Transport in Plants PDF

BIOLOGY  TRANSPORT IN PLANTS  Objectives  Describe the structure of the xylem vessels, sieve tubes and companion cells  Explain how the structure of the xylem vessel suits them for their function  Describe the process involved in transpiration  Demonstrate the effect...

BIOLOGY  TRANSPORT IN PLANTS  Objectives  Describe the structure of the xylem vessels, sieve tubes and companion cells  Explain how the structure of the xylem vessel suits them for their function  Describe the process involved in transpiration  Demonstrate the effect of external factors on the transpiration rate  State the function of phloem in the transport system of plants Plants also have a transport system. The XYLEM and PHLOEM VESSELS. Together they are called the VASCULAR BUNDLE. XYLEM VESSELS:- carry water and minerals PHLOEM VESSELS:- carry food material which the plants make  WHY PLANTS NEED A TRANSPORT SYSTEM?  To transport water and mineral salts absorbed from the roots  Water-solvent for bio-chemical reactions and reactant for cell metabolism ( light reaction in photosynthesis)  Mineral ions and salts are needed to synthesise chlorophyll, for healthy plant growth and development  To be able to synthesis organic substances  To transport carbohydrates (foos) produced by the leaves to stem and roots for respiration, growth and storage  PROBLEMS PLANTS CAN ENCOUNTER IN TRANSPORTING SUBSTANCES:- Plants are unable to pump necessary substances through great distances up the plant sometimes requiring the need to defy gravity  there is no “pump” to circulate materials around the plant  HOW IS IT OVERCOME? Plants use a combination of capillarity which involves adhesion and cohesion of molecules, root pressure, and transpiration pull to provide enough force to transport water up the xylem. THE XYLEM VESSEL IN RELATION TO TRANSPORT:- [pg 115] Xylem contains four (4) types of cells:-  They are dead cells that have no nuclei or cytoplasm  Xylem vessels  Tracheids  Parenchyma (to store food substances) and  Fibres (to provide support) a type of sclerenchyma  Xylem vessels and thracheids are water conducting cells  They are elongated cells arranged end to end  The end walls of xylem vessels are open this allows water to flow upwards continuosly  The cell walls are thickened with LIGNIN This makes the vessel strong so it does not collapse under the tension created by the upward pull of water during transpiration Make sure you know the cross section and longitudinal section of xylem THE STRUCTURE OF PHLOEM VESSEL IN RELATION TO TRANSPORT PG 115-116 Functions::  Transport organic substances downwards (from the leaves to the storage organs)  Also upwards (from the storage organs) such as the roots to the growing regions such as the buds. Structure:-Composed of 4 types of cells  sieve tubes:- where are organic substances are transported. They are cylindrical columns of long cells arranged end to end. It is a living cell but NO NUCLEUS. Its cytoplasm is pushed side of the cell.  