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Key Plant Concepts
1. Humans impact variation in other species.
 Artificial selection
 Loss of genetic diversity within a crop species
2. Autotrophs capture free energy from physical sources in the environment.
 Photosynthetic organisms capture free energy present in sunlight.
3. Different energy-capturing processes use different types of electron acceptors.
 NADP+ in photosynthesis
4. The light-dependent reactions of photosynthesis in eukaryotes involve a series of
coordinated reaction pathways that capture free energy present in light to yield ATP
and NADPH, which power the production of organic molecules.
a. During photosynthesis, chlorophylls absorb free energy from light, boosting
electrons to a higher energy level in Photosystems I and II.
b. Photosystems I and II are embedded in the internal membranes of chloroplasts
(thylakoids) and are connected by the transfer of higher free energy electrons
through an electron transport chain (ETC).
c. When electrons are transferred between molecules in a sequence on reactions as
they pass through the ETC, an electrochemical gradient of hydrogen ions
(protons) across the thylakoid membrane is established.
d. The formation of the proton gradient is a separate process, but is linked to the
synthesis of ATP from ADP and inorganic phosphate via ATP synthase.
e. The energy captured in the light reactions as ATP and NADPH powers the
production of carbohydrates from carbon dioxide in the Calvin cycle, which
occurs in the stroma of the chloroplast.
5. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that
prokaryotic (bacterial) photosynthesis was responsible for the production of an
oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of
eukaryotic photosynthesis.
6. Nitrogen moves from the environment to organisms where it is used in building
proteins and nucleic acids. Phosphorus moves from the environment to organisms
where it is used in nucleic acids and certain lipids.
7. Living systems depend on properties of water that result from its polarity and hydrogen
bonding.
 Cohesion
 Adhesion
8. Surface area-to-volume ratios affect a biological system’s ability to obtain necessary
resources or eliminate waste products.
 As cells increase in volume, the relative surface area decreases and demand for
material resources increases; more cellular structures are necessary to
adequately exchange materials and energy with the environment. These
limitations restrict cell size.
i. Root hairs
9. Cell walls provide a structural boundary, as well as a permeability barrier for some
substances to the internal environments.
 Plant cell walls are made of cellulose and are external to the cell membrane.
10. Negative feedback mechanisms maintain dynamic homeostasis for a particular
condition (variable) by regulating physiological processes, returning the changing
condition back to its target set point.
 Plant responses to water limitations
11. Positive feedback mechanisms amplify responses and processes in biological
organisms. The variable initiating the response is moved farther away from the initial
set-point. Amplification occurs when the stimulus is further activated which, in turn,
initiates an additional response that produces system change.
 Ripening of fruit
12. Organisms respond to changes in their environment through behavioral and
physiological mechanisms.
 Photoperiodism and phototropism in plants
13. Cell activities are affected by interactions with biotic and abiotic factors.
 Temperature
 Water availability
 Sunlight
14. Organisms are affected by interactions with biotic and abiotic factors.
 Symbiosis (mutualism – rhizobium bacteria, mycorrhizae (fungus-root))
 Water and nutrient availability, temperature, salinity, pH
15. Disruptions at the molecular and cellular levels affect the health of the organism.
 Dehydration
 Immunological responses to pathogens, toxins
16. Disruptions to ecosystems impact the dynamic homeostasis or balance of the
ecosystem.
 Invasive species
 Water limitation
 Salination
17. Plants, invertebrates and vertebrates have multiple, nonspecific immune responses.
 Plant defenses against pathogens include molecular recognition systems with
systemic responses; infection triggers chemical responses that destroy infected
and adjacent cells, thus localizing the effects.
18. Programmed cell death (apoptosis) plays a role in the normal development and
differentiation.
 Flower development
19. In plants, physiological events involve interactions between environmental stimuli and
internal molecular signals.
 Phototropism, or the response to the presence of light
 Photoperiodism, or the response to change in length of the night, that results in
flowering in long-day and short-day plants
20. Cooperative behavior within or between populations contributes to the survival of the
populations.
 Mutualistic relationships (mycorrhizae)
 Biology of pollination
21. Signal transmission within and between cells mediates gene expression.

Ethylene levels cause changes in the production of different enzymes, allowing
fruits to ripen.
 Seed germination and gibberellin
22. Cells communicate over short distances by using local regulators that target cells in the
vicinity of the emitting cell.
 Plant immune response
23. Organisms exchange information with each other in response to internal changes and
external cues, which can change behavior.
 Plant-plant interactions due to herbivory
24. Living systems have a variety of signal behaviors or cues that produce changes in the
behavior of other organisms and can result in differential reproductive success.
 Herbivory responses
25. Human impact accelerates change at local and global levels.
 Logging, slash and burn agriculture, urbanization, monocropping, infrastructure
development and global climate change threaten ecosystems and life on Earth.
26. Introduction of new diseases can devastate native species.
 Dutch elm disease
 Potato blight
27. Environmental factors influence many traits both directly and indirectly.
 Flower color based on soil pH
 Density of plant hairs as a function of herbivory
28. An organism’s adaptation to the local environment reflects a flexible response of its
genome.
 Alterations in timing of flowering due to climate change