Topic 2A: Cell Structure And Division

Question 1

What are the 4 examples of eukaryotic cells?

Answer 1

Animal, plant, algal and fungal cells.

Question 2

What organelles does a plant cell contain that an animal cel doesn’t?

Answer 2

• Cellulose containing cell wall.
• Plasmodesmata (exchanging substances between adjacent cells).
• Permanent vacuole
• Chloroplasts

Question 3

What is the difference between a plant cell and an algal cell?

Answer 3

• Algae can be unicellular (e.g. chlorella) or multicellular (e.g. seaweed), plants are always multicellular.
• Algal cells can contain different shaped/sized chloroplasts e.g. one large elongated chloroplast instead of multiple normal sized ones, plant cells just contain multiple normal sized chloroplasts.

Question 4

What is the difference between a plant cell and a fungal cell?

Answer 4

• A fungi can be unicellular (e.g. yeast) or multicellular (e.g. mushrooms), plants are only multicellular.
• A fungal cell doesn’t photosynthesise, so doesn’t contain chloroplasts, plant cells do.
• A fungal cell has a cell wall made from chitin, a plant cell has a cell wall made from cellulose.

Question 5

What are 5 differences between eukaryotic and prokaryotic cells?

Answer 5

• Prokaryotes are much smaller in size than eukaryotes.
• Prokaryotes have no membrane-bound organelles, eukaryotes have many e.g. nucleus.
• Prokaryotes contain 70S (smaller) ribosomes, eukaryotes contain 80S (larger) ribosomes.
• Prokaryotes don’t have a nucleus, eukaryotes do have a nucleus.
• Prokaryotic cell walls are made from murein, eukaryotic cell walls are made from cellulose or chitin.

Question 6

Where does a prokaryotic cell keep its DNA?

Answer 6

• A single nucleoid - A circular DNA molecule that floats freely in the cytoplasm and isn’t protein bound.
• May also contain DNA plasmids - loops of DNA that only carry a few genes, and give the bacterial cell antibiotic resistance.

Question 7

Why is the capsule around a prokaryotic cell important?

Answer 7

• Stops the bacteria from desiccating and protects the bacteria against the hosts immune system.

Question 8

Why is the flagella important in a prokaryotic cell?

Answer 8

Rotates around to enable the bacteria to move.

Question 9

What is the first step of binary fission?

Answer 9

• The prokaryotic cell replicates its circular DNA and plasmids.

Question 10

What is the second step of binary fission?

Answer 10

• The prokaryotic cell begins to grow and the circular DNA loops migrate to the ends of the poles.

Question 11

What is the third step of binary fission?

Answer 11

• The cytoplasm begins to divide and the new murein cell walls start to develop.

Question 12

What is the fourth step of binary fission?

Answer 12

• The cytoplasm fully divides producing two new daughter cells, each daughter cells containing copies of circular DNA and plasmids.

Question 13

When does the cell cycle start and end?

Answer 13

• Starts - When the cell is produced by cell division.
• Ends - When the cell divides by mitosis to produce two new identical cells.

Question 14

What are the orders of the cell cycle?

Answer 14

• Starts and ends at mitosis.
• Interphase (GP1-Synthesis-GP2).

Question 15

What is interphase?

Answer 15

When the cell prepares for cell division (mitosis) by:
• unravelling and replicating its DNA to double the genetic content.
• Replicating its organelles.
• Increasing the ATP content.

Question 16

What happens during gap phase 1 (1st period of interphase)?

Answer 16

• Cell grows and new proteins and organelles are made.

Question 17

What happens during synthesis (2nd period of interphase)?

Answer 17

Cell replicates its DNA for mitosis.

Question 18

What happens during gap phase 2 (3rd period of interphase)?

Answer 18

Cell continues to grow and new proteins are made for cell division.

Question 19

State 3 reasons why mitosis is important?

Answer 19

1. Growth of multicellular organisms.
2. Reparation of damaged tissues.
3. Asexual reproduction.

Question 20

What happens during prophase (1st phase of mitosis)?

Answer 20

• Chromosomes condense; getting shorter and fatter.
• Centrioles move to opposite ends of the cell, forming a network of protein fibres called the spindle.
• The nuclear envelope breaks down allowing the chromosomes to lie free in the cytoplasm.

Question 21

What happens during metaphase (2nd phase of mitosis)?

Answer 21

• Chromosomes line up along the middle of the cell and attach to the spindle fibres by their centromeres.

Question 22

What happens during anaphase (3rd phase of mitosis)?

Answer 22

• centromeres divide, separating each pair of sister chromatids.
• The spindle fibres contract, pulling the chromatids to opposite poles of the spindle by their centromeres.
• The chromatids form v-shapes.

Question 23

What happens during telophase (4th phase of mitosis)?

Answer 23

• Chromatids reach opposite poles of the spindle, uncoiling, becoming long and thin again.
• A nuclear envelope forms around both groups of chromosomes, forming two new nuclei’s.
• Two new daughter cells are formed: genetically identical to each other and the original parent cell.

