Plant Biology and Photosynthesis Flashcards
Name two organelles that are present in all plant cells, but not in all animal cells.
chloroplasts and vacuoles
Chloroplasts aid in photosynthesis and are actually never present in animal cells. Vacuoles are large structures used for the storage of waste, nutrients, or water. Some animal cells do have vacuoles, but they are much smaller than the vacuoles found in plant cells.
What structure, which human cells lack, surrounds the outer face of the plasma membrane in plant cells?
cell wall
Plants have cell walls made of cellulose (a carbohydrate), fungi have cell walls composed of chitin, and bacteria have cell walls that consist of peptidoglycan. Humans do not have cell walls; our cells are surrounded by the plasma membrane alone.
In the net reaction of photosynthesis, which molecules are reactants and which molecules are products?
Reactants:
- Carbon dioxide
- Water
Products:
- Glucose
- Oxygen
The purpose of photosynthesis is to make glucose (a carbohydrate food source) to fuel the plant’s cells.
Technically, light is also a reactant, but light is not a molecule.
What is the net reaction of photosynthesis?
6 CO2 + 6 H2O → C6H12O6 + 6 O2
Be sure to remember that C6H12O6 is the chemical formula for glucose, the carbohydrate (sugar) produced by photosynthetic plants.
Name the waxy covering that protects plant leaves from water loss.
cuticle
This structure is what you see when you look at the surface of a leaf. Without the cuticle, plants would lose excess water via evaporation.
Are plant cells eukaryotic or prokaryotic?
Eukaryotic, like animal cells.
Even fungal cells are eukaryotic; only bacteria and Archaea are prokaryotic.
What fluid fills the inner compartment of a chloroplast and serves as the location of the Calvin cycle?
stroma
The stroma is an enzyme-containing fluid encased by the inner membrane of the chloroplast. Here, the grana (stacks of thylakoids) can be found. The stroma is also the location of the Calvin cycle, or light-independent reactions of photosynthesis.
Define:
grana
In chloroplasts, grana are stacks of disc-shaped thylakoids found in the stroma, or fluid in the inner compartment.
The singular of “grana” is “granum.”
Define:
thylakoids
In chloroplasts, thylakoids are disc-shaped structures that contain chlorophyll, the pigment involved in photosynthesis.
Thylakoids are found in stacks known as grana.
Name the two types of vascular tissue in plants.
- xylem
- phloem
These tissues are structured as bundles that can transport water or nutrients. Xylem transports water (and some minerals) from the roots to the rest of the plant, including the leaves. Phloem transports nutrients (sugars, in particular) throughout the plant.
Define:
stomata
These are openings that allow gas exchange through the cuticle and epidermis of the plant.
Stomata are closed by guard cells when not needed. This reduces water loss, which would otherwise occur via desiccation (drying out).
Name the two broad reaction types that occur during photosynthesis.
- light-dependent reactions
- light-independent reactions
Light-dependent, or “light,” reactions directly involve light (photons). Light-independent, or “dark,” reactions do not. The light-independent reactions are also known as the Calvin cycle.
Name three pigments that participate in the light-dependent reactions of photosynthesis.
- Chlorophyll a
- chlorophyll b
- carotenoids
These pigments are colored molecules that can absorb energy from photons (light). This energy can be used to excite electrons.
Name the two major products of the light reactions of photosynthesis.
ATP and NADPH
ATP (or adenosine triphosphate) is the main energy storage molecule in cells. NADPH is an electron carrier that is used in the later steps of photosynthesis (the dark reactions, or Calvin cycle).
In which structures within plant cells do the light reactions of photosynthesis take place?
thylakoids
These reactions require the excitation of electrons within pigments, including chlorophyll. Remember, the thylakoids are the disc-shaped structures in which chlorophyll is found!
With regard to color, how does chlorophyll differ from the carotenoid pigments?
- Chlorophyll (both chlorophyll a and b) is green
- Carotenoids are yellow, orange, or red.
These differences in color stem from the wavelengths of light that are reflected (as opposed to absorbed) by these pigments.
