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ib hl biology > 1.2 Ultrastructure of cells > Flashcards

1.2 Ultrastructure of cells Flashcards

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1
Q

Prokaryotes are considered to be the ___

A

Earliest and most primitive type of cell, originating some 3.5 billion years ago.

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2
Q

Prokaryotes include ___

A
  • Bacteria and archaea.

- These unicellular organisms belong to different domains due to differences in the cell wall composition and RNA.

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3
Q

Where are prokaryotes found?

A

They are found everywhere, including the most inhospitable places; from boiling wells, to deep mine shafts, to the ocean floor.

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4
Q

Structure of prokaryotes

A
  • Simple unicellular organisms
  • No internal compartmentalisation, no nucleus, and no membrane-bound organelles.
  • All metabolic processes thus occur within the cytoplasm.
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5
Q

Diagram of an electron micrograph of a bacterial cell

A
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6
Q

Cellular structures of prokaryotic cells

A

1) Cell wall
2) Plasma membrane
3) Cytoplasm
4) Pili (singular: pilus)
5) Flagella (singular: flagellum)
6) 70S ribosomes
7) Nucleoid region (which includes naked DNA, that is, DNA not associated with proteins known as histones)
8) Plasmids

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7
Q

(Prokaryotic cell) Function of cell wall

A

Encloses the cell, protecting it and helping to maintain its shape; prevents the cell from bursting in hypotonic (dilute) media.

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8
Q

(Prokaryotic cell) Function of plasma membrane

A

Surrounds the cell, controlling the movement of substances in and out of the cell.

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9
Q

(Prokaryotic cell) Function of cytoplasm

A

The medium that fills the cell and is the site of all metabolic reactions.

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10
Q

(Prokaryotic cell) Function of pili

A

Protein filaments on the cell wall that help in cell adhesion and in transferring DNA between two cells.

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11
Q

(Prokaryotic cell) Function of flagella

A
  • Much longer than pili, these are responsible for the locomotion of the organism.
  • Their whip-like movement propels the cell along.
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12
Q

(Prokaryotic cell) Function of 70S ribosomes

A

Are the sites of protein synthesis

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13
Q

(Prokaryotic cell) Function of nucleoid region (which includes naked DNA, that is, DNA not associated with proteins known as histones)

A

Controls all the activities of the cell, as well as the reproduction of the organism.

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14
Q

(Prokaryotic cell) Function of plasmids

A

Small circles of DNA that carry a few genes; often these genes give the cell antibiotic resistance and are used in creating genetically modified bacteria.

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15
Q

Difference between 70S and 80S ribosomes

A

Ribosomes in prokaryotic cells (70S) are smaller than ribosomes found in eukaryotic cells (80S).

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16
Q

What do 70S and 80S refer to?

A

70S and 80S refers to the sedimentation rate of RNA subunits.

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17
Q

How do prokaryotes reproduce?

A

By binary fission (basically, they split in half) to produce two genetically identical cells.

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18
Q

Diagram showing binary fission in a prokaryotic cell

A
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19
Q

What is binary fission?

A

A means used by prokaryotes to reproduce asexually.

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20
Q

Steps of binary fission

A

1) The chromosome is replicated semi-conservatively, beginning at the point of origin.
2) Beginning with the point of origin, the two copies of DNA move to opposite ends of the cell.
3) The cell elongates (grows longer).
4) The plasma membrane grows inward and pinches off to form two separate, genetically identical cells.

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21
Q

Why is understanding the process of binary fission is of great interest to scientists?

A

Because it may help in the design of new chemicals or novel antibiotics that specifically target and interfere with cell division in bacteria.

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22
Q

Eukaryotes

A
  • Eukaryotes are organisms with complex cells, in which the genetic material is isolated from the cytoplasm by a membrane-bound structure called the nucleus.
  • Eukaryotes represent one of the three domains (Bacteria, Archaea, and Eukaryota) and include four kingdoms: Protoctista, Fungi, Plantae, and Animalia
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23
Q

Size of eukaryotes

A

Eukaryotes vary in size, from single-celled yeast, measuring only a few micrometers, to blue whales, which can reach up to 30 meters in length and weigh approximately 150 tonnes.

