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OCR Biology > ✨Module 2: Cell Structure > Flashcards

✨Module 2: Cell Structure Flashcards

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1
Q

Magnification is determined by …

A

Type of lens, distance between lens and object, size of the eyepiece.

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2
Q

How to increase magnification?

Increasing magnification will …

A

Higher power objective lens that will decrease the distance between the lens and object.
Decrease resolution.

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3
Q

Define resolution.

A

Minimum distance between 2 points where they’re seen as separate.

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4
Q

Resolution can be limited by …

A

Diffraction of light as it passes through samples and lenses.

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5
Q

What is diffraction?

A

Tendency of light waves to bend as they pass close to the edges of a specimen.

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6
Q

The light reflected from individual structures can …

A

Overlap, so they’re no longer seen as separate and detail is lost.

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7
Q

Resolution can be increased by …

A

Using a beam of electrons - x1000 shorter wavelength than light. Electron beams are still diffracted, but individual beams can come much closer before they overlap.

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8
Q

1000 micrometres

A

1 mm

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9
Q

Order of microscope discovery?

A

Light, electron (TEM/SEM), LSCM.

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10
Q

Microscopes allow us to discover …

A

Function of cells/organs, chromosomes dividing, investigating diseases.

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11
Q

All microscopes require a …

A

Radiation wave (light/electrons/laser beam) to be directed to the sample.

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12
Q

Define cell theory.

A

How scientific theories change overtime as new evidence is gained and knowledge increases.

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13
Q

What does the cell theory state?

A

‘Both plant and animal tissues are composed of cells, cells are basic unit of all life, cells only develop from existing cells’

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14
Q

Cell theory wasn’t fully developed before 19th century because …

A

Magnification was too low to see and identify cells.

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15
Q

How does an optical light microscope work?

A

White light passes through the specimen from underneath through the objective and eyepiece lens and into the observers eye where the brain forms an image.

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16
Q

Objective lens …
Eyepiece lens …

A

Focuses the light and magnifies the image.
Magnifies the image.

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17
Q

What is the condenser lens?

A

Focuses light onto the specimen, doesn’t magnify it.

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18
Q

What is the diaphragm?

A

Controls amount of light reaching the specimen.

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19
Q

Why is magnification and resolution low for light microscope images?

A

Cells don’t absorb a lot of light and light has a longer wavelength so more diffraction as it passes through the sample.

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20
Q

Structures you can’t see under a light microscope?

A

ER, ribosomes.

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21
Q

Steps to using a light microscope?

A
  1. Clip slide onto stage, select lowest power objective lens.
  2. Use coarse adjustment knob to move OL to just above the slide.
  3. Look down at eyepiece and adjust focus using fine adjustment knob, until a clear image forms.
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22
Q

What does the fine adjustment knob do?

A

Moves lens away from the slide.

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23
Q

Pro’s and Con’s of light microscopes?

A

Pro - can be living or dead specimen, small and portable, sample in colour, cheaper.
Con - lower mag and resolution, only shows 2D shape.

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24
Q

Stains in light microscopes are …

A

Dyes

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25
Q

What is the purpose of stains?

A

Increase contrast as components take up stains at different degrees, so you can easily visualise different structures.

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26
Q

Iodine stains starch …
Eosin stains cytoplasm …

A

Blue/black
Pink

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27
Q

Differential staining is when …

A

Multiple stains are used together. Each stain is picked up by different structures so each part can be identified differently.

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28
Q

What to ensure before staining?

A

That the stain used isn’t toxic to the live specimen.

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29
Q

Gram+ bacteria …
Gram- bacteria …

A

Has a thick cell wall to retain a stain.
Has a thin murein cell wall that doesn’t retain the stain.

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30
Q

List the sample preparation techniques.

A

Fixation, sectioning/embedding in resins, dehydration, staining, mounting.

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31
Q

Fixation involves …

A

Using chemicals to preserve specimens and prevent decomposition. Could also freeze.

