Photosynthesis Flashcards
What happens along an electron transport chain?
As electrons move through an electron transport chain, electron carriers alternate between reduced and oxidized states as they accept and then donate electrons. Electrons move from a less electronegative electron carrier (one with a lower affinity for electrons) to a more electronegative electron carrier down the chain, releasing free energy.
In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.
Carbon Dioxide (Less than 1% of the atmosphere is CO2, but that is enough to support photosynthesis)
How does carbon dioxide enter the leaf?
Through the stomata (These are the openings in the leaf for gas exchange)
What are Thylakoids?
A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis.
What do Thylakoids consist of?
Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana.
Chlorophyll molecules are in which part of the chloroplast?
The chlorophyll molecules are embedded in the thylakoid membranes of the chloroplasts
The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from __________.
The oxygen produced by photosynthesis comes from the splitting of water.
In photosynthesis, what is the fate of the oxygen atoms present in CO2? They end up where?
The oxygen atoms present in carbon dioxide appear in sugar and water.
How is molecular oxygen produced?
The light reactions of photosynthesis generate molecular oxygen when water is split.
The reactions of the Calvin cycle are NOT directly dependent on light, but they usually do NOT occur at night. Why?
The ATP and NADPH produced during the light reactions are necessary for the Calvin cycle.
What is the role of NADP+ in photosynthesis?
It is the source of NADPH for the Calvin cycle.
Question 10: What is the role of NADP+ in photosynthesis?
It is the source of NADPH for the Calvin cycle.
A photon of which of these colors would carry the most energy?
Blue, the shorter the wavelength, the greater the energy content.
What is the most important role of pigments in photosynthesis?
The pigments absorb the energy required for the light reaction
Based on the work of Engelmann, a plot of photosynthetic activity versus wavelength of light is referred to as __________.
An action spectrum. It plots the effectiveness of different wavelengths of light in driving photosynthesis
What happens when chloroplast pigments absorb light?
When a molecule absorbs a photon of light, one of the molecule’s electrons is elevated to an orbital where it has more potential energy. (becomes excited)
What happens when chloroplast pigments absorb light,
When a molecule absorbs a photon of light, one of the molecule’s electrons is elevated to an orbital where it has more potential energy.
What is a photosystem?
The structure formed by the reaction center, light-harvesting complexes, and primary electron acceptors that cluster, and is located in the thylakoid membrane
During photosynthesis in chloroplasts, O2 is produced from __________ via a series of reactions associated with __________.
H2O … photosystem II
When photosystem II absorbs light, the electron that is excited to a higher energy level in the special chlorophyll leaves a “hole” that is filled when an enzyme extracts electrons from the hydrogen of water, releasing oxygen.
Which of the following is cycled in the cyclic variation of the light reactions?
a) ribulose bisphosphate
b) NADPH
c) electrons
d) protons
e) ATP
c) electrons
During the light reactions of photosynthesis, there are two possible routes for electron flow: cyclic and linear.
What are the two possible routes for electron flow?
cyclic and linear
What do both mitochondria and chloroplasts have in common?
Use chemiosmosis to produce ATP
Chloroplasts and mitochondria both generate ATP by chemiosmosis. An electron transport chain in the membrane pumps protons across the membrane as electrons are passed through a series of carriers that are progressively more electronegative. Built into the same membrane is an ATP synthase that couples the diffusion of hydrogen ions down their gradient to the phosphorylation of ADP.
How would you distinguish a thylakoid membrane from an inner mitochondrial membrane?
The thylakoid membrane would have photosynthetic pigments
During photosynthesis in a eukaryotic cell, an electrochemical gradient is formed across what?
Thylakoid membrane
In chloroplasts, the electron transport chain pumps protons from the stroma to the thylakoid space; these locations are separated by the thylakoid membrane
The light reactions of photosynthesis generate high-energy electrons, which end up in __________ through linear electron flow. The light reactions also produce __________ and __________.
NADPH … ATP … oxygen
The electrons are transferred to NADP+, forming NADPH. ATP is formed via photophosphorylation, and oxygen is produced when water molecules are split.
