2.1.6 Cell division, diversity and differentiation

What is the cell cycle?

The highly ordered sequence of events in a cell that results in the production of daughter cells

What are the stages of the cell cycle?

interphase, mitosis, cytokinesis

What is the problem with uncontrolled cell division?

It would cause a tumor to grow

Briefly explain how the cell cycle is different in prokaryotes?

They divide by binary fission, not mitosis

What is interphase, and what are the three key phases within it?

It is the phase in which the cell is not dividing. It is broken down into 3 key phrases: G1 phase, S phase and G2 phase

What happens during the G1 phase of interphase?

The cell grows to its normal size, synthesises proteins and duplicates organelles

What happens at the G1 checkpoint?

The cell checks if it has grown correctly, got undamaged DNA and has sufficient growth factors. If it does, then it proceeds to S phase. If it doesn't then the cell enters G0 phase either temporarily or permanently

What is the G0 phase?

Phase where the cell leaves the cycle, either temporarily or permanently.

What could cause a cell to be in G0 phase?

Differentiation - most neurons remain in G0 permanently.

DNA damage - may undergo apoptosis or become sensecent (inactive)

What happens during S phase of interphase?

DNA replication of each chromosome to form two identical chromatids. The chromosomes unwind so that proteins can access the DNA

What is a chromatid?

a half of a chromosome that has been replicated for division

What happens during G2 phase of interphase?

Replicated DNA is checked for errors, and ATP is produced. It prepares for division

What happens at the G2/M checkpoint?

The cell checks if it has grown sufficiently, that the DNA has been duplicated and that the DNA is undamaged. If it passes these checks, it moves into mitosis. If not, it attempts to repair and correct DNA

What are the 3 key benefits/uses of cell division?

Growth, asexual reproduction and repair

What are the benefits of using mitosis for asexual reproduction?

It allows rapid population growth

How do multicellular organisms use asexual reproduction, and give an example?

New individuals can grown from the parent organism by cell division, and then bud off in different ways. Eg strawberries use runners

Where does growth occur in plants?

meristems

How does mitosis help with tissue repair?

Damaged tissues can be replaced by genetically identical cells. It humans, it often happens particularly quickly in the skin or the gut

What are the stages of mitosis?

prophase, metaphase, anaphase, telophase

What happens during prophase (3 points)?

1. DNA condenses, causing chromosomes to become shorter and thicker. They are now visible when stained.

2. Nuclear envelope disintegrates

3. Centrosomes move to opposite ends of the cell

What is mitosis?

Cell division resulting in the production of two genetically identical daughter cells

What is a centrosome?

An organelle which serves as the main microtubule organising centre for animal cells. It is responsible for forming the spindle fibres

What happens during metaphase (3 points)?

1. Centrosomes at the poles of the cell begin to produce spindle fibres

2. Chromosomes align randomly along the equator of the cell

3. Chromosomes attach to the spindle by their centromere

What happens during anaphase (2 points)?

1. Centromeres detach and chromatids separate

2. Spindle fibres contract and pull chromatids towards the opposite poles

What is a centromere?

The center of a chromosome that holds the two chromatids together

What happens during telophase (3 points)?

1. Chromatids have now separated and are called chromosomes again

2. A new nuclear envelope forms around each set of chromosomes

3. The cell now contains two nuclei, each genetically identical to each other and to the parent cell from which they arose

How does cytokinesis work in animal cells?

The plasma membrane folds inwards and 'nips in' the cytoplasm forming a cleavage furrow

How does cytokinesis work in plant cells?

An end plate forms where the equator of the spindle was. The new plasma membrane and cellulose cell wall are laid down on either side of this end plate

Why can't we use mitosis to produce gametes?

It would have too many chromosomes

What are the benefits of sexual reproduction?

It produces genetic diversity which helps the species survive in the long term

What does diploid mean?

two sets of chromosomes - 46 chromosomes in total

What does haploid mean?

one set of chromosomes - 23 chromosomes in total

What are the stages of meiosis (including 1 & 2)

Prophase 1, metaphase 1, anaphase 1, telophase 1, cytokinesis, prophase 2, metaphase 2, anaphase 2, telophase 2, and then cytokinesis

What does meisosis produce?

4 haploid gemetes

What happens during prophase 1 of meiosis (3 points)?

1. Chromosomes condense and nuclear envelope disintegrates

2. Chromosomes come together in the homologous pairs

3. Crossing over occurs

What are homologous pairs in meiosis?

Two chromosomes, each consisting of two identical sister chromatids, that pair up in meiosis and have the same genes at the same position

Explain crossing over/recombination works?

Non-sister chromosomes wrap around each other and exchange alleles, helping to generate genetic variation

What happens during metaphase 1 of meiosis (2 points)?

1. The homologous pairs attach along the equator of the spindle via their centromeres

2. The homologous pairs are arranged randomly ie which pole each copy faces is random

What happens during anaphase 1 of meiosis (2 points)?

1. The two chromosomes within each pair are pulled apart randomly by motor proteins on the tubulin threads

2. Independent assortment occurs

What is independent assortment?

Which chromosome will be pulled to which pole is randomly determined within each pair, helping to generate genetic variation

What happens during telophase 1 of meiosis (1 point)?

Two new nuclear envelopes form around around each set of chromosomes, and then cytokinesis occurs

What happens during prophase 2 of meiosis (3 points)?

