BIOL2 Flashcards
an arteriole contain muscle fibres. explain how these muscle fibres reduce blood flow to capillaries. (2)
- muscle contracts
- arteriole constricts
leopards, cheetahs and pumas are all members of the family Felidae. biologists used DNA hybridisation to investigate the evolutionary relationships between them. they found that hybrid DNA from a leopard and a cheetah separated into single strands at a higher temperature than hybrid from a leopard and a puma. these results suggest leopards are more closely related to cheetahs that to pumas. explain why. (2)
- more hydrogen bonds
- similar base sequences
all modern cheetahs are thought to have descended for a single female. this female was part of a small population that survived an ice age a long time ago that killed almost all cheetahs. after the ice age, the number of cheetahs increased. use this information to explain what is meant by a genetic bottleneck. (2)
- drop in population
- smaller gene pool
the fertility of cheetahs is low. the proportion of abnormal sperm cells produced is higher in cheetahs than in other members of the family Felidae. suggest an explanation for this. (2)
- errors in meiosis
- interbreeding
give 2 precautions the students should have taken when setting up the photometer to obtain reliable measurements of water uptake by the plant shoot. (2)
- cut shoot under water
- ensure no air bubbles present
a photometer measures the rate of water uptake rather than the rate of transpiration. give 2 reasons why the photometer does not truly measure the rate of transpiration. (2)
- water used in photosynthesis
- water produced in respiration
explain why the rate of water uptake decreases as the number of leaves removed from the plant shoot increases. (4)
- less surface area
- fewer stomata
- less transpiration
- less cohesion
describe what happens during anaphase that results in the production of 2 genetically identical cells. (2)
- sister chromatids
- move to poles
the variety of colours displayed by catfish is important in courtship. give ways in which courtship increases the probability of successful mating. (2)
- attracts same species
- synchronised mating
- form bond pair
- stimulates release of gametes
frequent treatment with antibiotics can result in resistant strains of bacteria. explain how. (3)
- mutation
- resistant gene
- bacteria survive and reproduce
- by binary fission
scientists can use protein structure to investigate the evolutionary relationship between different species. explain why. (2)
- amino acid sequence related to DNA sequence
- closer the amino acid sequence the closer the relationship
explain the importance of taking a large number of samples at each site. (1)
- more reliable mean
- identify anomalies
explain how oxygen is loaded, transported and unloaded in the blood. (6)
- haemoglobin carries oxygen
- in red blood cells
- loading in lungs
- at high partial pressure
- unloads in tissues
- at low partial pressure
explain the advantage to a person with anaemia having their oxygen dissociation curve shift to the right. (3)
- lower affinity for oxygen
- releases more oxygen
what is meant by species diversity. (1)
number of species in a community
explain the movement of oxygen into the gas exchange system of an insect when it is at rest. (3)
- oxygen used in aerobic respiration
- so oxygen concentration gradient established
- oxygen diffuses in
describe how temporary mounts are made. (2)
- thin section
- put in slide in stain
- add cover slip
describe how the scientists could have used the temporary mounts of leaves to determine the mean number of chloroplasts in mesophyll cells of a leaf. (3)
- select cells at random
- count number of chloroplasts
- divide number of chloroplasts by number of cells
what is meant by genetic diversity. (1)
difference in DNA
what is the function of coronary arteries? (2)
- carry oxygen
- to heart muscle
the rise and fall in blood pressure in the aorta is greater than in the small arteries. suggest why. (3)
- aorta is close to heart
- aorta has elastic tissue
- stretch and recoil
suggest and explain how companion cells are adapted for transport of sugars between cells. (2)
- Mitochondria release ATP
- For active transport
suggest and explain a way in which sieve cells are adapted for mass transport. (2)
- few organelles
- thick walls resist pressure
explain the role of independent segregation in meiosis. (2)
- genetic variation
- allow different combinations of maternal and paternal alleles
- produce haploid cells
the oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. explain the advantage of this shift. (3)
- lower affinity for oxygen
- oxygen to muscles
- for high respiration
the volume of water passing over the gills increases if the temperature of water increases. suggest why. (1)
increased enzyme activity
tetracycline can enter a bacterium through protein A. this protein is found in the plasma in the membrane. suggest how a change in the amino acid sequence of this protein could make a bacterium resistant to tetracycline. (2)
- different tertiary structure
- not complementary
there were differences in separation temperature of DNA formed from single- stranded DNA of the same species of primate. suggest why. (1)
different alleles
explain how the structure of DNA is related to its function. (6)
- double stranded => strength
- large => stores lots of information
- helix => compact
- base sequence => allows info to be stored
- double stranded => replication can occur semi- conservatively
- many hydrogen bonds=> replication
describe the role of the centromere in mitosis. (2)
- holds chromatids together
- attaches chromatids to spindle
DNA helicase is important in DNA replication. explain why. (2)
- breaks hydrogen bonds
- so nucleotides can attach
the oxygen dissociation curve of the fetus is to the left of that for its mother. explain the advantage of this for the fetus. (2)
- higher affinity for oxygen
- oxygen moves from mother to fetus
