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AQA A Level Biology 2018 > Cell Structure & Division > Flashcards

Cell Structure & Division Flashcards

1
Q

Magnification =

A

Imagine Size
—————
Real Size

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2
Q

Give the microscopy units in order from largest to smallest:

A

Cm
Mm
UM (micrometers)
Nm

x10 x1000 x1000

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3
Q

What are Eukaryotic Cells?

A

Any organism consisting of one or more cells that contain DNA in a nucleus and also have membrane bound organelles.

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4
Q

What are Algal cells like?

A

They are a lot like plant cells as they have the same organelles including a cell wall and chloroplast.

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5
Q

What do Algae do?

A

They carry out photosynthesis like plants but can be single called or multi cellular.

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6
Q

How are Fungal Cells different to plant cells? (2)

A
  • cell walls made of chitin not Cellulose.

- they don’t have chloroplast because they don’t photosynthesise.

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7
Q

What’s the significance of the nucleus?

A

It contains chromosomes which are made from protein bound linear DNA.

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8
Q

What’s the significance of the nuclear envelope?

A

It is a double membrane which surrounds the large organelle and controls entry.

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9
Q

What’s the significance of the nuclear pores?

A

It allows substances to love between the nucleus and cytoplasm e.g. ribosomes.

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10
Q

What’s the significance of the nucleolus?

A

It makes ribosomes and contains RNA.

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11
Q

What’s the significance of the Mitochondria?

A

It is oval shaped with a double membrane - the inner membrane folds to form Cristae and inside the folds is the Matrix which contains enzymes.

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12
Q

What’s the significance of the Golgi Apparatus?

A

A group of fluid filled membrane bound flattened sacks - proteins and lipids produced by ER are pases to here where they are modified and labelled allowing them to be sent to the right destination.

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13
Q

What’s the significance of the Rough Endoplasmic Reticulum?

A

System of membranes enclosing a fluid filled space with ribosomes on the surface - folds provide a large surface area for processing proteins that have been made at ribosomes and provides a pathway for the transport of materials through the cell.

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14
Q

What’s the significance of the Smooth Endoplasmic Reticulum?

A

Same as RER but without ribosomes - synthesises, stores and transports lipids and carbohydrates.

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15
Q

What’s the significance of the Vacuole?

A

Membrane bound organelle containing cell sap.
Sugars and amino acids may act as a temporary food store
Support herbaceous plants and herbaceous parts of Woody plants by making cells turgid.

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16
Q

What does the Cristae do in the mitochondria?

A

Provides a large surface area for the attachment of enzymes and other proteins involved in respiration.

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17
Q

What does the Matrix do in he mirochondria?

A

Makes up the remainder of it and contains protein, DNA, lipids etc that allows the mitochondria to control the production of some of their own proteins.

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18
Q

What does the Chloroplasts consist of: (3)

A

The chloroplast envelope - surrounds it and controls entry.

The grana - stacks of structures called thylakoids which contain chlorophyll. This is where the first stage of photosynthesis takes place.

The stroma - fluid filled matrix where the second stage of photosynthesis takes place.

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18
Q

How are Chloroplasts adapted to their functions: (3)

A

Granal membranes provide a large surface argue for attachment of chlorophyll and enzymes etc which are needed of photosynthesis.

Fluid of stroma has all enzymes needed to make sugars in second stage of photosynthesis.

Chloroplasts contain dna and ribosomes so they can quickly make proteins needed for photosynthesis.

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19
Q

Functions of the Golgi apparatus: (3)

A
  • Add carbs to proteins to form glycoproteins.
  • form lysosomes.
  • produce secretory enzymes.
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20
Q

How are Lysosomes formed?

A

When the vesicles produced by the Golgi Apparatus contain enzymes such as proteases and lipases. Also contain lysozemes - digestive enzymes.

