Plants Flashcards
(221 cards)
1
Q
What are the types of stresses experienced by plants?
A
*Can be biotic or abiotic
*Often deal with multiple stresses at any one point e.g. Heat, drought, salinity, and high UV often occur together
2
Q
What is osmosis?
A
The movement of water across a semi-permeable membrane, a change in solute concentrations on the inside and outside of the cell
3
Q
What are hypertonic conditions?
A
If you place a plant in salt water, with higher concentrations of ions on the outside, and draw water from the cell into the external environment, plant growth is limited, This happens if the water source is low too (Plasmolyzed). The cell is turgid
4
Q
What are isotonic conditions?
A
The cell is flaccid
5
Q
What does turgid mean?
A
A turgid cell is swollen and rigid due to the internal pressure of the vacuole pushing against the cell wall.
6
Q
What is one thing that limits plant growth?
A
Water stress
7
Q
When does water stress happen?
A
It occurs when the water potential of the soil is very low (the tendency for the plant system to donate water to its surroundings). Turgidity falls below the optimum for cell function. Photosynthesis and protein synthesis are also negatively affected by water stress
8
Q
What are the three main interacting components involved in a plant’s stress response?
A
Stress factors (e.g., water deficit, heat, light), gene expression of different genes and networks, and biochemical changes.
9
Q
What are the biochemical processes in plants that are often altered during stress?
A
Photosynthesis, respiration, translocation, ion uptakes, carbohydrates, nutrient metabolisers, and growth promoters
10
Q
What is the role of abscisic acid (ABA)?
A
It controls the opening and closing of stomata. It also mediates adaptation to environmental stresses (e.g., drought) and regulates developmental signals (e.g., seed maturation, root growth).
11
Q
Provide an example of a physiological phenomenon that plants employ as a stress response.
A
Stomatal closure.
12
Q
What is the benefit of stomatal closure during stress?
A
It helps prevent moisture loss, however, it prevents CO₂ from entering the cells, leading to decreased photosynthesis.
13
Q
Name three key stress hormones in plants
A
Abscisic acid (ABA), Ethylene, and Jasmonic acid (JA).
14
Q
What are two effects of the hormone Ethylene in plants?
A
Delays flowering and reduces growth; it also promotes ripening (though not explicitly linked to stress here).
15
Q
What is the main role of Jasmonic acid (JA) in plant stress response pathways?
A
It is an essential component of the signaling pathway triggering the expression of plant defense genes in response to various environmental stresses. It can promote the production of proline and glycine betaine (trimethylglycine).
16
Q
What is drought stress?
A
Drought stress is a moderate loss of water, leading to stomatal closure and a limitation of gas exchange. It is a climatic (meteorological) factor.
17
Q
How does drought stress impact plant growth?
A
Drought stress occurs when there is insufficient moisture supply, causing a reduction in plant growth.
18
Q
What is desiccation, and how does it differ from drought stress in terms of water loss?
A
Desiccation is a much more extensive loss of water than drought stress.
19
Q
What are some potential consequences of desiccation?
A
Gross disruption of metabolism and cell structure, potentially leading to the cessation of enzyme-catalyzed reactions (e.g., DNA replication, protein synthesis, digestion).
20
Q
Name three ways in which cell expansion and division are affected by drought.
A
Cell expansion is inhibited, and cell division is inhibited.
21
Q
What hormone accumulates in plants in response to drought stress?
A
Abscisic acid (ABA) accumulates in the whole plant.
22
Q
What is osmotic adjustment?
A
Osmotic adjustment is a drop in osmotic potential within the cytoplasm to prevent water loss.
23
Q
What amino acid often accumulates in xerophytes and halophytes as a protein protectant during drought?
A
Proline accumulates.
24
Q
What can happen to a plant’s photosynthetic capacity during drought stress?
A
Loss of photosynthetic capacity can occur due to the oxidative destruction of pigments.
25
How is enzyme activity generally affected by drought stress?
It is reduced
26
What type of secondary metabolites might increase in biosynthesis during drought stress, and what is their general role?
Protectants, such as antioxidants, may increase in biosynthesis.
27
What is a key challenge that sessile land plants frequently face regarding water availability?
They often face periods of drought, which can involve rapid diurnal and seasonal changes.
28
What is a key adaptation strategy used by halophytes to survive in salty habitats?
Osmotic adjustment due to high levels of ions.
29
Describe mesophytes in terms of their typical water habitat and their response to severe water loss.
Mesophytes are adapted to habitats with adequate water but are lethal if desiccation drops below 30% of their total water content due to disruption of membrane function.
30
Provide an example of a plant group adapted to dry habitats.
Xerophytes (e.g., cacti).
31
What type of habitat are hydrophytes adapted to?
Freshwater habitats
32
What does sessile mean?
