2 Cells: 3 Cell Structure

Question 1

What is the structure of the nucleus? What are the functions of the nucleus and its components?

Answer 1

Contains chromosomes (which are made from protein-bound, linear DNA), nucleoli, a nuclear envelope, nuclear pores, and nucleoplasm.

Control’s the cell’s activities.
DNA contains instructions to make proteins.
Pores allow substances move between.
Nucleolus makes ribosomes.

Question 2

What is the structure of mitochondria? What are the functions of mitochondria and its components?

Answer 2

Consists of a double membrane, cristae and a matrix.

Site of aerobic respiration where ATP is produced.
Matrix contains enzymes involved in respiration.

Question 3

What is the structure of cristae?

Answer 3

Extensions of the inner membrane of the mitochondria.

Question 4

What is the structure and function of chloroplasts?

Answer 4

Consists of a double membrane and thylakoid membranes which are stacked up to form grana, and stroma.

Site of photosynthesis.
Grana contains thylakoids which contain chlorophyll that absorb light for photosynthesis.

Question 5

What is the structure of the Golgi apparatus? What are the functions of the Golgi apparatus and its components?

Answer 5

Consists of cisternae and vesicles.

Processes and packages new lipids and proteins.
Makes lysosomes.
Vesicles store lipids and proteins made by the Golgi apparatus and transports them out of the cell.

Question 6

What is the process of the Golgi apparatus?

Answer 6

1. Proteins and lipids produced by the ER are passed through the Golgi apparatus in strict sequence.
2. The Golgi apparatus modifies these proteins, often adding non-protein components, such as carbohydrates, to them.
3. Labels them, allowing them to be accurately sorted and sent to their correct destinations.
4. Once sorted, the modified proteins and lipids are transported in Golgi vesicles which are regularly pinched off from the ends of the Golgi cisternae.
5. These vesicles may move to the cell surface, where they fuse with the membrane and release their contents to the outside.

Question 7

What is the structure and function of lysosomes?

Answer 7

A membrane-bound organelle that it a type of Golgi vesicle which contains lysozymes.
Can be used to digest invading cells or to break down worn out cell components.

Question 8

What is the structure and function of ribosomes? What are the types of ribosome and where are they found?

Answer 8

Small organelle made up of proteins and RNA.
They have two types, depending on the cells in which they are found - 80S (eukaryotic cells) and 70S (prokaryotic cells, mitochondria, and chloroplasts).

Site of protein synthesis.

Question 9

What is the structure and function of rough endoplasmic reticulum?

Answer 9

A system of membranes enclosing a fluid-filled space and is covered with ribosomes.

Folds and processes proteins made by the ribosomes.

Question 10

What is the structure and function of smooth endoplasmic reticulum?

Answer 10

A system of membranes enclosing a fluid-filled space.

Synthesises and processes lipids.

Question 11

What is the structure and the basic function of cell walls?

Answer 11

In plants and algae, mainly made of cellulose.
In fungi, made of chitin.

Supports cells and prevents them from changing shape.

Question 12

What is the function of cell walls?

Answer 12

Cellulose microfibrils are strong so contribute to the overall strength of the cell wall.
Provides mechanical strength.
Allows water to pass along it.

Question 13

What is the structure and function of cell vacuoles?

Answer 13

A membrane-bound (tonoplast) organelle which contains cell sap.

Helps to maintain pressure inside the cell and keep the cell rigid.
Stops plants wilting.
Isolates unwanted chemicals.

Question 14

How do prokaryotic cells differ from eukaryotic cells?

Answer 14

They are smaller.
Cytoplasm lacks membrane-bound organelles.
Smaller ribosomes.
No nucleus; instead, they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins.
A cell wall that contains murein, a glycoprotein.
One or more plasmids.
A capsule surrounding the cell.
One of more flagella.

Question 15

What are viruses?

Answer 15

Acellular and non-living agents.

Question 16

What is the structure of viruses?

Answer 16

Consists of genetic material enclosed in capsids (a protein coating made of capsomers).
Certain viruses have an additional envelope (made of phospholipids) with embedded attachment proteins.

Question 17

What is the function of attachment proteins on viruses?

Answer 17

They identify and bind to the receptor sites on the cell membrane of a host cell.