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32
Q

Sectioning involves …

A

Dehydrating specimens with alcohol and placed in a resin to see deeper structures, which can then be sliced thinly with a knife.

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33
Q

Dehydration prevents …

A

Vaporisation of water in a vacuum.

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34
Q

Specimens are often treated with stains or …

A

Heavy metals (electron microscope) to show different structures.

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35
Q

Mounting involves …

A

Securing the specimen to a microscopic slide and cover slip on top.

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36
Q

Scientific drawing rules.

A

Title, magnification, date. Smooth continuous lines, no shading, labels shouldn’t cross, no arrow head.

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37
Q

Define mount.

A

Where your specimen is placed on a microscopic slide.

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38
Q

Explain how a dry mount is prepared.

A

Specimen cut into a thin slice with a blade (sectioning). Place it in the middle of a clean slide using tweezers. Place a cover slip on top.

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39
Q

Purpose of a cover slip?

A

Holds the specimen in place and prevents damage.

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40
Q

What is dry mount often used with?

A

Hair, pollen, parts of insects, plants.

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41
Q

Why must specimens be thin?

A

So light can pass through and details can be seen.

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42
Q

Explain how to prepare a wet mount.

A

Put a drop of water in the middle of a clean slide using a pipette. Using tweezers to place specimen in water, and place a cover slip from one end at an angle, avoiding air bubbles. Put a drop of stain on one end of the cover slip then put a paper towel on the opposite edge, which draws the stain under and across the cover slip.

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43
Q

When do you use a wet mount?

A

Specimens in liquid such as water. It can be living like aquatic organisms.

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44
Q

Why do we need to avoid air bubbles?

A

Obstruct the view of the sample.

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45
Q

What is a smear slide?

A

Type of wet mount used for blood samples.

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46
Q

How to create a smear slide?

A

Place sample liquid at edge of microscopic slide. Use another slide to make a 45 degree angle, moving towards the sample and smearing it across the slide to create an even coating.

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47
Q

How is a squash slide prepared?

A

Wet mount is prepared, then a lens tissue is used to greatly press down the cover slip.

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48
Q

Define calibrate.

A

To find an unknown length.

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49
Q

What is an eyepiece graticule?

A

Ruler with no units and remains unchanged with sample size, but increases as mag increases.

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50
Q

Eyepiece graticule is slotted into the …

A

Eyepiece.

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51
Q

What is a stage micrometer?

A

Microscopic slide with a tiny scale with units (micrometres) which is used to work out the no. divisions on the eyepiece at a particular magnification.

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52
Q

1 division on stage micrometer =
1 whole divisions on stage micrometer =

A

0.1 mm
1 mm

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53
Q

Steps to calibrate an eyepiece graticule?

A
  1. Select wanted mag and objective.
  2. Place stage micrometer on stage and line up the scales of the micrometer and eyepiece graticule.
  3. Count no. divisions on eyepiece equivalent to each division on the stage micrometer.
  4. Calculate the length of 1 division of the eyepiece in micrometres.
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54
Q

To measure the size of the specimen …

A

Replace the stage micrometer with cell. You can then use the eyepiece graticule to measure the length of cells in micrometres.

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55
Q

Actual size =

A

number of divisions x length of 1 division

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56
Q

Define cell size.

A

Measure of volume/SA of a cell.

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57
Q

Larger cells may indicate …
Smaller cells may indicate …

A

Mature, differentiated cell.
Younger, more actively dividing cell.

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58
Q

Cell size may remain constant during …
Cell size would increase during …

A

Cell division.
Cell growth as it takes in more material and grows in volume.

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59
Q

What happens in an electron microscope?

A

Electrons penetrate the sample and interact with the atoms in it.

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60
Q

Why do electron microscopes have a better resolution than light?

A

Shorter wavelength than light waves.

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61
Q

List the sample preparation techniques for an electron microscope.

