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AQA A Level Biology > 2-4/5 Transport + Immunity > Flashcards

2-4/5 Transport + Immunity Flashcards

1
Q

What are the functions of phospholipids in the cell membrane?

A

Lipid and water-soluble molecules can enter

the membrane is flexible and self-healing

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2
Q

What are the two ways in which proteins are embedded in the bilayer?

A 
Only in surface
- Mechanical support, receptors with glycolipids
All the way through
- Water-filled channels for soluble ions
- Carrier proteins that bind
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3
Q

What is the function of cholesterol in the membrane?

A
  • Reduce lateral movement of other molecules
  • Makes cells less fluid when hot
  • Prevent leakage of water
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4
Q

What are the functions of glycolipids in the membrane?

A
  • Recognition sites
  • Maintain stability
  • Attach and form tissues
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5
Q

What are the functions of glycoproteins in the membrane?

A
  • Recognition sites

- attach and form tissues

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6
Q

Why can’t something cross the membrane?

A
  • Not lipid soluble so cannot pass through the phospholipid bilayer
  • Too large to pass through the channels in the membrane
  • Of the same charge as the charge on the protein channels so are repelled
  • Polar so have difficulty passing through the non-polar hydrophobic tails in the phospholipid bilayer
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7
Q

What is simple diffusion?

A

The net movement of molecules from an area of high concentration to low until even

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8
Q

What is facilitated diffusion?

A

A passive process that relies on kinetic energy of diffusing molecules, uses protein channels and carriers

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9
Q

What is osmosis?

A
  • The diffusion of water molecules from an area of high concentration to an area of low concentration of water
  • Needs a partially permeable membrane
  • Water tries to dilute out molecules that can’t move across the membrane until the concentration is equal
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10
Q

What is water potential?

A
  • The pressure created by water molecules measured in kPa
  • The addition of a solute to pure water lowers its water potential, the more that is added, the more negative the water potential is
    Under standard conditions of temperature and pressure, pure water has a water potential of zero
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11
Q

How does osmosis occur?

A

A low concentration of one solution on one side, higher on the other, all are in random motion, will split evenly

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12
Q

What is active transport?

A

Movement of molecules from high concentration to low concentration aided by ATP and carrier proteins

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13
Q

How is ATP used in active transport?

A

Used to individually move molecules using a concentration gradient which has been set up by direct active transport, known as cotransport
Metabolic energy in the form of ATP is needed
Carrier proteins act as pumps to transport materials

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14
Q

How does a Na/K pump work?

A

3 Na+ ions and 2 K+ ions are moved in opposite directions each against conc gradient, glucose moves the opposite way

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15
Q

How is the rate of movement across membranes increased?

A

The epithelial cells lining the ileum possess microvilli about 0.6 um long

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16
Q

How is active transport involved in absorption?

A

Glucose and amino acids can only diffuse into the blood until equal, co-transport is used to ensure all glucose and amino acids are taken in

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17
Q

What are specific and non-specific defence mechanisms?

A

Non-specific - physical barriers, phagocytosis

Specific - T/B lymphocytes

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18
Q

How does the body recognise its own cells from foreign material?

A

Cells contain antigens which act as markers for recognition, any lymphocytes that show a self-response will be suppressed

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19
Q

What is phagocytosis?

A

Abnormal cells release attractants/chemo toxins
phagocytes have receptors that will bind to the pathogen and engulf it, forming a phagosome, lysosomes release lysozyme which hydrolyses the pathogen and debris is absorbed or released

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20
Q

What are B and T lymphocytes?

A

B - bone marrow - humoral immunity

T - thymus - cell-mediated

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21
Q

What is cell-mediated immunity?

A

T-cells mature in body and circle in blood until needed, killer t cells (lysis), helper t cells (helps b), suppressor (turn off immunity)

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22
Q

How do cytotoxic T-cells kill infected cells?

A

Produce a protein called perforin that make holes in the cell-surface membrane, they become fully permeable

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23
Q

What is humoral immunity?

A

B cells encounter foreign antigens and divide by mitosis rapidly to produce antibodies and memory cells which stay around

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24
Q

How do antibodies destroy antigens?

A

Cause agglutination od bacterial cells so phagocytes can locate them

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25
Q

What are monoclonal antibodies used for?

A
  • Targeted therapy
  • Diagnosis (ELISA testing)
  • Pregnancy testing
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26
Q

What are the ethical issues surrounding use of monoclonal antibodies?

A
  • Live mice
  • Associated deaths
  • Multiple organ failures in trials
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27
Q

What is passive immunity?

A

Anti-venom - acquired immunity, no contact with pathogen, no antibodies produced

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28
Q

What is active immunity?

A

Natural - becoming infected, producing antibodies

Artificial - vaccines, induced immune response

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29
Q

What makes a successful vaccine program?

