1. 8.1 Movement of Gases
1.1. Review Processes - The simple story of photosynthesis and food - Amanda Ooten
1.1.1. Vascular Plants
1.1.1.1. VASCULAR AND NON-VASCULAR PLANT || TYPES OF PLANT IN THE PLANT KINGDOM || SCIENCE VIDEOS FOR KIDS
1.2. Stomata + Guard Cells p 123
1.2.1. Gas exchange in plants occurs through the process of passive diffusion. The entry of carbon dioxide and oxygen into the leaf occurs through the epidermis (surface layer).
1.2.2. Stomata (or stoma) are openings in the epidermis of leaves that control the movement of gases into or out of a plant.
1.2.3. When the stomata are open, gases including O2, CO2 and H2O(g) freely pass in and out. When the stomata are closed (e.g. during the heat of the day), gases cannot enter or leave and water is conserved.
1.2.4. Stomata
1.2.5. Stomata + Guard Cells
2. 8.2 Leaf Structure + Photosynthesis p 124
2.1. Interactive 3D model Leaf Structures Involved in Photosynthesis
2.2. Leaf Anatomy
2.3. Upper epidermis is covered by a thick, waxy cuticle (prevents water absorption which would affect transpiration).
2.4. Palisade mesophyll contains chloroplasts and is the site of photosynthesis; hence is located on the upper surface of the leaf (facing sunlight).
2.5. Spongy mesophyll have irregularly shaped cells and is the main site of gas exchange. Located on the lower surface of the leaf (near stomata).
2.6. Vascular bundles (including xylem and phloem) are located centrally to allow for optimal access by all leaf cells.
2.7. Stomata are on the underside of the leaf (prevents obstruction so as to maintain an open channel for gas exchange).
2.8. Bioninja- Leaf Tissue | BioNinja
2.8.1. Diagram
3. 8.3 Plant Transport Systems p 127
4. Why Trees Are Out to Get You
5. Xylem + Phloem Structure
5.1. Xylem transports water and nutrients as well as minerals absorbed from the soil through the root system. It is made up of two types of cells: tracheids and vessel elements.
5.1.1. Vessel elements form straight ‘straws’ that efficiently carry moving water. They are seen only in Angiosperms (flowering plants) and are one of the reasons for the success of this group of plants.
5.1.2. Conducts water and minerals
5.1.3. Movement is one way only
5.1.4. Composed of tracheids (all plants) and vessel elements (flowering plants – Angiosperms)
5.1.5. Walls composed of dead cells and are pitted (allows for water exchange)
5.1.6. Walls impregnated with lignin (structural polymer)
5.1.7. Water movement requires both cohesion and adhesion
5.2. Phloem Translocation
5.2.1. Phloem transports organic compounds (e.g. sugars and amino acids) around the plant through a process called translocation.
5.2.2. This movement starts from the source, that is the leaves where the compounds are synthesised, to sinks – where the compounds are delivered to for use or storage e.g. roots, fruits and seeds.
5.2.3. Sugars are mainly transported as sucrose (because it is soluble).
5.2.4. The nutrient-rich viscous fluid of the phloem is called plant sap.
5.3. Phloem Properties
5.3.1. Phloem is made up of two types of cells:
5.3.2. Sieve element cells are long, thin cells that are connected together and have large pores through the cell walls at either end (called sieve plates). Sieve elements have no nuclei and reduced numbers of organelles to maximise space for translocation. They also have thick, rigid cell walls to withstand the hydrostatic pressures which facilitate flow.
5.3.3. Companion cells have nuclei and provide metabolic support for sieve cells and facilitate the loading and unloading of materials at source and sink.
5.3.4. Sieve cells and companion cells are separated by tiny channels called plasmodesmata
5.3.5. Diagram
5.4. Comparison
6. 8.4 Transport of Water p 129
6.1. Root hairs provide increased surface area for both gas exchange and water and mineral uptake.
6.2. Water enters the root by osmosis while mineral ions move into the roots by diffusion or active transport. Once inside the root hair, water moves into the xylem vessels. The force of the water entering the root and ‘pushing’ its way into the cells, creates root pressure.