Define:
photophosphorylation
The formation of ATP using energy gained from light.
ATP is synthesized from ADP and phosphate.
What is the key structural difference between photosystem I and photosystem II?
The two photosystems contain different pairs of chlorophyll a molecules, causing them to have different wavelengths at which they absorb maximum light.
Photosystem I contains P700, which has its maximum absorption at 700 nanometers. Photosystem II contains P680, which has its maximum absorption at 680 nanometers.
Name the two types of photophosphorylation.
- cyclic
- noncyclic
Cyclic photophosphorylation involves photosystem I and generates only ATP (not NADPH). Noncyclic photophosphorylation involves both photosystems I and II and generates both ATP and NADPH.
Briefly explain the steps involved in noncyclic photophosphorylation.
- Electrons within the P680 reaction center of photosystem II are excited.
- These electrons are passed to a molecule termed the primary electron acceptor.
- The electrons move along an electron transport chain from one protein to another. During this process, protons are pumped into the thylakoid lumen, creating a proton gradient.
- Protons move out of the lumen through ATP synthase, generating ATP.
- The electrons end at photosystem I, where they are excited again, initiating a second electron transport chain that produces NADPH.
Briefly explain the steps involved in cyclic photophosphorylation.
- Electrons within the P700 reaction center of photosystem I are excited.
- The electrons move along an electron transport chain from one protein to another. During this process, protons are pumped into the thylakoid lumen, creating a proton gradient.
- Protons move out of the lumen through ATP synthase, creating ATP.
- The electrons eventually return to photosystem I, where they can take part in photophosphorylation again.
Define:
carbon fixation
The conversion of CO2 into other organic compounds, mainly carbohydrates.
In plants, carbon fixation is accomplished via the Calvin cycle, a set of light-independent (“dark”) reactions.
A plant is kept in a completely dark room for an extended period of time. At the end of this interval, is the Calvin cycle likely taking place in plant cells?
not likely to be occurring.
While the Calvin cycle (also termed the “dark” reactions of photosynthesis) does not directly require light, its reactants include ATP and NADPH. In plants, both of these molecules can only be generated in the light-dependent reactions, which will not be taking place here due to the dark surroundings.
In the Calvin cycle, how many carbon dioxide molecules are required to create one glucose molecule?
6
An easy way to remember this is to memorize the chemical formula of glucose, which is C6H12O6. Since this formula includes six carbon atoms and carbon dioxide only includes one, we must need six CO2 molecules to form one glucose.
In the Calvin cycle, how many ATP and NADPH molecules are required to create one glucose molecule?
- 18 ATP
- 12 NADPH
The other reactants involved in the Calvin cycle are carbon dioxide (CO2) and hydrogen ions (H+).
Which enzyme catalyzes the first step of the Calvin cycle?
Rubisco
ribulose bisphosphate carboxylase
This reaction involves the combination of carbon dioxide with ribulose bisphosphate (RuBP).
The compartment of the chloroplast that holds the stroma is analogous to which compartment of a mitochondrion?
mitochondrial matrix
Like chloroplasts, mitochondria are encased in both an outer and an inner membrane. The region between the membranes is termed the intermembrane space, and the region enclosed by the inner membrane is termed the matrix. In chloroplasts, the stroma, an enzyme-containing fluid, is found in this inner region.
In general, plants are able to gain energy from sunlight and use it to synthesize organic compounds. Organisms with this ability are known as:
photoautotrophs
Specifically, “photo-“ refers to the ability of plants to acquire their energy from photons (light). “Autotroph” refers to producers, or organisms able to make their own complex organic compounds.
The first step of the Calvin cycle is also known as C3 carbon fixation. In this name, to what does “C3” refer?
C3 refers to the fact that this first step produces a 3-carbon molecule as its first stable product.
Specifically, this molecule is 3-phosphoglycerate.
Define:
chemiosmosis
The movement of ions down their concentration gradient across a selectively permeable membrane.
Chemiosmosis is often tested in relation to cellular respiration.. Specifically, it refers to the movement of protons down their concentration gradient and through ATP synthase, a process that allows for the creation of ATP.