A

Economically viable
Limited side effects
Means to deliver
The possibility of herd immunity

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30
Q

What is herd immunity?

A

A sufficient portion of population is immune so pathogen cannot spread

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31
Q

Why might a vaccine fail to eliminate a disease?

A
  • Objectors
  • Faulty immune systems
  • Disease may develop
  • Pathogen may mutate
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32
Q

What are the ethical issues surrounding vaccines?

A
  • Animal testing
  • Side effects
  • Trialling
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33
Q

What is the structure of HIV?

A
  • Lipid envelope, embedded attachment proteins
  • Capsid containing two RNA strands + enzymes
  • One enzyme ‘reverse transcriptase’ as catalyses DNA from RNA
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34
Q

How does HIV replicate?

A
  • Enters into the bloodstream
  • Protein on HIV binds to CD4 (T helper)
  • Capsid fuses with membrane RNA and enzymes enter T helper
  • Reverse transcriptase converts RNA tp DNA and inserts into the cells DNA, mRNA makes new viral proteins
  • mRNA passes out to make new HIV cell
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35
Q

How does HIV cause symptoms of AIDS?

A

HIV attacks T helper cells and so the immune system is disrupted and the victim is susceptible to infection

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36
Q

How does the ELISA test work?

A
  • Sample on the surface, wash and add antibody, leave to bind then wash
  • Second antibody with colour, leave to bind then wash
    colour relates to the amount of antigen present
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37
Q

Why don’t antibiotics work for bacterial infections?

A

Viruses don’t have cell walls to break, can’t break through lipid envelope

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38
Q

What does the cell membrane do?

A

Separates the living cell from its environment and controls traffic in and out of the cell
Made of a collage of proteins and other molecules embedded in a fluid matrix of the lipid bilayer

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39
Q

What is the rate of diffusion affected by?

A

Steepness of concentration gradient
Temperature

Surface area
Type of molecule/ion

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40
Q

How does osmosis affect cells?

A

Cells placed in diluted water will burst because too much water will enter via osmosis
Cells placed in a concentrated solution will shrivel as water will leave via osmosis
A cell wall will stop a plant cell from bursting

41
Q

What are the types of water potential?

A 
🔱s = dissolved substances, solute potential, always a negative number
🔱p = pressure exerted on the membrane/wall, pressure potential
42
Q

Why does a plant cell not burst?

A

It has a rigid cell wall which prevents the membrane from bursting because the protoplast of the cell is kept pushed up against the cell wall and doesn’t brake

43
Q

What happens when a plant cell is placed in a solution of higher water potential?

A

It becomes turgid
Water enters the cell
The protoplast swells
Protoplast is pushed against the cell wall

44
Q

What happens when a plant cell is placed in a solution of equal water potential?

A

Water neither enters nor leaves
The protoplast doesn’t change
Called incipient plasmolysis
Protoplast begins to pull away from the cell wall

45
Q

What happens when a plant cell is placed in a solution with a lower water potential?

A

Water leaves the cell
The protoplast shrinks
The cell is plasmolysis
Protoplast is completely pulled away from the cell wall

46
Q

How do roots collect mineral ions?

A

Active transport

47
Q

What is cytosis?

A

The term for transport mechanisms for moving large quantities of cells

48
Q

What is endocytosis?

A

When a molecule causes the cell to bulge inward, forming a vesicles

49
Q

What is exocytosis?

A

Movement of material out of a cell

50
Q

How are small intestines adapted?

A

Long + large surface area to aid digestion

51
Q

What are villi?

A

Finger like projections

Contain blood capillaries

52
Q

What are microvilli?

A

Finger-like projections of cell-surface membrane
Called a brush order as they look like a brush
Provide more surface area for the insertion of protein channels and carrier proteins where diffusion/active transport/facilitated diffusion takes place

53
Q

How does glucose move into the blood?

A

Facilitated diffusion

54
Q

What happens to remaining glucose/amino acids at the end of the small intestine?

A

They’re moved by active transport

55
Q

How much of glucose and amino acids are absorbed by the small intestine?

A

Normally, all of it

56
Q

What is the ileum?

A

Another name for the small intestine

57
Q

What are the steps for the co-transport of sodium/potassium ions?

A

Sodium ions = actively transported out of epithelial cells via the sodium-potassium pump
Concentration of sodium inside epithelial cells is lowered

Concentration of sodium inside the lumen is higher
Sodium diffuses down this concentration gradient using a co-transport protein in the cell surface membrane
Sodium carries glucose or amino acids into the cells with them
The glucose or amino acids pass into the blood plasma via facilitated diffusion of a different carrier

58
Q

What are plasma membranes?

A

The membranes around and within all cells

59
Q

What is the cell surface membrane?

