1. food supply, plant growth and productivity Flashcards
what is food security
the ability of human populations to access food of sufficient quality and quantity
Explain why food security is of increasing concern
The increasing human population is leading to a demand for increased food production. So a higher quantity of food is needed.
what does agricultural production depend on
the factors that control photosynthesis and plant growth
what are the factors that control plant growth
-breeding of higher yielding cultivars (cultivated varieties),
-use of fertiliser,
-protecting crops from pests,
-diseases and competition.
why do livestock produce less food per unit area than crop plants
due to loss of energy between trophic levels
what is visible light in relation to photosynthesis
Visible light is the part of the spectrum which drives photosynthesis
what are the two fates of light hitting a leaf
-Light energy not absorbed by the leaf pigments is transmitted or reflected
-Light energy is absorbed by photosynthetic pigments to generate ATP and for photolysis (first stage of photosynthesis)
function and colour of pigment chorophyll A
initiates the light reactions / photolysis
blue / green
function and colour of pigment chlorophyll B
an accessory pigment
yellow / green
function and colour of pigment xanthophyll
an accessory pigment; a carotenoid
yellow
function and colour of pigment carotene
an accessory pigment; a carotenoid
orange
how does chlorophyll A initiate light reactions
The three accessory pigments capture light energy then pass energy on to chlorophyll A.
Chlorophyll A is the only pigment that can initiate the light reactions
The proportion of a particular wavelength absorbed by a pigment can be measured using a…
spectrophotometer (or spectroscope).
Explain why black bands appear in the spectrograph for the extracted leaf pigments
They are the wavelengths/colours of light that have been absorbed by the leaf pigments
what is an absorption spectrum
a graph which plots a pigment’s visible light absorption
what is an action spectrum
the rate of photosynthesis over all visible wavelengths
how are pigments involved in photosynthesis
Each pigment absorbs a different range of wavelengths of light.
Carotenoids extend the range of wavelengths absorbed and pass the energy to chlorophyll for photosynthesis.
what happens inside thylakoids
light energy is transformed to chemical energy in the form of the products ATP and NADPH
where does photolysis, the light-dependent reaction take place
in the membrane of thylakoids in the chloroplasts
describe Photolysis, the light-dependent reaction
-Light energy strikes the thylakoid membranes and is absorbed by the pigment molecules. Absorbed light energy excites electrons in the pigment molecule
-The transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase
-Energy is also used for photolysis, in which water is split into oxygen, which is evolved (released out of leaf), and hydrogen ions, which are transferred to the coenzyme NADP
what products do the light reactions produce
ATP [Used in the calvin cycle]
NADPH [Used in the calvin cycle]
oxygen – diffuses out of the chloroplast, out of the mesophyll cell then out through the stoma
where does The Carbon fixation stage (Calvin Cycle) take place
in the stroma of the chloroplast
At which point in the calvin cycle is the enzyme RuBisCO required
1
At which point in the calvin cycle is hydrogen required
2
what do carotenoids in green plants do
They extend the range of wavelengths of light absorbed and pass energy onto chlorophyll
describe the carbon fixation stage (the calvin cycle)
-the enzyme RuBisCo fixes carbon dioxide (which diffused into the leaf-chloroplast) by attatching it to ribulose bisphosphate (RuBP), producing 3-phosphoglycerate (3PG)
-the 3PG is phosphorylated by ATP and combines with hydrogen ions from NADPH to form glyceraldehyde-3-phosphate (G3P)
-G3P is used to regenerate RuBP and for the synthesis of glucose
-glucose may be used as a respiratory substance, synthesised into starch or cellulose or passed to other biosynthetic pathways. these biosynthetic pathways can lead to the formation of a variety of different metabolites such as DNA, protein and fat
