1.1 The Importance of Having a Transport System in Some Multicellular Organisms

•         LEARNING OUTCOMES :

•         To identify the problem that could be faced by multicellular organisms in obtaining their cellular requirements & getting rid of their waste products

•         To suggest how the problem is overcome in multicellular organisms

•      All living organisms need to constantly exchange substances between cells & their external environment (food, waste & gases).

•      All this process is performed by a transport system.

       

•         Small organisms have a large total surface area to volume (TSA/V) ratio. So, diffusion of substances occurs rapidly (short distance only).

•         Some simple organisms such as flatworms have thin flatten bodies à provide a large surface area

•         In Hydra, water enters through the mouth into the body cavity. As the body wall is only two cell layers thick, substances can move rapidly into or out of the body cells.

•         Do not require a specialised internal transport system

•      Larger organisms, increased need for more nutrients & oxygen to be supplied to the larger number of cells. Need to excrete more waste products.

•      The size increases, TSA/V ratio decreases.

•      Many of the body cells are too far away from the external surface or between different parts of the body.

•      Simple diffusion occurs at too slow a rate to sustain cellular activities.

•      Larger multicellular organisms have adapted by developing specialised structures to increase the surface area for exchange of substances.

•      Have developed an internal transport system of vessels or tubes.

•      In human & more complex animals, there is development of a blood circulation system to carry the substances.

•      In plants, transport of substances is carried out by the vascular system (xylem & phloem).

EXPERIMENT 1.1 : Determining the relationship between total surface area to volume ratio & its effect on the rate of diffusion

•      AIM : To determine the relationship between TSA/V ratio & its effect on the rate of diffusion

•      PROBLEM STATEMENT : What is the effect of TSA/V ratio on the rate of diffusion of substances?

•      HYPOTHESIS : the larger the size of the object, the smaller the total surface area to volume ratio & the lower the rate of diffusion

•      VARIABLES : Manipulated – size of potato cubes, Responding – Area stained relative to total surface area of cut surface, Fixed – red ink solution, potato

•      MATERIAL : potatoes,  coloured solution

•      APPARATUS : 400 ml beaker, white tile, knife, ruler & forcep.

•      PROCEDURE :

–     A knife is used to cut 3 potato cubes with the dimensions 1cm x 1cm x 1cm, 2cm x 2cm x 2cm, 4cm x 4cm x4cm

–     The 3 potato cubes are immersed in coloured solution for 30 minutes

–     The potato cubes are removed from the beaker. Each potato is cut in half.

–     The region stained by the colour solution are observed.

·         RESULT :

	A	B	C
Original length (cm)	1	2	4
Original width (cm)	1	2	4
Original height (cm)	1	2	4
Total surface area (cm2)
Volume (cm3)
TSA/V ratio
Relative rate of diffusion

•      DISCUSSION :

•      CONCLUSION :

–     Make your own conclusion

EXERCISE 1.1

1. State two problems faced by multicellular organisms in obtaining their cellular requirements & removing waste product.

2. State how these problems are overcome in multicellular organisms.

3. Explain why unicellular organisms do not face the problems listed in (Q1).