Cell Structure Flashcards
1. Cells and Organelles 2. Organelles Working Together 3. Prokaryotic Cells 4. How Microscopes Work 5. Using Microscopes
1
Q
What is the development of cell theory?
A
- Cells are the basic unit of all life
- Both plant and animal tissue is made up of cells
- Cells develop from existing cells
2
Q
Importance of microscope study of living organisms
A
- The idea that organelles need to be seen to determine their function
- Most cells and cell components are too small to see without microscope
3
Q
Why wasn’t cell theory fully developed before the mid 19th century?
A
Their microscopes were of low magnification to see and identify cells and cell components
4
Q
How does a light microscope produce image?
A
It uses a beam of light to produce an image. The light passes through the specimen and is focused through glass lenses which project a magnified image
5
Q
What is the maximum resolution and magnification of a light microscope?
A
Resolution - 200 nm
Magnification - x 500
6
Q
What are the 4 sample preparation techniques used by light microscope?
A
- Dry mount
- Wet mount
- Squash slides
- Smear slides
7
Q
Describe a dry mount
A
The specimen is viewed either whole or cut into thin slices by a sharp knife (microtome) and the specimen is then placed at the centre of the slide and a cover slip is placed on it.
8
Q
What specimens can be viewed using dry mount?
A
Hair, pollen, dust and insect parts
9
Q
Describe the wet mount
A
A sample is suspended in either water or immersion oil and placed on a slide. A cover slip is then placed on top at an angle (45 °)
10
Q
What specimens can be viewed this way?
A
Aquatic animals eg daphnia
11
Q
Describe the squash slides
A
A wet mount is first prepared, and a lens tissue is used to gently press down the cover slip.
12
Q
What can be done to prevent damage to the cover slip?
A
The specimen can be squashed between two microscope slides
13
Q
What specimen can be viewed this way?
A
Root tip squashes
14
Q
Describe the smear slide
A
The edge of a slide is used to smear a sample by creating a thin, even coating on another slide
15
Q
What specimen can be viewed this way?
A
Blood samples
16
Q
Things to consider when producing slides
A
- The specimen must be thin to allow light pass through it and details can be seen
- The refractive index of the sample should be similar to the glass slide to prevent distortion of the image
- A cover slip must be placed onto a wet mount at an angle to prevent air bubbles being trapped
17
Q
Why are stains used when preparing samples?
A
Stains increase contrasts as different components take up stains to different degrees
Stains are also used to make components of specimens visible so that they can be identified
18
Q
Why are differential staining used?
A
- It is used to distinguish between different organisms that would be difficult to identify
- It is used to differentiate between different organelles of a simple organism within a tissue sample
19
Q
What is the Gram stain technique?
A
It is used to separate bacteria into 2 groups: Gram positive and Gram negative
20
Q
Describe the Gram stain process
A
A bacterial cell is placed onto a slide and crystal violet stain is first added. Iodine is then added and alcohol is followed to decolourise
21
Q
What is the result for the technique?
A
Gram positive - The bacterial cell will appear purple or blue because the cell wall retained the stain
Gram negative- Their cell wall is too thin and so it will lose the stain. Safranin dye(a counterstain) is then added to the cell making it appear pink or red
22
Q
What are the stages involved in production of pre-prepared slides?
A
Fixing- Chemicals are used to preserve the specimens in as near-natural a state as possible
Sectioning- specimens are dehydrated with alcohol and then placed in a mould of wax and resin forming a hard block. it is then thinly sliced with a sharp knife (called a microtome)
Staining- specimens are treated with different stains to show different structures
Mounting- the specimen is placed on a microscope slide and a cover slip is placed on top.
23
Q
What are some rules of biological drawing?
A
- Draw straight, continuous lines
- Do not shade
- Label lines should be parallel to the top of the page and drawn with a ruler
- Drawing must be half a page
- Include the title and magnification
- Annotate the diagram if possible
24
Q
What is magnification?
A
It is how many times larger the image size is than the actual size of the specimen
25
What is resolution?
It is the ability to distinguish between two different objects as separate
26
How to find the actual size if scale bar is provided?
image length/bar length * bar scale
27
Equation for Magnification
Magnification=image size/actual size
28
Explain how diffraction limits resolution (5 marks)
Diffraction happens when light passes through structures (1). the light waves spread out (1) and overlap (1) and so the individual objects do not appear separate (1) causes blurring (1)
29
How does an EM produce image?
An electron gun fires electrons through a vacuum to prevent the electrons from bouncing off the molecules of air
30
What is an advantage of an EM?
It has a higher resolution and better magnification than a LM
31
What are some disadvantages of EM?