Plants are fixed in one place
33
Name four environmental factors that can vary significantly across different locations
Precipitation, nutrients, solar radiation, and climate (including temperature).
34
What are two geographical factors that influence the composition of plant communities?
The latitude and altitude of their habitat.
35
What is an additional factor, caused by human activity, that is influencing ecosystems?
Anthropogenic climate change
36
Why can't high concentrations of salts like NaCl be tolerated in the cytoplasm of plant cells?
They can damage enzymes within the cytoplasm.
37
What is osmoregulation in plant cells?
Osmoregulation is the maintenance of cell water content through the accumulation of solutes in the cytoplasm and the compartmentalization of salt ions.
38
What are compatible solutes?
Compatible solutes are compounds that can exist in high concentrations in the cytoplasm without damaging enzymes. Examples are glycine betaine and proline.
39
What cellular change can trigger the synthesis of compatible solutes?
Changes in cell turgor activate compatible-solute synthesis.
40
How does an increased concentration of compatible solutes affect the osmotic potential of the cytosol and water uptake?
Increased compatible solute concentration decreases the osmotic potential of the cytosol, increasing passive water uptake.
41
What two crucial functions must cell membranes perform in plants dealing with high salt concentrations?
Cell membranes must prevent external salt from entering and compatible solutes from leaking out.
42
How do plant cells actively manage salt ions to protect the cytoplasm?
Membranes actively pump salt ions out of the cytoplasm, and salt ions are maintained at a high concentration (10x) in the vacuole rather than the cytosol.
43
At what relative water content (RWC) does irreversible damage typically occur?
Irreversible damage typically occurs when RWC falls below ~70%.
44
What are bulliform cells?
Bulliform cells are specialized cells in grass leaves that shrink under water stress, causing the leaf to roll into a cylindrical shape.
45
Name and briefly describe the CO₂ fixation strategy of C4 photosynthesis, giving two examples of plants that use it.
Mesophyll cells capture CO₂ using PEP carboxylase, delivering it as a C4 sugar to bundle sheath cells where CO₂ is released for photosynthesis. Examples include maize and sugarcane.
46
What is a major advantage of C4 photosynthesis in hot and dry climates regarding photorespiration?
Almost no photorespiration occurs in C4 plants. This is advantageous when stomata close because O₂ doesn't build up to compete with CO₂ for the Rubisco enzyme.
47
Briefly describe Crassulacean Acid Metabolism (CAM) photosynthesis.
CO₂ is stored as organic acids during the night and released during the day for photosynthesis. CAM plants take up CO₂ at night when air temperatures are lower, helping to reduce water loss by keeping stomata closed during the day.
48
What percentage of vascular plants use CAM photosynthesis?
Less than 6% of vascular plants use CAM. It is also found in some lower plants (ferns).
49
What is the remarkable ability displayed by resurrection plants?
Resurrection plants can survive near total desiccation (loss of almost 95% of total water) and revive upon rehydration. An example is Selaginella lepidophylla.
50
What are some plant survival strategies?
*store water in their leaves, stems, or roots
*have a thick external covering to prevent water loss
*may have hairy leaves to insulate and trap moisture in the air and reduce losses
*have long taproots and reach down into the water table if present or have a wide network of roots to capture water
*may only open stomata at night so reduce moisture losses
*activate under conditions of less aridity
*may have spines to discourage predators
*may have reflective surfaces to reflect sunlight and prevent overheating
51
What is plant stress?
An external condition that adversely affects growth, development, and/or productivity
52
What are biotic stresses?
Imposed by other organisms, e.g., weeds, pathogens, insect predation
53
What are abiotic stresses?
excess or deficit in the physical or chemical environment, e.g., air pollution, temperature, flooding, drought, salt, metals
54
What plant responses does stress trigger?
*Cellular metabolism
*Altered gene expression
*Growth rates and yields *(productivity)* can be reduced by between 25% to 90% ,depending on the plant and type of stress
55
How is climate change affecting plants?
Plants cannot avoid stress after germination. Global climate change, and an increasing number of extreme events, is making high temperature a critical factor for plant growth and productivity e.g. Snowdon Lily in Eryri. Climate change has resulted in an increase in means and little change in variability. There are increases in extreme events.
56
What is plant tolerance?
The plants’ fitness to cope with an unfavourable environment. Stress resistance is often used interchangeably with stress tolerance. Environmental stress for one plant may not be stressful for another
57
What is plant acclimation?
When tolerance increases due to stress exposure, acclimation occurs (non-heritable). Plants alter their physiology and biochemical gene expression
58
What is plant adaptation?
Refers to a genetic level of resistance acquired by selection over many generations (heritable)
59
What is the general upper temperature limit for survival in most higher plants over extended periods?
Most higher plants are unable to survive extended periods of temperature above 45°C.
60
What is the maximum temperature that seeds can typically endure?
Seeds can endure 120°C.
