1995 AL Biology paper 1 marking scheme

1995 AL Biology paper 1 marking scheme - 1995 AL Biology...

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1995 AL Biology marking scheme p.1 of 13 Marks 1995 Paper I Section A ( * spelling mistakes of these terms, no mark) 1. prokaryotes eukaryotes No distinct nucleus/ lack nuclear membrane Distinct nucleus /with nuclear membrane 1 Circular DNA molecule in cytoplasm / no chromosome Chromosome present 1 Lack membraneous organelles Membraneous organelles present 1 Infolding of the cell membrane forms mesosomes for respiration Mitochondria for respiration 1 ______ (4) Mark deduction: No table, minus 1 2. Separate the pigments by * chromatography ( ½ ), spot the extracts onto 3 chromatographic/filter paper ( ½ ), develop in appropriate developing solvent ( ½ ) by hanging paper vertically in a chromatography jar/boiling tube/beaker ( ½ ). Identical extracts should have similar pigment pattern or similar Rfs for the different pigment spots.( ½ ). Describe the developing process ( ½ ). 3. for moss, the qametophyte is dominant and has independent existence(1), the sporophyte is partially dependent on the quametophyte, it is reduced / transient(1). For fern, the sporophyte is dominant and independent of the fern s life cycle(1), the gametophyte is also independent but reduced/ transient(1). For angiosperm, the sporophyte is dominant and independent(1), the gametophyte is buried inside the sporophyte/highly reduced and is totally dependent (1) on it for nutrition and protection. 6 (Tabulated answers are acceptable) 4. a) Transcription is the synthesis of messenger RNA ( ½ ) strand using a gene of DNA as a template ( ½ ). Translation is the synthesis of a polypeptide chain/peptide ( ½ ) according to the information (codon) on a messenger RNA ( ½ ). 2 PDF created with FinePrint pdfFactory trial version
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1995 AL Biology marking scheme p.2 of 13 b) ADH increases permeability to water ( ½ ) in * distal convoluted tubule and collecting duct ( ½ ). Aldosterone stimulates reabsorption of sodium ( ½ ) in distal convoluted tubule/collecting duct ( ½ ) of kidney nephron. 2 c) Causes of greenhouse effect accumulation of excessive CO 2 and methane/ hydrocarbon gases in the atmosphere ( ½ ) which 2 traps heat reflected from the earth s surface ( ½ ), causes of ozone depletion gases such as CFC/halons enter into the stratosphere( ½ ) irreversibly react with ozone molecules breaking them to oxygen gas ( ½ ) ____ (6) 5. curves (at least 2 ) with correct shape, plateau should not reach 100% saturation, (scale of 0% to 100% in Y axis should be indicated) shift and 2 label. Y axis with label ½ X axis with label ½ % saturation of haemoglobin with oxygen oxygen tension high CO 2 tension low CO 2 tension 100% PDF created with FinePrint pdfFactory trial version
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