A

Fixation, dehydration, embedding in resins, staining with heavy metals.

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62
Q

What is staining with heavy metals?

A

With uranium or lead, unlike light microscopy which are dyes. Metal ions cause electrons in the specimen to scatter, causing some areas of the specimen to appear darker than others.

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63
Q

Why is there a vacuum in an electron microscope?

A

Avoids electron scattering and ensures electron beams travel in straight lines.

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64
Q

Pro’s and con’s of electron microscopes?

A

Pro - Higher mag and resolution, 3D structure so you can see internal structures.
Con - More expensive to buy/operate, specialist training, electron beam can damage samples so has to be non-living, needs a vacuum.

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65
Q

Define artefact.

A

Structural detail visible in the microscopic image that isn’t a natural part of the specimen.

66
Q

What are artefacts caused by?

A

Distortion during preparation like bubbles that get trapped under the cover slip. This can happen in both light and electron microscopes.

67
Q

Examples of artefacts?

A

Loss of continuity in cell membranes, empty spaces in cytoplasm.

68
Q

How does a TEM work?

A

Beam of electrons is transmitted THROUGH the sample and produces a 2D image. You can see stacked grana inside a chloroplast.

69
Q

TEM shows the …

A

Cross section of the sample.

70
Q

Preparation techniques for TEM?

A

Set in resin and may be stained.

71
Q

Denser parts of an image …

A

Absorb more electrons, making them look darker on micrographs.

72
Q

In less dense regions …

A

Electrons can easily pass through, making them look lighter on an electron micrograph.

73
Q

Pro’s and con’s of TEM?

A

Pro - higher resolution and mag than SEM.
Con - must be in a vacuum so dead specimens, thin tissue only as thick tissue easily absorbs electrons and don’t get good images.

74
Q

The angle at which specimens are cut …

A

Can affect appearance.

75
Q

How does an SEM work?

A

Directs a beam of electrons across the sample. Shows the surface of the sample.

76
Q

Sample preparation in SEM?

A

Coated in heavy metal.

77
Q

Pro’s and con’s of SEM?

A

Pro - 3D, can be used on thick sample.
Con - Lower resolution and mag than TEM.

78
Q

What is a cell?

A

Basic unit of life performing necessary functions.

79
Q

Some cells look structurally different under a microscope as …

A

Cells may be cut in different angles/shapes e.g. transverse/longitudinal. Or may have been sliced thinly.

80
Q

Define tissue.

A

Group of cells with the same function.

81
Q

Define organ.

A

Group of different tissues that have specific functions.

82
Q

Define ultrastructure.

A

Fine detail in a cell observed only with an electron microscope.

83
Q

Most organelles in eukaryotic cells are … except the …

A

Membrane bound, nucleolus.

84
Q

What does the nucleus contain?
Function of the nucleus?

A

Genetic info in the form of DNA.
Controls the cells activity and replication.

85
Q

Define gene expression.

A

Process where specific genes are activated to produce a required protein.

86
Q

Genetic info in the nucleus is in what 2 forms?

A

Chromatin and nucleolus.

87
Q

How is chromatin formed?

A

When DNA winds around histones to give a compact shape. This then coils and condenses to form chromosomes, so they fit in the cell nucleus.

88
Q

When this happens …

A

Length of DNA is reduced so can pack in a smaller space. Prevents DNA from damage.

89
Q

DNA stores instructions to make …

A

Proteins.

90
Q

The nucleolus is made up of …

A

Proteins and RNA.

91
Q

Function of the nucleolus?

A

Produces ribosomes - RNA is used to produce rRNA, which is combined with proteins to form ribosomes necessary for protein synthesis.

92
Q

What happens to the ribosomes after?

A

Move out of the nucleus to latch onto the RER where they produce proteins.

93
Q

Nucleus is surrounded by a …

A

Double MEMBRANE called a nuclear envelope - protects DNA from damage in the cytoplasm.

94
Q

Why is DNA transcribed to RNA in the nucleus?

