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A-Level Biology > 2A | Cell Structure and Division > Flashcards

2A | Cell Structure and Division Flashcards

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1
Q

What is a Lysosome?

A

The Lysosome is a membrane-bound organelle that has enzymes called Lysozymes in it - it’s a type of Golgi Vesicle.

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2
Q

What is the function of the Lysosome?

A

Lysosomes have digestive enzymes, which allows it to break down worn out components of the cell or hydrolyze invading cells, such as pathogens.

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3
Q

List 3 differences between Prokaryotes and Eukaryotes.

A

Prokaryotes do not have a nucleus, Eukaryotes do

Prokaryotes are unicellular, Eukaryotes can make up complex organisms like animals and plants

Prokaryotes’ cell walls are made of Murein, Plant cell walls are mostly made of Cellulose.

Some prokaryotes have a capsule, most eukaryotes do not.

Prokaryotes lack a nucleus and so their DNA floats free in the cytoplasm, while in Eukaryotes they are kept in the nucleus.

Prokaryotic DNA does not have histones, Eukaryotic DNA does.

Some prokaryotes have one or more flagella, while all eukaryotes do not.

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4
Q

What is a Ribosome?

A

Ribosomes are organelles which have no cell membrane and either float free in the cytoplasm or are attached to the RER.

It is made up of proteins and RNA.

Prokaryotic Ribosomes (70S) are smaller than Eukaryotic Ribosomes (80S).

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5
Q

What is the function of the Ribosome?

A

Ribosomes are involved in the synthesis of proteins.

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6
Q

What is the Golgi Vesicle?

A

Golgi Vesicles are small, fluid-filled sacs in the cytoplasm. They are membrane-bound and are produced by the Golgi Apparatus.

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7
Q

What is the function of the Golgi Vesicle?

A

The Golgi Vesicle is needed for transport of substances like Lipids and Proteins out the cell via the cell-surface membrane.

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8
Q

What is a Cell membrane?

A

Cell membranes are small, semi-permeable barriers on the surface or below the cell wall of cells.
They are mostly made from lipids and proteins.

Animal cells feature cell membranes on their surface, while other cells, such as prokaryotes and Plants, feature cell membranes under the cell wall, protecting the organelles from the cell.

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9
Q

What is the function of the Cell membrane?

A

Cell membranes have many functions. Firstly, they have proteins on their surface [glycoproteins and glycolipids] which play a part in hormone recognition.

Cell membranes regulate the movement in and out the cell, and so conditions in the cell are established differently than out in the cytoplasm.

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10
Q

What is a cell wall?

A

Cell walls are rigid structures found on the outside of cells, right above the cell membrane.

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11
Q

What is the function of the cell wall?

A

Cell walls keep the shape and structure of the cell in place to prevent it from changing shape or becoming irregular.

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12
Q

What molecule are cell walls made of in Plants?

A

Cellulose

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13
Q

What molecule are cell walls made of in Fungi?

A

Chitin

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14
Q

What molecules are cell walls made of in Prokaryotes?

A

Murein

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15
Q

What is the name given to ribosomes which are smaller to Eukaryotes, and the name given to ribosomes larger than prokaryotes?

A

80S and 70S Ribosomes

Prokaryotes have smaller ribosomes, 70S
Eukaryotes have larger ribosomes, 80S

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16
Q

List 3 things a Plant cell has that an Animal cell does not.

A

Plasmodesma
Cell Wall
Chloroplast
Vacuole

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17
Q

What is a Golgi Apparatus?

A

A group of fluid-filled, membrane bound flattened sacs.

Vesicles are often seen at the edges of the sacs.

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18
Q

What is the function of the Golgi Apparatus?

A

The Golgi Apparatus processes and packages new lipids and proteins.

It also makes lysosomes.

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19
Q

What is a Rough Endoplasmic Reticulum?

A

A group of membranes enclosing a fluid filled space. The surface is covered with ribosomes.

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20
Q

What is the function of the Rough Endoplasmic Reticulum?

A

Folds and processes proteins made by the ribosomes.

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21
Q

What is a Smooth Endoplasmic Reticulum?

