Y12 Retrieval questions Flashcards
1
Q
Describe the structure of a cellulose cell wall
A
cellulose is made of long unbranded chains of B glucose joined by 1-4 glycosidic bonds, the bonds are straight so the cellulose chains are straight. 50 to 80 cellulose chains are held together by many hydrogen bonds forming micro fibrils, micro fibrils arranged in a mesh, micro fibrils held together by pectin and hemicelluloses
2
Q
Describe the structure of starch
A
mixture of two polysaccharides of alpha glucose. amylose is a long unbranched chain of a glucose containing only alpha 1-4 glycocidic bonds. the angles of the glycosidic bonds give it a coiled structure which makes it compact so good for storage. amylopectin is a long branched chain of a glucose that contains both 1-4 and 1-6 glycocidic bonds and is therefore branched. its side branches allow enzymes to get at the glycosidic bonds easily so glucose can be released quickly. it is insoluble in water
3
Q
Why are different enzymes needed to digest starch and cellulose?
A
different shape molecule requires a different enzyme as they have different active site shapes. cellulose is made of B glucose and starch of a glucose. 1,6 glycosidic bonds are only in starch. starch is made of amylose and amylopectin, cellulose is linear and starch is branched
4
Q
Describe the test for a reducing sugar and state the positive result
A
Add benedicts reagent, heat, positive result = turns from blue to orange-brown
5
Q
Why is the benedicts test known as a semi-quantitive test
A
Because it tells you how much sugar there is, but not exactly how much (i.e. it’s not quantitative)
6
Q
What’s the difference between quantitatve and qualitative results
A
Quantitative results are numbers - they tell you exactly how much. Qualitative results are words
7
Q
What is a disaccharide? What type of bond is involved?
A
Two monosaccharides joined together by a glycosidic bond
8
Q
What type of reaction joins monosaccharides together?
A
Condensation
9
Q
What type of reaction breaks polysaccharides apart
A
Hydrolysis
10
Q
What disaccharide is made by joining glucose and glucose?
A
Maltose
11
Q
What disaccharide is made by joining fructose and glucose?
A
Sucrose
12
Q
What disaccharide is made by joining glucose and galactose?
A
Lactose
13
Q
Describe the test (and result) for starch
A
add iodine solution. If starch is present it will change from orange/brown to blue/black
14
Q
Describe the structure of glycogen
A
Polymer of alpha glucose - highly branched
15
Q
What’s the differences and similarities between starch and glycogen?
A
Glycogen is always branched, starch isn’t. Starch found in plants, glycogen in animals. Both are energy stores, both made of alpha glucose
16
Q
Describe the structure of cellulose
A
A polymer of Beta glucose - straight, unbranched chains with cross linkages
17
Q
State 4 roles of lipids
A
source of energy, waterproofing, insulation, protection
18
Q
What does a tryglyceride consist of? Which type of bonds hold it together?
A
Glycerol and 3 fatty acids - ester bonds
19
Q
How is a phospholipid different to a tryglyceride? And how are they similar?
A
Only 2 fatty acids (Tryglyceride has three). Phosphate head (tryglyceride has no phosphate). Both have fatty acids.
20
Q
What are the monomers that make up a) proteins b) cellulose c) starch
A
amino acids, beta glucose, alpha glucose
21
Q
What type of bond joins amino acids together
A
peptide bond
22
Q
Draw the structure of an amino acid
A
diagram
23
Q
Which part of the amino acid is variable? Approx. how many different types are there
A
The r group - approx 20 amino acids
24
Q
What’s the difference between primary and secondary structure of polypeptides?
A
Primary = sequence of amino acids. Secondary - the shape in which the chain forms due to hydrogen bonds
25
Describe the test (and result) for proteins
The biuret test - add sodium hydroxide, then copper sulfate. If the blue solution turns purple then it's a postive result
26
How do enzymes speed up reactions?
They lower the activation energy
27
Describe the action of enzymes - how do they work?
The substrate binds to the active site making an enzyme substrate complex. The shape of the active site changes slightly as it binds (induced fit), as it changes shape, the enzyme puts a strain on the substrate, causing it to distort slightly so this lowers the activation energy
28
What’s the difference between a competitive and non-competitive inhibitor?
Competitive inhibitors bind to the active site, blocking it so the substrate can't bind. Non-competitive inhibitors bind elsewhere, causing the active site to change shape so the substrate can't bind
29
How can you find out if an inhibitor is competitive or non-competitive?
Increase the substrate concentration, if it is non-competitive, it will make no difference, if it is competitive, then more substrates should increase the rate of reaction
30
Describe (draw) how a monosaccharide is formed
Condensation reaction between two glucose monomers, 1-4 glycosidic bond
31
What type of reaction breaks a 1-4 glycosidic bond?
Hydrolysis reaction
32
Name the 4 bases found in DNA, name the bonds that form between them
Adenine - Thymine and Guanine -cytosine. Hydrogen bonds
33
Draw a nucleotide
diagram
34
Draw a polynucleotide. Label the phosphodiester bond
diagram
35
Which molecules make up the 'backbone' of a polynucleotide?
Phosphates and pentose sugars
36
Which enzyme separates the strands in DNA replication?
DNA Helicase
37
State the role of DNA polymerase
Joins nucleotides together in condensation reactions
38
Why is DNA replication known as 'semi conservative'?
Because the orginal strand is split in two and half of each new strand comes from the original. Half is 'conserved'
39
What are the inner folds of mitochondria called?
Cristae
40
What is the function of the Golgi Apparatus?
To process & package new proteins & lipids; makes lysosomes.
41
What is the function of a lysosome?
Contain enzymes- lysozymes used to digest broken/invaded cells.
42
What is a ribosome made of?
Proteins, RNA (NO MEMBRANE!)
43
What is the function of a ribosome?
Protein synthesis
44
Describe the difference between smooth & rough endoplasmic reticulum.