A

DNA is too large to leave the nucleus to the site of protein synthesis in the cytoplasm. RNA can leave the nuclear pore.

95
Q

Where are plasma cells found?
What are they made of?

A

Blood and lymph.
Protein.

96
Q

What is the plasma membrane made of?

A

Proteins and lipids. Contain receptors that respond to chemicals like hormones.

97
Q

What does the cytoplasm store?

A

Water, salts and where metabolic reactions occur.

98
Q

Animal cells can be …
Animal cells are …

A

Unicellular or multicellular.
Heterotrophic, so they can’t generate their own food.

99
Q

Plant cells are only …
Plant cells are …

A

Multicellular.
Autotrophic, so they do make their own food by photosynthesis.

100
Q

Function of ribosomes?
Where are they found?

A

Create proteins from amino acids.
Cytoplasm or on the RER.

101
Q

What are ribosomes made up of?
Surrounded by a membrane?

A

rRna and proteins.
NO.

102
Q

Function of the cell wall?

A

Gives cell shape, prevent cell bursting due to pressure, allows turgidity, protects against pathogens.

103
Q

Cell wall is also …

A

Freely permeable, so soluble substances can easily pass through its pores. Unlike the plasma membrane that forms a phospholipid bilayer.

104
Q

Fungal cell walls made of …

A

Chitin.

105
Q

Function of mitochondria?

A

Produce ATP through aerobic respiration. Bound by a double membrane called an envelope.

106
Q

Function of amyloplasts?

A

Synthesise and store starch in plant cells only. MEMBRANE bound.

107
Q

Adaptations of mitochondria?

A

Large SA and inner MEMBRANE is folded into projections called cristae, which contain all enzymes needed to produce ATP. It’s filled with matrix fluid.

108
Q

Explain the structure of a chloroplast. How is it adapted?

A

Network of double MEMBRANES called a thylakoid which are stacked to form grana. Grana are joined by membranes called lamellae. Also have starch grains to store photosynthesis products. Thylakoid/internal membrane gives a large SA for enzymes and proteins needed for photosynthesis.

109
Q

Where are the chlorophyll pigments?

A

In the grana.

110
Q

Where are chloroplasts found?

A

Stems and leaves, but not roots.

111
Q

Both mitochondria and chloroplasts have their own …

A

DNA and ribosomes, so can make their own proteins and reproduce themselves.

112
Q

How did the endosymbiosis theory happen?

A

The bigger prokaryotes engulfed smaller ones as an endosymbiont (but didn’t digest it), leading to eukaryotic cells. Also, mitochondria and chloroplasts were free living prokaryotes.

113
Q

Evidence supporting the endosymbiosis theory?

A

Both mitochondria and chloroplasts have 70S ribosomes (same size as bacteria). Both contain DNA necessary for protein synthesis. Both have a bacterial genome.

114
Q

What are plasmodesmata and how are they beneficial?

A

Small channels across cell walls that connect the cytoplasm of neighbouring plant cells. Substances can directly travel from the cytoplasm of one cell to the next rather than diffusing.

115
Q

Describe the structure of the cytoskeleton.
What are the 3 components it is split up into?

A

Network of protein fibres in cytoplasm. Present in both euk and pro cells, but made up of different proteins. Not MEMBRANE bound. Split up into: Microfilaments, microtubules, intermediate fibres.

116
Q

Function of the cytoskeleton?

A

Provides mechanical strength to cells, aiding transport within cells and enabling cell
movement (cilia and flagella).

117
Q

Give a biological example of the use of the cytoskeleton.

A

Movement of chromosomes during separation in cell division depends on contraction of microtubules in the spindle. Movement of vesicles around cells.

118
Q

This all relies on …

A

Proteins in the cytoskeleton, so would require a lot of energy from respiration. Therefore, the cytoskeleton can be prevented from functioning by using respiratory inhibitors.

119
Q

Microfilaments.

