Q Why do multi cellular organisms need mass transport systems (3) Diffusion 22/07/2019 Q Why do multi cellular organisms need mass transport systems (3) 1.1 Understand why many animals have a heart and circulation (mass transport to overcome limitations of diffusion in meeting the requirements of organisms). I can describe limitations of diffusion as a means of transport in large organisms in terms of surface area: volume ratio. I understand why large organisms require a mass transport system to supply materials and remove waste efficiently

Q Why do multi cellular organisms need mass transport systems (3) Diffusion is slower over larger distances. Rate of diffusion would be too slow to carry raw materials from specialised cells to other body cells And to effectively remove metabolic waste from these body cells.

Why do multicellular organisms need transport systems ? All cells need energy Deliver glucose and oxygen and remove waste products. Single celled organisms=diffusion directly from external environment (rate is quick due to short distance).

Quick iGCSE recap: Diffusion= The passive movement of particles (atoms ions or molecules) down a concentration gradient, or from regions of higher to regions of lower concentration. (iGCSE) Factors affecting diffusion: Distance Concentration gradient Temperature Particle size (a smaller particle at a given temperature moves faster than a larger particle) http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Diffusion of oxygen into a cell 9 The concentration of oxygen molecules is greater outside the cell than inside So the oxygen molecules diffuse into the cell The concentration of carbon dioxide is greater inside the cell than outside. Carbon dioxide molecules will diffuse out of the cell.

Because the cell is using up oxygen, the concentration of oxygen inside the cell is always lower then the concentration outside. The diffusion gradient is maintained The oxygen is used in respiration. Carbon dioxide is produced by respiration. The concentration of carbon dioxide inside the cell increases, so carbon dioxide diffuses out of the cell. So oxygen continues to diffuse in

Single-celled organisms are rarely more tan 1mm in diameter 13 In a single-celled organism (such as Amoeba) the distance is so small that diffusion is rapid enough for the cell’s needs maximum distance is 0.1 mm oxygen Single-celled organisms are rarely more tan 1mm in diameter Bacteria range from 1 - 10 microns (1-10 µ ) carbon dioxide Compared with its bulk, a cell like this has a huge surface area through which diffusion can occur ( 1 µ is one thousandth of a millimetre)

Inside the bodies of large animals, diffusion of oxygen into their cells is rapid enough For transport across the whole body, diffusion would be much too slow Large organisms have evolved mass transport Systems that carry oxygen from outside the body to the cells inside

Using oxygen as an example Inside the bodies of large animals, diffusion of oxygen into their cells is rapid enough For transport across the whole body, diffusion would be much too slow.-we will look in more detail at why later Large organisms have evolved mass transport Systems carry raw materials from specialised exchange organs body to the cells inside

Mammals = circulatory system. Mass transport systems: carry raw materials from specialised exchange organs to body cells, and to remove metabolic waste. Mammals = circulatory system. Heart = pump; cells in tissues and organs get nutrients and oxygen from the blood and dispose of metabolic waste back into the blood. Metabolism: the chemical processes that occur within a living organism in order to maintain life.

Earthworm 16 diffusion takes place through the thin skin of the worm CO2 diffuses out O2 diffuses in Section through worm’s skin 0.04mm the blood vessels absorb the O2 and carry it to the body

In mammals, birds, reptiles and amphibia, 22 In mammals, birds, reptiles and amphibia, oxygen and carbon dioxide are exchanged by diffusion in the lungs In fish, this exchange of gases takes place by diffusion through the gills The oxygen dissolved in the water diffuses into the blood vessels in the gills.

Leaf 26 O2 and CO2 diffuse through pores in the epidermis the ‘veins’ bring water The leaf needs carbon dioxide for photosynthesis and oxygen for respiration. These gases diffuse through pores in the leaf’s epidermis and enter the air spaces between cells. They then diffuse through the cell wall into the cytoplasm. In a thin leaf, the diffusion distance is short O2 and CO2 diffuse into the spaces between cells

Low surface area to volume ratios Large organisms diffusion too slow (rate) to supply cells tissue and organs with substance they need and remove waste substances due to large distances. Low surface area to volume ratios So we have mass transport systems. Little = high ratio Large = low ratio

Activity text book pg 60-61 (blue shaded box) As the size of an organisms increases Surface area increases by a factor of 4 Volume increases by a factor of 8 So SA:V ratio halves.