61
What is the maximum temperature that pollen grains can typically endure?
Pollen grains can endure 70°C.
62
How does the effect of increasing temperature typically differ between photosynthesis and respiration in plants?
Photosynthesis declines before respiration, leading to a negative carbon balance and a decline in carbohydrate reserves.
63
What physiological sign indicates membrane damage in plants experiencing heat stress?
Ion leakage.
64
Name three structural adaptations that plants may have to reflect solar radiation and reduce heat absorption.
Reflective leaf hairs, leaf waxes, trichomes/pubescent leaves.
65
Describe two leaf movements or orientations that can help plants avoid excessive heat.
Leaf rolling and vertical leaf orientation.
66
How might stomatal behavior (closure and numbers) be an adaptation to heat stress?
Stomatal closure reduces water loss through transpiration, and the number of stomata can be adapted to optimize gas exchange while minimizing water loss in hot conditions.
67
What leaf morphology, characterized by reduced surface area, can be an adaptation to minimize heat gain?
Small dissected leaves.
68
Describe dimorphic leaves as an adaptation to seasonal heat changes.
Dimorphic leaves are leaves that differ in morphology depending on the season; for example, a plant might have hairless leaves in the winter and pubescent (hairy) leaves in the summer.
69
What happens to proteins and enzymes when exposed to high temperatures?
They begin to unfold (denature). The process is called denaturation.
70
At what approximate temperature does protein denaturation typically start in plants?
Denaturation starts around 45°C, and most enzymes are completely denatured around 65°C.
71
How is membrane (lipid) function affected by high temperatures?
Membrane lipid function is lost because the lipids become too fluid. Acclimation is correlated with an increase in saturated fatty acids, which reduces fluidity at high temperatures.
72
Why might membrane-bound proteins become dysfunctional at high temperatures?
Due to denaturation or excessive fluidity, or leakage of the membrane.
73
What are heat shock proteins (HSPs)?
HSPs are proteins produced in response to sudden, 5-10°C rises in temperature.
74
How do heat shock proteins (HSPs) help cells withstand heat stress?
They act as molecular chaperones to prevent the misfolding of other proteins.
75
What happens to many enzymes and structural components within a cell during heat stress?
They become unfolded or misfolded, thereby losing enzyme function. Misfolded proteins can aggregate and solidify within the cell.
76
Is the production of heat shock proteins (HSPs) exclusive to heat-stressed cells?
No, some HSPs are also found in normal "unshocked" cells. HSP production can be upregulated within 3 minutes of heat shock.
77
What are reactive oxygen species (ROS)?
ROS are formed during certain redox reactions and during the incomplete reduction of oxygen or oxidation of water by the mitochondria or chloroplast electron transfer chain. Examples include H₂O₂ (hydrogen peroxide) and O₂⁻ (superoxide anion).
78
Why have plants developed defenses against reactive oxygen species (ROS)?
Because ROS can be damaging to cellular components.
79
Name one enzymatic defense mechanism that plants have against reactive oxygen species (ROS)
Superoxide dismutase (SOD) catalyzes the dismutation of superoxide into O₂ and H₂O₂.
80
What are the three factors that determine the impact of low-temperature stress on plants depends on?
*Plant development stage
*duration and severity of the frost event
*rates of cooling and warming.
81
Define chilling stress in plants in terms of temperature and its effects.
Chilling stress occurs at temperatures too low for normal growth but not low enough for ice to form. Injury occurs when plants growing between 25-35°C are cooled to 10-15°C, leading to slowed growth, discoloration, lesions, and wilting (if roots are chilled).
82
What is the basic structure of plant membranes?
Membranes consist of a lipid bilayer interspersed with proteins and sterols.
83
Why are some plants more sensitive to chilling temperatures than others in terms of their membrane lipid composition?
Sensitive plants have a high percentage of saturated fatty acid chains that can solidify into a crystalline state at temperatures above 0°C, disrupting membrane function.
84
What happens during intracellular ice formation?
Intracellular ice formation leads to the disintegration of the cell membrane, which is lethal.
85
What two factors limit a plant cell's tolerance to extracellular ice formation and the resulting dehydration?
Limited space and the capacity of the protoplast to withstand dehydration.
86
What is a critical strategy for plants to tolerate freezing stress related to ice crystal formation?
Limiting ice crystal formation is critical to tolerance. Osmotic adjustment can help lower the freezing point of cellular fluids.
87
What type of proteins can help plants tolerate freezing temperatures by interacting with ice crystals?
Antifreeze proteins bind to the surfaces of ice crystals, inhibiting their growth and preventing them from causing damage.
88
What are the two main categories of mechanisms that plants use to cope with cold stress?
Avoidance (preventing intracellular ice formation) and tolerance strategies.
89
Briefly describe what "cold acclimation" entails as a tolerance strategy.
