cells

Question 1

describe cell fractionation to separate organelles

Answer 1

• homogenise the tissue to break open the cell and remove any cellular debris
• place in a ice-cold, buffered and isotonic solution
• differention centrifugation : the solution is spun at a high speed so nucleus goes to the bottom.
• then it is spun at a higher speed so chloroplasts/mitochondria separate and go to the bottom. and same repeats but for at a higher speed for ribosomes.

Question 2

explain why a cell membrane may be described as a fluid mosaic

Answer 2

because the position of the molecules within the membrane is fluid - they are able to move around within the membrane.
membrane is made up from variety of different molecules arranged into a mosaic.

Question 3

describe how substances can cross a cell surface membrane by entering and leaving

Answer 3

• simple/facilitated diffusion from high to low concentration
• non polar molecules pass via phospholipids/bilayer
• water moves by osmosis from high wp to low wp.
• active transport is movement of from low conc to high conc / against conc grad.
• active transport/ facillitated diffusion requires carrier and channel proteins
• active transport requires energy from atp
• Na+ and glucose are co transported.

Question 4

describe the differences between passive and active immunity and vaccination

Answer 4

passive:

• no antibodies produced - antibodies are received from elsewhere
• no plasma/ memory cells
• so does not last long / short term as no memory cells produced
• quick and fast

active:

• plasma and memory cells are produced
• so antibodies are produced
• last long/ long term as memory cells are produced
• slower

Question 5

why are antibodies referred to as monoclonal

Answer 5

produced from the same B cell/plasma cell

Question 6

tests using monoclonal antibodies are specific. use your knowledge of protein structures to explain why

Answer 6

• specific primary structure
• so specific tertiary structure - complex 3d specific shape
• only binds to complimentary antigens

Question 7

describe the features of metaphase

Answer 7

• chromosomes align at the equator
• spindle fibers form on centriole
• spindle fibers attach onto the centromere

Question 8

describe anaphase

Answer 8

• spindle fibres shorten

- centromere splits and sister chromatids are separated and pulled to opposite poles

Question 9

describe telophase

Answer 9

• the cell splits apart as well as the nucleus

- chromatids uncoil and unwind to form chromatin

Question 10

what type of cells do each meiosis / mitosis cells make

Answer 10

meiosis:
- gametes (sperm and egg cells)

mitosis:
-body cells (stomach, skin cells)

Question 11

how is prophase different in mitosis than meiosis

Answer 11

• in mitosis the chromosomes just condense and supercoil
• however in meiosis the chromosomes are in homologous pairs( one from mum one from dad and contain same type of genes and are similar sizes.)
• and then the pairs cross over (transfer a section of DNA to each pair)`

Question 12

how is metaphase different in mitosis from meiosis

Answer 12

mitosis: chromosomes line up at the equator
meiosis: the homologous pairs line up at the equator.

Question 13

how is anaphase different in mitosis than meiosis

Answer 13

mitosis: spindle fibres pull chromatids away to opposite poles and centromere splits
meiosis: spindle fibres pull chromosomes away to opposite ends