cells past paper questions Flashcards
describe and explain how centrifuging the culture allowed the scientists to obtain a cell-free liquid? (3)
culture in test tubes spun in a centrifuge at high speed so DENSE CELLS(1) FORM PELLET AT THE BOTTOM OF THE TUBE(2) when centrifuged, then the SUPERNATANT CAN BE REMOVED (3)
give one function of lysosomes (1)
break down cells/ cell parts/ toxins
describe how you could use cell fractionation to isolate chloroplasts from leaf tissue (3)
- cells are broken open by being placed in a cold, buffered, isotonic solution (2) an placed in a homogeniser. Debris and whole cells are removed by filtering the homogenate (1)
-the filtered homogenate is placed in a test tube and spun in a centrifuge at a relatively slow speed, the densest organelle (nuclei) collects at the bottom of the tube as a pellet.
-supernatant removed and placed into another tube, centrifuged again and the second densest (chloroplast) forms pellet. (3)
name two structures in a eukaryotic cell which cannot be identified using an optical microscope (1)
-mitochondria
-ribosome
describe how you would make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical microscope (4)
- add drop of water to the glass slide (1)
-obtain thin section of plant tissue and place on the slide (2)
-stain with iodine in potassium iodide (3)
-lower cover slip (at an angle )with a mounted needle (4) to avoid trapping air bubbles
describe how the RER is involved in the production of enzymes (2)
-rough endoplasmic reticulum has ribosomes (1)
-which make protein via protein synthesis (2) and enzymes are proteins
describe how the golgi body is involved in the secretion of enzymes (1)
modifies proteins (1)
OR
packages modified proteins into Golgi vesicles (1)
OR
transport to cell surface (1)
explain why it is not possible to determine the identity of the structures labelled X using an optical microscope (2)
-resolution too low (1)
-because wavelength of light is extremely long (1)
describe the role of one named organelle in digesting bacteria in the cytoplasm? (3)
-lysosomes (1)
-fuse with phagosome (2)
-releases lysozymes (3) which hydrolyse cell wall of certain bacteria
outline the roles of organelles in the production, transport and release of proteins from eukaryotic cells (4)
-DNA in the nucleus codes for protein (1)
-ribosomes on the RER produce protein via protein synthesis (2)
-Golgi apparatus modifies proteins (3) e.g carbohydrate added to make glycoprotein
-vesicles transport (4) and vesicles fuse with the cell membrane to release contents via exocytosis
describe 3 properties of this solution and explain how each property prevented damage to the organelles (3)
-isotonic to prevent lysis (1)
-ice cold to reduce enzyme activity (2)
-buffered to maintain constant PH so prevent denaturing of proteins (3)
contrast how an optical microscope and a transmission microscope work and contrast the limitations of their use when studying cells (6)
-TEM uses electrons and optical uses light
-TEM greater resolution due to wavelength of beam of electrons shorter than wavelength of beam of light
-so with TEM smaller organelles can be observed
-TEM only view dead specimens and optical can view live specimens
-TEM black and white optical colour
-TEM thinner specimens
-TEM more complicated and time consuming preparation
-TEM beam of electrons focused with electromagnets and optical uses lenses
suggest an explanation for the appearance of the cell-surface membrane as two dark lines (3)
-cell surface membrane made of a phospholipid bilayer (1)
-stain binds to glycerol/ phosphate (2)
-on inside and outside of membrane (3)
