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郭日僑華

五是日八廿月五年一七九一百公年十六鲜民

英中會考生物科試題答案元

BIOLOGY

2 (6) Continued.

leaf

Experiment to compare the rates of transpiration of shoot under different environmental, "conditions by nieans of potometer..

Apparatus: potometer, leafy plant, beaker and blotting paper, Procedure & Precautions, a leafy plant in good physiological

condition was cut under water, the cut end was kept in water to prevent, entrance of a into the oylen vesseli, The potometer was completely filled with water, the fitting of various parts including the insertion of the Leafy shoot in a rubber bung was done under water to ens sure air was not trapped in any part of the potometer.

The potometer was the wapet ary on the outside, vasline was applied to fitting places to prevent Later leakage or air leakage. It was then lef under ordinary labora tory conditions, it served as the standard or control for comparison purpose. A bubble was introduced into the capillary tube by blotting away some water at the open- ing of the tube followed by dipping the end of the tube into water contained in a beaker if type. a potometer was. used.

The apparatus was love to remain undisturucu 201 about 30 mins. to enable the leafy shoot to adjust to any particular environment.

As water receded due to transpiration, the air bubbl inside the capillary tube moved along the horizontal capillary tube, indicating the rate of water absorbed which was assumed to be equivalent to the water trans spired.

When the movement of the air bubule was gradual and steady, readings were taken, this was carried ou by noting the initial position of the air bubble and the final position of it in a certain time interval, The air bubble was moved back to its original position by turning on the tap of the reservion to enable downflow of water, Several readings were taken in Similar man-

ner from which the average was obtained. Since the loss of water could be read directly from the graduated capil- lary tube or from the scale alongside 13, the volume hënce the weight also, of water lost could be expressed as Average rate of transpiration (under laboratory conditions)

Xc.cater/min.

gm water/min,

The experiment.

Conditions &

was repeated for other environmental

(*) temperature change - by putting a Dunnsen burner

the leafy shoot;

B) draught increase

using an electric fan to blow

against the leafy shoot;

a bell jar which contained on its immer wall some moistened blotting paper;

strong light by putting the apparatus under strong. sun light (assuming the temperature reading remained constant).

total darkness by covering the leafy shoot with i blaned. bell jar.

is it was found that the rates of water loss in the various environmental conditions as stated above sere:

(A) CLC. water/min.

(B) Bc.c.CH

(D)

Dolci we

By comparing the results so obtained with tile one taken from the staiard, it was found that results from A, B, & D all. showed a faster rate of water loss, where- as in Ca, the rate was found to be lower. It can be concluded that the rate of tran spiration is increased if,

(a) temperature is increased,

(b) air current increases, (c)light decreases.

(s) The 7 macro-elements absorbed from the soil by the roots

of green plants which are essential for healthy growth include

calcium

(a1) iron

magnesiu

(iv)

nitrogen

(vi)

(vii)

phosphorus - -potassium

sulphur

To show the effects of these elements mentioned above due to their deficiency, water culture (hydroponics) experi- ments may be employe

Culture

solution.

Plant? inger thread

glas red

clean celion meck Black Paper

9 culture bottles were sterilized to ensure not minéral salts, and bacteria, which might contaminate, the experiment. Black, paper was used to wrap round them t exclude light and to prevent algab growth. The apparatus: was then set up as shown. Bottle A contained a complete solution like the one mentioned above. Borile B contamed distilled water only. Bottles C, D, E, F, G, H, I`each': contained a culture, solution but with one element missing. Treplaced either by potassium (K) or by chlorides. (C1),

In the fitting process, cure, was taken to ensure that the seedlings were not damaged and their root parts. were completely immersed in the culture solution. Cotton wool was used to prevent damage as well as bacterio entering into the bottle. The upper surface of the bung Was waxed to prevent leakage to microorganisms and the under surface of it was kept dry, and clear of the culture solution.

The seedlings selected were all at about equivalent stages of development to ensure equal metabolic rate, The glass rod was for the support of the seedlings and the glass tubing for delivery of air for a daily supply of oxygen. The solution was replaced fortnightly,

All the culture bottles, were then placed in conditions, where the shoots all received sunlight equally.

RESULTS: After a few weeks, the seedlings were com pared by counting and measuring their roots. The results were tabulated below;

BOTTLE

MISSING

SYMPTOMS

Growth, normal

ELEMENTS

Nil

All

Hardly any growin

Nobud poor root &

shoot

Nig

7727 022

Chlorosis; "mottle" vein Chlorosis

Little growth chlorosis

Stunted growth; reddish

stem.

Chlorosis: premature death Slender stem chloròsis.

Conclusion: From the above experiment, it can be concluded that normal plant growth is possible provided all the essential elements are present,

(a) Mammals are homoiotherms and are regarded as the most

advanced form. of life. Among other outstanding features, one of them is the ability to keep their body temperature and their body fluid constant. There are advantages-in having constant body temperature:

(i) freed from temperature fluctuation

e. independent of the environment.

(ii) maintenance of a high and constant metabolic rate,

(ii) nervous system remains sound and efficient at high and

constant temperature,

hibernation can be avoided except in bats

Similarly advantages, in keeping the water content constant include:

(i) to maintain a constant osmostic pressure of the

(ii) to keep cells in the hydrated condition to allow

blupiological process to occur.

a) to keep the pH value of the body fluid constant, to allow for the osmotic equilibrium between the cellular contents and external body fluids to be kept constant.

4. (b) (1) The skin of the mammal is useful in a number of ways in keeping constant internal environment. Regulation of the body temperature is one of them. This is achieved by sweat evaporation, contraction and relaxation of the blood capillaries and the hair of the skin. The regulation. process, inay be divided into::

A. control of heat loss when the body temperature is high. In this case, the blood capillaries beneath the skin dilate to allow more blood to flow near the surface so that heal can be lost through convection and radiation 70-75%, The sweat gland is also stimulated to

gland is also stil

produce more sweat, the, evaporation of which can cool" off the body 10 The hair which is usually reduced. in thickness in summer may now be fattened to reduce the trapping of stagnant air layer which acts as an insulating blanket,

B Control of heat loss when the body temperature low. Here, the blood capillaries contract so as to decrease blood flow to the surface resulting in the reduction of heat loss by convection and radiation. There is also a reduction in sweat production and the latent heat of vaporization is not removed from the body. Similarly, the hair stands on end to trap the dir which forms # good insulating layer preventing heat loss. The fat layer beneath the skin is also important as it acts as another. insulating layer. This explains why in winter, there

a thicker fat deposit beneath the skin.

(b) (ii) Kidney is another structure in the mammalian body

helping to keep a constant internal environment. It deals with the regulation of water (and salts also) content of the body. The functional unit is the nepliron or malpigliar body as shown in the diagram.

Renal artery Comman's Capsule

Glime!

A nephron

育

敎

僑華

英中會考數學科A(二)答案

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