A

Contractile fibres formed from protein actin. Allow cell movement (phagocytes) and contraction during cytokinesis (where the cytoplasm of a single eukaryotic cell divides to form 2 daughter cells).
Their filament length changes by adding or removing monomer subunits, with a faster rate in one direction.

120
Q

Microtubules.

A

Tiny protein cylinders made from protein tubulin. Globular tubulin polymerises to form scaffold like structures that determine cell shape. They act as tracks for organelle movement like vesicles.

121
Q

Both microfilaments and microtubules form …

A

Centrioles and spindle fibres.

122
Q

Intermediate fibres.

A

Small strands that give mechanical strength to cells and have a fixed length for stability.

123
Q

Function of the permanent vacuole in plants?

A

Contains cell sap that stores minerals. It maintains turgor by pushing the cytoplasm against the cell wall, creating a rigid framework for the cell.

124
Q

What is the tonoplast and why is it important?

A

The MEMBRANE surrounding the vacuole.
It is semi-permeable, so acts as a barrier to separate harmful contents of the vacuole from the cytoplasm.

125
Q

Explain the structure of the RER. What does it have on its surface?

A

Flattened, fluid-filled, MEMBRANE bound sacs called cisternae. The nuclear membrane is continuous with the RER (on the same outer layer). The RER has a large SA for ribosomes on its surface.

126
Q

What is the function of the RER?

A

Ribosomes on RER translate mRNA to a polypeptide chain. It folds and processes proteins before it’s transported to Golgi when it’s needed.

127
Q

Why do secretory cells have more RER than cells that don’t release proteins?

A

They release hormones and enzymes.

128
Q

RER stands for …
SER stands for …

A

Rough endoplasmic reticulum.
Smooth endoplasmic reticulum.

129
Q

What is the SER?

A

Flattened, fluid-filled, MEMBRANE bound sacs called cisternae. They have no ribosomes though.

130
Q

Explain the functions of SER.

A

Produces and processes lipids like cholesterol, steroids and hormones needed by the cell. When exporting these molecules, the SER packages them and sends them to Golgi. This can happen inside or outside the cell.

131
Q

*Other functions of the SER?

A
  1. Detoxifies toxins either consumed or produced as products of metabolism.
  2. Maintain cellular homeostasis - SER contains calcium pumps that regulate the level of calcium ions in the cytoplasm. This prevents their levels getting too high and triggering damage.
132
Q

What would happen if the ER function is disrupted? (From e.g. Alzheimers)

A

Accumulation of misfolded proteins, leading to cellular damage and disease progression.

133
Q

Describe the structure of the Golgi apparatus.

A

Stack of fluid-filled, flattened, MEMBRANE bound sacs with cisternae and vesicles surrounding the edge. Similar structure to ER, but doesn’t contain ribosomes.

134
Q

What is the function of the Golgi apparatus?

A

Modifies, sorts and packages proteins from RER and lipids from SER, as they pass through its multiple stacked cisternae, into vesicles for transport around the cell to where they’re needed. It could be a secretory vesicle that leaves the cell, or a lysosome that stays in the cell.

135
Q

How does this mechanism happen?

A

The cis face receives proteins and lipids. The cisternae and inner lumen do the packaging. The trans face releases the proteins and lipids after packaging.

136
Q

Modifications in the Golgi include …

A

Adding or removing sugar groups to create glycoproteins, modifying phospholipids to create lipoproteins, changing the proteins conformation.

137
Q

Function of the vacuole?

A

Stores and transports substances into and out of the cell via the plasma membrane and between organelles. MEMBRANE bound.

138
Q

Endocytosis is …
Exocytosis is …

A

Entering the cell.
Leaving the cell.

139
Q

What is a lysosome?

A

A vesicle bound by a single MEMBRANE that contains hydrolytic/digestive enzymes. It has a protective wall made up of phospholipids.

140
Q

Explain the function of a lysosome.

