AQA BIOL2~3rd June 2013~AS Biology (Now Closed)

There was a page with all the 6 markers on but I can't find it

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I think my heads going to explode

(Not mine but here u go)
Describe how tissue fluid is formed and how it is returned to the circulatory system.


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;


Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf.


1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;


Root pressure moves water through the xylem. Describe what causes root pressure.


1. Active transport by endodermis;
2. ions/salts into xylem;
3. Lowers water potential (in xylem);
4. (Water enters) by osmosis;


Explain how oxygen is loaded, transported and unloaded in the blood.


1. Haemoglobin carries oxygen /
has a high affinity for oxygen /
oxyhaemoglobin;
2. In red blood cells;
3. Loading/uptake/association in
lungs;
4. at high p.O2;
5. Unloads/ dissociates / releases to
respiring cells/tissues;
6. at low p.O2;
7. Unloading linked to higher carbon
dioxide (concentration);






Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein.


Change in amino acid/s /primary
structure;
Change in hydrogen/ionic/ disulfide
bonds;
Alters tertiary structure;


Describe how gene transmission and selection have increased the difficulty of treating bacterial infections with antibiotics.


1. (Antibiotic) resistant gene/allele;
2. Vertical (gene) transmission;
3. Resistant bacteria (survive and)
reproduce / population of resistant
bacteria increases;
4. Increase in frequency of
(resistant) allele/gene (in future
generations);
5. Horizontal (gene) transmission;
6. Plasmid;
7. Conjugation / pilus (tube);
8. (Horizontal transmission/
conjugation) can occur between
bacteria of different species;


Farmers clear tropical forest and grow crops instead. Explain how this causes the diversity of insects in the area to decrease.


1. Lower diversity of plants/ few species of plants/less
variety of plants/few plant layers;
2. Few sources/types of food/feeding sites;
3. Few habitats/ niches;
4. Fewer (species of) herbivore so few (species of)
carnivores;
5. Aspect of agriculture (killing insects);


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.


Elastic tissue
1 Elastic tissue stretches under pressure/when heart
beats;
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;


The structure of cellulose is related to its role in plant cell walls. Explain how


Long/straight/unbranched chains (of glucose);
(Joined by) hydrogen bonds;
Form (micro)fibrils/(macro)fibrils;
Provide rigidity/strength/support;


Scientists’ analysis of blood proteins has indicated a lack of genetic diversity in populations of some organisms. Describe the processes that lead to a reduction in the genetic diversity of populations of organisms.


1. Mark for general principle of - reduced variety/number of
different alleles/DNA / reduced gene pool (in new
population);
2. Founder effect;
3. A few individuals from a population become isolated/form
colonies:
4. (Genetic) bottlenecks;
5. (Significant) fall in size of population
6. Selective breeding / artificial selection;
7. Using organisms with particular
alleles/traits/phenotypes/characteristics;


In children, some diets may result in a low concentration of protein in fluid F. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in fluid F and the accumulation of tissue fluid.


Water potential (in capillary) not as low/is higher/less negative /
water potential gradient is reduced;
More tissue fluid formed (at arteriole end);
Less/no water absorbed (into blood capillary);
by osmosis; (into blood capillary);
















Scientists studied two species of North American seahorse. They thought that these two species are closely related. Describe how comparisons of biological molecules in these two species could be used to find out if they are closely related.


(Compare) DNA;
Sequence of bases/nucleotides;
DNA hybridisation;
Separate DNA strands / break hydrogen bonds;
Mix DNA/strands (of different species);
Temperature/heat required to separate (hybrid) strands indicates
relationship;
Compare same/named protein;
Sequence of amino acids /primary structure;
Immunological evidence – not a mark
Inject (seahorse) protein/serum into animal;
(Obtain) antibodies/serum;
Add protein/serum/plasma from other (seahorse) species;
Amount of precipitate indicates relationship;


DNA hybridisation shows similarities between DNA samples. Explain why


The more similar the DNA, the more similar the base sequences;
The greater the number of hydrogen bonds/bonds between base pairs;
More energy/heat needed to separate strands; 3
(Q Correct terminology of base, base pair and hydrogen bond must be used
as specified in scheme.)