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21
Q

Function of Lysosomes: (3)

A
  • break down cells after they die
  • digest worn out organelles
  • hydrolyse things ingested by phagocytise Cells e.g. white blood cells and bacteria.
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22
Q

2 types of Ribosomes:

A
  • 80S found in Eukaryotic Cells.

- 70S found in prokaryotic cells, mitochondria and chloroplasts.

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23
Q

What is the significance of the Cell Wall?

A

It consists of microfibrils of the polysaccharide Cellulose embedded in a matrix. Give it lots of strength.

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24
Q

Functions of the cell wall:

A
  • give strength to the plant

- allow water to pass along it and contribute to the movement of water through the plant.

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25
Q

What are the cell walls of fungi made of?

A

Chitin

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26
Q

All membranes around and within cells are known as…

A

Plasma membranes

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27
Q

What is the cell surface membrane?

A

The name given to the plasma membrane that surrounds cells and forms the boundary between cytoplasm and the environment.

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28
Q

Phospholipids form..

A

A bilayer.

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29
Q

What are the heads of both phospholipid layers like?

A

Hydrophilic - they point to the outside of the cell surface membrane attracted by water on both sides.

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30
Q

What are the tails of the phospholipid layers like?

A

Hydrophobic - they point into the centre of the cell membrane, repelled by the water on both sides.

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31
Q

How do lipid soluble material move?

A

Via the phospholipid portion.

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32
Q

The functions of phospholipids in the membrane: (3)

A
  • allow lipid soluble substances to enter and leave the cell.
  • prevent water soluble substances entering and leaving the cell.
  • make the membrane flexible and self-sealing.
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33
Q

What can be found on the cell surface membrane?

A

Proteins - they are embedded in the phospholipid bilayer.

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34
Q

Give the 2 ways the proteins are embedded on the phospholipid bilayer:

A
  • some just occur in the surface of the bilayer and never extend completely across it - to give mechanical support or to act as cell receptors.
    EXTRINSIC
  • completley span the whole bilayer.
    INTRINSIC
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35
Q

Some proteins completely span the phospholipid bilayer. Give 2 examples:

A
  • some are protein channels which form water filled tubes to allow water soluble ions to diffuse across the membrane.
  • carrier proteins that bind to ions or molecules like glucose and amino acids then change shape in order to move these molecules across the membrane.
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36
Q

Give 3 examples of functions of the protein in the membrane:

A
  • provide structural support.
  • act as receptors.
  • allow active transport across the membrane through carrier proteins.
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37
Q

Cholesterol molecules occur…

A

Within the phospholipid bilayer of the cell surface membrane.

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38
Q

What do Cholesterol molecules do? (3)

A

They add strength to the membranes.

They are also hydrophobic so play a role in preventing loss of water and dissolved ions from cells.

They also pull together the fatty acid tails of the phospholipid molecules limiting their movement without making the membrane too rigid - provide stability & regulates fluid.

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39
Q

The functions of cholesterol: (2)

A
  • make the membrane less fluid at higher temperatures.

- prevent leakage of water and dissolved ions from the cell.

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40
Q

What are Glycolipids made up from?

A

A carbohydrate covalently bonded with a lipid.

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41
Q

What do Glycolipids do?

A

Extends from the phospholipid bilayer into the watery environment outside the cell where it acts as a cell surface receptor for specific chemicals.

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42
Q

Functions of Glycolipids: (3)

A
  • act as recognition sites.
  • help maintain the stability of the membrane.
  • help cells to attach to one another and so form issues.
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43
Q

What are Glycoproteins?

A

When carbohydrate chains are attached to many extrinsic proteins on the outer surface of the membrane.

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44
Q

Functions of Glycoproteins: (2)

A
  • act as recognition sites.

- help cells to attach to one another and so form tissues.

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45
Q

The cell surface membrane controls…

A

What can enter the cell.

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46
Q

What properties do molecules need to have to cross the membrane? (2)

A
  • small

- lipid soluble / non polar

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47
Q

What properties will make a molecule not be able to pass through a membrane: (2)

A
  • large

- water soluble / polar

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48
Q

How can polar and non polar molecules pass through the membrane?

