Paper 1: Topic 1 Cell Biology - Cell division (LV) Flashcards Preview

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Flashcards in Paper 1: Topic 1 Cell Biology - Cell division (LV) Deck (126)
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Name the genetic material found in all living cells



State where the genetic material is located in eukaryotic cells

Contained inside the nucleus


State where the genetic material is located in prokaryotic cells

Free in the cytoplasm

Exists as a nucleoid and some bacteria can also have additional small loops of DNA called plasmids


Describe how DNA is arranged in eukaryotic cells

As a linear chromosomes


Explain the term chromosome

A coiled length of DNA


State how many chromosomes are found in human somatic (body) cells



State how many chromosomes are found in human gametes



Explain the term diploid

A full set of chromosomes

This is represented as ‘2n’


Explain the term haploid

Half a set of chromosomes

This is represented as ‘n’


Explain the term ‘cell cycle’

A series of events in which a cell grows, replicates its DNA and then divides to form daughter cells


How do human somatic cells divide?



What is the function of mitosis?

To produce two GENETICALLY identical daughter cells


Why do multicellular organisms use mitosis?

To produce new cells: 

a) For growth of tissues and organs

b) To repair damaged tissues and organs

Remember do not just say “growth and repair” you must say ‘of tissues and organs’ as well


Describe what happens to the chromosome number when a cell undergoes mitosis

It is maintained/kept constant

i.e. remains as 2n (diploid)


State the 3 main events during mitosis

DNA replication

Division of DNA

Splitting of the cell into 2


Explain what events occur inside a human somatic (body) cell BEFORE it takes part in mitosis

The cell increases in size

The sub-cellular structures (organelles) are replicated

The DNA is replicated (copied) so that there is double the quantity of DNA inside the cell


Describe the shape of a chromosome after it has replicated

It will appear as a cross

The 2 strands of DNA are held together by a centromere


Describe the relationship between the 2 arms of a chromosome after it has replicated

They are genetically identical

This means they carry the same genes and alleles


Describe the main events that take place during mitosis Hint: 6 key events

1. The chromosomes line up in the middle of the cell along the equator

2. Special protein fibres pull the chromosomes apart

3. Half of each chromosome is pulled to the opposite pole of the cell

4. Membranes form around the outside of each set of chromosomes (to form 2 nuclei inside the one cell)

5. The cell splits equally into 2


Describe how prokaryotic cells divide

Binary fission


Explain the key events that occur during binary fission Hint: 4 events

1. The circular DNA (nucleoid) and plasmids replicate

2. The cell increases in size and the circular DNA moves to the poles of the cell

3. The cytoplasm divides and new cell walls are formed

4. 2 daughter cells are formed each has a circular DNA but they can have variable numbers of plasmids


Describe the main features of cell division in bacteria

Occurs by binary fission

Occurs very quickly (~once every 20 minutes)


How can you calculate the number of bacteria present after a given period of time?

Calculate the number of minutes in the time period

Divide the number of minutes by 20 (to calculate the number of divisions the bacteria will undertake).

Call this answer ‘x’

Calculate 2 to the power ‘x’ i.e. 2x

This will be the number of cells present after the specified time period.


Define the term stem cell

An unspecialised cell that can replicate to produce more unspecialised cells

All these cells can then differentiate to become specialised cells


Explain the term differentiation

The process of an unspecialised cell changing its shape, chemical content and organelle content to become a specialised cell


What controls differentiation?

The switching on and off of certain genes inside the unspecialised cell


State 2 sources of stem cell

Early embryos

Umbilical cord (after birth)

Adult bone marrow


What is special about early embryo stem cells?

They can differentiate into ANY type of specialised cell


How are adult stem cells different from embryo stem cells?

Embryo stem cells can differentiate into any type of specialised cell but adult stem cells can only differentiate into certain types of specialised cells e.g. red blood cells


How can stem cells be used in medical research

Either type of stem cell can be grown in science laboratories to produce clones

These clones can then be stimulated to differentiate into specific specialised cells

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