4.3: Photosynthesis. Flashcards
What is an autotroph?
Organisms that synthesise their own food from simple organic molecules using the energy from sunlight or chemical reactions.
What is the mode of nutrition of plants?
Autotrophy (they are autotrophs).
Why is photosynthesis critical to life on this planet?
Without plants turning sunlight into glucose, amino acids and starches animals would not be able to survive. It also uses up CO₂ and produces O₂.
What does photosynthesis produce?
Glucose and Oxygen(as a waste product).
What is the input for photsynthesis?
Water (provides H and O atoms) Carbon Dioxide (provides C and O atoms)
What do carnivorous plants use insects for?
As a nitrate and phosphate source as they live in poor soil conditions. They still perform photosynthesis.
In what plant cells does photosynthesis take place?
Most photosynthesis occurs in palisade cells. However there are also chloroplast present In Mesophyll cells and guard cells.
What is the endosymbiotic theory?
This suggests that chloroplasts and mitochondria evolved when a larger bacteria engulfed other bacterium. Chloroplasts are thought to have evolved through the endocytosis of a bacteria related to Cyanobacteria and mitochondria through the endocytosis of bacteria related to rickettsia.
What do chloroplasts contain in the stroma?
Thylakoid membranes Chloroplast DNA tRNA Ribosomes (prokaryotic 70S) Starch grains and lipid droplets
What is the purpose of the thylakoids and Grana?
To increase the surface area for the absorption of light and hence increase the amount of photosynthetic enzymes and therefore the amount of photosynthesis.
What are the two main groups of photosynthetic pigments?
Chlorophylls
Carotenoids
What Is the structure (roughly) of chlorophyll?
Chlorophyll has a porphyrin head and a hydrocarbon tail which is used to attach them to the thylakoid membranes.
What are the two main chlorophylls in flowering plants?
Chlorophyll A (P680 and P700)
Chlorophyll B
What is the main structural difference between chlorophylls A and B?
They have one different side chain on the porphyrin head.
Give two examples of carotenoids.
Beta carotene
And Xanthophyll (WJEC prefer this)
Why are there different photosynthetic pigments in plants?
Because the pigments absorb light at different wavelengths and so having different pigments allows more of the visible spectrum to be used for photosynthesis.
What is the best way to see what wavelengths of light different pigments absorb.
By looking at their absorption spectrum.
What is an absorption spectrum.
A graph of how well pigments absorb light of different wavelengths. A high absorption means that wavelength is taken in and can be used by that pigment. Low absorption means that the wavelengths are not absorbed and used but are instead reflected or transmitted.
In what region of the visible electromagnetic spectrum do chlorophylls absorb?
In the red (650-760nm) and blue-violet (440-510nm).
They do not absorb green light but reflect it.
In what region of the visible electromagnetic spectrum do carotenoids absorb?
In the blue-violet regions of the spectrum.
Green light is not absorbed but is reflected and red light is absorbed by chlorophyll so is also not absorbed.
What pigment do plants adapted to shady conditions tend to have more of?
They tend to have a higher concentration of chlorophyll. Resulting in dark green leaves.
Why do plants have different combinations of photosynthetic pigments?
Because different plants experience different light conditions. This gives rise to different coloured leaves.
What is an accessory pigment?
Chlorophyll is the main pigment involved in photosynthesis. The other pigments are accessory pigments - they absorb light energy at extra wavelengths and pass the energy from this on to chlorophyll.
What is an action spectrum?
A graph showing how much photosynthesis happens at the different wavelengths of light.
How could you test to see if a plant was performing photosynthesis?
You could test for an increase in the products:
Oxygen
Glucose-diastix
Starch-iodine
Or a decrease in the starting materials:
CO₂
How was the first action spectrum produced?
Filamentous alga (spyrogyra) are put in a suspension of aerobic bacteria. Not much oxygen dissolves in the water and so the bacteria move towards the highest sources of O₂ so that they can respire. He first showed that chloroplasts were the site of photosynthesis by shining white light at the suspension resulting in bacteria accumulating in the area nearest the chloroplasts. He then split the light and as O₂ is produced in the blue and red light the bacteria accumulated there.
What does the close correlation between the action spectrum and the absorption spectrum suggest?
It suggests that the pigments are probably responsible for absorbing the light energy used in photosynthesis.
What is the role of photosynthetic pigments?
To absorb the light energy to be used in the conversion light energy to chemical energy in the form of chemical energy in chemical bonds
How may you test to see what photosynthetic pigments are present in a plant?
You can extract pigments from leaves using ethanol or acetone to disrupt the cell and chloroplast membranes, releasing the photosynthetic pigments. You can then use thin layer chromatography (best solvent 50:50 hexane/ethanol) to separate out the photosynthetic pigments.
On what basis does chromatography separate the photosynthetic pigments?
On the basis of molecular mass and solubility in the solvent. I.e lightest pigments travel furthest and the heaviest take longer. Chromatography measures mass by comparing the distance travelled by each pigment and the distance travelled by the solvent line to give you an Rf value.
What is an Rf value?
(Distance travelled by component)/(distance travelled by solvent).
Lighter molecules will haves larger Rf. Heavier molecules will have a smaller Rf.
In what membrane are the photosynthetic pigments found?
In the thylakoid membrane.
How are the pigments arranged in the thylakoid membrane?
They are arranged in clusters called photosystems. Each Photosystem contains hundreds of pigment molecules.
