Flashcards
A Level Biology - Cell Division
Cards in this deck (52)
- 1What is the cell cycle?1) Highly ordered sequence of events taking place in a cell
2) Results in division of the cell, and the formation of two genetically identical daughter cells - 2Name all of the stages of the cell cycle, in chronological order of when they occur.1) G1
2) S
3) G2
4) Mitosis
5) Cytokinesis
6) G0 - 3Name the two phases involved in the cell cycle, giving a brief description of each.1) Interphase - cell actively prepared for cell division
2) Mitotic phase - cell division occurs - 4State 5 processes that occur during interphase.1) DNA replicated and checked for errors in nucleus
2) Protein synthesis occurs in cytoplasm
3) Mitochondria grow and divide - increase in number
4) Chloroplasts grow and divide in plant cells - increase in number
5) Normal metabolic processes of cells occur (e.g cell respiration) - 5Name the three stages of interphases and briefly describe what happens in each stage.1) G1 (first growth phase) - proteins synthesised, organelles replicated, cell increases in size
2) S - synthesis stage - DNA replicated in nucleus
3) G2 (second growth phase) - cell continues to increase in size - energy stores increased - duplicated DNA checked for errors - 6Name the two stages involved in the mitotic phase, briefly giving a description of what happens in each.1) Mitosis - genome replicated and divided - nucleus divides
2) Cytokinesis - physical division of the cell (cytoplasm) into two separate cells - 7Briefly describe what happens during the phase, G0.1) Cells no longer divide - differentiate and become specialised
2) Cell leaves the cycle temporarily or permanently - 8State 3 reasons why G0 might occur.1) Cell becomes specialised - differentiation
2) Cells become senescent
3) Increase in age - 9Define the term 'differentiation'.1) This is when a cell becomes specialised to carry out a particular function and is no longer able to divide
- 10Explain why cells become 'senescent', and explain why there is an increase in senescent cells as age increases.1) cells that have been damaged and are no longer able to divide (senescent)
2) Normal cells can only divide a limited amount of times - become senescent
3) As you become older there is an increase in senescent cells - more prone to disease such as cancer and arthritis - 11Name an example of a type of cell that can enter the cell cycle again after leaving via G0.1) Lymphocytes (white blood cells)
- 12Define the term 'checkpoint', in relation to the cell cycle.1) These are the control mechanisms of the cell cycle, that help to ensure the fidelity of cell division
2) They monitor and verify whether processes at each phase have been completed accurately to move on to the next phase - 13Name all of the checkpoints that are present in the cell cycle, briefly describing what happens at each checkpoint.1) G1 checkpoint (before S stage) - cell size, nutrients, growth factors, and DNA damage checked
2) G2 checkpoint (before mitotic phase) - cell size checked, duplicated DNA checked for errors and damage
3) Metaphase checkpoint (during mitosis) - check if chromosomes attached to spindles and aligned - 14Explain, with reference to the structure and function of proteins, the importance of the G2 checkpoint.1) DNA checked for errors
2) Change in sequence of amino acids (mutation) leads to change in protein structure
3) Function of protein changes with different shapes - 15Explain what telomeres are and describe their function.1) These are repetitive sequences of DNA at the ends of chromosomes
2) They protect the genes at the ends of chromosomes and stop the ends from fusing. - 16Explain what the Hayflick limit is.1) DNA not replicated all the way to the end every time DNA is replicated
2) This causes telomeres to shorten, limiting the amount of times cells can replicate - known as the Hayflick limit - 17Suggest a disadvantage of indefinite cell division (no limits to the amount of times cells can divide).1) Indefinite replication increases the chances of mutation during DNA replication
2) This increases the total number of mutations occuring, increasing the risk that one of these mutations is harmful - 18Name the enzyme that, when present, results in the elongation of telomeres and explain the possible effects that this could have.1) Telomerases (not usually present in differentiated cells)
2) causes indefinite relication - more prone to developing cancer, or tumours. - 19Describe the purpose of mitotic cell division and list 4 roles of mitotic cell division.The purpose is to produce two genetically identical daughter cells (same type and no. of chromosomes) which is important for:
1) Growth
2) Repair
3) Replacement
4) Asexual reproduction - 20Asexual reproduction is the production of genetically identical offspring from one parent. Name the types of organisms that can reproduce asexually.1) Plants
2) Fungi
3) Some animals
4) Bacteria - through binary fission
4) Eukaryotic single-celled organisms -e.g Amoeba - 21Explain what 'chromatids', 'centromeres', and 'chromatin' are in relation to mitosis.1) Before mitosis, in interphase, each chromosome is converted into two identical DNA molecules called 'chromatids'
2) Two chromatids are joined together at the 'centromere' during mitosis
3) During interphase, DNA combines with proteins called histones to form a dense complex called 'chromatin'. - 22Explain the importance of 'centromeres' during mitosis.1) Helps to keep chromatids together during mitosis - can be precisely manoeuvred and segregated equally into two new daughter cells.n
- 23Name the 4 stages of mitosis, in chronological order.1) Prophase
2) Metaphase
3) Anaphase
4) Telophase - 24The process of cell division can be viewd using a light microscope. Explain how.1) Growing root tips of plants obtained
2) Root tips treated with chemical to separate cells
3) Cells squashed onto a single layer of microscope slide
4) Stains that bind DNA used to make chromosomes visible - 25Briefly describe what happens during prophase.1) Chromatin fibres coil and condense to form chromosomes
2) Nucleolus disappears, nuclear membrane breaks down
3) Spindle fibres formed
4) Centrioles migrate to opposite sides of the cell
5) Spindle fibres attach to centromeres - start to move chromosomes to centre of cell - 26Briefly describe what happens during metaphase.1) Chromosomes moved by spindle fibres to form a plane in the centre of the cell - known as the metaphase plate
- 27Briefly describe what happens during anaphase.1) Centromeres holding chromatids in chromosome divide
2) Chromatids separated to opposite poles of cell by spindle fibres - 28Explain what 'sister' chromatids are.1) These are two identical copies of DNA joined at a centromere
- 29Briefly describe what happens during telophase.1) Chromatids reach each end of the pole
2) Two new sets of chromosomes assemble at each pole
3) Nuclear envelope reforms around them
4) Chromosomes uncoil, nucleolus is formed
5) Cytokinesis begins - 30Describe the process of cytokinesis in animal cells.1) During telophase, cytokinesis begins
2) Cleavage furrow forms around the middle of the cell
3) Cell-surface membrane pulled inwards by cytoskeleton until it is close enough to fuse in the middle, forming two cells - 31Describe the process of cytokinesis in plant cells, and how it is different to that of animal cells.1) Plant cells have cell walls - not possible for cleavage furrow to form
2) Vesicles from golgi app. assemble where metaphase plate was formed
3) Vesicles fuse together and with cell-surface membrane at plate
4) Cell is separated into two - 32Explain why we normally see chromosomes as a double structure containing two chromatids.1) Chromosomes only become visible under microscope during mitosis/meiosis
2) Chromosomes are replicated, consisting of two sister chromatids. - 33Explain why it is essential that NA replication results in two exact copies of the genetic material.1) So that each daughter cell has identical DNA after mitosis and the correct number of chromosomes
- 34What is 'meiosis'?1) Form of cell division producing sex cells (gametes)
2) Nucleus divides twice to produce four daughter cells
3) Each daughter cell contains only half the number of chromosomes from parent cell (haploid) - 35Explain the role of meiosis in life cycles1) Needed for sexual reproduction as it produces gametes
2) Halves the number of chromosomes present in sex cells to produce genetic variation in offspring - 36Define the term 'diploid' and 'haploid' in relation to mitosis and meiosis.1) Mitosis - nucleus divides once after DNA replication resulting in two genetically identical diploid daughter cells (diploid = two chromosomes of each type, one from father, one from mother
2) Meosis - nucleus DIVIDES twice producing 4 daughter cells (gametes) - each gamete contains half of the chromosome number of parent cell - 37Define the terms 'gamete' and 'zygote'.1) Gamete - haploid sex cell (two sex cells fuse to produce a zygote)
2) Zygote - fertilised egg cell in which an organisms develops - 38Explain why meosis is describe as a 'reduction division, and explain its importance.1) Each gamete only contains half of the chromosome number of the parent cell (haploid) - 'reduced' to half
