Personal notes by Almighty Artist

can be 3n,4n,5n etc

polyploidys with even number of sets of chromosomes are fertile as chromosomes can form as homologous pairs in meiosis.

Uneven numbers of sets of chromosomes are sterile as the chromosomes are unable to form as homologous pair in meiosis.

Cohesion holds hydrogen bonds together to create surface tension on water.

Since water is attracted to other molecules, adhesive forces pull the water toward other molecules. (Xylem walls)

Water is transported in plants through both cohesive and adhesive forces; these forces pull water and the dissolved minerals from the roots to the leaves and other parts of the plant.

Don't write in bullet points...

Viruses attack SPECIFIC host cells

Give an account of gene mutation under the following headings:

(i) Occurrence of mutant alleles and the effect of mutagenic agents1. Random/spontaneous/by chance2. Low frequency/rare3. One type of mutagenic agent eg chemicals or named chemical such as mustard gas4. A second type of mutagenic agent eg radiation or named type of radiation as X-rays, gamma rays, UV light5. Mutagenic agents cause or induce mutations/increase mutation rate/increase chance of a mutation occurring/increase frequency of mutation

(ii) Types of gene mutation and how they alter amino acid sequences6. Gene mutation is a change in the bases/base types/base sequence/base orderNote: this must be stated, and cannot be shown in a diagram. Also,nucleotidecanbe taken as equivalent tobase. Points 7, 8, 11 and 12 may be shown as suitably labelled diagrams with only bases A,T, G and C used.7. Substitution: base/bases – replaced with another/others8. Inversion: order of bases reversed/bases turned round9. Substitution/Inversion may change base order of codon OR Substitution/Inversion is a point mutation10. Substitution/Inversion may change only one/two amino acid(s)11. Deletion: base/bases – deleted from chromosome/removed/taken out12. Insertion: base/bases – inserted into chromosome/added/put in12a. Substitution, inversion, deletion and insertion ALL named 

Note: the mark for 12a can only be awarded if zero marks scored in 7+8+11+1213. Deletion/Insertion changes codons/triplets after the mutation OR Deletion/Insertion is a frameshift mutation14. Deletion/Insertion changes all amino acids after the mutation15. Protein made (following substitution or inversion) will work/will be unaffected OR Protein made (after deletion or insertion) will not function/will not work/is the wrong protein/enzyme

10 marks

---------------------------------------

Give an account of water movement through plants under the following headings:

(i) The transpiration stream1. Water enters root hairs2. Water moves from a high water concentration/from HWC down/along a concentration gradient OR Water moves from a hypotonic solution/moves by osmosis (accept any where but only once)3. Water moves across the cortex4. Water moves through cells/through cell walls/through intercellular spaces5. Continuous/Unbroken column/thread of water in the xylem/the vessels/the stem/theplant6. Root pressure helps move water up xylem/up stem/up plant7. A force /An attraction between water molecules (cohesion)8. A force/An attraction between xylem/vessels and water molecules (adhesion)8a. Cohesion and adhesion both named. Note: Award mark for 8a only if zero marks scored for 7+89. Transpiration draws/pulls water up xylem/up stem/up plant 10. Water evaporates into air spaces of leaf11. Water (vapour) diffuses out through stomata/through pore12. Transpiration rate can be increased by increase in temperature/increase in windspeed/increase in light intensity/decrease in humidity/decrease in air pressure OR any converse (any one for 1 mark)

(ii) Importance of the transpiration stream13. Uptake/Transport of minerals/nutrients/nutrient ions/salts/a named ion eg. nitrate14. Cooling effect15. Provides water for photosynthesis/turgidity/support

10 marks

---------------------------------------------

Give an account of meiosis under the following headings:

(i) first meiotic division 6

(ii) second meiotic division 2

(iii) importance of meiosis.2

Note: Marks may be awarded for carefully drawn and correctly labelled diagrams.

First meiotic division:1.start with a gamete mother cell/diploid cell 12.each chromosome made up of two chromatids 13.homologous chromosomes pair up (Not: homologous pairs join up) 14.crossing over may occur 15.at chiasmata16.nuclear membrane disappears OR spindle forms 17.independent assortment occurs OR (homologous) chromosomes line up on equator 18.homologous chromosomes/pairs are pulled apart 19.new nuclear membrane formed OR division of cytoplasm. 1Maximum 6 marks

Second meiotic division:10.chromosomes line up on equator and chromatids pulled apart 19. new nuclear membrane formed OR division of cytoplasm 1(award point 9 once only - EITHER in context of first OR second meiotic division)11.four cells produced. 1 Maximum 2 marks

Importance of meiosis:12.produces haploid gametes/cells OR chromosome number halved 113.crossing over gives recombination/ variation/diversity 114.independent assortment gives variation/diversity 115.meiosis/it gives variation/diversity 1(award point 15 ONLY if points 13+14 gain 0 marks)Maximum 2 marks

--------------------

Give an account of the evolution of new species under the following headings:(i)isolating mechanisms 4

(ii)effects of mutations and natural selection. 6

(10)

Note: Marks may be awarded for carefully drawn and correctly labelled diagrams.

