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Transport in flowering plants

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Transport in flowering plants Plants are less active than animals so their cells don't need materials so quickly. Also, the shape and structure of plants means that oxygen and carbon dioxide can diffuse into and out of cells. Substances such as glucose molecules and nitrate ions move naturally from a region of higher concentration to one of lower concentration by diffusion. Water diffuses through a selectively permeable membrane from a region of higher water potential to one of lower water potential, a process known as osmosis. These vital processes are essential but adequate only for a transport of molecules and ions over short distances within a living system. Diffusion by itself is not sufficient; it is often too slow, possibly in the wrong direction and inadequate over longer distances. The evolution of flowering plants has seen the development of efficient transport systems, which have enabled plants to colonise the land, to increase their size and to develop an established habit. Plants have two transport systems; the xylem carries water and dissolved minerals and the phloem carries the 'food' materials that the plant has made. These enable the movement of water, organic molecules and ions over long distances. Xylem and phloem tubes are found together in a group called a vascular bundle. Xylem vessels run from the roots, up through the stem and out into each leaf. The xylem is made of hollow dead cells joined end to end. The cells don't contain any cytoplasm or nuclei. The cell walls are made of cellulose and lignin, which is very strong and helps keep the plant upright. ...read more.


Active transport establishes lower water potential and helps the root hairs take in the necessary minerals dissolved in soil water. Lower water potential allows water to be drawn into the root cells by osmosis. When a water potential gradient is established between two areas, water will spontaneously diffuse from the high end (soil) to the low end (air). This gradient is necessary for plants to transport water. Water potential may be established by either increasing the concentration of solutes. Pure water has the highest potential while a saturated solution of ions etc. would have the lowest potential. Or on the other hand, converting water to a gas. Water potential is highest when water is a liquid and lowest when water is a gas in air. Four important forces combine to transport water solutions from the roots, through the xylem elements, and into the leaves. These forces are transpiration, adhesion, cohesion and tension. Transpiration involves the pulling of water up through the xylem of a plant utilising the energy of evaporation and the tensile strength of water. There are certain conditions that will effect the transpiration occurring in a plant. As temperature increases, there is more energy available for evaporation, so transpiration increases. Also humidity, this is the amount of moisture in the air. As humidity increases, there is more water in the air. This reduces the difference in water concentration between the inside and outside of the leaf, so diffusion is slower. So, the higher the humidity, the slower the transpiration rate. Transpiration also increases in windy weather. ...read more.


Some stomata may be in pits. Plants that live in very hot conditions often have spines rather than leaves; this decreases the surface area. These have a much smaller surface area than leaves, so there is less area for evaporation. Although this helps to conserve water, it also means that photosynthesis is slow. An actively photosynthesising plant has a strong need for water. The efficiency of photosynthesis increases as the surface area for CO2, the second reactant, increases. This is the purpose of the spongy mesophyll that is honeycombed with air sacs. The spongy mesophyll has 10 to 30 times more surface area than the corresponding external surface of a leaf. Photosynthesis requires water. The system of xylem vessels from root to leaf vein can supply the needed water. Several forces combine to overcome the pull of gravity. These combined forces culminate in a process called transpiration. Ultimately water is pulled molecule by molecule into the leaf. The pulling forces and energy needed involves; free energy of the water potential gradient, of evaporation, force of surface tension and also the force of hydrogen bonding between water molecule. Each force can be communicated to the next because water forms a strong continuous chain from root to leaf. In conclusion flowering plants have many different ways of transporting different substances e.g. xylem and phloem, and also many ways of moving substances within the plant. They can also adapt to different environments and treat different substances in different ways to get the most efficient use out of them. All of these characteristics of the plant make up the transport system which allows them to photosynthesise, transpire and respire at a quick rate in order to carry out all of the needs of the plant. ...read more.

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