2) Gametes fuse to produce zygotes with the standard diploid number of chromosomes at fertilisation
3) If gametes did not have half the chromosomes would double at fertilisation - 39What are 'alleles' and where are they found on chromosomes?1) Alleles are different versions of the SAME gene (gene variants)
2) Different alleles of a gene are found at the same locus (position on a particular chromosome) - 40Explain what 'homologous' chromosomes are.1) Matching pairs of chromosomes - one from each parent
2) These have the same genes but can have different alleles of each gene - 41Name the stages of meosis, and briefly describe what happens at each stage.1) Meiosis 1 (Prophase, Metaphase, Anaphase, Telophase 1) - reduction division - homologous chromosomes separated into two daughter cells
2) Meiosis 2 - similar to mitosis - pairs of chromatids separated - produces 4 haploid daughter cells - 42Briefly describe what happens during prophase 1 and state differences between prophase in meiosis and mitosis.1) Chromosomes condense, nuclear envelope disintegrates, nucleolus diasppers, spindle formation begins
Differences
-In meiosis, homologous chromosomes pair up, forming bivalents and cross over - 43Explain what 'bivalents' are.1) These are two homologous chromosomes that have paired up in Prophase 1 of meiosis
- 44Explain what 'crossing over is' and where it occurs, in relation to meiosis.1) This is the exchange of a part of a chromosome between chromatids of homologous pairs
2) This occurs at the CHIASMATA - 45Briefly describe what happens in Metaphase 1 of meiosis, and explain how it is different to that of metaphase in mitosis.1) Its the same as metaphase in mitosis but instead homologous PAIRS of chromosomes assemble at the metaphase plate instead of INDIVIDUAL chromosomes
- 46Explain how independent assortment of chromosomes occur in Metaphase 1, and how this results in genetic variation.1) Orientation of each homologous pair is random and independent - maternal/paternal chromosomes can face either pole (independent assortment)
2) This can result in many different combinations of alleles facing the poles, producing genetic variation - 47Briefly describe what happens in Anaphase 1 of meiosis, and describe how it is different to Anaphase in mitosis.1) Homologous chromosomes are pulled to opposite poles, however the sister chromatids STAY joined to each other (in mitosis, they are separated)
2) Sections of DNA that crossed over break off and rejoin together at the chiasmata
3) This forms recombinant chromatids - 48Explain how crossing over produces genetic variation in meosis.1) When sister chromatids cross over, they become entangled
2) When they break off and rejoin at chiasmata, this can result in an exchange of DNA
3) The genes exchanged may be different alleles of the same gene, meaning that the combination of alleles on on the recombinant chromatids are different to that of the original - producing genetic variation - 49Explain what 'recombinant chromatids' are.1) These are chromatids with a combination of DNA from both homologous chromosomes, formed by crossing over and chiasmata in meosis.
- 50Briefly describe what happens during Telophase 1 of meosis.1) This is the SAME as telophase in mitosis
2) Chromsomes assemble at each pole, nuclear membrane reforms, chromosomes uncoil
3) Cell undergoes cytokinesis and divides into two cells (chromatids stay together in meosis, in mitosis they are separated) - 51Briefly describe the differences between each phase in both Meiosis 1 and 2, if there any.1) Prophase 2 - same as in Prophase 1
2) Metaphase 2 - same as in Metaphase 1, however INDIVIDUAL chromosomes line up on metaphase plate instead of homologous pairs (more independent assortment occurs - more genetic variation
3) Anaphase 2 - same as Anaphase 1, however chromatids of chromosomes are pulled apart (in Anaphase 1 they stay together)
4) Telophase 2 - same as in Telophase 1 - however 4 HAPLOID daughter cells are produced instead of 2 - 52Suggest a difference between plant cell division and animal cell division, not including the inability to form a cleavage furrow.1) Plant cells do not have centrioles, and so they are not used to pull chromatids apart
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- Includes the cell cycle, mitosis, and meiosis
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- Czean Holgado
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