hard topics Flashcards
1
Q
Describe the role of antibodies in producing a positive result in an ELISA test. (4 marks)
A
1. (First) antibody binds/attaches /complementary (in shape) to antigen;
2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen;
Accept (second) antibody attaches to (first) antibody (indirect ELISA test).
4. (Substrate/solution added) and colour changes;
2
Q
State three roles of a Cytotoxic Killer T Cell (Tc cell)
A
- Locate and destroys infected body cells that present the correct antigen.
- Binds to antigen-presenting-cells
- Releases perforin (protein) which creates holes in the cell surface membrane which destroys the APC.
3
Q
State 4 roles of a T helper cell.
A
Specific T Helper cell binds to the antigen presenting cell and….
1) Release cytokines that attract phagocytes to the area of infection.
2) Release cytokines that activate Cytotoxic Killer T cell (TC).
3) Activates a specifically complementary B cell.
4) Form memory TH cells
4
Q
Describe the structure of the human immunodeficiency virus (HIV). [5]
A
- RNA (as genetic material);
- Reverse transcriptase;
- (Protein) capsomeres/capsid;
- (Phospho) lipid (viral) envelope OR Envelope made of membrane;
- Attachment proteins;
5
Q
Describe the difference between active and passive immunity. [4]
A
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells/memory cells whereas, Passive involves antibody introduced into body from outside/named source;
- Active long term, because antibody produced in response to antigen whereas, Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop/work, passive fast acting;
6
Q
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how [5]
A
- Vaccine contains antigen from pathogen;
- Phagocyte (other APC) presents antigen on its surface;
- T (helper) cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell divides to form clone secreting / producing same antibody;
- B cell secretes large amounts of antibody (by exocytosis);
7
Q
Describe and explain the role of antibodies in stimulating phagocytosis. [2]
A
- Bind to antigen OR Are markers (Opsinisation);
- (Antibodies) cause agglutination (clumping) OR Attract phagocytes;
8
Q
Describe how substances move across cell-surface membranes by facilitated diffusion. [3]
A
- Carrier / channel protein;
- (Protein) specific / complementary to substance;
- Substance moves down concentration gradient;
9
Q
Compare and contrast the processes by which water and inorganic ions enter cells. [3]
A
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
- Accept aquaporins (for water) and ion channels
- Contrast: ions can move against a concentration gradient by active transport (Carrier protein)
10
Q
Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane. [7]
A
- (Simple / facilitated) diffusion from high to low concentration / down concentration gradient;
- Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer;
- OR
- Large / polar / water-soluble molecules go through proteins;
- Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential;
- Active transport is movement from low to high concentration / against concentration gradient;
- Active transport / facilitated diffusion involves proteins / carriers; (Reject Both use channels)
- Active transport requires energy / ATP;
- Ref. to Na+ / glucose co-transport
11
Q
Explain why a cell membrane may be described as a fluid-mosaic? [2]
A
- Fluid – Each molecule within the membrane is able to move around within the membrane.
- Membrane is made up from a variety of different molecules (e.g, different proteins) arranged into a mosaic.
12
Q
Describe the process of crossing over and explain how it increases genetic diversity. [4]
A
- Homologous pairs of chromosomes associate / form a bivalent;
- Chiasma(ta) form;
- (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
- Producing new combinations of alleles;
13
Q
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. [7]
A
- Homologous chromosomes pair up;
- maternal and paternal chromosomes are arranged in any order;
- Independent segregation (RANDOM);
- Crossing over (RARE);
- (Equal) Portions of chromatids are swapped between chromosomes;
- Produces new combination of alleles;
- Chromatids separated at meiosis II/ later;
14
Q
Describe Viral replication [5]
A
- Attachment proteins attach to receptors
- (viral) nucleic acid enters cell
- Nucleci acid replicated in cell OR Reverse transcriptase makes DNA from RNA
- Cell produces (viral) protein/capsid/enzymes
- Virus assembled and released (from cell)
15
Q
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate. [2]
A
Description; Explanation;
E.g,
* Examine large number of fields of view / many cells;
* To ensure representative sample;
OR
* Repeat count;
* To ensure figures are correct;
OR
- Method to deal with part cells shown at edge /count only whole cells;
- To standardise counting;
16
Q
Define ‘Gene’
A
Section of DNA base sequences on a chromosome coding for one specific polypeptide
17
Q
Define ‘Gene’
A
Section of DNA base sequences on a chromosome coding for one specific polypeptide
18
Q
Describe the appearance and behaviour of chromosomes during mitosis: [5]
A
- During prophase, chromosomes supercoil and condense to become visible;
- Chromosomes appear as 2 identical sister chromatids joined by a centromere;
- During metaphase chromosomes line up on the equator of the cell;
- Chromosomes attach to the spindle fibres;
- By their centromeres;
- During anaphase, the centromere splits;
- Sister chromatids are pulled to opposite poles of the cell making a V shape;
- During telophase, chromatids uncoil and become thinner;
19
Q
Why is MITOSIS important? [3]
A
- Increasing cell numbers and growth of an organism
- Repair of damaged tissues (not cells)
- Replacement of worn out / dead cells
20
Q
Describe the features of Anaphase
A
- Spindle fibres shorten and centromere splits;
- Sister chromatids are separated;
- Chromatids pulled to opposite poles of the cell;
- Chromatids are in a V shape formation;
21
Q
Describe the features of Prophase
A
- Nuclear membrane begins to breakdown;
- Centrioles move to poles of the cell;
- Chromatin supercoils and condense into chromosomes around HISTONES;
- Each chomosome consists of two identical sister chromatids joined by a centromere;
22
Q
What is a virus?