Smooth= no ribosomes
45
What is the function of the smooth ER?
Synthesises & processes lipids
46
What makes up the cell wall of plants & algae?
Cellulose
47
What is a tonoplast?
The membrane of a plant-vacuole
48
Why would an epithelial cell in the small intestine need lots of mitochondria?
Respiration, to give energy needed for absorption of nutrients.
49
What is a tissue?
A group of similar cells performing a similiar function e.g. epithelial cells form epithelial tissue
50
What is an organ?
A group of similar tissues working together e.g muscular, epithelial & glandular tissues form the stomach.
51
Describe the function of the nucleolus.
Makes ribosomes
52
Give 2 differences between plant & fungal cells.
Fungi= no chloroplasts & chitin cell wall not cellulose
53
List 3 differences between eukaryotic & prokaryotic cells.
Prokaryotic = no membrane bound organelles, no nucleus, smaller ribosomes, murein cell wall
54
What is a plasmid?
A loop of DNA NOT part of main chromosomal DNA e.g. genes for antibiotic resistance. Not in all bacterial cells.
55
Why might a bacterial cell have a slime capsule?
To give protection against the cells of the immune system.
56
Why do prokaryotes undergo Binary Fission?
Bacteria replicate using binary fission
57
What replicates in Binary fission?
Chromosomal DNA replicates once- plasmids may replicate many times
58
What is the role of the attachment proteins of a virus?
To allow viruses to invade host cells, by using complemetary binding to receptors on host cells.
59
Briefly describe the steps of viral replication.
1. Viruses attach to host cells using attachment proteins 2. Genetic material is released into host cell 3. Host cell machinery replicates viral DNA/RNA/proteins 4. Viruses assemble & replicate 5. Viruses leave host cell
60
Describe the term resolution.
Level of detail seen in an image- how close together 2 objects are to be seen as separate.
61
Describe the term magnification.
The number of times larger an image of an object is compared with the actual size.
62
Describe 2 differences between a light microscope & SEM.
SEM- higher resolution (3-10nm rather than 200nm), higher magnification (200,000 rather than 2000), uses electrons rather than light, can see surface of cells- 3D image
63
Write down the formula for magnification.
magnification = size of image/ size of real object
64
1mm = ? μm
1mm = 1000 μm
65
50 μm = ? cm
0.005 cm
66
1mm = ? nm
1mm = 1,000,000m
67
Use standard form to write the number 0.00002 mm
2 x 10-5
68
List 3 organelles you cannot view with a light microscope.
ribosomes, ER, lysosomes
69
Describe when you would use a TEM.
To view a thin specimen, high resolution to see small objects.
70
Why is a stain used when preparing a slide?
Stains highlight objects in a cell- you can see certain organelles more clearly.
71
Why does a specimen need to be thin when preparing a slide?
Thin specimens allow light to pass through the object, so can be seen clearly.
72
Describe what an artefact is.
Artefacts are viewed underneath a microscope but should not be there e.g. air bubble, dust, fingerprint and usually arise from inaccurate preparation of a sample.
73
List the 3 steps involved in cell fractionation.
Homogenisation, filtration, ultracentrifugation
74
What is the heaviest organelle?
nucleus
75
What are the lighest organelles?
ribosomes
76
Explain why an ice-cold, isotonic, buffered solution is used in cell fractionation.
Ice- cold: slow enzyme activity, Isotonic: prevent damage to organelles, Buffered: control pH
77
What type of microscope would you use to study lysosomes?
TEM
78
Which type of microscope would be used to study replication of E.coli bacteria?
Light
79
Which type of microscope would be used to study the 3D structure of a red blood cell?
SEM
80
List the 4 stages of the cell cycle.
Mitosis, G1, Synthesis, G2
81
What is interphase?
Growth stages (most of cell cycle) ie G1, synthesis, G2
82
Describe what happens to a cell in interphase.
DNA unravels & replicates, organelles replicate & ATP increases.
83
What is the ultimate outcome of mitosis?
2 genetically identical daughter cells
84
Describe 2 uses of mitosis by organisms
For growth & repair of human cells (e.g. skin) embryonic development, asexual reproduction of plants.
85
List the stages of mitosis in order.
Prophase, Metaphase, Anaphase, Telophase
86
What is a centromere?
The centre point of a chromosome- holds 2 sister chromatids together.
87
What is a centriole?
Bundles of protein, which produce spindle fibres and move to poles of the cell in prophase.
88
Describe what occurs in Prophase.
Nuclear envelope breaks down, centriples move to either end, chromosomes condense.
89
List 2 events that happen in Metaphase.
Chromosomes lines up on spindle equator, spindle fibres attach to centromeres.
90
Describe what cells would look like when undergoing anaphase.
No nuclear envelope, v-shaped chromatids being pulled apart to opposite ends of the cell.
91
List 2 events that happen in Telophase.
Chromatids uncoil & nuclear envelope reforms.
92
What is cytokinesis?
Final stage of mitosis where the 2 joined cells separate into 2 daughter cells.
93
If 10 cells out of a total of 100 are in metaphase of mitosis & one complete cycle takes 15 hours, how long do the cells spend in metaphase? Give answer in minutes.
15 x 60 = 900 , 10/100 x 900 = 90 mins
94
Briefly, what causes cancer?
When the cell cycle is out of control (gene mutation)
95
Vincristine is a cancer drug which prevents spindle fibres from formed. Briefly describe how this will lead to treatment.
No spindle = no anaphase so mitosis cannot occur, cells can't divide & cancer can't develop further.
96
How can the overall magnification of a light microscope be calculated?
Objective lens x occular lens (usually x10)
97
What is the mitotic index?
The proportion of cells in a sample undergoing mitosis.
98
Write down the formula for mitotic index.
Mitotic index = number of cells with visible chromosomes / total number of observed cells
99
What is an eyepiece graticule?
A transparent ruler, attached to the eyepiece used to measure actual size of cells.