A

A group of membranes enclosing a fluid filled space. They have no ribosomes.

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22
Q

What is the function of the Smooth Endoplasmic Reticulum?

A

Synthesizes and processes lipids.

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23
Q

What is a Vacuole?

A

A vacuole is a membrane-bound organelle used to store cell sap, a weak solution of sugar and salts.

There is a small area near the vacuole surrounding it, called the tonoplast.

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24
Q

What is the Mitochondria?

A

The Mitochondria is an oval-shaped organelle with a double membrane.

They have cristae, structures extended from the inner membrane of the organelle to increase surface area.

They also contain a matrix, enzymes needed to carry out aerobic respiration.

Prokaryotes do not have mitochondria.

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25
Q

What is the function of the Mitochondria?

A

The function of the mitochondria is to carry out respiration, where ATP is synthesized for generation of energy.

Mitochondria is needed in cells which require a lot of energy.

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26
Q

What is a Chloroplast?

A

Chloroplasts are small, flattened structures found in plant cells. They have a double membrane.

Chloroplasts has membranes inside itself called thylakoid membranes - these membranes are stacked up in parts of the chloroplast to form grana. Grana are linked together by lamellae - thin, flat pieces of thylakoid membrane.

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27
Q

What is the function of the Chloroplast?

A

They carry out photosynthesis. Some parts of photosynthesis happen in the thylakoid membranes (specifically the grana).

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28
Q

What is a Nucleus, Nucleolus and Nuclear Envelope?

A

The Nucleus is a large organelle, consisting of a nuclear envelope and nucleolus.

The Nucleus contains chromosomes which are protein bound linear DNA.

The Nucleolus is a smaller part enclosed in the nuclear envelope.

The nuclear envelope is a double membrane which contains many pores.

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29
Q

What is the function of the Nucleus, Nuclear Envelope and Nucleolus?

A

The Nucleolus is the area of the nucleus where ribosomes are made.

The Nucleus is responsible for providing genetic information to the rest of the cell which gives the cell instructions on how to work, basically controlling the activities of the cell.
The Nucleus has DNA, which contains instructions on how to create proteins.

The Nuclear Envelope has pores which are holes in the double membrane which allows substances like RNA to move between the nucleus and the cytoplasm.

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30
Q

Do Fungal cells have chloroplasts? If not, why?

A

No, because they don’t photosynthesize.

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31
Q

Do Prokaryotes have mitochondria?

A

No.

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32
Q

Why is it important that some parts of cells in an organism vary?

A

Cells, depending on their function, will need to be specialized.

Specialization means that cells are able to do a function they are associated with better, so for example cells which produce mucus may need a lot of golgi and mitochondria in order to get the energy to release a lot of mucus at once.

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33
Q

Epithelial cells in the small intestine are specialized to absorb food efficiently.

The walls of the small intestine has a lot of finger like projections, called villi. How can this help the epithelial cells absorb food?

The cells on the surface of villi in Epithelial cells have even more finger like, curled up projections. What are they called, and why are they there?

A

Epithelial cells have villi to increase surface area so food can be absorbed at a faster rate into the cell.

The cells on the surface of villi are called microvilli and are used to increase surface area even more for an even faster rate of absorbtion.

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34
Q

How does a cell become a tissue, an organ and then an organ system?

A

Cells become tissues by becoming a group of cells that perform a particular function.
Different tissues work together to form organs.
Different organs work together to form organ systems.

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35
Q

Cilia are hair-like structures found on lung epithelial cells. Their function is to beat and move mucus out of the lungs.

Beating requires energy, and so suggest how ciliated cells are adapted to their function in terms of the organelles they contain.

A

Ciliated cells have a lot of mitochondria. Mitochondria is the cell needed to generate energy which is done by aerobic respiration.

Ciliated cells will have a lot of mitochondria because they need more energy.

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36
Q

Pancreatic cells make and secrete hormones (made of protein) into the blood.

From production to secretion, list, in order, four organelles involved in making hormones.