A
- Acellular and non living
- Consist of genetic material, a capsid and attachment proteins.
23
Q
Give the three structural features found in all virus particles and describe the function of one of these features. [2]
A
- Genetic material, capsid and attachment protein;
- Genetic material codes for (viral) protein
OR
Capsid protects the genetic material/RNA/DNA
OR
Attachment protein bind to receptors (on cell);
24
Q
Name two structures found in all bacteria that are not found in plant cells. [2]
A
- Circular DNA (molecule in cytoplasm);
- Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
- Small(er)/70s ribosomes (in cytoplasm);
25
Compare and contrast Nuclear DNA and Chloroplast / Mitochondrial DNA [5]
**Comparisons**
* Nucleotide structure is identical;
* Nucleotides joined by phosphodiester bond;
* OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
**Contrasts**
**DNA within the nucleus:**
* Is longer ;
* Contain introns, Chloroplast/MT DNA does not;
* Is linear, Chloroplast/MT DNA is circular;
* DNA is associated with / bound to protein / histones, Chloroplast/MT DNA is not;
26
What is the function of Lysosomes? [2]
* Contains hydrolytic (digestive) enzymes;
* Digests worn out organelles/autolysis;
27
What is the function of the Smooth Endoplasmic Reticulum?
Site of lipid synthesis;
28
What is the function of the Rough Endoplasmic reticulum? [3]
* Encrusted in Ribosomes;
* Site of protein synthesis;
* Transports and stores protein within the cell
29
What is the function of the cell (permanent) vacuole (plants)?
* Stores sugars/minerals/pigments
* Support
30
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)
1. Crush/grind;
2. With ethanol/ alcohol, to dissolve the lipid;
3. Then add water then shake;
4. Forms a white emulsion / goes white;
31
Describe how a triglyceride molecule is formed [3]
* ONE glycerol molecule **and** THREE fatty acids
* Condensation reactions **AND** removal of THREE molecules of water
* Ester bonds are formed.
32
What is the effect of pH on the rate of an enzyme controlled reaction [3]
* pH is changed from the optimum (more acidic or more basic)
* **charge** on the R groups of the amino acids is altered and **ionic bonds (and weak H bonds)** in the **tertiary structure** are broken.
* Active site **changes shape** and the substrate can no longer **bind** (no longer specifically complementary). **Less/No enzyme substrate complexes can be formed**, and the rate of the reaction decreases either side of the optimum. The enzyme is **denatured**.
33
How does oxygen moves through an insect? [4]
1. Oxygen diffuses in through the open spiracles;
2. Spiracle closes;
3. Oxygen moves through the trachea into the tracheoles;
4. Oxygen delivered directly to the respiring tissues;
34
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange. [6]
1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);
35
Describe the process of starch digestion [5]
(salivary/pancreatic) Amylase;
Starch to Maltose;
Maltase;
Maltose to glucose;
Hydrolysis;
Glycosidic bonds
36
Describe and explain two features you would expect to find in a cell specialised for absorption. [4]
1. Folded membrane/microvilli so large surface area (for absorption);
Accept ‘brush border’ for ‘microvilli’.
2. Large number of co-transport/carrier/channel proteins so fast rate (of absorption) OR
Large number of co-transport/carrier proteins for active transport OR
Large number of co-transport/carrier/channel proteins for facilitated diffusion;
3. Large number of mitochondria so make (more) ATP (by respiration) OR
Large number of mitochondria for aerobic respiration OR
Large number of mitochondria to release energy for active transport;
4. Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);
37
Describe the absorption of glucose (Cotransport) [4]
1. Sodium ions actively transported from ileum cell **in to blood**;
2. Maintains / forms **diffusion gradient** for sodium to enter cells from gut (and with it, glucose);
3. GLucose enters cell down the sodium ion gradient
4. Glucose enters by facilitated diffusion with sodium ions;
38
Describe the mechanism for the absorption of amino acids in the ileum. [5]
1. Facilitated diffusion of amino acid (into cell when higher concentration in lumen);
2. Co-transport;
3. Sodium ions actively transported from cell to blood/capillary/tissue fluid;
4. Creating sodium ion concentration/diffusion gradient;
5. Facilitated diffusion of amino acid into blood/capillary;
39
Describe two adaptations of the structure of alveoli for efficient gas exchange.