Cold acclimation involves regulation of gene expression and metabolic changes, leading to morphological, biochemical, and physiological alterations that enhance cold tolerance.
90
Name four examples of adaptations that allow plants to survive cold or freezing temperatures.
*Being annuals (fast growth in warm periods, seeds survive winter)
*forming bulbs (leaves die back)
*having rolled or reduced leaves (conifers)
*dropping leaves with dormancy (deciduous trees).
91
Describe the effect of a clear, cold night (-6°C) on the leaves of Monk's Rhubarb in the Alps
The frozen leaves wilted due to the disruption of cell membranes, causing cells to become leaky and lose turgor.
92
How did a late freezing event at the treeline affect Norway spruce at 1960m?
The freezing event killed new shoots. Old needles and dormant buds were unaffected. This suggests new growth is more vulnerable to late frosts.
93
What is the definition of plants?
Multicellular eukaryotes in the kingdom Plantae, they are embryophytes (nurture an embryo ‘sporophyte’), they are primary producers (Autotrophs), through photosyntehsis they harvest light energy and concert it to chemical energy, chemical energy is stored in bonds formed when they synthesise carbohydrates from CO2 AND H20, they release oxygen as a by-product of photosynthesis
94
What are the orders of plants?
mosses/liverworts (Bryophytes), ferns (pteridophytes), naked seed plants (gymnosperms) and flowering plants (angiosperms)
95
What percentage of water typically makes up actively growing plant tissues?
70% to 95% water. Plants can only grow when they are turgid.
96
What determines the amount of water present in a plant at any given time?
A balance between internal forces promoting water entry and environmental factors tending to withdraw water.
97
Name three key roles that water plays within plants.
Used in biochemical reactions (photosynthesis, growth), maintains turgor for plant structure, and acts as a solvent for transporting dissolved substances.
98
How does water enter most plants?
Through the roots. Spanish moss, lacking roots, absorbs water and nutrients from the atmosphere via specialized trichomes (scales) covering its shoots
99
How does water exit a plant?
Through the stomata via transpiration.
100
Define the transpiration stream and what it transports through the plant.
The transpiration stream is the movement of water and water-soluble minerals through the plant via the xylem.
101
How much water can a leaf potentially lose through transpiration in an hour?
A leaf may lose its own weight in water every hour.
102
Name four functions of transpiration in plants.
Transport of nutrients, temperature control (cooling), maintaining turgor for functional biochemistry, and providing most of the energy for water movement.
103
How does transpiration contribute to water movement through land plants in terms of energy and gradients?
It provides most of the energy for water movement by setting up the gradient of water potential from the roots to the leaves.
104
Is water flow in plants an active or passive process?
Passive. It is driven by water potential differences and regulated by hydraulic conductivity between the soil, root, shoot, and atmosphere.
105
How is mineral uptake by roots primarily achieved?
Mostly active and requires energy. Continuous elongation of roots is necessary because the soil near the root surface becomes depleted of nutrients.
106
Is water uptake by root cells an active or passive process?
Passive, by diffusion. The two main mechanisms are osmosis and facilitated diffusion via aquaporins.
107
Describe the short-distance transport of water from the soil to the xylem in the root.
Water moves from cell to cell by osmosis along a concentration gradient until it reaches the xylem vessels at the center of the root. This osmotic movement creates hydrostatic pressure in the root.
108
Name the three pathways for short-distance water transport in plant roots.
Apoplast, symplast, and transmembrane pathway.
109
Describe the apoplast pathway of water transport in roots.
Water moves through cell walls and dead cells (xylem elements), utilizing the connected extracellular spaces. Water and solutes can move through the cellulose cell walls by capillary action.
110
Describe the symplast pathway of water transport in roots.
Water moves through the living cytoplasm and connected intracellular spaces via plasmodesmata (cytoplasmic channels through cell walls). It requires crossing at least one cell membrane, and minerals are screened in this pathway.
111
Describe the transmembrane pathway of water transport in roots.
Water moves between cells, crossing the plasma membrane of each cell it passes through.
112
Plants can only grow when they are turgid. True or False
True.
113
What is the Casparian strip?
The Casparian strip is a belt made of suberin, a waxy polymer impermeable to water and dissolved minerals. It forces water and ions to travel symplastically into the xylem.
114
What is the endodermis?
The endodermis is the innermost layer of cells in the root cortex, surrounding the stele. It functions as a final checkpoint for the selective passage of minerals from the cortex into the vascular system.
115
What is xylem?
Xylem is the water-conducting tissue that carries water and minerals upwards from the root to the rest of the plant. It is mainly composed of dead cells strengthened with lignin.
116
What is phloem?
Phloem transports sugar and other organic nutrients throughout the plant. Its main cell types are sieve tubes (living elongated cells) and companion cells (with many mitochondria).
117
What are stomata?