after birth, fetal haemoglobin is replaced with adult haemoglobin. suggest the advantage of this to the baby. (2)
- lower affinity for oxygen
- oxygen to respiring tissues
abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. explain why. (2)
- oxygen enters more quickly
- maintains diffusion pathway
the insect opens its spiracles at a lower frequency in very dry conditions. suggest one advantage of this. (1)
no water lost
the tracheoles connect directly with the insect’s muscle tissue and are filled with water. when flying, water is absorbed into the muscle tissue. removal of water from tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. suggest one reason why. (1)
- greater surface area exposed to air
- gases diffuse faster in air than through water
- increases volume of air
mitosis is important in the life of an organism. give 2 reasons why. (2)
- growth
- repair tissue
explain why the biologist chose to examine 200 cells. (1)
representative
explain how the standard deviation helps in the interpretation of these data. (2)
- shows spread of data
- low SD means results more reliable
describe how tissue fluid is formed and how it is returned to the circulatory system. (6)
formation - high hydrostatic pressure - forces water out - large proteins remain in capillary return - low water potential in capillary - due to proteins - water enters by osmosis
explain why the values for the pressure in the xylem are negative. (1)
lower than atmospheric pressure
explain 1 way in which this palisade cell is adapted for photosynthesis. (1)
chloroplasts absorb light
an increase in respiration in the tissue of a mammal affects the oxygen dissociation curve of haemoglobin. describe and explain how. (2)
- increase in CO2
- curve moves to right
there is less oxygen at high altitudes that at sea level. people living at high altitudes have more red blood cells than people living at sea level. explain the advantage of this to people living at high altitude. (2)
- lower affinity for oxygen
- oxygen to tissues
the stomata on the leaves of pine trees are found in pits below the leaf surface. explain how this helps reduce water loss. (2)
- water vapour increases humidity
- water gradient reduces
the blood pressure is high at the start of the capillary. explain how the left ventricle causes the blood to be high at high pressure. (1)
contracts
the blood pressure decreases along the length of the capillary. what causes this decrease in pressure? (2)
- loss of water
- resistance of capillary wall
in children, some diets may result in a low concentration of protein in fluid F. this can cause the accumulation of tissue fluid. explain the link between a low concentration of protein in fluid F and the accumulation of tissue fluid. (3)
- water potential gradient is reduced
- more tissue fluid formed
- no water absorbed
- by osmosis
explain why it may be more useful to calculate the index of diversity than to record only the number of species present. (2)
- measures number of individuals and number of species
- some species only present in small numbers
the zoologist measured oxygen uptake per gram of body mass. explain why he measured oxygen uptake per gram of body mass, (2)
- allows comparison
- as animals differ in size
the scientist measured the volume of the tumours. explain the advantage of using volume rather than length to measure the growth of tumours. (1)
don’t grow uniformly
in cells, taxol disrupts spindle activity. use this information to explain the results in the group that has been treated with taxol. (3)
- mitosis
- as chromosomes cannot attach to spindle
- cell division slows down
give 2 ways in which courtship behaviour increases the probability of successful mating. (2)
- recognise members of same species
- recognition of mate
mikanolide is a drug that inhibits the enzyme DNA polymerase. explain why this drug may be effective against some types of cancer. (2)
- prevents DNA replication
- new strand not formed
the number of species present is one way to measure biodiversity. explain why an index of diversity may be a more useful measure of biodiversity (2)
- Also measures number of individuals in a species / different proportions of species;
- Some species may be present in low/high numbers;
explain the importance of elastic fibres in the wall of the aorta. (2)
- stretch and recoil to smooth blood flow
explain the importance of muscle fibres in the wall of the arteriole. (2)
- contracts
- arteriole constricts
the rate of blood flow decreases from the aorta to the capillaries. why. (1)
larger increase in cross sectional area
the student cut the shoot and put it into the potometer under water. explain why. (1)
prevent air entering
the student measured the rate of water uptake 3 times. suggest how the reservoir allows repeat measurements to be made. (1)
returns bubble to start
some of the gametes formed during meiosis have new combinations of alleles. explain how the gametes with the combinations of alleles Ef and eF have been produced. (2)
- crossing over
- exchange of alleles between chromosomes
only a few gametes have the new combination of alleles Ef and eF. most gametes have the combination of alleles EF and ef. suggest why only a few gametes have the new combination of alleles, Ef and eF. (1)
rare
describe how oxygen loads and unloads in the body. (3)
- loading of oxygen
- in lungs
- unloads oxygen
- in tissues
heat from respiration helps mammals to maintain a constant body temperature. explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins. (4)
- smaller mammal has greater SA: V ratio
- smaller mammals lose more heat
- greater rate of respiration
- oxygen required for respiration
scientists analysis of blood proteins has indicated a lack of genetic diversity in populations of some organisms. describe the processes that lead to a reduction in the genetic diversity of populations of organisms. (6)
- reduced gene pool
- founder effect
- few individuals become isolated
- genetic bottleneck
- fall in size of population
- selective breeding
