Gametes contain different genetic information to each other and to the parent cell. Meiosis is responsible for causing genetic variation.
I can compare mitosis and meiosis.	Differences: Mitosis produces diploid cells containing two sets of chromosomes and meiosis produces haploid cells containing one set of chromosomes.Mitosis produces body cells and meiosis produces gametes. Mitosis is used in growth, repair and asexual reproduction. Meiosis is used in just reproduction. In mitosis the cells produced are genetically identical, whereas, in meiosis they are not. Similarities: They both start with a diploid cell. Although, mitosis is asexual reproduction and meiosis is sexual reproduction, they both have a role in a type of reproduction.
I know how mitosis affects the body.	All the diploid cells are in the body should be genetically identical. This is because they have been produced by mitosis from the single cell of the zygote. However, a mutation during mitosis may mean the body cells are not completely identical. The sex cells/gametes which are haploid contain only half the genetic information that is found in a diploid body cell.
I know what n and 2n mean.	2n is the diploid number and n is the haploid number.
I know what the Hayflick limit is.	It means that cells should not divide more than 50 times.
I can describe how plants are cloned using cuttings.	In flowering plants, parts of the root, leaf or stem can grow into new plants. It is asexual reproduction. It produces new plants which are genetically identical to the parent plant, this is helpful for farmers who want plants with the desired characteristics. Cuttings are a piece of stem cut from a parent plant, which has the potential to develop roots and grow into a new plant. Cuttings are an example of asexual reproduction that produces genetically identical copies. You can clone plants by cutting off a small length of the stem, dip it in hormone rooting powder. Put the stem into a flowerpot full of damp compost. Cover the pot with a plastic bag to keep it moist and then it will grow.
I can describe how embryo transplants are used.	Donor eggs are taken from female animals and fertilised in the laboratory. Each embryo that forms is split up into its separate cells. Some of the separated cells are transplanted into the womb of the surrogate mother. The host mother later gives birth to several genetically identical youngsters. They are clones
I can discuss the advantages, disadvantages and risks of cloning.	Diadvantages: Expensive Time Consuming It may not have all the desired features, as some are controlled by the environment. Complicated process, chances of mistakes are high. Problems in the original organism will be passed on to the clone. Risks: Shortened life span prone to illnesses damaged organs Advantages: the beneficial features of the parent will be passed down. It helps to build up populations of rare animals which might be threatened with extinction. A person needing a transplant could use a brain dead clone of themselves as a source for tissues and organs. they would not be rejected as a result.
I can explain each stage of production of a cloned animal.	The haploid nucleus of a donor egg is removed and a nucleus is removed from a body cell. The diploid nucleus from the body cell is inserted into the enucleated(nucleus removed) cell. This is done by an electric shock. The egg cell divides by mitosis to form a blastocyst. At this stage, it is implanted into a surrogate mother. The offspring will be a copy of the animal who donated the diploid nucleus.
I know what it means that stem cells can differentiate.	Stem cells are undifferentiated biological cells found in a multicellular organism. Undifferentiated stem cells mean they are not specialised meaning they do not have a specific job, it means they can change into any cell found in the body.
I can recall how a stem cell matures.	Stem cells in the embryonic stage can differentiate into all other types of cells, but they loose that ability as they mature. This is why embryonic stem cells are favoured however they can be seen as unethical.
I understand why scientists are exited about the prospects of stem cells.	If stem can multiply and differentiate, we would have an unlimited supply of different types of cells, which could be transplanted into people who's tissues are damaged.
I know the definitions of an adult and embryonic stem cell.	Adult Stem Cell- Undifferentiated cells found among differentiated cells in a tissue or organ that can renew itself (e.g bone marrow). However they can only differentiate into a few types- platelets, red blood cell, white blood cells. Embryonic stem cells undifferentiated cells found in the inner cell mass of a blastocycst. They can develop into almost every cell found in the body.
I can describe how stem cell therapy could be used.	Example-leukemia The patient's existing stem cells are replaced with those from a healthy matching donor. The Patient's existing bone marrow and abnormal leukocytes are first killed using chemotherapy or radiation. Stem cells from a bone marrow from a matching donor is used. The stem cells are migrated into the patients bone marrow and produces healthy white blood cells.
I understand the process of therapeutic cloning.	Enucleated human egg cell is combined to a nucleus DNA from the patient's skin cell, through the electric shock process. It produces a cloned embryo. In the blastocyst stage, the stem cells are removed and the embryo dies. The Stem cells grown in a container of warm nutrients and then develop into required cell types
I can evaluate the use of stem cell therapy.	Embryonic Stem Cells Benefits- easier to remove from tissues. Can produce a wide range of specialised cells. Could offer the cure for diabetes, cancer and spinal chord injury. Drawbacks- ethical issues when deriving stem cells from embryos because the embryo would be destroyed. Risks- the cells may be rejected. Adult Stem Cells- Advantages- No ethical issues. If the stem cells are taken from a sibling or the patient, they are likely not to reject it. Drawbacks- difficult to identify and remove from tissues (the stem cells are mixed with cells in the tissue) Risks- rejection. Primary or secondary graft failure. They may carry genetic mutations for disease or may become defective. Risks for both- complications in the recipient, adverse immune responses or the development of cancers.
