• State three events that occur in G1 phase of the cell cycle

  Cells grow and increase in size; proteins from which organelles are made are synthesised (transcribed and translated); organelles replicate
• What happens during the S phase of the cell cycle?

  This is the synthesis phase, DNA is replicated.
• What happens during the G2 phase?

  Second growth phase, proteins which involved in making the chromosomes condense are synthesised (transcribed and translated).
• Describe what may happen in G0 phase of the cell cycle

  Cells may undergo apoptosis, differentiation or senescence
• State three cell cycle checkpoints and briefly describe what is being checked for at each

  G1/S - checks for size, growth factors, nutrients, DNA damage; G2/M - checks DNA has been properly replicated; spindle assembly - checks chromosomes have correctly attached to spindle fibres
• State three purpose of mitosis in life cycles

  Asexual reproduction; growth; tissue repair; replacement of cells
• Describe the main events of prophase

  Nuclear envelope breaks down; chromatin condenses (DNA supercoils); nucleolus disappears; spindle fibres start to form from centrioles
• Describe the main events of metaphase

  Chromosomes line up along equator (metaphase plate); spindle fibres attach through centromeres
• Describe the main events of anaphase

  Sister chromatids pulled to opposite poles of the cell by shortening tubulin spindle fibres
• Describe the main events of telophase


  Nuclear envelope reforms around each set of chromosomes; chromatin relaxes; nucleolus reappears
• Describe how cytokinesis differs between dividing animal cells and plant cells

  Animal cells - cleavage furrow forms and plasma membrane is pulled inwards, splitting the cytoplasm; plant cells - vesicles assemble around metaphase plate and fuse; new plasma membrane and cellulose cell wall are laid down
• Why would we use the root tip for investigating mitosis?

  It is the location of meristematic tissue (source of stem cells) in a plant, i.e. cells are actively dividing
• Explain why we warm the root tips in hydrochloric acid when preparing a root tip squash

  To break the links between cellulose cell walls in plant cells; this ensures the stain penetrates the cells and binds to the chromosomes
• Which stain would we use to stain chromosomes in a root tip squash?

  Acetic orcein
• What is meiosis?


  The formation of gametes. Genetically unique with half the genetic information of a somatic cell.
• Describe how meiosis produces genetic variation in the gametes produced

  Crossing over in prophase I; independent assortment in metaphase I; independent assortment in metaphase II
• Describe the difference between anaphase I and anaphase II

  In anaphase I, a homologous pair of chromosomes is separated so the chromosome number halves (2 haploid cells made); in anaphase II, sister chromatids of each chromosome are separated so chromosome number stays the same (haploid number maintained)
• In which stage of meiosis is the chromosome number halved

  Anaphase/telophase I
• Explain why genetic variation is important for a population of organisms

  More likely that some individuals are adapted to a change in the environment, so the population can survive
• What is differentiation?


  The process by which a cell develops to become more distinct in form and function
• Describe and explain how erythrocytes are adapted for their function

  Very small so have a large SA:vol (biconcave shape also ensures this) meaning oxygen can reach all regions inside the cell; well-developed cytoskeleton allows the erythrocytes to change shape and move through very narrow capillaries; no nucleus or organelles so more space for Hb molecules
• Explain why a neutrophil contains many lysosomes

  These contain hydrolytic enzymes which digest pathogens
• Describe and explain how sperm cells are adapted for their function

  Acrosome in head contains enzymes to penetrate the egg follicle during fertilisation; many mitochondria to generate ATP for flagellar movement; large haploid nucleus in head to fertilise haploid ovum
• Describe how guard cells open in sunny conditions

  Light energy --> ATP; ATP used to actively transport potassium ions from epidermal cells into guard cells; water potential of guard cells lowered; water moves in by osmosis and guard cells become turgid
• Describe the purpose of cytoskeleton threads and motor proteins in palisade cells

  Moves the chloroplasts to areas of appropriate light intensitySee an expert-written answer!We have an expert-written solution to this problem!
• Describe how a root hair cell plasma membrane is adapted for transport of mineral ions

  Contains specialised carrier proteins to transport specific mineral ions in by active transportSee an expert-written answer!We have an expert-written solution to this problem!
• Describe how cartilage is adapted for its function

  Connective tissue that contains elastin and collagen fibres; prevents ends of bones from rubbing together
• Define the term tissue

  A group of cells working together to perform a particular function
• State three types of muscle tissue, giving an example of where each is found

  Skeletal - bicep/tricep etc.; smooth - digestive tract, blood vessels; cardiac muscle - heart walls
• Give four features of meristematic cells that means they can differentiate easily

  Thin walls with very little cellulose; no chloroplasts; no large vacuole; divide by mitosis and have the ability to differentiate into many cell types
• Describe the differences between multipotent, pluripotent and totipotent stem cells

  Multipotent - found in bone marrow and can form a range of different cells including blood cells; pluripotent - found in early embryos (embryonic stem cells) and can form all tissue types except extra-embryonic cells; totipotent - found in first 16 cells post-zygote and can form all tissue types including extra-embryonic tissue (e.g. placenta, umbilical cord)
• State three characteristics of stem cells

  Undifferentiated; all genes able to be expressed; self-renewing; able to differentiate into any cell type