1. Nuclear envelope breaks down again

2. Chromosomes coil and condense

3. Tubulin spindle forms

What happens during metaphase 2 of meiosis (2 points)?

1. Chromosomes attach by their centromeres to the equator of the spindle

2. The chromatids of each chromosome are randomly arranged with respect to which pole they face

What happens during anaphase 2 of meiosis (2 points)?

1. Centromeres divide

2. Independent assortment of chromatids

What happens during telophase 2 of meiosis (2 points)

1. Nuclear envelope reforms around each of the 4 haploid nuclei

2. In animal cells, the two cells divide to give four haploid cells

What are the 4 ways in which meiosis produces genetic variation, and in which stage do they occur?

1. Crossing over during prophase 1

2. Independent assortment of chromosomes in anaphase 1

3. Independent assortment o chromatids in anaphase 2

4. Random fusion of the gametes during sexual reproduction

What are our 8 key specialised cells?

Erythrocytes, neutrophils, squamous epithelial cells, ciliated epithelial cells, sperm cells, palisade cells, root hair cells and guard cells

What is the function of erythrocytes and give two ways are they specialised for this?

Oxygen transportation around the body and carbon dioxide transportation to the lungs in vertebrates.

They are biconcave in shape which increases their surface area for oxygen absorption, and they don't have a nucleus so there is more space for haemoglobin molecules

What is the function of neutrophils and give two ways they are specialised for this?

They migrate to the infection area by chemotaxis and ingest pathogens by phagocytosis.

They have a flexible shape which allows the neutrophil to squeeze out of the capillary walls, and there is a large number of lysosomes present in the cell which enable the destruction of the pathogen

What is the function of squamous epithelial cells and give one way they are specialised for this?

They provide a surface covering or outer layer to a variety of organs.

They are thin due to a squashed shape which enables a short diffusion distance.

What is the function of ciliated epithelial cells and give two ways they are specialised for this?

They move substances across the surface of a tissue

The cilia on the surface waft material along the surface, and the goblet cells secrete mucus which help trap dust and dirt

What is the function of sperm cells and give two ways they are specialised for this?

They locate an ovum via chemotaxis and then fertilise the ovum.

They have a high concentration of mitochondria which provide ATP for the movement of the tail, and their head is covered by the acrosome which contains digestive enzymes

What is the function of palisade cells and give two ways they are specialised for this?

They carry out photosynthesis to produce glucose and oxygen

They have a large number of chloroplasts to maximise the absorption of light, and the tall thin cells are densely packed together

What is the function of guard cells and give one way they are specialised for this?

They control the opening of the stomata to regulate water loss and gas exchange.

The difference in thickness of the cell walls allows the cell to bend when turgid

What is the function of root hair cells and give two ways they are specialised for this?

They absorb water and mineral ions from the soil.

Root hair increases rate of water uptake via osmosis, and large number of mitochondria allow for the active transport of mineral ions

What is a tissue?

A group of cells that work together to perform a particular function

What is an organ?

A group of different tissues that work together to perform a certain function.

What are the 4 main types of tissue?

Epithelial tissue, connective tissue, muscular tissue, nervous tissue

What is epithelial tissue, give an example of where would you find it and how is it adapted (1 way)?

Tightly packed cells that form a continuous sheet. It can be found in the stomach. It is adapted by having a very short cell cycle due to the abrasive surface of its location

What is cartilage and give an example of where would you find it?

A tough but flexible connective tissue. It is found in the trachea in rings and helps to support it and keep it open.

What is muscle tissue, give an example of where would you find it and how is it adapted (2 ways)?

Muscle cells contain layers of fibres which allow them to connect. It is found in the bladder. They have a high density of mitochondria to provide sufficient energy for contraction, and layers of protein filaments slide over each other to allow contraction

What is phloem tissue, give an example of where would you find it and how is it adapted (1 way)?

It is used to transport dissolved sugars and amino acids. They are found in plant cells. They are joined end to end with sieve plates to allow things to flow through easily

What is a xylem tissue, give an example of where would you find it and how is it adapted (1 way)?

It transports tissue for water and dissolved mineral ions. They are found in plant cells. They are thickened with lignin which strengthens the tubes.

When does cell specialisation begin?

During embryonic development

Would a cardiac cell have the same genes in it as a neuron? Explain

Yes. Different genes will be expressed in different cells, but they all have the same genes

What is a stem cell?

a cell that can differentiate and become any type of human cell. it is a renewing source of undifferentiated cells

What does potency mean?

The ability of stem cells to differentiate into more specialised types

What are the three types of potency?

totipotent, pluripotent, multipotent

What are multipotent stem cells?

Stem cells that can divide an unlimited number of times, but can only produce a limited range of cells

What type of stem cells are found in bone marrow, and what can they differentiate into?

They are multipotent adult cells, and can only differentiate into blood cells (erythrocytes and neutrophils)

How are xylem and phloem tissues created?

Stem cells found in the meristem between the xylem and phloem can differentiate into the tissues

What is the name for the tissue found in between the xylem and phloem (the meristem tissue)

Cambium

What stimulates whether xylem or phloem will be created from differentiation?

The balance of hormones

How can stem cells be used in developmental biology?

They can study how stem cells develop to make particular cell types, and then see how the cell functions and what goes wrong when they are diseased