A LEVEL Biology > 🟣 2.1 - Cell structure > Flashcards

🟣 2.1 - Cell structure Flashcards

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1
Q

Describe how light microscopes work?

A

1) Lenses focus rays of light and magnify the thin slice of specimen
2) Different structures absorb different amounts & wavelengths of light
3) Reflected light is transmitted to the observer via objective lens & eyepiece

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2
Q

What is a photomicrograph?

A

A photo of the image seen using an optical microscope

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3
Q

What is a disadvantage of an optical microscope?

A

Resolution is limited
—> smaller organelles can’t be seen

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4
Q

Give an example of an organelle that can’t be seen using an optical microscope?

A

Ribosomes

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5
Q

What is the maximum resolution of an electron microscope?

A

Around 0.0002 µm (or 0.2 nm)

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6
Q

What is the maximum magnification of an electron microscope?

A

Over ×500,000

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7
Q

Why can’t live specimens be observed under an electron microscope?

A

Specimens must be placed in a vacuum, which is incompatible with living cells

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8
Q

What are the two types of electron microscopes?

A
  • Transmission Electron Microscope (TEM)
  • Scanning Electron Microscope (SEM)
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9
Q

Describe how a Transmission electron microscope works

A

1) High energy bean of electrons pass through a thin slice of specimen

2) More dense structures appear darker

3) Focuses image onto screen or photographic plate using magnetic lenses

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10
Q

Why are more dense structures appear darker in a Transmission electron microscope?

A

Since they absorb more electrons

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11
Q

What do we need to do with the specimen before using a TEM?

A
  • Chemically fixed by being dehydrated
  • Stained w/ metal salts
  • Embedded in wax
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12
Q

What type of image does a transmission electron microscope produce?

A

2D, black & white
—> Colour CANT be added

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13
Q

Describe how a Scanning electron microscope works?

A

1) Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses

2) Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate

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14
Q

What type of image does a scanning electron microscope produce?

A

Computer generated 3D image, black & white
—> BUT colour can be added

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15
Q

Why do TEM images appear in black and white?

A

Electrons have no colour, and the image represents electron density

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16
Q

What is the main limitation of SEM compared to TEM?

A

SEM has a lower resolution than TEM

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17
Q

What are the disadvantages of electron microscopes?

A
  • Very large
  • Very expensive
  • Skill & training needed
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18
Q

Equation for magnification?

A

Image/ actual = mag

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19
Q

Give me the definition for magnification

A

The number of times larger an image appears compared to the size of the object

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20
Q

Give me the definition for resolution

A

The ability of an optical instrument to see or produce an image that shows fine detail clearly

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21
Q

Why does resolution differ between light and electron microscopes?

A

Electrons have shorter wavelengths than visible light, allowing electron microscopes to resolve smaller structures

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22
Q

Why do light microscopes have a lower maximum magnification than electron microscopes?

A

Light diffraction limits resolution, reducing effective magnification

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23
Q

What is a stain?

A

Coloured chemicals that bind to molecules in or on the specimen
—> Makes it easy to see

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24
Q

What is differential staining?