Where does the energy used to produce ATP in the light reactions of photosynthesis come from?
The movement of H+ through a membrane
Termed “chemiosmosis,” the diffusion of hydrogen ions through ATP synthase provides the energy to produce ATP.
What is the role of NADP+ in photosynthesis?
It is reduced and then carries electrons to the Calvin cycle.
Electrons received from photosystem I reduce NADP+ to NADPH, which then carries them to the Calvin cycle
What occurs during the Calvin cycle involving ATP and NADPH?
ATP is hydrolyzed and NADPH is oxidized.
What is Rubisco?
The enzyme that catalyzes the first step of the Calvin cycle (incorporation of a molecule of carbon dioxide by attaching it to a five-carbon sugar, named ribulose biphosphate, or RuBP) is RuBP carboxylase, or rubisco. (The enzyme in plants that captures CO2 to begin the Calvin cycle)
In the Calvin cycle, CO2 is combined with what to form an unstable six-carbon compound?
a five-carbon compound to form an unstable six-carbon compound, which decomposes into two three-carbon compounds
What correctly describes the relationship between the light reactions and the Calvin cycle?
The light reactions produce ATP and NADPH, both of which are used in the Calvin cycl
Why are C4 plants more suited to hot climates than C3 plants?
Unlike C3 plants, they keep fixing carbon dioxide even when the concentration of carbon dioxide in the leaf is low.
You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?
While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.
When donating its activated electron, the chlorophyll in photosystem II is a very powerful oxidizing agent. How is this best shown?
It’s ability to force the oxidation of oxygen in water to oxygen gas. Water is so energetically expensive, based on water being an end product of cellular respiration. it needs a powerful oxidising agent
What is the reason for carrying out the production of oxygen gas in the space surrounded by the thylakoid membranes, and not in the stroma of the chloroplasts?
That the hydrogen ions released can contribute to the H+ electrochemical gradient being generated.
If you were a cell that needed a large amount of ATP, what part of photosynthesis/the chloroplast would be most important?
PS I, Cyclic photophosphorylation exists to provide energy for the calvin cycle and involves only p680 in photosystem ll and its product is ATP
If a cell contained a radioactive version of rubisco, where would the radioactivity be located?
Stroma
Suppose you were preparing to visit a space station that uses photosynthesis to provide you with oxygen. What color lightbulbs should you take with you?
red and blue
What links photosynthesis and cellular respiration?
Chemiosmosis
What happens to the energy entering the chloroplasts?
The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds
What is the function of the sugar made in chloroplasts
Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells
Plants store excess sugar as starch in chloroplasts and other structures such as roots, tubers, seeds, and fruits
What are chloroplasts?
Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in plant and algal cells.
What is photosynthesis?
Photosynthesis is the process that converts solar energy into chemical energy within chloroplasts
What are autotrophs?
An autotroph or producer, is an organism that produces complex organic compounds from simple substances present in its surroundings, generally using energy from light or inorganic chemical reactions. They are the producers in a food chain, such as plants on land or algae in water.
Autotrophs are “self-feeders” that sustain themselves (from CO2 and other inorganic molecules) without eating anything derived from other organisms
Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules
In what kind of organisms does photosynthesis occur?
Photosynthesis occurs in plants, algae, certain other unicellular eukaryotes, and some prokaryotes
What is a heterotroph?
A heterotroph is an organism that cannot produce its own food, relying instead on the intake of nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are secondary and tertiary consumers
Where are chloroplasts found?
Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf
Each mesophyll cell contains 30–40 chloroplasts
What is the stroma?
A chloroplast has an envelope of two membranes surrounding a dense fluid called the stroma
Where is chlorophyll found?
Chlorophyll, the pigment that gives leaves their green color, resides in the thylakoid membranes (which are stacked in columns called grana)
Give the equation of photosynthesis
6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O
Photosynthesis is a redox process, how?
H2O is oxidized and CO2 is reduced
Is photosynthesis endergonic or exergonic?
