Variation and Selection

Question 1

Variation

Answer 1

differences between individuals of the same species

Question 2

Continuous variation

Answer 2

results in a range of phenotypes between two extremes; examples include body length and body mass.

Question 3

Discontinuous variation

Answer 3

results in a limited number of phenotypes with no
intermediates; examples include ABO blood groups, seed shape in peas and seed
colour in peas

Question 4

Discontinuous variation is usually caused by

Answer 4

genes only and continuous variation is
caused by both genes and the environment.

Question 5

Mutation

Answer 5

genetic change

Question 6

The mutation is the way in

Answer 6

which new alleles are formed?

Question 7

Ionising radiation and some chemicals increase the

Answer 7

rate of mutation.

Question 8

Gene mutation

Answer 8

random change in the base sequence of DNA.

Question 9

sources of genetic
variation in populations

Answer 9

Mutation, meiosis, random mating and random fertilisation

Question 10

An adaptive feature

Answer 10

the inherited feature that helps an organism to survive and
reproduce in its environment, i.e. increase fitness.

Question 11

Adaptive features of hydrophytes:

Answer 11

1 submerged leaves are divided ;
2 providing large area for, photosynthesis
/ absorption ;
3 leaves have large surface area ;
4 to float ;
5 (floating leaves so) little xylem/ little
lignin ;
6 water provides support ;
7 little/ no roots /root hairs ;
8 roots for anchorage only / no need for
roots to absorb water or mineral ions ;
9 little/ no, cuticle ;
10 no need to conserve water ;
11 stomata only on upper surface ;
12 only upper surface exposed to air/ to
allow diffusion of gases ;
13 lots of air spaces (between cells) ;
14 for flotation/ buoyancy ;
15 floating leaves ;
16 to allow, diffusion/AW of (named)
gas(es) ;
17 aerial roots ;
18 to allow roots to receive oxygen ;

Question 12

Adaptive features of xerophytes:

Answer 12

few stomata / low stomatal density ;
sunken stomata ;
stomata close during the day and
open at night ;
rolled leaves ;
thick epidermis / thick cuticle ;
few / no / small, leaves ;
hairs on leaves ;
low rates of transpiration ;
deep roots / AW ;
to absorb water from the water table /
AW
long and spread out below the
surface ;
to absorb water when it rains ;
root cells have low water potential ;
to absorb water by osmosis ;
from (very) salty soils / AW ;
roots branch many times ;
have many roots hairs ;
to give a large surface area (for
absorption of water) ;

Question 13

Natural selection:

Answer 13

genetic variation within populations
production of many offspring
struggle for survival, there is competition for resources
a greater chance of reproduction by individuals that are better adapted to the
environment than others
these individuals pass on their alleles to the next generation

Question 14

Selective breeding:

Answer 14

selection by humans of individuals with desirable features
crossing these individuals to produce the next generation
selection of offspring showing the desirable features.

Question 15

Selective breeding by artificial selection is carried out over

Answer 15

many generations to
improve crop plants and domesticated animals

Question 16

Adaptation

Answer 16

process, resulting from natural selection, by which populations
become more suited to their environment over many generations.

Question 17

example of natural
selection

Answer 17

The development of strains of antibiotic-resistant bacteria

Question 18

Difference between natural and artificial
selection:

Answer 18

features are adaptive
caused by environment
slower changes
increase in fitness
explained: ability to survive AND
reproduce (in natural environment)
maintain (genetic) variation/ less
(genetic) variation in selective breeding
random mating

Question 19

Difference between artificial and
natural selection:

Answer 19

human choice (rather than
environmental pressures) /
AW ;
less, diversity / variation ;
faster change ;
AVP ; e.g. mating is not
random