A
  • Stains that bind to specific cell structures
  • Each structure will be a stained a different colour
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25
What is a graticule, and how is it used?
A graticule is a small ruler in the eyepiece of a microscope used to measure specimens after calibration with a stage micrometer
26
Why is staining necessary in light microscopy?
To increase contrast and make specific structures visible
27
What is the purpose of a coverslip?
To protect the specimen and lens, and prevent dehydration of the sample
28
What are the types of *preparation techniques* when preparing **microscope slides**?
* Dry mount - dead specimens * Wet mount - live specimens
29
Why must specimens be thin when preparing microscope slides?
To allow light or electrons to pass through for clear visualization
30
What is the purpose of using ethanol during specimen preparation?
To dehydrate the specimen
31
What does **Acetic Orcein** stain?
* Chromosomes dark red * Binds to DNA
32
What does **Eosin** stain?
Cytoplasm dark red or pink
33
What does **Iodine** stain?
Starch blue-black ---> (Appears violet under the microscope)
34
What does **Iodine in a potassium iodide solution** stain?
Stains cellulose yellow
35
What does **Hematoxylin** stain?
Stains RNA/DNA a purple-blue colour
36
What does **Methylene blue** stain?
Stains DNA blue ---> All purpose stain
37
*Describe* the *structure* of the **nucleus**
* Double membrane (nuclear envelope) * Contains Chromatin * Nuclear pores
38
What does the **nuclear pores** allow?
Substances to enter and exit
39
What is the role of the tonoplast in plant cells?
It is the membrane surrounding the permanent vacuole, regulating the movement of substances
40
What do plasmodesmata do in plant cells?
Enable transport and communication between adjacent plant cells
41
What is the function of the nucleolus?
It synthesizes ribosomes
42
What does the **nucleolus** contain? djd
RNA
43
*Describe* the *structure* of **Rough ER**?
* Many ribosomes attached for protein synthesis & transport * Cisternae
44
*Describe* the *function* of **Rough ER**?
* Intracellular transport system * Large surface area for ribosomes
45
How is the **Rough ER** an *'Intracellular transport system'*?
Cisternae form channels for transporting substances from one area of a cell to another
46
How is the **Rough ER** a *'Large surface area for ribosomes'*?
* Amino acids to proteins * Proteins pass through the membrane into the cisternae * Then transported to the Golgi apparatus for modification & packaging
47
*Describe* the *structure* of **Smooth ER**?
* No ribosomes on its surface * Cisternae
48
*Describe* the *function* of **Smooth ER**?
* Contains enzymes that catalyse reactions involved with lipid metabolism * Involved with absorption, synthesis and transport of lipids (from the gut)
49
Give some *examples* of some reactions involved with lipid metabolism
Synthesis of: * Cholesterol * Lipids * Steroid hormones
50
What is **cisternae**?
A system of membranes, containing fluid-filled cavities that are continuous with the nuclear membrane
51
*Describe* the *structure* of **Ribosomes**?
A complex of protein & rNA
52
*Describe* the *function* of **Ribosomes**?
* Site of translation (protein synthesis) * Each ribosome is a complex of ribosomal RNA (rRNA) and proteins
53
What does **rRNA** stand for?
Ribosomal RNA
54
Where are **ribosomes** found in a cell?
* Found freely in the cytoplasm * Part of the Rough ER
55
*Describe* the *structure* of **Golgi apparatus**
* Stack of membrane bound flattened sacs * Secretory vesicles bring materials to & from Golgi apparatus
56
*Describe* the *function* of **Golgi apparatus**?
* Proteins are modified * Proteins are packaged into vesicles that are pinched off
57
Give some *examples* on how the **Golgi apparatus** *modifies proteins*
* Adding sugar molecules to make glycoproteins * Adding lipid molecules to make lipoproteins * Being folded into their 3D shape
58
What happens after *'proteins are packaged into vesicles that are pinched off'*?
* Stored in the cell OR * Moved to plasma membrane ---> Either to be incorporated into the plasma membrane ---> Exported to outside the cell
59
*Describe* the *structure* of **Mitochondria**
* Spherical, rod shaped or branched * Surrounded by 2 membranes (fluid filled space in between them) * Inner part of the mitochondria is a fluid filled space * 2-5 micrometers long
60
*Describe* the *function* of **Mitochondria**
