3.2.10 Cells Divide by Binary Fission and Mitosis

Question 1

Cells that keep their ability to divide follow the ____ ____

Answer 1

cell cycle

Question 2

What is interphase?

Answer 2

Period of cell growth and DNA replication

Question 3

Name the 2 phases that the cell cycle consists of

Answer 3

1. Interphase
2. Mitosis

Question 4

Name the 3 growth stages that interphase is subdivided into

Answer 4

1. Gap phase 1
2. Synthesis
3. Gap phase 2

Question 5

Where does the cell cycle start and end?

Answer 5

At mitosis

Question 6

Draw the cell cycle

Answer 6

Question 7

What happens in gap phase 1?

Answer 7

Cells grows and new organelles and proteins are made

Question 8

What happens in synthesis?

Answer 8

Cell replicates its DNA, ready to divide by mitosis

Question 9

What happens in gap phase 2?

Answer 9

Cell keeps growing and proteins needed for cell division are made

Question 10

What is mitosis?

Answer 10

When a parent cell divides to produce 2 genetically identical daughter cells

(Contain exact copy of DNA of parent cell)

Question 11

Why is mitosis needed?

Answer 11

For growth of multicellular organisms and repairing damaged tissues

Question 12

Describe what occurs before mitosis, during interphase

Answer 12

1. Caries out its normal functions but prepares to divide
2. DNA unravels and replicates, organelles are replicated
3. ATP content increased

Question 13

Name the 4 main stages in mitosis

Answer 13

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 14

As mitosis begins why are chromosomes made of 2 strands (chromatids) joined by a centromere?

Answer 14

∵ each chromosome has already made an identical copy of itself during interphase

Question 15

When mitosis is over, what do the chromatids end up as?

Answer 15

One-strand chromosomes in the daughter cells

Question 16

Describe Prophase

Answer 16

1. Chromosomes condense and super coil & become visible
2. Centrioles (tiny bundles of protein) move towards opposite end of cell, forming the spindle (network of protein fibres)
3. Nuclear envelope breaks down allows chromosomes to move

Question 17

Describe Metaphase

Answer 17

1. Chromosomes line up along centre of cell
2. Become attached to the spindle by their centromere

Question 18

Describe Anaphase

Answer 18

1. Centromeres divide, separating each pair of sister chromatids
2. Spindles contract, pull chromatids to opposite poles of the spindle, centromere first (are separated)
3. Makes chromatids appear v-shaped

Question 19

Describe Telophase

Answer 19

1. Chromatids reach opposite poles on spindle
2. They uncoil & become long and thin again = chromosomes
3. Nuclear envelope reforms preventing chromosomes moving away
4. Cytoplasm divides (cytokinesis) so they’re now two daughter cells that are genetically identical to original cell
5. (Each daughter cells starts interphase)

Question 20

Describe how you use root tips to observe mitosis

Answer 20

1. Cut 1 cm from tip of growing root (e.g. onion)
2. Hydrochloric acid in boiling tube, put in water bath at 60°C
3. Transfer root tip into boiling tube & leave for 5 mins
4. Use pipette to rinse root tip with cold water
   
   • Leave tip to dry on paper towel
5. Place root tip on microscopic slide & cut 2 mm from very tip of it
   
   • Discard the rest
6. Use mounted needle to break tip open and spread cells thinly
7. Add few drops of stain and leave it for few minutes
8. Place cover slip over cells and push down firmly to squash tissue
9. Look at all stages of mitosis under optical microscope

Question 21

Investigating Mitosis

Why do you have cut the from the tip of a growing root?

Answer 21

Has to be tip ∵ it’s where growth occurs (i.e. mitosis)

Question 22

Investigating Mitosis

Why do you have add stain to the sample?

Answer 22

Stain makes it easier for chromosomes to be seen

Question 23

Investigating Mitosis

Why do you squash the tissue (by pushing down the cover slip firmly over the cells)?

Answer 23

This makes tissue thinner = allows light to pass through it

Question 24

Investigating Mitosis

Why shouldn’t you smear the cover slip sideways?

Answer 24

∵ you’ll damage the chromosomes

Question 25

Label the stages of mitosis and interphase

Answer 25

Question 26

Describe how you would use an optical microscope to observe cells

Answer 26

1. Clip prepared slide onto the stage 2. Select lowest-powered objective lens 3. Use coarse adjustment knob to bring stage up to just below objective lens 4. Look down eyepiece & use coarse adjustment knob to move stage downwards until image is roughly in focus 5. Adjust focus with fine adjustment knob until you get clear image of slide 6. If you need a greater magnification, swap to higher-powered objective lens and refocus

Question 27

What is mitotic index?

Answer 27

Proportion of cells undergoing mitosis

Question 28

Why do we work out the mitotic index?

Answer 28

To find out how quickly a tissue is growing

Question 29

State the formula for the mitotic index

Answer 29

Question 30

Why does a plant root tip have a high mitotic index (i.e. lots of cells in mitosis)?

Answer 30

∵ it's constantly growing

Question 31

Why may other tissues have a high mitotic index?

Answer 31

∵ tissue repair is taking place or there's cancerous growth

Question 32

What is an artefact?

Answer 32

Things that you can see down microscope that aren't part of cell or specimen you're looking at e.g. bits of dust, air bubbles and fingerprints, to inaccuracies caused by squashing and staining your sample

Question 33

When are artefacts made?

Answer 33

During preparation of your slides

Question 34

What is binary fission?

Answer 34

When a prokaryotic cell replicates its genetic material before splitting into 2 daughter cells

Question 35

Describe Binary Fission

Answer 35

1. Circular DNA and plasmid(s) replicate * Main DNA loop is replicated once but plasmids can be replicated loads of time 2. Cells get bigger and DNA loops move to opposite 'poles' (ends) of cell 3. Cytoplasm begins to divide (and new cell walls begin to form) 4. Cytoplasm divides and 2 daughter cells produced * Each daughter cells has 1 copy of variable DNA but can have variable no. of copies of plasmid(s)

Question 36

What can occur during conjugation?

Answer 36

DNA may be passed from one species of bacterium to another (species)

Question 37

"DNA may be passed from one species of bacterium to another (species) during conjugation" What is this known as?

Answer 37

Horizontal gene transmission

Question 38

What is vertical gene transmission?

Answer 38

When genes are passed down from one generation (of a species) to next generation (of same species)

Question 39

Describe how DNA transfers by conjugation in bacteria

Answer 39