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A-Level Biology [AQA] > [Y1] Cells > Flashcards

[Y1] Cells Flashcards

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1
Q

What is Magnification?

A
  • By how much an image is enlarged under a microscope.

- It is controlled by the power of the lens used.

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2
Q

What is Resolution?

A
  • The minimum distance between two objects at which a microscope can distinguish them as separate entities.
  • It is controlled by the wavelength of the illumination used.
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3
Q

Why aren’t Light Microscopes used in labs? And what is used instead?

A
  • Light microscopes have a poor resolution as a result of a relatively long wavelength of light.
  • (as of 1930s) electron microscopes have been used instead.
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4
Q

What are the two types of Electron Microscopes?

A
  • Transmission electron microscopy (TEM)

- Scanning electron microscope (SEM)

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5
Q

What are the Advantages of TEMs?

A
  • High Magnification
  • High Resolution
    • due to shorter wavelength
  • Focuses using a condenser electromagnet.
  • 2D photomicrograph
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6
Q

What are the Advantages of SEMs?

A
  • High Magnification
  • High Resolution
    • due to shorter wavelength
  • Focuses using a condenser electromagnet.
  • Produces a 3D image.
  • Does not require a thin specimen.
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7
Q

What are the Disadvantages of TEMs?

A
  • Living specimen cannot be used.
  • Must be in a vacuum.
  • Must be a thin cut specimen.
  • Complicated preparation may create artefacts.
  • Non-coloured image.
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8
Q

What are the Disadvantages of SEMs?

A
  • Living specimen cannot be used.
  • Must be in a vacuum.
  • Complicated preparation may create artefacts.
  • Non-coloured image.
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9
Q

Who is the actual size of a specimen calculated?

A

Image Size / Magnification

  • remember to convert your units.
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10
Q

What are the units of size and their magnitude (compared to ‘m’)?

A 
km     1x10^3
m       1x10^0
cm     1x10^-2
mm    1x10^-3
μm     1x10^-6
nm     1x10^-9
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11
Q

What is an eyepiece graticule and how can it be used?

A
  • A glass disc with a scale etched on it.
  • It can be placed in the eyepiece of a microscope to be used to measure the size of an object.
  • However, this will not directly measure the object, as the objective lens will magnify it to a different degree.
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12
Q

Before using an eyepiece graticule, what must you do and how is this done?

A
  • It must be calibrated for a particular objective lens.

- This can be done by using a stage micrometre, this also has a scale etched onto it.

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13
Q

What is Cell Fraction and Centrifugation?

A
  • The process by which cells are broken up and their organelles are separated, by size, ready for study.
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14
Q

What conditions are made for Cell Fraction and Centrifugation?

A

Cold: to reduce enzyme activity that could damage the organelle.

Buffered: to maintain a constant pH and prevent protein damage.

Isotonic: to prevent cell organelles from bursting or shrinking bt osmosis.

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15
Q

What are the 3 stages of Cell Fraction and Centrifugation?

A
  • Homogenisation.
  • Filter (filtration).
  • Ultracentrifugation.
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16
Q

What happens in the 1st stage of Cell Fraction and Centrifugation?

A

Homogenisation:

- Cells are broken up by a homogeniser (blender) releasing the organelle.

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17
Q

What happens in the 2nd stage of Cell Fraction and Centrifugation?

A

Filter:
- Tissue is filtered through a sieve to remove insoluble material (e.g. cell wall, large pieces of unhomogenised tissue, connective tissue).

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18
Q

What happens in the 3rd stage of Cell Fraction and Centrifugation?

A

Ultracentrifugation:
- The centrifuge is filled with filtrate and spun a slow speed so the heaviest organelle (e.g. nuclei) are forced to the bottom and form a thin pellet.

  • The fluid at the top (the supernatant) is removed and re-spun at a faster speed to gain the next heaviest organelle (e.g. chloroplast).
  • This process is repeated again until all of the organelles have been separated.
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19
Q

What organelles are present in animal cells?

A
  • Cell-surface membrane
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Golgi apparatus (with vesicle)
  • Lysosome
  • 80s Ribosome
  • Rough endoplasmic reticulum (RER)
  • Smooth endoplasmic reticulum (SER)
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20
Q

What organelles are present in plant cells?

A
  • Cell-surface membrane.
  • Nucleus.
  • Cytoplasm.
  • Mitochondria.
  • Golgi apparatus (with vesicle).
  • Lysosome.
  • 80s Ribosome.
  • Rough endoplasmic reticulum (RER).
  • Smooth endoplasmic reticulum (SER).
  • Cell wall.
  • Cell vacuole.
  • Chloroplasts
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21
Q

What organelles are present in bacterial cells?

A
  • Cell-surface membrane.
  • 70s Ribosome.
  • Cell wall.
  • Capsule.
  • Pilus.
  • Flagellum.
  • Chromosomal DNA in the nucleoid region.
  • Cytoplasm.
  • Plasmid.
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22
Q

Are viruses living?

A

No, as they are not made up of cells.

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23
Q

What organelles are present in viruses?

A
  • Attachment protiens
  • Lipid envelope
  • Nucleoprotiens
  • RNA / DNA
  • Capsid
  • Matrix
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24
Q

Describe viral attachment proteins.

A

These are proteins that stick out f the virus and is used to attach on to host cells.

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25
Q

Describe a viral lipid envelope.

A

The outer-most layer of a virus, this is derived from host cells.

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26
Q

Describe viral nucleoproteins.

A

Accessory proteins found inside a capsid.

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27
Q

Describe viral DNA/RNA.