A

Ribosome
Rough Endoplasmic Reticulum
Golgi Apparatus
Golgi Vesicle

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37
Q

What is a flagellum?

A

A flagellum is a long, hair-like structure.

Not all prokaryotes have a flagellum, and some can have more than one.

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38
Q

What is the function of the flagellum?

A

The flagellum rotates in order to make the cell move.

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39
Q

List 3 organelles prokaryotes have.

You can include what they ‘may’ have as well.

A 
Capsule
Cell Membrane
Cell Wall
Ribosome
Plasmid
Flagellum
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40
Q

List 3 organelles prokaryotes may have which eukaryotes won’t.

A

Flagellum
Plasmid
Capsule

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41
Q

List 3 organelles eukaryotes may have which prokaryotes won’t.

A

Nucleus
Mitochondria
Chloroplast
Vacuole

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42
Q

What is a capsule?

A

The capsule is an organelle on the surface of some prokaryotes, usually bacteria. It is made from secreted slime.

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43
Q

What is the function of the capsule?

A

The capsule offers protection to the cell against the immune system.

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44
Q

What is a plasmid?

A

The plasmid is a round, circular loop of DNA that isn’t part of the main circular DNA molecule in a prokaryote.

Prokaryotes can have variable numbers of plasmids, sometimes none.

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45
Q

What is the function of the plasmid?

A

The plasmid contains genes for things like antibiotic resistance and can be passed onto or between other prokaryotes.

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46
Q

What is different about the storage of DNA in prokaryotes and eukaryotes?

A

DNA is stored in the nucleus in eukaryotes.
DNA is stored in the cytoplasm in prokaryotes.

DNA has histones to help it coil in eukaryotes.
DNA does not have histones in prokaryotes, instead, it coils from a process called supercoiling.

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47
Q

What does ‘acellular’, ‘multicellular’ and ‘unicellular’ mean?

A

‘Acellular’ means that the named does not consist of even one cell.

‘Multicellular’ means that the named is made of multiple cells.

‘Unicellular’ means that the named consists of only one cell.

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48
Q

From viruses, prokaryotes, and eukaryotes, use the term which best describes them:

Acellular
Multicellular
Unicellular

A

Viruses are acellular.

Prokaryotes are unicellular.

Eukaryotes can be unicellular, but are usually multicellular.

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49
Q

What is a virus?

A

A virus is an acellular particle made of amino acids and proteins.

They are acellular, meaning they are not cells as they lack many of the biological functions needed, such as lacking ribosomes, cell membranes and cytoplasm.

50
Q

What do viruses lack that prokaryotes have?

A

Ribosome
Cell Membrane
Cytoplasm

51
Q

Describe the structure of viruses.

A

Viruses have a protein coat around them, called a capsid.

The capsid has small projections called attachment proteins which are used to cling onto host cells.

Inside the virus, there is a core of genetic material which can either be DNA or RNA.

52
Q

Describe binary fission.

A

Binary fission is the process in which prokaryotes replicate.

Before binary fission occurs, the prokaryotic cell replicates its genetic material. During this process, a variable number of plasmids can be made, not just double.

After this, the cell gets slightly larger and DNA loops move to the opposite sides of the cell. Plasmids do not need to be equally spread throughout, but the two pieces of circular DNA must be on opposite sides of the cell.

The cytoplasm begins to divide from the middle and new cell walls begin to form.

The cytoplasm divides, and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have variable number of plasmid copies.

53
Q

Outline the way viruses attach to cells to inject it’s genetic information.

A

Viruses replicate by using their attachment proteins to bind to complementary receptor proteins on the surface of host cells.

Different viruses have different attachment proteins and therefore require different receptor proteins on host cells. As a result, some viruses can only affect one type of cell.

After the virus has attached to the complementary host cell’s proteins on the cell surface membrane, it can inject it’s genetic information into the host cell.

54
Q

Describe the Lytic cycle.

A

Firstly, the virus will bind onto the host cell using it’s attachment proteins.

The virus will then inject it’s genetic information into the host cell. In that host cell, the new genetic information is kept separate from the cellular DNA.

