1972-04-29 — Page 23

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六期星

日九十月四年二七九一曆公年一十六國民奘十

(接第六張第三頁)

1972英文中學會考試題預習專欄:

each chromosome

splits to two

-membrane

1972

堅道英文書院主編、

and move to opposite sides.

disappeared

生物科(十六)

中文中學會考試題預習專欄 C

世界歷史科 (廿六)

歐陽者放

蟹鐵

化學科

1912英文中學會考試題預習專欄

(六)

Biology (26)

Ca11 Cell Division and Gametogenesis

A cell is the basic unit of life-

from which living organisms are built up. Each cell containa a mucleus with cytoplasm around. The living semiperme¬ able boundary membrane on the outside. is called plasma mendrana (-cell membrane cytoplasmic membrane). In plant cell an additional non-living rigid cell wall is found enclosing this protoplasmic struc- ture.

plasma membrane.

Lactoplasm

groups of chrosones formed

Animal Cell

(clear)

endoplasm granular

2 daughty zuclei

2 daughter cells produced also diploid as mother cell

cytoplasm divides

chromo

ytoplasm

The proceÈS

Tat divis-

nucleus

cell wall

nucleus

Plant

plasma membrane-

call

vacuole (with sap)

qucleus + cytoplasm - protoplas

are

Diploid and haploid cells

With the nucleus of a cell there thread-like structured called chromo- somes (chron-colour; some-body) which become distinct during cell division owing to their ability to take up basic dyes sasily after staining,

Bomes

There is a number of chromosoma inside the nucleas which can be disting. uished into different types. Chromosomes are often present in paire i.e. the cell possesses two of each tind of chromos-> It is said to be in the diploid or (21) state." But in certain cella such as the gametes. Only one of each kind of chromosomes is present and is said to be in the haploid" or (n) condition.

nucleus

Diploid cell

(20)

chromosomes:

nucleus

Haploid cell' ~(n)

Different organisms may have diff? ferent number of chromosomes; human being

23 pairs, frog-7 pairs, fruit-fly JennA PRÁTOL maize-10 pairs.

Cell Division

Definition's Cell division is the the

omatic splitting of the live ing cell body into two or more parte,

There are two main types of cell division namely, niste. osis or ordinary cell divie-

Fion and Meiosis in the for!

mation of gametes'.

Meiosis

diploid nother

20

ist divison

diploid

to ther cell

cell

20

Vitosis

The process.

chromsenes,

"diploid mother

cell..

nucleus

2nd divi

Вод

duplication

of chromosome;"

spindies

chr

4: hapI- oid

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duplication chromosome

"A (1) (2)

B (3)(4):

Bpindles

similar chromo-

separation chromosome pair

omes pair toga.

thar

haploid nuglei Cormed

Splitting of

2 haploid cells completed (2nd 23x3"- aploid nuclei

chromosomes to a and move

to opposite sides

(as in mitosis)

haploid cells produced,

Compare mitosis & merusaS

mitosis

The process. One other cell produces 2 daugh ter cells Daughter cella having same num- ber of chromosomes. as the mother cel

2n) (2n

Occurrence

3. In different parts of the. multicellular

organism.

Ригорве

1.0815

Ons mother celi produces 4 daugh- ter cells.

2. Halving the num ber of chromos- Oree in daughter cells.

4. Provide more cells4.

for growth and re- -pair of worm away

tissues,

(3)

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of male gametes in animal is called Spermatogenesis, while the process of eza formation is called daxenesit. Sperm and ovum are produced as a result of maiosië..

Spermatogenesis

in + testis

diploid Sperm mother call (primary

Spermatocyte)

ondary/ spermato n cyte

habloid apera

In sex organs:

genes

Formation of gametes for. sexual reproduc- tion

In unicellular org-5. Allow mixing anise this is a of genetic Method products from tion binary fission, both parents as in Amoeba and Para- during fortii-

zation. Such mecium.

that the off spring poss68 pen. certain characteristics of bothe

Gametogenesis

Gametogenesis is the process of gamete formation in the sex organs, sucл ae in the testis and ovary of animale The formation and flowers or plants.

3 small polar

bodies. (useless and

die away

Ovary

diploid egg

mother cell (primary Oocyte)

secondary:oocyte,

Bingle large haploid övün

One sperm mother cell will give rise to four small eperm, while one egg mother cell is producing only One single large. ovum containing food storage which is used for the early stage of developmen of the embryo after fertilization.

Chemistry 26

(2) Manufacture of ammonia by Haber

process. M

The essence of this industrial

process is the catalytic combinatio of nitrogen and hydrogen

(A) Hydrogen can be obtain form water

gas. The latter is a mixture of carbon monoxide and hydrogen, prod- uced by passing steam over red hot coke

C+

CO water gar

9) Nitrogen can be obtained either from

fractional distillation of liquid

air or from producer gas. The lat ter ie made by passing air over. heated cokes:

air. C.

producer gas

(C) In the reaction chamber one vpiURE I

of nitrogen combines with three volumes of hydrogen in the presence: of iron as catalyst, aluminium oxide as promotor. This reaction takes place at about 500 C and a pressure of 250 atmospheres.

3H

500°C

2 NH

250 ata.

(D) Carbon monoxide can be converted into more hydrogen and carbon dioride by reaction with steam under specific conditions. CO2 is removed in solution under pressure and hydr- ogen 18 channelled to the reactio chamber for further reaction.

80 + CO LÀ HA

(E) The ammonia gas is condersed and

purified. The unreacted gases: are recirculated for further proces- sing.

VOLUMETRIC ANALYSIS.

In the following paragrapna, certain Stud- useful experiments are considered. ents should familiarise themselves with problems which are set on experimental basis in volumetric analysis.. Experiment (1)

To determine the equivalent weight of a civen acid, e.ɛ. tartaric acid or citric acid, using a standard solution of sodium hydroxide.

Step (1) Prepare a standard solution of the given acid, f.e dissolves

known weight of the acid in known volume of solution, Steipii) Titrate 25 al. of the acid solution against the given standard sodium hydroïide solution; note the volume of: or alkali required to change the solution just pink. Phen-

used as the

Step (iii

indicator in a weak acid,. strong base titration

By making use of the equation NAV the normality of

the acid solution be found

top (iv) Equivalen weight, E.W.

Concentration of acid solution în normality of acid solution

Experiment (2).

To determine the number of molecules of water of crystallization in, for exam ples, Na, 00 • xH o

Step (1) Dissolve a known weight, say a

, of Na C. XHO crystals in a known volume of solution. Step (ii) The weight of anhydrous sodium carbonate, bg, in these cry- stals is determined by titra.... tion against a standard acid solution.

the

Step (111) Hence, a gn crystals contain.

bg anhydrous saitidez weight of water-

of water

(a:

of anhydrous sodium carbonate

(iv) The molecular wt. of water

18

The molecular wte of annydr-. Que Bodium carbonate 106 If x- the number of molecules of water of crystallization

then

182

106

From this equation, where a and ara round from experiment, I can be calculated.”