9.1.1-7 Plant Structure and Growth
9.1.2
3 Differences Between Dicotyledonous and Monocotyledonous Plants:
1) Dicots have taproot systems where Monocots have a fibrous root system
2)The veins on the leaves of dicots are network-like, monocots have parallel veins
3)Dicots have 2 cotyledons; monocots have 1 cotyledon; "Mono-" meaning 'one' or 'single' and "Di-" meaning 'two'
9.1.3
Explain the Relationship Between the Distribution of Tissues in the Leaf and Their Functions:
WAXY CUTICLE: secreted by the outer “skin” of the leaf (epidermis) to reduce water loss
EPIDERMIS: like the leaf's skin, (a barrier against infection); conserves water
PALISADE MESOPHYLL: the tightly packed cells in the upper region of the leaf where photosynthesis occurs
SPONGY MESOPHYLL: the loosely packed cells in the lower region of the leaf that it allows for the diffusion of gases; the secondary site of photosynthesis
XYLEM: distributes water and minerals from roots to the shoot system
PHLOEM: collects sucrose (made via photosynthesis in leaves) and distributes it to the root system
STOMA: spaces between two specialized guard cells on the leaf’s epidermis. They close to hold water or open to allow gas exchange.
9.1.4
Identify Modifications of Roots, Stems and Leaves for Different Functions: Bulbs, Stem Tubers, Storage Roots and Tendrils:
BULBS: modified leaves, and are mainly for food storage (i.e, onions, garlic)
TUBERS: modified stems, again for food storage (i.e, potatoes)
STORAGE ROOT: a root for storage (i.e, carrots)
TENDRILS: modified leaf (i.e, ivy)
9.1.5
State that Dicotyledonous Plants have Apical and Lateral Meristems:
-Dicots have apical and lateral meristems
-meristems generate new cells for growth for the plant
Apical Meristems: (primary meristems) the plants ability to grow upwards, increasing length
Lateral Meristems: (secondary meristems) the plants ability to grow width-wise, increasing diameter
9.1.6
Compare Growth Due to Apical and Lateral Meristems in Dicotyledonous Plants:
Apical meristems: at the tip of the root and stem, increasing the plants length + also producing new leaves and flowers
Lateral meristems: found in vascular bundles and increase the width of the plant and root by producing xylem and phloem
9.1.7
Explain the Role of Auxin in Phototropism as An Example of the Control of Plant Growth:
- Auxin is a plant hormone that stimulates cell elongation but also controls the directional growth towards the source of light (phototropism)
- In shoot tips, phototropins absorb light and change shape in response to certain light wavelengths; they bind to receptors which stimulate the transcription and translation of genes producing glycoproteins
- The glycoproteins make the transport of Auxin between cells easier
- The side of a shoot with less light produces more Auxin to make it grow longer and therefore bend towards the light
- Auxin stimulates the pumping of H+ ions out of cells, into cell walls and this causes a lowering of pH which affects microfibrils in the cells
- Then cell turgor pressure causes causes cell expansion due to the lesser resistance from the microfibrils
- High concentrations of Auxin on shadier side of shoot tip causes greater cell elongation, and the shoot tip's bend towards the light source
Transport in Angiospermophytes (9.2.1 - 11)
9.2.1
Outline How the Root System Provides a Large Surface Area for Mineral Ions and H2O Uptake Through Branching and Root Hairs:
- BRANCHING: Extensive branching increases the roots and the surface area exposed to the extracellular fluid
- ROOT HAIRS: Individual root epidermal cells elongate and therefore increase the individual epidermal cell's surface area
9.2.2
List Ways In Which Mineral Ions in the Soil Move to the Root
- DIFFUSION OF MINERAL IONS: The ions diffuse down concentration gradients
- MASS FLOW OF Water: Water flows into the soil carrying these ions
- MUTUALISM: The ions move into fungal hyphae, which grows around roots in a mutualistic relationship, and then from the hyphae into the root
9.2.3
Explain the Process of Mineral Ion Absorption From the Soil Into Roots by Active Transport:
- The concentration of mineral ions is usually lower in the soil, active transport is used to concentrate the ions in the root
- Active Transport needs ATP; root epidermal cells are rich in mitochondria and require a supply of O2 for cellular respiration
- ATP oxidation provides the energy from protons to be pumped from the inside to the outside of root epiderman cells (chemiosmosis), a H+ membrane is produced
- Mineral ions (cations like K+) are driven from the outside to inside through membrane channels by their electrical charge, repulsion from the H+'s concentrated on the outside
- Other mineral ions (anions like NO3-) move from the outside in through the channels by co-transport with H+'s as they move down their concentration gradients
9.2.4
State that Terrestial Plants Support Themselves by Means of Thickened Cellulose, Cell Turgor and Lignified Xylem:
- Terrestrial plants support themselves with
-THICKENED CELLULOSE: Xylem and Phloem cells have thick secondary cell walls composed primarily of cellulose, providing rigidity
-CELL TURGOR: Plant cell vacuoles have low water potential; Water enters the cell and the vacuole through osmosis, the cell swells against its walls providing rigidity
-LIGNIFIED XYLEM: Vascular tissue cells are reinforced with circular or helical shaped thickenings of the cellulose cell wall filled with lignin which consolidates the cell walls
9.2.5
Define Transpiration:
Transpiration: the loss of water vapor from the leaves and stems of plants
9.2.6
Explain How Water is Carried by the Transpiration Stream, Including the Structure of Xylem Vessels, Transpiration Pull, Cohesion, Adhesion, and Evaporation:
XYLEM VESSEL: thick-walled, elongated vascular tissue cells; arranged end-to-end and connected by perforated end-plates
: xylem cells die when matured leaving a continuous pathway for transporting water and mineral ions from the root system to the shoot system
TRANSPIRATION PULL: -in EVAPORATION, water vapor diffuses from the moist air spaces of the spongy mesophyll where water potential is higher; the drier air outside where water potential is lower through the stoma
- in COHESION, as the mesophyll air spaces lose water, its water potential decreases and water flows from the xylem (with higher water potential) through the mesophyll- the air spaces down the gradient; the cohesion of water molecules enables transpiration to pull water up the xylem vessels without water columns breaking apart
- in ADHESION the cell walls of xylem vessels are charged, attracting water molecules; this adhesion of water to the xylem walls moves it up the stem against gravity; also important when sap starts to rise in plants that were leafless through the winter and help prevent the column of water-filled xylem from breaking.
