Biology paper two model exam question answers Flashcards
compare meosis and mitosis (8)
MITOSIS
two daughter cells
one cell division
full number of chromosomes
genetically identical cells
MEIOSIS
one daughter cell
two cell divisions
half number of chromosomes
genetically different cells
describe how to use a rule drop to work out reaction time (4)
hold ruler above hand of other student
drop ruler so that other person catches it
record where ruler is caught
use conversion table to turn distance in mm into seconds
how could we more accurately measure reaction time
use a computer programme
what is a reflex?
a fast, automatic response that does not go to the conscious part of the brain
how does the nervous system co-ordinate the reflex action (5)
receptor detects stimulus
impulse passes along sensory neuron
crosses synapse via chemicals to the relay neuron
in the spinal cord or central nervous system
passes along motor neuron to effector/muscle
how does information pass across a synapse?
chemical diffuses across synapse, binds to receptors on next neuron
what is a hormone?
a chemical messenger that is released into the blood stream by a gland and travels through the blood stream
describe how hormones control the menstrual cycle (4)
FSH produced in the pituitary gland- matures an egg
Oestrogen produced in the ovaries- thickens uterus lining and inhibits release of FSH
LH produced in pituitary gland- ovulation
progesterone produced in ovaries- inhibits LH and FSH and keeps uterus lining thick
explain the effect of insulin on blood glucose concentration (5)
insulin released by pancreas
effects liver cells
causes more glucose to be taken into cells
causes glucose to change into glycogen
blood glucose concentration increases
explain the effect of glucagon on blood glucose concentration (4)
glucagon released by pancreas
effects liver cells
causes glycogen to turn into glucose
blood glucose concentration increases
describe the process of IVF (5)
FSH and LH given to mature egg
eggs collected from ovaries
fertilized with sperm
egg divides to form embryos
embryo inserted into uterus
explain how blood vessels in the skin can decrease body temperature (4)
blood vessels supplying the skin dilate
more blood flow near surface of skin
more heat/energy is lost from blood
cools blood which cools body
describe how plants grow towards the light (4)
make auxin in tip of shoots auxin
auxin moves to shaded side of plant
stimulates more cell growth on shaded side
so bends towards light
describe how the water content of the blood is controlled when it is too low (3)
if water content of blood too low, ADH released from pituitary gland
increases permeability of tubules in kidney
more water reabsorbed into blood
explain how a persons eye adjusts to form a clear image of a near object (5)
cilliary muscles contract
suspensory ligaments loosen
lens thickens/becomes more curved
lens refracts light more
light rays more focused on retina
explain how a persons eye adjusts to from a clear image of a distant one
cilliary muscles relax
suspensory ligaments tighten
lens get thinner
less light refraction
light rays less focused on retina
explain why a long-sighted person has difficulty seeing near objects clearly (2)
eyeball is too short/ lens not thick enough
light focused behind retina
explain why a short-sighted person has difficulty seeing distant objects clearly (2)
eyeball is too long/too thick
light focused in front of retina
describe how lenses can correct long-sightedness (3)
convex lens
refracts light inwards
light ray focuses on retina
describe how lenses can correct short-sightedness (3)
concave lens
refract light outwards
light ray focuses on retina
describe the process of natural selection (5)
there is a genetic variation in the population
individuals with beneficial alle (refer to exam question)
these are more likely to survive
therefore more likely to breed
pass on beneficial alle to future generations
describe how a natural selection leads to antibiotic resistance (5)
variation between the bacteria
a random mutation causes a bacteria to become resistant to anti-biotics
the resistant bacteria survives whereas non-resistant bacteria are killed by antibiotics
antibiotic resistant allele passed on
population of resistant strain of bacteria increases
use lamarks theory to explain how an organisms characteristics evolve (eg. longer neck in giraffes) (2)
used characteristic more in its lifetime (eg. stretched to get food)
trait passed on to offspring
describe the process of selective breeding (5)
organisms with desired trait is selected
organism with second desired trait is selected
breed two organisms together
select offspring with both traits and breed again
repeat for many generations
describe the process of speciation (6)
variation in the population
population gets geographically isolated
there is different environmental factors in each area
natural selection occurs and the best adapted individuals in each location survive and reproduce
different alleles are passed on in each population
populations can no longer interbreed to from fertile offspring-therefore have formed a new species
describe how a fossil is formed in rock (4)
organism dies and gets buried in sediment
soft parts of organism decay
hard parts (bones/shell) do not decay
bones get replaced with minerals
random sampling method (6)
lay two tape measures to make a grid
get random co-ordinates using a random number generator
place quadrat at co-ordinates and count individuals
repeat to get 20 samples
calculate mean number of individuals
estimate size of population by doing: mean number of individuals x area
transect sampling method (5)
use a random number generator to randomly lay a tape measure in a straight line
place a quadrat next to the transect and count number of individuals
repeat every 2m along the transect
repeat this transect in another random location
compare data
describe how water content is controlled when water content of blood too high (3)
small volume of concentrated urine is formed
no ADH released
less water reabsorbed into blood