A

The membrane that surrounds cells and forms the boundary between the cytoplasm and the environment
Controls movement of substances into and out of the cell

60
Q

What is the role of phospholipids in the cell-surface membrane?

A

Two layers of phospholipids make up the membrane
Hydrophilic phosphate heads point to the outside of the membrane, attracted by water on both sides

Hydrophilic tails point towards the centre, repelled by water on both sides
Allows lipid-soluble substances to enter and leave the cell
Prevents water soluble substances from entering and leaving the cell
Makes the membrane flexible and self healing

61
Q

What is the role of proteins in the cell-surface membrane?

A

Provide structural support
Act as channels transporting water soluble substances across the membrane

Allows active transport across the membrane through carrier proteins
Forms cell-surface receptors for identifying cells
Helps cells to adhere together
Acts as receptors

62
Q

What is the role of cholesterol in the cell-surface membrane?

A

Reduce movement of other molecules
Makes the membrane less fluid at high temperatures

Prevents leakage of water and dissolved ions from the cell
Pulls together fatty acid tails to limit movement without creating a rigid structure
Adds strength

63
Q

What is the role of glycolipids in the cell-surface membrane?

A

Acts as a recognition site
Helps to maintain the stability of the membrane

Helps cells to attach to one another and so form tissues

64
Q

What is the role of glycoproteins in the cell-surface membrane?

A

Act as recognition sites
Help cells to attach to one another and so form tissues

Allows cells to recognise one another
Cell-surface receptors

65
Q

What are the functions of membranes within cells?

A

Control entry and exit of material
Separates organelles from the cytoplasm

Provides an internal transport system
Isolates enzymes that might damage the cell
Provides surfaces on which reactions can occur

66
Q

Why is the cell-surface membrane known as a fluid mosaic model?

A

Fluid: individual molecules can move relative to each other, flexible structure, constantly changing shape
Mosaic: proteins vary in shape, size and pattern just like the tiles of a mosaic

67
Q

Why is the co-transport of glucose into the blood considered indirect active transport?

A

It is the sodium ion concentration gradient, rather than the ATP directly which powers the movement of glucose

68
Q

What is the process of active transport involving carrier proteins?

A

Molecules bind to the carrier protein and ATP attaches to the membrane protein on the inside of the cell/organelle
Binding of phosphate ion to protein causes the protein to change shape so that access for the molecules is open to the inside of the membrane but closed to the outside

69
Q

What is an antigen?

A

Any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response
Usually proteins that are a part of the cell-surface membrane or cell walls of invading cells

70
Q

What is the physical barrier of immunity?

A

Mucous membranes: mucous traps pathogens
Dead skin cells block pathogens

Hydrochloric acid kills pathogens in the stomach

71
Q

What is a phagocyte?

A

Cells which engulf pathogens

They move through blood and lymph into connective tissue

72
Q

What is the process of phagocytosis?

A

Phagocyte is attracted to the pathogen by its chemical products
The phagocytes have several receptors on their cell surface membrane that attach to chemicals on the surface

Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium
The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium
The hydrolysis products of the bacterium are absorbed by the phagocyte

73
Q

What is the process of B cells?

A
  1. The surface antigens of an invading pathogen are taken up by a B cells
  2. The B cell processes the antigens and presents them on its surface
  3. Helper T cells attach to the processed antigens on the B cells thereby activating the B cell
  4. The B cell is now activated to divide by mitosis to give a clone of plasma cells
  5. The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogen’s surface
  6. The antibody attaches to antigens on the pathogen and destroys them
  7. Some B cells develop into memory cells. These can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies. This is the secondary immune response
74
Q

What is the process of T helper cells?

A

Associated with cell-mediated immunity
1. Mature in the thymus gland
2. Bacteria has foreign antigens on its surface
3. Pathogens invade body cells or are taken in by phagocytosis
4. The phagocyte places antigens from the pathogen on its cell-surface membrane
5. Receptors on a specific helper T cell fit exactly onto these antigens
6. The attachment activates the T cell to divide rapidly by mitosis and form clones of genetically identical cells
7. The cloned cell:
Develop into memory cells that enable a rapid response to future infections by the same pathogen
Stimulate phagocytes to engulf pathogens by phagocytosis
Stimulate B cells to divide and secrete their antibody
Activates cytotoxic T cells

75
Q

How do cytotoxic T cells kill infected cells?

A

They produce a protein called perforin which makes holes in the cell-surface membrane
These holes make the membrane freely permeable

The cell dies as a result
Associated with cell-mediated immunity

76
Q

How does agglutination occur?

A

Each antibody binds to two pathogens due to its two active sites
This clumps the pathogens together to make them easier to engulf by phagocytes

77
Q

What is an antibody?

A

A protein produced by lymphocytes in response to the presence of the appropriate antigen

78
Q

Why are monoclonal antibodies needed?

