chapter 12 - nutrition and transport in flowering plants Flashcards
lamina
- large surface area to maximise absorption of light energy
- allows rapid diffusion of carbon dioxide to reach inner cells of leaf
petiole
positions lamina for maximum absorption of light energy and gaseous exchange of carbon dioxide and oxygen
cuticle
waxy : layer above the epidermis to prevent excessive water lost via evaporation
transparent : to allow light to penetrate and reach the mesophyll cells
upper epidermis
- single layer of closely packed cells
- no chloroplasts
- protects inner parts of leaf from injury
- no stomata here to prevent excessive loss of water through evaporation
palisade mesophyll
- few layers of closley packed cells
- long and cylindrical
- contains the most amount of chloroplasts and is found at the top of the leaf for the maximum absorption of light energy for photosynthesis
spongy mesophyll
- lesser chlorplasts than palisade mesophyll
- loosely packed with intercellular air spaces to facilitate diffusion of carbon dioxide and water vapour + for water plants ; provides buoyancy for the leaf to float on water
- surface covered with layer of moisture to allow carbon dioxide to dissolve before diffusing into cells
vascular bundle
xylem : transports water and mineral salts from roots to leaves + strengthens leaf to prevent tearing
phloem : transports sucrose and amino acids from leaves to other parts of the plant through translocation
lower epidermis
- single layer of protective cells
- presence of stomata for gaseous exchange. in presence of light energy, stomata will open wider to allow carbon dioxide to diffuse in and oxygen and water vapour to diffuse out
guard cells
- regulates the opening adn closing of stomata
- contains chloroplasts
opening of stomata
photosynthesis takes place in guard cells. glucose formed during photosynthesis will release chemical energy through aerobic respiration. the chemical energy is used to pump potassium ions into the guard cells via active transport. concentration of potassium ions increases in the guard cells, decreasing the water potential of the cell sap in the guard cells. there is a net movement of water molecules from adjacent epidermal cells into the guard cells by osmosis. guard cells swell and become more turgid, causing the guard cells to become curved and pull the stoma open wider.
closing of stomata
at night, potassium ions diffuse out of the guard cells. water potential of the cell sap in guard cells increase, leading to net movement of water molecules out of the guard cells by osmosis. guard cells becomes flaccid and stoma closes
xylem
- long narrow hollow lumen, without protoplasm and cross-walls : reduces resistance to water and dissolved mineral slats flowing through the xylem, enabling faster transportation of water and dissolved mineral salts up the lumen of xylem vessel
- inner walls are lignified to provide the plant with mechanical support and prevent the plant from collapsing
phloem
- sieve tube elements have very little protoplasm and are arranged to form a continuous colum to reduce resistance for rapid transport of sucrose and amino acids within the phloem
- presence of pores within sieve plates to allow faster rate of transport of sucrose and amino acids within the phloem
- companion cells have numerous mitochondria to release more energy for active transport of sucrose and amino acids from the mesophyll cells into the phloem sieve tube cells
- every phloem sieve tube cell has an associated companion cell to ensure the survival of the sieve tube cells
cambium
divide and differnetiate to form new xylem and phloem tissues
cortex/pith
storage tissues
epidermis
protected by a waxy, waterproof cuticle that greatly reduces evaporation of water from the stem
similarities and differences between xylem and phloem
similarities :
- xylem and phloem both transport materials to different parts of the plant
- xylem and phloem both transport substances as a solution to different parts of the plant
differences :
- xylem transports water and dissolved mineral salts but phloem transports sucrose and amino acids
- xylem transports water and dissolved mineral salts in one direction up the plant but phloem transports sucrose and amino acids in both directions
- xylem transports water and mineral salts from the roots to the leaves while phloem transports from the leaves to other parts of the plant
- xylem transports water and mineral salts by root pressure, transpiration pull and capillary action while phloem transports sucrose and amino acids as a result of loading sucrose into the phloem via active transport
how does water move in from the soil to the root hair cells
- each root hair grows between the particles between the soil particles
- a thin film of dilute solution of mineral salts surround each soil particle
- water moves into the root hair by osmosis
- water moves from the root hair cells to the inner cells via osmosis
adaptations of root hair cells for absorption of water
- long and narrow extension to increase surface area to volume ratio to increase rate of absorption of water and dissolved mineral salts form soil solution to root hair cells
- numerous mitochondria to release more energy for faster rate of respiration for active transport of dissolved mineral salts from soil solution to root hair cell
- cell membrane to prevent cell sap from leaking out
- concenrated cell sap with lower water potential than soil solution to allow net movement of water molecules into the root hair cell via osmosis, down a water potential gradient
photosynthesis
process in which light energy is absorbed by chlorophyll and converted into chemical energy, which will be used to synthesis glucose by using carbon dioxide and water as raw materials, and releasing oxygen as a product
photosynthesis equation
6 CO2 + 6 H2O → C6H12O6 + 6O2
carbon dioxide + water → glucose + oxygen (give conditions : chlorophyll and light energy)
what happens during photosynthesis
during photosynthesis, chlorophyll absorbs light energy converts it to chemical energy which is stored glucose that is synthesized from water and carbon dioxide, and oxygen is released as a by-product.
