🩶 3.2.2 All Cells Arrise From Other Cells

Question 1

Can all multicellular organisms divide?

Answer 1

No, within multicellular organisms, not all cells retain the ability to divide

Question 2

What do eukaryotic cells that do determine the ability to divide show?

Answer 2

They show a cell cycle

Question 3

When does DNA replication occur?

Answer 3

It occurs during interphase of the cell cycle

Question 4

What is the purpose of mitosis?

Answer 4

• For eukaryotes to grow
• For eukaryotes to replace damaged cells
• For eukaryotes to asexually reproduce

Question 5

Define mitosis

Answer 5

The process of cell replication in eukaryotes resulting into genetically identical daughter cells

Question 6

Define chromosome

Answer 6

Double or single structure composed of linear DNA wrapped around histone proteins

Question 7

Define chromatid

Answer 7

Identical sister chromatids make up the double structure of a chromosome when joined together with a centromere

Question 8

Define centromere

Answer 8

These join the identical sister chromatids together

Question 9

Define centriole

Answer 9

Organelles which produce spindle fibres in order to make the chromosomes

Question 10

Define spindle fibres

Answer 10

Proteinous structures which connect the centrioles to the centromeres

Question 11

Define cytokinesis

Answer 11

Division of the cytoplasm during telophase

Question 12

What is the first step of mitosis called and what happens during it ?

Answer 12

It is called prophase.
- the chromosomes shorten, thicken and therefore condense thus becoming more visible
- each chromosome can be seen to consist of two identical, sister chromatids joined via a centromere
- the nuclear membrane breaks down and centrioles move towards either pole

Question 13

What is the second step of mitosis called and what happens during it?

Answer 13

It is called metaphase.
- each chromosome is joined, via its centromere, by spindle fibres to the centrioles
- the chromosomes are lined up in single file along the equator of the cell

Question 14

What is the third step of mitosis called and what happens during this stage ?

Answer 14

This step is called anaphase.
- the spindle fibres contract and each of the identical, sister chromatids are pulled to the opposite pole
- the centromeres divide
- the chromatids form a characteristic ‘ V ‘ shape

Question 15

What is the fourth step of mitosis called and what happens during this stage?

Answer 15

It is called telophase.
- the identical sister chromatids now start to be referred to as chromosomes again
- the chromosomes start to lengthen again
- the cytoplasm divides (cytokinesis) and the cell membrane of the two identical, daughter cells (clones) reforms
- the nuclear membrane reforms in the two new cells

Question 16

What is the product of mitosis?

Answer 16

Two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication

Question 17

What kind of process is mitosis?

Answer 17

It is a controlled process

Question 18

What can uncontrolled cell division lead to ?

Answer 18

The formation of tumours of cancer

Question 19

What do many cancer treatments focus on doing ?

Answer 19

Many cancer treatments are directed at controlling the rate of cell division

Question 20

Which organisms don’t undergo cell division and why?

Answer 20

Viruses don’t undergo cell division as they are non living. Instead, after the injection of their nucleic acid, the infected host cell replicates the virus particles

Question 21

Which organisms do binary fission?

Answer 21

Prokaryotes - specifically bacteria cells

Question 22

Give the method for binary fission

Answer 22

1- circular DNA replicates
2- plasmids replicate many times unpredictably
3- semi conservative replication occurs
4- circular DNA moves to either pole
5- plasmids move to poles
6- the cell elongates
7- cytoplasm divides
8- cell wall reforms
9- plasmids may divide unequally so they are not referred to as clones or identical cells

Question 23

Describe the steps of how to prepare a temporary mount and estimate the size of a cell

Answer 23

• cut the specimen thinly to allow light to penetrate the single layer of cells
• a drop of water can assist this
• when adding the specimen to the slide, add stain to make organelles visible and supply contrast
• add the coverslip to the specimen, lowering it with a mounted needle, and press firmly down to ensure the specimen is one cell thick and so any air bubbles are removed
• the microscope needs to be calibrated in order for cells to be measured
• a random number generator can be used to choose the cells to measure in order to not be biased
• many cells need to be measured in order to make the sample representative
  (The above two points are done to increase reliability)
• a mean size of cells can be calculated

Question 24

When measuring an organism on the stage what do you use ?

Answer 24

An eye piece graticule

Question 25

How to use the eye piece graticule ?

Answer 25

- the eye piece graticule needs calibrating at each new magnification - the EPG is lined up against the stage micrometre so that each EPV can be assigned a length - once this is achieved the stage micrometre can be discarded and the specimen can be measured