100
Would you expect the mitotic index of root tip cells to be higher or lower than cells from a mature leaf?
Higher- root tip divides to extend.
101
Description and function of the cell wall?
rigid structure, mainly made of cellulose, that surrounds and supports plant cells.
102
Description and function of the chloroplast
small flattened structure. has a double membrane and membranes inside called thylakoid membranes. thylakoid membranes are stacked up in some parts to form grana. grana are linked together by lamellae (thin pieces of thylakoid membrane). Site of photosynthesis
103
Description and function of the vacuole and tonoplast
vacuole is a compartment surrounded by a membrane called a tonoplast. vacuole contains cell sap which is made up of water, enzymes, minerals and waste products. vacuoles keep cells turgid - stops plants from wilting. also involved in the breakdown and isolation of unwanted chemicals in the cell. tonoplast controls what enters and leaves vacuole
104
How is HIV spread?
Through infected bodily fluids. via sex, sharing needles, direct blood to blood transfer and maternal transmission from mother to unborn child
105
What is a capsid?
Protein coat around the core
106
What are the attachment proteins on a virus?
Attachment proteins?stick out from the edge of the capsid of envelope, let the virus cling on to a suitable host cell
107
What is the envelope on a virus?
Extra outer layer stolen from the cell membrane of a previous host cell
108
Describe the basic structure of a virus
A strand of nucleic acid (DNA or RNA) enclosed within a protein coat
109
How does the HIV virus replicate?
Attaches to receptor molecule on host cell membrane. capsid is released into cell and it uncoats and releases nucleic acid. reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template. double stranded DNA is made and inserted into the human DNA (using integrase). host cell enzymes are used to make viral proteins from the viral DNA within the human DNA. the viral proteins are assembled into new viruses and releases from the cell via cell lysis
110
How does HIV invade T helper cells?
(gp120) glycoprotein molecules on the virus surface bind to CD4 receptors on the surface of t helper cells. they then combine with a second receptor. this allows the envelope surrounding the virus to fuse with the T helper cell membrane, enabling the viral RNA to enter the cell
111
What are opportunistic infections?
Infections that occur when the body's defenses are weakened
112
What are the initial symptoms of AIDS?
Minor infections of mucosal membranes and recurring respiratory infections caused by a lower than normal number of T helper cells
113
When are people with HIV classed as having AIDS?
When symptoms of failing immune system start to appear or their T helper cell count drops below a certain level
114
What is AIDs?
When the immune system deteriorates and eventually falls
115
Description of nucleus
Large organelle surrounded by a nuclear envelope which contains pores. the nucleus contains chromatin (which is made from DNA and proteins and a structure called the nucleolus.
116
What is the function of nucleus ?
Controls the cells activities by controlling the transcription of DNA. DNA contains instructions to make proteins. Pores allow substances to move between the nucleus and cytoplasm. The nucleolus makes ribosomes
117
Description of lysosome
A round organelle surrounded by a membrane with no clear internal structure
118
What is the function of the lysozyme?
Contains digestive enzymes which are used to digest invading cells or break down worn components of the cell
119
Describe a ribosome
A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It is made up of proteins and RNA. No membrane
120
Describe the RER
A system of membrane bound flattened sacs. the surface is covered with ribosomes
121
What is the function of the RER?
Folds and processes proteins that have been made at the ribosomes
122
Describe the SER
Description of smooth endoplasmic reticulum ?a system of membrane bound flattened sacs but with no ribosomes
123
What is the function of the SER?
Function of smooth endoplasmic reticulum ?synthesises and processes lipids
124
Describe the Golgi apparatus
A group of fluid filled membrane bound flattened sacs. formed by the fusion of vesicles from the ER
125
Describe the mitochondria
Description of mitochondria ?Double membrane- inner one is folded to form a structure called cristae. inside is the matrix which contains enzymes involved in respiration
126
What is the function of the mitochondria?
Function of mitochondria ?site of aerobic respiration, where ATP is produced. found in large numbers in cells that are very active and require a lot of energy.
127
Describe the centriole
small hollow cylinders made of microtubules. found in animal cells but only some plant cells
128
What is the function of the centriole?
Involved with the separation of chromosomes during cell division
129
What type of proteins do ribosomes make?
Ribosomes on the rER make proteins that are excreted or attached to the cell membrane. Free ribosomes in the cytoplasm make proteins that stay in the cytoplasm.
130
What happens once the new proteins are made ?
They enter into the rER and are folded and processed. Then they are transported to the Golgi apparatus in vesicles. The vesicles fuse to form the flattened sacs of the Golgi and the Golgi further processes the proteins. The proteins enter more vesicles and are transported around the cell
131
What is found in the cytoplasm in prokaryotic cells?
No membrane bound organelles and has smaller ribosomes than in eukaryotic cell
132
What is the flagellum?
long hair like structure that rotates to make the prokaryotic cell move. not all prokaryotes have a flagellum and some have more than one
133
What is circular DNA?
Long coiled up strand of DNA that is not attached to any histone proteins
134
What kind of cell does mitosis produce ?
genetically identical daughter cells
135
What is mitosis needed for ?
growth, repairing damaged tissues and for asexual reproduction
136
What does the cell cycle consist of ?
Interphase which is a period of cell growth and DNA replication (G1, S and G2) then Mitosis
137
What happens during Interphase?
Gap phase 1 - cell grows and new organelles and proteins are made. Gap phase 2 - cell keeps growing and proteins needed for cell division are made. ATP content is increased. Synthesis - cell replicates its DNA ready to divide by mitosis
138
Order of stages in mitosis
prophase, metaphase, anaphase and telophase
139
What happens in prophase?
Chromosomes condense, becoming shorter and thicker, each chromosome is visible as 2 strands called chromatids. centrioles start moving to opposite ends of the cell, forming a network of protein fibers called a spindle. nuclear envelope breaks down and the chromosomes lie free in the cytoplasm
140
What happens in metaphase?
