Lecture 3

Question 1

What were the earliest life forms on Earth?

Answer 1

Single-celled organisms.

Question 2

What groups include early single-celled life?

Answer 2

Bacteria, Archaea, and single-celled eukaryotes.

Question 3

Why are single-celled organisms important for understanding multicellularity?

Answer 3

They provide insight into how multicellularity evolved.

Question 4

What is Valonia ventricosa?

Answer 4

A species of single-celled alga with a diameter of 1–4 cm.

Question 5

What basic cellular components do single-celled organisms contain?

Answer 5

DNA/RNA for genetic information, a cell membrane, and cytoplasm for metabolic activity.

Question 6

What types of metabolism can single-celled organisms exhibit?

Answer 6

Photosynthesis (e.g. cyanobacteria) and chemosynthesis (some archaea).

Question 7

Can single-celled organisms exist at different sizes?

Answer 7

Yes, they can grow at all sizes.

Question 8

What evolutionary step preceded true multicellularity?

Answer 8

The evolution of multicellular colonies.

Question 9

Give an example of colonial organisms.

Answer 9

Cyanobacteria forming long chains of individual cells.

Question 10

How many times has multicellularity evolved in eukaryotes?

Answer 10

Multiple times independently.

Question 11

Which groups evolved multicellularity independently?

Answer 11

Animals, plants, multicellular fungi, and cellular slime moulds.

Question 12

What does repeated evolution of multicellularity suggest?

Answer 12

There are strong evolutionary drivers favouring multicellularity.

Question 13

From which ancestor did multicellular eukaryotes evolve?

Answer 13

The Last Eukaryotic Common Ancestor (LECA).

Question 14

When did the last common ancestor of modern eukaryotes live?

Answer 14

During the Mesoproterozoic era, approximately 1.6–1 billion years ago.

Question 15

How does the timing of LECA relate to multicellular algae?

Answer 15

It is roughly the same age as the oldest multicellular algae.

Question 16

What is a key protective advantage of multicellularity?

Answer 16

Larger size reduces vulnerability to predation.

Question 17

How does multicellularity buffer organisms from the environment?

Answer 17

Larger organisms are more stable against external environmental changes.

Question 18

What biological capability does multicellularity enable?

Answer 18

The development of specialised cell types.

Question 19

How many cell types do humans have?

Answer 19

Over 200 distinct cell types.

Question 20

What question arises from cell specialisation?

Answer 20

What caused specialised cells to evolve?

Question 21

What does the Flagellar Synthesis Constraint Hypothesis propose?

Answer 21

A trade-off between cell movement and cell division due to shared machinery.

Question 22

what is the method for flagellar synthesis constraint hypothesis

Answer 22

The microtubule organising machinery needed for formation of
flagella is also required for the formation of spindle apparatus
used in cell division.

• There is competition for the use of this machinery for the
  process of cell movement and cell division.
• Presence of both specialised flagellated and non-flagellated cells
  in a simple colony allows the organism to move and grow at the
  same time

Question 23

Why are flagella important in simple multicellular organisms?

Answer 23

They allow the organism to move.

Question 24

What cellular machinery is shared between flagella and cell division?

Answer 24

Microtubule organising machinery.

Question 25

Why does this shared machinery create a constraint?

Answer 25

It cannot be efficiently used for movement and division simultaneously.

Question 26

How does cell specialisation solve this constraint?

Answer 26

Having both flagellated and non-flagellated cells allows movement and growth at the same time.

Question 27

What is mosaic development?

Answer 27

A theory proposing unequal inheritance of genetic determinants during cell division.

Question 28

Who proposed the idea of nuclear “determinants”?

Answer 28

August Weismann.

Question 29

What experimental work challenged mosaic development?

Answer 29

Sea urchin experiments by Hans Driesch.

Question 30

What did Driesch conclude about development?

Answer 30

All cells contain the full information needed for normal development.

Question 31

Why is Dolly the sheep significant?

Answer 31

She demonstrated that differentiated adult cells retain full genetic information.

Question 32

How was Dolly created?

Answer 32

By nuclear transfer from a mammal cell nucleus into an oocyte.

Question 33

What concept did Dolly challenge?

Answer 33

The irreversibility of cell differentiation.

Question 34

What does Dolly show that gene specialisation depends on?

Answer 34

It depends on gene expression, not gene content.

Question 35

Who demonstrated the importance of cell signalling in development?

Answer 35

Hans Spemann and Hilde Mangold.

Question 36

What was the key result of the Spemann–Mangold experiment?

Answer 36

Transplanted tissue caused the formation of a secondary embryo.

Question 37

What can cell fate be influenced by?

Answer 37

interactions with neighbouring cells.

Question 38

Why is balance of cell types important in multicellular organisms?

Answer 38

Too many of the wrong cell types prevents proper function.

Question 39

Why must cell lineage depend on gene regulation?

Answer 39

All cells have the same genetic material.

Question 40

What key process controls which genes are active during development?

Answer 40

Cell-to-cell signalling.

Question 41

Why is signalling essential for homeostasis?

Answer 41

It allows regulation of the internal environment despite external changes.

Question 42

What developmental processes require signalling?

Answer 42

Cell cycle regulation, movement, differentiation, and patterning.

Question 43

Why must cells recognise self vs non-self?

Answer 43

To organise into a coherent multicellular structure.

Question 44

Why is cell adhesion important?

Answer 44

It allows cells to form tissues, structures, and extracellular matrices.

Question 45

What organisms are closely related to animals based on genome analysis?

Answer 45

Choanoflagellates.

Question 46

Why are choanoflagellates important for understanding multicellularity?

Answer 46

They possess genes for signalling pathways found in animals.

Question 47

What signallinh predates multicellularity?

Answer 47

Intercellular signalling predates multicellularity.

Question 48

What are examples of cellular responses to signalling?

Answer 48

Cell movement, contraction, gene expression changes, metabolic changes, ion concentration changes, and protein activity changes.

Question 49

What does gene expression cause that is especially important in development?

Answer 49

Changes in gene expression leading to cell specialisation.

Question 50

What is gene expression

Answer 50

The process by which a gene’s coded information is converted into cellular structures or functions.

Question 51

Does gene expression always produce proteins?

Answer 51

No, it can also produce functional RNAs such as tRNA, rRNA, and regulatory RNAs.

Question 52

Why is the central dogma important for development?

Answer 52

It shows multiple points where gene expression can be regulated.

Question 53

What experimental techniques are linked to this content?

Answer 53

End-point PCR, RT-qPCR, and Western blotting.

Question 54

At what levels can gene expression be regulated?

Answer 54

Transcription, RNA processing (e.g. splicing), nuclear export, and post-translational modification.