A

The virus’s genetic information, that is also injected into host cells, found inside a capsid.

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28
Q

Describe a viral capsid.

A

Protein coat holding DNA / RNA.

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29
Q

Describe a viral matrix.

A

A Protein layer inside the envelope.

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30
Q

Describe a eukaryotic cell-surface membrane.

A

The lipid/protein membrane found on the surface of an animal cell and just inside the cell wall of other cells.

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31
Q

What is the function of a eukaryotic cell-surface membrane?

A
  • Regulates the movement of substance into and out of the cell.
  • It also has receptor molecules on it, which allows it to respond to chemicals (like hormones).
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32
Q

Describe a eukaryotic nucleus.

A
  • A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores.
  • The nucleus contains chromosomes (which are made from protein-bound linear DNA) and one or more structures call a nucleolus
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33
Q

What is the function of a eukaryotic nucleus?

A

The nucleus contains the cell’s activities, by controlling the transcription of DNA, to code for proteins.

The Pores allow substances (e.g. RNA) to move between the nucleus and the cytoplasm.

The nucleolus makes ribosomes.

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34
Q

Describe a eukaryotic mitochondrion.

A

They are usually oval-shaped.

They have a double membrane (proof of endosymbiosis) - the inner one is folded in to form structures called cristae.

Inside is the matrix, which contains enzymes involved in respiration.

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35
Q

What is the function of a eukaryotic mitochondrion?

A

The site of aerobic respiration where ATP is produced.

They are found in large numbers in cells that are very active and requires a lot of energy.

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36
Q

Describe a eukaryotic chloroplast?

A
  • A small, flattened structure found in plant and algal cells.
  • It’s surrounded by a double membrane, and also has membranes inside the thylakoid membranes.
  • Theses membranes are stacked up in some parts of the chloroplast to from grana.
  • Grana are linked together by lamellae - thin pieces of thylakoid membrane.
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37
Q

What is the function of a eukaryotic chloroplast?

A
  • The site where photosynthesis takes place.
  • Some part of photosynthesis happens in the grana, and other parts happen in the stroma (a thick fluid found in chloroplasts
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38
Q

Describe a eukaryotic golgi apparatus?

A
  • A group of fluid-filled, membrane-bound flattened sacs.

- Vesicles are often seen at the edge of the sacs.

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39
Q

What is the function of a eukaryotic Golgi apparatus?

A
  • Adds carbohydrates to proteins to form glycoproteins.
  • Produces secretory enzymes.
  • Transports, modifies and stores lipids.
  • It also makes lysosomes.
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40
Q

Describe a eukaryotic golgi vesicle?

A
  • A small fluid-filled sac in the cytoplasm, surrounded by a membrane and produces by the golgi apparatus.
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41
Q

What is the function of a eukaryotic golgi vesicle?

A
  • Stores lipids and proteins made by the golgi apparatus and transports them out of the cell (via the cell-surface membrane).
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42
Q

Describe a eukaryotic lysosome?

A
  • A round organelle surrounded by a membrane with no clear internal structure.
  • It’s a type of golgi vesicle.
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43
Q

What is the function of a eukaryotic lysosome?

A
  • Contains digestive enzymes called lysozyme that hydrolyses material.
  • Releases enzymes to the outside of the cell (exocytosis) to destroy material.
  • Digests invading cells and breaks down worn-out components of the cell to re-use.
  • Completely breaks down the cell after they have died (autolysis)
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44
Q

Describe a eukaryotic ribosome?

[What ribosomes are found in prokaryotic cells?]

A

[80s ribosomes]
- A very small organelle that wither floats free in the cytoplasm of is attaches to the rough endoplasmic reticulum.

  • It’s made up of protein and RNA.
  • It’s not surrounded by a membrane.

[70s Ribosomes are in prokaryotes]

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45
Q

What is the function of a eukaryotic ribosome?

A
  • The site where proteins are made.
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46
Q

Describe a eukaryotic rough endoplasmic reticulum?

A
  • A system of membranes enclosing a fluid-filled space.

- The surface is covered with ribosomes.

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47
Q

What is the function of a eukaryotic rough endoplasmic reticulum?

A
  • Provides a large surface area for the synthesis of proteins and glycoproteins.
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48
Q

Describe a eukaryotic smooth endoplasmic reticulum.

A
  • Similar to the rough endoplasmic reticulum, but with no ribosomes.
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49
Q

What is the function of a eukaryotic smooth endoplasmic reticulum?

A
  • Synthesis, stores and processes lipids and carbohydrates.
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50
Q

Describe a cell wall.

A
  • A rigid structure that surrounds cells in plants, algae and fungi.
  • In plants and algae it’s made mainly of carbohydrate cellulose.
  • In fungi, it’s made of chaitin.
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51
Q

What is the function of a cell wall?

A
  • Supports cells and prevents them from changing shape.
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52
Q

Describe a eukaryotic cell vacuole.

A
  • A membrane-bound organelle found in the cytoplasm of plant cells.
  • It contains cell sap - a weak solution of sugar and salts.
  • The surrounding membrane is called the tonoplast.
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53
Q

What is the function of a eukaryotic cell vacuole?

A
  • Helps to maintain pressure inside the cell and keeps the cell rigid.
  • This stops plants wilting.
  • Acts as a temporary sugar and amino acid store.
  • Can store pigments (e.g. to colour petals to attract pollinators).
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54
Q

Describe a prokaryotic Plasmid.

A
  • Circular genetic material found in the nucleoid region of a cell.
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55
Q

What is the function of a prokaryotic plasmid?