A

Non polar molecules can just diffuse through while polar require proteins to enable them to pass.

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49
Q

Describe the structure and function of the Glycoproteins:

A

They are carbohydrates attached to proteins and are used for cell recognition.

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50
Q

Carrier proteins act to transport…

A

Large or charged water molecules.

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51
Q

What is the name given to describe the way the various molecules (proteins etc) are combined on the structure of the cell surface membrane?

A

The Fluid Mosaic Model.

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52
Q

Why is the arrangement of the cell surface membrane described as the Fluid Mosaic Model?
Describe ‘Fluid’

A

Fluid because the individual phospholipid molecules can move relative to one another giving the membrane a flexible structure that is constantly changing shape.

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53
Q

Why is the arrangement of the cell surface membrane described as the Fluid Mosaic Model?
Describe ‘Mosaic’

A

Because the proteins that are embedded vary in shape size and pattern in the same way as the stones or tiles of a mosaic.

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54
Q

If all the cells in an organism are produced by mitotic divisions with the same genes then how are cells specialised?

A

Every cell contains he genes needed for it to develop into any other cell but only some of these genes are switched on in cells.

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55
Q

As a result of specialisation…

A

The whole organism functions efficiently.

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56
Q

What is a tissue?

A

A group of similar cells working together to perform a function.

57
Q

Give an example of a tissue in animals and what their functions are: (3)

A

Epithelial tissues - consist of sheets of cells.

  • protective.
  • the alveoli of the lungs is made of thin, flat cells for diffusion.
  • secretory function.
58
Q

Give an example of a tissue in plants and it’s use:

A

Xylem Tissue - used to transport water and mineral ions throughout the plant and gives mechanical support too.

59
Q

What is an organ?

A

A group of tissues working together to perform one major function.

60
Q

What is the stomach made of? (3)

A
  • muscle to churn contents.
  • connective tissue to hold together the other tissues.
  • epithelium to protect the stomach wall.
61
Q

What is the leaf made of? (5)

A
  • palisade mesophyll made of lead palisade cells carry out photosynthesis.
  • spongy mesophyll adapted for gaseous diffusion.
  • epidermis to protect leaf and allow diffusion.
  • phloem to transport organic materials away from the leaf.
  • xylem to transport water and ions into the leaf.
62
Q

Is a capillary an organ or a tissue? Why?

A

Tissue because it is just made up of one tissue.

63
Q

Are arteries and veins organs or tissues? Why?

A

Organs because they’re made of many tissues e.g. muscle and epithelial.

64
Q

What is an organ system?

A

When organs work together as a single unit known as an organ system.

65
Q

Give 3 examples of organ systems in humans:

A
  • digestive system which is used to digest and process food.
  • respiratory system which is used for breathing and gas exchange.
  • circulatory system pumps and circulates blood.
66
Q

What is the respiratory system made of? (4)

A
  • trachea
  • bronchi
  • bronchiole
  • lungs
67
Q

What is the circulatory system made of? (3)

A
  • heart
  • arteries
  • veins
68
Q

What is the digestive system made of? (7)

A
  • salivary Glands
  • oesophagus
  • stomach
  • duodenum
  • ileum
  • pancreas
  • liver
69
Q

Prokaryotic cells, compared to Eukaryotic are…

A

Smaller and have no nucleus or nuclear envelope.

70
Q

Bacteria store food reserves as…

A

Glycogen, granules and oil droplets.

71
Q

The genetic material in bacteria is in the form of…

A

A circular strand of DNA.

72
Q

What are plasmids and what can they do?

A

Smaller circular pieces of DNA - they can reproduce independently and may give the bacterium resistance to chemicals like antibiotics.

73
Q

Differences in cell wall between Eukaryotic and Prokaryotic?