In the Lytic cycle, The new genetic information will instantly command the cell to reassemble and assemble new viruses by using the cell’s own machinery.

After there are many new viruses, there will eventually be so many of them that the host cell literally bursts because it can’t hold them in - this is called lysis.

This results in the release of many new viruses that will go to invade other host cells.

55
Q

Describe the Lysogenic cycle.

A

Firstly, the virus will bind onto the host cell using it’s attachment proteins.

The virus will then inject it’s genetic information into the cell.

In the Lysogenic cycle, the genetic information integrates into the DNA of the cell and stays dormant. Whenever the cell replicates by mitosis, the genetic information of the virus is carried over.

Eventually, the genetic information of the virus will eventually not become dormant and all the host cells infected with the viral RNA/DNA will enter the lytic cycle, causing them all to burst at once and creating many new copies of viruses.

56
Q

What is the protein coat around a virus called?

A

Capsid

57
Q

What is attached onto the protein coat of a virus?

A

Attachment proteins

58
Q

What is inside the capsid of a virus?

A

Genetic information (RNA or DNA)

59
Q

Cholera is a disease caused by the prokaryotic organism Vibrio cholerae.

Name the polymer that makes up the cell wall of Vibrio cholerae.

Outline the process by which Vibrio cholerae replicates.

There are different strains of Vibrio cholerae. One strain has a capsule, but the other does not. Explain the benefit having a capsule may have.

A

Murein

Firstly, the vibrio cholerae will replicate it’s genetic information. Plasmids can be replicated to create variable amounts, but circular DNA only replicates once to create two copies.
The prokaryote expands and the circular DNA strands move to opposite sides of the cell - plasmids don’t spread out equally.

A cell wall is then formed down in the middle as the cytoplasm begins to divide.
After the cytoplasm has divided, you now have 2 cells with circular DNA and a variable number of plasmids.

The strain of Vibrio cholerae that has a capsule allows it to have extra protection against the immune system.

60
Q

What is magnification and what is resolution?

A

Magnification is how much bigger the image is than the specimen.

Resolution is how detailed the image is. More specifically, it’s how well a microscope distinguishes between two points that are close together.

61
Q

What is the formula for magnification?

A

The formula for magnification is:

size of the image ÷ size of the real object

62
Q

If you have a magnified image of a specimen that’s 5mm wide and the real size of the specimen is 0.05mm, what is the magnification?

A

5 ÷ 0.05 = x 100

63
Q

What does an optical microscope use to form an image?

A

Light

64
Q

What is the maximum magnification and resolution of an optical microscope?

A

x 1500 and 0.2μm.

65
Q

Evaluate the usage of electron microscopes (in general).

A

Uses electrons to form an image

Has more detail than the optical microscope, as the maximum resolution for an electron microscope is 0.002μm.

The maximum magnification of an electron microscope is x 1,500,000.

Using electron microscopes allows you to see the internal structures of organelles depending on the type of electron microscope used.

Please note that to use an electron microscope the cell must be dead as a vaccum must be established inside the electron microscope in order for electrons to pass through it.

This makes electron microscopes much more expensive and laborious to use.

66
Q

Evaluate Transmission electron microscopes (TEMs).

A

TEMs use electromagnets to focus a beam of electrons which is transmitted through the specimen, so the specimen must be thin so there is a penetration.

Denser parts of the specimen will absorb more electrons, making the denser area darker.

With TEMs, you can see the internal structure of organelles which is extremely useful as you cannot with SEMs or optical microscopes.

67
Q

Evaluate the usage of Transmission Electron Microscopes.

A

Good things:

The TEM has the maximum resolution of 0.002μm. This is the highest of an electron microscope and allows cells internal structure to be viewed in very high detail.

The TEM has a much higher useful magnification than the SEM meaning more organelles can be seen in detail.

Bad things:

Specimen must be thin as electrons must penetrate it.

The image generated is 2D.

68
Q

Summarize Scanning Electron Microscopes (SEMs).

A

SEMs do not penetrate the specimen, instead, a beam of electrons is scanned across the specimen which forms an image.

The images you end up with show the surface of the specimen and they can be 3-D, as well as having color.