Metaphase ?chromosomes, each with 2 chromatids line up along the middle of the cell and become attached to the spindle fibers at their equator by their centromeres.
141
What happens in anaphase?
Anaphase ?centromeres divide, separating each pair of sister chromatids. the spindles contract, pulling chromatids to opposite poles of the spindle, centromere first
142
What happens in telophase?
Telophase ?chromatids reach the opposite poles on the spindle. they uncoil and become long and thin and are called chromosomes again. a nuclear envelope forms around each group of chromosomes so there are 2 nuclei. The cytoplasm divides and there are now 2 genetically identical daughter cells.
143
How does mitosis ensure genetic consistency ?
DNA replication before mitosis. The arrangement of chromosomes on the spindle and the separation of chromosomes to the pole
144
Which part of a phospholipid is hydrophobic?
Tail
145
What is the role of cholesterol in the plasma membrane?
add strength, reduce lateral movement, stop leakage
146
Describe the importance of a partially permeable membrane.
The membrane will only allow certain molecules through- regulates movements of solutes
147
What does the fluid mosaic model describe?
The phospholipid bilayer is interspersed with proteins (like tiles in a mosaic), & constantly move (fluid)
148
The centre of the bilayer is hydrophobic. So which type of molecules can diffuse through.
Small & non-polar. (Water also does! As it's so small).
149
How would chloride (Cl-) ions move across the membrane?
Across a channel protein
150
What is a glycoprotein?
Proteins with a carbohydrate attached- usually protrude from the membrane.
151
Would you expect a red blood cell, or an epithelial cell of the small intestine, to contain more cholesterol in the plasma membrane?
Red blood cell- unsupported & free-floating cell, so needs to maintain own shape.
152
If high temperatures are applied to the Plasma membrane, what happens?
Channel/carrier proteins denature, so membrane becomes more permeable (it can't control what is going in/out)
153
What is diffusion?
The net movement of molecules from an area of high concentration to an area of low concentration (DOWN the conc. gradient)
154
Is diffusion a passive or active process?
Passive-no energy is needed.
155
Give an example of a molecule which can use simple diffusion to pass through the membrane.
Small, non-polar e.g. oxygen, carbon dioxide
156
Describe the role of a carrier protein.
Use to move large molecules across the membrane- when ion/molecule attaches to protein, it changes shape & releases molecules on other side of membrane.
157
What is facilitated diffusion?
Movement of particles from a high to low concentration, down the conc. gradient, using a membrane protein.
158
Which types of molecules would be transported using facilitated diffusion across the membrane?
Large, polar, water-soluble (e.g. glucose, amino acids)
159
Describe the role of a channel protein.
Acts as a pore in the membrane to allow larger/polar molecules to diffuse across.
160
A graph showing the uptake of glucose by GLUT1 carrier proteins, shows that the rate increases as the number of glucose molecules increases. However the graph plateaus, why?
The system reaches equilibrium- there are only so many carrier proteins- if most of these are in use, then the rate of glucose uptake would slow.
161
How can the gradient of a straight line or tangent by calculated?
Change in y / change in x
162
Is facilitated diffusion a passive or active process?
Passive-no energy is needed.
163
What is osmosis?
The net movement of water molecules through a partially permeable membrane, from an area of high to low concentration OR from an area of high water potential (less negative) to an area of lower water potential (more negative).
164
What is the water potential of pure water?
Water potential ψ = 0
165
If more of a solute (e.g. salt) is added to a beaker of water, what would happen to the water potential of the solution?
More solute = less water molecules, so LOWER water potential (more negative)
166
Describe the term isotonic.
2 solutions are isotonic if they have the same ψ, so no net movement of water occurs.
167
Describe how you would use a calibration curve to identify the water potential of a sample.
Identify the point at which the curve meets the x axis (where % change in mass is 0). Find the concentration at this point & look up water potential.
168
Pieces of potato with a ψ of -350 kPa are placed into a solution with a ψ of -275 kPa. Explain what will happen to the potato.
Potato gains mass (has a lower ψ than the solution OR MORE negative ψ) so water moves from solution into the potato.
169
What is active transport?
The movement of particles from an area of lower concentration to higher concentration, requiring energy. (AGAINST a conc. gradient)
170
How does ATP release energy to a cell?
ATP undergoes hydrolysis to form ADP + Pi, releasing energy.
171
What are co-transporters?
A type of carrier protein, which binds 2 molecules at a time and uses the gradient of one molecule, to move the other against it's conc. gradient.
172
Will the rate of active transport increase or decrease if the number of carrier proteins in the membrane is increased?
Increase
173
Describe the importance of sodium ions in the transport of glucose from the ileum into the blood.
Na + ions diffuse through a carrier protein down their conc. gradient, carrying glucose in simultaneously, which is moving AGAINST it's gradient. Glucose can then diffuse into the blood & be transported around the body.
174
Describe the importance of the villi in the small intestine.
Villi- increase surface area of ileum, so more products of digestion can be absorbed.
175
What is an antigen?
A molecule (usually protein) which triggers an immune reponse.
176
Define diffusion
Diffusion - Net movement of particles from an area of higher concentration to an area of lower concentration. Passive process
177
Define concentration gradient
Path from an area of higher concentration to an area of lower concentration. Particles diffuse down it
178
Define osmosis
Diffusion of water molecules from a dilute solution (an area of higher concentration of water molecules) to a concentrated solution (an area of lower concentration of water molecules) across a partially permeable membrane
179
Define facilitated diffusion
Larger molecules and charged particles cannot diffuse through the phospholipid bilayer as they are insoluble. They diffuse through carrier or channel proteins in the cell membrane instead. Passive process
180
What are carrier proteins?
Move large molecules into or out of the cell down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules
181
How do carrier proteins work?
