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Crypt A level Biology > Module 2: Cell Structure > Flashcards

Module 2: Cell Structure Flashcards

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1
Q

Define magnification

A

The degree to which the image size is larger than the object itself.

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2
Q

Define resolution

A

The ability to distinguish between two separate points close together, in detail.

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3
Q

Describe how light microscopes work

A

The objective lens placed near the specimen produces a magnified image. This is further magnified by the eye-piece lens. The combination of both reduces chromatic aberration. Illumination is provided by a light under the stage and specimen.

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4
Q

What is the maximum magnification and resolution which can be achieved by a light microscope?

A 
Magnification = x1500
Resolution = 0.2 um
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5
Q

What are the advantages of a light microscope?

A

Cheap, portable, can use live specimens, and stains can be used.

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6
Q

What are the disadvantages of light microscopes?

A

Lower magnification and resolution, meaning only small sub-cellular organelles are visible.

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7
Q

Describe how a laser scanning confocal microscope works

A

A laser beam is focussed through a lens and aimed at a beam splitter. The beam is split and some of the light is directed onto the specimen. The laser hits the specimen (tagged with fluorescent dyes), and a fluorescent light is given off. This light is then forced through a pinhole onto a detector. An image is produced on a computer.

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8
Q

What is the maximum resolution that can be achieved with a laser scanning microscope?

A

180nm

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9
Q

Give some advantages of a laser scanning microscope

A

Can produce 3D images, and can view specimen at different depths.
Use of a pinhole aperture so unfocused light is blocked.

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10
Q

Give some disadvantages of a laser scanning microscope

A

Lower resolution than electron microscopes.

Time consuming and expensive.

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11
Q

Describe how transmission electron microscopes (TEM) work

A

A beam of electrons is transmitted through the specimen to produce a 2D image. Denser parts of the specimen absorb more electrons, making the image look darker.

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12
Q

What is the maximum magnification and resolution that can be achieved with a TEM?

A 
Magnification = x500 000
Resolution = 0.5nm
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13
Q

Give some advantages of TEM

A

Higher resolution and magnification. Used to look at the ultra structure of internal organelles. Shows more detail.

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14
Q

Give some disadvantages of TEM

A

Only show 2D images, very expensive to use and set up, can only use dead specimens (to prevent artefacts forming) and colour must be added.

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15
Q

Describe how scanning electron microscopes (SEM) work

A

A beam of electrons is scanned across the surface of the specimen. This knocks off any electrons from the specimen, which gather in a cathode ray tube to form an image. This is connected to a computer to view the image.

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16
Q

What is the maximum magnification and resolution of a SEM?

A 
Magnification = x500 000
Resolution = 3-10nm
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17
Q

Give some advantages of a SEM

A

High resolution and magnification, can show 3D images, and show greater detail of the cell ultrastructure.

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18
Q

Give some disadvantages of a SEM

A

Very expensive, only use dead specimens, lower resolution than TEM, and colour must be added.

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19
Q

Why do electron microscopes have a higher resolution?

A

Electrons have a shorter wavelength, meaning a clearer image is produced. Light microscopes use visible light which has a longer wavelength, so lower resolution.

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20
Q

How is magnification calculated?

A

Magnification = image size / actual size

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21
Q

What units should magnification measurements always be in to calculate?

A

Millimetres

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22
Q

Why are stains used on specimen?

A

This adds contrast to the image, allowing greater detail of the ultrastructure to be viewed.

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23
Q

Give some example of stains, and the specimens they highlight

A

Acetic orcein = binds to DNA and stains chromosomes dark red.
Eosin = stains cytoplasm.
Sudan red = stains lipids.
Iodine = stains cell walls in plants yellow and starch granules blue/black.

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24
Q

What is an artefact, and how do they form?

A

Visible structural detail caused by processing the specimen. This is not a feature of the specimen. Appear in both light and electron microscopes. An example is an air bubble under a cover slip in the preparation of the specimen with light microscopes.