69
Q

Evaluate the usage of Scanning Electron Microscopes.

A

Good things:

SEMs form a 3-D image, giving people a more clear understanding of organelles when looking into surface area, etc.
SEMs give color, meaning organelles are easier to identify and gives more information on a certain organelle.

Bad things:

SEMs have a lower magnification and resolution than the TEM.
SEMs cannot be used to view the internal structure of organelles, only the surface.

70
Q

How do you set up a specimen to be viewed under a microscope?

A

Here’s how you prepare a ‘temporary mount’ of specimen on a slide:

Star by pipetting a small drop of water onto the slide (a slide is a strip of clear glass or plastic), then use tweezers to place a thin section of your specimen on top of the water drop.

Add a drop of stain. Stains are used to highlight objects in a cell, for example iodine in potassium iodide is used for starch grains.

Finally, add the cover slip (a square of clear plastic that protects the specimen). To do so, stand the slip upright onto the slide next to the water droplet. Then carefully tilt and lower it so it covers the specimen. Try not to get any air bubbles under it as it may destruct the view of the specimen under the microscope.

71
Q

What is an artefact?

A

Artefacts are things that you see on a microscope but aren’t part of the actual cell or specimen that you’re looking at.

These could be water bubbles or some particles of dust.

72
Q

Explain the steps to prepare a root tip to be viewed under a microscope.

A

Firstly, cut 1cm from the tip of a growing root, usually from an onion. It must be from the tip as that will be where the root is actively growing the most as it extends, so you will see most mitotic activity there.

Then, after cutting, put the cut root into a boiling tube of hydrochloric acid and keep it there for 5 minutes. The boiling tube must be at 60°C.

After that, drain the hydrochloric acid out of the boiling tube, then take your root tip and make sure it is rinsed out with cold water from a pipette.

Leave the tip to dry on a paper towel. Then, place the tip on a microscope slide and cut 2mm from the very tip of it. Get rid of the rest.

Use a mounted needle to break the tip open and spread the cells out thinly. Add a few drops of stain and leave it for a few minutes, it must be toluidine blue.

Place a cover slip over the cells and push down firmly to squash the tissue. This will make the tissue thinner and allow light to pass through it. Don’t smear the cover slip sideways as that will damage chromosomes.

Now you can look at all the stages of mitosis under the optical microscope.

73
Q

Explain how to determine the size of a cell starting from a stage micrometer and eyepiece graticule.

A

‘Calibrate’ the eyepiece graticule to the stage micrometer by lining the eyepiece graticule to one of the divisions on the stage micrometer so they are parallel.

You must know one division on the stage micrometer is 0.1mm.

Count up the amount of divisions in the eyepiece graticule that’s needed in order to get to the next division on the stage micrometer. For example, depending on the magnification, you may need 3 divisions on the eyepiece graticule for 1 division on the stage micrometer.

74
Q

5 divisions on the eyepiece graticule is equal to one division on the stage micrometer. How much is one division of the eyepiece graticule equal to?

A

One division on stage micrometer = 0.1mm
Five divisions on eyepiece graticule = 0.1
0.1 ÷ 5 = 0.02

One division of the eyepiece graticule is equal to 0.02mm.

75
Q

Fill in the blank:

1 m = _ cm
1 m = _ mm
1 cm = _ mm
1 mm = _ µm
1 µm = _ nm
100 nm = _ µm

1m = _ µm

A 
1 m = 100 cm
1 m = 1000 mm
1 cm = 10 mm
1 mm = 1000 µm
1 µm = 1000 nm
100 nm = 0.1 µm

1m = 1000mm
1mm = 1000µm
100 * 10,000 = 1,000,000

76
Q

Describe how to observe a prepared slide of cells using an optical microscope.

A

Clip the slide you’ve prepared onto the stage.

Select the lowest powered objective lens (the lens on your microscope that produces the lowest magnification).

Use the coarse adjustment knob to bring the stage up to just below the objective lens.

Look down the eyepiece, and as you’re looking, use the coarse adjustment knob to move the stage up and down until you reach a point where the specimen is roughly in focus.