1. Living specimens cannot be viewed as they need air to breathe which an EM doesn't have
2. Artefacts are produced which is caused by more sample preparation which leads to damage in specimen
3. It requires careful staining and specimen has to be thin
32
Types of EM
Transmission EM
Scanning EM
33
How does TEM produce images?
The electron beam passes through the specimen
34
Advantage of TEM
Has a higher resolution of 0.5nm than a SEM
35
Disadvantages of TEM
It produces a 2D image and the specimen has to be thinly sliced
36
How does SEM produce image?
The electrons are scattered across the surface of the specimen and are detected
37
Advantage of SEM
Produced 3D image
38
Disadvantages of SEM
It has a lower resolution of 3-10 nm and magnification than TEM
39
Explain why you would see more details with an electron microscope than with a LM (2 marks)
An EM uses electrons which have a shorter wavelength than light (1) and produces an image with higher resolution (1)
40
Define the term artefacts with reference to microscopy (2 marks)
Artefacts are visible objects (1) present in an EM because of sample preparation (1)
41
Explain why artefacts are more likely to be produced when preparing samples for EM than for LM (3 marks)
Artefacts are more likely to be produced for an EM because more sample preparations (1) leads to more damage in specimens (1) which results in artefacts (1)
42
What is the function of the nucleus?
It contains coded genetic information in the form of DNA, which directs the synthesis of proteins needed by all cells in the body
43
What is the structure of the Nucleus?
1. It has a double membrane which is known as the "nuclear envelope"
2. It also has a substance known as "nucleoplasm" which contains molecules like nucleotide or enzymes that are needed in RNA and DNA synthesis.
3. It also has chromatin which is DNA wrapped around proteins called histones which condense to form chromosomes.
44
What is the function of the nucleolus?
It produced Ribosomal RNA (rRNA) which is combined with proteins to make Ribosomes
45
What is the function of the nuclear envelope?
1. It protects the nucleus from damage in the cytoplasm
2. It also has nuclear pores which controls what enters or leaves the nucleus into the cytoplasm.
46
What is the function of the Mitochondria?
1. It releases energy from aerobic respiration in the form of ATP
2. It is also the site for the last two stages involved in respiration; (The Krebs cycle and the oxidative phosphorylation)
47
What is the structure of the Mitochondria?
1. It has a double membrane which is known as the "inner mitochondrial membrane", and the "outer mitochondrial membrane" (Also has intermembrane space in between the two membranes)
2. The inner membrane is folded and the folds are called "cristae"
3. The Mitochondria also has a fluid which is known as "matrix"
4. It also has its own DNA and ribosomes which are known as "mitochondrial DNA" and "mitochondrial ribosomes"
48
What is the function of the "matrix"?
It contains enzymes that are used in the "Krebs Cycle"
49
What is the function of the cristea?
It provides a large SA for the enzymes that are needed in "oxidative phosphorylation"
50
What is the function of the Mitochondrial ribosomes?
It is responsible for synthesizing the proteins encoded in the mitochondrial DNA
51
What is the structure of the Endoplasmic Reticulum
It is a network of flattened membrane bound sacs known as cisternae
It is connected to the outer membrane of the nucleus
52
What is the structure of the RER?
1. It has ribosomes studded on the outer membrane
2. The cisternae are connected together
53
What is the function of the RER?
It is responsible for the synthesis and transport of proteins
54
What is the structure of the SER?
1. It does NOT have ribosomes studded on it's outer memrane
2. Its cisternae are also connected together
55
What is the function of the SER?
It is responsible for synthesizing and storing lipids and carbohydrates
56
What is the structure of the Golgi Apparatus?
1. It also does NOT have ribosomes studded to it
2. Its cisternae are NOT connected together
57
What is the function of the Golgi Apparatus?
It is responsible for modifying and packaging proteins into vesicles
58
What is the structure of the Ribosomes?
1. It does NOT have a membrane
2. It is constructed of RNA molecules that are made in the nucleolus of the cell
3. It attaches to the ER, which forms RER
59
What is the function of the Ribosomes?
It is the site of protein synthesis
60
What are Lysosomes?
They are specialized vesicles that contain hydrolytic enzymes
61
What are the features of lysosomes?
1. The internal fluid of a lysosome is acidic
2. They contain digestive enzymes which break down larger molecules into smaller soluble molecules
62
What are the functions of lysosomes?
1. They play a big role in digesting pathogens that are ingested by phagocytic cells
2. They transfer their enzymes outside of the cell through exocytosis
3. They also destroy organelles that are damaged or no longer useful
63
Difference between cristae and cisternae
Cristae is the fold of the inner mitochondrial membrane while cisternae is a flattened membrane bound sac
64
What are some additional organelles that are found in plant cells?
