hard topics Flashcards
Describe the role of antibodies in producing a positive result in an ELISA test. (4 marks)
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;
State three roles of a Cytotoxic Killer T Cell (Tc cell)
- 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.
State 4 roles of a T helper cell.
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
Describe the structure of the human immunodeficiency virus (HIV). [5]
- RNA (as genetic material);
- Reverse transcriptase;
- (Protein) capsomeres/capsid;
- (Phospho) lipid (viral) envelope OR Envelope made of membrane;
- Attachment proteins;
Describe the difference between active and passive immunity. [4]
- 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;
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how [5]
- 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);
Describe and explain the role of antibodies in stimulating phagocytosis. [2]
- Bind to antigen OR Are markers (Opsinisation);
- (Antibodies) cause agglutination (clumping) OR Attract phagocytes;
Describe how substances move across cell-surface membranes by facilitated diffusion. [3]
- Carrier / channel protein;
- (Protein) specific / complementary to substance;
- Substance moves down concentration gradient;
Compare and contrast the processes by which water and inorganic ions enter cells. [3]
- 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)
Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane. [7]
- (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
Explain why a cell membrane may be described as a fluid-mosaic? [2]
- 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.
Describe the process of crossing over and explain how it increases genetic diversity. [4]
- 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;
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. [7]
- 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;
Describe Viral replication [5]
- 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)
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]
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;
Define ‘Gene’
Section of DNA base sequences on a chromosome coding for one specific polypeptide
Define ‘Gene’
Section of DNA base sequences on a chromosome coding for one specific polypeptide
Describe the appearance and behaviour of chromosomes during mitosis: [5]
- 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;
Why is MITOSIS important? [3]
- Increasing cell numbers and growth of an organism
- Repair of damaged tissues (not cells)
- Replacement of worn out / dead cells
Describe the features of Anaphase
- 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;
Describe the features of Prophase
- 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;
What is a virus?
- Acellular and non living
- Consist of genetic material, a capsid and attachment proteins.
Give the three structural features found in all virus particles and describe the function of one of these features. [2]
- 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);
Name two structures found in all bacteria that are not found in plant cells. [2]
- Circular DNA (molecule in cytoplasm);
- Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
- Small(er)/70s ribosomes (in cytoplasm);
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;
What is the function of Lysosomes? [2]
- Contains hydrolytic (digestive) enzymes;
- Digests worn out organelles/autolysis;
What is the function of the Smooth Endoplasmic Reticulum?
Site of lipid synthesis;
What is the function of the Rough Endoplasmic reticulum? [3]
- Encrusted in Ribosomes;
- Site of protein synthesis;
- Transports and stores protein within the cell
What is the function of the cell (permanent) vacuole (plants)?
- Stores sugars/minerals/pigments
- Support
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)
- Crush/grind;
- With ethanol/ alcohol, to dissolve the lipid;
- Then add water then shake;
- Forms a white emulsion / goes white;
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.
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.
How does oxygen moves through an insect? [4]
- Oxygen diffuses in through the open spiracles;
- Spiracle closes;
- Oxygen moves through the trachea into the tracheoles;
- Oxygen delivered directly to the respiring tissues;
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);
Describe the process of starch digestion [5]
(salivary/pancreatic) Amylase;
Starch to Maltose;
Maltase;
Maltose to glucose;
Hydrolysis;
Glycosidic bonds
Describe and explain two features you would expect to find in a cell specialised for absorption. [4]
- Folded membrane/microvilli so large surface area (for absorption);
Accept ‘brush border’ for ‘microvilli’. - 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; - 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; - Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);
Describe the absorption of glucose (Cotransport) [4]
- Sodium ions actively transported from ileum cell in to blood;
- Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
- GLucose enters cell down the sodium ion gradient
- Glucose enters by facilitated diffusion with sodium ions;
Describe the mechanism for the absorption of amino acids in the ileum. [5]
- Facilitated diffusion of amino acid (into cell when higher concentration in lumen);
- Co-transport;
- Sodium ions actively transported from cell to blood/capillary/tissue fluid;
- Creating sodium ion concentration/diffusion gradient;
- Facilitated diffusion of amino acid into blood/capillary;
Describe two adaptations of the structure of alveoli for efficient gas exchange.
- Thin walls or squamous epithelia is one cell thick
- (Total) surface area is large;
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;
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;
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
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);
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;
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
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;
If the dissociation curve is to the LEFT…..
- Loads MORE oxygen
- at LOWER partial pressures
- Haemoglobin has HIGHER affinity (for oxygen)
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)
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;
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;
Describe the cohesion-tension theory of water transport in the xylem [5]
- 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;
- Lowers water potential of mesophyll / leaf cells;
- Water pulled up xylem (creating tension); (negative pressure)
- Water molecules cohere / ‘stick’ together by hydrogen bonds;
- (forming continuous) water column;
- Adhesion of water (molecules) to walls of xylem;
- Accept Ψ
