Ib Biology Plant Science

IB Biology

Plant Science

A.S. 9.1.1

Instruction Draw and label diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.

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9.1.2

Outline three differences between the structures of dicotyledonous and monocotyledonous plants.

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9.1.3

Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues. Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils. State that dicotyledonous plants have apical and lateral meristems. Compare growth due to apical and lateral meristems in dicotyledonous plants. Explain the role of auxin in phototropism as an example of the control of plant growth. Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs. List ways in which mineral ions in the soil move to the root. Explain the process of mineral ion absorption from the soil into roots by active transport. State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem. Define transpiration. Explain how water is named by the transpiration stream including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation. State that guard cells can regulate transpiration by opening and closing stomata. State that the plant hormone abscisic acid causes the closing of stomata. Explain how the abiotic factors light, temperature, wind and humidity affect the rate of transpiration in a typical terrestrial plant. Outline four adaptations of xerophytes that help to reduce transpiration. Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots). Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower. Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed. Distinguish between pollination, fertilization and seed dispersal. Explain the conditions needed for the germination of a typical seed. Outline the metabolic processes during germination of a starchy seed. Explain how flowering is controlled in long-day and short day plants, including the role of phytochrome.

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9.1.4 9.1.5 9.1.6 9.1.7 9.2.1 9.2.2 9.2.3 9.2.4 9.2.5 9.2.6 9.2.7 9.2.8 9.2.9 9.2.1 9.2.1 9.3.1 9.3.2 9.3.3 9.3.4 9.3.5 9.3.6

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Assessment Statement 9.1.1 Draw and label diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant. Stem

Leaf

Assessment Statement 9.1.2 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

Assessment Statement 9.1.3 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues. Absorption of light The lamina has a great surface area to absorb maximum sunlight. Photosynthetic tissues in the palisade mesophyll are positioned at the upper surface where light intensity is the highest. Gas exchange Rounded cells with minimal chloroplasts provide main gas exchange in the spongy mesophyll layer in dicotyledenous plants. Stomata diffuse gas. Support Densely packed cylindrical cells with many chloroplasts are in the palisade mesophyll for maximum support. Water Conservation The upper epidermis prevents water loss from the upper surface even when heated by sunlight. Transport of Water The xylem replaces water lost through transpiration. Products of Photosynthesis The phloem transports products of photosynthesis out of the leaf.

Assessment Statement 9.1.4 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.

Assessment Statement 9.1.5 State that dicotyledonous plants have apical and lateral meristems. Dicotyledonous plants have apical and lateral meristems, which are used for generating new cells for the growth of the plant.

Assessment Statement 9.1.6 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.

Assessment Statement 9.1.7 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 9.2.1 Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs. The branching of roots and the growth of root hairs simultaneously increase absorption of water and mineral ions by roots. Plants absorb potassium, phosphate, nitrate and other material ions from the soil through active transport. Root hair cells have mitochondria and protein pumps in their plasma membranes. Roots themselves generally only absorb ions if the cells have enough energy to create sufficient ATP.

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

Assessment Statement 9.2.3 Explain the process of mineral ion absorption from the soil into roots by active transport. Concentration of ions is lower than root cells, so they are absorbed by active transport. Root hair cells have mitochondria and protein pumps in their plasma membranes. Most roots only absorb mineral ions if they have a supply of oxygen because they produce ATP for active transport by aerobic cell respiration.

Assessment Statement 9.2.4 State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem. Terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem.

Assessment Statement 9.2.5 Define transpiration. Transpiration is the loss of water vapour from the leaves and stems of plants.

Assessment Statement 9.2.6 Explain how water is named by the transpiration stream including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation.

Xylem vessels contain long, unbroken columns of water. When transpiration occurs, water moves upwards from the roots to the leaves [transpiration stream]. Mature xylem vessels are dead and water flows through passively. Heat from the environment provides energy for evaporation of water from cell walls of spongy mesophyll cells in the leaf. The water is pulled out of xylem vessels and through pores in spongy mesophyll cell walls by capillary action. Low pressure of suction is created inside xylem vessels when water is pulled out. This is called the transpiration pull. The suction extends down through the columns of water in xylem vessels to the roots. These columns of water do not usually break because of the cohesion of water molecules. Water molecules are cohesive due to the hydrogen bonds between them. The adhesion of water to the walls of the vessel also contributes to the transpiration of water upwards in the xylem.

Assessment Statement 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.

Assessment Statement 9.2.8 State that the plant hormone abscisic acid causes the closing of stomata. The plant hormone abscisic acid causes the closing of stomata.

Assessment Statement 9.2.9 Explain how the abiotic factors light, temperature, wind and humidity affect the rate of transpiration in a typical terrestrial plant. Light – guard cells close the stomata in darkness, so transpiration is much greater in the light Temperature – heat is needed for evaporation of water from the surface of spongy mesophyll cells, so as temperature rises, the rate of transpiration rises. Higher temperatures also increase the rate of diffusion through the air spaces in the spongy mesophyll, and reduce the relative humidity of the air outside of the leaf. Humidity – Water diffuses out of the leaf when there is a concentration gradient between the air spaces inside the leaf and the air outside. The air spaces are always nearly saturated. The lower the humidity outside the leaf, the steeper the gradient will be and therefore the faster the rate of transpiration. Wind – pockets of air saturated with water vapour tend to form near stomata in still air, which reduce the rate of transpiration. Wind blows the saturated air away and so increases the rate of transpiration.

Assessment Statement 9.2.10 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.

Assessment Statement 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 (fruits, seeds, roots). 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.

Assessment Statement 9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower.

Assessment Statement 9.3.2 Distinguish between pollination, fertilization and seed dispersal. The fusion of a male gamete (pollen) with the female gamete (stigma) inside of the ovule to form a zygote is called fertilization. Pollination is the transfer of pollen from an anther to a stigma. Ovaries containing fertilized ovules become fruit, responsible for seed dispersal.

Assessment Statement 9.3.3 Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed.

Assessment Statement 9.3.4 Explain the conditions needed for the germination of a typical seed. Water must be available to rehydrate the dry tissues of the seed. Oxygen must be available for aerobic cell respiration. Some seeds respire anaerobically if oxygen is not available, but oxygen is not toxic, like ethanol, a byproduct of anaeorobic respiration. Suitable temperatures to promote healthy enzyme activity are also important, as high and low temperatures will slow enzyme activity or cause dormancy in the plant.

Assessment Statement 9.3.5 Outline the metabolic processes during germination of a starchy seed. After absorbing water, the growth hormone, gibberellins is produced in the embryo’s cotelydons. Next amylase, (a digestion catalyzing enzyme) is produced to break starch down into maltose, which is diffused to the embryo for either aerobic cell respiration as an energy source, or for growth.

Assessment Statement 9.3.6 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

Pfr Far red light (rapid conversion)

Slow conversion during darkness