Cell Division, Diversity and Organisation

• What happens in Meiosis 1?

  -Splits up and homologous chromosomes

  -Reduction division as cell goes from diploid to haploid

  -Each sell contains one set of chromosomes
• What happens in prophase 1?

  -DNA super coils and chromosomes condense

  -Nuclear envelope breaks down and spindle fibres form

  -Homologous pairs come together (synapsis) to form a bivalent (gets tangled)

  -Crossing over/recombination occurs, where non sister chromatids wrap around each other and swap genetic material
• What happens in the metaphase 1?

  -Pairs of homologous chromosomes (still crossed over) attach along the metaphase plate, by its centromere

  -Independent assortment of homologous pairs along the line gives variation
• What happens in the anaphase 1?


  -1 chromosome from each homologous pair is pulled to each pole of the cell

  -Centromeres do not divide (like in anaphase of mitosis)

  -Crossed over areas seperate, shuffling alleles
• What happens in the telophase 1?

  -Nuclear envelopes form around each set of chromosomes and the cell divides by cytokinesis

  -2 daughter cells
• What happens in the Prophase 2?

  -Nuclear envelope breaks down (if not ready)

  -DNA supercoils and chromosomes condense

  -Non sister chromatids linked by centromere

  Spindle fibres form
• What happens in the metaphase 2?

  -Chromosomes attatch to the metaphase plate by their centromere

  -Chromosomes are randomly arranged here (independent assortment)
• What happens during Anaphase 2?

  -Centromeres divide

  -Spindle fibres retract and chromatids are pulled apart
• What happens during Telophase 2?

  -Nuclear envelopes form around each of the 4 haploid cells

  -Cytokinesis occurs to give 4 cells
• Whats a haploid cell?

  The presence of a single set of chromosomes in an organisms cell
• Whats a diploid cell?

  An organism or cell that has two complete sets of chromosomes with one set from each parent.
• What is mitosis essential for?

  Its essential for asexual reproduction
• What are the 4 stages of mitosis?

  Prophase,metaphase,anaphase and telophase
• What are the stages of the cell cycle?

  G1, G2 and S
• What happens in G1?

  • Make organelles such as ribosomes/mitochondria/Er
  • Makes proteins
  • Makes RNA
  • Provides nutrients
• Whats at the end of G1?

  Checkpoint 1

  -checks the size and organelle nutrients through molecular signals

  -at the end of check the chromosomes replicate
• What happens in the S stage?

  • DNA synthesis
  • DNA replication
• What happens in G2 stage?

  • Prepare for mitosis
• What happens at checkpoint 2?

  • Cell division goes smoothly
  • Has all organelles replicated
• What happens in prophase?

  • DNA supercoils causing chromosomes to condense and become visible
  • The nuclear membrane breaks down
  • The centriole divides and centrioles move apart to opposite poles of the cell
  • Spindle fibres form
• What happens at the metaphase?

  • Each chromosome lines up in the middle of the cell and attached to a spindle fibre by their centromeres
  • Sister chromatids are facing opposite poles of the cell
• What happens at the anaphase?

  • Spindle fibres contract
  • Centromere of each chromatid splits and chromatids are pulled to opposite poles of the cell
• What happens at the telophase?

  • Nuclear membrane forms around each group of chromosomes
• What happens at cytokinesis?

  • The cytoplasm divides by a process called clearage-usually starts during anaphase
  • The membrane around the middle of the cell is perpendicular to the spindle axis and between daughter nuclei is drawn inward to form cleavage furrow which gradually deepens
  • The thin bridge or mid body may persist for some time before it breaks at each end leaving 2 seperate daughter cells
• What are the adaptations of a spermatozoa (sperm cell)?

  • Plasma membrane contains receptors that bind with the egg
  • Mitochondria in tail provides ATP
  • Acrosome - a lysosomes containing hydrolytic enzymes to digest a path into the egg cell to allow fertilisation
• Whats the adaptations of neutrophils?

  • Destroy invading organisms by phagocytosis
  • Granular cytoplasm- contains lysosome and glycogen stores
  • Can change shape allows for them to fit through blood vessels to get to site of infection
• What are the adaptations of erythrocytes (RBC)?

  • Cytoplasm contains hemoglobin temoprarily binds with oxygen to form oxyhaemoglobin
  • Binocave shape provides large surface area to volume ratio
  • Enucleate- has no nucelus
  • Flexible to fit through capillary
• Adaptations of root hair cell?

  • Absorbs water and minerals from soil but not larger molecules
  • Creates a water potential gradient
  • creates large surface area
  • Allows for faster absorption
• What are the adaptations of a palisade cell?

  • Contains chloroplasts packed with chlorophyll for photosynthesis
  • Vertical alignment minimizes cross walls that light has to penetrate
  • Regular shape means that cell can closely pack together to form a continuous layer for efficient light absorption
• What are the adaptations of guard cell?

  • Controls gas exchange and water loss
  • Work in pairs with a pore (stomata) between them
  • As guard cells become turgid they expand
  • Outer walls expand more tha inner walls due to greater flexibility