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25
Q

How are changes in the ultrastructure of cells seen as in electron microscopes?

A

Loss of continuity in membranes, distortion of organelles and empty spaces in the cytoplasm of cells.

26
Q

What are the two types of cell?

A

Eukaryote and prokaryote

27
Q

What does metabolism involve?

A

Both the synthesis and breaking down of molecules.

28
Q

How is the cytoplasm divided?

A

Into membrane-bound compartments known as organelles.

29
Q

How are organelles beneficial?

A

Provide distinct environments and conditions for different cellular reactions.

30
Q

What is the structure and function of the plasma membrane?

A

Comprised of a phospholipid bilayer. 7nm thick. Fragile.

Selectively permeable to control the movement of substances in and out of the cell and organelles.

31
Q

Describe the nucleus

A

In animals and plants.
Surrounded by a double membrane (nuclear envelope) with nuclear pores. Contains the nucleolus.
Stores DNA as chromatin (chromosomes). Coordinates the cells activities e.g. metabolism, growth, protein synthesis etc.

32
Q

What is the function of nuclear pores?

A

Allow molecules to move in and out of the nucleus (cell communication). E.g. RNA

33
Q

How is DNA arranged in the nucleus of eukaryotic cells?

A

Associated with histone proteins to form a complex called chromatin. This is coiled and condensed into chromosomes.

34
Q

What is the function of the nucleolus?

A

Responsible for the production of ribosomes. Composed of proteins and RNA. Ribosomes produced from rRNA. This is combined with proteins.

35
Q

Describe mitochondria

A

In animals and plants.
Surrounded by a double membrane which is semi-autonomous. Some organism lack them. The inner membrane is folded to form cristae and the fluid interior is called the matrix.
Generate chemical energy needed to power the cell’s biochemical reactions. Energy produced is stored as ATP and used for aerobic respiration.

36
Q

Describe ribosomes

A

In eukaryotes and prokaryotes.
Sphere shaped structure composed of RNA and proteins. Free in the cytoplasm and often attached to the RER.
Protein synthesis in decoding mRNA and the formation of peptide bonds.

37
Q

Describe vesicles

A

Membranous sacs that have storage and transport roles. Consist of a single membrane with fluid inside. Used to transport materials inside the cell, as well as outside the cell in exocytosis.

38
Q

Describe lysosomes

A

Specialised forms of vesicles containing hydrolysis enzymes. Responsible for the breaking down of waste material in cells, including old organelles.

39
Q

Describe centrioles

A

In animals, and sometimes plants.
Cylindrical organelle composed of tubulin. Has a 9:2 arrangement.
Produces cilia during interphase and the aster and spindle fibers during mitosis.

40
Q

Describe rough endoplasmic reticulum

A

In animals and plants.
Series of connected flattened sacs covered in ribosomes, in the cytoplasm. Called cisternae. Main role is protein synthesis, producing essential proteins for bodily function e.g. secretory and membrane proteins. Metabolises carbohydrates.

41
Q

Describe smooth endoplasmic reticulum

A

In animals and plants.
Meshwork of fine disc-like tubular membranous vesicles - flattered sacs called cisternae. No ribosomes. Part of a continuous membrane organelle.
Synthesis of lipids and steroid hormones. Detoxification of harmful metabolic byproducts, and storage and metabolism of calcium ions.

42
Q

Describe chloroplasts

A

In plants only.
Double membrane structure. Fluid enclosed in chloroplast in stroma. Internal network of membranes (flattened sacs) called thylakoids. These, when stacked are called granum (contain chlorophyll in a high concentration, giving plants a green pigment.)
Site of photosynthesis, where energy from the sun is converted into glucose and oxygen. Used for growth, respiration etc.