Stomata are the 'valves' that control the loss of water from the plant. They consist of a pore surrounded by two kidney-shaped guard cells.
118
What is the role of adjacent epidermal cells to the guard cells?
They are also involved in stomatal function and are known as subsidiary cells.
119
What is the driving force for water loss through stomata?
A difference in the pressure of water vapor drives transpiration. The relative humidity of the outside air is the main factor influencing this gradient.
120
How does the cuticle of a leaf affect water loss when stomata are closed?
The cuticle offers very high resistance to water loss when stomata are closed. When stomata open, the resistance decreases.
121
What causes stomata to open?
Stomata open because the guard cells absorb water and swell, rapidly altering their turgor. Special features in their cell walls, specifically the arrangement of cellulose microfibrils, contribute to this opening mechanism.
122
Describe the CO₂ feedback loop that leads to stomatal opening.
Light promotes photosynthesis, lowering CO₂ levels in the leaf. This triggers the movement of K⁺ into the guard cells, followed by water (osmosis), causing the guard cells to gain turgor and the stomata to open.
123
Describe the H₂O feedback loop that leads to stomatal closure during water stress. What hormone is involved?
When more water is lost through transpiration than taken up by the roots, abscisic acid (ABA) is produced in mesophyll cells. This causes K⁺ to move out of the guard cells, followed by water (osmosis), leading to a loss of turgor and stomatal closure.
124
Define water potential.
Water potential is the measure of the ability of water molecules to move freely in a solution. Pure water has the highest possible water potential.
125
How does water move in relation to the water potential gradient during osmosis?
Water molecules move down the water potential gradient, from a high water potential to a lower water potential. Soil typically has a higher water potential relative to the air.
126
What is radial transport?
The movement of water and solutes laterally across the root or stem, from the outer layers towards the vascular cylinder (xylem and phloem) at the center.
127
What is plasmodesmata?
Microscopic channels that traverse the cell walls of plant cells and some algal cells, enabling transport and communication between their cytoplasm.
128
How does evaporation from leaves initiate the process described by the cohesion-tension theory?
Evaporation from leaves lowers their water potential, causing water to move from the xylem to evaporate from cells across the leaf tissue.
129
What is a crucial requirement for the water column within the xylem to function effectively in the cohesion-tension theory?
The column of water in the xylem must be continuous, forming a soil-plant-air continuum.
130
What structural property of xylem walls prevents their collapse under the tension created by transpiration?
Xylem walls are lignified and strong, so they do not collapse under tension.
131
What property of water allows it to withstand significant tension without the water column breaking?
Water has high cohesive forces. It can be subjected to several hundred MPa before columns break.
132
What establishes the movement of water from the soil into the roots and towards the transpiring surfaces in the leaves?
Gradients in pressure (water potential) are established along transpiring plants; this causes an inflow of water from the soil into the roots and to the transpiring surfaces in the leaves.
133
What are Eukaryotes?
Multicellular, and the first primitive plants were formed 470 million years ago. Eukaryotes engage in mitosis (completely copying genetic material) and meiosis (cell division, reducing genetic material by half—important for gametes and reproduction)
134
What type of ancestral organisms did all land-dwelling organisms evolve from?
Unicellular aquatic ancestors. Terrestrial plants descended from photosynthetic algae.
135
What is the approximate contribution of terrestrial plants to global primary production (carbon fixed)?
Terrestrial plants produce about 55% of primary production, and marine plants/algae produce about 45%.
136
Name four potential advantages for plants that colonized the land compared to their aquatic ancestors.
*Greater levels of available light
*high CO₂ concentrations
*escaping competition
*escaping herbivores.
137
Name eight significant problems or challenges that plants faced when moving from the sea to land.
*Support
*Water for metabolism
*Temperature variation
*High O₂ concentrations
*No medium to disperse sex cells (gametes)
*Hydration of cells
*Nutrient uptake (requiring roots)
*Damaging light levels/wavelengths
*Desiccation of sex cells and propagules.
138
Approximately when did plants first arrive on land?
Around 500 million years ago. High temperatures, high CO₂, and limited suitable habitats initially prevented photosynthetic organisms (Chlorophyta) from fully colonizing the land.
139
What likely happened to some marine algae that facilitated their initial adaptation to land?
Brown, red, and green algae became stranded in rock pools and adapted to withstand some dry periods. The Charophyceae (green algae) are considered the ancestral group.
140
Name four adaptations to dry conditions that evolved over time and are found in bryophytes.
*Cuticle
*Archegonia and antheridia (sex organs)
*Embryo
*Thick-walled spores.
141
List six key features that characterize terrestrial land plants.
*Non-motile organisms (Sessile)
*Growth from apical meristems
*Ability to reproduce without water (for some groups)
*Mechanisms/structures for transport
*Specialized tissues/organs
*Structurally reinforced, multicelled embryo.
142
What is a major evolutionary advantage of sexual reproduction in eukaryotes?