1. Thin walls or squamous epithelia is one cell thick
2. (Total) surface area is large;
40
Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell. [6]
* Oxygen combines (reversibly) to produce oxyhaemoglobin;
* each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
* high partial pressure of oxygen / oxygen tension / concentration in lungs;
* haemoglobin (almost) 95% / 100% saturated;
* unloads at low oxygen tension(in tissues);
* presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
* allows more O2 to be unloaded;
* increase temp/ acidity allows more O2 to be unloaded;
* low pO2 / increase CO2 / increase term / increase acid occur in vicinity of respiring tissue;
41
Explain how oxygen in a red blood cell is made available for respiration in active tissues. [4]
* CO2 (increased) respiration;
* (increased) dissociation oxygen from haemoglobin;
* Low partial pressure in tissues/plasma;
* Oxygen diffuses from r.b.c. to tissues;
42
The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus. [3]
* Foetal **haemoglobin** has Higher affinity / loads more oxygen;
* At low/same/high partial pressure/pO2;
* Oxygen moves from mother/to fetus;
Reject foetus has higher affinity for oxygen
43
Explain how oxygen is loaded, transported and unloaded in the blood. [5]
* Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
* In red blood cells;
* Loading/uptake/association in lungs at high p.O2;
* Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
* Unloading linked to higher carbon dioxide (concentration);
44
Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. [4]
* Many alveoli/ alveoli walls folded provide a large surface area;
* Many capillaries provide a large surface area (So) fast diffusion;
Alveoli or capillary walls/ epithelium/ lining are thin/ one cell thick / short distance between alveoli and blood;
* Flattened/ squamous epithelium (So) short diffusion distance/ pathway / (So) fast diffusion;
* Ventilation / circulation; So Maintains a diffusion / concentration gradient (So) fast diffusion;
45
Arteries and arterioles take blood away from the heart.
Explain how the structures of the walls of arteries and arterioles are related to their functions. (6)
**Elastic tissue **
1 Elastic tissue **stretches** under pressure/when heart contracts;
2 **Recoils**/springs back;
3 Evens out pressure/flow;
**Muscle **
4 Muscle contracts;
5 Reduces diameter of lumen/vasoconstriction/constricts vessel;
6 Changes flow/pressure;
**Epithelium **
7 Epithelium smooth;
8 Reduces friction/blood clots/less resistance
46
Describe how tissue fluid is formed and how it is returned to the circulatory system. (6)
**Formation**
1. High blood / hydrostatic pressure / pressure filtration;
2. Forces water / fluid out;
3. Large proteins remain in capillary;
**Return**
4. Low water potential in capillary / blood;
5. Due to (plasma) proteins;
6. Water enters capillary / blood;
7. (By) osmosis;
8. Correct reference to lymph;
47
If the dissociation curve is to the **LEFT**.....
* **Loads** MORE oxygen
* at **LOWER** partial pressures
* Haemoglobin has **HIGHER** affinity (for oxygen)
48
If the dissociation curve is to the **RIGHT**....
* **Unloads** **MORE** oxygen
* for **MORE** aerobic **Respiration** so **more** ATP
* **More** heat energy **released**
* at **same** partial pressures
* Haemoglobin has **LOWER** affinity (for oxygen)
49
Explain why water moves up the plant stem. [3]
1. Water evaporates/is transpired out of leaves through stomata;
2. Water potential gradient/lower water potential creates tension/pulls up water
OR Omosis creates tension/pulls up water; OR Osmosis creates negative pressure.
3. Hydrogen bonds/cohesion/adhesion maintains ((continuous) column;
50
Describe the cohesion-tension theory of water transport in the xylem [5]
1. Water lost from leaf because of transpiration / evaporation of water (molecules) / diffusion from mesophyll / leaf cells through **stomata**; OR Transpiration / evaporation / diffusion of water (molecules) through stomata / from leaves;
2. Lowers water potential of mesophyll / leaf cells;
3. Water pulled up xylem (creating tension); (negative pressure)
4. Water molecules cohere / ‘stick’ together by hydrogen bonds;
5. (forming continuous) water column;
6. Adhesion of water (molecules) to walls of xylem;
2. Accept Ψ
