Cell Division And Natural Selection

Question 1

What are diploid cells?

Answer 1

A cell which contains two copies of each chromosome

Question 2

What is mitosis ?

Answer 2

A process where a single cell divides into two identical daughter cells (genetically identical to the parent)

Question 3

What two things are needed for mitosis ?

Answer 3

1) copy each chromosome before it divides - involves DNA replicating and more protein being added to the structure
2) it must divide in a way that each daughter cell receives one copy of every chromosome

Question 4

Order of mitosis

Answer 4

Prophase
Metaphase
Anaphase
Telophase

Question 5

What happens in prophase ?

Answer 5

DNA replicates and chromosomes form 2 exact copies - chromatids

Chromatids become visible

Nuclear membrane breaks down

Question 6

What happens in metaphase?

Answer 6

Spindle forms

Chromosomes line at the equator of the spindle, attached by centromere

Question 7

What happens in anaphase

Answer 7

Spindle fibres shorten and pull chromatids to opposite ends of the cell

Chromatids separate to become 2 daughter cells

Question 8

What happens in telophase

Answer 8

2 new nuclei form at poles of cell

Cytoplasm starts to divide to produce 2 daughter cells - both daughter cells have a copy of each chromosome from the parent cell

Question 9

Example of mitosis

Answer 9

Cancer cells divide by mitosis

Question 10

What is cytokinesis

Answer 10

The cytoplasmic division of cells at the end of mitosis, bringing about the separation into 2 Daughter cells

Question 11

What is meiosis

Answer 11

A process where a single cell divides twice to produce four cells containing half the original amount of genetic material

Question 12

During meiosis the parent cell must do 2 things:

Answer 12

It must copy each chromosome so that there is enough material to be shared between 4 daughter cells

It must divide twice - the daughter cell revives just one chromosome from each homologous pair

Question 13

2 main events during meiosis

Answer 13

1) during 1st division one chromosome from each homologous pair goes into daughter cell
2) during 2nd division chromosome separated into 2 parts, 1 part goes into each daughter cell

Question 14

Gametes formed by meiosis……..

Answer 14

Don’t all have same combinations of alleles 1 genetic variation in cells

Question 15

Number of cell divisions

Answer 15

Mitosis - 1

Meiosis - 2

Question 16

Number of daughter cells produced

Answer 16

Mitosis - 2

Meiosis - 4

Question 17

Daughter cells H or D

Answer 17

Mitosis - diploid

Meiosis - haploid

Question 18

What is evolution

Answer 18

The Change in the frequency of a phenotype in a population over many generations

Question 19

What was Darwin’s theory

Answer 19

• individuals in a species show a range of variation caused by differences in genes
• individuals with characteristics most suited to the environment have higher chance of survival and more chances to reproduce
• therefore these characteristics are passed to there offspring at a higher rate than those with characteristics less suited to survive
• this idea of natural selection became known as ‘survival of the fittest’

Question 20

What is natural selection

Answer 20

A mechanism for evolution

Question 21

Summary of how we think natural selection works

Answer 21

• variation within a species
• changing conditions in the environment (selective pressure) favours one particular form of the species
• the frequency of the favoured form increases under these conditions
• the frequency of the less well adapted form decreases under these conditions

Question 22

Describe resistance

Answer 22

1) resistance starts when a random mutation gives a bacterium resistance to a particular antibiotic
2) new resistant bacterium has an advantage over non resistant bacteria of the same type
3) the resistant strain of bacterium will survive and multiply in greater numbers than the non resistant type
4) resistant bacteria will not be killed by the antibiotic, meaning the antibiotic is no longer effective in controlling the disease

Question 23

Steps to answer question of natural selection:

Answer 23

1) genetic variation within a species due to random mutation
2) competition within the species
3) best adapted will survive
4) more likely to reproduce and pass on beneficial alleles
5) over time there will be a change in species

Question 24

What reasons do the offspring from sexual reproduction vary genetically

Answer 24

1) huge variation in gametes

2) random way in which fertilisation takes place

Question 25

Identical twins:

Answer 25

Formed from same zygote (monozygotic twins)

Question 26

Describe asexual reproduction

Answer 26

When organisms reproduce asexually there is no fusion of gametes

• the cells it contains were formed by mitosis
• a part of the organism grows and breaks away form parent organism
• asexual reproduction produces offspring that are genetically identical to the parent and each other

Question 27

Several environmental factors can influence height of plants:

Answer 27

• may not all receive same amount of light
• may not all receive same amount of water and mineral ions from soil
• may not all receive same amount of CO2