A
  • Processes genes that may aid the survival of bacteria in adverse conditions
  • (e.g. produces enzymes that break down antibiotics)
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56
Q

Describe a prokaryotic flagella.

A
  • A tail like organelle at the back of the cell.

- There may be more than one.

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57
Q

What is the function of a prokaryotic flagella?

A
  • Used for locomotion (moving around).
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58
Q

Describe a prokaryotic capsule

A
  • A mucilaginous layer of slime.
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59
Q

What is the function of a prokaryotic capsule

A
  • Protects bacterium from other cells and helps groups of bacteria to stick together for further protection.
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60
Q

Describe a prokaryotic pili.

A
  • A thin, rigid fiber made of protein that protrudes from the cell surface.
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61
Q

What is the function of a prokaryotic Pili?

A
  • To attach a bacterial cell to specific surfaces or to other cells
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62
Q

Describe the prokaryotic nucleoid.

A

The nucleoid is the region of the cell that contains primary DNA material

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63
Q

Describe a prokaryotic cell wall.

A
  • 10 - 80nm thick, made of murein.
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64
Q

What is the function of a prokaryotic cell wall?

A
  • Supports cells and prevents them from changing shape.
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65
Q

Describe a viral attachment protein.

A

Proteins that stick out of the virus.

The virus either has this or a lipid membrane.

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66
Q

What is the function of a viral attachment protein?

A

This attaches on the surface of a specific host cell, in order to inject its genetic material into the host

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67
Q

Describe a viral capsid.

A

A protein coat that encloses the cells nucleic acid.

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68
Q

What is the function of a viral capsid?

A

To contain the viruses nucleic acid.

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69
Q

Describe a viral lipid envelope.

A

This surrounds the capsid in some cells (which don’t have attachment proteins).

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70
Q

What is the function of a viral lipid envelope?

A

To attach onto host cells, and acts as another form of protection for the viruses nucleic acid.

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71
Q

What are the two types of cell division?

A
  • Mitosis: 2 daughter cells have the same number of chromosomes as the parent cell.
  • Meiosis: 4 daughter cells have half the number of chromosomes as the parent cell.
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72
Q

Describe the two parts of a chromosome.

A
  • Centromere: centre of the chromosome

- 2 Chromatids: each an identical copy of DNA from the parent cell

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73
Q

What happens before mitosis?

A

Interphase

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74
Q

What is interphase?

A

A period of considerable cellular activity that includes replication of DNA. The DNA remains joined at their centromere.

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75
Q

What are the stages of mitosis?

A
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
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76
Q

What happens during the prophase?

A
  • Chromosomes condense
  • (Animal cells) two centrioles move to opposite ends and develop spindle fibres.
  • The nucleolus disappears and the nuclear envelope breaks down.
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77
Q

What happens during the metaphase?

A
  • Microtubules attach to the centromere and pull the chromosomes along the spindle apparatus.
  • These arrange themselves across the equator of the cell.
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78
Q

What happens during the anaphase?

A
  • The centromere divide into two and the spindle fibres pull the individual chromatids.
  • Mitochondria gather around spindle fibres and provide energy to it.
  • Chromatids move rapidly to opposite poles.
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79
Q

What happens during the Telophase?

A
  • Chromosomes reach their poles and become longer and thinner.
  • Chromosomes disappear, leaving widely spread chromatin.
  • Spindle fibres disintegrate.
  • Nuclear envelope and nucleolus re-form.
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80
Q

What happens during cytokinesis?

A

The cytoplasm divides.

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81
Q

How do prokaryotic cells divide?

A

Binary fission.

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82
Q

What happens during binary fission?

A
  • Circular DNA molecules replicate and both copies attach to the cell membrane.
  • The plasmids replicate
  • Cell membrane begins to grow between the 2 DNA molecules and begin to pinch inwards (dividing the cytoplasm into 2)
  • A new cell wall forms between the two molecules of DNA.

Dividing this into two identical daughter cells, each with a single copy of circular DNA and a variable number of plasmids

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83
Q

Do viruses undergo cell division?

A

No.

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84
Q

How do viruses replicate?

A
  • They attach to their host cell with attachment proteins.
  • They then inject their nucleic acid into the host cell.
  • This provides ‘instructions’ for the host cell’s metabolic processes to start producing viral components.
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85
Q

What are the three stages of the cell cycle?

A
  • Interphase.
  • Nuclear Division.
  • Cytokinesis.
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86
Q

What is a cancer?

A

A growth disorder of cells that leads to uncontrolled growth and division of cells.

As a result, a tumour develops and constantly expands in size.

87
Q

Where are tumours common?

A
  • Lungs.
  • Prostate gland.
  • Breast and ovaries.
  • Large intestine.
  • Stomach.
  • Oesophagus.
  • Pancreas.
88
Q

When do tumours become cancerous?

A

When they change from being benign to malignant.

89
Q

What is the difference between the two types of tumour?

A

Malignant: grow rapidly, are less compact, likely life-threatening.

Benign: grow more slowly, more compact, less likely to be life-threatening.

90
Q

How do cancers form?

A
  • The rate of mitosis is controlled by two types of gene.
  • A mutation of one of these can result in uncontrolled mitosis.
  • These calls are often different structurally and functionally.
  • Most mutated cells died.
  • If they survive they are able to divide to form clones of themselves, thus forming tumours.
91
Q

How are cancers treaded?

A
  • Cancer treatment involves killing dividing cells by blocking a part of the cell cycle.
  • thus the cell cycle is disrupted and cell division and hence cancer growth ceases.
  • The drugs used (chemotherapy) usually:
    Prevent DNA replication
    Inhibit metaphase by interfering with spindle formation.
92
Q

What is the problem with cancer treatment drugs?

