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AQA A Level Biology > Cells > Flashcards

Cells Flashcards

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1
Q

What is meant by facilitated diffusion?

A

Movement down concentration gradient through a channel/carrier protein

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2
Q

What is meant by active transport?

A

Movement against concentration gradient via a carrier protein using ATP/energy (from respiration)

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3
Q

What is meant by osmosis?

A

Movement of water from higher to lower water potential/down water potential gradient across a partially/selectively permeable membrane

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4
Q

How does resolution affect clarity?

A

Higher resolution, higher clarity

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5
Q

Magnification times what equals image size?

A

Actual size

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6
Q

Image size divided by actual size equals what?

A

Magnification

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7
Q

What is the resolution of a transmission electron microscope?

A

0.1 nm

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8
Q

How does a transmission electron microscope work?

A

A beam of electrons is passed through a very thin section of specimen. Some electrons are absorbed, and so show up as dark.

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9
Q

What is the resolution of a scanning electron microscope?

A

20nm

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10
Q

What are the disadvantages of an electron microscope?

A

The specimen needs to be in a vacuum (therefore must be dead)
The image is black and white (colour can be added)
Prep may be result in artefacts

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11
Q

What is an advantage of electron microscopes?

A

They have a short wavelength and so have a high resolving power.
Electrons are charged, and so the microscopes can be focused using electromagnets

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12
Q

Describe the process of cell fractionation.

A

Chop up and place in cold, isotonic, buffered solution
Homogenation (blender)
Filter homogenate
Ultracentrifugation (spin)
Look at sediment - low = larger mass organelles, high speed - smaller mass organelles

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13
Q

Elijah uses cell fractionation to study the organisms inside a cell. Using this technique, he is able to see the mitochondria. At what speed was the homogenate spun to get this?

A

Medium speed

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14
Q

Give an example of an organelle that would be separated from the homogenate if it was spun at a high speed.

A

Lysosomes
Membranes
Ribosomes

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15
Q

In cell fractionation, why is the solution isotonic?

A

To prevent osmotic damage

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16
Q

In cell fractionation, why is the solution cold?

A

To reduce enzyme activity that could damage organelles

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17
Q

In cell fractionation, why is the solution buffered?

A

To maintain a constant pH

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18
Q

Describe how you would calibrate the eyepiece graticule

A

Lowest power objective on microscope
Align scale on microscope with graticule scale
Calculate calibration factor

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19
Q

What is a key function of the nucleus?

A

Manufacture rRNA and ribosomes
Control cell activity
Contains genetic information

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20
Q

What are the key structures of a chloroplast?

A

Grana (made up of thylakoids)
Stroma
Chloroplast envelope

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21
Q

What are the key functions of a chloroplast?

A

To harvest sunlight to be converted into chemical energy in photosynthesis

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22
Q

What are the key functions of a lysosome?

A

Hydrolysis of ingested materials from phagocyte cell
Digest worn out cells
Break down cells after death
Release enzymes for destruction of material outside cell

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23
Q

What are the key functions of a smooth endoplasmic reticulum?

A

Predominantly store, but also synthesis and transport, lipids and carbohydrates

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24
Q

What are the key functions of a mitochondria?

A

Site of aerobic respiration (release ATP)

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25
Q

What are the key structures found in a mitochondria?

A

Cristae (the folds), matrix (the space inside)

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26
Q

What are the key structures found in a nucleus?

A

Nuclear envelope, nuclear pores, nucleolus, (chromosomes, nucleoplasm)

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27
Q

What are the key functions of a vacuole?

A

Supports herbaceous plants by making cells turgid
May act as a temporary food store
May contain pigments which colour petals to attract pollinating insects

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28
Q

What are the key functions of a rough endoplasmic reticulum?

A

Pathway for transport of materials

Increase the SA for protein synthesis

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29
Q

What are the key functions of a golgi apparatus?