fate of glucose in plants
- glucose formed is used for respiration and formation of cellulose cell walls.
- glucose is converted to sucrose and transported to storage organs via translocation.
- excess glucose is stored as starch or fats, andd converted into proteins to form new protoplasm
how does carbon dioixde reaches mesophyll cells in a leaf
carbon dioxide is rapidly used up, together with water, as the raw materials for photosynthesis. carbon dioxide concentration inside the leaf is lower than that in the atmosphere. carbon dioxide diffuses from the surrounding air into the leaf, via the stomata, down a concentration gradient. carbon dioxide moves into the intercellular air spaces and dissolves into the thin film of moisture on the surface of spongy mesophyll cells and finally, diffuses into the cells and chloroplasts for photosynthesis.
effects of varing light intensity
- by varying the distance of the light source from the plant
- as light intensity increase, rate of photosynthesis increase
effect of varying carbon dioxide concentration
- by varying the concentration of dilute sodium hydrogen carbonate solution
- as the carbon dioxide concentration increases, the rate of photosynthesis increases
effect of varying temperature
- by varying the temperature of the water bath
- as the temperature increases, the rate of photosynthesis increases until the optimum temperature is reached. increasing the temperature beyond the optimum temperature causes the enzymes to be denatured and rate of photosynthesis to decrease.
limiting factors
a factor directly affecting or limiting a process if its quantity or concentration is altered
translocation
process by which sucrose and amino acids are transported in the phloem, from the leaves to other parts of the plant.
root pressure
pressure resulting from constant entry of water into the roots, allowing water to move up the xylem vessel
capillary action
tendency of water to move up narrow tubes and depends on the forces of cohesion and adhesion
transpiration
loss of water vapour from the aeriel parts of the plant, especially through the stomata of the leaves, to the surrounding air
transpiration pull
suction force caused by transpiration, results in water to move up the xylem
how is water transported from the root hair cells to the mesophyll cells?
water enters the root hair cells from the soil by osmosis down a water potential gradient as there is a higher water potential in the soil than the cell sap of the root hair cell. the water moves from cell to cell, via osmosis until it reaches the xylem. in the xylem, water moves up the xylem through root pressure, cohesion and adhesion of water molecules through capillary action and transpiration pull. in the leaves, water moves out of the xylem and moves from the cell to cell, via osmosis until it reaches the mesophyll cells.
water movement in the leaf
water that moves out of the mesophyll cells from a thin film of moisture around the cells. water from the thin film of moisture evaporates to form water vapour in the air spaces. the higher concentration of water vapour accumulates in the air spaces near the stomata. water vapour diffuses out of the stomata into the enviroment. movement of water out of the cells to replace the thin film of moisture that has evaporated decreases the cell sap’s water potential. the mesophyll cells absorb water via osmosis from the adjacent cells. these cells will then absorb water from the xylem vessels, resulting in the production of a suction force that pulls water in the xylem vessels up. this suction force is known as transpirational pull
appearance of a mesophyll cell in a wilted leaf
plant cell will become flaccid and plasmolysed. volume of large central vacuole and cytoplasm shrunk in size, cell membrane will be detached from cell wall
factors affecting rate of transpiration
lower humidity, faster wind speed, higher temperature and higher light intensity - increases trasnpiration
