Cell Structure Flashcards
0
Q
What is the total magnification?
A
The power of the objective lense multiplied by the power of the eyepiece lense.
1
Q
How does a light microscope work?
A
By projecting light through a specimen, then by focusing it with a series of lenses to magnify the image.
2
Q
What is magnification?
A
How much larger an image appears than an object actually is.
3
Q
What magnification are light microscopes capable of?
A
x1500
4
Q
Why won’t further increasing the magnification be useful in seeing more detail?
A
There may be limits of resolution of light.
5
Q
What is resolution?
A
The ability to distinguish between 2 separate points.
6
Q
What does increasing the resolution allow you to do?
A
See in more detail.
7
Q
How do you work out the magnification?
A
Size of image / actual size of specimen
8
Q
What is one disadvantage of light microscopes?
A
The limit of its resolution is 200nm, anything smaller than this cannot be resolved from its background.
9
Q
What are the advantages of light microscopes?
A
- Relatively cheap
- Living organisms can be viewed
- Thin sections of larger specimens can be studied
10
Q
Why might slides be stained?
A
Slides are stained by chemicals which bind to chemicals in the specimen to allow them to be seen. Some stains bind to specific cell structures e.g. Gentain violet stains bacterial cell walls.
11
Q
How do Electron Microscopes work?
A
They generate a beam of electrons with a wavelength 100,000 times smaller than that of light.
12
Q
What is the maximum resolution of Electron Microscopes? What does this allow for?
A
The maximum resolution is 0.2nm which allows much smaller structures to be seen.
13
Q
How is the beam focused in an Electron Microscope?
A
With a series of magnets.
14
Q
How does a Transmission Electron Microscope work?
A
Passes the beam of electrons through a prepared sample.
15
Q
What type of image does a TEM produce?
A
2D
16
Q
What is the maximum magnification if a TEM?
A
x500,000
17
Q
How does a Scanning Electron Microscope work?
A
Bounces the electron beam off the sample.
18
Q
What type of image does an SEM produce?
A
3D
19
Q
What is the maximum magnification of an SEM?
A
x100,000
20
Q
What are the advantages of Electron Microscopes?
A
- Much higher magnification than light microscope
- Much greater resolution than light microscopes
- Colour can be added later by computer software, producing false-colour micrograph which are easy to study.
21
Q
What are the disadvantages of Electron Microscopes?
A
- Electron beams are stopped by air and water molecules, so the specimens must be dried out (killed) and placed in a vacuum
- Very expensive and difficult to prepare specimens for - often damage specimens in the process
22
Q
What does cell theory state?
A
- All living things consist of cells
- New cells can only be formed from the division of pre-existing cells
- All cells contain information that instructs for the growth of that cell
23
Q
What is the maximum resolution of Light Microscopes?
A
200nm
24
Describe the Nucleus and state its structure, function and size.
Description: Major cell organelle containing chromatin (DNA and histones).
Structure: The largest organelle surrounded by a nuclear envelope with chromatin and a nucleolus inside.
Function: Houses nearly all the cell's DNA - carries hereditary information. Regulates cell activity.
Size: 20 micrometer diameter.
25
Describe the Nucleolus and state its structure, function and size.
Description: Specialised region of the nucleus, not surrounded by a membrane.
Structure: A dense, spherical structure.
Function: The synthesis of RNA and ribosomes which then pass into the cytoplasm and proteins are assembled at them.
Size: 2 micrometer diameter.
26
Describe the Nucleus Envelope and state its structure, function and size.
Description: Paired (double) membrane surrounding the nucleus. Has nuclear pores.
Structure: Two membranes with fluid between them. A lot of holes called nuclear pores which go right through the envelope. These holes are large enough for relatively large molecules to pass through.
Function: Regulates exchange between nucleus and cytoplasm. Some protein synthesis (when continues into Rough ER.
Size: 2 x 10 nm
27
Describe Rough Endoplasmic Reticulum and state its structure, function and size.
Description: Intercellular membrane system, encrusted with ribosomes. Often found close to nucleus.
Structure: A series of flattened, membrane-bound sacs called cisternae. Rough ER is studded with ribosomes.
Function: Synthesis of proteins for transport. Intracellular transport.
Size: Variable
28
Describe Smooth Endoplasmic Reticulum and state its structure, function and size.
Description: Intracellular membrane system without ribosomes.
Structure: A series of unflattened, membrane-bound sacs called cisternae. They do not have ribosomes.
Function: Synthesis of lipids including steroids.
Size: Variable.
29
Describe the Golgi Apparatus and state its structure, function and size.
Description: Specialised Smooth ER, forming a stack of disk shaped cavities (disternae).
Structure: A stack of membrane-bound, flattened sacs.
Function: Modification and packaging of molecules such as glycoproteins, polysaccharides, hormones. The production of lysosomes.
