Bio MS

Question 1

how is chromosome number halved in meiosis

Answer 1

homologous chromosomes separate so one of each goes to each daughter cell

Question 2

enzymes work in opposite directions to build DNA in DNA replication (4)

Answer 2

DNA has antiparallel strands
shape of nucleotide is aligned differently
enzymes have an active site with specific shape
only substrates with complementary shape can bind with active site of DNA polymerase

Question 3

effect of hunting on genetic diversity (3)

Answer 3

few types of alleles left
inbreeding
few surviving populations

Question 4

why populations might show low levels of genetic diversity (3)

Answer 4

population may have been small
population started with a small number of individuals (one pregnant female)
inbreeding

Question 5

explain how tissue fluid is formed (2)

Answer 5

overall outward pressure

small molecules are forced out of the capillary

Question 6

why is there a high hydrostatic pressure in the arteriole end than the venule end

Answer 6

water loss

Question 7

how does high blood pressure lead to tissue fluid formation (3)

Answer 7

high blood pressure is high hydrostatic pressure
increases outward pressure from arteriole end of capillary
more tissue fluid formed than reabsorbed

Question 8

water potential in blood plasma more negative at venule end than arteriole (3)

Answer 8

water moves out of capillary
proteins too large to leave capillary
higher concentration of blood proteins so lower water potential

Question 9

advantage of high % cholesterol in red blood cells

Answer 9

not supported by other cells as it is free in the plasma so needs cholesterol to maintain shape

Question 10

inactive (virus) definition

Answer 10

virus is not replicating

Question 11

why push coverslip down and not sideways

Answer 11

spreads tissue

avoids rolling the cells together

Question 12

describe appearance of chromosome

Answer 12

two sister chromatids held together by a centromere due to DNA replication

Question 13

describe role of haemoglobin in supplying O2 to tissues of the body

Answer 13

associates with O2 at high ppO2 to form oxyhaemoglobin

dissociates with O2 at lower ppO2

Question 14

how O2 in air reaches capillaries near alveoli (5)

Answer 14

trachea, bronchi, bronchioles
down pressure gradient
down diffusion gradient
across alveolar epithelium 
across capillary epithelium

Question 15

how does an asthma attack decrease the volume of air breathed out (4)

Answer 15

muscle walls of bronchi contract
walls of bronchi secrete more mucus
diameter of airway reduced
flow of air reduced

Question 16

why are cats experimented on instead of humans other than ethical reasons (3)

Answer 16

small enough to keep in the lab
can use a large number
similar physiology to humans

Question 17

why do mutations not spread to other species (4)

Answer 17

mutations are random
rate of mutations are only affected by environment
different species do not interbreed
alleles are not able to be passed from one species to another

Question 18

why does it take time for appearance of species with mutation to appear

Answer 18

few individuals with favourable alleles
individuals with allele have more offspring
takes generations for alleles to be the most common allele

Question 19

how is high pressure produced in leaves (3)

Answer 19

water potential is low as sugar enters phloem
water enters phloem by osmosis
increased volume of water increases pressure

Question 20

difference between active and passive immunity (4)

Answer 20

active has memory cells, passive does not
active produces antibodies by plasma and memory cells so is long term
passive involves antibodies introduced into the body from outside source so is short term
active takes time to work/ passive is fast acting

Question 21

mass flow theory (5)

Answer 21

sucrose enters into COMPANION CELLS by facilitated diffusion
sucrose enters PHLOEM BY ACTIVE TRANSPORT with H+
LOWERS WATER POTENTIAL of sieve cell so water enters phloem by osmosis
INCREASES PRESSURE causing mass flow from source to sink
SUGARS USED FOR RESPIRATION

Question 22

why does the potometer not measure rate of transpiration (2)

Answer 22

water used for photosynthesis

water produced in respiration

Question 23

advantage of lipid droplet and micelle formation (3)

Answer 23

droplets increases SA, so faster hydrolysis

micelles carry fatty acids through membrane of cell

Question 24

properties of water which are important for biology (3)

Answer 24

metabolite
solvent
has cohesion/ H bonds between molecules

Question 25

estimate the length of a cell using an optical microscope (2)

Answer 25

calibrate eye piece graticule with stage micrometer

measure length with eyepiece graticule

Question 26

monoclonal antibody

Answer 26

a single type of antibody specific to one antigen only

Question 27

how does an increase in temperature cause pigments to be released (3)

Answer 27

damage to membrane
membrane proteins denature
increases fluidity

Question 28

why should control variable (2)

Answer 28

if control variable increases, affect on results

allows results to be comparable

Question 29

cohesion tension theory (6)

Answer 29

water lost from leaves by evaporation
lowers water potential in the leaf
water is pulled up the xylem
water molecules cohere by hydrogen bonds
forms a water column
adhesion of water to walls of the xylems