Ends of the walls are perforated by pores called the SIEVE PLATES. Each sieve tube cell is kept alive and supported in their function by one or more COMPANION CELLS Structure of phloem continued:- COMPANION CELL:- Contains a nucleus and a large number of mitochondria, indicating that it is very active metabolically Cell wall does not contain lignin ARRANGEMENT OF VASCULAR BUNDLE IN THE ROOTS ARRANGEMENT OF VASCULAR BUNDLE IN THE STEM MOVEMENT OF WATER THROUGH A PLANT (PG 117) The movement of water through a plant can be broken down in five stages:- Absorption of water by the root hair cells Movement of water across the root cortex to the xylem Movement of water up the xylem Movement of water across the leaf cells Evaporation of water from the leaves  EVAPORATION OF WATER FROM THE LEAVES pg 117 The concentration of water molecules inside the cells is higher than in the air space,and higher there than outside the leaf. So some of the water evaporates from the cells into the air space and diffuses out of the leaf through the stomata down the concentration gradient. FROM WHAT CELLS /STRUCTURE WATER PASSES FROM THE LEAF ANS :- STOMATA  TRANSPIRATION IS THE LOSS OF WATER BY EVAPORATION FROM THE SURFACE OF THE LEAVES pg 118. MOVEMENT OF WATER WITHIN THE LEAF :- as water evaporates from the surface of the cells near the air spaces, its concentartion in those cells (A) is lowered. The concebtration in the adjacent cells (B)is now higher than the A cells.This results in the movement of water from cell B to cell A by osmosis.  MOVEMENT OF WATER UP THE XYLEM PG 118 Water moves up the xylem because of three factors:-  CAPILLARITy  ADHESION:- ATTARCTION BETWEEN THE WATER MOLECULES AND THE WALLS OF THE XYLEM VESSELS  COHESION:- WHEREWATER MOLECULES STICK TOGETHER  ROOT PRESSURE:-  TRANSPIRATION PULL CAPILLARITY  ROOT PRESSURE  WATER CONSTANTLY MOVES INTO ROOTS CELLS BY OSMOSIS BECAUSE THE PRESENCE OF SUGARS AND OTHER DISSOLVED SUBSTANCES IN THE ROOT MEANS THAT THE WATER CONCENTRATION CAN NEVER BE AS HIGH IN THE ROOT CELLS AS IN THE SOIL. WATER ABSORBED INTO THE PLANT FROM THE SOIL CREATES A PRESSURE IN THE ROOT XYLEM. THE PRESSURE THERE IS GREATER THAN IN THE LEAF XYLEM BECAUSE WATER IS PULLED OUT OF THE LEAF XYLEM BY TRANSPIRATION. SO WATER MOVES FROM THE HIGH PRESSURE IN THE ROOTS UP THE XYLEM VESSELS IN THE STEM TO THE LOW PRESSURE IN THE LEAVES  TRANSPIRATION PULL THE FLOW IN THE SYSTEM IS MAINLY BY COHESIVE FORCES HOLDING WATER MOLECULES TOGETHER AND THE LOSS OF WATER BY EVAPORATION IN THE UPPER AREAS OF A PLANT CREATING A TENSION THAT ‘PULLS’ WATER UPWARDS. THIS IS THE TRANSPIRATION PULL ABSORPTION OF WATER BY ROOT HAIR CELLS AND ACROSS THE ROOT CORTEX [PG 119] TRANSPIRATION TRANSPIRATION IS THE EVAPORATION OF WATER FROM A PLANT. IT IS IMPORTANT TO THE PLANT BECAUSE:- IT PULLS WATER UP TO THE LEAF FOR PHOTOSYNTHESIS THE MOVING WATER CARRIES DISSOLVED MINERAL SALTS UP TO THE LEAVES THE EVAPORATION OF WATER COOLS THE PLANT  TRANSPIRATION RATE THE RATE AT WHICH THE PLANT TAKES UP WATER DEPENDS ON THE RATE AT WHICH IT IS LOST. THE FASTER THE TRANSPIRATION RATE , THE FASTER THE PLANT TAKES UP WATER. FACTORS THAT AFFECT TRANSPIRATION RATE INCLUDES:-  TEMPERATURE:- WITH HIGH TEMPERATURES , AS ON A HOT DAY,EVAPORATION OCCURS RAPIDILY THUS INCREASING THE RATE OF TRANSPIRATION  HUMIDITY:- High humidity means the air has plenty water molecules or saturated with water molecules.The concentration gradient of water between the air spaces and the outside air is low and the rate of evaporation of water through the stomata is slow, thus, transpiration decreases as humidity increases.  WIND (AIR MOVEMENT):- In windy conditions , water vapor is carried rapidly away from the leaves and the rate of transpiration is fast. Transpiration increases as wind speed increases  LIGHT INTENSITY:- During bright light, the stomata are fully opened. When the stomata are fully opened the rate of transpiration is high. ADAPTATION IN PLANTS TO CONSERVE WATER