43
Q

Describe Golgi apparatus

A

In animals and plants.
Complex of vesicles and folded membranes, in the cytoplasm, known as cisternae.
Modifies proteins, by adding carbohydrates and lipids. These are packaged into vesicles, which may be secretory vesicles. Also produce lysosomes.

44
Q

Describe the cell wall

A

In plants and prokaryotes.
Made of cellulose in plants, and peptidoglycan in prokaryotes.
Provides tensile strength and protection from osmotic strength. Creates turgor pressure in plants, and provides shape in prokaryotes.

45
Q

Describe cytoplasm

A

In eukaryotes and prokaryotes.
Solution composed of water, salts and proteins. All enclosed by the plasma membrane.
Acts as a buffer and protects the genetic material of the cell and sub-cellular organelles from damage from movement and collisions.

46
Q

Describe vacuole

A

Only in plants.
Closed sacs made of membranes with inorganic and organic molecules like enzymes. Can change shape and be temporary. Surrounded by a membrane called the tonoplast.
Used for turgor pressure in plants. Stores water, nutrients and waste material of the cell. Supports growth, and protect the cell in plants.

47
Q

How is genetic material arranged in eukaryotes and prokaryotes?

A

‘Naked’ DNA in prokaryotes. Not associated with proteins, lipids, or any other molecules to protect it.
DNA is in chromosomes and associated with histone protein in eukaryotes. This is linear and bound in a nucleus.

48
Q

What are average cell diameters in eukaryotes and prokaryotes?

A

0.5-5µm in prokaryotes

10-100µm in eukaryotes

49
Q

What are the sizes of ribosomes in eukaryotes and prokaryotes?

A

70S of 18nm in prokaryotes

80S of 22nm in eukaryotes

50
Q

What is the function of the nucleiod (chromosomal DNA) in bacteria?

A

Irregularly shaped region of cytoplasm that contains all or most of the DNA.

51
Q

What is the function of plasmids (bacteria)?

A

Autonomous circular DNA that may be transferred between bacteria (horizontal gene transfer).

52
Q

What is the function of the cell wall in bacteria?

A

Rigid peptidoglycan covering maintaining shape and prevents bursting (lysis).

53
Q

What is the function of the slim capsule in bacteria?

A

Polysaccharide layer used for protection against desiccation (drying out) and phagocytosis.

54
Q

What is the function of the flagella in bacteria?

A

Projection containing a motor protein to enable movement.

55
Q

What is the function of pili in bacteria?

A

Hair like extensions that enable adherence to surfaces or mediate bacterial conjugation.

56
Q

What is the cell wall made of in fungi?

A

Chitin

57
Q

Describe the process of protein production

A

DNA is transcribed and forms a single strand of RNA. This is able to leave the nucleus via the nuclear pore, into either the cytoplasm or to the rough endoplasmic reticulum.
From here the proteins produced in translation (protein synthesis) move to the cis face of the Golgi apparatus in transport vesicles, via the cytoskeleton.
Modified to form glycoproteins (carbs) and lipoproteins (lipids) or enzymes etc. Leave from the trans face after being packaged into vesicles.
Transported to the plasma membrane by the cytoskeleton, where the vesicles fuse.
Exocytosis takes place and the vesicles leave the cell (secretory vesicles). Other remain in the cell, e.g. lysosomes.

58
Q

What are microfilaments?

A

Contractile fibres from the protein actin. Responsible for cell movement and cell contraction during cytokinesis.

59
Q

What are intermediate fibres?

A

Provide mechanical strength to cells, and help maintain integrity.

60
Q

What are microtubules?

A

Globular tubulin proteins polymerise to form tubes that are used to form a scaffold-like structure to determine the shape of the cell. Also pathways for the movement of organelles, like vesicles. Composition of spindle fibres, used to segregate chromosomes in mitosis.

61
Q

What is the function of the cytoskeleton?

A

Network of fibres for the shape and stability of a cell. Also help with the movement of organelles within cells, and provide mechanical strength.

Crypt A level Biology (8 decks)

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