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24
Q

Define compartmentalization

A

The formation of compartments within the cell by membrane-bound organelles.

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25
Q

Compartmentalization in eukaryotic cells

A
  • All eukaryotes have a compartmentalized cell structure, wherein membranes are used to isolate certain parts of the cell from the rest to form separate organelles.
  • For instance, the inside of the mitochondrion is completely sealed from the cytoplasm by the mitochondrial envelope, allowing it to carry out reactions without being affected by other reactions occurring in the cell.
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26
Q

Advantages of eukaryotic cells being compartmentalized

A

1) Greater efficiency of metabolism as enzymes and substrates are enclosed, and therefore much more concentrated, in the particular organelles responsible for specific functions.
2) Internal conditions such as pH can be differentiated in a cell to maintain the optimal conditions for different enzymes.
3) Isolation of toxic or damaging substances away from the cytoplasm, such as the storage of hydrolytic enzymes in lysosomes.
4) Flexibility of changing the numbers and position of organelles within the cell based on the cell’s requirements.

27
Q

Eukaryotic cells can be observed using a ___

A
  • Light microscope.
  • At this magnification, only larger structures such as cell membrane, cell wall, nucleus, central vacuole, and chloroplasts can be seen.
28
Q

What is used for a detailed view of eukaryotic cells?

A
  • An electron microscope is usually used.

- This allows the finer subcellular structures to be seen more clearly.

29
Q

Diagram of the ultrastructure of a eukaryotic cell- an animal cell.

A
30
Q

Diagram of the ultrastructure of a eukaryotic cell- a plant cell

A
31
Q

Cellular structures in plant and animal cells (eukaryotic cells)

A

1) Plasma membrane
2) Cytoplasm
3) Mitochondria (singular: mitochondrion)
4) 80S ribosomes
5) Nucleus
6) Nucleolus
7) Smooth endoplasmic reticulum
8) Rough endoplasmic reticulum
9) Golgi apparatus
10) Vesicle
11) Lysosomes (absent from plant cells)
12) Centrioles (absent from plant cells)
13) Vacuole
14) Cell wall (absent from animal cells)
15) Chloroplast (absent from animal cells)

32
Q

(Eukaryotic cells) Function of plasma membrane

A

Controls the movement of substances in and out of the cell.

33
Q

(Eukaryotic cells) Function of cytoplasm

A
  • Fills the cell and holds all organelles.

- It also contains enzymes that catalyze various reactions (such as glycolysis) occurring within the cytoplasm.

34
Q

(Eukaryotic cells) Function of mitochondria

A

A site of cellular respiration in which ATP is generated.

35
Q

(Eukaryotic cells) Function of 80S ribosomes

A

The sites of protein synthesis. Free ribosomes produce proteins used inside the cell itself.

36
Q

(Eukaryotic cells) Function of nucleus

A

Controls all the activities of the cell, as well as the reproduction of unicellular organisms.

37
Q

(Eukaryotic cells) Function of nucleolus

A

Part of the nucleus which is involved in the production of ribosomes.

38
Q

(Eukaryotic cells) Function of smooth endoplasmic reticulum

A

Responsible for producing and storing lipids, including steroids.

39
Q

(Eukaryotic cells) Function of rough endoplasmic reticulum

A

Transports the protein produced by the ribosomes on its surface to the Golgi apparatus. These proteins are usually for use outside of the cell.

40
Q

(Eukaryotic cells) Function of Golgi apparatus

A

Processes and packages proteins, which are ultimately released in Golgi vesicles.

41
Q

(Eukaryotic cell) Function of vesicle

A

A small sac that transports and releases substances produced by the cell by fusing with the cell membrane.

42
Q

(Eukaryotic cell) Function of lysosomes

A

Contain hydrolytic enzymes and play important roles in the destruction of microbes engulfed by white blood cells, as well as in the destruction of old cellular organelles.

43
Q

(Eukaryotic cell) Function of centrioles

A

Play an important role in the process of nuclear division by helping to establish the microtubules.