A

Consume old organelles and waste materials through endocytosis and digest them to smaller components. Can also digest pathogens ingested by phagocytic cells. These can then be recycled for use in other cellular processes.

141
Q

If a cell is damaged beyond repair …

A

The cell will undergo programmed cell death (apoptosis).

142
Q

Why is membrane compartmentalisation important for a lysosome?

A

It protects the rest of the cell from the enzyme’s digestive activity.

143
Q

Describe the structure of centrioles.

A

Hollow cylinders composed of rings called microtubules arranged at right angles to each other. Not MEMBRANE bound. 2 associated centrioles form the centrosome.

144
Q

Function of centrioles?

A

The centrosome organises and forms spindle fibres which evenly separate the chromosomes in mitosis. They also make cilia and flagella. Centrioles migrate to the poles during prophase.

145
Q

Cilia.

A

Hair-like structures that beat (due to the action of microtubules) to move objects/fluids across cell surfaces. MEMBRANE bound. Stationary cilia act as sensory organs like the nose.

146
Q

Flagella.

A

Whip like appendages allowing cell movement. MEMBRANE bound. For flagella to move, microtubules contract and parallel ones slide over each other.

147
Q

Flagella are …
Cilia are …

A

Longer and thicker.
Found in greater number.

148
Q

Examples of cell compartmentalisation?

A

The nucleus with a double membrane containing genetic material, ER, Golgi, mitochondria.

149
Q

What is the endomembrane system?

A

Network of organelles that work together by modifying, packaging and distributing proteins + lipids. Composed of nuclear envelope, ER, Golgi, vesicles, lysosome.

150
Q

Example of unicellular eukaryote?

A

Amoeba.

151
Q

Ribosomes on RER make …
Ribosomes in cytoplasm make …

A

Proteins for attachment to the cell membrane.
Proteins that stay in cytoplasm.

152
Q

The DNA is not …

A

MEMBRANE bound - it’s 1 molecule that is super-coiled to make it compact.

153
Q

How is the flagellum in bacteria different?

A

Made of protein flagellin instead, arranged in a helix. Doesn’t have a 9 + “ arrangement. Energy to rotate flagellum is supplied from chemiosmosis, not ATP in eukaryotes. The flagellum is attached to the cell membrane of bacterium via the basal body.

153
Q

What is the mesosome?

A

Site of aerobic respiration in bacteria. Connected to the cell membrane.

154
Q

Pilli transfer …

A

DNA between bacteria.

155
Q

What are fimbrae?

A

Little hairs that help bacteria to colonise an area by latching onto its surface.

156
Q

Differences between prokaryotes and eukaryotes.

A

Prokaryotic: Smaller ribosomes (70S), no membrane-bound organelles, circular loop of DNA, no nucleus, all are unicellular, cell wall made of murein, proteins fold and condense into DNA.
Eukaryotes: 80S ribosomes, both membrane and non-membrane bound organelles, linear DNA with 2 distinct ends, DNA associated with histones instead, multicellular and unicellular.

157
Q

Explain the pathway of proteins in a cell. (6 marks)

A

Proteins are produced on ribosomes on RER. Proteins pass into its cisternae, where it’s folded and processed, packaged into transport vesicles.
Vesicles move towards Golgi via cytoskeleton. Vesicles fuse with cis face of Golgi and proteins enter it.
Further processing and protein structure is modified e.g. by adding a sugar chain to the protein surface.
Also packaged into vesicles for transport around the cell (lysosomes) and some leave by exocytosis.
Fusion of vesicle with plasma membrane.

158
Q

Larger 80S ribosomes are involved in …

A

Formation of more complex proteins. The ‘S’ mean the rate at which they settle or form a sediment solution.

159
Q

What is the capsule?

A

Protective layer can help evade the host’s immune system.

160
Q

What are hyphae?

A

Threads that join up to make the mycelium, release enzymes and absorb nutrients.

OCR Biology (12 decks)

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