A

They also disrupt the cell cycle of normal cells.

Because they are more effective against rapidly dividing cells, cancer cells are damaged to a greater degree.

But so are normal rapidly dividing cells, like hair-producing cells, hence hair loss.

93
Q

What is the cell surface membrane?

A

A plasma membrane that surrounds cells and forms a boundary between the cell cytoplasm and the environment.

94
Q

Why are phospholipids important to the cell surface membrane?

A
  • Both hydrophilic heads point outside and are attracted by water on both sides.
  • Both hydrophobic tails point inside and repel water on both sides.
95
Q

What is the function of phospholipids in the cell surface membrane?

A
  • Allow lipid-soluble substances to entre and leave the cell.
  • Prevent water-soluble substance from entering and leaving the cell.
  • Make the membrane flexible and self-sealing.
96
Q

How are proteins embedded in the phospholipid bilayer of the cell surface membrane?

A
  • Extrinsic on the surface of the bilayer and never extend completely across it. Either: mechanically support the membrane OR in conjunction with glycolipids as receptor molecules.
  • Intrinsic which completely span the bilayer. Either: water-filled protein channels (allowing in/out water-soluble ions) OR carrier proteins that bind to ions and change shape to move them across the bilayer.
97
Q

What are the functions of proteins in the cell surface membrane?

A
  • Structural support.
  • Channels for transporting water-soluble substances.
  • Allow active transport through carrier proteins.
  • Form cell-surface receptors for identifying cells.
  • Help cells adhere together.
  • Act as receptors (e.g. for hormones).
98
Q

What are the functions of cholesterol in the cell surface membrane?

A
  • Reduce lateral movement of other molecules including phospholipids (adding strength)
  • Make the membrane less fluid at high temperatures (without making it too rigid).
  • Prevent leakage of water and dissolved ions from the cell.
99
Q

What are glycolipids made up of and how is it arranged on the cell-surface membrane?

A

Carbohydrates covalently bonded with a lipid.

The carbohydrate portion extrudes from the cell-surface and acts as a receptor for specific chemicals.

100
Q

What are the functions of glycolipids in the cell surface membrane?

A
  • Act as recognition sites.
  • Help maintain the stability of the membrane.
  • Help cells to attach to one another and form tissues.
101
Q

What are glycoproteins made up of and how is it arranged on the cell-surface membrane?

A

Carbohydrates bonded to many extrinsic proteins.

They extrude from the cell-surface and acts as a receptor for hormones and neurotransmitters.

102
Q

What are the functions of glycoproteins in the cell surface membrane?

A
  • Act as recognition sites.
  • Help cells to attach to one another and so form tissue.
  • Allow cells to recognise one another (e.g lymphocytes can recognise an organism’s own cells).
103
Q

What are the functions of membranes within cells?

A
  • Control the entry and exit of material in discrete organelles (e.g. mitochondria and chloroplasts).
  • Separate organelles from cytoplasms so that metabolic reactions can take place within them.
  • Provide an internal transport system (e.g. ERs)
  • Isolate enzymes that might damage the cell (e.g. lysosomes)
  • Provide surfaces on which reactions can occur (e.g. protein synthesis using ribosomes on RER)
104
Q

Why can some molecules not freely diffuse across the cell-surface membrane?

A
  • non-lipid-soluble so cannot pass through bilayer.
  • too large to pass through channels.
  • same charge as the charge of the protein channels (so they are repelled (even if they are small enough to fit)).
  • are polar (electrically charged) and so have difficulty passing through non-polar hydrophobic tails.
105
Q

Why does the fluid-mosaic model have its name?

A

Fluid: individual phospholipids can move relative to one another. Giving them a flexible structure that can change shape.

Mosaic: embedded proteins vary in shape, size and pattern (like stone/tiles in a mosaic)

106
Q

What is the average thickness of the cell-surface membrane (in the fluid mosaic model)?

A

7 nm

7 x 10⁻⁹m

107
Q

All movement involves energy. How is diffusion passive?

A

The energy comes from the natural, inbuilt motion of particles.

108
Q

What 3 features of particles help explain passive movement?

A
  • All particles are constantly in motion due to kinetic energy that they have.
  • This motion is random, with no set pattern to the way the particles move around.
  • Particles are constantly colliding with each other or other objects (like the vessels they are contained in).
109
Q

Particles in a __1__ vessel will on their own accord, distribute themselves __2__ throughout the vessel as a result of __3__.

A

Particles in a closed¹ vessel will on their own accord, distribute themselves evenly² throughout the vessel as a result of diffusion³.

110
Q

Define diffusion.

A
  • The net movement of molecules or ions from a region what they are more highly concentrated…
  • … to on where their concentration is lower …
  • … until evenly distributed.
111
Q

What must molecules be in order to diffuse across membranes?

A
  • small
  • non-polar

(like oxygen and carbon dioxide)

112
Q

What is facilitated diffusion?

A

The movement of molecules across a membrane that is made easier by transmembrane channels and carries that span the membrane.

113
Q

Is facilitated diffusion passive or active? / How does it work?

A

Passive.

It relies on the inbuild motion (kinetic energy) of the diffusing molecule at specific points on the plasma membrane.

114
Q

Which two proteins are involved in facilitated diffusion?

A

Protein channels.

Carrier proteins.

115
Q

Describe a protein channel.

