BIOL 1030 Introduction to Biology: Organismal Biology. Fall 2009 Sections B & D Steve Thompson: stthompson@valdosta.edu http://www.bioinfo4u.net 1
How plants get the stuff they need Feed me... feed me... 2
But first, check this out... http://www.accessexcellence.org/rc/vl/gg/ecb/ecb_images/ Panel_21_01HigherPlants.pdf All the parts laid out, with those connections I was talking about. I found the illustration a lecture late, but it should help you study for this section s exam. 3
On to soil and air provide plants water and inorganic nutrients Autotrophic, but still require essential nutrients,... Which are chemicals required for metabolism, growth, and reproduction. At least 16 essential to all plants. Nine of the 16 are... Macronutrients needed in fairly large amounts Carbon (C), hydrogen (H), oxygen (O), phosphorus (P), potassium (K), nitrogen (N), sulfur (S), calcium (Ca), and magnesium (Mg). Micronutrients are required in smaller amounts. 4
The macronutrients C, H, and O are the most abundant: 96% of dry weight of plant. But, N, P, & K are limiting. 5
Fertilizer numbers reflect the N:P:K ratio N, P, and K are often limiting in the environment and, therefore, are common ingredients in fertilizer to prevent or treat nutrient deficiencies. 6
The micronutrients They re less than half a percent of a plant s dry weight. 7
All these nutrients come from soils, which develop distinct layers. The layers are composed of... Litter (layer of dead, decomposing leaves and twigs, etc.) lies on the soil surface. Microorganisms release carbon from decaying litter as CO2. However,... Some carbon remains as humus, which is a... Chemically complex, hard-to-digest, spongy organic material. Topsoil is the upper layer of soil. It s also known as the... A horizon. Most humus is located there. Less organic matter is found in the B horizon, but roots are still present. The C horizon is just above bedrock, and is quite inorganic. 8
Layers of soil Like most things in biology it s a gradation with no clear start and stop. 9
What comes from where? Plants obtain C, H, and O from water and the atmosphere. Water enters through the roots. Carbon and oxygen come from the atmosphere as CO2 gas. Plants use water and CO2 to produce glucose through photosynthesis. Roots take up all other the other required elements from the soil. 10
However,... Nitrogen availability often limits plant growth. N2 is 78% of the atmosphere, but it s chemically unavailable to plants. Several types of bacteria use nitrogenfixation to convert N2 into usable forms. Rhizobium lives in legumes nodules. Carnivorous plants obtain nitrogen from the insects they consume. 11
Check out the carnivorous plants video http://www.youtube.com/watch?v=kygwgzehf6c 12
Who cares about nitrogen? All of life! It s a part of almost all biological molecules. So, the assimilation of nitrogen into organic compounds matters. Ammonia is incorporated into organic compounds by all organisms. Some bacteria are capable of converting atmospheric nitrogen to ammonia, and most bacteria, fungi, and plants can utilize nitrate from soil. 13
Nitrogen fixation? Many species would die without this. It converts atmospheric nitrogen gas (N2) to ammonia (NH3) fixing nitrogen for the ecosphere. Rhizobium live in legume (e.g. peas, soybeans, beans, alfalfa) root nodules in a symbiotic relationship. 14
Nitrogen fixation in legumes A good infection Rhizobium in Leguminosae. 15
Nitrogen-fixing bacteria-legume symbiosis Rhizobia are able to fix N2 alone only under microaerophilic conditions (too much O2 inhibits nitrogenases). In the nodule, O2 levels are kept low by the O2 binding protein leghemoglobin. 90% of leguminous plants can undergo nodulation, but the legume-rhizobia symbiosis is speciesspecific. 16
Nitrogen-fixing Rhizobium, cont. A number of nod genes are required for nodulation. The nod genes control speciesspecific nodulation in rhizobia. The nif genes are required for nitrogen fixation. They are often found on plasmids. 17
Getting stuff around transport A plant may use 200-1000 liters of water to produce one kg of tissue in one growing season; a large temperate, hardwood tree could use 70 gallons a day during the growing season! Plant cells are mostly water. It is needed for metabolism hydrolysis and photosynthesis directly use it. Plus... Turgor pressure keeps plants upright. And... Leaf mesophyll cells must remain moist for CO2 diffusion. But this accounts for only a tiny bit of the water a plant goes through the rest simply evaporates. Xylem and phloem from a continuous plumbing system throughout plant: Phloem distributes the products of photosynthesis. And... Xylem transport xylem sap water and dissolved minerals. 18
Check out the flows 19
Part of the BBC series The Private Life of Plants. http://www.youtube.com/watch?v=j1pqub7tu3y 20