Question 18

What is the pathway of a virus?

Answer 18

1.Virus gains entry to the human body and fuses with the cell membrane of a cell.
2.Viral genetic material is released into the cytoplasm and moves towards to the nucleus.
3.Viral DNA is incorporated into the host’s DNA.
4.By transcribing its own genes, the host begins to replicate and transcribe the viral DNA.
5.This results in the production of proteins and viral genetic material needed for the assembly of new viruses.
6.Thousands of newly assembled viruses bud off the cell membrane and destroy the host cell.

Question 19

What are the principles and limitations of transmission electron microscopes?

Answer 19

->Electrons are transmitted through the sample.
->Denser parts of the specimen absorb more electrons, which makes them look darker on the image.
-> uses magnets

+ High resolution (0.1nm)
- can only be used on thin, non-living specimens.
- no colour
- near vacuum condition needed
- more complex preparation

Question 20

What are the principles of scanning electron microscopes?

and advantages and disadvantages

Answer 20

-> A beam of electrons is scanned across the specimen, which are gathered in a cathode ray tube to form an image.
+ Image produced shows the specimen’s surface and can be in 3D.
+ Thick, living specimens can be used.
- Lower resolution (20nm)
- No colour

Question 21

What is the formula for magnification?

Answer 21

Magnification = size of image/ size of real object.

Question 22

Name the stages of cell fractionation.

Answer 22

Homogenisation and ultracentrifugation.

Question 23

What is stage 1 of cell fractionation?

Answer 23

Homogenisation:
1. Tissue is homogenised.
2. The homogenate is filtered through a gauze to separate any large cell/tissue debris or unbroken cells.

Question 24

What is stage 2 of cell fractionation?

Answer 24

Ultracentrifugation:
1. The homogenate is poured into a tube which is put into a centrifuge and spun at a low speed, creating centrifugal force.
2. The heaviest organelles, like nuclei, separate out first and form a pellet at the bottom of the tube.
3. The supernatant is drained off and poured into another tube and spun again at a higher speed.
4. This process is repeated at increasingly higher speeds until all the organelles have separated out in order of mass (nuclei, mitochondria, lysosomes, endoplasmic reticulum and ribosomes).

Question 25

What happens in mitosis?

In general

Answer 25

A eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication.

Question 26

What must the solution used in cell fractionation be?

Answer 26

Cold, have the same water potential and have a buffer solution.

Question 27

What happens in the stages of mitosis?

Answer 27

Prophase:
- Chromosomes condense by coiling up from chromatin.
- Centrioles move to the poles of a cell (not present in plants).
- Spindle apparatus forms and spindle fibres develop.
- Nucleolus and nuclear envelope dissolve.
- Spindle fibres attach to the centromeres and the chromosomes are drawn towards the equator.

Metaphase:
- Chromosomes are in the form of two sister chromatids, joined at the centromere.
- The spindle apparatus aligns the chromosomes across the equator of the cell.

Anaphase:
- Centromeres divide into two.
- Spindle fibres pull individual sister chromatids towards the poles.
- Mitochondria around the spindle fibres provide the energy for this process.

Telophase:
- Chromosomes reach their respective poles and de-coil to become chromatin.
- Spindle fibres disintegrate.
- Nuclear envelope and nucleolus re-form.

Cytokinesis:
- The division of cytoplasm which begins during anaphase or telophase.
- Cytoplasm divides by the cleavage furrow.

Question 28

What can uncontrolled cell division lead to?

Answer 28

The formation of tumours and cancers.

Question 29

What are many cancer treatments trying to do?

Answer 29

Controlling the rate of cell division.

Question 30

What do prokaryotic cells go through instead of mitosis?

Answer 30

Binary fission.

Question 31

What does binary fission involve?

Answer 31

The replication of the circular DNA and plasmids.
Division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.

Question 32

What are the principles and limitations of optical microscopes?

Answer 32

-> They use light to form an image.
-> uses lenses
+ living specimens
+ colour
- thin specimens
- Low resolution (0.2um)
- Low magnification (x1500).

Question 33

What is the difference between magnification and resolution?

Answer 33

Magnification is how much bigger the image is than the specimen.
Resolution is how well a microscope distinguishes between two points that are close together.