An insect lives in air. Describe how the insect is able to obtain oxygen and limit water loss.


1 Air enters through (open) spiracles;
2 Through tracheae;
3 Diffusion gradient in trachea
4 Tracheae associated with all cells/closely associated with cells;
5 Oxygen diffuses into cells;
6 Ventilation replacing air in tracheae;
7 Body covered with (waterproof) waxy layer/cuticle;
8 Spiracles are able to close;




















What is X and how does it help uptake.


casparian strip;
So water/mineral ions must cross cell membranes/go via
symplast (Accept goes through cytoplasm) / apoplast blocked;
Mineral ions move by active transport (into xylem);
Creating water potential / osmotic gradient for water to diffuse
into xylem / lowers water potential in xylem;


Muscles and backflow
muscles contract;
Giving high pressure/ increase pressure of blood in vein;
Valve behind/below closes and prevents backflow/ only valve in front/
above will open; 3


Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how


1 Homologous chromosomes pair up/ bivalents form;
2 Crossing over/ chiasmata form;
3 Produces new combination of alleles;
4 Chromosomes separate;
5 At random;
6 Produces varying combinations of chromosomes/ genes/ alleles (not twice) ;
7 Chromatids separated at meiosis II/ later;


Root pressure is a force that is partly responsible for the movement of water through xylem in stems. Explain how the active transport of mineral ions into xylem vessels in the roots results in water entering these vessels and then being moved up the xylem tissue.


Water potential in xylem reduced (by entry of ions);
Water potential gradient established between xylem and surrounding cells;
Plasma membranes of surrounding cells are partially permeable;
Water enters xylem by osmosis;
Volume of water in xylem increases;
Cannot move back due to gradient;
Pressure in xylem increases (and forces water upwards);


The presence of an air bubble in a xylem vessel in the stem blocks the movement of water through that vessel. Use the cohesion-tension theory to explain why


Evaporation from leaves / transpiration;
Water in xylem under tension*/negative pressure/pulled up;
Water molecules cohere*/stick together/form hydrogen bonds;
[Ignore: references to adhesion]
So water a single column;
Air bubble breaks column / prevents cohesion;


Explain how water enters a plant root from the soil and travels through to the endodermis.


water enters root hair cells;
by osmosis;
because active uptake of mineral ions has created a WP gradient;
water moves through the cortex;
(by osmosis) down a WP gradient;
through cell vacuoles and cytoplasms / symplastic pathway;
through cell walls / apoplastic pathway;


From the root, water is transported upwards through the stem. Explain how evaporation from the leaves can cause the water to move upwards.


WP in leaf cells decreases / becomes more negative;
therefore water moves out of xylem (into surrounding tissues) by osmosis;
this creates a pull/tension on the water in xylem;
(c) which is in a continuous column / water molecules cohere;
cohesion due to H bonding;
column doesn’t break because of adhesion with xylem walls;




How is fish gills adapted for gaseous exchange?


1 Large surface area provided by lamellae/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);




Cohesion tension


Evaporation of water;
Water potential gradient created across leaf / mesophyll cells;
Tension created in xylem / water column;
Cohesion (or description) of water molecules maintains column;
Due to H-bonding / polarity / charges of water molecules


Root Pressure


Involves active transport; Secretion / movement of salts into xylem;
Reference to role of endodermis; Water moves along water
potential gradient.


How is water transported up trunks


evaporation / transpiration from leaves;
through stomata;
cohesion of water molecules;
leaf cells have more negative water potential, so water enters from xylem;
water drawn up as column/continuous stream;
adhesion of water to walls;
capillarity due to narrow lumen of xylem (vessels);
lignified walls keep xylem (vessels) open;
root pressure forces (some) water up;


Describe what happens to chromosomes in meiosis.


Chromosomes shorten/thicken/condense;
2. Chromosomes associate in homologous/(described) pairs /
formation of bivalents / tetrads;
3. Crossing-over / chiasma formation;
4. Join to spindle (fibres) / moved by spindle;(*)
5. (At) equator/middle of cell;(*)
6. (join via) centromere / kinetochore;(*)
7. (Homologous) chromosomes move to opposite poles /
chromosomes separate/move apart; (ALLOW „are pulled apart‟)
8. (Pairs of) chromatids separated in 2nd division; max 6
(*) OR “ independent assortment”


Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction. Describe how meiosis causes this variation and explain the advantage of variation to the species.