Transpiration evaporation of water from a leaf (relates to xylem) Heat causes water to evaporate. Which... Helps to cool the leaf. But this establishes a... Concentration gradient and water vapor diffuses out of the open stomata, to try to equalize the gradient. Any environmental factor that increases evaporation increases transpiration, e.g.... Low humidity, high wind or temperatures; although stomata do close down when conditions get too extreme. The water that evaporates is replaced by water drawn up through the stem if there is enough available. Plant wilts and eventually dies if water cannot be replaced. 21
Cohesion-tension theory Since all the cells of the xylem are dead at maturity, they can t power up the water from the roots to the leaves how s it get up the stem? Physical properties: Cohesion water molecules cling to each other. Water molecules are pulled toward the leaf, because... The system is under tension (negative pressure). Water in xylem forms a continuous hydraulic system through plant body. Adhesion helps to counter gravity water sticks to walls of xylem tubes with hydrogen bonds. This is called capillary action. 22
Water is pulled up the tree. Transpiration creates the tension. The physical properties of water allow it to climb the xylem. 23
Here s a nice transpiration animation http://www.youtube.com/watch?v=at1bjjdcxhk 24
Additional water enters from the roots as evaporation pulls water up the stem The root epidermis is fringed with root hairs that dramatically increase available surface area for water and mineral absorption. Mycorhizzal fungi increase surface area even more. There s usually less solute concentration outside the plant than inside, so water enters roots by osmosis. Can take two different pathways: Extracellular moves in spaces between and along cell walls; versus... Intracellular moves from cell to cell via plasmodesmata (remember them). 25
Eventually water and minerals contact the endodermis, the innermost layer of the cortex And the impermeable Casparian strip forces water to enter cells at this point. Ion-channel transport proteins in the endodermal cells only admit certain ions. Water and dissolved minerals enter xylem at this point for transport to all the tissues of the plant. 26
Two routes for water in the roots The Casparian strip ensures that it all goes through the living endodermis to get to the xylem. 27
Water conservation! The waxy cuticle is an important watersaving adaptation in land plants. It is... Impermeable to water and gases. Stomata permit the leaf to exchange gases. Guard cells border and control stomata. Plentiful water K + enters guard cells, water follows, guard cell swells and opens. Drought abscisic acid triggers loss of K +, guard cells collapse and stomata closes. 28
They re pretty cool little organs Guard cells actively pump K + ions into themselves when water is abundant. Hormonal signals stimulate K + to leave when water is scarce. 29
However, whenever stomata are closed... Plants can t get any CO2 for photosynthesis (or O2 for respiration), nor get rid of 02 waste products. Most plants close their stomata at night when photosynthesis can t occur anyway, to conserve water. But CAM desert plants open theirs at night, then store the CO2 until the next day when they can photosynthesize behind closed stomata during the day. 30
YouTube has a decent lesson... http://www.youtube.com/watch?v=clw_ocdx5li 31
But what about the sugar and other organics? Phloem transport. Remember phloem is made of live cells sieve tube elements and perforated sieve tube plates. Phloem sap dissolved organic compounds are carried in the phloem. This includes... Carbohydrates, amino acids, hormones, enzymes, mrnas.... An aside: aphids can harvest phloem sap without triggering wound response scientists collect honeydew to study phloem. 32
A direct hit Aphids can collect phloem sap without the plants knowing it. We can use that trick. 33
Pressure flow theory Phloem sap moves under positive pressure from sources to sinks. This is the opposite of xylem flow! But it s still driven by an osmotic gradient. Source produces or releases sugars (makes an increased concentration of sugar there); Sink any plant part that does not photosynthesize (as sugar gets used up by respiration, its concentration falls). Companion cells load sucrose into sieve tube elements by active transport (this requires energy, i.e. ATP). Water moves by osmosis out of the xylem and into the phloem sap, because of this sugar concentration gradient. Resulting increased turgor pressure drives phloem sap through sieve tube elements (pumps it throughout the plant). 34
Plant organs may be a sink or a source, depending on needs A sink takes up compounds through facilitated diffusion or active transport. Water moves by osmosis out of the phloem and into the xylem, depending on the gradient. This relieves pressure. Any particular organ may be sink or source, e.g.... A potato tuber is a... Sink when storing starch; but a... Source when releasing starch for growth. 35
Here s an illustration 36
So that s how plants can keep living, once they get going... But what about their reproduction and development? That s what we ll cover next time the way plants have succeeded as well as they have on the earth all these eons through reproductive success! 37