A

A pathogen has many different proteins on its surface, all of which act as antigens
Each toxin molecule also acts as an antigen

Therefore many different B cells make clones, each of which produces different antibodies
These antibodies are called monoclonal antibodies as they’re antibodies which all work on the same pathogen

79
Q

What is direct monoclonal antibody therapy?

A

Monoclonal antibodies are produced that are specific to cancer cells
Antibodies are given to a patient which attaches themselves to receptors on cancer cells

They attach to the surface of the cells and block chemical signals that stimulate uncontrolled growth

80
Q

What is the ELISA test?

A

Using antibodies to detect antigens in a sample of blood/urine, combined with an enzyme that will give a colour change

81
Q

How are monoclonal antibodies used in pregnancy tests?

A 
A hormone (HCG) is released by the placenta during pregnancy which is excreted in the urine
Monoclonal antibodies show its presence
82
Q

Do vaccines work if you have an autoimmune disease?

A

No because no antibodies are produced and so the person will not be immune to the disease

83
Q

What does a vaccine do?

A

It can’t stop the pathogen from entering your body but it stops you from experiencing any symptoms because the pathogen is defeated too quickly

84
Q

How does a vaccine work?

A

It contains dead or inactive pathogen cells
The immune system destroys the pathogen easily

The memory cells remember the antibodies used so that it can kill the pathogen if it returns

85
Q

Why do vaccinations need to be repeated?

A

A booster allows for a better immune response because the pathogen could overwhelm the immune response and cause symptoms

86
Q

How does HIV replicate inside T helper cells?

A

It can’t replicate himself so uses the host cell’s machinery
1. HIV enters the bloodstream and circulates

  1. Protein on the HIV readily binds to (mostly) helper T cells
  2. Protein capsid fuses with the cell-surface membrane. RNA and enzymes of HIV enter the helper T cell
  3. HIV reverse transcriptase converts the virus’s RNA into DNA
  4. DNA moves into the helper T cell nucleus and is inserted into the cell’s DNA
  5. HIV DNA creates messenger RNA using the cell’s enzymes
  6. mRNA passes out of the nucleus through a nuclear pore
  7. The cell’s protein synthesis mechanisms use the mRNA to make HIV particles
  8. HIV particles break away from the host with a piece of its cell-surface membrane surrounding them to form the lipid envelope
87
Q

What are the stages from HIV to AIDS?

A
  1. Few/no symptoms, infection can spread
  2. Free from symptoms, low level of HIV in blood, lasts for 10 years, HIV antibodies are detected in the blood
  3. Mild symptoms, immune system deteriorates, opportunistic infections
  4. Opportunistic infections cause AIDS
88
Q

How is HIV spread?

A

Bodily fluids

E.g. sexual intercourse, infected needles, blood transfusions,

89
Q

How can lymphocytes distinguish between the body’s cells and foreign cells?

A

The highly specific protein molecules on the cell surface membrane

90
Q

What are the two types of defence mechanisms against pathogens?

A

Non-specific (same for every pathogen): physical barriers and phagocytosis
Specific (specific to each pathogen): response is slower, cell-mediated response by T lymphocytes, humoral response by B lymphocytes

91
Q

What happens to lymphocytes with receptors matching those of the host’s body?

A

In the foetus: lymphocytes either die or are suppressed

In the bone marrow: undergo programmed cell death (apoptosis) before they differentiate

92
Q

What is the function of phagocytes?

A

To ingest and destroy pathogens via phagocytosis

93
Q

How can T lymphocytes determine whether a body cell has been infected with non-self material?

A

Phagocytes that have engulfed a pathogen and body cells invaded by viruses present some of the antigens on their cell-surface membrane
Transplanted cells from members of the same species and cancer cells present different antigens on their cell-surface membranes

94
Q

What is the name for cells that display foreign antigens on their surface?

A

Antigen presenting cells

95
Q

What do T lymphocytes respond to?

A

Antigens that are presented on a body cell rather than to antigens within bodily fluids
This is called cell-mediated immunity

The receptors on each at cell respond to a specific antigen

96
Q

What microorganisms are T cells most effective against?

A

Viruses because they replicate inside cells so the sacrifice of body cells prevents viruses from multiplying

97
Q

Why is humoral immunity called as such?

A

It involves antibodies

Antibodies are soluble in the blood and tissue fluid of the body

98
Q

What are plasma cells?

A

Cells that secrete antibodies usually into blood plasma
They rapidly produce antibodies during their brief lifespan

The antibodies lead to the destruction of the pathogen
The production of antibodies and memory cells is known as the primary immune response

99
Q

What are memory cells?

A

Secondary immune response
Live longer than plasma cells

Divide rapidly at a later date to produce plasma and memory cells when encountering an antigen
Provide long-term immunity
Ensures a fast response so that symptoms do not arise

AQA A Level Biology (19 decks)

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