Cells

• Describe how HIV is replicated?

  1. Attachment proteins attach to receptors on helper T cell
  2. Nucleic acid/RNA enters cell
  3. Reverse transcriptase converts RNA to DNA
  4. Viral protein/enzymes/capsid produced
  5. Virus particles assembled and released from cell
• Why can optical microscopes not be used in some situations?

  1. Resolution too low
  2. Because wavelength of light is too long
• Describe the role of one organelle in digesting bacteria?

  1. Lysosomes
  2. Fuse with vesicles
  3. Releases hydrolytic enzymes
• Give 2 structures found in all prokaryotic and in all eukaryotic cells?

  1. Ribosomes
  2. Cytoplasm
• Describe how a sample of chloroplasts can be isolated from leaves?

  1. Homogenize leaves and filter
  2. In cold, isotonic, buffered solution
  3. Centrifuge and remove cell debris
  4. Centrifuge at higher speed, chloroplasts settle out
• Outline the roles of organelles in the production, transport and release of proteins from eukaryotic cells?

  1. DNA in nucleus is code for protein
  2. Ribosomes produce protein
  3. Mitochondria produce ATP for protein synthesis
  4. Golgi apparatus package and modify
  5. Vesicles transport and fuse with cell-surface membrane
• Contrast how an optical microscope and a TEM work and contrast the limitations of their use when studying cells?

  1. TEM uses electrons and optical uses light
  2. TEM allows a greater resolution, so smaller organelles can be viewed
  3. TEM does not show colour and optical can
  4. TEM requires thinner specimen
  5. TEM view only dead specimens, and optical can view live specimens
  6. TEM requires a more complex preparation
• Why do solutions need to be ice-cold, isotonic and buffered?

  1. Ice-cold - Slows enzyme activity to prevent digestion of organelles
  2. Isotonic - Prevents osmosis so no lysis
  3. Buffered - Maintains pH so enzymes don't denature
• Give 2 ways in which the nucleotides in DNA are different from the nucleotides in RNA?

  1. DNA contains thymine and RNA contains uracil
  2. DNA contains deoxyribose and RNA contains ribose
• Describe how you could make a temporary mount of a piece of plant tissue to observe the positions of starch grains?

  1. Add drop of water to glass slide
  2. Obtain thin section of plant tissue and place on slide
  3. Stain with iodine in potassium iodide
• Describe binary fission in bacteria?

  1. Replication of (circular) DNA
  2. Replication of plasmids
  3. Division of cytoplasm
• What happens during prophase, anaphase and metaphase?

  1. In prophase, chromosomes condense
  2. In prophase, centromeres attach to spindle fibres
  3. In metaphase, chromosomes line up at equator of cell
  4. In anaphase, centromeres divide
  5. In anaphase, chromosomes pulled to opposite poles of cell
• Describe the appearance and behaviour of chromosomes during mitosis?

  1. During prophase, chromosomes condense and appear as 2 sister chromatids joined at the centromere
  2. During metaphase, chromosomes line up at the equator of the cell attached to spindle fibres by their centromeres
  3. During anaphase, the centromere divides and chromosomes are pulled to opposite poles of the cell
  4. During telophase, chromosomes uncoil
• How do you know if anaphase is occurring?

  1. Chromosomes are in two groups at poles of spindle
  2. V-shape shows that sister chromatids have been pulled apart at their centromeres
• Describe and explain 2 aseptic techniques?

  1. Wear gloves, to prevent contamination from bacteria on hands
  2. Use sterile pipette to maintain a pure culture of bacteria
• Why would preventing the formation of spindle fibres stop the cell cycle?

  1. Chromosomes cannot attach to spindle
  2. So no metaphase
• Name and describe 5 ways substances can move across the cell-surface membrane into a cell?

  1. Simple diffusion of small/non-polar molecules down a concentration gradient
  2. Facilitated diffusion down a concentration gradient via carrier/channel protein
  3. Osmosis of water down a water potential gradient
  4. Active transport against a concentration gradient via carrier protein using ATP
  5. Co-transport of 2 different substances using a carrier protein
• The movement of Na+ out of the cell allows the absorption of glucose into cells lining the ileum?