A large molecule binds to a specific site in the carrier protein. The protein changes shape and releases the molecule on the opposite side of the membrane
182
What is a channel protein?
Channel proteins - Form pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles. All have a specific shape and can be opened or closed
183
Define active transport
Active transport - Uses energy to move molecules and ions across the plasma membranes against a concentration gradient. Use carrier proteins
184
Explain how active transport works
A molecule attaches to the carrier protein. ATP is hydrolysed in the cell to release energy. This energy is used to make the carrier protein change shape. This moves the molecule across the membrane, releasing it on the other side.
185
Describe the process of endocytosis
A cell surrounds a substance with a section of its cell membrane. The cell membrane pinches off to form a vesicle inside the cell containing the ingested substance. Process uses ATP for energy
186
Why are substances taken in to the cell by endocytosis?
They are too large to be taken in by carrier proteins
187
Describe the process of exocytosis
Some substances produced by the cell need to be released from the cell. Vesicles containing the substances fuse with the cell membrane and release their contents outside the cell. Uses ATP for energy
188
How does the human body distinguish between self & non-self cells?
Marker molecules (proteins) are present on the membrane of cells, enabling the body to recognise these as 'self' cells.
189
What is a toxin?
A protein (antigen) released by pathogens which are poisonous to the body.
190
Why must patients who receive organ donations, take anti-rejection medicines?
The organ has non-self antigens- which will trigger an immunne response. The anti-rejection medicines prevent this response.
191
Briefly, what is phagocytosis?
When foreign cells are engulfed by phagocytes, digested by lysozymes released by lysosomes in the cell.
192
How does a phagocyte use chemotaxis?
Phagocytes are attracted to pathogens by chemicals released by the pathogen( phagocytes move down conc.gradient)
193
Describe the role of T-helper cells.
Recruit & signal to phagocytes AND activate B cells
194
Describe the role of T-cytotoxic cells.
Kill abnormal & foreign cells (produces proteins to do this e.g. perforin)
195
What is a B plasma cell?
A type of B cell which secrete LOTS of monoclonal antibodies (all complementary to a specific antigen)
196
Describe the importance of the variable region of an antibody.
Has a unique protein structure, which provides specificity to one type of antigen.
197
What does the humoral immmune response consist of?
B cells- antibodies, clonal selection.
198
What does the cellular immune response consist of?
T cells- phagocytes, cell signals etc.
199
Describe the primary response of the immune system.
When the body first detects a type of pathogen, a slow response, which creates memory cells. The body will show symptoms until enough antibodies are made.
200
Explain why the secondary response is quicker than the primary immune response.
B- memory cells are activated and divide into plasma cells, producing antibodies. T-memory cells are activated and produce T-cells to kill the pathogen. FEWER STEPS!
201
What is active natural immunity?
When a person is immune, after naturally contracting an infection.
202
What is passive immunity?
When a person is immune, by being given antibodies rather than making them. e.g. natural from breastfeeding.
203
Give 2 differences between passive & active immunity.
Active- lasts longer, memory cells are produced, response takes longer to happen, needs antigen to trigger response.
204
What is a vaccine?
A low dose of an inactive/dead pathogen are injected- contain antigens to trigger immune response, creating protective memory cells.
205
What is herd immunity?
If more members of a population have had a vaccine, more people are then protected as a disease can spread less rapidly, even if they haven't had the vaccine themselves.
206
What is antigenic variation?
Where a pathogen can change the antigens on its surface (e.g. different strains of flu)
207
Explain why people must receive a different flu vaccine annually.
The flu virus undergoes antigenic variation, so memory cells from one vaccine will not always protect against new strains.
208
What are monoclonal antibodies?
Antibodies which are all made from identical B plasma cells- complementary to the same specific antigen.
209
Describe how monoclonal antibodies can be used in anti-cancer drugs.
Antibodies are specific to antigens on cancerous cells (tumour markers)- the drug binds& accumulates in specific area (much fewer side effects than conventional cancer treatments).
210
What is an ELISA test?
Where antibodies are attached to an enzyme, which produces a coloured substrate- used in diagnosis.
211
What is the main difference between a direct & an indirect ELISA test.
Direct- one type of antibody applied to sample/antigen. Indirect- many antibodies present.
212
Which part of the immune system does HIV initially affect?
T-helper cells
213
Describe how HIV uses reverse transcriptase to replicate in host cells.
HIV attaches to the host cell, releasing the capsid containing viral RNA. Reverse transcriptase is then used to generate complementary DNA- inserted into human DNA and uses host enzymes to to create new proteins- new viruses which can affect more host cells.
214
Why should HIV testing not occur on a newborn baby?
Would give inaccurate results- need to wait 18 months before baby can be tested as HIV can pass from the mother into baby's bloodstream.
215
Explain why antibiotics cannot be used on HIV.
Antibiotics are specific to bacteria e.g. murein cell walls, so would be ineffective on viral structure.
216
What conditions do bacteria need to survive and reproduce?
source of nutrients to grow and respire, oxygen of aerobic respiration, temperature and pH is important
217
Why is aseptic technique important?
prevents contamination of cultures by unwanted microorganism
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What is phagocytosis?
Phagocyte recognises the antigens on a pathogen. endocytosis. pathogen is contained in a phagocytic vacuole. lysosomes, containing digestive enzymes fuse with the vacuole, enzymes are released and they destroy the pathogen. phagocyte presents antigen on its surface
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What do the receptors on T cells do?
bind to antigens displayed by antigen presenting cells
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How are T cells activated?
When their receptors bind to complementary antigens on the surface of antigen presenting cells. once activated by this binding each t helper cell produces a clone of active t helper cells and a clone of t memory cells
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What does a T cell differentiate into?
T helper cells, T killer cells, T memory cells
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Give a short summary of how HIV weakens immune system
HIV invades T helper cells, preventing the activation of macrophages, B cells and T killer cells, which weakens the immune response
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What do T helper cells do?
