B2: Cell division

What is in the nucleus of cells?

Chromosomes

What molecule are chromosomes made up of?

DNA

How many of each chromosome do body cells contain?

2

• Paired

Are chromosomes in body cells single or paired?

Paired

What is special about the chromosomes in gametes?

Not paired

How many chromosomes do human gametes have?

23 single chromosomes

What do chromosomes carry?

Large no. of genes

What do genes do?

Determine many of our features

Cell cycle

Series of stages in which cells divide

How can cells divide?

• Mitosis

• Meiosis

How many stages of the cell cycle are there?

3

What happens in the cell cycle in terms of genetic material?

• GM doubled

• Then divided into 2 identical cells

Stage 1 of the cell cycle

• DNA replicates (to form 2 copies of each chromosome)

• Cell grows + increases no. of sub-cellular structures (mitochondria, ribosomes)

Stage 2 of the cell cycle

Mitosis

• 1 set of chromosomes pulled to each end of cell

• Nucleus divides

Stage 3 of the cell cycle

Cytoplasm + cell membrane divide to form 2 identical cells

What does mitosis do?

Copy 1 cell into 2

What happens during mitosis?

• 1 set of chromosomes pulled to each end of cell

• Nucleus divides

Are the cells produced by mitosis gentically identical?

Yes

What is cell division by mitosis important for?

Growth + development of multicellular organisms

When does mitosis occur?

• When an organism repairs itself

• Asexual reproduction

What happens to cells as an organism develops?

Cells differentiate to form different types of cells

When do most types of animal cells differentiate?

Early stage

What is special about a plant cells ability to differentiate?

Most retain the ability to differentiate throughout life

In mature animals, what is cell division restricted to?

• Repair

• Replacement

A cell differentiates to become?

A specialised cell

What happens as a cell differentiates to become a specialised cell?

Acquires diff sub-cellular structures to enable it to carry out a certain function

Fertilisation

Sperm cell joins with egg cell (ovum)

How do humans start?

1. Fertilisation- sperm cell joins with egg cell = fertilised ovum

2. Fertilised ovum undergoes mitosis = embryo

3. Overtime, these cell continue to undergo mitosis + change to form specialised cells

Embryo

Ball of cells

Differentiation

Process of cells becoming specialised

Stem cell

An undifferentiated cell of an organism which can give rise to more cells of the same type + can differentiate to form other types of cells

Where are embryonic stem cells found?

Early stage embryo

• Cells are undifferentiated

What does it mean if a cell is undifferentiated?

Any cell is capable of differentiating into any type of body cell

• Embryonic

Where are adult stem cells found?

Bone marrow

Adult vs embryonic stem cells

ASC can’t differentiate into any other cell type

What types of body cells can stem cells in adult bone marrow differentiate to form?

Cells found in blood

• RBC

• WBC

• Platelets

What are stem cells used for in medicine?

1. Bone marrow transplant

2. Therapeutic cloning

What parts of a plant contain meristem tissue?

• Roots

• Buds

What is special about the stem cells in meristem tissue in plants?

Can differentiate into any type of plant cell, throughout the life of the plant

What can stem cells from meristems in plants be used to produce?

Clones of plants quickly + economically

What types of plants would farmers want to clone?

1. Rare plants- prevent from going extinct

2. Crop plants w special features (disease resistance)

Cloning plants

Producing a large no. of identical plants for farmers by asexual reproduction

Leukaemia

Cancer of bone marrow

Steps of how is leukaemia treated?

Bone marrow transplants

1. Patient’s existing BM destroyed using radiation

2. Patient receives BM transplant from donor

3. Stem cells in BM divide + form new BM

4. + they differentiate + form blood cells

Issues with bone marrow transplants

1. Donor must be compatible with patient

• Otherwise WBC produced by donated BM could attack the patient’s body

2. Risk that viruses can be passed from donor to patient

Why must the donor be compatible with the patient in a bone marrow transplant?

If not, WBC produced by donated BM could attack the patient’s body

What is produced in therapeutic cloning?

Embryo with same genes as patient

Why is it a pro that therapeutic cloning produced an embryo with the same genes as the patient?

Stem cells from the embryo can be transplanted into the patient w/o being rejected by the patient’s immune system

Embryos produced by therapeutic cloning have the same genes as the patients so…

SC fm the embryo produced aren’t rejected + can be used for medical treatment

What happens after an embryo with same genes as patient is produced in therapeutic cloning?

Once inside the patient, SC differentiate to replace cells that have stopped working correctly

What medical conditions could therapeutic cloning be used to treat?

1. Diabetes

2. Paralysis

Cons of the use of stem cells

1. Potential risks- eg transfer of viral infection

2. People have ethical / religious objections to the procedure

Cloning

Producing identical offspring

How do bacteria divide?

Binary fission (simple cell division)

What conditions do bacteria need to divide quickly

• Enough nutrients

• Suitable temp

How often can bacteria divide if they have enough nutrients + a suitable temp?

Once every 20 minutes

What can bacteria be grown in?

1. A nutrient broth solution

2. As colonies on an agar gel plate

What is needed for investigating the action of disinfectants + antibiotics?

Uncontaminated cultures of microorganisms

What type of microorganism is bacteria and what does this mean?

Prokaryotes

• Genetic info not enclosed in nucleus

What happens in binary fission?

1 bacterial cell splits into 2 bacterial cells

Equation to calculate the no. of bacteria after a given time

2ⁿ

Why do scientists need to grow lots of microorganisms in a lab to study them?

MO are v small

What does a nutrient broth solution contain?

All nutrients bacteria need to grow + divide

Why is the nutrient broth cloudy?

Contains large no. of bacteria

What do agar gel plates contain?

• Nutrient broth set into a jelly using agar

• Poured into petri dish + set

How do bacteria grow in agar gel plates?

In divisible colonies

How to avoid contamination when making nutrient broth solution? Aseptic techniques

1. Sterilise all Petri dishes, bacterial nutrient broth, agar, inoculating loop → kills unwanted MO + prevents contamination

2. Transfer bacteria onto dish + attach lid of Petri dish using adhesive tape → stops lid falling of + unwanted MO from entering

3. Place agar plate upside down into an incubator → stops moisture from dripping down onto bacteria + disrupting colonies

4. In school labs, cultures should be incubated at 25°C

Why we have to avoid contamination when making nutrient broth solution?

Lots of MO (bacteria, fungi) naturally in environment → could contaminate our culture

Inoculating loop

Used to transfer bacteria into the culture

How do you sterilise an inoculating loop?

Pass it thru a Bunsen burner flame

In school labs, what temp should bacteria cultures should be incubated at?

25°C

In school labs, why are bacteria cultures incubated at 25°C?

Reduces chances that harmful bacteria will grow

Zone of inhibition

Region around antibiotic discs where bacteria haven’t growth