A
  • cell wall in prokaryotic is made of murein (and is 10-80nm thick)which is a polymer of polysaccharides and peptides while in Eukaryotic cells it’s made of Cellulose.
74
Q

Differences in nucelus between Eukaryotic and Prokaryotic?

A
  • no true nucleus in prokaryotic cells but a distinct nucelus with an envelope in Eukaryotic cells.
75
Q

Differences in protein association between Eukaryotic and Prokaryotic?

A

Prokaryotic DNA is not associated with proteins while in Eukaryotic, DNA is associated with proteins called histones.

76
Q

Differences in membrane bound organelles between Eukaryotic and Prokaryotic?

A

No membrane bound organelles in Prokaryotic cells while there are many in Eukaryotic cells.

77
Q

Differences in Ribosomes present between Eukaryotic and Prokaryotic?

A

Ribosomes are smaller in PRO - cells (70S) but are larger in Eukaryotic cells (80S)

78
Q

What is the capsule and what does it do in a prokaryotic cell?

A

It’s a layer of slime which surrounds the cell wall and protects it from other cells and helps groups of bacteria to stick together for further protection.

79
Q

What is Flagellum for in a Prokaryotic Cell?

A

Used for locomotion.

80
Q

What are Viruses?

A

Acellular, non living particles - smaller than bacteria. 20-300nm range.

81
Q

What do they contain? (Viruses)

A

Nucleus acids (DNA or RNA) and this is enclosed within a protein coat called capsid.

82
Q

Some viruses are further surrounded by…

A

A lipid envelope.

An example of a virus with one is the Human Immunodeficiency virus.

83
Q

The lipid envelope or the capsid also have…

A

Attachment proteins which are essential to allow the virus to identify and attach to a host cell.

84
Q

What are Microscopes?

A

Instruments that produce a magnified image of an object.

85
Q

Light had a long wavelength, what does this mean?

A

It means that light microscopes can only distinguish between two objects if they are 0.2um or further apart.

86
Q

Magnification =

A

Image size / real Size

87
Q

What is the resolution/ resolving power?

A

The minimum distance apart that two objects can be in order for them to appear as separate items.

88
Q

Greater resolution means…

A

Greater clarity.

89
Q

Increasing the magnification increases…

A

The size of an image.

90
Q

What works better than a light microscope?

A
  • Electron Microscope as electrons have a short wavelength meaning they have a high resolving power.
91
Q

As electrons are negatively charged,

A

The beam can be focused using electromagnets.

92
Q

There are two types of electron microscopes:

A
  • the transmission electron microscope TEM

- the scanning electron microscope SEM

93
Q

How does the TEM do?

A

TEM uses electromagnets to focus a beam of electrons, which is then transmitted through the specimen.

Denser parts absorb more electrons and appear darker.

94
Q

Advantages of TEM: (2)

A
  • shorter wavelength means higher resolution (1000x times higher than light microscope)
  • magnification is higher than light by 100x.
95
Q

Disadvantages of TEM: (3)

A
  • whole system must be in a vacuum so only dead specimens can be viewed.
  • complex standing process but the image isn’t even in colour.
  • only thin specimens & artefacts are produced.
96
Q

Advantages of Light microscopes: (3)

A
  • colour
  • easy to use
  • cheap
97
Q

Disadvantages of Light Microscopes: (3)

A
  • lower resolution and magnification
  • lower wavelength
  • can only see large organelles
98
Q

How does the SEM work?

A

The SEM directs a beam of electrons on the surface of the specimen from above - electrons are scattered and the pattern of this scattering depends on the contours of the specimen surface.

99
Q

Disadvantages of the SEM

Except…

A

Basically the same as the disadvantages of the TEM except the specimen does not have to be thin.

100
Q

Advantages of the SEM:

A
  • 3D
  • doesn’t need a thin specimen
  • higher resolution and magnification than light microscopes.
101
Q

How to prepare a ‘temporary mount’ of a specimen on a slide: (3)

A
  • pipette a drop of water on a slide then use tweezers to add onion skin on top.
  • add a drop of stain (used to highlight objects)
  • add the cover slip and try not to get air bubbles as they obstruct your view.
102
Q

What is Cell Fractionation?