A 
Transport, modify and store lipids
Form lysosomes
Secrete carbs
Produce secretory enzymes
Add carbs to proteins to form glycoproteins
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30
Q

What are the key functions of a cell wall?

A

Provide mechanical strength –> prevent cell from bursting from osmotic pressure
Allow water to pass along it

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31
Q

What are the key functions of a ribosome?

A

Site of protein synthesis

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32
Q

What are the key differences between eukaryotic and prokaryotic cells?

A

Pro = smaller, have cytoplasm that lacks membrane-bound organelles, smaller ribosomes, no nucleus (circular, free-floating DNA), a cell wall that contains murein. Many proks also have one or plasmids, a capsule surrounding the cell, one or more flagella

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33
Q

Virus are living creatures. True or false?

A

False

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34
Q

What are the key structures of a virus?

A

A strand of nucleic acid, capsid, attachment protein

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35
Q

Which eukaryotic structures are found in plants cells, but not animal cells?

A

Chloroplasts, cell wall, cell vacuole

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36
Q

Chloroplasts are found in what types of cell? (animal, plant etc)

A

Plant and algae

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37
Q

A cell wall is found in what types of cell? (animal, plant etc)

A

Plant, fungi, algae

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38
Q

What is the difference between magnification and resolution?

A

Magnification is the ability to make small objects seem larger
Resolution is the ability to distinguish between two objects

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39
Q

Within multicellular organisms, not all cells retain the ability to divide. True or false?

A

True

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40
Q

At which stage does DNA replication occur?

A

Interphase

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41
Q

What are the stages of the cell cycle?

A

Interphase, prophase, metaphase, anaphase, telophase

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42
Q

What is binary fission?

A

When the fully grown parent cell splits into two halves to produce two new cells. It is the most common form of reproduction in prokaryotes (e.g. bacteria)

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43
Q

What happens during prophase?

A

Centrioles move to opposite poles

Nucleolus breaks down

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44
Q

What happens during metaphase?

A

Chromosomes line up at the equator, pulled by the microtubules attached at their centromeres

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45
Q

What happens during anaphase?

A

The attached microtubules shorten, splitting the centromere and chromatids in half and separating them, pulling them to opposite sides of the cell

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46
Q

What happens during telophase?

A

As the chromosomes reach opposite ends of the poles, the spindle fibres disintegrate, and the nucleolus and nuclear membrane begin to reform

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47
Q

What happens during cytokinesis?

A

The cytoplasm divides

Essentially the cytoplasm ‘pinches through’ until they separate

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48
Q

What happens if cell division is not controlled?

A

Tumours and cancers may form

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49
Q

What are cancer treatments often directed at?

A

Controlling the rate of cell division

50
Q

Describe the structure of a cell-surface membrane (5)

A

It is a phospholipid bilayer, whereby the hydrophobic tails point inwards to avoid the surrounding aqueous environment. It is a fluid mosaic, meaning that the individual molecules vary in size, shape and pattern, and can move relative to one another. Proteins, glycoproteins and glycolipids all form part of this selectively permeable membrane. These in turn allow the movement of molecules across the membrane by either diffusion, osmosis or active transport (carrier and channel proteins) or allow other cells to attach (glycolipids/proteins)

51
Q

Describe and explain the key features of a phospholipid bilayer

A

Fluid - individual molecules can move relative to one another
Mosaic - molecules vary in shape, size and pattern

52
Q

Which type of carrier protein spans the bilayer completely?

A

Intrinsic

53
Q

How many millimetres are in a micrometer?

A

1 um = 0.001mm

1mm = 1000um

54
Q

How many millimetres are in a nanometer?

A

1,000,000nm in 1 millimetre

55
Q

Other than as carrier proteins, state two functions of membrane born proteins

A

Receptors/recognition sites
Help maintain stability of membrane
Structural

56
Q

Through what kind of membrane can osmosis occur?

A

Semi-permeable

57
Q

Cholesterol may also be present in cell membrane. What is its role?

