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

Question 1

Prokaryote (Key Term)

Answer 1

A single-celled organism lacking membrane-bound organelles, such as a nucleus, with its DNA free in the cytoplasm.

Question 2

Eukaryote (Key Term)

Answer 2

An organism containing cells that have membrane- bound organelles, with DNA in chromosomes within the nucleus.

Question 3

What may resemble the first living cells?

Answer 3

The cells of prokaryotes may resemble the first living cells.

Question 4

Describe the evolution of prokaryotes.

Answer 4

The oldest fossil prokaryotes are from rocks formed 3.5 billion years ago.

Hence they must have evolved before then, within the first billion years of Earth’s history.

Question 5

Describe the evolution of eukaryotes.

Answer 5

The cells of eukaryotes probably evolved from prokaryotic cells.

The oldest fossilised examples are from rocks about 2.1 billion years old.

Question 6

Which groups of living organisms all have eukaryotic cells?

Answer 6

Fungi, Protoctista, plants and animals all have eukaryotic cells.

Question 7

Are viruses made of cells?
Are they classified with living organisms?

Answer 7

Viruses are not made of cells and are not classified with living organisms.

Question 8

At what interface do viruses exist?

Answer 8

They seem to exist at the interface between living and non-living systems.

Question 9

Give examples of prokaryotic cells.

Answer 9

Examples of prokaryotic cells are bacteria and Archaea.

Question 10

What is the major distinguishing feature of prokaryotic cells?

Answer 10

The major distinguishing feature of prokaryotic cells is that:

1. They have no nucleus
2. They have no internal membranes,
3. They have no membrane-bound organelles which eukaryotic cells have.

Question 11

Describe the mesosome.

Answer 11

In some prokaryotes,, there is an infolding of the cell membrane in a mesosome or photosynthetic lamellae.

This increases the membrane’s surface area.

Question 12

Describe the cellular nature of prokaryotes.

Answer 12

1. Prokaryotes rarely form multicellular structures.
2. They are often described as ‘unicellular’.
3. Their cells are not subdivided, so they are sometimes described as ‘acellular’.

Question 13

Draw a table summarising the appearances of prokaryotes.

Answer 13

Question 14

Can viruses be seen under the light microscope?

Answer 14

No, viruses are so small that they cannot be seen in the light microscope.

Question 15

Can viruses pass through filters that trap bacteria?

Answer 15

They pass through filters that can trap bacteria

Question 16

When could viruses be finally seen?

Answer 16

They could not be seen until the electron microscope was invented, although experiments in the late nineteenth century suggested their existence.

Question 17

Draw a labelled diagram of a generalised bacterial cell.

Answer 17

Question 18

In a table, summarise the differences between eukaryotic and prokaryotic cells.

Answer 18