A

The process where cells are broken up and the different organelles they contain are separated out.

103
Q

What happens before Cell Fractionation can happen?

A

The tissue is placed in a cold buffered solution of the same water potential as the tissue.

104
Q

Why does the solution have to be cold?

A

To reduce enzyme activity that might break down the organelles.

105
Q

Why does the the solution have to be of the same water potential as the tissue?

A

To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.

106
Q

Why does the solution have to be buffered?

A

So that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.

107
Q

What is Homogenisation?

Second step of Cell Fractionation

A

When cells are broken up by a blender which releases the organelles from the cell - the fluid known as the homogenate is filtered to remove any complete cells and large pieces of debris.

108
Q

What is Ultracentrifugation?

A

The process by which the fragments in the filtered homogenate are filtered at a very high speed in order to create a centrifugal force.

109
Q

Give the steps for Ultracentrifugation of an animal cell: (5)

A
  • the tube of filtrate is placed in the centrifuge and spun at a slow speed
  • the nuclei and heavy organelles are forced to the bottom of the tube where they form a thin sediment.
  • the fluid (supernatant) at the top is removed leading the sediment of the nuclei.
  • the supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before
  • this continues with the next heavies organelles. And the pellet at the bottom of the tube is made up of lighter and lighter organelles.
110
Q

How can we measure the size of objects using a light microscope?

A

Use an eyepiece graticule

A glass disc placed in the eyepiece which has a scale typically 10mm long and is divided into 100 small lines.

111
Q

Why can the scale on the eyepiece gesticule not be used directly to measure the size of objects?

A

Because each objective lens will magnify to a different degree - it must be calibrated for a particular objective lens.

112
Q

How can you calibrate an eyepiece graticule?

A

Use a special microscope slide called the stage micrometer.

Scale is usually 2mm long and it’s smallest sub divisions are 0.01mm

You set the units on the micrometer scale equal to the units on the graticule scale and find 1 unit.

113
Q

How are organelles usually separates? What’s this order?

A

In order of mass (heaviest first)

Nuclei, chloroplasts, mitochondria Lysosomes then ER then the ribosomes.

114
Q

How do Prokaryotic cells replicate?

A

By Binary Fission.

115
Q

What happens in Binary Fission?

A
  • circulate DNA and plasmids are replicated and cell gets bigger.
  • DNA loops move to opposite end of the cell and the cytoplasm divides = new cell walls form.
  • Cytoplasm divides and two identical daughter cells are produced.
116
Q

How do Viruses replicate themselves?

A

They use their attachment proteins to bind to complementary receptor proteins on the surface of host cells.

117
Q

Do Viruses undergo cell division?

A

No, they’re dead.
So they inject their DNA or RNA into the host cell which uses its own machinery (Ribosomes enzymes etc) to replicate the viral particles.

118
Q

Why can some Viruses only infect one type of cell?

A

Because different cuts used have different proteins so they require different receptor proteins on host cells.

119
Q

What happens to a parent cell in Mitosis?

A

It divides to produce two identical daughter cells.

120
Q

Why is Mitosis needed?

A

For the growth of multicellular organisms and for repairing damaged tissues.

121
Q

Mitosis is part of …

A

The cell cycle.

122
Q

Name the 5 stages of Mitosis:

IN ORDER:

A

Interphase

Prophase

Metaphase

Anaphase

Telophase

123
Q

What is the Interphase?

What happens to the ATP content and why is the ATP content important?

A

The cell is carrying out its normal functions but also prepares to divide e.g. the DNA is replicated and so are the organelles.

The ATP content also increases which provides the energy needed for cell division.

124
Q 
Stage 1 - Prophase
What happens here?
To the chromosomes:
To the centrioloses:
To the nuclear enevelope:
A

Chromosomes condense, get shorter and fatter.

