photosynthesis Flashcards
Photosynthesis
all organisms require energy and this energy comes from food. plants are different to animals. in that they can make their own food using light energy
glucose that is made normally stored in the from of starch
photosynthesis takes place in the green parts of plants where the green pigments chlorophyll is found inside chloroplasts
chlorophyll traps light from the sun to drive the process
absorption energy means photosynthesis is described as endothermic
and endothermic process or reaction is one of which absorbs energy from its surroundings
carbon dioxide is taken into the plant through stomata and oxygen is released as a waste product
water is taken in from the roots for photosynthesis
photosynthesis word equation
carbon dioxide + water to glucose + oxygen
Destarching
place pant in dark place for 24 to 48 hours. During this time the plant cannot photosynthesize and so it has to use up any starch it has stored to stay alive
balanced chemical equation
6CO2+6H20>C6H1206+602
Investigating need for light
destarch a plant by keeping it in a cupboard for 2 days
test a leaf from the destarched plant for presence of starch
cover a part of the leaf with lightproof paper or foil as shown above
make a drawing of the destarched leaf at the end of the experiment
place leaf in bright light for several hours
test leaf from plant for starch
investigating need fir chlorophyll
destarch a variegated plant by keeping it in a cupboard for two days. remember to wear eye protection
test a leaf from destarched plant for presence of starch. if leaf tests negative
place plant in bright plant for several hours
test leaf from plant for starch
to show carbon dioxide is needed for photosynthesis
set up apparatus. ensure no air gets in flask. Leave the plant in a warm sunny place for a few days
test each leaf for starch
measuring rate of photosynthesis
set up apparatus
add some sodium hydrogen carbonate to provide extra co2 if not using pondwater
make sure there are no air bubbles in the test tube
leave apparatus beside lamp for a set time
measure volume of oxygen gas produced in the set time
effect of light intensity on the rate of photosynthesis
as light intensity increases the rate of photosynthesis increases then levels off because of another factor
effect of temperature on rate of photosynthesis
the experiment can be repeated at different temperatures, rate of photosynthesis increases at higher temperatures
increasing temperatures gives molecules energy making them move faster and collide more often, which increases number of reactions
above 35* rate declines as enzymes becomes denatured at high temperatures
how odes photosynthesis take place at its maximum rate
all of the environmental factors must be present at peak or optimum levels. However if one or factors is in short supply rate if photosynthesis will be limited.
these materials become limiting factors and rate of photosynthesis will be determined by whichever factor is in shortest supply
increasing amounts of each will increase rate of photosynthesis, shown to be a limiting factor
limiting factor
a limiting factor in photosynthesis is any of the environmental factors which prevent reactions of photosynthesis taking place at their maximum rate
Economic implications
to maximize crop production photosynthesis must take place at its optimum rate
availability of raw materials can be increased, to ensure that they do not limit rate of photosynthesis and hence production
much easier to control environmental factors that affect photosynthesis in a glass house or open felid
Examples of increasing environmental factors
increasing heat using Bunsen burner
increasing c02 from gas cylinders
increasing light from lamps
increasing water using sprinklers
increasing nutrients in the soil
how light absorption in a leaf is maximized by
short distance between upper and lower surfaces, which allow all cells to receive light
large surface area
thin transparent cuticle covering epidermis
which reduce waterless by evaporation, while allowing light to enter leaf
presence of chloroplasts rich in pigment chlorophyll which absorbs light
the regular structure of the palisade mesophyll which ensures many cells are packed near the upper surface of the leaf
the epidermis allows light into the leaf as it lacks chlorophyll
they are also adapted for defence against disease by the cuticle and cell walls of the epidermis providing a physical barrier, which reduces entry of disease causing organisms
Gas exchange in a leaf is maximized by
the intercellular spaces in the spongy mesophyll which allow carbon dioxide to enter and oxygen to leave the photosynthesizing cells that are mainly concentrated in the palisade layer
stomata which allow carbon dioxide and oxygen to leave and enter the leaf
stomata are small pores that can occur between cells in the epidermis on the bottom of leaves
each stoma is surrounded by two guard cells. that regulate the opening and closing of the stomata
in many plants the stomata are open during the day and and are closed at night
water also moves through the intercellular air spaces as a gas. it is formed by evaporation from the moist surfaces of the spongy mesophyll cells and then diffuses through the air spaces and stomata and out of the leaf
Epidermis
allows light to pass through to reach the palisade cells
stomata
allows gas exchange and lets water out
palisade mesophyll
contains many chloroplasts which absorb sunlight for photosynthesis
spongy mesophyll
allows carbon dioxide to pass quickly from stomata to the palisade cells
veins
helps photosynthesis to take place and removes the products
use of hydrogen carbonate indicator
if photosynthesis exceeds respiration plants will, overall, remove carbon dioxide and add oxygen
if photosynthesis is less than respiration plants will overall, remove oxygen and add carbon dioxide
demonstrating gas exchange
the overall change in carbon dioxide in the atmosphere can be demonstrated using hydrogen carbonate indicator, c02 produces a weak acid, carbon acid, and this indicator is sensitive to changes in pH caused by the acid
compensation point
in the dark rate of respiration greatly exceeds rate of photosynthesis, plant cells are living on sugars they manufactured during previous periods of photosynthesis
as light intensity increases after dawn, there comes a point where rates of respiration and photosynthesis exactly balance each other and there is no net uptake or loss of carbon dioxide or oxygen
called compensation point and at this point glucose consumed by respiration is exactly balanced by the glucose produced during photosynthesis. means amount of c02 taken in my photosynthesis is the same amount of c02 give out during respiration
hydrogen carbonate colors
purple- rate of photosynthesis exceeded the rate of respiration, resulting in concentration of carbon dioxide in the tubes decreasing turning the indicator purple
yellow- only respiration taking place( foil prevented photosynthesis. carbon dioxide concentration in the boiling tubes increased turning the indicator yellow.
red- both photosynthesis and respiration were taking place but the rate of photosynthesis were much reduced( due to the partial shading)- the rates of photosynthesis and respiration were equal and the amount of carbon dioxide used in photosynthesis was the same as the amount released in respiration.
no change in c02 levels and indicator remained red. the point at which rates of photosynthesis and respiration are equal is called compensation point.