Adjust the focus with the fine adjustment knob until you get a clear image of what’s on the slide.

If you need to see a slide with a greater magnification, swap to a higher powered objective lens and refocus.

77
Q

Name parts 1 to 6:

https://media.discordapp.net/attachments/352951793187029005/804811556122394674/unknown.png

A

1 = Lowest and highest powered objective lens

2 = Microscope stage

3 = Light

4 = Fine Adjustment Knob

5 = Coarse Adjustment Knob

6 = Eyepiece

78
Q

Mitosis is a type of cell division.

Does the process of mitosis end up with genetically identical cells, or genetically different cells?

A

Genetically identical cells.

79
Q

List the three stages of Interphase.

A

Gap phase 1
Synthesis
Gap phase 2

80
Q

Outline what happens in gap phase 1 in Interphase.

A

The cell grows, with new organelles and proteins being made.

81
Q

Outline what happens in synthesis in Interphase.

A

Cell replicates and unravels its DNA, ready to divide by mitosis.

82
Q

Outline what happens in gap phase 2 in Interphase.

A

Cell replicates it’s organelles, with proteins necessary for cell division being made

83
Q

Outline one thing Mitosis is needed for in organisms.

A

Mitosis is needed for growth of multicellular organisms.

Mitosis is also needed for the repair for damaged tissues.

84
Q

The cell cycle consists of a period of cell growth and DNA replication before Mitosis.

What is this called?

A

Interphase

85
Q

Summarize Interphase.

A

Interphase is a stage in the cell cycle before Mitosis.
The cell carries out normal functions, but also prepares to divide.

The cell’s DNA is unraveled and replicated, in a stage called synthesis, to double its genetic content. The organelles are also replicated in gap phase 2, and proteins necessary for cell division are also synthesized in gap phase 2.

86
Q

Name the four stages of Mitosis.

A

Prophase
Metaphase
Anaphase
Telophase

87
Q

Describe what happens to a cell in Prophase.

A

Prophase is one of the four stages in Mitosis, where the cell begins its division process.

Firstly, the chromosomes (each with two chromatids) condense, getting shorter and fatter. Tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibers across it called the spindle.

The nuclear envelope breaks down and chromosomes lie free in the cytoplasm.

88
Q

Describe what happens to a cell in Metaphase.

A

Metaphase is one of the four stages in Mitosis, where the cell begins its division process.

The chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.

89
Q

Describe what happens to a cell in Anaphase.

A

Anaphase is one of the four stages in Mitosis, where the cell begins its division process.

The centromeres divide, separating each pair of sister chromatids.

The spindles contract, pulling chromatids to opposite poles of the spindle, centromere first. This makes the chromatids appear v-shaped.

90
Q

Describe what happens to a cell in Telophase.

A

Telophase is one of the four stages in Mitosis, where the cell begins its division process.

The chromatids reach the opposite poles on the spindle.

They uncoil, becoming long and thin again and becoming chromosomes.

A nuclear envelope forms around each group of chromosomes, so there are now two nuclei.

The cytoplasm divides (cytokinesis) and there are now two daughter cells that are genetically identical to the original cell and each other. Mitosis is finished

91
Q

What stage of the cell cycle is this cell in?

https://media.discordapp.net/attachments/352951793187029005/813168710449758218/unknown.png

A

Interphase

This is because the nuclear envelope has not visibly dissolved yet.

92
Q

What stage of mitosis is this cell in?

https://media.discordapp.net/attachments/352951793187029005/813168735296290867/unknown.png

A

Prophase

This is because the chromosomes have condensed and the nuclear envelope has dissolved.

It is not the other stages as you can see that the chromosomes have not been lined up or separated.

93
Q

What stage of mitosis is this cell in?

https://media.discordapp.net/attachments/352951793187029005/813168764509225030/unknown.png

A

Metaphase

You can see this as chromosomes are being visibly lined up along the middle of the cell, and have yet to be separated.

