37 WJEC Biology AS Level - Marianne Izen - 2nd Edition

Question 1

Compare the size of ribosomes in prokaryotic vs eukaryotic cells.

Answer 1

Ribosomes are smaller in prokaryotic than eukaryotic cells.

Question 2

State the size of ribosomes in prokaryotic and eukaryotic cells.

Answer 2

In prokaryotic cells they are 70S in size, whereas those in the cytoplasm of eukaryotic cells are 80S.

Question 3

Where are ribosomes found in eukaryotic cells?

Answer 3

They are found in the cytoplasm, where they occur singly or attached to membranes on the RER.

Question 4

What is the structure of the ribosome?

Answer 4

Ribosomes have one large and one small subunit.

Question 5

How are ribosomes made?

Answer 5

They are assembled in the nucleolus from ribosomal RNA (rRNA) and protein.

Question 6

What are ribosomes important for?

Answer 6

They are important in protein synthesis because they are the site of translation.

In the ribosomes, mRNA and tRNA are used to assemble the polypeptide chain.

Question 7

Compare the size of ribosomes to the nucleus and mitochondria.

Answer 7

Ribosomes are much smaller than the nucleus and mitochondria.

Question 8

How do ribosomes appear in electron micrographs

Answer 8

They often appear as black dots in electron micrographs.

Question 9

Draw a diagram of ribosome and name its parts.

Answer 9

Question 10

How do scientists measure the size of the ribosomes?

Answer 10

To measure the size of ribosomes, scientists see how fast they sink through a solution spun very fast in an ultracentrifuge.

Larger and denser structures sink faster.

Question 11

What is the unit of measurement for sedimentation rate?

Answer 11

Sedimentation rate is measured in S units.

S stands for Svedberg, the Swedish scientist who invented the ultracentrifuge.

Question 12

What is the structure of the Golgi body?

Answer 12

It is made up of a stack of membranes.
It resembles the structure of ER
It is more compact than the ER

Question 13

What happens in the Golgi body?

Answer 13

Vesicles containing polypeptides pinch off from the RER and fuse with the Golgi body.

Proteins are modified and packaged in the Golgi body.

At the other end of the Golgi body, vesicles containing the modified proteins are pinched off.

Question 14

What happens to the vesicles that are pinched off from the Golgi body?

Answer 14

These may carry proteins elsewhere in the cell.

They may move to and fuse with the cell membrane, secreting the modified proteins by exocytosis.

Question 15

What are the functions of the Golgi body?

Answer 15

The functions of the Golgi body include:

1. Producing secretory enzymes, packaged into secretory vesicles.
2. Secreting carbohydrates, e.g. for the formation of plant cell walls.
3. Producing glycoprotein.
4. Transporting and storing lipids.
5. Forming lysosomes, containing digestive enzymes.

Question 16

What are lysosomes? How are they formed?

Answer 16

Lysosomes are small, temporary vacuoles surrounded by a single membrane.

They are formed by being pinched off from the Golgi body.

Question 17

What do lysosomes do?

Answer 17

1. They contain and isolate potentially harmful digestive enzymes from the remainder of the cell.
2. They release these enzymes when the cell needs to recycle worn out organelles.
3. The enzymes in lysosomes can also digest material that has been taken into the cell, e.g. lysosomes fuse with the vesicle made when a white blood cell engulfs bacteria by phagocytosis and their enzymes digest the bacteria.

Question 18

Are lysosomes and lysozymes the same?

Answer 18

Do not confuse lysosomes with lysozyme.

Question 19

What is apoptosis?

Answer 19

Some cells are programmed to die in a process called apoptosis

Question 20

Name a place in the embryo where apoptosis occurs.

Answer 20

Spaces between the fingers and toes in the embryo.

Question 21

Which organelle has an essential role in apoptosis.

Answer 21

Lysosomes and their enzymes have an essential role in this.

Question 22

What is this picture?

Answer 22

Question 23

Draw a diagram of the Golgi body and name its parts

Answer 23