Photosynthesis is an endergonic process; the energy boost is provided by light (absorbs light energy)
What are the two ‘‘steps’’ in photosynthesis?
Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
Describe pathway one light stage
Suns energy is trapped by chlorophyll
Energy is passed to reaction centre chlorophyll
Electrons become excited or energised and pick up an electron acceptor molecule
The electrons spin out of control and to chlorophyll via enzymes
This joins ADP + energy + P = ATP
What are the roles of photosynthesis?
Plants = make food Animals = food for plants Organisms = oxygen to breathe
What are the factors necessary for photosynthesis?
Light, water, co2 and chlorophyll
Where do plants get water for photosynthesis?
Water in the soil that is absorbed by root hairs and transported to xylem cells
How do plants get co2 for photosynthesis?
Atmosphere
Respiration
What is chlorophyll made up of?
Magnesium
What are the roles of energy carriers such as NADP+ and ATP
Trap and transfer energy in cellular activities
What can gardeners do to increase the rate of photosynthesis in greenhouses?
Increasing Co2 concentration = adding co2 into the air by burning gases
Increasing light intensity = artificial light or a very bright light bulb
Increasing temperature = enzymes involved to work faster
Describe light stage pathway two
The Suns light energy is trapped by chlorophyll
The energy is passed to a reaction centre chlorophyll
The electrons become excited/energised and are picked up by an electron acceptor
This releases electrons and together with NADP+ form NADPH
The Suns energy is used to split water = photolysis
Electrons move via enzymes back to the reaction centre chlorophyll
What is photolysis?
Splitting of water into three products
What are the three products of photolysis and their functions
Oxygen - released or used in respiration
Hydrogen - used to make NADPH
Electrons - replenish chlorophyll
Where does the calvin (dark) cycle occur?
In the stroma
What is the purpose of the calvin cycle
The Calvin cycle forms sugar from CO2, using ATP and NADPH
Describe the dark stage (calvin cycle)
Co2 diffuses into the chloroplasts and joins up with a 5 carbon acceptor molecule to produce a 6 carbon molecule
This 6C molecule is unstable and breaks up into 3C molecules
Some of the 3c molecules are used to replace the 5C carbon molecule, but most are reduced to from glucose
This reduction involves ATP and NADPH from rah light stage
ADP + P = recycled in pathway one
NADP+ = recycled in pathway two of lightstage!
What does ATP provide glucose with
It provides energy for glucose formation in dark stage
What does NADPH provide glucose with
Electrons
Protons
NADP+
What happens to what remains after the dark stage? [ADP and NADP+]
ADP + P = recycled in pathway one
NADP+ = recycled in pathway two
of lightstage!
Why is photosynthesis affected by temperature?
Because it depends on the activity of enzyme in both the light and dark stage
What is CO2 reduced to?
Glucose
Outline how oxygen is produced
Photolysis, which water is split into hydrogen, oxygen and electrons
Give both fates of oxygen
Respiration
Released into atmosphere
What is the energy source for the dark stage?
ATP
Give two main uses of the main product of the dark stage
Glucose
Respiration [broken down]
Converted to starch [storage]
Give one reason why the second stage cannot happen without the first stage
The second stage needs ATP to supply energy [from pathway one] and NADPH which provides glucose with electrons protons and NADP+ [formed in pathway two]
Suggest one possible benefit to plants of having more than one chlorophyll pigment
Absorb more colours
State a precise role of carbon dioxide in photosynthesis
Supplies carbon for conversion to glucose
Where do these energised electrons come from?
Chlorophyll
Name the simple compound from which a plant obtains the H used to make glucose
H20
Is the dark stage of photosynthesis anabolic or catabolic and explain
Anabolic - small molecules [co2 and h20] form larger molecules [glucose]
Name the two types of particle transferred from NADPH to CO2 in the dark stage?
Electrons
Protons
In which stage of photosynthesis is oxygen produced and what is it produced from?
Light Stage, Water
Give an account of the role of NADP?
Accepts electrons and hydrogen carrier in dark stage
