plant system Flashcards
describe the chloroplast
all green parts of plant have chloroplast
leaves are the main site of photosynthesis in most plants
colour of the leaf is due to chlorophyll, the green pigment in chloroplast and chloroplast are found mainly in the cells of the mesophyll layer in a leaf
structure of chloroplast
a typical mesophyll cell has about 30 to 40 chlorophyll. an envelope of two membranes encloses the stroma, the dense liquid within chloroplast
a system of interconnected membranous sacs are known as thylakoids and it separates the stroma from the interior of the thylakoid. chlorophyll is found in the membrane of the thylakoid.
how does chlorophyll trap light and convert into chemical energy
the green pigment chlorophyll is the principal element involved in photosynthesis. chlorophyll absorbs light from the violet blue and red region and reflects green light giving leaves their green appearance. chlorophyll traps light and converts it into chemical energy for the formation of glucose
describe the process of photosynthesis
photosynthesis is the process where light energy absorbed by chlorophyll is used to synthesize glucose from water and carbon dioxide. oxygen is released in the process. photosynthesis depends on the enzymatic reactions in the chloroplasts
what happens in the light dependant stage
light energy is absorbed by chlorophyll and converted into ATP
light energy is also used to split water molecules into oxygen gas and hydrogen ions. this is known as photolysis of water. 12 molecules of water are split to yield 6 molecules of oxygen gas and 24 hydrogen ions.
oxygen is then released out of the leaf via stomata
what happens during independent stage
hydrogen ions released during photolysis is used to reduce carbon dioxide to glucose. the ATP needed for this process comes from the light dependent stafe
24 hydrogen ions are sed to reduce 6 molecules of carbon dioxide to form 1 molecule of glucose
what are the uses of glucose formed during photosynthesis
glucose is used during respiration to produce ATP for cellular activities
form cellulose cell walls
when rate of photosynthesis is higher than rate of respiration, excess glucose is converted into starch for storage. starch is converted back to glucose for usage when photosynthesis stops
glucose converted into lipids for storage and synthesize of cell membranes
converted into sucrose for transport to other parts of the plant via the phloem
structures of the leaf
cuticle: waxy and transparent no chloroplast. to reduce water loss from evaporation and invasion of bacteria and viruses
upper and lower epidermis: single layer of cells closely packed together containing no chloroplast. to protect inner cells and allow light to pass through.
palisade mesophyll: long and cylindrical cell with the largest number of chloroplast to take in light energy for photosynthesis. closely packed together filled with chloroplast
spongy mesophyll: irregular shaped cells containing chloroplast for photosynthesis. loosely packed cells with large intercellular air spaces to increase surface area for diffusion of carbon dioxide and oxygen in and out of the mesophyll cell.
vascular bundle: contains transport tissue, xylem and phloem. xylen transports water and mineral salts to other mesophyll cells. phloem transports sucrose and amino acids away from the leaf to other parts of the plant
guard cells: contains chloroplast and regulates size of stomata for gaseous exchange and transpiration. cell wall near stomata is the thickest so that uptake of water causes cell to curve causing stomata between two guard cells to open.
large intercellular air spaces: for circulation of air inside cell for photosynthesis and respiration. the system of interconnected air spaces in the spongy mesophyll allows rapid diffusion of carbon dioxide and oxygen into and out of mesophyll cells.
how is leaf adapted to photosynthesis
stomata present in the epidermal layers: stomata opens in the presence of sunlight allowing carbon dioxide to diffuse in and oxygen to diffuse out of the leaf
chloroplast containing chlorophyll found in all mesophyll cells: chlorophyll absorbs energy from sunlight and converts it into chemical energy in glucose molecules.
palisade have highest concentration of chloroplasts: so more light can be absorbed near upper leaf surface for photosynthesis.
veins containing xylem and phloem are situated close to mesophyll cells: to provide effective transport of water and mineral salts through xylem to mesophyll cells. water is required as a raw material for photosynthesis
effective transport of manufactured food through phloem in form of sucrose and amino acids away from leaf to all parts of the plant.
how do guard cells control size of stomata
In the day: guard cells photosynthesize, chemical energy is used to pump potassium ions into the guard cell from neighbouring epidermal cell. concentration of K+ ions increases and water potential of guard cell decreases. hence water enters the guard cell by osmosis, guard cell swells and become tugid. due to difference in thickness of cell wall, one side expands more than another and stoma opens
at night: potassium ions move out of the cell by diffusion, hence water potential is guard cell increases and water move out of the cell by osmosis, cell become flaccid and stoma closes
describe intake of carbon dioxide
due to photosynthesis, carbon dioxide in leaf is used up. hence carbon dioxide concentration in leaf is lower than the atmosphere hence CO2 diffuses into the air spaces in the leaf through stomata. it then diffuses into the mesophyll cells into chloroplast.
describe function of xylem and phloem in herbaceous dicotyledonous leaf stem and root
in the leaf: xylem tissue is positioned above phloem tissue within vascular bundle
in the stem: vascular bundles are arranged in a ring around a region known as the pith, with phloem tissue closer to exterior of the stem. a layer of cambium which consist of undifferentiated cells which can divide to from new xylem and phloem be found between the phloem and xylem. pith and cortex regions store food substances such as starch. epidermis consists of epidermal cells and waterproof cuticle. epidermis consist of epidermal cells and a layer of cuticle to reduce evaporation of water.
in the roots: xylem and phloem are found in the central region of the root with xylem tissue radiating from the centre and phloem tissue developing in the wedges between extension of xylem tissue
explain function of xylem vessels
xylem vessels are arranged end to end longitudinally. when mature cross walls in adjacent cells are remove. cell membrane and cellular contents break down forming long and continuous hollow tubes. this tube is to transport water and mineral salts to all parts of the plant. it has empty lumen consisting of dead cells to reduce water resistance to flow of water
inner walls of vessels have lignin deposits. lignin can deposit in different patterns. walls are strengthened to provide mechanical support for the plant
explain the structure of phloem
living sieve tube cells with reduced cytoplasm and absence of nucleus. sieve plates present. companion cells beside sieve plates with many mitochondria.
function of phloem
phloem transports manufactured food substances like amino acids and sucrose throughout the plant known as translocation. it is an active process and requires energy.
sieve tube cells are living because translocation is an active process. reduced cytoplasm and absence of nucleus reduces flow of resisatnce of food substances. many mitochondria present provides energy needed by seive tube cells for translocation. companion cells perform many of the metabolic functions to keep sieve tube cells alive
define transpiration
transpiration is the loss of water vapour from the leaf through the stomata. it occurs when the stomata is open during the day when more sunlight is present, more stomata is open to facilitate gaseous exchange for photosynthesis. it is a consequence of gaseous exchange in plants.
