Unit 18 Variation and selection Flashcards
variance
differences between
individuals of the same species
adapted feature
an inherited feature that helps an organism to survive and reproduce in its environment
adaptation
the process, resulting from natural selection, by which populations become more suited to their environment over many generations
mutation
- define
- way in which…….
genetic change
- mutation is the way in which new
alleles are formed
gene mutation
a random change in the base sequence of DNA
what increases rate of mutation / likelihood - mutagens
ionising radiation and some chemicals
[increase the rate of mutation]
sources of genetic variation in populations
mutation, meiosis, random mating
and random fertilisation
continuous variation
results in what? e.g.?
- results in a range of phenotypes between two extremes;
-caused by both genes and the environment
examples include body length and body mass
discontinuous variation
results in what? e.g?
- results in a limited number of phenotypes with no intermediates;
- usually caused by genes only
examples include ABO blood groups, seed shape in peas and seed colour in peas
exam ques - how discontinuous & continuous differ
discontinuous variation – influenced by genes alone;
discontinuous variation – no effect of the environment
limited number of phenotypes;
birds
- wings
-beak
-feathers
scales on legs/feet
explain why wing length is an example of continuous
- quantitative feature
-range between two extremes - influenced by environment and genetics or genotype
- not in distinct groups
another continuous variation feature
body mass, age
adaptations - examples
xerophytes -
plants adapted for living in extremely dry soils such as in deserts
hydrophytes -
plants adapted for watery habitats like rivers, ponds and lakes
xerophytes (4 adaptations + 1)
- thick waxy cuticles prevents loss of water from leaf
- needle-shaped leaves reduces surface area exposed to air
- thickened stems & leaves can store water
- shallow but extensive root system. Allows them to soak up as much of the occasional rain as possible
+ leaf rolled with stomata inside - slows down air movement; prevents water loss; reduces surface area exposed
hydrophytes (4 adaptations)
- air spaces in leaves allow them to float on top of water
- flat leaves maximise photosynthesis and help them float
- bottom of leaf is submerged in water. stomata are on upper epidermis so they can exchange gases more easily
- small roots as plenty of water
natural selection [e.g. development of strains of antibiotic resistant bacteria. Causes evolution] -
applies to every exam question [5]
a) genetic variation within populations
(b) production of many offspring
(c) struggle for survival/existence, including competition for resources [between individuals]
(d) a greater chance of survival and reproduction by individuals better adapted to environment than others
(e) these individuals pass on their alleles to the next generation, becomes more common in population
selective breeding
(a) selection by humans of individuals with
desirable features
(b) crossing these individuals to produce the next generation [trying to combine traits]
(c) selection of offspring showing the desirable features [and bred together]
repeat over multiple generations
differences between natural and
artificial selection
natural: 1) occurs naturally, 2) results in development of populations with features that are better adapted to environ. & survival, 3) usually takes long to occur
artificial: 1) only occurs when humans intervene, 2) results in development of populations with features that are useful to humans & not necessarily to survival of individual, 3) takes less time as only individuals w/ desired features allowed to reproduce
Explain why oxygen passes out of the leaf during the daytime. [3]
- oxygen is a product of photosynthesis
- concentration inside the leaf is greater than outside
- oxygen moves down its concentration gradient
- by diffusion
[more oxygen is produced than used in respiration ;
rate of photosynthesis is greater than the rate of respiration;]
Describe the path taken by a carbon dioxide molecule after it has passed through the
stomata during the daytime until it becomes part of a glucose molecule
carbon dioxide passes through air spaces. carbon dioxide dissolves in water in cell wall. carbon dioxide passes through cell membrane and through cytoplasm, enters chloroplast and reacts with water to form glucose
Suggest explanations for distribution & density of stomata in white water lily & common myrtle [5] white water lily?
common myrtle?
[explain how the leaf area and distribution and density of stomata help different species of plant survive in their different habitats]
white water lily:
(all) stomata (on upper surface) in contact with air. for absorption of, carbon dioxide.
no stomata (on lower epidermis) in contact with water. diffusion (much) faster in air (than in water)
common myrtle
all stomata on lower surface in the shade away from sun. reduces transpiration. so less water is lost
Explain the importance of meiosis in sexual reproduction. [2]
chromosome number halved / becomes haploid ;
genetic / DNA variation ;
cross-pollination [RMBR]
- one feature visible in Fig. 4.2 that helps to attract insects
- one environmental reason why lilies that grow at lower altitudes flower earlier
than the lilies at higher altitudes.
transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
- large petals
-temperature
Explain why flowering time is an example of continuous variation. [2]
-influenced by environment and genes;
-range of phenotypes;
-measureable;
Scientists think that plants of L. polyphyllum growing at high altitudes may evolve into a new species.
Explain how natural selection could lead to the evolution of a new species of lily [5]
📌 different environments have different selection [or competition] pressures ;
📌 variation occurs (at fertilization / meiosis) ;
📌 mutation occurs, genetic change
📌 best adapted organisms most likely to survive ;
📌 (those that survive) pass on their alleles / genes ;
📌competition for survival ;
The populations of Soay sheep on St. Kilda show much more variation in their
phenotype than modern breeds of sheep.
Explain, by using an example from Fig. 6.1, what is meant by variation in their
phenotype. [2]
there are different forms of one, feature / characteristic ;
coat / fur, colours;
Explain how natural selection could account for the adaptive features of Soay sheep. [4]
REMEMBER THIS
variation among the sheep in the population. some are better, adapted than others. survive and have offspring. pass on their alleles. over time better adapted, features / traits, become more common ;
Suggest and explain what happens to the seeds when they are exposed to ionising
radiation. [2]
+ Suggest how selective breeding is carried out with plants. [4] 📍 PLANT EXAMPLE EXAM QUESTIONS!!!
mutation ;
change in, gene(s) / DNA ;
+ 📌 choose plants with desired feature(s). cross / breed plants. collect seeds. cross plants showing features with original variety. keep crossing and selecting.
Australia have put a gene from the bacterium Bacillus thuringiensis (Bt)
into the cowpea, an important crop in Africa. This gene gives resistance against the cowpea pod borer, an insect pest that reduces the yield of cowpeas.
Explain how the method used by the Australian scientists differs from the technique used by the Ghanaian scientists. [2]
+ advantages to farmers of growing legumes and maize together in the
same field at the same time
genetic engineering / genetic modification ;
introduced a gene from a different species;
results, after one generation ;
+ 📌 2 of: products of fixation / nitrates provide a source of protein ;
increases nitrogen in soil when beans decay ;
maintain / higher, yields (of maize) ;