Binds to an antigen-presenting B cell and produces cytokines that stimulate B cell to divide and become capable of producing antibodies. they also enhance the activity of phagocytes
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What are B cells?
lymphocytes that secrete antibodies in response to antigens. antibodies bind to the antigens on the cell surface membrane to form an antigen antibody complex. each b cell has a different shaped antibody which binds to only one specific antigen. they allow phagocytes to recognise and destroy the cell.
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What is B cell division also known as
Clonal selection
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Describe the antibody structure
Four polypeptide chains, 2 heavy and 2 light. each chain has a variable region and a constant region
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State the variable region on an antibody
Form the antigen binding site. The shape is complementary to a particular antigen, its shape varies between antibodies
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What is a memory cell?
Remain for years in the body, enabling an individual to respond more quickly to the same antigen in the future
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What is an antibody?
Bind to antigens to form an antigen-antibody complex
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How do pathogens enter the body?
Cuts in the skin, digestive system, respiratory system by being inhaled, mucosal sueaces
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What is the purpose of stomach acid?
Acidic conditions kill pathogens
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What is the purpose of skin?
Physical barrier to pathogens, blood clots form to prevent pathogens entering when skin is damaged
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What is herd immunity?
When enough people are immunised, the disease is less likely to be transferred from one person to another, so there is less disease in the community as a whole.
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What is lysozyme?
Mucosal surfaces produce secretions that contain lysozyme. It kills bacteria by damaging their cell walls making them burst open
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What is natural active immunity?
When your immune system makes its own antibodies after being stimulated by an antigen (after catching a disease)
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What is passive natural immunity?
When a baby receives antibodies from its mother through the placenta and in breast milk
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What does active immunity give you?
Long term protection but it develops after a time lag
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What does passive immunity give you?
Short term but immediate protection
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Why is the primary response slow?
there aren't many B cells that can make the antibody needed to bind to the antigen
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What are T memory cells?
remember specific antigen and recognise it a second time around
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What are B memory cells?
Record the specific antibodies needed to bind to the antigen. they remain or months or years in the body, enabling the individual to respond more quickly to the same antigen in the future.
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What is the primary immune response?
Immune response the first time the body is exposed to a particular foreign antigen. B cells take 10 to 17 days to produce sufficient antibody producing cells. the person is likely to suffer symptoms of the infection during this time
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How does the body prevent attack by own immune system?
some of the membrane proteins on the surface of our cells mark the body cell as 'self'. they allow us to distinguish between our cells and invaders
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What is the secondary response?
if the same pathogen enters the body again the immune system will produce a quicker stronger immune response. the b memory cells produced in the primary response can differentiate immediately to produce plasma cells and release antibodies.
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What is the constant region?
Allow binding to receptors on immune system cells. It is the same in all antibodies.
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How do antibodies help clear up an infection?
Agglutinating pathogens, neutralising toxins, preventing the pathogen binding to human cells
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State the two forms of antibodies
Membrane bound and secreted
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What is the purpose of the capsule in bacterial cells?
Made of secreted slime protects the bacterium from attack by cells of the immune system. also prevents dehydration and allows bacteria to form colonies
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What is the bacterial cell wall made of?
made of murein glycoprotein
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What is a bacterial chromosome?
Long circular coiled up strand of DNA floating free in the cytoplasm
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If the zone of inhibition is wider, what does this indicate about the antibiotic?
the wider the clear zone, the more effective the antibiotic is at preventing growth
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why do bacteria populations evolve very quickly?
bacteria reproduce very fast. bacterial populations are usually in billions, so the number of cells containing mutations is vast. some of these random mutations will be advantageous to the cell containing them so they are more likely to survive reproduce and spread
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What is the ventilation rate ?
The volume of air breathed in or out in a period of time
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Why does the ventilation rate increase during exercise ?
because the breathing rate and depth increase
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What is the cardiac output?
The total volume of blood pumped by a ventricle every minute
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What is the equation for cardiac output and units ?
Cardiac output (cm3/min) = heart rate (beats per minute) x stroke volume (cm3)
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What is the stroke volume ?
the volume of blood pumped by the left ventricle each time it contracts
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What is tidal volume?
The volume of air in breathed in and out at each breath at rest
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What is total lung capacity?
Volume of lungs at maximal inflation
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What is breathing rate?
Number of breaths are taken per minute
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Describe inhalation
Diaphragm contracts, external intercostal muscles contract, chest volume increases, pressure in chest decreases, atmospheric pressure forces air into lungs, lungs expand to equalise pressure
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Describe exhalation
Diaphragm relaxes, external intercostal muscles relax, chest volume decreases, pressure in chest decreases, air is forced out of lungs until air pressure inside and outside chest is equal
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Describe an open circulatory system
Blood is not contained in blood vessels but circulates in large spaces
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Define a closed circulatory system
Blood is enclosed within vessels/diffusion of substances only takes place within vessels
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Define a single circulatory system
Blood flows through the heart once for each complete circuit of the body
Blood is pumped at a low blood pressure. Suitable for organisms with a low metabolic rate
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Define a double circulatory system
Blood flows through the heart twice for each complete circuit of the body (i.e simultaneously pumps to lungs and heart)
Maintains a high blood pressure to meet demands of a high metabolic rate
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Why cant complex multi cellular organisms rely on diffusion to transport substances around the body?
They are too large for diffusion to transport substances quickly enough (small SA:V)
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How does blood circulate in an open circulatory system?
A simple heart pumps blood out into the cavities surrounding the organs. The heart muscle relaxes so the pressure decreases and blood is drawn from the cavity back into the heart through open valves
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Why is a closed circulatory system more efficient?
The blood is forced through fairly narrow tubes so it travels faster and under pressure.
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What are the benefits of a mass transport system?