- in TRANSPIRATION solar-powered evaporation from the leaves creates a continuous transpirational pull transmitted all the way from the leaves -to the roots.
9.2.7
State That Guard Cells Can Regulate Transpiration by Opening and Closing Stomata
- Guard cells can regulate transpiration by opening and closing stomata
9.2.8
State That the Plant Hormone Abscisic Acid Causes the Closing of Stomata
- The plant hormone abscicic acid causes the closing of stomata
9.2.9
Explain How the Abiotic Factors: Light, Temperature, Wind and Humidity, Affect the Rate of Transpiration in a Typical Terrestial Plant:
- LIGHT: guard cells close stomata at night and transpiration is greater in light; open stomata increase the rate of diffusion of CO2 needed for photosynthesis but also increases water loss through transpiration
- TEMPERATURE: rate of transpiration, water loss through stomata is doubled for every 10 degrees Celsius increase in temp.; higher temps. also increase the rate of diffusion and reduce the relative humidity in the air outside the leaf
- WIND: removes water vapor from leaf, reducing water's potential around the leaf, increasing the water potential gradient between the leaf and surroundings, therefore increasing the rate of water loss through transpiration
- HUMIDITY: as it decreases, water potential around the leaf is reduced, thereby increasing the water potential gradient between leaf and surroundings which increases the rate of water loss through transpiration
9.2.10
4 Adaptations of Xerophytes That Help to Reduce Transpiration:
- REDUCED LEAVES: minimizes water loss thru leaf surface area reduction
- THICKENED WAXY CUTICLE: minimizes water loss by limiting water loss thru epidermis
- REDUCED NUMBER OF STOMATA: minimizes water loss thru leaves
- SUCCULENCE: stems specialized for water storage; maximizes retention of water available during infrequent rains
9.2.11
Outline the Role of Phloem in Active Translocation of Sugars (sucrose) and Amino Acids From Source (photosynthetic tissue and storage organs) to Sink (fruit, seeds, roots)
- translocation= the movement of substances in the phloem
- SYMPLASTIC ROUTE: sucrose made in the mesophyll cells travels intracellularly to phloem sieve-tube members (STMs)
- APOPLASTIC ROUTE: sucrose made in mesophyll cells travels extracellularly to companion cells and STMs; through the movement of H+ out then into companion cells and STMs, sucrose co-transports
- PRESSURE FLOW: loading sucrose into the STMs at the source reduces water potential inside STMs making water enter via osmosis; this absorption generates hydrostatic pressure that forces the phloem sap to flow along the tube; the gradient of pressure in the tube is reinforced by unloading sucrose and the subsequent water loss, from the tube at its sink
Reproduction in Angispermophytes (9.3.1-6)
9.3.2
Distinguish Between Pollination, Fertilization, and Seed Dispersal
- POLLINATION: the transfer of pollen grains from the anther to the stigma
- FERTILIZATION: the fusion of male and female gametes
- SEED DISPERSAL: mechanisms for distributing seeds away from the parent plant
9.3.4
Explain the Conditions Needed for the Germination of a Typical Seed:
- EVOLUTION OF THE SEED: key adaptations of plants to terrestial life
- SEED DORMANCY: increases chance that germination will occur at appropriate time
- ENVIRONMENTAL CUES:
-Oxygen and Water: needed by all plants to germinate, initiate inhibition and activate cellular respiration
-Desert: substantial rainfall that wahses away inhibitors from seed coat (testa)
-Chaparral: fire and intense heat
-Temperature and Subarctic Zones: extended exposure to cold
-Passage Through Animal Digestive Tract: exposure to digestive enzymes wears down seed coat - the LENGTH OF DORMANCY varies from days to decades
9.3.5
Outline the Metabolic Processes During the Germinaton of a Starchy Seed:
- Imbibition is the absorption of water, due to low water potential in dry seed and causes seed to swell, rupturing the seed coat and triggering metabolic changes in the embryo, causing it to resume growth.
- Gibberellic acid (GA) is released by embryo, diffuses through-out seed, reaching aleurone, the outer layer of seed
- A-amylase ( a digestive enzyme) is released when aleurone triggered by GA
- Endosperm starch is hydrolyzed into maltose by digestive enzyme
- Cotyledon absorbs maltose from endosperm into embryo
- Seedling grows from embryo fueled by the energy from maltose; stored lipids and proteins; hydrolyzed allowing for embryo's growth and development
9.3.6
Explain How Flowering is Controlled in Long-day and Short-day plants, Including the Role of Phytochrome:
- Phytochrome is a pigment that exists in plants in 2 forms:
1.) Pr - absorbs white/red light
2.) Pfr - absorbs dark/far-red light
-in white/red light, Pfr is converted to Pr
-acts as a promoter of flowering in long-day plants
-it also acts as an inhibitor of flowering in short-day plants
Taken from the IB Biology Syllabus from Mr. Ghosh, Partially paraphrased by me...
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