Question 24

What is cytokinesis and when does it start/finish?

Answer 24

• The division of the cytoplasm.
• Starts in anaphase and finishes in telophase.

Question 25

Describe the structure of the cell membrane:

Answer 25

• On the outside of animal cells and just inside the cell wall of other cells. • Mainly made up of lipids and proteins.

Question 26

Explain the function of the cell membrane:

Answer 26

• Regulates the movement of molecules in and out of the cell. • Contains receptor molecules which allow it to respond to chemicals such as hormones.

Question 27

Describe the structure of the nucleus:

Answer 27

• Contains a nuclear envelope and many pores. • Contains chromosomes (made by protein bound linear DNA), and a nucleolus.

Question 28

Explain the function of the nucleus:

Answer 28

• Controls the cells activates by controlling the transcription of DNA. • DNA is given instructions to make proteins. •Nuclear pores allow substances to move between the nucleus and cytoplasm. • Nucleolus makes ribosomes.

Question 29

Describe the structure of the mitochondria:

Answer 29

• Oval shape • Double membrane; inner membrane is folded to form crista • Inside crista is the matrix, containing enzymes for respiration.

Question 30

Explain the function of the mitochondria:

Answer 30

• Site of aerobic respiration, which produces ATP. • Mitochondria are found in large numbers in cells that are very active and require lots of energy.

Question 31

Describe the structure of chloroplasts:

Answer 31

• Small flattened organelle in plant + algal cells. • Double membrane • Has thylakoid membranes inside, which are stacked in some parts of the chloroplast to form grana. •Grana are linked together by lamella (thin, flat pieces of thylakoid membranes). •Contains a thick fluid called stroma.

Question 32

Explain the function of chloroplasts:

Answer 32

• Site of photosynthesis • Some parts of photosynthesis occur in the grana, others in the stroma.

Question 33

Describe the structure of the Golgi body/appartus:

Answer 33

• A group of fluid-filled membrane bound flattened sacs. • Vesicles are often seen at the edge of the sacs.

Question 34

Explain the function of the golgi appartus:

Answer 34

• Processes and packaged new lipids and proteins • Makes lysosomes.

Question 35

Describe the structure of the golgi vesicles:

Answer 35

• A small fluid-filled membrane bound sac in the cytoplasm, made by the Golgi apparatus.

Question 36

Explain the function of the golgi vesicles:

Answer 36

Stores lipids and proteins made by the golgi apparatus and transports them out of the cell via the cell-surface membrane.

Question 37

Describe the structure of lysosomes:

Answer 37

• A round membrane-bound organelle with no clear internal structure.

Question 38

Explain the function of lysosomes:

Answer 38

• Contains lysozymes (enzymes) which are used to digest invading cells or break down worn out components of a cell.

Question 39

Describe the structure of a ribosome:

Answer 39

• A very small organelle that floats freely in the cytoplasm or is attached to the rough endoplasmic reticulum.

Question 40

Explain the function of a ribosome:

Answer 40

• the site of protein synthesis.

Question 41

Describe the structure of the rough endoplasmic reticulum:

Answer 41

• A system of membranes enclosing a fluid filled space and surrounded by ribosomes.

Question 42

Explain the function of the rough endoplasmic reticulum:

Answer 42

• folds and processes proteins made at the ribosomes.

Question 43

Describe the structure of the smooth endoplasmic reticulum:

Answer 43

• a system of membranes enclosing a fluid-filled space.

Question 44

Explain the function of the smooth endoplasmic reticulum:

Answer 44

• Synthesises and processes lipids.

Question 45

Describe the structure of the cell wall:

Answer 45

• a rigid outer layer surrounding plant, algae and fungi cells. • Plant and algae cells: cell walls are made from cellulose. • Fungi cells: cell wall is made from chitin.

Question 46

Explain the function of the cell wall:

Answer 46

• supports the cell and maintains the cell shape.

Question 47

Describe the structure of the permanent vacuole:

Answer 47

• a membrane bound organelle in the cytoplasm, containing cell sap (a weak solution of sugar and salts). • The surrounding membrane is called the tonoplast.

Question 48

Explain the function of the permanent vacuole:

Answer 48

• Helps to maintain pressure inside the cell and keep the cell rigid, which stops plants wilting. • Involved in the isolation of unwanted chemicals inside the cell.

Question 49

Define magnification:

Answer 49

How many times bigger an object appears compared to the actual size of the object.

Question 50

Define resolution:

Answer 50

The minimum distance between two objects in which they can be viewed as separate.

Question 51

The resolution in an optical microscope is determined by?

Answer 51

The wavelength of the beam of light.

Question 52

The resolution of an electron microscope is determined by?

Answer 52

The wavelength of the beam of electrons.