Carries raw material from specialised exchange organs to the body cells to remove metabolic waste
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Describe the structure of capillaries
Very narrow lumen for short diffusion distance, single layer of cells so it can lie very close to the cells. joins the arteries and venues together, medium pressure, large surface area - Structure of the capillaries
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What is the function of the capillaries?
Where metabolic exchange occurs so substances are exchanged between cells and the capillaries -
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Describe the stretch and recoil in arteries
Heart contracts and blood is forced into the arteries. The elastic walls stretch a little to accommodate the blood. The heart relaxes and the elasticity of the walls causes them to recoil a lot behind the blood pushing it forward. This causes a pulsing flow through the arteries
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Describe how blood flows in veins
Blood flow is assisted by the contraction of skeletal muscles during movement of limbs and breathing. Low pressure in thorax when breathing draws blood back into the heart from veins -
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State the four chambers of the heart
Left atria/left ventricle/right atria/right ventricle
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State the four vessels entering/exiting the heart
aorta/vena cava/pulmonary artery/pulmonary vein
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How is the left side of the heart identified?
Presence of a thicker muscular wall
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What is present inside the heart to prevent backflow?
AV valves (tricuspid = right, bicuspid = left) and semi-lunar valves.
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Why are the ventricle walls thicker than atria walls?
Blood needs to be under higher pressure to travel a further distance
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Why are valves important?
Prevent backflow/allow build up of pressure
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State what happens to the heart during ventricular diastole and atrial systole
Ventricles are relaxed/atria contract/increases pressure in atria/AV valves open/blood flows into ventricles
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How does the structure of xylem allow them to transport water?
Hollow as no cytoplasm, vessels have no end walls and pits, vessels are strong so do not collapse, lignin makes the walls waterproof
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How does no ATP production affect transport of substances in plants?
translocation inhibited by transpiration stream not inhibited. Phloem contains cytoplasm but xylem does not. Cytoplasm has mitochondria involved in metabolism.
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Function of xylem vessels
transports water and mineral ions up the plant and provides support
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Function of phloem tissue?
transport organic solutes from where they are made in the plant to where they are needed . this is translocation
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Structure of xylem vessel?
very long tube like structures formed from dead cells joined end to end. tubes found together in bundles. hollow lumen as no cytoplasm and no end walls makes an uninterrupted tube allowing water and mineral ions to pass through the middle easily. walls thickened with lignin. pits in walls where there is no lignin.
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Structure of phloem tissue?
Sieve tube elements (living cells) joined end to end to form sieve tubes. Sieve parts are the end walls which have lots of holes to allow solutes to pass through. There is a companion cell for every sieve tube element
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Structure of sieve tube elements and companion cells?
Sieve tube elements have no nucleus, a very thin layer of cytoplasm and few organelles. cytoplasm of adjacent cells is connected through holes in the sieve plates. lack of nucleus and other organelles means they cant survive on their own. companion cells carry out the living functions for both themselves and their sieve cells
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Why do plants need water?
for photosynthesis, to transport minerals, maintain structural rigidity and to regulate temperature
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Why do plants need nitrate ions?
for production of DNA, proteins and chlorophyll. they are required for plant growth, fruit production and seed production
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What happens during mRNA splicing?
Introns removed and exons joined, and possibly rearranged, to form mRNA
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What is an intron?
Non coding sections of DNA
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What is pre-mRNA?
mRNA strands containing both introns and exons
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What is an exon?
Coding sections of DNA
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Describe the process of translation
Ribosome attaches to mRNA. tRNA carries amino acid to ribosome. Complementary base pairing between anticodon on tRNA and codon on mRNA. Hydrogen bonds form between the tRNA and mRNA. A peptide bond forms between amino acids by condensation reaction. The tRNA is released from the ribosome. The ribosome detaches from the polypeptide chain on mRNA when it reaches a stop codon
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How can a gene mutation result in a protein not being synthesised?
Mutation changes sequence of bases, A premature stop codon or frame shift is changed by the mutation. Transcription/translation does not occur
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Describe the structure of tRNA
tRNA is folded, has hydrogen bonds holding the structure together, is a fixed size, has an anticodon, has an amino acid binding site
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How are amino acids joined together to form the 3D structure of a protein?
Peptide bonds between amine group and carboxyl group of another. Primary structure is sequence of amino acids in a protein. The primary structure is folded and held together by bonds. These bonds are disulphide bonds, ionic bonds, hydrogen bonds and are between the R groups
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Why does transcription occur?
Because DNA is too large to move out of the nucleus so a section is copied onto mRNA
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What is mRNA?
Made in the nucleus during transcription, has a codon, carries the genetic code from the DNA in the nucleus to the cytoplasm. Single stranded. Shorter than DNA
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What is a codon?
Three adjacent bases
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What is tRNA?
Found in cytoplasm, has an amino binding site at one end and an anticodon on the other end, carries amino acids that are used to make proteins to the ribosomes
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Define the genetic code
The sequence of base triplets in DNA or mRNA which codes for specific amino acids
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What does it mean by 'non overlapping'?
Each base triplet is read in sequence, separate from the triplet before and after it. base triplets do not share their bases
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Explain the term 'degenerate'?
There are more possible combinations of triplets than there are amino acids. Some amino acids are coded for by more than one base triplet
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What are the stop and start codons?
Triplets that tell the cell when to start and stop production of the protein. Found at the beginning and end of the gene
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What happens when the RNA polymerase attaches to the DNA at the start codon?
The hydrogen bonds between the 2 DNA strands in the gene break, separating the strands and the DNA molecule unwinds
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What is the template strand also known as?
Antisense strand
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What happens when the RNA polymerase lines up free RNA mononucleotides alongside the template strand?
Complementary base pairing occurs so that the mRNA strand ends up being a complementary copy of the DNA template strand. RNA polymerase joins the mononucleotides together by phosphodiester bonds in condensation reactions
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What happens when RNA polymerase reaches a stop codon?
It stops making mRNA and detaches from the DNA. mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm
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What is semi conservative replication?