44
Q

(Eukaryotic cell) Function of vacuole

A
  • Helps in the osmotic balance of the cell and in the storage of substances.
  • It may also have hydrolytic functions similar to lysosomes.
45
Q

(Eukaryotic cell) Function of cell wall

A

Protects the cell, maintains its shape, and prevents it from bursting in hypotonic media.

46
Q

(Eukaryotic cell) Function of chloroplast

A

These are double-membrane-bound organelles. They contain pigments (in this case mainly chlorophyll) and are responsible for photosynthesis.

47
Q

Diagram of exocrine cell from the pancreas (an animal cell)

A
48
Q

Exocrine gland cell from the pancreas (animal cell)

A
  • An exocrine gland secretes enzymes into a duct.
  • In the case of the exocrine cell from the pancreas, it secretes digestive enzymes via the pancreatic duct into the small intestine, where they aid the digestion of food.
  • Since enzymes are proteins, exocrine cells will have a well-developed network of rough endoplasmic reticulum for protein synthesis, as well as Golgi apparatus that produce vesicles containing these enzymes.
  • The vesicles merge with the plasma membrane to release their content into the small intestine.
49
Q

Diagram of palisade mesophyll cell

A
50
Q

Palisade mesophyll cell

A
  • Contains many chloroplasts.
  • These organelles are the site of photosynthesis.
  • In plants, the palisade mesophyll tissue contains the greatest number of chloroplasts per cell and is positioned right under the upper epidermis where it is exposed to the highest amount of light.
  • The main function of the palisade mesophyll cells is to photosynthesize; producing complex organic compounds, using carbon dioxide and water as starting materials.
51
Q

How to interpret electron micrographs to identify organelles and deduce the function of specialized cells.

A
  • If the cell has many mitochondria, for example, then that cell has a large energy requirement.
  • A cell with a dense network of rough endoplasmic reticulum and numerous bound ribosomes will be producing many proteins for use out of the cell.
52
Q

Define microscope resolution

A

Microscope resolution is the shortest distance between two separate points in a microscope’s field of view that can still be distinguished as distinct objects.

53
Q

Electron microscopes vs. light microscopes

A
  • Electron microscopes have a much higher resolution than light microscopes.
  • The resolution of a light microscope is 200 nm compared to 0.1 nm for an electron microscope.
  • This means that if two points are 100 nm apart, they will not be well-defined and their positions will be unclear when viewed using a light microscope, but they will appear much clearer under an electron microscope.
54
Q

Low-resolution image vs. high-resolution image

A
55
Q

The higher the value, the ___ the resolution.

A

Lower.

E.g. a resolution of 0.1nm is higher than a resolution of 200nm.

56
Q

Magnification of electron vs. light microscopes.

A
  • An electron microscope can magnify very small objects by about 500,000 times which makes them suitable for studying small cellular structures, as well as disease-causing particles, such as prions (abnormally folded proteins can cause diseases) and viruses.
  • However, a light microscope with a magnification of about 2,000 times remains a useful way to study tissues and living cells as it allows observation of living organisms in colour.
  • Additionally, light microscopes can be used to observe living specimens.
  • In contrast, an electron microscope can be used to observe non-living or dead specimens in black and white.
57
Q

Why is an electron microscope better than the light microscope for observing viruses?

A

An electron microscope has a higher resolution than a light microscope.

58
Q

What is the advantage of using a light microscope compared to using an electron microscope?

A
  • It allows observing living specimens.
  • Electron microscopes can be used to study subcellular structures in great detail e.g. membranes or organelles, but importantly, they must be dead before imaging.
59
Q

What type of DNA replication takes place during binary fission?

A

Asexual

60
Q

What type of DNA replication takes place during binary fission?

A

Semi-conservative

61
Q

Lysosomes are often absent from plant cells and so a different organelle will take on the role of the lysosome.

State the name of the plant cell organelle that is capable of doing this role.

A

Vacuole

62
Q

The smooth endoplasmic reticulum is responsible for the synthesis and storage of ___

A

Lipids

63
Q

The smooth endoplasmic reticulum is responsible for the synthesis and storage of ___

A

Lipids

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