It produces heritable variation, which is the raw material for evolution.
143
Describe the basic eukaryotic sexual lifecycle
It involves an alternation between haploid (n, gametophyte in plants) and diploid (2n, sporophyte in plants) cells.
144
What is the ploidy of cells in a diploid organism?
Diploid cells (2n) contain two complete sets of genetic instructions, one derived from each parent.
145
What process occurs during eukaryotic gamete formation to produce haploid gametes?
Meiosis occurs, producing haploid gametes (n).
146
What is fertilization?
Fertilization is the fusion of two haploid gametes, forming a diploid zygote (2n)
147
Describe the general structural organization of early non-vascular plants.
Small, unbranched structures lacking true leaves, stems, or roots.
148
How do early non-vascular plants typically disperse to new locations?
Via desiccant-resistant spores.
149
What are rhizoids?
Small root hairs that primarily anchor the plant and do not penetrate the soil deeply for extensive nutrient uptake.
150
How do early non-vascular plants absorb water and nutrients?
Directly through the single-celled 'leaves', allowing rapid absorption throughout the whole plant.
151
What are two common features, or lack thereof, in bryophytes regarding water retention?
Most lack a cuticle, and some do not have stomata.
152
What environmental conditions are generally required for the growth and reproduction of bryophytes?
Damp conditions
153
Which generation is the more prominent or conspicuous one?
The gametophyte is the conspicuous generation. Water is needed for motile sperm to reach the eggs.
154
What evolutionary development allowed vascular plants to become larger and less dependent on moist habitats?
The evolution of the vascular system, with specialized transport systems and tubular xylem strengthened with lignin.
155
What is the primary mode of reproduction in ferns?
Sexual reproduction (fusion of gametes) is the primary mode for over 90% of ferns. The majority of ferns are outcrossed.
156
What was the dominant type of vascular flora at the beginning of the Tertiary period?
Ferns
157
What happened to ferns as angiosperms diversified?
Some ferns became extinct, but many evolved to dominate the understory. Ferns are often first colonizers (due to spore dispersal). Today, ferns are approximately 3% of the flora.
158
What does the term "Gymnosperm" literally mean?
"Naked seeds." Their ovules/seeds are exposed on the surface of the sporophyte (rather than within a carpel).
159
Name three different types of ovule-bearing structures found in gymnosperms.
*Leafy or reduced megasporophylls (cycads)
*axillary stalks subtended by leaves (Ginkgo)
*on the surface of a cone scale (conifers).
160
What is the defining feature of angiosperms?
The defining feature is the ovule being enclosed within the inner walls of carpels.
161
Where do male and female gametophytes develop in angiosperms?
Within the flowers, but they are almost invisible. Male gametophytes develop in pollen grains, and female gametophytes develop within ovules.
162
What are the two main categories of pollination in angiosperms?
About 85% are animal-pollinated (vectors include insects, birds, bats), and about 15% are wind-pollinated or self-pollinated.
163
Where must pollen be carried for fertilization to occur?
To the stigma at the tip of a carpel.
164
Name two mechanisms that can reduce the likelihood of self-pollination in angiosperms.
*Stamens and carpels of the same flower may mature at different times
*they may be arranged so that self-pollination is unlikely.
165
Where does the pollen tube grow after germination?
It grows down through the style of the carpel and penetrates a pore (micropyle) in the ovule.
166
Describe double fertilization in angiosperms.
Two sperm cells are released into the embryo sac. One sperm fertilizes the egg, forming a diploid zygote (2n). The other sperm fuses with the two nuclei in the large central cell of the female gametophyte, producing a triploid cell (3n).
167
What does the zygote develop into within the angiosperm seed?
The zygote develops into a sporophyte embryo.
168
What is zoochory?
The dispersal of fruits by insects or animals.
169
Name two advantages that seeds provide to plants
Plants are no longer reliant on water for fertilization, allowing colonization of more habitats. Seeds protect the embryo and allow it to wait for favorable germination conditions.
170
What is autotrophy?
The ability to fix carbon from inorganic CO₂ into organic molecules (self-feeding), which supports all life on Earth.
171
What are the two basic types of autotrophy?
*Chemoautotrophy: energy from inorganic chemicals (chemosynthesis), e.g., oxidation of H2S, NH4+
*Photoautotrophy: energy from light (photosynthesis), e.g., purple sulphur bacteria, cyanobacteria, algae
172
Where does photosynthesis primarily take place?
*In Green leaves
*In other green parts of the plant
*All in chloroplasts = Albino seedlings, lacking chloroplasts, are unable to perform photosynthesis.
173
Write the balanced chemical equation for photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (energy source: sunlight).
174
Approximately when did the first autotrophs appear on Earth?
Around 3.8 billion years ago, using anaerobic, dark carbon fixation.
