Topic 3 Three Star LOs 2024 PDF

3.3) Draw a diagram of a prokaryotic cell, label the structures listed and describe their function: cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA 3.4) Draw a diagram of a eukaryotic cell, label the structures listed and describe their function: nucleus,...

3.3) Draw a diagram of a prokaryotic cell, label the structures listed and describe their function: cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA 3.4) Draw a diagram of a eukaryotic cell, label the structures listed and describe their function: nucleus, nucleolus, ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, and Golgi apparatus  Mitochondrion: composed of a double membrane outer layer surrounding the matrix. The inner membrane is folded into Nucleus: enclosed by a double membrane cristae. They are involved in nuclear envelope. Contains chromosomes aerobic respiration. and a nucleolus. The DNA that the chromosomes are made up of are genes Centrioles: every animal cell has one pair – that control protein synthesis. they are hollow cylinders made up of protein microtubules. They are involved in the Nucleolus: a darker area of the nucleus formation of the spindle during nuclear where ribosomes are made. division. Rough Endoplasmic reticulum (rER): A system of membrane bound tubes with ribosomes attached to the outer surface. Protein is transported through these tubes to other parts of the cell. Ribosomes: Made of RNA and protein, these are found in the cytoplasm or Lysosome: Spherical membrane-bound attached to endoplasmic reticulum. They sacs containing digestive enzymes. are the site of protein synthesis Involved in the breakdown of unwanted (translation). or damaged organelles within the cell. Cell surface membrane: Phospholipid bilayer forming a partially permeable barrier to control what enters and leaves the cell. Golgi apparatus: Stacks of flattened, membrane-bound sacs formed by fusion of vesicles from the rER. Smooth Endoplasmic reticulum (sER): A system Modifies proteins and packages them into vesicles for of membrane bound tubes without ribosomes. transport around and out of the cell. Makes lipids and steroids.  3.6)Identify cell structures from photographs or electron micrographs of cells E, F, G and H are from plant cells and so are important once topic 4 has been studied A B E C D F G I K L H J A: Smooth Endoplasmic Reticulum (SER) B: Ribosome C: Rough Endoplasmic Reticulum (RER) D: Mitochondrion (notice: double membrane, cristae and matrix) E: Chloroplast (notice: double membrane, thylakoids and stroma) F: Granum – or a stack of thylakoids G:Vacuole H: Cell wall I: Nucleus (notice: double membrane) J: Nucleolus K: Golgi apparatus L: Vesicle / Lysosome (Lysosomes are often very darkly coloured) 3.10)Draw a flow chart that shows how different organelles and molecules are involved in the process of protein production and trafficking in a cell  Protein trafficking process starts at step 3 & transported to the Golgi Polypeptide detaches from ribosome and enters RER lumen Secretory By exocytosis 3.12)Draw an ovum (egg cell), label the structures and describe their function Haploid nucleus: contains half the number of chromosomes as a diploid nucleus Lysosomes (or cortical granules): release enzymes by exocytosis to thicken the zona pellucida once one sperm nucleus (haploid) enters ovum Follicle cells: release chemicals which stimulate the start of the acrosome reaction Zona pellucida: thickens after one sperm nucleus has entered ovum– prevents polyspermy Lipid droplets: an energy store for the developing embryo Note that egg cells have all the organelles of a eukaryotic cell as well 3.14)Draw a sperm cell, label the structures and describe their function  Head Middle section section Acrosome Flagellum Haploid nucleus Mitochondria Haploid nucleus: contains half the number of chromosomes as a diploid nucleus Acrosome: modified lysosome. Contains hydrolytic enzymes released in the acrosome reaction. Mitochondria: produce energy in the form of ATP to power the flagellum to propel the sperm towards the egg. 3.15) Draw a flow chart that shows how a sperm reaches an ovum and fertilisation is achieved (including the stages in the acrosome reaction, the cortical reaction and the fusion of nuclei)  (i.e. the follicle cells) 9. The cortical granules (lysosome) release enzymes by exocytosis into the zona pellucida. This causes the zona pellucida to thicken, preventing entry of other sperm / polyspermy i.e. the zona pellucida 3.16)Define the terms chromosome, homologous pair, gamete, haploid and diploid Chromosome = One DNA molecule that is made up of coding DNA (genes) and non-coding DNA between, and within, genes. Associated with histone proteins Homologous pair = Two chromosomes that are made up of the same genes in the same order (one is inherited from the mother and the other from the father). These chromosomes pair up in meiosis. Gamete = A sex cell. Haploid = Containing one copy of each type of chromosome. Diploid = Containing two copies of each type of chromosome. 3.19)Explain why it is important for gametes to be haploid Gametes need to be haploid in order to restore the diploid number of chromosomes at fertilisation prevent the doubling of chromosome in each generation. 