Half of the strands in each new DNA molecule are from the original DNA molecule
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What are gametes?
The male and female sex cells found in all organisms that reproduce sexually
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Why is it important that gametes only have one set of chromosomes ?
So that the diploid number of chromosomes can be restored after fertilisation
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Describe a haploid nucleus
one set of chromosomes. half the number of chromosomes found in a normal body cell. contains one chromosome from each homologous pair, type of nucleus found in gametes
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Describe a diploid nucleus
Two sets of chromosomes
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Describe meiosis
Type of cell division that produces gametes
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Define genetic variation
Differences that exist between individual's genetic material
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How does meiosis produce cells that are genetically different ?
Through crossing over of chromatids and independent assortment of chromosomes
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Explain the crossing over process
During first division in meiosis, the homologous pairs of chromosomes come together and pair up. two of the chromatids in each homologous pair twist around each other. the twisted bits break off their original chromatid and rejoin on the other chromatid, recombining their genetic material, exchanging sections of DNA.
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What are the chiasma?
The point where chromatids break
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How does crossing over increase genetic variation ?
each four new cells formed from meiosis contains chromatids with different combinations of alleles
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Describe independent assortment
Independent assortment ?the random distribution of genes with loci on different chromosomes in the gametes. When gametes are produced, different combinations of the maternal and paternal chromosomes go into each cell. only one chromosome from each pair ends up in each gamete
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Explain the importance of meiosis in gametes production
To half the chromosome number producing a haploid nucleus, so at fertilisation the diploid number of chromosomes is restored. it allows genetic variation through independent assortment and crossing over.
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Why does asexual reproduction lead to low genetic diversity ?
Low genetic diversity means there are few different alleles in the gene pool. Asexual reproduction leads to all offspring being genetically identical. No meiosis.
325
Define a recessive genetic disorder
A defect in the genes where both defective alleles need to be present
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What is a recessive allele?
Both alleles need to be present in order for recessive phenotype to be expressed. a different form of a gene
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What is a mutation?
Change to the base sequence of DNA. Caused by errors during DNA replication
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What is a substitution mutation?
Substitution - one base is substituted with another
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What is a deletion mutation?
Deletion - one base is deleted
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What is an insertion mutation?
Insertion - an extra base is added
331
What is an duplication mutation?
Duplication - one or more bases are repeated
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What is an inversion mutation?
Inversion - a sequence of bases is reversed
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What is a point mutation?
Point mutation - a change in a single nucleotide
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What is a frame shift mutation?
Frame shift mutation - the reading frame changes and this results in a different protein structure
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What is biodiversity?
the variety of living organisms in an area. includes species diversity and genetic diversity
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What is species diversity
The number of different species and the abundance of each species in an area
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What is genetic diversity?
The variation of alleles in the gene pool of a species
338
How is species richness counted?
counting the number of species in a known area using a quadrat
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Why does biodiversity need to maintained?
loss of biodiversity means there are fewer species. Loss of endemic species leads to extinction. Some species have not yet been discovered that may be useful
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Why is little genetic diversity bad?
no selective advantage when the environment changes, less likely to survive, so this increases risk of extinction
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Why is increased genetic diversity good?
greater chance of survival as higher chance of having beneficial alleles, increased mating with genetically different individuals decreases inbreeding
342
Species richness is…
the number of different species
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A niche is…
The role of a species within its habitat. It includes its interactions with other living organism (biotic( and its interactions with the non living (abiotic) environment
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Why is there variation in the phenotypes of individuals of a population?
random mutations introduce new alleles
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What is a species?
A group of similar organisms that can reproduce to give fertile offspring
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What does taxonomy involve?
naming organisms and organising them into groups based on their similarities and differences. This makes it easier for scientists to identify them and study them
347
Why are species in the same genus separate species?
because they cannot breed successfully to produce fertile offspring
348
What is the binomial system?
first word is the genus name and the second word is the species name.
349
Why is important that species are given a scientific name?
enables scientists to communicate about organisms in a standard way that minimises confusion
350
What did early classification systems use and why was this problematic?
only used observable phenotypes to place organisms into groups. scientists don't always agree on the relative importance of different features and groups based solely on physical features may not show how related organisms are.
351
What do classification systems use now and why are they useful?
new technologies that enable organisms genotypes to be determined have resulted in new discoveries and the relationships between organisms clarified
352
What are the five kingdoms?
prokaryote, protoctista, fungi, plants and animals
353
What is an example and features of prokaryote?
Bacteria, unicellular, no nucleus,
354
What is an example and features of protoctista?
algae, eukaryotic cells, live in water, single celled or simple multicellular organisms
355
What is an example and features of fungi?
moulds, eukaryotic, chitin cell wall, saprotrophic
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What is an example and features of plants?
mosses, eukaryotic, multicellular, cellulose cell walls, autotrophic
357
What is an example and features of animals?
mammals, eukaryotic, multicellular, no cell walls, heterotrophic
358
Where did new data for the three domain classification system come from?
molecular phylogeny
359
What does phylogeny tell you?
which species have common ancestors with which and how recently they shared common ancestors
360
How does the new three domain system classify organisms?
all organisms are placed into one of three domains which are above the kingdoms in the taxonomic hierarchy. The three domains are bacteria, archaic and eukaryote
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Why was prokaryote reclassified into two domains?
because molecular phylogeny suggested that archaic and bacteria are more distantly related than originally thought
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Why is a sample of a population taken instead of counting all individuals ?
it is too time consuming to count every individual organism in a habitat. estimates about the whole habitat are based on the sample
363
When is a quadrat used?
for plants
364
What does sampling involve?
choosing an area to sample. the sample should be random to avoid bias, use a random number generator to select coordinates for a grid, count the number of individuals of each species in the sample area, repeat the process as it gives a better indication of the whole habitat,
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What do related organisms have ?
similar DNA sequences and so similar amino acid sequences in their proteins