175
When did the first photoautotrophs emerge?
Around 3.2 billion years ago. It was anoxygenic, meaning no oxygen was produced.
176
When did oxygenic photosynthesis begin?
Around 2.5 billion years ago. The buildup of O₂ in the Great Oxygenation Event changed Earth from a carbon-dominant to an oxygen-dominant environment.
177
What are the two main stages of photosynthesis?
*Photo stage: the harvesting of energy (stored in the molecules NADPH and ATP, which aren’t fixed and can move around) from light and passing it to the synthesis stage. This takes place in thylakoids.
*Synthesis: this uses energy to fix inorganic carbon into organic molecules (mostly Calvin-Benson cycle = food)
178
What are the electron and hydrogen sources and the final energy-rich product in photosynthesis?
Water is the electron and hydrogen source, and glucose (sugar) is the energy-rich product. Water is oxidized (loses electrons and hydrogen), and CO₂ is reduced (gains electrons and hydrogen).
179
What is the overall energy conversion that occurs during photosynthesis?
Solar energy is converted to chemical energy. Around 180 billion tonnes of carbohydrates are produced annually (about 55% terrestrial and 45% oceanic).
180
What happens when photons of light interact with molecules capable of absorbing their energy?
The molecules become energized. Shorter wavelengths have higher energy, and longer wavelengths have lower energy.
181
What are photosynthetic pigments?
Molecules that absorb light. Chlorophyll a is the major pigment, absorbing blue and red light and reflecting green light.
182
What are accessory pigments in photosynthesis?
Pigments that also absorb light energy and transfer it to chlorophyll a.
183
What is the crucial central atom of chlorophyll molecules?
Magnesium (Mg).
184
Describe the long phytol tail of chlorophyll and its properties.
It is hydrophobic (made of lipids). This amphipathic nature allows chlorophyll to integrate into thylakoid membranes.
185
What is the source of the oxygen produced during photosynthesis in plants, algae, and cyanobacteria?
Electrons are produced from the photolysis (splitting) of water in Photosystem II.
186
What two main energy-carrying molecules are produced during the light-dependent reactions of photosynthesis?
Adenosine triphosphate (ATP) and nicotinamide dinucleotide phosphate (NADPH).
187
Where does the synthesized ATP accumulate, and where is it immediately used?
ATP accumulates in the stroma and is used there for the synthesis phase. NADP reductase is located on the stroma side of the thylakoid membrane and reduces NADP⁺ to NADPH using protons from the stroma.
188
What key enzyme was discovered through experiments on the Calvin-Benson cycle?
RUBISCO. It is the most abundant protein.
189
What two types of reactions does the enzyme RUBISCO catalyze?
Carbon fixation and photorespiration.
190
Name the three different strategies for carbon fixation during photosynthesis and the approximate percentage of plants that use each.
*C3 plants (90%)
*CAM plants (7%)
*C4 plants (1%).
191
What property is associated with the hydrophilic functional groups of the chlorophyll molecule?
Water-loving parts of the molecule that contribute to its amphipathic nature, allowing it to interact with both watery and fatty environments within the chloroplast.
192
What are ATP and NADPH used for?
To fix carbon dioxide, this process doesn't depend directly on light but dependent on the products of the light reaction
193
What are the four steps in the Calvin cycle?
*Carbon Fixation: CO₂ combines with RuBP (ribulose-1,5-bisphosphate) catalyzed by RUBISCO, forming an unstable 6-carbon molecule that quickly splits into two 3-PGA molecules.
*Reduction Phase: 3-PGA is converted to G3P (glyceraldehyde-3-phosphate) using energy from ATP and NADPH produced during the light-dependent reactions.
*Carbohydrate Formation: Some G3P molecules exit the cycle to be used for the synthesis of glucose and other carbohydrates.
*Regeneration Phase: The remaining G3P molecules are used, along with ATP, to regenerate RuBP, allowing the cycle to continue.
194
What are some adaptations of the leaves of a plant growing in high light levels?
*longer and/or more palisade cells
*Increased specific leaf area
*more Rubisco, but less chlorophyll per unit leaf weight
*increased leaf area index
195
Why is maintaining a high CO₂ concentration in the chloroplast essential for C3 plants?
To maximize the efficiency of Rubisco and minimize photorespiration
196
Describe the characteristics of leaves in C3 plants that grow in full sunlight.
Thicker leaves provide sufficient mesophyll surfaces occupied by chloroplasts, ensuring adequate area for CO₂ dissolution and transport, and maintaining a high CO₂ concentration within the chloroplast.
197
How do leaves of C3 plants grown in shade differ from sun leaves?
Thinner leaves with more chlorophyll per unit weight and more thylakoids in grana to maximize light capture in low light conditions.
198
What is the general effect of increased atmospheric CO₂ concentration on the rate of photosynthesis and overall productivity in C3 plants?