3.21)Draw a sequence of diagrams that show the process of meiosis and annotate them with what is happening at each stage  Chromosomes replicate before division. After replication each chromosome is made up of two chromatids joined at a centromere Homologous chromosomes pair up and then separate Chromatids separate and gametes are formed, each with half the original number of chromosomes 3.23)State the two ways in which meiosis can produce genetic variation 1) Crossing over of non-sister chromatids of homologous chromosome pairs 2) Independent assortment of homologous chromosome pairs 3.24)Describe the process of crossing over and explain how it can produce genetic variation During meiosis I homologous chromosomes pair. At points where they make contact, called chiasmata, the chromatids break and re-join. The non-sister chromatids exchange corresponding sections of DNA. This is known as crossing over. Crossing over produces chromosomes that contain new combinations of alleles from both parents 3.25)Describe the process of independent assortment of homologous chromosomes and explain how it can produce genetic variation Each homologous chromosome pair lines up randomly on the midline of the cell during meiosis I. Different arrangements result in different combinations of maternal and paternal chromosomes in daughter cells. The diagram below shows an example using a cell with 3 pairs of chromosomes. 3.28)List the stages in the cell cycle in order and state what happens during each stage 1) Interphase (G1, S, G2) Cell prepares for cell division – see LO 3.25 for details 2) Mitosis Nuclear division. One nucleus becomes two nuclei – see LO 3.26 for details 3) Cytokinesis The cell divides to produce two identical cells 3.29)List the stages of interphase in order and state what happens during each stage 1) G1 Cell grows: more cytoplasm, more membrane, more cellular proteins, more organelles, larger energy store 2) S Synthesis of DNA (DNA replicates) 3) G2 Centrioles replicate, spindle fibres start to form, mitochondria and chloroplast replicate. 3.30)List the stages of mitosis in order and, with the help of diagrams, describe what is happening at each stage Prophase Chromosomes condense and become visible Nuclear envelope starts to break down, nucleolus disappears Centrioles migrate to opposite poles of cell Spindle formation completed Metaphase Chromosomes line up on the equator of the cell Chromosomes become attached to the spindle fibres by their centromeres Anaphase Spindle fibres shorten (by enzyme hydrolysis) The pairs of chromatids making up the chromosomes are pulled apart (centromere breaks) to opposite poles of cell Telophase Chromosomes de-condense New nuclear envelopes form around each group of chromosomes  3.32)Identify what stage of the cell cycle a cell is in from a photograph or a diagram A D G K B H E L F I J M C A: Telophase B: Metaphase C: Cytokinesis D: Interphase E: Prophase F: Interphase G: Telophase H: Anaphase I: Prophase J: Anaphase K: Prophase L: Anaphase M: Metaphase If you can do the photos then diagrams are easy! See LO 3.26 for diagrams 3.33) Describe a safe, reliable method to prepare cells from a garlic plant in order to see cells in different stages of the cell cycle (including the stages of mitosis) Core practical: 3.33) Describe a safe, reliable method to prepare cells from a garlic plant in order to see cells in different stages of the cell cycle (including the stages of mitosis 1) Use garlic root tips (actively growing plant tissue where mitosis is occurring) 2) Put root tips in acid (to dissolve the middle lamella and allow cells to separate) 3) Put root tip on a microscope slide 4) Gently break up (macerate) the root tip with a mounted needle (to allow the dye to reach to all cells) 5) Add toluidine blue (to stain the chromosomes) and rinse off excess 6) Add a coverslip and press downwards to squash the preparation (to spread out the cells to a one cell thick layer. This allows cells to be seem clearly) 7) Count the number of cells in each stage of mitosis Safety: Lab coat to prevent dye getting on clothes Goggles to prevent dye getting in eyes 3.37)Define the terms totipotent, pluripotent, multipotent, stem cell and differentiated Totipotent = A cell that can divide by mitosis to produce other totipotent cells and that can differentiate into ANY other cell type – animal cells tend not to remain this way. Pluripotent = A cell that can divide by mitosis to produce the same pluripotent cell type and that can differentiate into MOST other cell types Multipotent = A cell that can divide by mitosis to produce the same multipotent cell type and that can differentiate into SOME other cell types Stem cell = (1) an undifferentiated cell (genes not switched on) that (2) divide by mitosis to produce other stem cells and (3) that can differentiate into different types of cell by switching certain genes on and off Differentiated = a cell that has particular genes permanently switched on or off and is specialised to perform a particular function 3.39)Describe the development of a zygote into a blastocyst, and describe the structure of a blastocyst and state the fate of the cells in a blastocyst  The blastocyst MITOSIS Inner cell mass Trophoblast – develops into the placenta – develops into the embryo Fluid filled blastocyst cavity Inner cell mass – develops into the embryo Trophoblast – develops into the placenta Fluid filled