Size: Variable
30
Describe Ribosomes and state their structure, function and size.
Description: Small, complex structures. Either attached to Rough ER or free in cytoplasm.
Structure: Tiny organelles formed of two subunits.
Function: Synthesis of proteins. They act as an assembly line where coded information (mRNA) from the nucleus is used to assemble proteins from amino acids.
Size: 25nm diameter.
31
Describe Mitochondria and state its structure, function and size.
Description: Double membrane organelle containing enzymes on their surfaces for aerobic respiration.
Structure: Spherical or sausage-shaped. They have two membranes separated by a fluid-filled space. The inner membrane is highly folded to form cristae. The central part of the mitochondrion is called the matrix.
Function: Carries out aerobic respiration to produce ATP.
Size: 2-5 micrometer diameter.
32
Describe Lysosomes and state their structure, function and size.
Description: Spherical membrane bound vesicles containing enzymes.
Structure: Spherical sacs surrounded by a single membrane.
Function: Carries out intracellular digestion. Their role is to break down material.
Size: 50nm diameter.
33
Describe Chloroplasts and state their function and size.
Description: Plant cell organelle with double membrane.
Function: Carries out photosynthesis.
Size: 4-10 micrometers across.
34
Describe Plasma Membrane and state its function and size.
Description: Surrounds cell. Has a fluid mosaic structure.
Function: Selective barrier, retaining cell contents.
Size: 7-10nm thick.
35
State the structure and function of Centrioles.
Structure: Small tubes of protein fibres (microtubules). There is a pair of them next to the nucleus in animal cells and in the cells of some protoctists.
Function: Take part in cell division. They form fibres, known as the spindle, which move chromosomes during nuclear division.
36
Describe Flagella and state its function.
Description: Hair-like extensions that stick out from the surface of the cells. Each one is made up of a cylinder that contains nine microtubules arranged in a circle. There are also two microtubules in a central bundle.
Function: Allows the cell to move e.g. Sperm cells move due to the long, whip-like undulipodium (flagella) which moves the whole cell.
37
Describe Cilia and state its function and size.
Description: Shorter structure of Flagella.
Function: Moving the cell e.g. In ciliated epithelial tissues, the sweeping movements of the cilia move substances such as mucus across the surface of the cells.
Size: less than 10um.
37
Outline the interrelationship between the organelles involved in the production and secretion of proteins.
A gene from the chromatin in the nucleus is copied into mRNA. This is called transcription. This copy then passes out of the nuclear pore into the cytosol and to one of the ribosomes (either located in the RER or the cytoplasm). The mRNA is then 'read' and the instructions are translated into a polypeptide chain. The next stage is Post-Translation Modification and it involves finishing the final protein. This can be done by adding sugars to create glycoproteins etc. This is done in the Golgi Apparatus, and it travels to fuse with Golgi in a membrane bound vehicle that is pinched off from the ER. The protein then travels off in another vesicle, either to another part of the cell or fuses with the cell surface membrane to secrete the protein.
38
Explain the importance of the cytoskeleton in providing mechanical strength to cells, aiding transport within cells and enabling cell movement.
The cytoskeleton is a network of protein fibres which gives the cell stability by providing mechanical strength and allows it to move. It provides an internal framework for the cell, preserving its shape and holding the organelles in position.
39
Compare and contrast, with the aid of diagrams and electron micrographs, the structure of prokaryotic cells and eukaryotic cells.
Prokaryotic cells:
- DNA is circular
- Small cells (less than 2um across)
- Small Ribosomes
- No nucleus (DNA is free in the cytoplasm)
- Cell wall made polysaccharide, not cellulose or chitin
- Few organelles, no mitochondria
- Photosynthesis (if carried out) is on a mesosome
- Has pili for adhesion
- Has plasmids
- No internal plasma membranes
Eukaryotic cells:
- DNA is linear
- Larger cells (2-200um)
- Larger Ribosomes
- Nucleus present (DNA inside nucleus)
- No cell wall in animals, cellulose wall in plants and chitin wall in fungi
- Many organelles, mitochondria present
- Photosynthesis (if carried out) is in chloroplast
- Has glycoproteins and glycolipids for adhesion
- Does not have plasmids
- Has internal plasma membranes
40
Compare and contrast, with the aid of diagrams and electron micrographs, the structure and ultrastructure of plant cells and animal cells.
Plants:
- Has chloroplasts
- Cellulose cell wall
- Has a tonoplast surrounding a permanent vacuole filled with cell sap
- Has plasmodesmata with a middle lamella between cell walls of different cells
- Does not have centrioles
- Does not have lysosomes
Animals:
- Doesn't have chloroplasts
- No cell wall
- Has temporary vacuoles
- Does not have plasmodesmata or lamella
- Has centrioles
- Has lysosomes