A
  • Water-filled hydrophilic channels that allow specific water-soluble ions to pass through.
  • These are selective and open in the presence of a specific ion.
  • It has control over the entry and exit of ions.
116
Q

How do protein channels work?

A

The ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens the other side.

117
Q

How do carrier proteins work?

A

When a molecule, such as glucose, that is specific to it is present, it binds with the protein.

This causer it to change shape in such a way that the molecule is released to the inside of the membrane.

118
Q

Protein channels and carrier proteins have ____ sites.

A

Protein channels and carrier proteins have binding sites.

NOT active sites.

119
Q

Define osmosis.

A
  • The passage of water from a region where it has a higher water potential to a region where it has a lower water potential…
  • …through a selectively permeable membrane.
120
Q

What does ‘selectively permeable’ mean?

A

Permeable to water and a few other small molecules, but not larger ones.

121
Q

What is a solute?

A

Any substance dissolved in a solvent.

122
Q

What is a solution?

A

When a solute is dissolved in a solvent.

123
Q

What is water potential?

A

The pressure created by water molecules.

Symbol: Psi Ψ
Units: kPa

124
Q

What is the water potential of pure water at STP?

A

(STP = 25°C and 100kPa)

0

125
Q

What happens to the water potential when a solute is added to pure water?

A

Lowered

126
Q

The water potential of a solution is always…

A

… less than 0.

127
Q

Describe osmosis in terms of water potential.

A

Water will move from a less negative Ψ (e.g. -20kPa) to a more negative Ψ (e.g. -30kPa).

higher Ψ to lower Ψ.

128
Q

How can you find the water potential of cells of tissue?

A

Place them in varying Ψ, where there is no net movement the Ψ inside = Ψ outside.

129
Q

Explain what happens when a selectively permeable plasma membrane separates two solutions?

The left has a low concentration of solute while the right has a high concentration.

A
  • Both the solute and water molecules are in random motion due to their kinetic energy.
  • The selectively permeable membrane only allows water across it.
  • Water diffuses from the high partial pressure (left) to the low partial pressure (right), down the water potential gradient.
  • Once the water potential on either side is equal, a dynamic equilibrium is established and there is no net movement of water.
130
Q

What would happen if a red blood cell was placed in pure water?

A
  • I would absorb water by osmosis because it has a lower water potential.
  • Although its cell surface membrane is flexible, it cannot stretch to any great extent.
  • This therefore breaks, bursting the cell and releasing its contents (haemolysis).
131
Q

What has the same water potential as blood cells?

A

Plasma.

132
Q

Define active transport.

A

The movement of molecules or ions into or out of a cell…

…from a region of lower concentration to a region of higher concentration…

…using ATP and carrier proteins.

133
Q

In active transport what is ATP used for?

A
  • Directly move molecules.
  • Individually move molecules using a concentration gradient which has already been set up by (direct) active transport (aka cotransport).
134
Q

How does active transport differ from passive forms of transport?

A
  • Metabolic energy is needed.
  • Moved against the concentration gradient.
  • Carrier proteins which act as pumps are involved.
  • Selective process (only specific substances are transported).
135
Q

Describe the direct active transport of a single molecule or ion.

A
  • Carriere proteins bind to the molecule on one side of it.
  • This is binded to its receptor site.
  • ATP binds to the other side and is turned into ADP and a phosphate molecule.
  • As a result, the protein changes shape and opens on the opposite side.
  • The molecule is released to the other side.
  • The phosphate molecule is released from the protein to revert its original shape.
136
Q

What is the difference between active transport and facilitated diffusion?

A

Both use carrier proteins but:

Facilitated diffusion is DOWN a concentration gradient.

Active transport is AGAINST a concentration gradient.

137
Q

How is metabolic energy provided in active transport?

A

As ATP.

138
Q

Are the same carrier proteins used in active transport as in facilitated diffusion?

A

No.

Any given carrier protein is very specific about what it carries and by which method.

139
Q

Can multiple molecules or ion be moved at once during active transport?

A

Yes.

140
Q

What happens in a sodium-potassium pump.

A

Sodium ions are actively removed.

Potassium ions are actively taken in.

This happens at the same time.

141
Q

How can the rate of movement across membranes be increased?

A
  • Microvilli, to increase the SA for the insertion of carrier proteins through which diffusion, facilitated diffusion, and active transport can take place.
  • Increase the number of protein channels and carrier proteins in any given area of membrane (e.g. increase their density).
142
Q

Describe the role of diffusion in absorption.

A
  • Carbs and proteins are continuously being digested, increasing the concentration of glucose and amino acids.
  • This creates a concentration gradient from the ileum to the blood.
  • Because blood is being circulated. The gradient is maintained.
  • Thus the rate of facilitated diffusion across epithelial cell-surfaces are increased.
143
Q

Describe the role of active transport in absorption.

A
  • With only diffusion the concentration of glucose/amino acids in the blood and the ileum would reach a state of dynamic equilibrium.
  • Thus active transport must take place to allow all the glucose/amino acids to be absorbed into the blood.
  • This is actually done by co-transport.
144
Q

Describe co-transport in absorption.

A
  • Sodium ions are actively transported out of epithelial cells, by the Na-K pump into the blood.
  • This happens on one type of protein - carrier molecule.
  • This means their is a much higher concentration of Na ions in the lumen than inside epithelium cells.
  • Na ions diffuse down this gradient through a different type of protein carrier (co-transport protein).
  • As this happens they carry either amino acid ore glucose into the cell with them.
  • The glucose/amino acid can then pass into blood plasma by f.diffusion using another type of carrier.
145
Q

How is co-transport in absorption an indirect form of active transport?