Increased rate of photosynthesis, leading to higher productivity.
199
What is the primary carbon-fixing enzyme in C4 plants?
Phosphate-Enolpyruvate Carboxylase (PEPc). PEPc has a higher affinity for CO₂ than Rubisco, allowing it to function efficiently at lower CO₂ concentrations.
199
Explain why C3 plants are not very efficient at photosynthesis under conditions of low CO₂ concentration
Rubisco's efficiency decreases at low CO₂ levels, and photorespiration increases. Stomatal closure, while preventing water loss, further limits CO₂ availability for the Calvin cycle.
199
List four adaptations that can occur in the leaves of a C3 plant growing in an environment with high CO₂ concentrations.
*Longer and/or more palisade cells
*increased specific leaf area
*reduced stomata density
*increased water use efficiency.
200
What is the energetic cost of C4 photosynthesis compared to C3 photosynthesis?
C4 photosynthesis requires two additional ATP molecules per CO₂ molecule fixed compared to C3.
201
Describe the spatial separation of initial CO₂ fixation and sugar formation in C4 plants
Initial CO₂ fixation by PEPc occurs in mesophyll cells, producing a 4-carbon compound that is transported to bundle sheath cells where it releases CO₂ for fixation by Rubisco in the Calvin cycle. This spatial separation keeps Rubisco away from high oxygen concentrations, minimizing photorespiration.
202
What is the defining characteristic of CAM photosynthesis?
CAM plants are extreme water savers. The trade-offs include slower growth rates and a higher energy expenditure
203
Describe the typical leaf structure observed in CAM plants
CAM plants typically have few palisade cells, more spongy mesophyll cells, and enlarged vacuoles for storing organic acids.
204
Explain the temporal separation of carbon fixation and sugar formation in CAM photosynthesis
CAM plants open their stomata only at night to minimize water loss, taking up CO₂ and fixing it into organic acids (using PEPc) which are stored in vacuoles. During the day, the stomata close, and the stored CO₂ is released for sugar synthesis via the Calvin cycle.
205
What percentage of plants are CAM?
6% of vascular plants are CAM
206
What are meristems?
Meristems are regions of plant tissue consisting of undifferentiated cells capable of cell division by mitosis.
207
Name the two primary meristems that are established during embryo development in a seed
*The shoot apical meristem (SAM) gives rise to the cells that become the above-ground organs, including leaves and flowers
*The root apical meristem (RAM) gives rise to the cells responsible for future root growth.
208
When do secondary meristems typically arise in plants?
Secondary meristems appear after germination. In dicots, they occur in the vascular cambium (producing secondary xylem and phloem) and the cork cambium (producing bark). In monocots, they are typically located just above the nodes (intercalary meristems) and contribute to stem elongation and leaf development.
209
What is the general term for undifferentiated plant cells found in meristems?
Meristematic cells.
210
Define the process of determination in plant development
Determination is the process by which undifferentiated cells become committed to develop into specific cell types, even though they may not yet exhibit the characteristics of that cell type.
211
What is the typical lifespan of leaves in many plant species?
Leaves are short-lived organs that can be replaced annually or if they are damaged, allowing the plant to adapt to changing environmental conditions or resource availability.
212
Describe a microphyll leaf
A microphyll is a leaf with only one vascular bundle and lacks a complex network of veins. Examples include horsetails and lycopods.
213
Describe a megaphyll leaf
A megaphyll is a leaf with several or many large veins that branch apart or run parallel and are connected by a network of smaller veins. Examples include angiosperms (monocots and dicots), ferns, and gymnosperms.
214
How do the leaf-like structures of bryophytes differ fundamentally from the leaves of vascular plants?
Bryophytes do not have true leaves; their moss 'leaves' are typically a single layer of cells, lack vascular tissue and roots, have limited control over water loss, and are situated close to the ground.
215
Describe the leaves of lycopods
Lycopod leaves are small and possess a single vein, classifying them as microphylls. They are considered to resemble early forms of leaves.
216
List three strategies by which plants maximize light capture
*Competition (for light resources)
*Self-shading phyllotaxy (arrangement of leaves to minimize overlap)
*Abscission (shedding of leaves to optimize light capture in different seasons).
217
Provide five examples of functions that leaves can perform in addition to photosynthesis.
*Spore bearing (in ferns)
*Water and food storage (succulents)
*Regulation of water loss (via stomata and cuticle)
*Defence (e.g., spines)
*Structural support (tendrils in some climbing plants)
218
Define xeromorphy in plants
Xeromorphy refers to structural adaptations in plants that reduce water loss in arid or dry environments. Examples include stomata located in pits (to trap humid air) and the presence of hairs or trichomes (to create a boundary layer of humid air).
219
Define the term homoiohydric
Homoiohydric plants are able to maintain a relatively stable internal water content despite fluctuations in the surrounding environment.
