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

Question 1

What is present within the stroma of the chloroplast?

Answer 1

Within the stroma are many closed, flattened sacs called thylakoids.

Question 2

What is a granum?

Answer 2

A stack of thylakoids is a granum.

Question 3

What is a granum comprised of?

Answer 3

Each granum comprises between two and a hundred parallel sacs.

Question 4

What is found in the thylakoids?

Answer 4

The photosynthetic pigments, such as chlorophyll, are found in the thylakoids.

Question 5

What is the significance of the arrangement of thylakoids in the chloroplasts?

Answer 5

This arrangement produces a large surface area, efficient for trapping light energy.

Question 6

What does electron micrograph show about the thylakoid membrane?

Answer 6

Electron micrographs show that the thylakoid membrane is an infolding of the inner membrane of the
chloroplast envelope.

Question 7

Draw and label the basic structure of a chloroplast

Answer 7

Question 8

What does this figure show?

Answer 8

Question 9

Theory (Key Term)

Answer 9

The best explanation of a phenomenon, taking all the evidence into account.

A theory represents the highest status a scientific concept can have.

Question 10

What is endosymbiosis?

Answer 10

Endosymbiosis is a theory that describes the origin of chloroplasts and mitochondria.

Question 11

What did the division of chloroplasts closely resemble?

Answer 11

As far back as 1883, the division of chloroplasts was seen to closely resemble that of free- living cyanobacteria.

Question 12

What was mitochondria thought to be originally?

Answer 12

In the 1920s, the idea that mitochondria were once independent bacteria was also suggested.

Question 13

What are the commonalities between mitochondria and chloroplats

Answer 13

Mitochondria and chloroplasts have 70S ribosomes and circular DNA.

Question 14

What do scientists think happened 1.5 x 10e9 years ago?

Answer 14

It is suggested that at least 1.5 x 10e9 years ago, some ancient bacteria with very fluid membranes engulfed others and maintained a symbiotic relationship with them.

Question 15

What do we think evolved into mitochondria?

Answer 15

Some of those engulfed bacteria were very good at turning glucose and oxygen into ATP, evolving eventually into mitochondria.

Question 16

What do we think evolved into chloroplasts?

Answer 16

Some could turn carbon dioxide and water into glucose, evolving eventually into chloroplasts.

Question 17

What was published in 1967 about endosymbiosis?

Answer 17

In 1967, Lynn Margulis published a paper titled ‘On the origin of mitosing cells’ which substantiated the idea of endosymbiosis.

Question 18

What do biologists think the origin or chloroplasts and mitochondria are?

Answer 18

Now, biologists have plenty of evidence that both chloroplasts and mitochondria have their origins in free-living prokaryotes.

Question 19

What is the endoplasmic reticulum?

Answer 19

The endoplasmic reticulum (ER) is an elaborate system of parallel double membranes forming flattened sacs with interconnected, fluid-filled spaces between them, called cisternae.

Question 20

What is the ER connected to?

Answer 20

The ER is connected with the nuclear envelope.

Question 21

What does the ER system do?

Answer 21

This system allows the transport of materials through the cell.

Question 22

What are the types of ER?

Answer 22

There are two types of ER:

Rough ER (RER)
Smooth ER (SER)

Question 23

What is the structure and function of rough ER?

Answer 23

Rough ER (RER) has ribosomes on the outer surface and transports the proteins made there.

Question 24

Where is RER present in large amounts?

Answer 24

RER is present in large amounts in cells that make a lot of protein, such as cells making amylase in the salivary glands.

Question 25

What does smooth ER comprise of?

Answer 25

Smooth ER (SER) comprises membranes that lack ribosomes.

Question 26

What is the function of smooth ER?

Answer 26

It is associated with the synthesis and transport of lipids.

Question 27

Which cells have extensive ER?

Answer 27

Cells that store large quantities of carbohydrates, proteins and fats, including liver and secretory cells, have extensive ER.

Question 28

What does this figure show?

Answer 28