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

Question 1

Name the genetic material found in all living cells

Answer 1

DNA

Question 2

State where the genetic material is located in eukaryotic cells

Answer 2

Contained inside the nucleus

Question 3

State where the genetic material is located in prokaryotic cells

Answer 3

Free in the cytoplasm

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

Question 4

Describe how DNA is arranged in eukaryotic cells

Answer 4

As a linear chromosomes

Question 5

Explain the term chromosome

Answer 5

A coiled length of DNA

Question 6

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

Answer 6

46

Question 7

State how many chromosomes are found in human gametes

Answer 7

23

Question 8

Explain the term diploid

Answer 8

A full set of chromosomes

This is represented as ‘2n’

Question 9

Explain the term haploid

Answer 9

Half a set of chromosomes

This is represented as ‘n’

Question 10

Explain the term ‘cell cycle’

Answer 10

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

Question 11

How do human somatic cells divide?

Answer 11

Mitosis

Question 12

What is the function of mitosis?

Answer 12

To produce two GENETICALLY identical daughter cells

Question 13

Why do multicellular organisms use mitosis?

Answer 13

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*

Question 14

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

Answer 14

It is maintained/kept constant

i.e. remains as 2n (diploid)

Question 15

State the 3 main events during mitosis

Answer 15

DNA replication

Division of DNA

Splitting of the cell into 2

Question 16

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

Answer 16

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

Question 17

Describe the shape of a chromosome after it has replicated

Answer 17

It will appear as a cross

The 2 strands of DNA are held together by a centromere

Question 18

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

Answer 18

They are genetically identical

This means they carry the same genes and alleles

Question 19

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

Answer 19

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

Question 20

Describe how prokaryotic cells divide

Answer 20

Binary fission

Question 21

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

Answer 21

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

Question 22

Describe the main features of cell division in bacteria

Answer 22

Occurs by binary fission

Occurs very quickly (~once every 20 minutes)

Question 23

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

Answer 23

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. 2^x

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

Question 24

Define the term stem cell

Answer 24

An unspecialised cell that can replicate to produce more unspecialised cells

All these cells can then differentiate to become specialised cells

Question 25

Explain the term differentiation

Answer 25

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

Question 26

What controls differentiation?

Answer 26

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

Question 27

State 2 sources of stem cell

Answer 27

Early embryos

Umbilical cord (after birth)

Adult bone marrow

Question 28

What is special about early embryo stem cells?

Answer 28

They can differentiate into ANY type of specialised cell

Question 29

How are adult stem cells different from embryo stem cells?

Answer 29

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

Question 30

How can stem cells be used in medical research

Answer 30

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

Question 31

Explain what is meant by the term ‘specialised cell’

Answer 31

A cell that has changed its shape, chemical content and/or the organelle content of itself to become suited for a specific function

Question 32

Describe what changes occur in stem cell when it differentiates into a red blood cell

Answer 32

Change in shape = it changes from spherical to biconcave

Change in chemical content = it produces a lot of haemoglobin

Change in organelle content = it breaks down its mitochondria and nucleus

Question 33

State 3 examples of how stem cells can be use to cure disease

Answer 33

1. Adult stem cells taken from the bone marrow of a healthy person can be used to replace faulty blood cells in a patient
2. Embryonic stem cells can be used to replace faulty cells e.g. insulin producing cells can be used to treat people with diabetes nerve cells can be used to treat people with spinal cord injuries (paralysis)
3. Stem cells can be used for therapeutic cloning – they are taken from the patient stimulated to differentiate into the required specialised cells and then returned to the same patient.

Question 34

What is the advantage of using a patient’s own stem cells in therapeutic cloning?

Answer 34

The specialised cells formed from the patient’s stem cells are genetically identical to the patient’s cells and are therefore not rejected

Question 35

What are carried on each chromosome?

Answer 35

Each chromosome carries a large number of genes.

Question 36

What is a gene?

Answer 36

A section of DNA that codes for the production of one specific protein

Question 37

Describe how chromosomes are normally found in somatic (body) cells

Answer 37

In body cells the chromosomes are normally found in pairs.

Question 38

Where are stem cells found in plants?

Answer 38

In the meristematic tissue i.e. root tips and shoot tips

Question 39

What is special about meristematic tissue in plants?

Answer 39

Meristem tissue in plants can differentiate into ANY type of plant cell, THROUGHOUT the life of the plant.

Question 40

State two concerns people have with stem cell treatments

Answer 40

The use of stem cells has potential risks such as transfer of viral infection

Some people have ethical or religious objections.

Question 41

State an advantage for horticulturists who using plant stem cells

Answer 41

Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.

Question 42

State 2 benefits of the use of plant stem cells in research and treatments

Answer 42

Rare species can be cloned to protect from extinction.

Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.