Photosynthesis Flashcards
Define photosynthesis, what is photosynthesis?
the process by which light energy from the sun is converetd into chemical energy and used to synthesis larger complex organic molecules from inorganic molecules
what is the importance of photosynthesis?
photosynthesis produces…
- complex organic molecules needed for growth
- releases energy for processes within an organism
- oxygen which is used for respiration
- organic molecules from the plant are used to provide energy to organisms higher up the food chain
- oxygen is released into the atmosphere and is available for other organisms to use
what are the 3 main stages for photosynthesis?
- collecting light energy
- Light DEPENDANT reaction (LDR)
- Light INDEPENDANT reaction (LIR)
Explain how a leaf is adapted for photosynthesis
- large surface area
- arrangement of leaves to minimise overshadowing
- thin
- transparent cuticle and epidermis
- long ad narrow mesophyll
- many stomata
- stomata open and close in repose to light intensity
- spongy mesophyll
- network of xylem and phloem
what are the products of the LDR?
reduced NADP, ATP, and Oxygen
what are the roles and adaptations of chloroplasts in photosynthesis?
- Grana- stacks of thylakoid disks
large surface area for the attachment of chlorophyll, enzymes, and electron carriers. - network of proteins holding the grana together in a way to maximize light absorption
- ATP synthase embedded within grana membranes, catalyzing the phosphorylation
- membrane is selectively permeable which allows the EC gradient to form
- contains both DNA and ribosomes so they can quickly and easily make the proteins needed for the LDR
Describe how light energy is converted into chemical energy in the light dependant stage of photosynthesis (8)
- At PSII chlorophyll absorbs light energy which excites electrons to a higher energy level releasing them. This is photoionisation.
- electrons pass down the electron transfer chain via a series of redox reactions, losing energy.
- Some of the energy during this is conserved in the production of ATP and reduced NADP (NADPH)
- energy is used to actively transport protons (H+) across from the stroma into the thylakoid membrane
- this creates an electrochemical gradient
- protons move down the electrochemical gradient via ATP synthase embedded into the thylakoid membrane
- energy from this allows the phosphorylation of ATP.
- this is the chemiosmotic theory
- electrons are re-excited at PSI and transfer to NADP + to reduce NADP to form NADPH
- photolysis of water produces oxygen, electrons, and protons
How are electrons replaced at PSI?
from the electron transport chain as PSII transfers electrons to PSI
How are electrons replaced at PSII?
from the photolysis of water at PSII, light energy splits water into electrons, hydrogen, and oxygen.
Explain what is meant by the term ‘photosynthetic pigment’
- absorbs light energy
- and excites electrons and released
- used in LDR
- absorbs light of different wavelengths
what are the products of the LIR?
sugars and other organic molecules like amino acids or nitrates
where does the Light- independent reaction take place?
the stroma of the chloroplast
explain what happens in the light-independent reaction
- LIR takes place in the stroma of the chloroplast
- CO2 combines with RuBP using rubisco to form 2 molecules of GP
- GP is the first product of photosynthesis
- REDUCTION of GP using NADPH + H+ and ATP–> ADP + Pi to produce TP
- release of TP used to synthesise complex organic molecules, like amino acids and starch
- RuBP regenerated using TP and ATP
what are the uses of ATP and NADPH in the light-independent reaction?
ATP provides the LIR with energy
NADPH provides the reaction with reducing power
how many carbons do each intermediate product in the Calvin cycle have?
RuBP- 5 carbons
GP- 3 carbons per molecule
TP- 3 carbons per molecules