Isolating mechanisms:1.a species is a group of organisms interbreeding to produce fertile offspring 1

2.common gene pool 1

3.a species/a population separated into two by an isolating mechanism/barrier 1

4.prevents gene exchange/gene flow/interbreeding between populations/groups 1

5.two types of isolation given (eg geographical/ecological) 1

6.third type of isolation given (eg reproductive). 1

Maximum 4 marks

Effects of mutations and natural selection:

7.mutations occurring in each population/group will be different OR mutation occurs in one group 1

8.(mutation) gives variation/different phenotypes/new genes/new alleles/alters gene pool 1

9.different environments 1

10.selection is different for each population/group 1

11.best adapted/best suited survive OR survival of the fittest OR converse 1

12.(they/best adapted/best suited/fittest) pass on favourable characteristics/genes/alleles tooffspring/next generationOR less well adapted/less suited/less fit do not pass their characteristics/genes/alleles tooffspring/next generation 1

13. many generations/long period of time 1

14. new species formed when populations/groups can no longer interbreed. 1

2B Give an account of the transpiration stream and its importance to plants. 1 water moves into root (hair cells)by osmosis/from HWC to LWC/down water concentration gradient OR water diffuses into root (hair) cells 1 2 water moves across/enters the cortex by osmosis/from HWC to LWC/down water concentration gradient/via cell walls 1 3 water enters/reaches/goes into xylem 1 4 water rises/travels/moves through xylem(vessels) 1 5 cohesion is attraction between/sticking together of water molecules 1 6 adhesion is attraction between water (molecules) and xylem (walls)/sticking of water molecules to xylem 1 5a adhesion and cohesion named (if neither 5 nor 6 is scored) 1 7 water moves into leaf cells by osmosis/from HWC to LWC /down a water concentration gradient OR water diffuses into leaf cells 1 8 water evaporates into (leaf) air spaces 1 9 water vapour diffuses from leaf surfaces/ lost through stomata 1 Max 6 (from 9) 10 water (provides raw material) for photosynthesis/photolysis OR water provides turgidity/keeps cells turgid OR causes cooling/cools the plant 1 OR minerals/nutrients/ions supplied/transported (any 1) 11 Any one other 1 12 Any one other 1 Max 2 (from 3) Coherence • Divided into clear sections • At least 4 points on transpiration stream (Points 1 – 9) • And at least 1 point on importance (Points 10 – 12) All three points 1 Relevance • No mention of details of xerophytes or hydrophytes, mineral deficiencies • At least 4 points on transpiration stream (Points 1 – 9) • And at least 1 point on importance (Points 10 – 12) All three points 1 Total 10

----------------------------------------------------------------------------------------------------

2A Give an account of the importance of isolating mechanisms, mutations and natural selection in the evolution of new species. 1 isolating mechanisms prevent gene flow between (sub-)populations/groups are barriers to gene exchange between breeding between mutations being passed between OR isolating mechanisms split a gene pool 1 2 geographic, ecological, reproductive (any two) 1 3 third 1 Max 2 (from 3) 4 mutations occur randomly 1 5 different mutations occur in each (sub-)population/group 1 6 Mutations increase/decrease survival OR beneficial or not OR provide a selective advantage or not 1 Max 2 (from 3) 7 different conditions/habitat/environment exist for each (sub-)population 1 8 natural selection acts differently on/there are different selection pressures on each (sub-)population/groups 1 9 surviving/best suited/fittest individuals are able to breed/pass on (favourable) genes/alleles/characteristics/mutations 1 10 over long periods/after a long time/after many generations 1 11 (a) new species formed/speciation has occurred 1 12 new species are unable to interbreed/breed together to produce fertile young 1 Max 4 (from 6) Coherence • divided into 3 clear sections OR isolation separate from mutation and natural selection • At least 1/2 points on isolation (Points 1 – 3) • At least 1/2 points on mutation (Points 4 – 6) • And at least 2/3 points on natural selection (Points 7 – 12) • (must be 5 points in total) All five points 1 Relevance • no mention of artificial selection • At least 1/2 points on isolation (Points 1 – 3) • And at least 1/2 points on mutation (Points 4 – 6) • And at least 2/3 points on natural selection (points 7 – 12) • must be 5 points in total All five points 1 Total 10