Crossing-over; [IGNORE any wrong ref. to timing]
2. Independent/random assortment/orientation/segregation of
(homologous) chromosomes in meiosis I;
3. Independent/random assortment/orientation/segregation of
chromatids in meiosis II;
+ Any three from:
4. Different adaptations / some better adapted;
5. Some survive / example described;
6. To reproduce;
7. Pass on gene/allele;
8. Allows for changing environment/different environment/example














Cells also contain suppressor genes, which code for proteins that control cell division and growth. Describe what is meant by a mutation, and explain how a mutation in a suppressor gene might lead to the development of a malignant tumour.


1. Mutation is a change in the DNA / sense strand;
2. Base sequence altered / e.g.;
3. Suppressor gene produces wrong instructions / has different code;
4. (Therefore) different amino acid sequence;
5. Different protein structure / non-functional protein;
Malignant tumour – up to 2 marks
6. Cell division by mitosis;
7. Tumour cells growth abnormal / continuous / uncontrolled / rapid;
8. Tumour cells spread / invade other tissues / form secondary
tumours / metastasis;
9. Via blood / lymph system;


Explain why the sperms produced by a man are genetically different from each other.


produced by meiosis;
crossing over;
independent assortment of chromosomes;


Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells.


1. made from β-glucose;
2. joined by condensation/removing molecule of water/glycosidic bond;
3. 1 : 4 link specified or described;
4. “flipping over” of alternate molecules;
5. hydrogen bonds linking chains/long straight chains;
6. cellulose makes cell walls strong/cellulose fibres are strong;
7. can resist turgor pressure/osmotic pressure/pulling forces;
8. bond difficult to break;
9. resists digestion/action of microorganisms/enzymes;


Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.


chromosomes shorten/thicken/supercoiling;
2 chromosomes (each) two identical chromatids/strands/copies Sciencemathsmaster.weebly.com 8
(due to replication);
3 chromosomes/chromatids move to equator/middle of the spindle/cell;
4 attach to individual spindle fibres;
5 spindle fibres contract / centromeres divide / repel;
6 (sister) chromatids/chromosomes (separate)
move to opposite poles/ends of the spindle;
7 each pole/end receives all genetic information/
identical copies of each chromosome;
8 nuclear envelope forms around each group of chromosomes/
chromatids/at each pole;

Can someone bullet point about starch, glycogen and cellulose

Starch:
- Main energy storage in plants
-Mixture of: Amylose which is unbranched alpha-glucose coiled tightly and so good for storage
Amylopectin which is branched and so easier to hydrolyse
- Starch is insoluble and so does not affect water potential

Glycogen:
- Main energy storage in animals
- More branched than starch so it can be quickly hydrolysed for fast energy release
- Compact and so good for storage
- Glycogen is insoluble and so does not affect water potential

Cellulose:
- Major component of cell walls
- Beta-glucose joined together
- Every other beta-glucose molecule is rotated 180degrees to allow 1-4 carbon bonds
- Cellulose chains are joined together by hydrogen bonds. The large number of these hydrogen bonds makes cellulose very strong

10)b) First figure out how many cases there are per year in the 410000 group:

(6/100000) x 410000 = 24.6

Then multiply this by the time period:

24.6 x 8.5 = 209.1


The idea of Cohesion Tension is basically that as water transpires and diffuses out of a leaf, the water potential across the mesophyll cells of the leaf is lowered. So water moves into the cells by osmosis, out of the xylem. This puts tension on the xylem (the tension part of the theory). As water evaporates it must be replaced. Due to the cohesive properties of water (the fact that hydrogen bonds are able to form between molecules) as water moves into the mesophyll cells, more water is pulled up the xylem to replace it (the cohesion part of the theory).

Root Pressure is the idea that when minerals and ions are actively transported into the xylem from the endodermis, the water potential in the xylem in lowered (due to the increase in ion concentration). This means that a water potential gradient in established and water moves into the xylem by osmosis. As more water enters the xylem, it is forced up it. Water is basically being pushed into and up the xylem.

Guys what do we think is gonna be on it?

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