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BIOLOGY FORM 5 1 SUBTOPICS • The Importance of Having a Transport System in • • • • • • • Some Multicellular Organisms The Circulatory System The Mechanism of Blood Clotting The Lymphatic System The Role of the Circulatory System in the Body’s Defence Mechanism Appreciating a Healthy Cardiovascular System The Transport of Substances in Plants The Transport of Organic Substances & Water in Plants 2 3 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 4 1.1 - The Importance of Having a Transport System in Some 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. 5 • 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 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 6 • 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. 7 • 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). 8 END OF SUBTOPIC 1.1 OPPS…DON’T FORGET TO COPY EXERCISE ON THE NEXT PAGE!! 9 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). 10 Iyah..iyah. .Iyah…. 11