Amyloplasts containing starch grains
Permanent vacuole
Cell wall
Chloroplasts
65
Describe the structure of the chloroplasts
1. It has a double membrane
2. Inside, it has flattened membrane discs known as thylakoids
3. the thylakoids are stacked and this is known as granum
4. Thylakoids are connected to different grana by a flattened membrane known as lamellae
5. The chloroplast also has a fluid known as stroma
6. The chloroplast has its own loop of DNA and ribosomes
66
What is the function of the thylakoids?
It is where light dependent reaction takes place
It contains chlorophyll and enzymes needed for the reaction
67
What is the function of the lamellae?
It allows chemicals to be transferred between the grana
It also plays a role in light dependent reactions
68
What is the function of the stroma?
It is where light independent reactions take place
69
What is the function of the chloroplast?
It is the site of photosynthesis
70
Describe the structure of the vacuole?
1. It is surrounded by a membrane known as the tonoplast
2. It also contains a fluid called the cell sap
71
What is the function of the tonoplast?
It controls what chemicals enter or leave the vacuole
72
What is the function of the vacuole?
It provides turgidity which helps to support the plant
73
What is the structure of the cell wall?
1. It is made up of cellulose
2. It also has pores known as plasmodesmata which connect two cells together by the cytoplasm
74
What is the function of the plasmodesmata?
It enables the exchange and transport of substances
75
What is the function of the cell wall?
It provides shape and rigidity
76
What is the cytoskeleton made up of?
It is made up of micro-filament, intermediate fibres, and micro tubules
77
What protein is the micro-filament made of?
Actin
78
What is the structure of the micro-filament
The actin forms two intertwined strands
79
What is the function of the micro-filament?
1 Motility
2. Maintains cell shape
3. Cytokineses of cell division
80
What is the structure of the intermediate fibres?
Fibres wound into thicker cables
81
What protein is the intermediate fibres made of?
Fibrous proteins eg keratin
82
What is the function of intermediate fibres?
1. Maintains cell shape
2. Anchors the nucleus and organelles
83
What protein are the micro-tubules made of?
Tubulin protein
84
What is the structure of the micro-tubules?
Hollow tubes
85
What is the function of the micro-tubules?
1. Maintains cell shape
2. Involved in the formation of spindle fibres that is involved in the movement of chromosomes during cell division
3. Moving organelles
86
Describe the structure and function of the cytoskeleton (5 marks)
Microfilaments(1) are contractile fibres made of actin that bring about cell movement during cytokinesis (1). Microtubules(1) are formed from the cylindrical protein tubulin and form scaffold-like structures used as spindle fibres in the segregation of chromosomes in cell division (1). Intermediate fibres give mechanical strength to cells (1)
87
What is the structure of centrioles?
It is made up of nine microtubules that are found near the nucleus
88
What is a pair of centrioles called?
Centrosomes and they lie at right angle to each other
89
What is the function of the centrioles?
1. Making of cilia and flagella
2. Assembling of spindle fibres during cell division
90
What is the structure of the cilia?
Made up of microtubules
91
What is the function of the cilia?
It wafts dust particles along the alveoli out of the lungs
92
What is the function of the flagella?
For locomotion
93
Where does transcription take place?
In the nucleus
94
Describe the process of transcription
The DNA gets transcribed into mRNA and this leaves the cell via the nuclear pores to the ribosomes on the RER
95
Where does translation take place?
On the RER
96
Describe the process of translation
The mRNA is translated into polypeptide which is packaged into transport vesicles to the Golgi apparatus, which modifies and packages the protein into secretory vesicles which fuses with the cell surface plasma membrane and release the protein outside of the cell. That process is known as exocytosis.
97
What are prokaryotic cells?
They are single-celled organisms with NO nucleus and membrane bound organelles
98
What organelles are always present in a prokaryotic cell?
1. Ribosomes- 70S
2. Circular loop of DNA
3. Cytoplasm
4. Cell surface plasma membrane
5. Cell wall (made up of peptidoglycan)
99
What are some additional organelles found in prokaryotic cells?
1. pili
2. capsule
3. plasmids
4. flagella
100
What is the function of the pili?
It helps to attach a bacterial cell to another bacteria cell
2. It also allows DNA to be transferred between them.
101
What is the function of the capsule?
It provides additional protection (e.g from white blood cells against phagocytosis)
102
What are plasmids?
They are small rings of DNA which contain a small amount of genes
103
What is the function of the flagellum?
It aids locomotion
104
Describe the cell wall test
1. Add iodine, crystal violet, wash with alcohol to decolourise
2. Then ADD safranin (pink in colour)
105
' What is the result for the test?
If Gram positive, the bacteria cell wall will be purple = Has lots of peptidoglycan
If Gram negative=pink=Less of peptidoglycan
