Plant Transport PDF

LEAF STRUCTURE External features leaf blade it has a large surface area to volume ratio this enables it to obtain the maximum amount of light for ph...

LEAF STRUCTURE External features leaf blade it has a large surface area to volume ratio this enables it to obtain the maximum amount of light for photosynthesis carbon dioxide can rapidly reach the inner cells of the leaf network of veins it consist of the xylem and phloem leave arrangement leaves are arranged in a regular pattern around the stem to ensure that the leaves are not blocking one another from light leaf stalk grasses and maize do not have a leaf stalk Internal Structure upper epidermis a single layer of closely packed cells covered on the outside by cuticle mesophyll main site of photosynthesis consist of 2 types of tissue - palisade mesophyll and spongy mesophyll palisade mesophyll consists of one or two layers of closely packed, long and cylindrical cells contains the most number of chloroplast - closer to the spongy medophyll contains loosely packed cells with irregular shapes has chloroplast but lesser than palisade mesophyll cells covered with a thin film of moisture  contains transport tissue - xylem and phloem which are grouped together to form a vascular bundle lower epidermis a single layer of closely packed cells covered on the outside by cuticle cuticle reduces water loss through epidermal cells stomatal pore (stoma) the opening between guard cells guard cell helps to regulate the rate of transpiration by opening and closing the stoma contains chloroplasts Adaptation for photosynthesis adaptation function waxy cuticle on upper and lower epidermis it reduces water loss through evaporation from the leaf it is transparent for light to enter the leaf stomata present in the epidermal layers stomata open in the presence of light, allowing CO2 to diffuse in and oxygen to diffuse out of the leaf chloroplasts containing chlorophyll in all chlorophyll absorbs energy from light and mesophyll cells transfers it to chemical stores of energy in glucose molecules more chloroplast in upper palisade tissue more light can be absorbed near the upper leaf surface interconnecting system of air spaces in the the air spaces allow rapid diffusion of carbon spongy mesophyll dioxide and oxygen into and out of mesophyll cells veins containing xylem and phloem situated xylem transports water and mineral salts to close to the mesophyll cells mesophyll cells phloem transports sucrose away from the leaf How do guard cells control the size of stomata stomata open as a result of turgid guard cells light triggers the active uptake of potassium ions by guard cells from nearby cells lowers the water potential of guard cells and water enters by osmosis  the uneven thickness of cell walls of guard cells result in the cells bowing with water intake, opening the pore of the stoma stomata close when the water leaves the guard cells by diffusion of potassium ions out of the guard cells this increases the water potential of the guard cells and water leaves by osmosis the guard cells become flaccid and the stoma closes How do the leaf cells receive water and carbon dioxide water and mineral salts are transported through the xylem vessels from the roots they move from cell to cell through the mesophyll ^^ carbon dioxide diffuses into the leaf through the stomata it dissolves in the water around the cells it then diffuses into the cells  Xylem vs Phloem xylem phloem function to conduct water and mineral to transport food (sucrose and salts up from the roots amino acids) from the leaves to to provide mechanical support other parts of the plant adaptation it is a long hollow tube made up it has a column of sieve tube of dead cells without cross walls cells forms a long sieve tube reduced the resistance to water flowing through the sieve plates, which are the xylem ‘cross-walls’ between the cells have many minute pores that there is lignin The inner onof walls thethe inner walls xylem enable rapid flow of inner walls are have lignin that allow vessels manufactured food such as strengthened to withstand pressure in order sucrose and amino acids to provide mechanical support through the sieve tubes for the plant companion cells load sugars from the mesophyll cells into the sieve tube via active transport companion cells have many mitochondria to provide the energy needed for active transport type of cell xylem vessel sieve tube cells and companion cell living/dead vessel cell dead living  lignin present absent direction of flow unidirectional - upwards bidirectional - up and downwards end walls broken down completely partially partially or completely process by which substances transpiration translocation are moved Translocation definition - translocation is the movement of materials in plants from the leaves to other parts of the plant mesophyll cells —> phloem —> phloem in vascular bundle of fruits —> cells Vascular tissue in stems, leaves & roots the xylem and phloem vascular bundles are in form a vascular bundle the spongy mesophyll the phloem is in the layer outer part the xylem is nearer to the cambium lies the upper surface of the between the xylem and leaf phloem stem is covered by a layer of cells called epidermis the epidermis of the root is the outermost layer of cells and bears root hairs  the long narrow extension of the root hair increases the surface area to volume ratio of the root hair cell, increasing the rate of absorption of water and mineral salts Take note 1. mesophyll cells contains stomata chloroplast which are import at in absorbing light energy for photosynthesis 2. the phloem xylem transports water and mineral salts to mesophyll cells while the xylem phloem transports sucrose away from the leaf 3. guard cells stomata are minute openings in the leaf that are important in gaseous exchange 4. translocation is the transport of water in plants substances such as sugars and amino acids in plants  MOVEMENT OF WATER IN A PLANT Entry of water in a plant 1. the thin film of