Topic 3 Two Star LOs 2024 PDF Biology Past Paper

3.5) State 3 similarities and 3 differences between prokaryotic and eukaryotic cells Feature Prokaryote Eukaryote Size of cell Small, mean diameter 0.5 - 5 Larger, often up to 50 m m Nucleus Absent...

3.5) State 3 similarities and 3 differences between prokaryotic and eukaryotic cells Feature Prokaryote Eukaryote Size of cell Small, mean diameter 0.5 - 5 Larger, often up to 50 m m Nucleus Absent Present DNA and location Circular strands (NOT loops) in Form linear chromosomes in a cytoplasm nucleus Organelles Few, none is membrane-bound Many, mostly membrane-bound Cell wall Present, but not cellulose Present in plants only – made of (made of peptidoglycan cellulose instead) Ribosomes Smaller Larger Capsule Present in some Absent 3.7) Manipulate and use the formula:- magnification = size of image/size of real object in order to calculate size information about an organelle 3.7) Manipulate and use the formula:- magnification = size of image/size of real object in order to calculate size information about an organelle 3.8)  Convert numerical size information about an organelle between ordinary (e.g. 3,000,000) and standard form (e.g. 3.0 x 106) 3.8)  Convert numerical size information about an organelle between ordinary (e.g. 3,000,000) and standard form (e.g. 3.0 x 106) 3.9)  Calculate the surface area and volume of a cell which has a regular shape 3.9)  Calculate the surface area and volume of a cell which has a regular shape 3.17) Explain the terms linkage of genes and sex-linkage of genes Genetic linkage is the tendency of alleles that are located close together on a chromosome to be inherited (cross-over) together during meiosis. The nearer two genes are on a chromosome, the lower is the chance of a swap occurring between them, and the more likely they are to be inherited together. Sex linkage applies to alleles / genes that are located on the sex chromosomes, and are responsible for a specific trait. These genes are considered sex-linked because their expression and inheritance patterns differ between males and females. That is, the expression of the trait is related to gender (one gender inherits only one allele for a trait). 3.40) State 3 examples of multipotent stem cells in adult humans 3.40) State 3 examples of multipotent stem cells in adult humans (i) neural stem cells which can develop into the various types of cell found in the nervous system (particularly in the brain) (ii) blood stem cells, in the bone marrow, which can become white blood cells, red blood cells, or platelets (iii) muscle stem cells (required as mature muscle cells cannot reproduce, so once they die they are not otherwise replaced). 3.42) Describe the potential uses of stem cells in medicine and explain why they may be so useful Because totipotent embryonic stem cells have the unique ability of forming any type of human cell, scientists believe that this makes them ideal tools for studying disease and developing new treatments. For example, researchers are investigating whether they can turn embryonic stem cells into brain cells to replace those lost in Parkinson’s disease. Other diseases likely to benefit include Alzheimer's disease, heart disease, stroke, arthritis, diabetes, burns and spinal cord damage. Furthermore, by turning embryonic stem cells into, say, lung cells, scientists can use them to discover what goes wrong in the course of certain disease, such as cystic fibrosis. 3.44) Explain why some people are “for” the use of embryonic stem cells and others are “against” it by using the frameworks for ethical decisions For a) An embryo is a collection of cells not a human, so requires and deserves no particular moral attention b) Spare embryos are destroyed anyway c) The benefit to humans outweighs ethical concerns Against 1. An embryo should never be used for research purposes as it should have full human status from the point of conception 2. Can’t give consent 3. Equivalent to murder 4. May cause cancer 5. May cause an infection 3.45) Explain how therapeutic cloning and somatic cell nuclear transfer can overcome the problem of possible rejection of transplanted organs 3.45) Explain how therapeutic cloning and somatic cell nuclear transfer can overcome the problem of possible rejection of transplanted organs Skin cell (diploid, somatic cell) taken from patient. Skin cell nucleus is transferred to an ovum which has had its own nucleus removed. This process is known as somatic cell nuclear transfer. Ovum containing diploid nucleus is the equivalent of a zygote. This divides by mitosis until the blastocyst stage is reached. ES cells removed from inner cell mass of blastocyst and grown into desired cell/tissue/organ type New cells/tissue/organ are not rejected when transplanted into patient as they have the same cell surface molecules (self-antigens) as the patient. This means an immune response is not initiated 3.47) State 3 dangers of stem cell therapy 3.47) State 3 dangers of stem cell therapy a) When injecting stem cells there will always be a risk of introducing an infection b) The patient’s body may reject the stem cells c) There is a risk that the stem cells will become cancerous 3.49) Sketch and label a diagram of the nucleus to show its 3 main features 3.49) Sketch and label a diagram of the nucleus to show its 3 main features Double nuclear envelope Nuclear pores Nucleolus 3.51) Explain how, by having a diploid nucleus, a cell can be produced that is able to produce any protein that an organism requires A diploid cell contains all of the genes required to make any protein the body requires, so in each case the cells are only using the specific genes to make the specific protein they need to produce. In scientific terms, they are only expressing some of their genes. 