Tiny bundles of protein ‘centrioles’ love to the opposite end of the cell, forming a network of protein fibres called the ‘spindle.’

The nuclear envelope breaks down and chromosomes lie freely in the cytoplasm.

125
Q

Stage 2 - Metaphase

What happens here?

A

The chromosomes line up along the middle of the cell and become attached to the spindle by their centromere.

126
Q

Stage 3 - Anaphase

What happens here?

A

The centromeres divide, separating each pair of chromatids. The spindles contract and the chromatids are pulled to opposite ends of the spindle.

127
Q

Stage 4 - Telophase

What happens here?

A

The chromatic s reach the opposite poles on the spindle & uncoil to be long and thin again.
They are chromosomes again.

128
Q

What’s the final thing that happens in Mitosis during the Telophase stage?

A

A nuclear envelope forms around each group of chromosomes - two nuclei and then the cytoplasm divides (cytokinesis).

Mitosis is finished = two identical daughter cells.

129
Q

What happens if there’s a mutation in a gene that controls cell division?

A

The cells can grow out of control - and keep on dividing to make more and more cells.

This forms a tumour.

130
Q

What is Cancer?

A

A tumour that invades surrounding tissue.

131
Q

What are treatments for Cancer designed to do?

A

Control the rate of cell division in tumour cells by distrusting the cell cycle = kills tumour cells.

132
Q

What is the issue with treatments for cancer?

However…

A

They don’t distinguish tumour cells from normal cells do they can also kill normal body cells - however, tumours divide more so treatments are more likely to kill the tumour cells.

133
Q

Name 2 cell cycle targets of cancer treatments:

A
  • G1 (cell growth and protein production)

- S Phase (DNA replication)

134
Q

What does the G1 cell cycle target treatment do:

A

E.g. Chemotherapy.

This prevents the synthesis of enzymes needed for DNA replication. If these aren’t produced, the cell can’t enter the synthesis phase = disrupts and kills cell.

135
Q

What does the S phase cell cycle target treatment do?

A

Radiation and some drugs may damage DNA. At many points in the cell cycle, the cell is checked for damage. If severe damage is detected, the cell will kill itself which prevents further tumour growth.

136
Q

Give the overall stages for the CELL CYCLE (not just Mitosis)
There are 4 stages again.

A

Mitosis
(cycle starts and ends here)

GAP PHASE 1
(cell grows and new organelles are made)

SYNTHESIS
(Cell replicates it’s DNA, ready to divide by Mitosis)

GAP PHASE 2
(cell keeps growing & proteins needed for cell division are made)

137
Q

How can you observe cells using an optical microscope? (4)

A
  • clipping the slide on stage & select the lowered objective lens.
  • use coarse adjustment knob to bring the stage up to just below the objective lens & look in eyepiece.
  • use coarse adjustment knob to move the stage downwards until the image is roughly in focus.
  • adjust the focus with the fine adjustment knob to get a clear image of te slide.
  • u can use a higher mag.
138
Q

What is the Mitotic Index?

A

The promotion of cells undergoing Mitosis.

139
Q

A plant root tip is constantly growing so…

A

You’d expect a high mitotic index.

140
Q

Give the Mitotic Index Formula:

A

Number or cells with visible chromosomes
——————-
Total number of cells observed.

141
Q

How can prepare root tips to observe Mitosis? (6) using an optical microscope.

A
  • cut 1cm from the tip of a root (that’s where growth occurs)
  • prepare a boiling tube with 1M hydrochloric acid n put in a 60 water bath. Put root tip into the boiling tube for 5mind.
  • rinse root tip with a pipette. Put root tip on a slide and cut 2mm from the very tip of it.
  • use a mounted needle to break the tip open and spread the cells out thinly.
  • add stain (leave for few mins) makes it easier to see chromosomes.
  • place a cover slip and push firmly to squash it - Makes it thinner so light can pass.

AQA A Level Biology 2018 (17 decks)

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