A

Add strength to the membranes

Reduce lateral movement of other molecules inc. phospholipids

58
Q

What are the roles of proteins in the cell-surface membrane?

A

Provide structural support
Allow transport across membrane (channel, carrier)
Form cell-surface receptors for identifying cells
Act as receptors (e.g. for hormones - 2nd messenger model)
Help cells adhere together

59
Q

In the cell-surface membrane, what are the roles of glycolipids?

A

Act as recognition sites
Help cells attach to one another and so form tissues
Help maintain stability of the membrane

60
Q

In the cell-surface membrane, what are the roles of glycoproteins?

A

Act as recognition sites
Helps attach to one another and so form tissues
Allows cells to recognise one another

61
Q

Which types of molecules are NOT able to freely diffuse across the cell-surface membrane?

A 
They can't if they are:
too large
polar
same charge as protein channels
not lipid soluble
62
Q

State what is meant by ‘diffusion’

A

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower, until evenly distributed

63
Q

What is the role of proteins in facilitated diffusion across a cell-membrane?

A

Molecules bind with a protein causing it to change shape, thus allowing it through (some rotate)

64
Q

Channel proteins allow what types of molecules through?

A

Water soluble (filled with water)

65
Q

What is water potential measured in?

A

psi

66
Q

Under standard conditions, what is the water potential of pure water?

A

0kPa

67
Q

What is an example of passive transport?

A

Diffusion (simple and facilitated)

Osmosis

68
Q

How do channel proteins help control entry and exit of ions across the cell-membrane?

A

Most channel proteins are selective and so will only let certain ions through

69
Q

State what is meant by 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

70
Q

How does active transport work?

A

An ion attaches to the carrier protein

A Pi from ATP attaches, causing the protein to change shape. This shape change ‘pump’ the molecule/ion across

71
Q

Describe and explain what happens if the solution outside the cell is hypotonic

A

Hypotonic - higher water potential outside cell

Water rushes into the cell to balance the concentrations, causing the cell to swell and burst

72
Q

Describe and explain what happens if the solution outside the cell is hypertonic

A

Hypertonic - lower water potential outside

Water rushes from inside the cell to outside to balance the concentrations causing the cell to shrivel/shrink

73
Q

Describe and explain the co-transport of glucose

A

Na-K actively transports Na+ out of epithelial cells into the blood stream
This therefore lowers the concentration of Na+ in the epithelial cells, increase conc. outside
Na+ reenters the epithelial cell, this time coupled with glucose
They enter via the Na-glucose pump by facilitated diffusion

74
Q

Describe and explain how is the small intestine adapted for the absorption of glucose

A

Villi and microvilli increase SA
Thin walls means smaller diffusion distance
Good blood supply and movement of villi maintains concentration gradient

75
Q

Which two carrier proteins are involved with the co-transport of glucose?

A

Na-K and Na-glucose pumps

76
Q

The molecular formula of galactose in C6H12O6. What is the molecular formula of lactose?

A

C12H22O11

77
Q

What is an example of a non-specific defence mechanism?

A

Phagocytosis, physical barrier

78
Q

What is an example of a specific immune response?

A 
Cell-mediated response (involves T-lympho)
Humoral response (involves B-lympho)
79
Q

Define ‘antigen’

A

A protein or glycoprotein found on the surface of cell membranes and foreign material that indicate to the immune system if that cell is self or non-self

80
Q

Describe phagocytosis of pathogens

A

Phagocyte attracted to the pathogen by chemical products
Phagocyte has several receptors on its cell-surface membrane that attach to chemicals on the pathogen
A phagosome begins to form around the pathogen (engulf). Lysosomes migrate towards this
Lysosome and phagosome fuse. Lysosomes release lysozymes which break the pathogen down by hydrolysis
Debris either displayed on cell surface or released by exocytosis

81
Q

What is the difference between specific and non-specific immunity?

