UNIT 1 - Cell Structure

Question 1

Preparations of cellular material suitable for
viewing with a light microscope

Answer 1

Specimen should be thin in order for light to pass through. Place tissue on glass slide, cover with a water based liquid, place cover slide on top.

Question 2

Magnification calculations

Answer 2

The magnification (M) of an object can be calculated if both the size of the image (I), and the actual size of the specimen (A), is known actual = image/magnification

Question 3

Light microscopes have two types of lenses:

Answer 3

An eyepiece lens, which often has a magnification of x10 -A series of (usually 3) objective lenses, each with a different magnification

Question 4

Which part of the light microscope collects light passing through the specimen and produces a magnified image?

Answer 4

Objective lens

Question 5

Which lens in a light microscope does not magnify the image?

Answer 5

Condenser lens - this is below the stage and focuses the light onto the specimen.

Question 6

What are the two forms of radiation used in microscopy?

Answer 6

Light and electrons

Question 7

What is the study, within Biology, of the preparation of specimens for examination using microscope?

Answer 7

Cytology

Question 8

Which unit of measurement is smaller, micrometers or nanometers?

Answer 8

Nanometers (nm)

Question 9

What is the maximum resolution of a light microscope?

Answer 9

200nm

Question 10

1um = nanometres

Question 11

1mm = micrometres

Question 12

1m = millimetres

Question 13

Cell surface membrane

Answer 13

Both eukaryotes and
prokaryotes.
It is partially
permeable.
Controls the exchange of materials
between the cell and its environment.
Formed from a phospholipid bilayer of phospholipids spanning a diameter of around 10 nm.

Question 14

Describe the plant cell wall

Answer 14

Formed outside of the cell membrane.
Structural support provided by the polysaccharide cellulose in plants, and peptidoglycan in most bacterial cells.
1um thick.
Fully permeable.
Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells’

Question 15

Describe the nucleus.

Answer 15

Largest organelle in eukaryotic cell (10-25um diameter). Separated from cytoplasm by a double membrane (the nuclear envelope) has many pores. (Nuclear pores).
The nucleus contains chromatin (the material from which chromosomes are made).
Usually, at least one or more darkly stained regions can be observed – these regions are individually termed ‘nucleolus’

Question 16

What is the purpose of nuclear pores?

Answer 16

Allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in.

Question 17

Describe the nucleolus.

Answer 17

Found within nucleus. Darker staining body. Contains DNA with copies of genes that code for rRNA. rRNA is synthesised here and early stages of ribosomal formation takes place. (1 - 3 um)

Question 18

Where are mitochondria found?

Answer 18

Cytoplasmic matrix (cytosol).

Question 19

Describe mitochondria

Answer 19

The site of aerobic respiration within eukaryotic cells.
Visible with a light microscope.
Surrounded by double-membrane with the inner membrane folded to form cristae.
The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP
Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)

Question 20

Describe the membranes of mitochondria.

Answer 20

Outer layer - smooth surface layer enclosing it.
Inner layer - Convoluted to form cristae which extend into matrix.
Separated by inter membrane space.

Question 21

Describe chloroplast

Answer 21

Larger than mitochondria, also surrounded by a double-membrane.
Membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana.
Grana are joined together by lamellae (thin and flat thylakoid membranes).
Chloroplasts are the site of photosynthesis:
The light-dependent stage takes place in the thylakoids
The light-independent stage (Calvin Cycle) takes place in the stroma
Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis

Question 22

Describe ribosomes

Answer 22

Up to 30nm (Very small) Made of protein + RNA in equal quantities. Site of protein synthesis.
80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells.
70S (composed of 50S and 30S subunits) ribosomes in prokaryotes, mitochondria and chloroplasts.

Question 23

Describe the endoplasmic reticulum.

Answer 23

Network of membranes found in cell cytoplasm, consisting of complex system of pairs of membranes arranged parallel to each other enclosing cisternae. Some membranes are covered in ribosomes (RER) Those that aren’t are called the SER.

Question 24

Describe the Smooth Endoplasmic Reticulum

Answer 24

Does not have ribosomes on the surface, its function is distinct to the RER.
Involved in the production, processing and storage of lipids, carbohydrates and steroids.

Question 25

What is the main function of the SER?

Answer 25

Synthesises, secretes + stores carbohydrates, lipids + other non-protein products.

Question 26

Describe the Rough Endoplasmic Reticulum

Answer 26

Surface covered in ribosomes.
Formed from continuous folds of membrane continuous with the nuclear envelope.
Processes proteins made by the ribosomes.