October November 2010 Bio

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October/November 2010 Biology









Answ er s for MCQ



October/November 2010 Biology Paper 2

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Answer



Answ er s

8E (a) Photosy nthesi s i s a process requires several (factor s ) AW; the one i n the shortest supply ; control s the rate at w hich the process occur s; even though other s are plentiful ; 2 mark s for three factor s mentioned (CO2, w ater, light, temp.);; (one for t w o mentioned) ( Accept poi nt s on an annotated graph / equation ); [max. 5]

(b) (i n the dark) from atmos phere / environment ; by diffu sion (any w here); through i ntercellular s paces / stomata / mesophyll ; (i n the light) from photosy nthesi s; i n cell / chloroplast s; ref. leaves / stems; (at all times ) from the soil ; via the root s; [max. 5] [Total: 10]

8O(a) a u nit of life; can u ndergo / are formed by divi sion; means of transferri ng genetic i nformation; often i ncapable of i ndependent exi stence; can bemodified to do many different jobs / e.g. of t w o different cell s; nucleu s + cytoplasm + membrane; ref. to their significance i n any metabolic process; [max. 3] (R ju st a li st of metabolic processes )

(b) mu scle ti ssue; i n artery w all s; to mai ntai n blood pressure; conti nual contraction i n heart / pumpi ng / beati ng; to keep blood movi ng AW; nerve / nervou s ti ssue; i n heart to control rate (or any correct ref.); blood as a ti ssue; trans port medium / any e.g. of trans portation; epithelial ti ssue AW; toreduce damage to b.v. w all s; any t w o organs identified (heart, artery / vei n / or named);; blood vessel are tubes for blood ; [max. 7] [Total: 10]



Trans port i n Plant s

Xylem Phloem

Fu nctions:1. To trans port w ater and di ssolved mi neral salt s 2. To provide mechanical support for the plant

Characteri stic s:

1. Conductive cell s dead at maturity 2. Thick cell w all s arranged from end to end form

empty passages

Fu nctions:1. To trans port organic material s up and down the

plant body, called translocation 2. To trans port manufactured food substances such as

sugar s and ami no acid s from leaves to the other

part s of the plant

Characteri stic s:1. Conductive cell s livi ng at maturity 2. Sieve cell s are elongated, arranged end to end for

conduction 3. Companion cell s help nouri sh sieve tube cell s and

assi st for translocation



Movement of w ater and mi neral salt s i nto the root s

1. W ater moves i nto the root s by osmosi s and passes from cell to cell tow ard s to xylem

2. Mi neral salt s e.g. nitrates can either diffu se i nto the root or be taken i n by active trans port.

How does w ater move up the stem?

1. Root pressureFlow of w ater i nto the root s cau ses root pressure w hich can pu sh w ater up the stem, but i s not the mai n reason w hy w ater moves up the stem

2. Capillary action W ater molecules have high cohesion forces. Thi s enables w ater to move up narrow tubes like the xylem.

3. Trans piration pull As w ater i s lost from the aerial part s of the plant , thi s cau ses a suction force that pull s w ater from the low er part s of the plant , thu s cau si ng w ater toenter the root s. Thi s i s the mai n cau se for w ater movi ng up the plant.Trans piration The lost of w ater from the aerial part s of the plant, es pecially the leaves via the stomata

Factor s that affect trans piration

1. Low humidity i n the atmos phere creates a w ater potential gradient so w ater moves out of the leaves = trans piration rate i ncreases

2. Strong w i nd s blow aw ay w ater vapour s arou nd the leaf, thu s mai nti ng a low concentration gradient out side the leaf so w ater moves out of theleaves.

3. High temperatures w ill i ncrease the evaporation of w ater and thu s i ncreasi ng trans piration rate.

4. I n bright light , the stomata open so much that w ater i s lost so trans piration rate i ncreases.

5. If the plant does not obtai n enough w ater , the plant w ill lose it s turgor and w ilt. W ilti ng cau ses the stem and leaves to droop and trans piration ratedecreases.

Importance of trans piration

1. The evaporation of w ater helps plant s to stay cool as they remove latent heat and prevent the plant from bei ng scorched by the su n.

2. The pulli ng of w ater due to trans piration i s the mai n factor i n lifti ng w ater and mi neral salt s through the stem, from root s to the leaves. Thi sensures the leaves have enough w ater for photosy nthesi s and mi neral salt s for cellular metaboli sm, and the production of other organic compou nd ssuch as ami no acid s.

W ilti ngThe loss of turgidity i n plant ti ssue w hen the i ntake of w ater i s i nsufficient to replace w hat i s lost by trans piration or other means thu s cau si ng adeflation of plant cell s.

Advantages Trans piration rate w ill decrease. Thi s means the plant w ill reduce their loss of w ater becau se the leaves w ill fold up to reduce the surface area that i sexposed to the su n. Thi s cau ses the guard cell s to become more flaccid and the stomata w ill close.

Di sadvantages W ater i s now a limiti ng factor for photosy nthesi s. The stomata are closed and the amou nt of carbon dioxide enteri ng the leaves for photosy nthesi s i sal so reduced .

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October November 2010 Bio