94
Q

What stage of mitosis is this cell in?

https://media.discordapp.net/attachments/352951793187029005/813168792300814407/unknown.png

A

Anaphase

This is because the sister chromatids have been separated by centrioles contracting on opposite poles of the cell, dividing the centromere, separating the sister chromatids from each other and going to opposite poles of the cell.

95
Q

What stage of mitosis is this cell in?

https://media.discordapp.net/attachments/352951793187029005/813168826761609236/unknown.png

A

Telophase

This is because the nuclear envelope has been reformed and the cell is currently undergoing cytokinesis to create two genetically identical daughter cells.

96
Q

A scientist observes a section of growing tissue under the microscope.

He counts 100 cells undergoing mitosis, and of those, 10 are in metaphase.

One complete cell cycle of the tissue lasts 15 hours. How long do the cells spend in metaphase?

Give your answer in minutes.

A

Firstly, 10 / 100 = 0.1, also known as 10%

10% are in metaphase in 15 hours

15 x 0.1 = 1.5 hours

1.5 x 60 = 90 minutes

97
Q

What is the mitotic index?

A

The mitotic index is defined as the percentage of cells undergoing mitosis in a given population of cells.

98
Q

A scientist observed a microscope and viewed 100 cells.

Of those, 70 were in Mitosis.

What is the Mitotic index?

A

To find the % of cells undergoing mitosis:

70 / 100 = 0.7

70%

99
Q

Define a cancerous cell.

A

A cancerous cell is a cell which divides uncontrollably, wherein they can form a tumor inside the organism.

100
Q

How can cancer occur in an organism?

A

A mutation in a gene that controls cell division may cause cells to grow out of control, causing cancerous cells which have uncontrollable cell division.

101
Q

Some cancer treatments target the cell cycle, with the end result forcing cells to go through apoptosis.

These cancer treatments cannot identify the difference between cancerous and non-cancerous cells.

Describe a disadvantage as a result of using this treatment.

A

Cancer treatments that can’t identify cancer cells among other cells mean that they will attack cells indiscriminately.

This means that cancer treatments often aren’t very efficient unless used in a large period of time, due to the fact that it can’t target specifically what it’s supposed to. As a result, cancer treatments are often needed in large doses to be effective, which can make the patient very ill from mass cell death.

102
Q

Some chemical drugs prevent the synthesis of enzymes needed for DNA replication.

Assuming this chemical drug affects a cell in an organism, describe what will happen to the cell.

A

It will kill itself (apoptosis), as it is unable to enter the Synthesis phase.

103
Q

Describe two locations in the cell cycle where the DNA in a cell is checked for damage.

A

Just before and after the Synthesis phase

If the cell is seen having dramatic damage to their DNA, the cell will kill itself by apoptosis.

104
Q

Some drugs damage DNA which gets synthesized during the Synthesis phase.

Concerning the cells that get their DNA damaged, what will happen to them?

A

The cells will kill themselves by apoptosis as a result of the drug due to the fact that there is a checkpoint just after and before the synthesis phase which checks for damaged DNA - severe damage will lead to apoptosis.

105
Q

Outline the stage of Homogenization in the process of Cell Fractionation.

A

Firstly, grind up the cells you are going to be observing using a blender.

This beaks up the plasma membrane and releases the organelles into the solution. The solution must be ice-cold, isotonic and buffered.

106
Q

Why must the solution in which cells are put into during homogenization be ice cold?

A

To reduce enzyme activity that break down organelles.

107
Q

Why must the solution in which cells are put into during homogenization be isotonic?

A

This is so the solution should have the same concentration as the cells to prevent lysis by osmosis

108
Q

Why must the solution in which cells are put into during homogenization be buffered?

A

To maintain the pH to make sure cells don’t get damaged or die if the pH level fluctuates and gets too high or low.

109
Q

Outline the stage of Filtration in the process of Cell Fractionation.

A

The homogenized cell solution should be filtered through a gauze to separate any large cell debris or tissue debris, like connective tissue, from the organelles.

The organelles are much smaller than the debris, so they pass through the gauze.

110
Q

Outline the stage of Ultracentrifugation in the process of Cell Fractionation.