  1. Maintains a concentration gradient for Na+
  2. Na+ moves in by co-transport, bringing glucose with it
• Describe and explain 2 features you would expect to find in a cell specialised for absorption?

  1. Microvilli, so large surface area for absorption
  2. Large number of mitochondria, so make more ATP by respiration
• The movement of substances across cell membranes is affected by membrane structure. Describe how?

  1. Phospholipid bilayer allows movement of non-polar substances
  2. Carrier proteins allow active transport
  3. Channel proteins allow facilitated diffusion
  4. Shape of channel protein determines which substances move
  5. Cholesterol affects fluidity
• Give 2 similarities in the movement of substances by diffusion and osmosis?

  1. Movement down a gradient
  2. Passive process
• Contrast the processes of facilitated diffusion and active transport?

  1. Facilitated diffusion involves carrier or channel proteins whereas active transport only involves carrier proteins
  2. Facilitated diffusion is passive but active transport uses ATP
  3. Facilitated diffusion takes place down a concentration gradient, active transport occurs against a concentration gradient
• Suggest and explain 2 adaptations to allow rapid transport of nutrients?

  1. Membrane folded, so increased surface area
  2. Large number of protein carriers for active transport
• Compare and contrast the processes by which water and inorganic ions enter cells?

  1. Both move down concentration gradients
  2. Ions can move against a concentration gradient by active transport
• Describe how HIV is replicated once inside helper T cells?

  1. RNA converted into DNA using reverse transcriptase
  2. DNA inserted into helper T cell
  3. DNA transcribed into HIV mRNA
  4. HIV mRNA translated into viral proteins
• Describe how a phagocyte destroys a pathogen present in the blood?

  1. Phagocyte engulfs pathogen
  2. Forming phagosome and fusing with lysosome
  3. Enzymes digest
• Give 2 types of cell, other than pathogens, that can stimulate an immune response?

  1. Cells from transplants
  2. Cancer cells
• Explain how HIV affects the production of antibodies when AIDS develops in a person?

  1. Less/no antibody produced
  2. Because HIV destroys helper T cells
  3. So few B cells activated
• What is a monoclonal antibody?

  1. Antibodies with the same tertiary structure
• Give 1 example of using monoclonal antibodies in a medical treatment?

  1. Blocks receptors on cells
• Describe the role of antibodies in producing a positive result in an ELISA test?

  1. First antibody binds to antigen
  2. Second antibody with enzyme attached is added
  3. Second antibody attaches to antigen
  4. Substrate added and colour changes
• Describe and explain the role of antibodies in stimulating phagocytosis?

  1. Bind to antigen
  2. Cause agglutination
• Explain how treatment with antivenom works and why passive immunity is essential?

  1. Antibodies bind to the venom and cause its destruction
  2. Active immunity would be too slow
• During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom.Use the humoral immune response to explain this vaccination programme?

  1. B cells specific to venom reproduce by mitosis
  2. B cells produce plasma cells and memory cells
  3. The second dose produces antibodies in higher concentration and quickly
• Describe how phagocytosis of a virus leads to presentation of its antigens?

  1. Phagosome fuses with lysosome
  2. Virus destroyed by lysozymes
  3. Antigens from virus are displayed on the cell membrane
• Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen?

  1. Helper T cell binds to the antigen
  2. Helper T cell stimulates a specific B cell
  3. B cell clones
  4. Forms plasma cells that release antibodies
• What is an antigen?

  1. Foreign protein
  2. That stimulates an immune response
• What is an antibody?

  1. A protein specific to an antigen
  2. Secreted by plasma cells
• Nm is a leading cause of bacterial meningitis. In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis?

  1. Antigen binds to surface receptor on a specific B cell
  2. Activated B cell divides by mitosis
  3. Division stimulated by cytokines
  4. Plasma cells release antibodies
  5. Some B cells become memory cells
  6. Memory cells produce antibodies faster
• When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how?

  1. Vaccine contains antigen from pathogen
  2. Macrophage presents antigen on its surface
  3. T cell with complementary receptor protein binds to antigen
  4. T cell stimulates B cell with complementary antibody on its surface
  5. B cell secretes large amounts of antibody