A
  • Na ions move down their concentration gradient.
  • glucose moves against their concentration gradient.
  • It is the Na ions concentration rather than a ATP directly theat powers this movement.
146
Q

What is immunity?

A

When the body’s defences seem to be better prepared for a second infection from the same pathogen and can kill it before it can cause any harm.

147
Q

Which immune responses involve lymphocytes?

A
  • Cell-mediated (T lymphocytes)

- Humoral (B lymphocytes)

148
Q

What do protein molecules with a specific 3D structure allow the immune system to identify?

A
  • Pathogens.
  • Non-self material (cells of other organisms from the same species.
  • Toxins.
  • Abnormal body cells.
149
Q

What can be done to ensure donated organs are not regrected?

A
  • For the organ to come from relatives that are genetically close.
  • Immunosuppressant drugs are can be administered.
150
Q

How is there a high probability that , when a pathogen gets into the body, the body has the lymphocytes with the complementary one protein there

A
  • There are so many different types of lymphocytes.
151
Q

Why is there a time lag between exposure to the pathogen and body’s defences bringing it under control?

A

Clonal selection has to take place.

  • Because there are few of each type of lymphocyte, the one which has complementary proteins it is stimulated to divide to build up its numbers to a level where it can effectively work.
152
Q

How does the body ensure lymphocytes don’t attack self cells?

A
  • Lymphocytes produced in the bone marrow initially only encounter self-antigens.
  • If they respond to these they undergo programmed cell death (apoptosis) before they differentiate into mature lymphocytes.
  • Thus no clones of these anti-self lymphocytes will appear in the blood.
153
Q

How do specific and nonspecific defence mechanisms differ?

A

Specific:
- slower and specific to each pathogen.
(cell- mediated & humoral)

Non Specific:
- response is immediate adn the same for all pathogens.
(physical barriers & phagocytosis)

154
Q

What is phagocytosis?

A

When phagocytes ingest and destroy pathogens.

155
Q

What happens in phagocytosis?

A
  • Chemical producs from the pathogen/dead, damages, or abnormal cells attract phagocytes to move toward the pathogen/ dead, damaged, or abnormal cell.
  • The phagocytes receptors attach to the chemicals.
  • They engulf the pathogen to form a vesicle known as a phagosome.
  • Lysosomes move towards the vesicle and fuse with it.
  • Lysozymes in the lysosome destroy it by the hydrolysis of their cell walls.
  • The products from the hydrolysis are absorbed into the cytoplasm of the phagocyte.
156
Q

What is an antigen?

A

Any part or substance that is recognised as non-self by the immune system and stimulates an immune response.

157
Q

What do antigens trigger?

A

The production of antibodies

158
Q

What are the two types of lymphocyte?

A

B lymphocyte: because they mature in the bone marrow.
Associated with humoral immunity

T lymphocyte: because they mature in the thymus gland.
Associated with cell-mediated immunity

159
Q

How can T lymphocyte distinguish between invader cells from normal cells?

A
  • Phagocytes present some of a pathogen’s antigens on their cell-surface membrane.
  • Invaded body cells presents some of the viral antigens on their cell-surface membrane.
  • Transplanted cells from individuals of the same species have different antigens on their cell-surface.
  • Cancer cells are different from normal body cells and present antigens on their cell-surface membrane.
160
Q

What is an antigen-presenting cell?

A

Cells that display foreign antigens on their surface.

161
Q

What is cell-mediated immunity / the cellular response?

A

T cells only responding to antigens that are presented on a body cell (rather than to antigens within body fluids)

162
Q

How specific are T-cells?

A

Very, The receptors on each T-cell responds to a single antigen.

Thus there are many different types of T-Cells, each responding to different antigens.

163
Q

Describe the stages in the response for T cells to pathogens?

A
  • Pathogen invade body cell or are taken in by phagocytes.
  • The phagocyte places antigens from the pathogen on its cell surface membrane.
  • Receptors on a specific helper T cell (Tₕ cell) fit exactly onto these antigens.
  • This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
164
Q

In the stages of the responses of T lymphocytes to infection by pathogen, the cloned T cell can…

A
  • Develop into memory cells that enable a rapid response to future infections by the same pathogen.
  • Stimulate phagocytosis.
  • Stimulate B cells to divide and secrete their antibody
  • Activate cytotoxic T cells (T꜀ cells)
165
Q

How do cytotoxic T cells kill abnormal cells and body cells that are infected by pathogens?

A

By producing a protein called perforin that makes holes in the cell-surface membrane.

This makes the cell membrane freely permeable to all substances and the cell dies as a result.

166
Q

Why is the action of T cells effective against viruses?

A

Viruses use living cells in to replicate.

So the sacrifice of body cells prevents viruses multiplying and infecting more cells.

167
Q

What is humoral immunity?

A

Immunity involving antibodies.

168
Q

Why are there so many different types of B Cell?

A

Because each B cell produces a specific antibody that responds to one specific antigen.

169
Q

After the antibody has attached to its complementary antigen, how does it enter the B cell?

A

Endocytosis, it then gets presented on its surface.

170
Q

What happens once the B cell presents the pathogenic antigen?

A

Helper T Cells bind to the antigens and stimulate for the B cell to divide by mitosis to form a clone.

This clone will also produce the antibody specific to the foreign antigen.

This is know as clonal selection.

171
Q

What does clonal selection account for?

A

The body’s ability to respond rapidly to any vast number of antigens.

172
Q

What is a monoclonal antibody?

A

Antibodies produced for the same colony of clone B cell, thus producing the same antigen.

