Session 2: Plant Transport Flashcards
How does water loss contribute to weather?
Stomata are open so plants are constantly losing water (99% of water in plants is lost in stomata) which is inefficient and plants can die but it contributes to the water cycle and hence the weather.
What are stomata used for?
gas exchange - Oxygen and carbon dioxide.
What are source and sink?
Source = source of nutrient production
Sink = where the nutrients are stored
Finish the sentence:
Vascular bundles/tissue are…
and roots and root hairs are…
…similar to veins - they run through leaves/plants.
…similar to villi and microvilli.
What is mineral uptake?
Plants absorbing the minerals they need from the soil.
What is the Casparian strip?
impermeable barrier which water cannot cross in the endodermis.
What is mass flow in plants?
The definitive movement of fluid down a pressure gradient which powers movement (high to low pressure). Leaves have lower pressure due to evaporation and roots have higher pressure due to osmotic uptake, hence, water flows from roots to leaves.
Describe general structure: roots, stems, xylem and phloem.
Roots are branched for uptake of water and minerals from soil, they anchor the plant, and sometimes store food. Stems have vascular bundles to transfer materials between leaf and root, they also provide support. Xylem and phloem are the vascular tissue that provide support in the stem.
What do xylem and phloem transport and what is it called?
Xylem transport water and this is called transpiration, and phloem transport sugar, minerals, hormones, and amino acids and this is called translocation.
Describe the structure of leaves.
Leaves have two layers of inner tissue: upper palisade mesophyll and lower spongy mesophyll. The upper layer is tightly packed with many chloroplasts for light absorption. The lower level is loosely packed with air spaces near stomata for gas flow, specialised guard cells on either side of the stomata allow them to open and close. Vascular bundles exist between the two layers.
Describe root structure and processes.
Plants need maximal surface area in roots for uptake, so the epidermis of roots (outermost layer of cells) may have root hairs which increase SA for absorption. Absorbed materials then diffuse across the cortex (tissue between epidermis and vascular tissue layer) towards the central stele where xylem (vascular tissue) is located. The stele is surrounded by endodermis layer which is impermeable to the passive flow of water and ions (Casparian strip) which allows rate of uptake to be controlled.
How does mineral uptake work?
Fertile soil typically contains negatively charged clay particles to which positively charged mineral ions (cations) may attach. Mineral ions may passively diffuse into the roots but will more commonly be actively uploaded by indirect active transport. Indirect active transport is where root cells release H+ ions which can displace (swap places with) the positively charged mineral ions from the clay, allowing them to diffuse into the root along a pressure gradient.
How does water uptake work?
Water follows mineral ions into the root via osmosis through either the symplasts or apoplast pathways. The symplast pathway is where water move continously through the cytoplasm of cells which are connected via plasmodesmata (interior pathway). The apoplast pathway is where water moves through non-living spaces of the plants (exterior pathway –> cellulose cell walls until Casparian strip because water cannot cross it and is transferred to the cytoplasm with the symplastic pathway.
What is transpiration? Describe all its factors.
Approximately 99% of water a plant absorbs from soil and transports through xylem is lost by evaporation (mostly through stomata) due to process of transpiration. The continous flow of water is called the transpiration stream and it is responsible for water moving up the plant. Water moves in 3 ways: evaporation and transpiration pull, capillary action (co-hesion tension), and root pressure.
Water goes in the roots, soil has the highest water concentration and lowest solute concentration so water moves up to leaves. Leaves have highest solute concentration and lowest water concentration and evaporative water loss occurs from leaves as water vapour.
Describe the structure of xylem.
Specialised structure that facilitates the movement of water throughout plant: there are vessel elements which are larger, sparser tubes, and tracheids which are smaller more abundant tubes. In vessel elements, end walls have fused to form a continous tube resulting in faster rate of water transfer. Tracheids are tapered cells that exchange water solely via pits leading to a slower rate of water transfer. When mature, xylem tissue is dead so water transport is passive - cell walls of dead tissue is what remains which is reinforced with a substance called lignin.
