Biology Notes- Plant Science

13.1.1 Outline the wide diversity in the plant kingdom as exemplified by the structural differences between bryophytes, filicinophytes, coniferophytes and angiospermophytes. Bryophytes (mosses and liverworts): •

No roots, vascular system, or cuticle.

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Rhizoids similar to root hairs.

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Mosses with simple leaf-like structures.

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Liverworts have flattened shape called a thallus.

Filicinophytes (ferns): •

Roots, leaves in fronds, and vascular system.

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Cuticle on leaves.

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Can form small trees but not woody.

Coniferophytes (conifers): •

Shrubs to very large trees.

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Advanced vascular system.

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Woody stems and roots.

Angiospermophytes (flowering plants): •

Highly variable in structure-tiny herbaceous to large trees

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Roots, stems and leaves.

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Advanced vascular system.

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Can form woody tissue.

13.1.4 Explain the relationship between the distribution of tissues in the leaves and the function of these tissues. •

Xylem: Bring water to replace losses due to transpiration, and inorganic minerals from the soil.

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Phloem: Transports products of photosynthesis out of the leaf.

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Stoma: A pore that allows CO2 for photosynthesis to diffuse in and O2 to diffuse out.

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Guard Cells: this pair of cells can open or close the stoma and so control the amount of transpiration.

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Upper Epidermis: a continuous layer of cells covered by a thick waxy cuticle. It prevents water loss from the upper surface even when heated by sunlight.

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Lower Epidermis: is in a cooler position and has a thinner waxy cuticle.

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Spongy mesophyll: consists of loosely packed rounded cells with few chloroplasts. This tissue provides the main gas exchange surface so must be near the stomata in the lower epidermis.

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Palisade mesophyll: consists of densely packed cylindrical cells with many chloroplasts. This is the main photosynthetic tissue and is positions near the upper surface where the light intensity is highest.

13.2.1 Explain how root systems provide a large surface area for mineral ion and water uptake by means of branching, root hairs, and cortex cell walls. Root hairs provide a large surface area for mineral ion and water uptake. Cortex cells absorb ions that are dissolved in water, drawn in by capillary action through cortex cell walls. Branching increases quantity and area roots can absorb ions from. 13.2.2 Describe the process of mineral ion uptake into roots by active transport. Plants absorb potassium, phosphate, nitrates, and other mineral ions from the soil. Active transport pump ions into the roots. Root hairs provide large surface area for ion uptake. 13.2.5 Define transpiration Transpiration - loss of water vapor from the leaves and stems of plants

13.2.6 Explain how water is carried by transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, and evaporation. Transpiration causes a flow of water from roots to stem and leaves. This movement is called transpiration stream. 1. Evaporation of water from spongy mesophyll cell walls of leaves 2. Evaporated water is replaced from xylem, pulled out of the xylem through mesophyll pores by capillary action 3. Low pressure is created inside xylem vessels when water is pulled out (transpiration pull). Xylem vessels contain long, unbroken columns of water where the pressure is transmitted across. 4. To equalize the pressure, water travels up the vessels through its property of cohesion 13.2.7 State that guard cells open and close stomata to regulate transpiration. 13.2.8 Explain how abiotic factors affect the rate of transpiration in a typical terrestrial mesophyllic plant. •

Light - The intensity of light increases or decreases the rate of evaporation of water from the top of leaves, causing an increase or decrease in the rate of transpiration.

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Temperature - High temperatures increase the rate of evaporation of water from the top of leaves, resulting in an increase in the rate of transpiration. Conversely, low temperatures decrease the rate of evaporation of water from the top of leaves, resulting in a decrease in the rate of transpiration.

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Wind - High wind also increases evaporation by allowing more air molecules to collide with the water molecules on leaves, resulting in an increase in evaporation of water and transpiration. Low wind results in more stagnant, saturated air around the stomata which decreases evaporation and transpiration.

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Humidity - High humidity decreases the rate of evaporation and transpiration of a plant.

13.2.9 Outline the role of phloem in active translocation of biochemicals. Phloem have sieve tubes that transport organic compounds. Column cells develop into sieve tubes by breaking down nuclei and cytoplasm, making large pores in their end walls to allow a flow of sap. The plasm membrane pump organic compounds into sieve tubes using ATP. This creates a high concentration of solute causing water to diffuse in, reulting in a positive pressure gradient allowing organic compounds to be pumped anywhere in the plant. Sugars and amino acids are transported inside plants by phloem tissue. This process is called active translocation because phloem cells have to use energy to make it happen. Sugars and amino acids are loaded into the phloem in parts of the plant called sources and are translocated to sinks, where they are unloadeded. Examples of sources are parts of the plant where photosynthesis is occurring (stems and leaves) and storage organs where the stores are being mobilized. Examples of sinks are roots, growing fruits and the developing seeds inside of them. 13.3.3 Distinguish between pollination, fertilization, and seed dispersal. •