liquid surrounding each soil particle is a dilute solution of mineral salts 2. the cell sap in the root hair cell has a lower water potential than the soil solution (is relatively concentrated solution of sugars and various salts) a. water moves from the soil solution to the root hair cell by osmosis 3. the entry of water dilutes the cell sap. The cell sap of the root hair cell (cell A) has a higher water potential than that of the next cell (cell B) a. water moves from the root hair cell into the inner cell by osmosis 4. this process continues until water enters the xylem vessels Recall osmosis is the movement of water molecules from a solution with a high concentration of water molecules to apotential higher water solution to with a lowerwith a solution concentration lower waterofpotential water molecules, through a cell's partially permeable membrane Entry of ions or mineral salts in a plant 1. diffusion a. when the concentration of ions in the soil solution is higher than that in the cell sap, ions diffuse down the concentration gradient 2. active transport a. when the concentration of ions in the soil solution is lower than that in the root hair cell sap b. the root hairs have to absorb the ions against a concentration gradient by active transport c. the energy for this process comes from cellular respiration in the root hair cell Recall active transport is a process that involves the movement of molecules from a region of lower concentration to a region of higher concentration against a gradient with the use of external energy Adaptations of root hair cell to absorption adaptation function long and narrow extension of the root hair cell increases the surface area to volume ratio which in turn increases the rate of absorption of water and mineral salts by the root hair cell the cell membrane prevents the cell cep from the cell sap contains sugars, amino acids and salts. leaking out It has a lower water potential than the soil solution, resulting in water entering the root hair by osmosis contains many mitochondria aerobic respiration in the mitochondria releases energy for the active transport of ions into the cell Capillary Action capillary action is the ability of a liquid to flow through narrow spaces without any assistance and even against gravity it occurs when the adhesive forces between the liquid and the walls of the space are stronger than the cohesive forces between the liquid molecules ○ this helps water move up the narrow xylem vessels of plants  Transpiration 🧑💻 definition: transpiration is the loss of water from the aerial parts of a plant by evaporation, mainly definition: transpiration is the loss of water vapour from the aerial parts of a plant, mainly through the stomata of the leaves in the form of water vapour through the stomata of the leaves Transpiration pull ○ the evaporation of water from the leaves removes water from the xylem vessels, regulating in a suction force which pulls water up the xylem vessels ○ this suction force is known as transpiration pull, it is the main force in drawing water and mineral salts up the plant as transpiration occurs a only through the stomata it is links to gas exchange between the plants and environment ○ in daylight stomata open to allow carbon dioxide to diffuse into the leaf for photosynthesis ○ oxygen and water vapour are more concentrated in the intercellular air spaces, so they diffuse out of the leaf through the stomata [exam ans] Describe the process of transpiration Water evaporates from the mesophyll cells and forms a thin film of moisture over the cell surfaces Water evaporates from the thin film of moisture and then moves into the intercellular air spaces Water vapour accumulates in the intercellular air spaces near the stomata and diffuses out through the stomata via transpiration to the drier atmosphere Importance of transpiration 1. transpiration pull draws water and mineral salts from the roots to the stems and leaves 2. evaporation of water from the surface of cells in the leaves cools the plants preventing it from being scorched by the hot sun 3. water transported to the leaves can be used in photosynthesis to keep cells turgid (they keep leaves spread out widely to trap light for photosynthesis) and to replace water lost by the cells Factors affecting the rate of transpiration 1. wind or air movement a. water vapour that diffuses out of the leaf is blown away by the wind and does not accumulate outside the stomata, resulting in the concentration gradient of water vapour inside and outside the leaf to be steeper —> higher rate of transpiration 2. temperature of the air a. When rise in temperature temperature results increases, inisthe there increase a high kinetic in theirofrate energy waterofmolecules evaporation ofwater to form water fromresulting vapour, the in a higher rate of evaporation of water from the cell surface. There is a steeper water concentration gradient between cell surfaces the leaf and the surrounding air, hence there is a higher rate of transpiration 3. light a. light affect the size of the stomata When there is no light, the rate of photosynthesis of the guard cells decreases, the stomata closes and becomes smaller, decreasing the rate of transpiration  b. in the presence of light, the stomata open and become wider, increasing the rate of transpiration 4. humidity of air a. increasing the humidity of the air will make the water concentration gradient between the leaf and the surrounding air less steep —> reducing rate of transpiration  Wilting wilting occurs when the rate of transpiration is higher than the rate of absorption by the roots the turnaround pressure in the leaf mesophyll cells helps to support the leaf and keep it firm, enabling it to spread out widely to absorb light for photosynthesis cells lose their turgor in strong light as the rate of transpiration exceeds the rate of absorption of water by the roots. they become flaccid and wilt advantage - rate of transpiration decreases disadvantage - rate of photosynthesis decreases ^^