A

After filtration, you’re left with a solution containing a mixture of organelles. To separate a particular organelle from all the others, you must use them in a centrifuge.

The cell fragments are poured into a tube which is put into a centrifuge and is spun at a low speed. The heaviest organelles, like nuclei, get flung to the bottom of the centrifuge.

They form a thick sediment at the bottom known as the pellet. The rest of the organelles stay suspended in the fluid above the sediment, known as the supernatant.

The supernatant is then drained off, poured into another tube and spun in the centrifuge at a higher speed.
Again, the heaviest organelles, this time, the mitochondria, form a pellet at the bottom of the tube. The supernatant containing the rest of the organelles is drained off and spun in the centrifuge at an even higher speed.

The process is repeated at higher and higher speeds, until all the organelles are separated out. Each time, the pellet at the bottom of the tube is made up of lighter and lighter organelles.

111
Q

List these organelles in order of heaviest to lightest:

Mitochondria
Ribosomes
Lysosomes
Endoplasmic Reticulum
Nuclei
A 
Nuclei
Mitochondria
Lysosomes
Endoplasmic Reticulum
Ribosomes
112
Q

What is a supernatant?

A

A supernatant is the liquid lying above a solid residue.

This term is used in centrifugation in cell fractionation, wherein when the cell contents are initially spun in a tube, the nucleus (heaviest) lie at the bottom as a solid residue, and the rest lie above it as a liquid, known as the supernatant.

113
Q

What is a pellet?

A

A solid residue, wherein cell fractionation is formed at the bottom of a centrifuge.

For example, when initially having your cell contents spun in a centrifuge in cell fractionation, the nuclei (heaviest) sink to the bottom, becoming a solid residue. This is known as a pellet.

114
Q

Name A to M:

https://media.discordapp.net/attachments/352951793187029005/838462779014119484/unknown.png

What cell is this?

A 
A = Plasma membrane
B = Chloroplast
C = Rough ER
D = Plasmodesma
E = Mitochondria
F = Golgi Apparatus
G = Vacuole
H = Smooth ER
I = Cytoplasm
J = Nucleolus
K = Nucleus
L = Ribosome
M = Cell Wall

Plant cell

115
Q

Produce a scientific drawing of a nucleus.
A scale does not have to be included.

Label the following in your image:

  • Nucleolus
  • Chromatin
  • Nuclear Pore
  • Nuclear Envelope
A

https://media.discordapp.net/attachments/352951793187029005/838466235624062996/unknown.png

  • A sharp pencil must have been used when you made it
  • Label of the Nucleolus, Chromatin, Nuclear Pore, Nuclear Envelope is required, not the Nucleoplasm
    Label arrows must not overlap at all
  • Pens, including any colored pencil or pen, are not allowed.
116
Q

The linked image shows a photograph of part of a mitochondrion from a mouse liver cell taken using a transmission electron microscope at × 62 800 magnification:

https://media.discordapp.net/attachments/352951793187029005/838479048362950686/unknown.png

Produce a scientific drawing of the mitochondrion in the linked image.

Label the following parts of the mitochondrion on your drawing:

  • Matrix
  • Crista
A

https://media.discordapp.net/attachments/352951793187029005/838467494053675028/unknown.png

  • A sharp pencil must have been used when you made it
  • Label of the Matrix and Crista must be featured
    Label arrows must not overlap at all
  • Pens, including any colored pencil or pen, are not allowed.
  • A scale of x62,800 is required to be included on the image.
117
Q

What goes first, the cell wall or the cell membrane?

A

Cell wall - cell membrane is then under it in cells that do have a cell wall.

118
Q

What is a tissue?

A

A tissue refers to a group of cells working together to form a particular function.

119
Q

What is an organ?

A

An organ refers to a group of tissues working together to form a particular function.

120
Q

What is an organ system?

A

An organ system refers to a group of organs working together to form a particular function.

121
Q

How do SEMs form an image?

A

SEMs scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.

122
Q

How do TEMs form an image?

A

TEMs use electromagnets to focus a beam of electrons, which is then transmitted through the specimen.

A-Level Biology (20 decks)

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