173
Q

When a B cell clones, the cell produced can turn into on of two types of cells, what are these?

A

Plasma cells:

  • Part of primary immune response.
  • They secrete antibodies (mainly into plasma)
  • Can survive for a few days, but makes around 2000 antibodies per second.
  • It’s antibodies lead to the destruction of the antigen.

Memory Cell:

  • Part of secondary immune response.
  • Do not secrete antibodies (and circulate in blood and tissue fluid).
  • Can survive for decades.
  • Once they encounter the same antigen they rapidly divide and develop into plasma cells.
174
Q

Once the secondary response is triggered, how can it be faster than the primary response

A

An increased quantity of antibodies are secreted at a faster rate than the primary immune response, as it doesn’t have to go through the whole fist cycle.

175
Q

How are B cells produced in response to pathogens?

A

They are not!

They are present from birth and simply multiply in response to the pathogen.

176
Q

Describe the role of B cells in immunity.

A
  • The surface antigens of an invading pathogen are taken up by B cells.
  • The B cell processes ant presents the antigen on it surface.
  • Helper T cells activate them by attaching to the antigens.
  • B cells divide by mitosis to give clones of plasma cells.
  • The plasma cell produce and secrete specific antibodies that exactly fit the antigen on the pathogens surface.
  • The antibodies attach to the antigens and destroys the pathogen.
  • Some B cells develop into memory cells instead and can respond to the same pathogen in the future.
177
Q

What are antibodies?

A

Proteins with specific binding sites.

178
Q

How is a massive variety of antibodies possible?

A

Because they are made of proteins, with occur in an almost infinite number of forms.

179
Q

Describe the general structure of antibodies.

A
  • Made of four polypeptide chains.
  • One pair are long and are called heavy chains.
  • The other pair is shorter and are called light chains.
  • Has a variable region on top.
  • And a constant region on the bottom.
  • Chains connected via a disulfide bridge.
180
Q

Describe the variable region of the structure of antibodies.

A
  • A specific binding site that fits very precisely on a specific antigen.

Binding site consists of:

  • a sequence of amino acids that form a complimentary tertiary structure.
  • this binds directly to a specific antigen.
181
Q

What is the function of the constant region?

A

It binds to receptors on cells such as B cells.

182
Q

What is the induced fit model of enzyme action (and thus antibody binding)?

A

The molecule is flexible and fits like a around its substrate, before applying strain.

183
Q

What do antibodies do to antigens?

A

They do NOT destroy them.

But rather prepare the antigen for destruction.

Different antibodies lead to its destruction in a range of ways.

184
Q

How can antibodies assist in the destruction of antigens (e.g. bacterial cells)?

A

Agglutination: Clumps of bacterial cells form, making it easier for the phagocyte to locate them.

Serve as markers: Theses markers stimulate phagocytes to engulf the bacterial cell to which they are attached.

185
Q

What does direct monoclonal antibody therapy treat?

A

Cancer, as it can target cancer cells.

186
Q

How does monoclonal antibody therapy work?

A
  • Monoclonal antibodies are produced that are specific to antigens on cancer cells.
  • They attach their receptors.
  • And block the chemicals signal that stimulates uncontrolled growth.
187
Q

What is an advantages of monoclonal antibody therapy?

A

Since antibodies are not toxic and are highly spesific, they lead to fewer side effect than other forms of therapy.

188
Q

What do indirect monoclonal antibody therapy involve?

A

Attaching a radioactive or cytotoxic drug to the monoclonal antibody.

When the antibody attaches it kills the cancer cell.

189
Q

Why are monoclonal antibodies in general a good use of treatment to cancer?

A
  • They can be used in smaller doses as they are targeted on spesific sites.
  • This makes the cheaper and reduces any side effect the drug might cause.
190
Q

Why are monoclonal antibodies in general better than conventional methods for diagnosis?

A

They produce a much more rapid result.

used in diagnosing influenza, hepatitis, and chlamydia.

191
Q

How do monoclonal antibodies used in pregnancy test work?

A
  • The placenta produces a hormone called human chorionic gonadotropin (hCG) which is found in the urine.
  • Monoclonal antibodies on the strip are linked to coloured particles.
  • If hCG is present in the urine it binds to these antibodies.
  • The hCG-antibody-colour complex moves along the strip until it is trapped by a different type of antibody, crating a coloured line.
192
Q

What are some of the ethical issues raised by the use of monoclonal antibodies?

A

MICE

  • mice are used to produce both antibody and tumor cells.
  • This means the mice are deliberately introduced to cancer.
  • Although guidelines minimis any suffering, people are still sceptical with animal testing.

DEATH

  • Although it is clear they have a use in saving lives, there have been a few death (in the treatment of multiple sclerosis).
  • And informed consent is important for patients.

HUMAN TESTING

  • This is vital but can sometimes go wrong.
  • In Mar 2006, 6 healthy volunteers took part in a monoclonal antibody test.
  • Within minutes they suffer multiple organ failure (likely due to T cells overproducing chemicals that stimulate an immune response causing them to attack body tissue).
193
Q

What is passive immunity?

A

The introduction of antibodies with no direct contact with the pathogen or its antigens.

This means they are not replaced when broken down, this this immunity is not lasting.

Example, anti-venom and antibodies being gained by the fetus.

194
Q

What is active immunity?

A

The production of antibodies by the individuals’ own immune system caused by direct contact with the pathogen, or its antigen.

This takes time to develop but is generally long-lasting.

It can either be Natural: where the person is infected under normal circumstances.

