Gas Exchange and Mass Transport in Plants Flashcards
(33 cards)
What is adhesion?
Attraction of molecules of one kind for molecules of a different kind, and it can be quite strong for water, especially with other molecules bearing positive or negative charges.
What is cohesion?
Attraction between molecules of the same type - how water molecules form hydrogen bonds between one another and hence tend to stick together.
What is the cohesion-tension theory?
The main factor that is responsible for the movement of water up the xylem, from the roots to the leaves. Transpiration pull puts the xylem under tension (there is negative pressure within the xylem) and because of the cohesive nature of water (due to hydrogen bonds between water molecules) there is a continuous stream of water being pulled across the mesophyll cells and up the xylem.
What is a companion cell?
Since the sieve tube element lacks organelles, the companion cell with its nucleus, mitochondria, ribosomes, enzymes etc., controls the movement of solutes and provides ATP for active transport in the sieve tube element. Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell.
What is diffusion?
The movement of molecules or ions form a region where there are in high concentration to one where their concentration is lower
What are guard cells?
One of a pair of cells that surround a stoma in plant leaves and controls its opening and closing
What are hydrogen bonds?
Chemical bond formed between the positive charge on a hydrogen atom and the negative charge on another atom of an adjacent molecule
What is hydrolysis?
The breaking down of large molecules into smaller ones by the addition of water molecules
What are ions?
An atom or group of atoms that has lost or gained one or more electrons
What are ion channels?
A passage across a cell-surface membrane made up of a protein that spans the membrane and opens and closes to allow ions to pass in and out of the cell
What does isotonic mean?
Solutions that possess the same concentration of solutes and therefore have the same water potential
What is the mass-flow theory?
The bulk movement of a substance through a given channel or area in a specified time. Sucrose is transferred into sieve elements from photosynthesising tissue and there can be mass flow of sucrose solution down a hydrostatic gradient in sieve tubes (caused by active transport of sucrose into sieve tubes at the source and out of sieve tubes at the sink, and osmosis - movement of water into sieve tubes near source and out of sieve tubes near sink).
What are the mesophyll?
Tissue found between the two layers of epidermis in a plant leave comprising an upper layer of palisade cells and a lower layer of spongey cells
What is metabolism?
All the chemical processes that take place in living organisms
What are microvilli?
Tiny finger-like projections from the cell-surface membrane of some animals
What is the middle lamella?
Layer made up of pectins and other substances found between the walls of adjacent plant cells
What is mitosis?
The type of nuclear division in which the daughter cells have the same number of chromosomes as the parent cell
What are monomers?
One of many small molecules that combine to form a larger one known as a polymer
What is osmosis?
The passage of water from a region of high water potential to a region where its water potential is lower, through a partially permeable membrane
What are palisade cells?
Long, narrow cells packed with chloroplasts that are found in the upper region of a leaf and which carry out photosynthesis
What is the phloem?
Plant tissue that transports the products of photosynthesis from leaves to the rest of the plant
What is a potometer?
A piece of apparatus which enables the rate of water loss in a plant to be measured
What is the protoplast?
The living portion of a plant cell (i.e. the nucleus and cytoplasm along with the organelles it contains)
What is ringing?
An experiment when a section of outer lavers (protective laver and phloem) is removed around the complete circumference of a woody stem while it is still attached to the rest of the plant. This results in the region of the stem immediately above the missing ring of tissue swelling because the sugars of the phloem accumulate above the ring and it leads to tissues dying below the ring because of the interruption of flow of sugars to this region. It shows that the phloem is responsible for translocating sugars.
