13396883
Description
Flashcards by Emma Lloyd, updated more than 1 year ago
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Created by Emma Lloyd
over 6 years ago
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| Question | Answer |
| What is transpiration? | The process by which water evaporates from the leaves, resulting in water drawn up from the roots |
| What does the xylem do? | Transports water and solutes from roots to leaves |
| What does the phloem do? | Transports food (sucrose) from leaves to other parts of the plants |
| What is the epidermis of the plant? | -Single layers of cells that form surface tissue -Continuous except for stomatal pores -Protects against water loss |
| What is the hypodermis? | Layer of cells laying beneath the epidermis |
| What is the cortex? | The outer layer comprised of cells, beneath the hypodermis |
| What is the endodermis? | -Central layer bordering the cortex -Contains the Casparian strip -Present in seedless, vascular plants -Absent from stems but present in the roots of seeded plants -regulates movement of water, ions and hormones |
| What is the stele? | Central part of the root or stem. Contains the xylem and phloem. |
| What is the Casparian strip? | 'Mortar in the wall'. Band of cell wall (suberin) material in endodermis (lignin). It prevents water and solutes from leaking back out into the cortex. |
| When does root pressure occur? | -Soil moisture level high at night -Transpiration is low in the day |
| What is guttation? | The exudation of xylem sap drops on tops or edges of leaves of plants such as grasses |
| What causes guttation? | -High moisture levels in the soil -Water entering roots due to osmotic pressure -The accumulation of said water creating root pressure -Said root pressure forcing water through leaf tip |
| What is the function of the phloem? | It translocates sap from sources to sinks. A source is a plant organ (like mature leaves) in which sugar is produced by photosynthesis or starch breakdown. A sink is a place where sugar is needed in the plant, eg, roots for growth. |
| Structure of the phloem? | There are tubes formed by chains of cells known as sieve-tube members. At the end walls of these, there are sieve plates that have pores to facilitate the flow of fluid between cells. Sieve-tube members contain very few organelles so there is a companion cell attached to them which have the organelles. |
| What are plasmodesmata? | Microscopic channels which transverse plant cell walls to enable transport and communication. They can be used negatively by plant viruses. |
| How does water flow through the phloem? | Higher levels of sugar at source lowers water potential and allows water to flow into the tube. At the sink, sugar is removed so the water potential is increased and water flows out. The difference in hydrostatic pressure drives phloem sap from the source to the sink. |
| What is phloem loading and how does it occur? | it is the transfer of sugars from mesophyll cells to the sieve tubes and it can occur through the apoplastic or the symplastic pathway. |
| How do we sample the phloem sap scientifically? | We use the feeding mouthparts of aphids. We snap them off of the aphid when the aphid is feeding from the phloem and can collect the droplets of phloem sap |
| Why don't damaged plants 'bleed ' to death? | Sieve plats block when damaged through proteins (effective within minutes) and callose (which take hours) |
| How does the phloem act as an 'information highway'? | 1. Translation of DNA in companion cell 2. Transport of mRNA in sieve tube 3. Translation of mRNA in the sink |
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