* Site of ATP energy production during respiration * Self-replicating (so more can be made if the cell's energy needs increase) * Abundant in cells where much metabolic activity takes place
61
*Describe* the *structure* of **Chloroplasts**
* Found only in plant cells/ some protists * Thylakoids stack to form grana * Surrounded by a double membrane/envelope * Loops of DNA or starch grains
62
What do **Thylakoids** contain?
Chlorophyll
63
What is the **stroma**?
Fluid filled matrix
64
*Describe* the *structure* of **Lysosome**
* Sac surrounded by a single membrane * Acidic conditions * Glycoprotein coat
65
*Describe* the *function* of **Lysosome**
* Contains hydrolytic enzymes * Digests contents of phagosome * Exocytosis of digestive enzymes
66
What is the function of intermediate filaments in the cytoskeleton?
They provide mechanical strength and maintain cell shape
67
How are mitochondria self-replicating?
They contain their own DNA and ribosomes for protein synthesis
68
What happens in the stroma of chloroplasts?
The Calvin Cycle (light-independent stage of photosynthesis) occurs
69
What is the role of lysosomes in apoptosis?
They release hydrolytic enzymes to break down cell components during programmed cell death
70
*Describe* the *function* of the **Cell wall**
* Structural support to the cell
71
*Describe* the *structure* of the **Cell wall**
* Narrow threads of plasmodesmata connect cytoplasm of neighbouring plant cells * Cellulose - plants & Peptidoglycan - bacteria
72
*Describe* the *function* of the **Permanent vacuole**
Storage of cell sap
73
*Describe* the *structure* of the **Permanent vacuole**
A sac surrounded by the tonoplast
74
What is the **cytoskeleton**?
An extensive network of protein fibres
75
What is the *structure* of the **cytoskeleton**?
* Protein fibres * Cytoskeletal motor proteins
76
What are the main **types** of **protein fibres** the *cytoskeleton* is made up of?
* Microfilaments * Microtubules
77
What are **Microfilaments**?
Solid strands - mostly made of the protein actin
78
What are **Microtubules**?
Tubular strands - mostly made of the protein tubulin
79
What are the **functions** of the **cytoskeleton**?
* Cell support * Intercellular movement (exocytosis) * Cellular movement (movement of chromosomes)
80
How does the cytoskeleton assist in intracellular transport?
Motor proteins move organelles along microtubules using ATP
81
What type of protein makes up microtubules?
Tubulin
82
How does the **cytoskeleton** do *cellular movement*?
Enables cell movement via cilia & flagella ---> Hair-like structures contain microtubules (responsible for movement)
83
How does the **cytoskeleton** do *INTRAcellular movement*?
Aids transport by forming 'tracks' along which motor proteins can transport organelles
84
How does the **cytoskeleton** do *support & strengthening*?
* Mechanical strength - helps retain cell shape * Keeps organelles in position
85
What is the *function* of **cytoskeletal motor proteins**?
* Hydrolysis of ATP * They are enzymes * Molecular motors
86
How do **prokaryotes** divide?
Binary fission ---> NO SPINDLE INVOLVED
87
How do **eukaryotes** divide?
Mitosis or Meiosis ---> SPINDLE INVOLVED
88
Role of **spindle fibre**?
Separates chromosomes
89
What type of **ribosomes** are found in **prokaryotes**?
70S
90
What type of **ribosomes** are found in **eukaryotes**?
80S
91
What is the **cell wall** in **prokaryotes** made out of?
* Peptidoglycan * Murein
92
What is the **cell wall** in **eukaryotes** made out of?
* Plants - Cellulose or Lignin * Fungi - Chitin
93
What **organelles**(/ type) does **eukaryotes** have?
Membrane bound organelles
94
What **organelles** have **SINGLE membranes**?
* Lysosomes * Golgi complex * Vacuoles
95
What **organelles** have **DOUBLE membranes**?
* Nucleus * Mitochondria * Chloroplast
96
What **organelles** have **NO membranes**?
* Ribosomes * Centrioles * Microtubules
97
What are **plasmids**?
Small loops of DNA that are separate from the main circular DNA molecule ---> Contains genes
98
Purpose of **slime capsule**?
Helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism
99
What is the function of plasmids in prokaryotes?
They carry genes that can provide advantages, such as antibiotic resistance
100
What is the slime capsule made of in prokaryotes?
Polysaccharides
101
What is the function of flagella in prokaryotes?
To enable movement
102
What is the **size** of **prokaryotes**?
0.5 - 5 micrometres diameter
103
What is the **size** of **eukaryotes**?
Up to 100 micrometres diameter
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