3.53) State what is meant by gene “induction” 3.53) State what is meant by gene “induction” Switching on a gene is given the name “induction” or “activation”, or “expression”. 3.54) Describe the connection between a “switched on” gene and the presence of active mRNA, and hence the ability to make proteins  3.54) Describe the connection between a “switched on” gene and the presence of active mRNA, and hence the ability to make proteins mRNA is only transcribed from activated (“switched on”) genes. mRNA is translated into proteins on ribosomes The proteins made in a cell decide the characteristics of the cell – the cell becomes specialised. 3.55) Describe what is meant by the “lac operon” The lac operon is a segment of DNA found in some prokaryotes allowing for regulation over protein synthesis (translation), comprising the promoter region, operator gene, and gene to be transcribed. 3.60) Describe 2 ways in which a gene can be switched off by the presence of a protein repressor molecule 3.60) Describe 2 ways in which a gene can be switched off by the presence of a protein repressor molecule (1) Repressors attach to the promoter region and block it. This prevents the RNA polymerase from attaching to the promoter. (2) Repressors may also attach to transcription factors and prevent them from attaching to the promoter region. In both cases, the gene is switched off. 3.61) Define the following terms: cell, tissue, organ, organ system  3.61) Define the following terms: cell, tissue, organ, organ system Cell – the basic unit from which living organisms are built up. They have a specific function in multicellular organisms (e.g. muscle cell, sperm cell, red blood cell). Tissue – a group of similar specialised cells working together to carry out one function. (e.g. epithelial tissue, muscle tissue, nerve tissue). Organ – a structure made up of different tissues, which work together to carry out one or many functions (muscle tissue, blood tissue, nerve tissue and connective tissue work together in the heart). Organ system - a group of organs working together to carry out a particular function (e.g. circulatory system comprising heart, arteries, veins). 3.62 Describe an adhesion molecule 3.63  Explain the role of adhesion molecules in tissue structure CSM Cell 1 with adhesion molecules / proteins Tissue fluid CSM Cell 2 with matching adhesion molecules / proteins Cell adhesion molecules are recognition proteins. In this way similar cells can attach to each other. 3.66) Describe how master genes are thought to switch on genes (mentioning mRNA and signal proteins) mRNA transcribed from master genes is translated into signal proteins. These signal proteins (often transcription factors) switch on the genes responsible for producing the proteins needed for specialisation of other cells. 3.69) Define the term variation (using the term “species”) 3.69) Define the term variation (using the term “species”) Variation is the differences that exist between members of a single species. The characteristics of an organism (e.g. head circumference, skin colour, body mass etc) are called the phenotype. 3.71) Name the 2 types of variation, and give 2 examples of each in humans Continuous variation is where there is a complete range of measurements from one extreme to the other. Individuals do not fall into discrete categories. It is based on measurable features (hence “quantitative variation”). e.g. height, hair colour, IQ, skin colour Discontinuous variation is where individuals fall into distinct categories. It is based on features which are not measured. Because they are either present or not, it is sometimes referred to as qualitative variation. There are no intermediate categories. e.g. blood group, physical gender. Sample size – as large as possible so that the results are representative of thew whole population. Random samples – so results are unbiased and stats tests can be applied. 3.73) Sketch typical graphs for both continuous and discontinuous variation Continuous variation Discontinuous variation (normal distribution) (bar chart) Blood groups 3.75)  Calculate the mean, median and mode of a set of data for a given phenotype 3.75)  Calculate the mean, median and mode of a set of data for a given phenotype 3.82) Describe what happens to epigenetic markers during semi-conservative replication of DNA, and the importance of this During DNA replication, the epigenetic markers are copied with the DNA so that the correct set of genes remain active. 3.83) Describe some evidence that epigenetic changes can be passed on following cell division When daughter cells are produced during mitosis, the new cells need to take on the role of the parent cell. So if you cut your skin by accident and kill some cells, other skin cells will reproduce by mitosis to replace them. Epigenetic markers are copied into the new DNA of the new cells, so the same genes are switched on or off as in the parent cell. 3.84) Describe what happens to the epigenetic markers found on sperm and egg cells, during fertilisation, and the importance of this Sperms and eggs are obviously specialised cells, so it is logical that they will have changes to their epigenome that have helped determine their specialised structure and function. However, the zygote is totipotent, and can produce all types of cells, so presumably epigenetic markers must be removed at some point, shortly after fertilisation. Sometimes epigenetic modifications do get passed between parent and offspring (called imprinted genes), via sperm and egg – but this type of inheritance is rare (the vast majority of the mammalian genome gets reset when the egg and sperm fuse). Presumably in such a case some of the epigenetic tags are not removed at fertilisation.