Pollination - transfer of pollen from anther to stigma

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Fertilization - fusion of male and female gametes in the ovum

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Seed dispersal - fertilized ovums develop into fruits which are designed for seed dispersal

13.3.5 Describe the metabolic events in the germination in a typical starchy seed. 1. Absorption of water rehydrates living cells in seed 2. Plant growth hormone gibberellin produced 3. Stimulates production of amylase, catalyzing the digestion of starch to maltose 4. Maltose is transported to growth regions of seedling 5. Maltose converted to glucose 1. Used in cellular respiration until leaves can start photosynthesis above ground

2. Used to synthesize cellulose of other substances for growth 13.3.6 Explain the conditions needed for the germination of a typical seed. •

Abundance of water - rehydrates dry tissue

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Oxygen - aerobic cellular respiration before photosynthesis can occur

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Suitable temperatures - Germination involves enzymatic activity in digestion of starch and cellulose synthesis. If temperatures :*fall outside of temperature ranges for these enzymes, germination does not occur. This causes seasonal germination in many places.

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Seeds vary in their light requirements and,therefore, this factor need not be included

13.1.3 Draw plan diagrams to show the distribution of tissues in the stem, root and leaf of a generalized dicotyledonous plant.

13.3.1 Draw the structure of a dicotyledonous animal-pollinated flower, as seen with the naked eye and hand eyes.

13.3.4 Draw the external and internal structure of a named dicotyledonous seed.

Outline three differences between the structures of dicotyledonous and monocotyledonous plants. Factor Leaf veins Vascular bundles Number of stamens and other organs Roots

Monocotyledonous plant (monocot) Parallel to one another Spread through stem randomly Multiples of three

Dicotyledonous plant (Dicot) Form in a net-like pattern In a ring near outside of stem Multiples of 4 or 5

Unbranched roots grow from stems

Roots grow from other roots

Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils.

Bulbs In some monocots, leaf bases grow to form bulbs, underground organs used for food storage. They can be identified from the series of leaf bases fitting inside each other, with a central shoot apical meristem. Stem Tubers In some dicotyledon plants, stems grow downwards into the soil and sections of them grow into stem tubers, also used for food storage. They are identified as their vascular bundles are arranged in rings reminiscent of stem bundles. Storage Roots These roots are swollen with stores of food, identified by the central location of vascular tissue. Tendrils These narrow outgrowths from leaves rotate through the air until they touch a solid support to which they attach, allowing the plant to climb upwards. Compare growth due to apical and lateral meristems in dicotyledonous plants. Apical meristems All flowering plants have them Located at the tip of the roots and stems Shoots produces new leaves and flowers

Lateral Meristems They are developed as they are not necessary for a plant’s growth. In young stems, they consist of cambium in vascular bundles. In older stems, they are a complete ring of cambium, and form similarly in roots. Growth makes roots/trunk thicker. Lateral meristems are located inside of the bark.

Explain the role of auxin in phototropism as an example of the control of plant growth. Auxin is a plant hormone. It controls phototropism, directional growth in response to the source of light. Auxin is redistributed from the shoot tip (as shoot tipes can detect light intensity) on the lighter to the shadier side. Auxin efflux Carriers (pumps) in the plasma membrane transport genes, so growth of cells accelerates.

Assessment Statement 9.2.2 List ways in which mineral ions in the soil move to the root. -Diffusion of mineral ions -Fungal hyphae -Mass flow of water in ion-carrying soil

Outline four adaptations of xerophytes that help to reduce transpiration. -Vertical stems absorb sunlight early and late in the day, but not at midday when light is most intense. - Thick waxy cuticle covers the stem - CAM (crassulacean acid metabolism) physiology, which involves the opening of stomata during the cool nights instead of in the intense heat of the day - Spines take the place of leaves to reduce surface area, preventing transpiration.

Explain how flowering is controlled in long-day and short day plants, including the role of phytochrome. Phytochrome is a pigment, which exists in two interconvertible forms. Pr – the inactive form of phytochrome, absorbs red light with a wavelength of 660 nm. After absorbing the light, it turns into Pfr. Pfr – the active form of phytochrome, absorbs far red light with a wavelength of 730 nm, and is transformed back to Pr rapidly after the absorption of light. In normal daylight, there is much more red light than far red light, so phytochrome exists more in the form Pfr. Thus, in darkness it reverts back to Pr. Enough Pfr remains in long-day plants at the end of short nights to stimulate flowering. Red light (sunlight) Rapid conversion

Pr

Far red light (rapid conversion)

Slow conversion during darkness

Pfr

State that dicotyledonous plants have apical and lateral meritsems. State that terrestrial plants support themselves by means of thickened cellulose, cell turgor, and lignified xylem. State that plant hormone abscisic acid causes the closing of stomata.