A

Specific distinguishes between pathogens, non-specific doesn’t

82
Q

Describe the humoral response of the immune system

A

Proteins are released by Th cells which stimulates the rapid production of B cells
These B cells produce plasma cells, which in turn produce antibodies

83
Q

What type of lymphocytes does the humoral response involve?

A

B lymphocytes

84
Q

Where do T-lymphoctes mature?

A

Thymus gland

85
Q

Where do B-lymphocytes mature?

A

Bone marrow

86
Q

Describe the response of T-lymphocytes to a foreign antigen (cell-mediated response)

A

Receptors on a specific T helper (Th) cell bind to their complementary antigen. They recognise the cell as non self, and are activated to rapidly divide by mitosis. They release proteins which stimulate the rapid production of B cells. Lymphokines stimulate phagocytes to do phagocytosis
Interlukin stimulates cytotoxic T cells (killer/Tc cells)
Tc cells replicate to become effector Tc cells (which identify and secrete proteins to kill infected cells) and Tm cells (which migrate to lymph nodes to be rapidly activated if another invasion)

87
Q

Define what an antibody is

A

They are specialised protein molecules that bind specifically to antigens

88
Q

Antibodies are able to make it easier for phagocytes by agglutination. What does this mean and how does it make it easier?

A

Antibodies are able to cause microbes to clump together, thus making it easier for antibodies to engulf them

89
Q

Antibodies assist in the destruction of microbes in 2 ways. What are these two ways?

A

They act as markers for phagocytes

Agglutination

90
Q

Describe the structure of an antibody

A

A double lined Y shaped molecule
Has a light chain and a heavy chain, and constant and variable regions
The antigen binding site is located at the variable regions
Held together by disulphide bridges

91
Q

What is a monoclonal antibody?

A

A pure antibody, highly specific to one antigen. It comes from a single cell line and consists of identical antibody molecules

92
Q

Describe how monoclonal antibodies are produced

A

A mouse is injected with some antigen to stimulate production of complementary antibodies
The spleen of this mouse is removed, and from it, the B cells are removed
These cells are fused to myeloma (cancerous) cells. They are grown in culture to produce a hybridoma
These hybridomas multiply and so produce relatively large amounts of antibody molecules

93
Q

How can monoclonal antibodies be used in medication?

A

They can be produced to target the problem cell
Once attached they can help by:
acting as markers for the immune system
blocking growth signals by attaching to receptors
deliver a radioactive/cytotoxic drug

94
Q

How can monoclonal antibodies be used in medical diagnosis?

A

Many illnesses affect levels of proteins. Monoclonal antibodies can be produced to interact with these proteins, allowing a level of it to be measured

95
Q

How are monoclonal antibodies used in pregnancy testing?

A

Pregnant women produce a hormone called human chronic gonadotrophin which can be found in the urine. mABs with coloured compounds attached are complementary specific to hCG. If it is present they bind. The complexes move along the strip until another antibody stops them, causing a coloured line to form

96
Q

What is passive immunity?

A

Antibodies introduced to individual from an outside source
No direct contact w/ the pathogen/antigen is necessary and immunity is acquired immediately
Antibodies not being produced by self, so antibodies broken down –> no memory cells formed, no lasting immunity

97
Q

Give an example of natural passive immunity

A

Maternal antibodies

98
Q

Give an example of artificial passive immunity

A

Anti-venom

99
Q

What is active immunity?

A

Production of antibodies stimulated by the individual’s own immune system
Direct contact w/ pathogen/antigen necessary
Immunity takes time to develop
Generally long-lasting

100
Q

Give an example of natural active immunity

A

A normal infection

101
Q

Give an example of artificial active immunity

A

Vaccination

102
Q

What is herd immunity?

A

When a sufficiently large enough proportion of the population has been vaccinated to make it difficult for a pathogen to spread

103
Q

How do vaccination help prevent disease?

A

Induce an immune response so memory cells are present. If there is another infection, the memory cells are activated and induce a faster and stronger response

104
Q

What does HIV stand for?