Or can be Artificial: from the basis of vaccination (immunisation), this can be asymptomatic.

195
Q

What is vaccination?

A

The introduction of the appropriate disease antigens into the body, either by injection or by mouth.

This is done by a vaccine, with one or more antigen from the pathogen to elicit an immune response.

This make memory cells.

196
Q

What factor affects the success of a vaccination program?

A
  • Must be economically available in sufficient quantity to immunise most of the vulnerable population.
  • Minimal side effects. Unpleasant ones may discourage populations.
  • Means of producing, storing and transporting the vaccine must be available. (Tech advanced, hygienic, refrigerated).
  • Means of administering it properly at the appropriate time. (Training staff with the skills at different centres around a population).
  • Must be possible to vaccinate a vast majority. (herd immunity).
197
Q

What is herd immunity?

A

When a sufficiently large population has been vaccinated making it difficult for a pathogen to spread with that population.

198
Q

Why is herd immunity important?

A

It is never possible to vaccinate everyone in a large population (e.g. babies and people with people with a compromised immune system).

So by making it harder for a pathogen to spread you protect these vulnerable groups.

199
Q

Why might vaccinations not eliminate a disease?

A
  • They fail to induce immunity in defective systems.
  • Individuals may get the pathogens before immunity is high enough.
  • Mutating pathogens, in pathogens with antigenic variability. (e.g. Influenza).
  • Large varieties of pathogens, making a unified vaccination impossible.
  • Some pathogens ‘hide’ from immune system, by concealment or living out of reach. (e.g. cholera).
  • Religious, medical, or ethical objections.
  • Misconceptions (e.g. MMR causing autism).
200
Q

What are the ethical issues of using vaccines?

A
  • Animal testing
  • Side-effects. Sometimes long-term.
  • Who should test it?
  • Target countries based on gain?
  • Only truly effective if everyone has it. Should this be forced?
  • Money taken from treatment.
  • Health risk Vs controlling disease (person Vs population).
201
Q

What does HIV stand for?

A

Human Immunodeficiency Virus.

202
Q

What does AIDS stand for?

A

Acquired Immune Deficiency Syndrome.

203
Q

List the structures of HIV.

Outside –> In

A
  • Attachment proteins.
  • Lipid envelope.
  • Matrix.
  • Capsid.
  • RNA.
  • Reverse Transcriptase.
204
Q

Why does HIV belong to a group of viruses called retroviruses?

A

The presence of reverse transcriptase, and consequent ability to make DNA from RNA.

205
Q

How does HIV replicate?

A
  • HIV enters bloodstream and circulates around the body.
  • Protein on HIV readily binds to a protein called CD4. This is found in a number of cells, but it mostly attaches to the ones in Helper T cells.
  • Capsid fuses with the cell-surface membrane.
  • The RNA and enzymes of HIV enter Helper T cell.
  • HIV reverse transcriptase converts the virus’s RNA into DNA.
  • Newly made DNA moves int Helper T cell’s nucleus where it is inserted into the cell’s DNA.
  • HIV DNA makes mRNA with instruction to make viral proteins and the RNA goes into the new HIV.
  • mRNA leaves nucleus and used ribosomes to synthesize HIV particles.
  • These break away the Helper T cells with a piece of its cell-surface surrounding them to form their lipid envelope.
206
Q

How does HIV cause symptoms of AIDs?

A
  • Attacks Helper T cells, killing or interfering with their normal functions.
  • can reduce Helper T cell count from 1200mm^-3 to as low as 200mm^-3.
  • This limits the stimulation ofB cells to produce antibodies or T C cells to kill cells infected by pathogens.
  • Memory cells may also become infected and destroyed.
  • Thus, body has an inadequate immune response and becomes susceptible to other infections and cancer.
207
Q

What causes AIDs deaths?

A

Secondary diseases caused by AIDs’ compromised immune response.

208
Q

What does ELISA stand for?

A

Enzyme linked immunosorbent assay.

209
Q

What does the ELISA test do?

A

Uses antibodies to not only detect the presence of a protein in a sample but also the quantity.

Its extremely sensitive and so can detect very small amounts of a molecule.

210
Q

How is the ELISA test done?

A
  • Apply the sample to a surface. (e.g. a slide to which all the antigens in the sample will attach)
  • Wash the surface several times to remove unattached antigens.
  • Add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together.
  • Wash the surface to remove excess antibodies.
  • Add a second antibody that binds with the first antibody. This second antibody has an enzyme attached to it.
  • Add the colourless substrate of that enzyme. This acrs on the substrate to change it into a coloured product.
  • The amount of the antigen present is relative to the intensity of the colour that develops.
211
Q

What is bacterial cell walls made of?

A

Murein- a tough, inelastic material.

212
Q

How do antiboitics kill bacteria?

A
  • Water, entering via osmosis, is resited from expanding the cell by the murein cell wall.
  • Thus halting further entry of water.
  • Antibiotics, like penicillin, inhibit certain enzymes required for the synthesis and assembly of the peptide cross-linkage in bacterial cell walls.
  • This weakens the walls, making the m unable to withstand pressure.
  • The cell burst, as more water enters, and the bacterium dies.
213
Q

Why don’t antibiotics work on viral cells?

A
  • Viruses rely on a host to carry out their metabolic activities.
  • Therefore, they lack their own metabolic pathways and cell structures.
  • As a result antibiotics are ineffective, as there are no metabolic mechanism or cell structure to disrupt.
  • They also have a protein coat, not a murein cell wall, and thus do not have sites where antibiotics can work.

A-Level Biology [AQA] (8 decks)

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