Question 53

State and explain the differences between an optical microscope and an electron microscope:

Answer 53

1. Optical microscope condenses a beam of light to produce an image; whereas electron microscope condenses a beam of electrons to produce an image. 2. Optical microscopes have lower resolution as the beam of light has a longer wavelength, whereas electron microscopes have higher resolution as the beam of electrons has a shorter wavelength. 3. Optical microscopes have lower magnification, whereas electron microscopes have higher magnification. 4. Optical microscopes produce a coloured image, whereas electron microscopes produce a black/white image. 5. Optical microscope: sample can be alive, whereas electron microscope: sample must be in a vacuum (therefore non-living).

Question 54

State and explain the differences between a transmission electron microscope and a scanning electron microscope:

Answer 54

1. In a TEM, the specimen must be thin, whereas in an SEM, the specimen can be thick. 2. In a TEM, a 2D image is produced, whereas in an SEM, a 3D image is produced. 3. In a TEM, a higher resolution image is produced, whereas in an SEM a lower resolution image is produced. 4. A TEM uses electromagnets to focus a beam of electrons, whereas an SEM scan the beam of electrons across the specimen.

Question 55

What is the formula for magnification?

Answer 55

Magnification = Image Size/Real Size

Question 56

What is an eyepiece graticule and what is it used for?

Answer 56

• Its a scale on a glass disc inside an optical microscope. • it’s used to measure the size of an object under the microscope.

Question 57

Why must you calibrate the eyepiece graticule?

Answer 57

When objective lens is changed, the magnification is changed therefore the eyepiece must be calibrated to work out the distance represented between each division at that magnification.

Question 58

How do you calibrate an eyepiece graticule (summarised answer, not full method):

Answer 58

• Using a stage micrometer: a glass slide with a scale on it which you place on the stage; its usually 2mm long; with each subdivision being 10 micrometers apart.

Question 59

How do you calibrate an eyepiece graticule (step by step method)?

Answer 59

Step 1 - Line up the eyepiece graticule with the micrometre stage whilst looking through the eyepiece. Step 2 - Count how many divisions on the eyepiece graticule fit into one division on the micrometre stage. Step 3 - each division on the micrometre stage is 10 µm, use this to calculate what one division on the eyepiece graticule is at that magnification.

Question 60

How is a cancer tumour formed?

Answer 60

• Mitosis/the cell cycle is controlled by genes. • Normally, once the cells have divided enough to produce enough cells, they’ll stop. • However, if a mutation occurs in a gene that codes for cell division, the cell will grow and divide uncontrollably, leading to the formation of a tumour.

Question 61

Cancer treatments:

Answer 61

• some cancer treatments are designed to control the rate of cell division in tumour cells by disrupting the cell cycle. • However, these cancer treatments are unable to distinguish between tumour cells and normal cells, so may also kill normal cells that are dividing. • Although tumour cells tend to divide much more frequently than normal cells, so it’s more likely the tumour cell is killed off.

Question 62

Cancer treatments targeting specific parts of the cell cycle:

Answer 62

1. Gap Phase 1 (new organelles and proteins made): - Chemical drugs (e.g. chemotherapy) prevent the synthesis of enzymes for DNA replication, meaning the cell is unable to enter the synthesis phase. - This disrupts the cell cycle and forces the cell to kill itself, preventing any further tumour growth. 2. Synthesis phase (DNA replication): - Radiation and some drugs damage DNA. - At several points in the cell cycle, the cell is checked for any damaged DNA. If any severe DNA damage is detected, the cell will kill itself, preventing any further tumour growth.

Question 63

In cell fractionation, the cells must be prepared in what conditions and why?

Answer 63

1. Cold - to reduce enzyme activity. As the cells must breaks open, enzymes are released which can damage the organelles. 2. Isotonic - The water potential must be the same to prevent osmosis, which can cause the cell to shrivel or burst. 3. Buffered - the solution has a pH buffer to prevent damage to organelles.

Question 64

What is step 1 of cell fractionation and how is it performed?

Answer 64

Homogenisation (breaking open the cell): - Use a blender to blend the cells/tissue in the cold, isotonic, buffered solution. - Filter the solution to get rid of any large cell debris.

Question 65

What is step 2 of cell fractionation and how is it performed?

Answer 65

Ultracentrifugation (separating the organelles): - The filtered solution is spun at different speeds in a centrifuge. - As it spins, the organelles separate out according to their densities.

Question 66

Differential centrifugation:

Answer 66

1. The centrifuge spins and the centrifugal forces cause pellets of the most dense organelles to form at the bottom. 2. The process starts at a low speed; and then is repeated at increasing speeds. 3. Each time the supernatant (liquid) is removed, leaving behind pellets of organelles. 4. The supernatant is then spun again to remove the next pellet of organelles.

Question 67

What is the order of organelles in differential centrifugation?

Answer 67

Nuclei -> Chloroplasts (if plants) -> Mitochondria -> Lysosomes -> endoplasmic reticulum -> ribosomes.