I understand that each protein has its own specific sequence of amino acids, resulting in different shaped molecules and that the order of bases in a gene decides the order of amino acids in a protein.	Cells make, or synthesise, proteins by joining together amino acid units in the correct order. Proteins have a complicated shape that helps them to carry out their jobs. Protein molecules that are the wrong shape cannot perform their functions properly. The more amino acid units joined together, the larger the molecule. Peptides are chain of 2-20, ploypeptides contain 21-50.
I can describe why the order of bases in a gene decides the shape and function of the protein.	Each gene acts as a code, or set of instructions, for making a particular protein. The order of the gene decides the shape and function of the protein.
I can explain the process of protein synthesis	The stages are TransCription and TransLation. Remember transcription comes first because c is before l in the alphabet. Transcription: The DNA in a gene unzips so that both strands are separate – one strand is used as a template. Complementary bases attach to the strand being copied – C joins to G and so on. Thymine (Base T) is not present and a different base, U, joins with A in the way that T would have done. This forms a strand of messenger RNA (mRNA), the strands of mRNA separate from their respective complementary strands of DNA. mRNA is small enough to leave the nucleus. Translation: Each strand of mRNA binds to a ribosome. The ribosome "reads" the mRNA in codons and lines tRNA with it, which are complementary to bases in mRNA. In RNA, the thymine pairs with uracil. The tRNA is specific to an amino acid that it collects and returns to the mRNA. The amino acids are now lined up in order of the instructions on the mRNA. Bonds form between the amino acids and a polypeptide chain is formed. The polypeptide chain folds and becomes a specific shape forming a protein.
I can explain what a mutation is.	Gene mutation-A sudden change in the bases that makeup the genetic code. (sickle cell anemia) Chromosome mutation-when the chromosomes are deleted, added or copied. (down syndrome) Each gene has a unique sequence of bases. The mutation changes the base code in the gene. This means that the amino acid chain does not code for the correct shaped protein.
I can describe how mutations can be harmful, beneficial or neither.	Harmful-sickle cell mutation on a cell shape is that it changes the round blood cell into a disc shape. They can easily get stuck in vessels and cause fatigue, pain and breathing difficulties. Beneficial- bacteria have mutated to become resistant to the effects of antibiotics. Rats are now resistant to the poisson-warfarin. Neither-the protein that a mutated gene produces may work just as well as the protein from the non-mutated gene.
I know that enzymes are biological catalysts and can state what conditions affect their activity.	A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. For this reason, enzymes are called biological catalysts. The conditions that affect their activity are: Temperature PH Substrate Concentration
I can use the lock and key hypothesis.	The active site(a region on an enzyme that binds to a protein or other substance during a reaction) in the enzyme allows the substrate (the substance on which an enzyme acts) to fit neatly. Active sites have different sized in different enzymes. Changing the PH or temperature changes the active site shape. The substrate would not fit as well. Too much change breaks the hydrogen bonds that hold the structure together in the enzyme, this will denature the shape.
I can explain why a change in conditions will affect the activity of an enzyme.	Enzymes are proteins, they are sensitive to changes in temperature and PH. Temperature- As the temperature falls below optimum(37 degrees C), the time taken for digestion gets increasingly slow. This is because the molecules of both the enzyme and substrate have less energy, so they do not collide with each other and join as quickly. As the temperature increases above optimum, the time taken to digestion gets slower again because the heart starts to alter the shape of the enzyme (it denatures) so it can't hold the molecules in the active site as well as during the reaction. PH- Most enzymes work fastest in neutral conditions. Making the solution more acidic or alkaline will slow the reaction down. At extremes of pH the reaction will stop altogether. Some enzymes, such as those used in digestion, are adapted to work faster in unusual pH conditions and may have an optimum pH of 2 (very acidic) if they act in the stomach. Substrate concentration- Enzymes will work best if there is plenty of substrate available. As the concentration of the substrate increases, so does the enzyme activity. When all the active sites are filled with substrate molecules, the rate of reaction levels off. Adding more enzymes increases the rate of reaction because there are more active sites available to fill.
I can explain the role of enzymes in DNA replication.	DNA replication occurs before a cell divides. The process: DNA helicase unzips and undwinds the double helix structure of the DNA. The weak hydrogen bonds split, separating strands (DNA Helicase) DNA helicase provides new bases a single strand of DNA to line up against the DNA. DNA polymerase join the nucleotides. The result is two identical DNA molecules. New molecule of DNA is made up of one new strand and one old strand of DNA.
I can explain the role of enzymes in protein synthesis.	When a protein is built from amino acids, during protein synthesis (look through notes of the process) an enzyme called Aminoacyl tRNA is used to join one amino acid to another.
I understand the effect of competitive inhibitor.	An inhibitor (a molecule that binds to enzymes and decreases their activity) competes with the substrate. If there are more inhibitors, the proper chemical reactions would not take place.

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