blastocyst cavity 3.58)Explain how E. coli “know” how to respond differently, by reference to genetic switches (repressor proteins)  When lactose is absent: The repressor molecule is attached to the operator gene. RNA polymerase cannot bind to the promotor region. Transcription of the gene does not occur. When lactose is present: Lactose binds to the repressor molecule. The repressor molecule can’t bind to the operator gene. RNA polymerase binds to the promotor region. Transcription of gene occurs and mRNA is made. 3.59)Describe the role of the enzyme RNA polymerase in determining whether a gene will transcribe or not (mention the “promoter” region of the gene and the role of regulator proteins) For a gene to be transcribed to produce mRNA: 1) The promoter region of the gene must be free from repressor molecules 2) Transcription factors and RNA polymerase bind to the promoter region of the gene (transcription initiation complex formed) 3) mRNA is transcribed from active gene. 3.68)Define and distinguish between the following terms: gene, allele, locus, phenotype, genotype, multifactorial condition  Gene = a sequence of nucleotides on DNA that code for a protein Allele = one form of a gene Locus = the location of a gene on a chromosome Phenotype = the appearance of the characteristic in an individual (e.g. Blue eyes, Brown eyes) Genotype = the alleles the individual has for a particular characteristic (e.g. BB, Bb, bb) Multifactorial condition = where several genetic and one or more environmental factors are involved in a condition (e.g. heart disease) 3.70)List the 2 main causes of variation Genetic factors / genotype Environmental factors 3.72)Distinguish between the 2 types of variation in terms of the number of genes that have an influence (using the terms “locus” and “polygenic”) and the relative influence of the environment  Continuous variation Discontinuous variation Caused by different alleles of the same Caused by different alleles of the same genes at many loci = polygenic (many gene at a single locus – often only one genes) gene The genes often have multiple alleles The gene usually has only two or a and many loci small number of alleles Large environmental influence on the There is no environmental influence on phenotype the phenotype There many be many environmental factors that all contribute to the phenotype = multifactorial 3.78 Define the terms: Genetics Epigenetics Genome Epigenome Genetics – the study of genes and how they are inherited, and genetic variation in organisms Epigenetics – the study of heritable (can be passed from parents to offspring) changes in gene expression without a change in DNA base sequence – instead caused by changes in the environment Genome – all the alleles and genes in the DNA of a diploid cell Epigenome – chemical tags attached to the surface of DNA and histone proteins, affecting gene expression. Tags are added and removed by enzymes. 3.80)  Describe the effect of DNA methylation on gene expression A methyl group (-CH3) is added to the cytosine or adenine of DNA nucleotides, or histone proteins (eukaryotes use cytosine only, prokaryotes use cytosine and adenine). DNA is now tightly wound around the histone proteins, preventing the binding of RNA polymerase, so the gene is switched off. Methylation is usually more permanent than acetylation. 3.81)  Describe the effect of histone modification on gene expression Addition of acetyl groups (-COCH3) to histone proteins. The DNA is less tightly coiled around histones. DNA is accessible to transcription factors and RNA polymerase, so transcription can occur. The gene is switched on. This is normally less permanent than DNA methylation. List the steps to answer a describing data question List the key steps and exam technique points to answer a describing data question 1) Describe patterns in the data – not the biology that explains them 2) Read the question carefully and only describe the aspect of the data that the question is asking about 3) Describe a general trend 4) Use the words in table column headings or axes labels to phrase you answer 5) Use specific word like “increases”, “decreases”, “remains constant” “higher than”, “lower than”. When talking about the rate at which something increases/decreases use “quickly” or “slowly” or “the rate is increasing/decreasing” – do not use steady 6) Describe different sections of the data if there are differences from the general trend and identify points of interest (e.g. highest / lowest / same as…) 7) When describing make sure you are exact in your description and in your use of values from a table or graph 8) Read off from graphs accurately, use a ruler to check and remember to work out what one small square represents (it’s not always 1 or 0.1) 9) If asked to compare then make sure every sentence is a comparison and use comparative words (e.g. more than, less than, higher, lower, the same as) 10)Manipulate figures to quantify one of the points you’ve made (e.g. there is an increase of….). Usually subtracting one value from another to show the value of an increase or decrease should be enough The way to answer a describing data question Do Think DTHLAC GSM or LATCH’D The way to answer a describing data question Do Think General trend Describe Sections / Points Target Manipulate Headings Language Accuracy Compare? DTHLAC GSM or LATCH’D