Chapter 17: Variation And Selection

Question 1

define Variation

Answer 1

differences between the individuals of the same species

Question 2

What are the two types of variations

Answer 2

-discontinuous variation
-continuous variation

Question 3

define discontinuous variation

Answer 3

variation in which there are distinct categories of phenotype,with no intermediates

Question 4

Example of discontinuous variation

Answer 4

-blood groups
-seed colour in peas
-seed shape in peas

Question 5

Define population

Answer 5

a group of organisms of one species,living in the same area at the same time

Question 6

Define continuous variation

Answer 6

variation in which there is a continuous range of phenotypes between two extremes

Question 7

Example of continuous variation

Answer 7

Height
Body mass

Question 8

what are the causes of discontinuous variation

Answer 8

their genotypes are different

Question 9

What are the causes for continuous variation

Answer 9

-their genotypes and the different environment they are in

Question 10

Define mutation

Answer 10

a random change in a gene,which can produce new alleles;mutations involves a change in the base sequence in DNA

Question 11

State two things which may increase the rate of mutation

Answer 11

-ionising radiation (they can damage the bases in DNA molecules)
-different chemicals : such as lead and mercury

Question 12

How are new alleles formed

Answer 12

By mutation

Question 13

define adaptive feature

Answer 13

an inherited feature that helps an organism to survive and reproduce in its environment

Question 14

Define xerophyte

Answer 14

A plant that has adaptive features that help it to survive in an environment where water is scare

Question 15

What are the common adaptations in a xerophyte

Answer 15

-closing stomata
-waxy cuticle
-hairy leaves
-sucked stomata on w underside of leaves
-Reducing the surface area of the leaves
-having deep or spreading roots

Question 16

Why do xerophytes have a closing stomata

Answer 16

If the stomata is closed,transpiration slows down to an almost complete stop.
However photosynthesis cannot happen as carbon dioxide cannot diffuse into the leaf

Question 17

Why does xerophytes have a waxy cuticle

Answer 17

It cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers the temperature

Question 18

Why does xerophytes have hairy leaves

Answer 18

The hairs trap a layer of most air next to the leaf.the most air reduces the diffusion gradient for water vapour from the leaf into the air,so less water vapour diffuses out of the leaf

Question 19

Why does xerophytes have a reducing surface area of the leaves

Answer 19

The smaller the surface area of the leaf,the less water vapour will diffuse out of it.

Question 20

Why do xerophytes have deep or spreading roots

Answer 20

Desert plants may have to seek water very deep down in the soil or across a wide area

Question 21

Define hydrophytes

Answer 21

Hydrophytes are a plant that has adaptive features that help to survive in water

Question 22

State 3 advantages of hydrophytes

Answer 22

-wide and flat leaves
-large air spaces
-thin waxy cuticle

Question 23

Define natural selection

Answer 23

a process in which individuals with advantageous features are more likely to survive,reproduce and pass on their alleles to the next generation

Question 24

describe the process of natural selection

Answer 24

1: variation - the variation within a population of organisms,some of these variations are caused by having different alleles of genes while some affect the adaptive features of the organisms
2: over production - within a wild population,many more offspring are produced than will survive
3: Best adapted individuals more likely to survive and reproduce - the individuals have the best chance of surviving and reproducing
4: Alleles that confer useful adaptions more likely to be passed on - the alleles that confer the best chance of survival therefore increase in the population while alleles that are not advantageous become less common

Question 25

Name two ways natural selection can cause change in a population

Answer 25

1.a new allele could arise by mutation so if the allele gives an organism a better adaptive feature than any of the individuals in the population,then this organism will be selected for- that is it will have a good chance of surviving and reproducing
2. the environment could change,so that features that once helped an organism to survive are are no longer as useful.