6.3. Root Hairs
6.4. Time Lapse - Bean Time-Lapse - 25 days | Soil cross section
6.5. Plant Movement
6.5.1. Arabidopsis thaliana plants were genetically labelled with a plasma membrane marker (in green) and a nuclear marker (in purple). The root tips were imaged using time-lapse microscopy
6.5.1.1. https://www.biointeractive.org/sites/default/files/media/image/2019-05/Root%20Movement%20animation.gif
6.5.2. Towards the end of his life, Charles Darwin, assisted by his son Frances, wrote several books on plants including “The Power of Movement in Plants” (1880). They performed experiments on plants and observed that the cells near the end of the root tip, use the movement of organelles and the release of hormones to sense gravity, which affects the timing and location of cell division and root elongation. These processes enable a root to grow down into the soil.
6.6. Shoot Systems - Mono V Di
6.6.1. Water and dissolved minerals enter into vascular tissue that is bundled and arranged differently in the stem to save space. A vascular bundle consists of several xylem and phloem tubes grouped together.
6.6.2. There are two possible arrangements of these vascular bundles. In monocotyledon plants (monocots), e.g. wheat and sugar cane, the vascular bundles are scattered randomly throughout the stem. In dicotyledon plants (dicots), e.g. apples and Eucalypts, the vascular bundles are arranged in a single ring with the xylem towards the inside of the stem and the phloem towards the outside.
6.6.3. Differences
6.6.3.1. Structure
6.7. Transpiration
6.7.1. Transpiration is the loss of water vapour from the stems and leaves of plants
6.7.2. Light energy converts water in the leaves to vapour, which evaporates from the leaf via stomata
6.7.3. New water is absorbed from the soil by the roots, creating a difference in pressure between the leaves (low) and roots (high)
6.7.4. Water will flow, via the xylem, along the pressure gradient to replace the water lost from leaves (transpiration stream)
6.7.5. Water Loss
6.7.5.1. Water is lost from the leaves of the plant when it is converted into vapour (evaporation) and diffuses from the stomata.
6.7.5.2. Some of the light energy absorbed by leaves is converted into heat, which evaporates water within the spongy mesophyll
6.7.5.3. This vapour diffuses out of the leaf via stomata, creating a negative pressure gradient within the leaf
6.7.5.4. This negative pressure creates a tension force in leaf cell walls which draws water from the xylem (transpiration pull)
6.7.5.5. The water is pulled from the xylem under tension due to the adhesive attraction between water and the leaf cell walls.
6.7.6. Factors affecting
6.7.6.1. Environmental factors that can increase the rate of transpiration include:
6.7.6.2. High temperatures
6.7.6.3. Low humidity
6.7.6.4. Wind
6.7.6.5. Long days with strong sunlight (as in summer)
6.7.7. Adapations
6.7.7.1. Adaptations that help to minimise or prevent excessive water loss include:
6.7.7.2. Thick, waxy leaves
6.7.7.3. Minimal stomata
6.7.7.4. Modified leaves (e.g. spine-like)
6.7.7.5. Closing stomata during the hot part of the day
7. 8.5 Obtaining and Distributing Nutrients p 134
7.1. Algae Architecture
7.1.1. World's First Algae Bioreactor Facade Nears Completion
7.2. Distribution
7.2.1. Photosynthesis produces the monosaccharide glucose.
7.2.2. However, plants cannot transport glucose directly because it would be used on route around the plant and is easily digested in the plant’s cytoplasm (or sap).
7.2.3. Therefore, photosynthesising cells combine glucose and fructose, a metabolite – which is a transitionary molecule formed and modified during metabolic reactions, to form sucrose.
7.2.4. Sucrose is a more stable molecule and is then sent to the phloem for translocation around the plant.