Topic 3: Controlling development experiments

Question 1

Every cell in an embryo contains the same ________ ________ as they are all formed from the same fertilised egg by mitosis.

Answer 1

genetic material (DNA)

Question 2

How do embryonic cells differentiate into different cell types? (1 point)

Answer 2

1. By making different proteins.

Question 3

In the 1930s–1950sJoachim Hämmerling conducted experiments with Acetabularia to find out what controlled development.

What is Acetabularia? (2 points)

Answer 3

1. Acetabularia is a genus of green algae (usually found in subtropical waters)
2. It is a single cell, but is large in size (can be up to 10cm tall).

Question 4

Name parts of Acetabularia from top to bottom

4 parts

Answer 4

1. Hat
2. Stem tip
3. Stem
4. Rhizoid (containing nucleus and organelles)

Question 5

(Acetabularia experiment to find out what controlled development)

Hats are removed and the stems are swapped.

Plants develop intermediate hats with mixed features of both species (disc shaped but branched).

Explain what happened (4 steps)

Answer 5

1. A messenger molecule travels from the rhizoid to the stem tip and initiates hat development.
2. When the hats were cut off, some of the original messenger molecules was still in the stems and travels up to the stem tip.
3. A different messenger molecule was also made by the rhizoid and travels up to the stem tip.
4. Mixed messenger molecules lead to intermediate hats (disc shaped but branched too - mixture of both).

Question 6

(Acetabularia experiment to find out what controlled development)

Hats are removed and the stems are swapped.

Plants develop intermediate hats with mixed features of both species (disc shaped but branched).

Hats are cut off again.

New hats grow which match the rhizoid NOT the stem.

Explain what happened (2 steps)

Answer 6

1. When the intermediate hats are cut off there is no original messenger molecule left in the stems.
2. Therefore the next hats that grow are only determined by new messenger molecules from the rhizoid.

Question 7

Give a summary of what Hammerling’s experiment found out
(Acetabularia experiment to find out what controlled development)
(3 things)

Answer 7

1. The nucleus in the rhizoid (foot) produces a specific messenger molecule, which controls which hat is produced.
2. The stem is merely a channel that carries the specific messenger molecule from the nucleus to top of stem.
3. The messenger could be mRNA or a protein/enzyme made on the ribosomes in the cytoplasm.

Question 8

How does the nucleus control cell processes, like the development of the new hat?
(7 steps)

Answer 8

1. The nucleus contains DNA
2. DNA for a particular gene is transcribed to make mRNA
3. mRNA moves into cytoplasm
4. Translation on ribosomes
5. Makes proteins/enzymes
6. Proteins/enzymes are chemical messengers
7. Which travel to the stem tip to direct the synthesis of
   a new hat

Question 9

(mRNA from differentiated and undifferentiated cells experiment)
Give cells used in Dawid and Sargent’s experiments. (1 point)

Answer 9

1. In 1983, Dawid and Sargent used frog embryos.

Question 10

Give a summary of what Dawid and Sargent found out
(mRNA from differentiated and undifferentiated cells experiment)
(frog embryo cells experiment)
(3 points)

Answer 10

1. The undifferentiated and differentiated cells are expressing some of the SAME genes, but also some DIFFERENT genes.
2. double stranded hybrid (cDNA and mRNA bind) shows the genes which are expressed in both cells.
3. free cDNA (that has no mRNA from undifferentiated cell to bind to) shows genes only expressed in one cell (the differentiated cell).

NOTE: Undifferentiated cells are from early frog blastula. Differentiated cells are from later in the development but still embryonic.

Question 11

Give a summary of what we found out from creating Dolly the cloned sheep
(3 points)

Answer 11

1. All the genetic information for making a complete organism is present in the nucleus of every single cell in the organism,
2. even adult cells that have differentiated/become specialised.
3. So, no genetic information is deleted when a cell differentiates.