ch7 Flashcards
define photosynthesis
it is a process by which green plants use carbon dioxide and water in the presence of light, to produce simple sugar
equation of photosynthesis
6CO2 + 6H2O (in presence of sunlight and clorophyll) -> C6H12O6 + 6O2
How to obtain the raw materials of photosynthesis
CO2 -> passes by diffusion from the atmosphere to leaves through the stomata
water -> absorbed by osmosis from soil to the root hair cell, to he xylem vessels to the leaves
light -> absorbed by chlorophyll
what is clorophyll ? and what is its function?
it is a green pigment found in chloroplasts
function : absorb light energy from sun and changes it into chemical energy , in the process of photosynthesis
what happens to excess glucose after photoynthesis [4]
- changed to starch and stored inside the plant cell
- changed to cellulose and used to form the cell wall
- changed to sucrose and translocated to all parts of the plant by the phloem vessels
-changed to nectar sugar in flowers to attract insects for pollination
what is a limiting factor?
it is the factor which is present in minimum supply , it controls the rate of the biological process
define compensation point
it is the point where the rate of photosynthesis = the rate of respiration ; it occurs at dawn and dusk
how photosynthesizing cells obtain co2?
co2 diffuses through the stomata from its high conc. in atmospheric air to its low conc. inside the leaf air space. then co2 diffuses inside the air spaces in spongy layer to the palisade cells. where it crosses the cell wall and cell membrane to reach cloroplasts inside the palisade cell
compare the palisade cell and spongy cell? [4]
- palisade is rectangular and spongy is rounded
-palisade has much chloroplasts and spongy has less chloroplasts
-palisade has less air spaces, and spongy has much air spaces
-palisade performs photosynthesis but spongy exchanges gases
compare the upper epidermis and lower epidermis layer? [4]
- lower epidermis has guard cells
-lower epidermis has stomata
-lower epidermis has chloroplasts
-upper epidermis has a thick cuticle
what excretes the cuticle
the upper epidermal cell
functions of the cuticle? [2]
- protection, prevents entry of bacteria and microbes
-prevent excess water loss
describe the structure of the upper epidermis ? [2]
- 1 layer of flat transparent cell
-has no chloroplasts, to alllow passage of light to the next layer to make photosynthesis
function of upper epidermis
protection
describe the palisade layer, and its function?
1 layer of rectangular palisade cells, full of chloroplasts
f = photosynthesis
describe the structure of the spongy layer
rounded spongy cells with much air spaces and few chloroplasts
function of spongy layer
exchange in gases and share in photosynthesis
lower epidermis structure?
- layer of flat cells , guard cells and stomata pores
function of lower epidermal cell
protection
adaptation of leaf to its function? [2]
- thin, so allow easy diffusion of gases
- large S.A, to absorb maximum amount of light and co2
describe the structure of the stomata? [2]
they are small pores, present in the lower epidermis of the leaf
-they are surrounded by guard cells
function of stomata? [2]
- exchange of gases
-transpiration
how does stomata change during day and night? and why?
during day, they are open to allow entry of co2 for photosynthesis
during night, they are closed , as no photosynthesis so they close to avoid losing too much water
why is there more stomata in the lower epidermis ? [2]
- as the upper epidermis is more exposed to accumalation of dust
-upper epidermis more exposed to agents of evaporation of water (light and heat)