A

Human immunodeficiency virus

105
Q

What is the structure of a HIV virus?

A

from inside out:

RNA, reverse transcriptase, capsid, matrix, lipid envelope, attachment proteins

106
Q

Describe the process of HIV’s replication of Th cells

A

HIV enters bloodstream and circulates
Protein on HIV readily binds to CD4 protein (found on many cells, but mostly binds to Th)
Protein capsid fuses with the cell surface membrane
HIV enzymes and RNA enter the cell
HIV reverse transcriptase converts the rNA to DNA, which is moved into the nucleus of the Th cell. Then inserted into Th DNA
HIV DNA creates mRNA using the cell’s enzymes. mRNA contains instructions for making new viral proteins and RNA for new HIV
mRNA exits nucleus and uses cell’s protein synthesis mechanisms to make HIV particles
HIV particles break away w/ piece of Th cell surface membrane surrounding (acts as lipid envelope)

107
Q

How does HIV cause AIDs symptoms?

A

By affecting Th cells and therefore the immune system

108
Q

What does HIV reverse transcriptase do?

A

Convert the HIV RNA to DNA

109
Q

Once HIV RNA has been converted to DNA, it creates mRNA. What does this mRNA do?

A

Uses the cell’s protein synthesis mechanisms to make HIV particles

110
Q

What does ELISA stand for?

A

Enzyme linked immunosorbant assay

111
Q

What does the ELISA test do?

A

Detects the presence of a protein and quantity

112
Q

Describe how you’d carry out the ELISA test

A

Apply sample to surface to which all desired proteins will attach to
Wash surface several times to remove any unattached
Add complementary specific antibody and leave to bind
Wash to remove all excess antibody
Add 2nd antibody which has an enzyme attached that can bind to first
Add a colourless substrate. The enzyme will act on it, to change it to a coloured product
More intense colour –> more of desired proteins

113
Q

What is one way antibiotics work?

A

Inhibitng enzymes nec. for the synthesis and assembly of peptide cross linkages in the bacterial cell wall. Weakened wall can’t withstand the pressure and so bursts

114
Q

Why are antibiotics ineffective against viruses?

A

One way antibiotics is by weakening the cell walls. Viruses don’t have cells (use hosts to carry out metabolic functions) therefore have no enzymes to inhibit or cell walls to weaken

115
Q

What is an attenuated microorganism?

A

A weakened microorganism

116
Q

Explain how antigenic variability has caused some people to be infected with the same virus more than once

A

Memory cells don’t recognise
Antibodies previously produced aren’t effective
Takes time to produce effective antibodies

117
Q

When a vaccine is given to a person, it leads to the production of antibodies against a
disease-causing organism. Describe how (5) PPQ

A
  1. Vaccine contains antigen from pathogen;
  2. Macrophage presents antigen on its surface;
  3. T cell with complementary receptor protein binds to antigen;
  4. T cell stimulates B cell;
  5. (With) complementary antibody on its surface;
  6. B cell secretes large amounts of antibody;
  7. B cell divides to form clone all secreting/producing same antibody;
118
Q

Describe the difference between active and passive immunity (5) PPQ

A
  1. Active involves memory cells, passive does not;
  2. Active involves production of antibody by plasma cells/memory cells;
  3. Passive involves antibody introduced into body from outside/named source;
  4. Active long term, because antibody produced in response to antigen;
  5. Passive short term, because antibody (given) is broken down;
  6. Active (can) take time to develop/work, passive fast acting;
119
Q

Give two key features of passive immunity

A

No direct contact w/ the pathogen/antigen is necessary and immunity is acquired immediately
Antibodies not being produced by self, so antibodies broken down –> no memory cells formed, no lasting immunity

120
Q

Give two key features of active immunity

A

Direct contact w/ pathogen/antigen necessary
Immunity takes time to develop
Generally long-lasting

AQA A Level Biology (11 decks)

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